Journal of Cerebral Blood Flow and Metabolism 19:1365-1375 © 1999 The International Societv for Cerebral Blood Flow and Metabolism Published by Lippincott Williams & Wilkins, Inc., Philadelphia

Cerebral Functional Magnetic Resonance Imaging Activation

Modulated by a Single Dose of the Monoamine

Neurotransmission Enhancers Fluoxetine and Fenozolone During

Hand Sensorimotor Tasks

*Isabelle Loubinoux, *Keder Boulanouar, :j:Jean-Philippe Ranjeva, *tChristophe Carel,

*:j:Isabelle Berry, *Olivier Rascol, *Pierre Celsis, and *tFranc;ois Chollet

*lNSERM U455 and Departments of tNeurology and tNeuroradiology, H6pita/ Purpan, Tou/ouse, France

Summary: Fluoxetine inhibits the reuptake of serotonin, and dextroamphetamine enhances presynaptic release of mono­amines, Although the excitatory effect of both noradrenaline and dopamine on motor behavior generally is accepted, the role of serotonin on motor output is under debate, In the current investigation, the authors evidenced a putative role of mono­amines and, more specifically, of serotonin in the regulation of cerebral motor activity in healthy subjects. The effects on ce­rebral motor activity of a single dose of fluoxetine (20 mg), an inhibitor of serotonin reuptake, and fenozolone (20 mg/SO kg), an amphetamine-like drug, were assessed by functional mag­netic resonance imaging, Subjects performed sensorimotor tasks with the right hand, Functional magnetic resonance im­aging studies were performed in two sessions on two different days, The first session, with two scan experiments separated by 5 hours without any drug administration, served as time-effect controL A second, similar session but with drug administration

Fluoxetine is well known to inhibit the reuptake of serotonin, and dextroamphetamine to enhance presynap­tic release of monoamines (noradrenaline, dopamine, se­rotonin), Fluoxetine and dextroamphetamine may facili­tate motor recovery in poststroke patients undergoing rehabilitation (Dam et aI., 1996; Walker-Batson et aI" 1995), Many lines of evidence suggest that amphet­amine-promoted recovery of function is mediated mainly noradrenergically (Goldstein et aI" 1991, 1993; Boyeson et aI" 1990), Intracerebral reorganization has been dem-

Received February 3, 1999; final revision received June 1, 1999; accepted June 1, 1999.

Supported by a fellowship of la Societe de Secours des Amis des Sciences, Paris, France (1. Loubinoux).

Address correspondence and reprint request to Prof. F. Chollet, INSERM U455, pavilion Riser, H6pital Purpan, 31059 Toulouse, France,

Abbreviations used: BA, Brodmann area; fMRI, functional magnetic resonance imaging; 5-HT, serotonin; SMA, supplementary motor area.

1365

after the first scan assessed drug effects, A large increase in evoked signal intensity occurred in the ipsilateral cerebellum, and a parallel, large reduction occurred in primary and second­ary motor cortices (P < 10-

3), These results are consistent with

the known effects of habituation, Both drugs elicited compa­rable effects, that is, a more focused activation in the contra­lateral sensorimotor area, a greater involvement of posterior supplementary motor area, and a

_�idespread decrease of bilat­

eral cerebellar activation (P < 10 ), The authors demonstrated for the first time that cerebral motor activity can be modulated by a single dose of fluoxetine or fenozolone in healthy subjects, Drug effects demonstrated a direct or indirect involvement of monoamines and serotonin in the facilitation of cerebral motor activity, Key Words: Human-Functional magnetic resonance imaging-Sensorimotor tasks-Cerebral activation-Fluoxe­tine-Monoamines,

onstrated to occur after stroke in humans (Chollet et aI., 1991, 1994). We postulate that these drugs can interact with reorganization processes. Although the beneficial effect of noradrenaline (Goldstein et aI., 1993, 1995; Small et aI., 1994), and, to a lesser extent, of dopamine (Feeney et aI., 1982), has been demonstrated in animal and clinical studies, the incidence of serotoninergic modulation on motor recovery is highly controversial (Dam et aI., 1996; Boyeson et aI., 1996, 1994). Dam et al. found that chronic fluoxetine treatment at clinical doses enhanced the rate of recovery of poststroke pa­tients, whereas Boyeson et al. found that serotonin modulation was ineffective in improving motor deficit in animals. Moreover, the excitatory effect of both nor­adrenaline and dopamine on motor behavior generally is accepted (McMillen et aI., 1993; Kuczenski et aI., 1995), whereas the role of serotonin on motor output is being discussed. It has been reported to be excitatory (Geyer et aI., 1996; Hasbroucq et aI., 1997; Veasey et aI., 1995),

1366 1. LOUBINOUX ET AL.

inhibitory (Porrino et aI., 1997), or both excitatory and inhibitory (Geyer et aI., 1996; Jacobs et aI., 1993; Elliot et aI., 1992; Mangan et aI., 1994a,b). Although the role of serotonin in motor control has been only vaguely sug­gested, it cannot be discarded and could consist of a modulation of behavioral activity (Jacobs et aI., 1993, 1997). In addition, because poststroke depression is a common sequel of stroke, 5-HT (serotonin) involvement in motor or nonmotor functions (i.e., visual, linguistic) and in motor or nonmotor recovery should be evidenced.

The current investigation demonstrates the putative r'ole of monoamines, including that of serotonin, in the regulation of cerebral motor activity in healthy subjects. The study addresses the pharmacologic modulation of motor-evoked responses and does not deal with the main effects of drugs per se. Pharmacologic compounds were chosen to modulate monoamine neurotransmission. Fenozolone (Ordinator), an amphetamine-like drug, in­creases transmission of all monoamines. Fluoxetine (Prozac) increases serotoninergic transmission more spe­cifically because of its selective inhibition of serotonin reuptake. Blockade of uptake increases synaptic avail­ability of serotonin, thereby, enhancing receptor activa­tion and serotoninergic transmission. Effects on cerebral motor activity of single and low doses of fenozolone or fluoxetine were assessed separately by functional mag­netic resonance imaging (fMRI). The fMRI studies were performed in two sessions on two different days. Such pharmacologic studies need to be performed with cau­tion, since reproducibility problems or habituation-like effects may happen. The first session, with two scan experiments separated by 5 hours, without any drug ad­ministration, was used to check for time or habituation

, effects. Habituation is likely to occur when experiments are separated by 5 hours. A second, similar session with drug administration after the first scan assessed drug ef­fects. As a first approach, we deliberately chose not to administer a placebo to bring out time effects alone. Time effects then were taken into account in the evalu­ation of drug effects.

MATERIALS AND METHODS

Our experiment investigated the pharmacologic modulation of motor-evoked hemodynamic responses. This is a drug-by­condition interaction. However, because the drug could be ad­ministered only after a period of predrug motor activation, drug-by-condition interactions also could be explained by time­by-condition interactions. To check this possibility, we re­peated the same experiment on a separate day but without any drug. The modulatory effect of the drug that cannot be ex­plained by time-dependent habituation or augmentation of re­sponse then is simply the drug x condition x day interaction. This is indeed a drug-dependent difference in motor-evoked responses that persists once differences caused by nonspecific adaptation have been subtracted.

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Subjects The study was performed with the approval of our Institu­

tional Human Studies Committees. All subjects gave written informed consent to the study.

Twelve healthy, right-handed volunteers (six women and six men; mean age, 48 ± 7 years; range 41 to 63 years) were studied.

Paradigm Time effects between two examinations performed at a few

hours' interval were assessed during a first session in which subjects repeated two identical MRI examinations separated by 5 hours without taking any drugs (EI: examination I, day 1 at 8 AM; E2: examination 2, day 1 at 1 PM).

Drug effects were assessed in a second session in which the same subjects repeated the same two examinations once more: one before drug administration (E3: examination 3, day 2 at 8 AM), and one after drug administration (E4: examination 4, day 2 at I PM) . Subjects in group I (n = 6) were given fenozolone (20 mg/50 kg; 2 hours before E4), and subjects in group II (n =

6) were given fluoxetine (20 mg; 4 hours before E4) at the peak plasma concentrations (Lemberger et aI., 1985; Altamura et aI., 1994). Several weeks separated the two sessions to avoid ha­bituation from taking place (group I, mean 60 days; group II, mean 42 days). Sessions assessing time or drug effects were not counterbalanced within subjects because time separating the two sessions was long (2 months). However, this point was taken into account in the statistical assessment of drug effects.

Task paradigm The task paradigm consisted of eight 30-second epochs al­

ternating between rest (R) and activation (A), resulting in an acquisition time of 4 minutes per functional time series. During "activation," subjects were instructed to perform an auditory I-Hz paced task that alternated between two fist closings and sequential touching of the thumb with each of the four digits of one single hand. During "rest," subjects were told to relax and not think about finger movements. Subjects were instructed to keep their eyes closed. The I-per-second auditory signal con­tinued throughout the activation and rest periods, To increase the signal-to-noise ratio, the task was repeated over three runs (R-A-R-A-R-A-R-A was repeated over run I, run 2, and run 3) so that each run included four pairs of rest-activation periods.

Before the subjects were positioned in the scanner, the tasks were explained to them in a preliminary session without any further training. We verified that the subjects performed the task correctly. The execution of the tasks during scanning was inspected visually, and all subjects were seen to comply with the auditory pacing. Head motion was minimized by using foam padding and ear blocks.

Data acquisition Magnetic resonance imaging was performed on a 1.5-T scan­

ner (Siemens Vision, Erlangen, Germany) equipped for echo­planar imaging. A three-dimensional, high-resolution Tl­weighted data set of the whole brain (three-dimensional mag­netization-prepared rapid acquisition gradient echo) was acquired for each volunteer (repetition time 15 milliseconds; echo time 7 milliseconds; inversion time 300 milliseconds; 12° flip angle; 30 x 30 cm field of view, 256 x 256 matrix, voxel size = 1.17 x 1.17 x I mm

3, 128 slices). After sagittal local­

ization images, 12 contiguous, 5-mm thick, axial anatomic im­ages were obtained from the plane of the anterior-posterior commissural line through the vertex and four contiguous im­ages of the cerebellum were acquired (T2-weighted images, repetition time 418 milliseconds, echo time 10 milliseconds, 30° flip angle, 20 x 20 em field of view, 128 x 128 matrix).

MONOAMINE ENHANCERS MODULATE BRAIN MOTOR ACTIVITY 1367

For fMRI studies, blood oxygen level-dependent imaging was performed using a T2*-weighted single-shot echo-planar imaging sequence (repetition time 8 milliseconds, echo time 60 milliseconds, 90° flip angle, 20 x 20 field of view, 64 x 64 matrix, 3.125-mm inplane resolution, 5-mm slice thickness). Sixteen slices (12 + 4) were acquired every 3 seconds, coinci­dent with the T2-weighted reference images.

Functional magnetic resonance

image postprocessing Image analysis was carried out on a SPARC workstation

(Sun Microsystems, Surrey, U.K.) using interactive image dis­play software (Analyze, Biodynamics Research Unit, Mayo clinic, Rochester, MN, U.S.A.), matlab (Math Works, Inc., Natick, MA, U.S.A.), and SPM96 4 2.c software (Wellcome Department of Cognitive Neurology, London, U.K.). The first four images of each time series were discarded to eliminate signal intensity variations arising from progressive saturation. Echo-planar imaging images were realigned to the first func­tional image of each time series to remove residual head move­ment. The functional images of each subject and of each time series were coregistered with the first functional image of one subject taken as a model. Images then were resized into the standard anatomic space defined by the atlas of Talairach and Tournoux (1988) to perform a group analysis. The images were smoothed with a Gaussian kernel of full-width at half­maximum of 6 mm to reduce the anatomic and functional vari­ability between the subjects.

Next, statistical parametric maps were generated to identify areas of interest that covaried positively with movements (Fris­ton et aI., 199;i). The differences between baseline and activa­tion were assessed with the t statistic at each voxel for each run of each subject separately. All images were inspected for evi­dence of misregistration (e.g., edge effects, rims of activity

FIG. 1. (A) Activated foci by right fin­ger movements (ACT I - REST) > 0 superimposed on T1-weighted mag­netic resonance images (n = 12). Three transaxial images of -25, 40, and 45 mm under and above the an­terior-posterior commissural line are shown. The pixels in yellow show level of statistical significance above P < 0.001 for peak height and P <

0.05 for spatial extent (corrected for multiple comparisons). A corre­sponding Z score bar is provided. Left side of the figure corresponds to the right hemisphere. Notice a large activation mainly in the cerebellum ipsilateral to the movement and in primary and secondary motor corti­ces. (8) Comparisons of activations (ACTI - REST) between E1 and E2 examinations superimposed on T1-weighted magnetic resonance im­ages (n = 12) (Z score> 2.32, P <

0.01 uncorrected and corrected for spatial extent). A corresponding Z score bar is provided. Three trans­axial images of -25, 40, and 45 mm under and above the anterior­

A.

B. z = ·25mm

along the cortical surface, absence of activity). Scans in which obvious movement artifacts were identified were excluded from subsequent analysis. A thirteenth subject was excluded because of excessive movement. All subjects displayed activa­tion foci in the contralateral primary sensorimotor cortex (S 11 MI).

Group analysis then was performed on the 12 remaining subjects.

First, runs were averaged giving statistical parametric maps of the difference [ACTI - REST1E1 > O. These maps were calculated for the first examination EI (n = 12) and thresh­olded: Z score > 3.09 for peak height and P < 0.05 for the cluster (corrected for multiple comparisons) (Friston et aI., 1995) (Fig. I A). They were overlaid onto the anatomic three­dimensional images. Only changes in these activated areas were considered for the following statistics (the condition EJ > ° is specified as a mask with SPM software).

Second, the statistical parametric maps ACTI - REST of examinations EI and E2 were compared to determine putative time effects. We generated statistical parametric maps of the following:

[(ACTI - REST)E2 - (ACTI - REST)E11 > 0, and [(ACTI -REST)E2 - (ACTI - REST)E11 < 0, which is, in a more simplified form,

E2 - EI > ° increased evoked signal with time, and E2 - E1 < 0 decreased evoked signal with time (n = 12; Z score> 2.32, P < 0.01 uncorrected for multiple

comparisons, corrected for spatial extent, EI 2: 0). Third, drug effects were assessed in each group by the sta­

tistical differences between E4 and E3, from which were sub­tracted the time effects previously assessed between E1 and E2 within each group:

z =40mm z =45mm

z =40mm z =45mm

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posterior commissural line are shown. Left side of the figure corresponds to the right hemisphere. Areas of activation are outlined. Notice that a large increase in signal intensity (red-yellow clusters) occurred in a restricted area of the ipsilateral cerebellar cortex, and a parallel large reduction of signal intensity (green-blue clusters) occurred in some parts of primary and secondary motor cortices.

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1368 I. LOUBINOUX ET AL.

(E4 - E3) - (E2 - El) < 0 (fenozolone group: n = 6; fluoxetine group: n = 6; Z score> 2.32, P < 0.01 uncorrected for multiple comparisons, cor­rected for spatial extent, EJ 2: 0). In a conservative ap­proach and because the time effect evaluated between EI and E2 could not be perfectly reproducible between E3 and E4 despite the long delay that separated the sessions, we evalu­ated only drug effects that were inversely correlated to time effects:

Case 1: (E4 - E3) - (E2 - EI) > 0 and E2 - EI ::; 0 and E4 - E3 > 0, postdrug-evoked signal increases

Case 2: (E4 - E3) - (E2 - EI) < 0 and E2 - EI 2: 0 and E4 - E3 < 0, postdrug-evoked signal decreases.

RESULTS

Activation maps

Figure lA shows the group statistical parametric maps for the condition ACT! - REST> 0 obtained during the first examination EJ (n = 12). Areas of activation in­cluded mainly contralateral and, to a lesser extent, ipsi­lateral primary sensorimotor cortex (S 11M 1), parietal cortices (Brodmann area [BA] 40, BA 7), supplementary motor area (SMA), cingulate cortex (BA 24, BA 32), bilateral premotor cortices, frontal cortices (BA 8-9), contralateral thalamic nuclei, and cerebellum. Presence

and size of all activated areas, including the contralateral SllMl cortex, were variable among subjects.

Interaction between time and movement:

time effects

Significant evoked signal intensity changes were ob­served between examinations EJ and E2 (P < 10-

3; n =

12). A large increase in signal intensity occurred in a restricted area of the ipsilateral cerebellar cortex, and a parallel large reduction of signal intensity occurred in some parts of the primary and secondary motor cortices, including the posterior SMA (Fig. lB; Table 1). Notice that the decrease in sensorimotor activation spared the center of the SliM 1 area (knob of the central sulcus) so the area of activation was restricted, whereas the inten­sity of activation remained stable in the center of the SllMl area between examinations EJ and E2.

Beyond a good intraindividual reproducibility found when the two control experiments of the first session were compared (no significant difference between E] and E2 evoked signal intensities in many areas, including motor cortices, anterior SMA, vermis, and most of the cerebellum; P < 0.01), time effects in specific cerebellar and cortical areas were evidenced when experiments were repeated after only 5 hours. When the group of 12 subjects was split at random into two groups of 6 and when this time effect was considered, no statistical dif­ference was found between the time effect of the two groups. This statistic validated that such a time effect existed and was reproducible among groups of subjects.

TABLE 1. Comparisons of activations [ACTI-REST} between E} and E2 examinations

Extent of area Talairach coordinates

Activated areas z (mm) x y z Z score

E2 - EI > 0 Cerebellum

Ipsilateral [-25;-20] -17 -47 -25 6.18 E2 - E1 < 0 MI

Contralateral [40;45] 30 -14 40 6.86 Ipsilateral [30;45] -26 -l3 40 4.00

Sl Contralateral [35;45] 34 -33 40 7.62 Ipsilateral [40] -39 -27 40 4.17

PMC Ipsilateral [30;45] -38 -8 40 3.19

Parietal (BA 40) Contralateral [20;45] 35 -46 40 6.08 Ipsilateral [20;40] -27 -58 40 4.77

Post-SMA; cingulum (BA 24-32) [35;45] 3 -23 45 4.58 BA 8-9

Contralateral [30;40J 14 34 40 3.74 Ipsilateral [30;40] -21 27 40 6.87

Z score >2.32, P < 0.01 uncorrected for multiple comparisons, corrected for spatial extent. Coordinates of local maxima (Talairach coordinates) with significant changes as indicated by the highest Z score within an area. x: lateral distance from the midline (+: left hemisphere contralateral to the movement, -: right hemisphere ipsilateral to the movement). Extent of activated areas relative to commissural (AC-PC) plane is provided.

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MONOAMINE ENHANCERS MODULATE BRAIN MOTOR ACTIVITY 1369

Interaction between drug and movement:

drug effects

Evaluation of time effects was considered as a neces­sary step before a pharmacologic study could be per­formed. To correctly assess drug effects, the time effects previously evidenced were taken into account (see Ma­terials and Methods). Fluoxetine or fenozolone intake did not change the mean arterial blood pressure or heart rate of healthy volunteers. The subjects mentioned no clinical side effects during the procedure. No vascular effects are expected from these pharmacologic types of drug. In functional images, no effects of fluoxetine or fenozolone were observed in areas that were not activated or deac­tivated by the sensorimotor tasks.

The main effects of administration of a single dose of either fluoxetine or fenozolone concerned cerebellum and contralateral sensorimotor cortices.

Both drugs elicited a highly significant and wide­spread decrease of activation in bilateral cerebellum and vermis (fenozolone group: approximately -55% at the maximum peak; fluoxetine group: approximately -133% at the maximum peak; P < 10-6) (Figs. 2 and 3, green and blue clusters; Tables 2 and 3). The plots of a local maxi­mum in ipsilateral cerebellum for the fluoxetine group show evoked signal changes through E1, E2, E3, and E4 examinations: (Fig. 4). A time effect occurred in this part of the ipsilateral cerebellum (E2 - El > 0), and fluoxetine intake reversed it (E4 - E3 < 0). Cerebellar activity de­crease was more pronounced in the fluoxetine group. Two foci that were less activated after fluoxetine also appeared in the brain stem and may suggest changes in the activation state of somatosensory fibers, that is, of the spinothalamic tract and of the fasciculi gracilis and cu­neatus, in the medial lemniscus.

The second main effect was a large reduction of the spatial extent of activation and of the evoked signal in­tensity in the contralateral sensorimotor area (fenozolone group: approximately -37% of signal intensity decrease at the maximum peak; fluoxetine grollr approximately -67% at the maximum peak; P < 10 ) (Figs. 2 and 3, green and blue clusters; Tables 2 and 3). Both drugs also elicited a more focused increase in evoked signal inten­sity in the same area (Figs. 2 and 3, red clusters).

For the fenozolone group, the focus of hyperactivity clearly seen at z = 45 mm along the contralateral central sulcus (approximately +83% at the maximum peak, P <

-3 10 ) was surrounded by large areas of decreased evoked signal encompassing sensorimotor and premotor areas.

For the fluoxetine group, sensorimotor foci of hyper­activity were larger and more significant (Fig. 3). The evoked signal intensity was increased by approximately

-6 +73% at the maximum peak (P < 10 ). Figure 5 shows plots of the increase after fluoxetine intake for the maxi­mum peak. A similar pattern also was seen along the ipsilateral central sulcus (Fig. 2). The foci also were

surrounded by decreased signal areas in the sensorimotor and premotor fields.

Both drugs elicited the same pattern of changes in the mesial motor areas, SMA, and cingulate cortex (BA 6, BA 32, BA 24): a depressed activity in anterior mesial areas and an enhanced activity in posterior mesial areas (Figs. 2 and 3). Again, this effect was more prominent in the fluoxetine group.

Therefore, when the fluoxetine group was compared with the fenozolone group, we found a greater increase of activation in executive motor areas (primary motor cortex, premotor cortex, posterior cingulate cortex, and posterior SMA). The greater changes observed after fluoxetine treatment could not be explained by a group effect, that is, by a greater activation [(ACTI - REST)El > 0] of the fluoxetine group compared with the fenozolone group, but a difference of dose effect between the two drugs cannot be discarded.

A significant increase in activation also was observed in the contralateral thalamus after fluoxetine administra­tion. Changes in the amplitude of the activation also were observed in Brodmann's areas 40 and 7 (Tables 2 and 3). In fact, both drugs induced similar changes in the differ­ent motor areas, but fenozolone increased signal activa­tion in Brodmann's area 40, whereas fluoxetine de­creased it (Figs. 2 and 3).

DISCUSSION

We demonstrated, for the first time, that cerebral mo­tor activity can be modulated by a single low dose of fluoxetine or fenozolone in healthy subjects and that fMRI sensitivity is high enough to evidence such changes. Our results showed that both drugs induced similar profound changes in the entire motor pathway, including primary and secondary cortices, thalamus, and cerebellum. We also noticed time effects between two examinations in accordance with a habituation phenom­enon.

Time effects

The first methodologic session of the current study showed that time effects occurred between two exami­nations separated by 5 hours. We found no published studies assessing the reproducibility of fMRI signals be­tween two experiments separated by several hours. Nev­ertheless, a reduced extent of cortical motor activated areas was demonstrated when 10 to 30 minutes separated the experiments (Ramsey et aI., 1996). Such changes can reflect merely a diurnal effect or, more likely, a habitu­ation effect. The lower cortical activity in the second experiment is consistent with the known effects of ha­bituation (Karni et aI., 1995). These time effects are in­terpreted as a routinization of the task when experiments are repeated over a short time scale of few hours. How-

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1370 I. LOUBINOUX ET AL.

z = -25 mm z=-20mm

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FIG. 2. Fenozolone effects on sensorimotor activation. Hyperac­tivated areas (red-yellow clusters, Case 1) and hypo activated areas (green-blue clusters, Case 2) after fenozolone treatment (n = 6) superimposed on T1-weighted magnetic resonance im­ages (Z score> 2.32, P < 0.01 uncorrected and corrected for spatial extent). A corresponding Z score bar is provided. Six transaxial images of -25, -20, 45, and 50 mm under and above the anterior-posterior commissural line are shown. Left side of the figure corresponds to the right hemisphere. Notice a signifi­cant and widespread decrease of activation in bilateral cerebellar cortices and vermis (green-blue clusters). A red focus clearly seen at z = 45 mm on the knob of the contralateral central sulcus demonstrates enhanced activity (approximately +83% at the maximum peak, P < 10-3). It is surrounded by large areas of decreased signal encompassing sensorimotor and premotor ar­eas. Notice the increased participation of the posterior part com­pared with the anterior part of mesial areas (cingulum and supplementary motor area [SMA]).

ever, the neural substrate triggering the process had never been suggested or demonstrated. We showed that, in parallel with the decreased cortical activity, a re­stricted cerebellar cortical area displayed a strongly in­creased activity in the second examination compared with the first one. Thus, this cerebellar area seems to be the assumed triggering neural substrate that inhibits cor­tical activity. Our hypothesis is in line with the known effects of the cerebellum, which would assume a greater role as the task becomes "automatic" (Shadmehr et aI., 1997). Karni et al. (1998) and Brashers-Krug et al. (1996) demonstrated that some gains continue to develop after motor practice has ended and require time to be­come effective. It should result in less effort and less energy demand to perform the task, and maybe in de­creased use of inefficient brain areas (Haier et aI., 1992). This study emphasizes the cerebellum participation in

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motor planning, motor performance, and in monitoring and adjustment of sensory acquisition to optimize pro­cessing in the rest of the brain (Parsons et aI., 1997).

Drug effects

Cerebral motor activity was seen to be modulated by a single low dose of fluoxetine or fenozolone in healthy subjects, and the pattern of changes was in accordance with the known neuroanatomy of monoaminergic trans­mitter systems. The densities of adrenergic and sero­toninergic sites were found to be high in the sensorimo­tor cortex (Geyer et aI., 1997). It would be difficult to explain a change in the activation pattern such as a fo­calization in the sensorimotor cortex by a general vascu­lar effect, and no effect on cardiovascular systems or psychological variables with low doses of drugs, such as those used in this study, have been reported (Gelfin et aI., 1998; Wong et aI., 1990; Walker-Batson et aI., 1995). Specific neurovascular effects on regional CBF and me-

z = -25 mm z = -20 mm

z =45 mm z =50 mm

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FIG. 3. Fluoxetine effects on sensorimotor activation. Hyperac­tivated areas (red-yellow clusters, Case 1) and hypoactivated areas (green-blue clusters, Case 2) after fluoxetine treatment (n = 6) superimposed on T1-weighted magnetic resonance images (Z score> 2.32, P < 0.01 uncorrected and corrected for spatial extent). A corresponding Z score bar is provided. Six transaxial images of -25, -20, 45, and 50 mm under and above the ante­rior-posterior commissural line are shown. Left side of the figure corresponds to the right hemisphere. Notice a highly significant and widespread decrease of activation in bilateral cerebellar cor­tices and vermis (green-blue clusters). A red focus clearly seen at z = 45 mm near the knob of the contralateral central sulcus demonstrates enhanced activity (approximately +73% at the maximum peak, P < 10-6). It is surrounded by large areas of decreased signal encompassing sensorimotor and premotor ar­eas. Notice the increased participation of the posterior part com­pared with the anterior part of mesial areas (cingulum and SMA).

MONOAMINE ENHANCERS MODULATE BRAIN MOTOR ACTIVITY

TABLE 2. Coordinates of local maxima (Talairach coordinates) in hyperactivated and hypoactivated areas after fenozolone treatment (n = 6)

Talairach coordinates

Extent of area % of Activated areas z (mm) x y z Z score change

Post-drug increases: case no. 1 SIIMI

Contralateral [45] 38 -16 45 3.48 83 Ipsilateral [45] -27 -23 45 2.97 125

Parietal (BA 40) Contralateral [45] 29 -58 45 3.69 533 Ipsilateral [40;45] -39 -46 40 3.45 92

Post-SMA; Cingulum [45] 5 -17 45 2.87 75 Post-drug decreases: case no. 2 Vermis [-30;-20] 0 -61 -20 5.11 -55 Cerebellum

Ipsilateral [-30;-20] -17 -54 -30 3.63 -58 SIIMI

Contralateral [40;45] 36 -26 40 6.08 -37 PMC

Ipsilateral [45] -32 -10 45 4.23 -ISO Contralateral [30;45] 53 -I 35 4.87 -130

SMA; Cingulum [45] 9 -6 45 2.94 -50

Post-drug signal increases correspond to case No. I and post -drug signal decreases corre­spond to case No. 2 (see Materials and Methods). Significant changes as indicated by the highest Z score within an area (Z score >2.32, P < 0.01 uncorrected for multiple comparisons, corrected for spatial extent). x: lateral distance from the midline (+: left hemisphere contra­lateral to the movement, -: right hemisphere ipsilateral to the movement). Percentage of signal changes of local maxima are calculated. Extent of activated areas relative to commis­sural (AC-PC) plane is provided.

TABLE 3. Coordinates of local maxima (Talairach coordinates) in hyperactivated and hypoactivated areas after fluoxetine treatment (n = 6)

Talairach coordinates

Extent of area % of Activated areas z (mm) x y z Z score change

Post-drug increases: case no. I SIIMI

Contralateral [35;45] 36 -23 40 5.99 73 Post-SMA; Cingulum [45;50] 12 -6 45 3.63 142 Thalamus [5;10] 24 -18 10 5.21 125 Post-drug decreases: case no. 2 Cerebellum

Ipsilateral [-25;-20] -17 -47 -25 7.70 -1.33 Contralateral [-25;-20] 35 -45 -25 6.52 -193

SIIMI Contralateral [35;50] 49 -14 45 4.74 -67 Ipsilateral [45] -30 -26 45 7.14 -180

SI Contralateral [40;45] 47 -26 40 4.72 -47

Parietal (BA 40) Contralateral [45;50] 38 -43 50 5.60 -62

SMA; Cingulum [45;50] I -2 50 3.76 -68 BA 7 ipsilateral [45;50] -12 -64 45 5.61 -140 Medial lemniscus [-20] -I -23 -20 3.53 -80

Post-drug signal increases correspond to case No. and post-drug signal decreases correspond to case No. 2 (see Materials and Methods). Significant changes as indicated by the highest Z score within an area (Z score >2.32, P < 0.01 uncorrected for multiple comparisons, corrected for spatial extent). x: lateral distance from the midline (+: left hemi­sphere contralateral to the movement, -: right hemisphere ipsilateral to the movement). Percentage of signal changes of local maxima are calculated. Extent of activated areas relative to commissural (AC-PC) plane.

1371

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1372 I. LOUBINOUX ET AL.

Cerebellum

Case n02:

(E4 - E3) - (E2 - E1) <0

with E2 - E1 � 0

and

with E4 - E3 < 0 ,

%2��E� __ � __ �E�� Rest • Acti Rest· Acti

1.5

0.5

0

-0.5

-1

-1.5 0 30 800 30 80

seconds

E E %2

1.5 .

Decrease with. drug

-1.5 '--------'------'-----'--------' o 30 800 30 80

seconds fluoxetine

OIl �

FIG. 4. Plots of the local maximum in ipsilateral cerebellum (x =

-17; Y = -45; z = -25) for the fluoxetine group showing signal changes through E1, E2, E3, and E4 examinations (mean ± SD). Results are expressed in d% [(x - meanRes,)/meanRes,l where meanRes' is a mean value for E1, E2, E3, and E4 rest values. These plots illustrate Case 2, a decrease in signal activation after drug administration: (E4 - E3) - (E2 - E1) < 0 (Z score = 7.70). A time effect is visible in this part of the ipsilateral cerebellum: E2 -E1 > 0 (i.e., [(ACT I - REST)E2 - (ACTI-REST)E11 > 0), and fluox­etine intake reversed such an effect: E4 - E3 < 0 (i.e., [(ACT I -REST)E4 - (ACTI - REST)d < 0).

tabolism can occur with this type of drug (Freo, 1996; Mann et aI., 1996; Meyer et aI., 1996). High doses of 5-HT serotonin reuptake inhibitors (approximately 40 mg/kg) reduced regional CMRglc selectively in limbic areas and in brain stem monoaminergic nuclei in animals (Freo, 1996). Significant regional changes were observed after a low dose of D,L-fenfluramine (Kapur et aI., 1994; Mann et aI., 1996) and of D-fenfluramine (0.3 mg/kg) (Meyer et aI., 1996) in the frontal cortex, temporal cor­tex, and thalamus using positron emission tomography.

J Cereb Blood Flow Metab, Vol. 19, No. 12, 1999

However, these effects may be independent of neuronal activity. Also, we did not observe any clinical side ef­fects in the volunteers. At first sight, a placebo effect cannot be eliminated. However, data analysis shows that this is unlikely. Indeed, both drugs induced similar ef­fects except in Brodmann's area 40 where opposite ef­fects were observed. Similar effects in both groups would be expected with a placebo. An order effect seems dif­ficult to suspect as a possible confound. It looks unlikely because the time between the two groups of sessions was

and

E E %2� __ � __ �� ____ A-�

Rest . Acti Rest. Acti •

1.5

- 1

-1,5 0 30 SO 0 3D SO

seconds

%2 E3 E4

1.5

0.5

o

-0.5

-1 Increa�e with.

drug -1.5 L-_-'--_-----!'--_--'-_---'

o 30 800 30 80 seconds

fluoxetine OIl �

FIG. 5. Plots of the local maximum in the contralateral sensori­motor cortex S1/M1 for the fluoxetine group showing signal changes through E1, E2, E3, and E4 examinations (mean ± SD). Results are expressed in d% [(x - meanRes,)/meanRes,l where mean Res' is a mean value for E1, E2, E3, and E4 rest values. These plots illustrate Case 1 , an increase in signal activation after drug administration: (E4 - E3) - (E2 - E1) > 0 (x = 36, Y = -23, Z

= 40; Z score = 5.99). A time effect is visible at this point: E2 - E1 < 0 (i.e., [(ACTI - REST)E2 - (ACTI- REST)E11 < 0), and fluox­etine intake reversed such effect: E4 - E3 > 0 (i.e., [(ACTI -REST)E4 - (ACTI- REST)d > 0).

MONOAMINE ENHANCERS MODULATE BRAIN MOTOR ACTIVITY 1373

too long (2 months). Moreover, we evaluated only drug effects that were inversely correlated to time effects.

The drugs affect the cerebral motor activity, suggest­ing their specific action and a direct or indirect involve­ment of monoamines, including 5-HT serotonin, in the regulation of cerebral motor activity. This is the first demonstration of the cerebral pattern induced by an as­sumed excitatory action of a monoaminergic drug such as fenozolone on motor activity. Notice that fluoxetine induced an enhanced activation of motor executive areas: motor and premo tor cortices and the posterior SMA. This confirms the role of 5-HT serotonin in motor control. Fluoxetine is not a purely selective serotoninergic reup­take inhibitor because it also is a weak inhibitor, but an inhibitor, nonetheless, of noradrenergic uptake (Wong et aI., 1990). However, it has been repeatedly shown that fluoxetine, at the concentration used in this study, does not alter noradrenaline uptake directly (Wong et aI. , 1974) and that several indirect mechanisms instead should be taken into consideration.

Fenozolone modulation of cerebral activity is norad­renergic but also dopaminergic and serotoninergic, whereas fluoxetine modulation is specifically serotonin­ergic, but the similarity of the effects of the two drugs remains striking. However, these results are in accor­dance witt. the distribution of the densities of eBJprazozin and eBJ5-HT ligands that bind to adren­ergic and serotoninergic sites, respectively, which are similar in the sensorimotor cortex (Geyer et aI., 1997). Also, it is probably impossible to manipulate the sero­toninergic system or one aminergic system alone without affecting the other aminergic systems.

In the motor cortices, the focus with an increased ac­tivation is located directly on the knob of the central sulcus that is thought to be the center of the motor hand area (Yousry et aI., 1997). This focus, surrounded by less activated areas, is interpreted as an enhanced activation of more efficient neurons sparing peripheral and less concerned neurons. As more restricted activation goes with simpler tasks (Shibasaki et aI., 1993), facilitating the effect of the two drugs on monoaminergic transmis­sion may increase motor performance and render the task easier. Increase in motor performance and efficiency of information processing in simple sensorimotor tasks has been demonstrated after the administration of flu vox­amine, another selective inhibitor of serotonin reuptake (Hasbroucq et aI., 1997). The pattern of drug effects presented in this study suggests excitatory brain motor responses coexisting with inhibitory brain motor re­sponses in local cortical areas. This may be explained by the fact that serotonin terminals in the cerebral cortex exert their main effect by activating pyramidal neurons and also by activating inhibitory gamma-aminobutyric acid interneurons, which have relatively local cortical effects (Mann et aI., 1996).

A greater involvement of the posterior cingulum and posterior SMA compared with the anterior part of these structures on administration of the two drugs suggests that enhanced monoaminergic transmission favored the execution rather than the programming of the movement (Deiber et aI., 1996) as far as such functions can be attributed to these structures. There is growing evidence that development of easiness and automaticity on a mo­tor task results in such changes in the SMA (Jenkins et aI., 1994, see Picard and Strick, 1996, for review).

The large decrease in the activation of cerebellar cor­tices after drug treatment suggests less involvement of cerebellum in performing the task and may be related to a reduction of information processing as performance is increased. Attenuation of activation in the lateral cerebel­lum and in cerebellar nuclei during the execution of overlearned writing movements has been found (Seitz et aI., 1994).

We demonstrated a drug effect that countered the ha­bituation phenomenon evidenced in the time effect. To­gether, these data are in line with the hypothesis that brain monoamine systems, including the 5-HT system, facilitate motor output. Accumulating evidence indicates that the 5-HT serotonin link to motor activity is related both to the coactivation of the noradrenergic nervous system and to the modulation of the afferent inputs of this system (Jacobs et aI., 1997). Its seems that the pri­mary functions of the 5-HT system in the brain are to facilitate motor output and concurrently inhibit sensory information processing (Jacobs et aI., 1993).

In conclusion, drug effects have been demonstrated on motor task-dependent physiologic responses. The ana­tomic, physiologic, and pharmacologic arguments pre­sented are in accordance with a real pharmacologic effect and not a pure placebo effect. The action of both drugs on sensorimotor cortices, SMA, cingulate cortices, and cerebellum suggests a facilitatory or stimulating function of the monoaminergic systems on motor activity. Also, it was shown that dextroamphetamine tends to "focus" neural activity in the specific network involved in par­ticular cognitive tasks (Mattay et aI., 1996). Because a pharmacologic effect of fenozolone and fluoxetine has been demonstrated, similar studies of more specific nor­adrenergic, dopaminergic, and serotoninergic agonists may be considered. Methodologic problems like habitu­ation have been evidenced; further studies will take them into account as well as the placebo effect. Neurotrans­mitter systems, like monoaminergic systems, largely in­nervate all brain regions, suggesting that they are in­volved in many physiologic cerebral functions. How­ever, the heterogeneity of the receptor types and SUbtypes and the differences in their cerebral distribution for each monoaminergic systems point out that more specific functions exist. Their determination will be a major con­cern in clinical studies on patient recovery where the

J Cereb Blood Flow Metab. Vol. 19. No. 12, 1999

1374 1. LOUBINOUX ET AL.

development of facilitatory drugs is needed, and where more specific drugs influencing precise cerebral func­tions without blocking others, reducing or avoiding un­desired side effects, are seriously warranted.

Acknowledgments: The authors thank Pr. Richard Frakow­iak for helpful discussion, and Dr. Claire Thalamas and Ie Centre d'Investigation Clinique du CHU (Centre Hospitalier de Toulouse) for their assistance.

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