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International audience; Idiopathic Parkinson's disease (PD) is characterized by mesencephalic dopaminergic neuron cell death and striatal dopamine (DA) depletion. The factors involved in the pathogenesis of the disease are still unknown. Transforming growth factor beta1 (TGFbeta1) is increased in the striatum of patients with PD. However, the effect of this increase is not known. Here, we show that overexpression of TGFbeta1, by recombinant adenovirus TGFbeta1 gene transfer, in the mesostriatal system of an MPTP mouse model of PD decreased the number of mesencephalic dopaminergic neurons. This effect also involved more extensive DA depletion in the striatum. Striatal enkephalin mRNA levels are augmented, suggesting a decrease in dopaminergic transmission to the postsynaptic target. In the absence of MPTP, TGFbeta1 greatly decreased the number of dopaminergic neurons in the ventral mesencephalon of fully mature mice. These results show that an increase in TGFbeta1 levels aggravate the parkinsonian status of MPTP mice and may therefore be a risk factor for the development of PD.

To investigate the contribution of the dopamine (DA) synthesis to both the calcium-dependent and the carrier-mediated, mechanisms of DA release in the striatum, anaesthetized rats were locally superfused in the striatum with a push‐pull cannula supplied with an artificial CSF containing tritiated tyrosine. DA, dihydroxyphenylacetic acid (DOPAC) and their respective specific activity were measured in eCuent and used to evaluate changes in the DA synthesizing rate. Excluding calcium ions from the CSF only partially reduced spontaneous DA release (70%) still leaving a possible carrier-mediated DA release. This eAect was not additive with a local superfusion with 0.1 mM a-methyl-p-tyrosine, a blocker of DA synthesis, suggesting that synthesis could already be reduced by calcium-free superfusion. Local superfusion with 100 mM cadmium in the presence or not of calcium ions, increased the DA release (220 and 350%, respectively), simultaneously reducing DA synthesis. Local application of 1 mM calcium ionophore (A23187) was without eAect on the basal release of DA but enhanced DA synthesis and increased the amphetamine-evoked and carrier-mediated amine release. We conclude that DA synthesis can be a modulatory process of the firing-independent and carrier-mediated amine release while it weakly aAects the classical calcium-dependent release. # 1999 Elsevier Science Ltd. All rights reserved.

A push-pull cannula supplied with artificial CSF was implanted in the striatum of anaesthetized rats, and the basal extracellular DA and DOPAC was assayed in the superfusates using HPLC and electrochemical detection. Simultaneously, a carbon fibre electrode was implanted in close proximity of the cannula and the evoked DA release was detected by differential pulse amperometry during stimulation of the DA axons. Local treatments with cadmium (100 μM) blocked the evoked DA release (−90%), but substantially increased the basal extracellular DA (+ 125%). The effects of glutamate agonists NMDA (1 mM) and kainate (0.1 mM), known to increase basal extracellular DA were confirmed (+150% and +60% respectively). It was, however, simultaneously observed that the evoked DA release was inhibited (−80% and −50%, respectively). Amphetamine (1 μM) released DA (+150%) and produced also an increase (+100%) of the evoked DA release. These results, apparently conflicting, show that the two mechanisms releasing dopamine (firing-dependent and not) can be directly and simultaneously observed. These two releasing processes appear to be not strictly antagonist. They are also differently and independently modulated by calcium and by local influences such those conveyed by glutamate.

The effects of a chronic imipramine treatment on the mesoamygdaloid pathway of rats were examined. Using semiquantitative immunocytochemical techniques, it was observed that the level of TH mRNA was decreased in the ventral tegmental area (VTA). In contrast, the TH protein was increased in both the VTA and amygdala. The TH activity was decreased in the amygdala when assessed under normal conditions but increased after a preincubation to phosphorylate the enzyme, suggesting a lowering of the protein-specific activity in the terminals. These results show that TH protein turnover in the mesoamygdaloid neurons can be reduced by chronic imipramine treatments, thereby producing an accumulation of inactive TH protein in the neurons while also decreasing TH gene activity in the cell bodies.

Twenty weeks after ibotenic acid lesions of the striatum, the amount of tyrosine hydroxylase (TH) in this structure was markedly increased. This was accompanied by a 3-fold increase in TH mRNA levels in the ipsilateral subtantia nigra (SN). Striatal levels of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) were markedly reduced. In the nucleus accumbens, spared by the lesion, DA neurotransmission was also altered, as evidenced by a reduction of DA and DOPAC, but no increase in TH could be detected. TH mRNA levels were moderately enhanced in the ventral tegmental area (VTA). Thus, lesioning in the striatum induces TH gene activation in both SN and VTA neurones, not strictly related to DA function at the terminal level.

The short-term inhibition by estradiol of tyrosine hydroxylase (TH) in tuberoinfundibular dopaminergic neurons was examined in vitro on hypothalamic slices from ovariectomized rats. TH activity (determined by L-3,4-dihydroxyphenylalanine accumulation in the median eminence after blockade of decarboxylase with NSD 1055) showed a 30-40% decrease within 1 h of incubation with estradiol. To determine whether a dephosphorylation process was involved in this decline in TH activity, we studied the sensitivity of the enzyme to dopamine (DA) feedback inhibition: In controls, we observed that two kinetically different forms of TH coexisted, with one exhibiting a Ki(DA) of 26.4 +/- 2 microM and the other being approximately 10-fold more sensitive to DA inhibition, with a Ki(DA) of 2.56 +/- 0.17 microM, likely corresponding to a phosphorylated and active form and to a nonphosphorylated and poorly active form, respectively. Conversely, after estradiol treatment all TH molecules exhibited the same Ki(DA) of 2.5 +/- 0.3 microM. This effect was stereospecific, because 17 alpha-estradiol could not promote it, whereas with 17 beta-estradiol, it could be observed at only 10(-11) M and after a short delay (30 min). Finally, this decrease in the Ki(DA) of the purported active form of TH could be prevented by okadaic acid (an inhibitor of protein phosphatases). These results suggest that estradiol can act directly on the mediobasal hypothalamus to trigger a rapid decline in TH activity and that this action may involve a decrease in TH phosphorylation.

A possible interference of the GnRH-associated peptide (GAP) with the metabolism of dopamine in the rat striatum was investigated. The presence of the precursor of the peptide in this central region of dopaminergic terminals was first evidenced using specific RIA. The action of GAP on dopamine release was investigated in the caudate nucleus using the local superfusion with a push-pull cannula supplied with an artificial CSF containing the tritiated precursor of dopamine [( 3H]tyrosine). Addition of GAP (1 microM) to the superfusing fluid resulted in an increase of the release of the newly synthesized dopamine without a significant modification of the total amine release. In situ neutralization of GAP by addition in the CSF of a rabbit serum containing antibodies directed against the GAP produced opposite effects evidencing a tonic function for this peptide. In addition to the increased specific activity of the dopamine released during GAP treatment, the alterations observed in the efflux (and the specific activity) of dihydroxyphenyl acetic acid and the activation of dopamine synthesis obtained in vitro in striatal slices in the presence of GAP led us to conclude that the GAP system could be considered as a positive control of dopamine synthesis.

The effects of acute estradiol (E(2)) treatment on both the activity of tyrosine hydroxylase (TH) in the median eminence and the serum level of prolactin (PRL) were investigated. Twelve-day-ovariectomized rats were injected with 17beta-E(2) (25mug sc) at 1100 h and sacrificed hourly from 1200 to 2300 h. TH activity was quantified by measuring the amount of exogenous tyrosine converted to L-DOPA in vitro by aliquots of median eminence homogenates. Serum PRL levels were evaluated by radioimmunoassay. A biphasic response of TH activity to treatment was observed: an immediate decrease occurred-preceding and accompanying a rise in serum PRL-followed by an increase beyond control levels 2 h after the maximal release of PRL. The increase in TH activity could be prevented by the pretreatment of rats with a specific rat PRL antiserum, suggesting it was not due to E(2) per se but rather mediated by the E(2)-induced PRL elevation. To pin-point the process underlying the E(2)-induced decrease in TH activity, we evaluated the kinetic parameters of TH in the median eminence as well as its quantity (by Western blot analysis) in the median eminence and arcuate nucleus. Finally, we used a sensitive dot-blot assay to quantify specific TH messenger ribonucleic acid in the arcuate nucleus. The decrease in TH activity after E(2) treatment paralleled an immediate decrease in the affinity of TH for its pterin cofactor (6-MPH4), while V(max) remained unchanged. A decrease in the amount of TH protein in the arcuate nucleus and median eminence as well as in the TH messenger ribonucleic acid level in the arcuate nucleus was also observed, but the latency of these effects precluded a major involvement in the immediate decline of TH activity. Therefore, when observed separately from those of PRL, E(2) effects on TH in tuberoinfundibular dopaminergic neurons are clearly inhibitory consisting of a 'deactivation' of the enzyme together with a reduction of its synthesis.

Forskolin (FSK) was locally injected into the substantia nigra (SN) of anesthetised rats. The day after injection (24 and 36 hr), tyrosine hydroxylase (TH) activity increased locally in this structure but remained unmodified in the ipsilateral caudate nucleus (CN). The amount of messenger RNA for TH (TH-mRNA) was also increased in the SN 24 hr after the injection. However, TH protein content was modified neither locally in the SN nor in the ipsilateral CN. In addition, the decrease of the ratio between dopamine and its first metabolite in the CN and the SN suggested a decreased activity of the dopaminergic nigral cells. The absence of increase of the protein synthesis in spite of the fact that TH-gene transcription was initiated could be the consequence of the inhibition of dopaminergic cells by the drug. These results confirm that, in vivo, TH induction is cAMP-dependent and demonstrate that the TH-gene activity is not strictly coupled to the activity of dopaminergic cells in the SN.

Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment.

Polyamine contents were determined in human temporal lobe epilepsy. In the seven patients studied, stereoelectroencephalography (SEEG) located the epileptogenic focus in Ammon's horn and neuropathological findings were limited to hippocampal gliosis and sclerosis. Each polyamine exhibited a specific regional distribution. The most important variations were observed for spermidine and spermine while putrescine levels varied less. The regional variation was predominant in middle > posterior > anterior parts of the temporal lobe. Spermine contents and the spermidine/spermine (SPD/SPM) index varied especially in the middle and posterior parts of the hippocampus. Metabolic SPD/SPM index and spermidine levels were found to be drastically increased in almost all limbic parts when compared to neocortical regions. The opposite was observed for spermine. The heterogeneous distribution of polyamines was compared to abnormal electrical activities recorded by SEEG: SPD/SPM index and spermidine levels were sharply increased in seizure onset areas and high levels of spermine were detected in temporal cortex propagation areas. The presently reported heterogeneity of polyamine contents might contribute to modulate differentially the local control of excitability in human temporal epilepsy.

The effects of moderate changes in extracellular dopamine concentrations on the in vivo binding of specific dopaminergic D2 radioligands with different affinities and kinetics were investigated in rats. Either ( 125 I)NCQ298 (Kd 5 19 pM), or ( 125 I)iodolisuride (Kd 5 0.27 nM) or ( 3 H)raclopride (Kd 5 1.5 nM) were administered intravenously (IV) to animals 1 h after the intraperitoneal (IP) injection of either a-methyl-p-tyrosine (AMPT) (250 mg/kg) or nomifensine (15 mg/kg), or saline. The kinetics of radioactivity concentration in the striatum, cerebellum, and plasma were measured for up to 4 h after ( 125 I)NCQ298 or ( 125 I)iodolisuride injection and up to 1.5 h after ( 3 H)raclopride injection. For each tracer, the striatum-to- cerebellum radioactivity concentration ratios (S/C) and the binding potential (BP), calculated as the association to dissociation binding rate constant ratios (k3/k4), were assessed and related to the changes in extracellular dopamine concentration induced by drug treatments. Results show that S/C and BP of ( 3 H)raclopride were significantly diminished by pretreatment with nomifensine, a drug that increases extracellular dopamine concentration. Nomifensine pretreatment induced no changes in the in vivo binding indexes of the high affinity ( 125 I)NCQ298 and a slight but not significant decrease of the binding indexes of ( 125 I)iodolisuride. Treatment with AMPT, which induced a 40% reduction in dopamine concentration, did not change ( 125 I)NCQ298 binding indexes but slightly increased those of ( 3 H)raclopride and ( 125 I)iodoli- suride. In conclusion, the change of dopamine concentration induces modification of radiotracer kinetics. Thus, the combined use of tracers with high and low affinities could allow us to obtain information both on receptor density and neurotransmitter release in vivo. However, as indicated by the ( 3 H)raclopride study with AMPT, small changes in the concentration of intrasynaptic dopamine cannot be easily detected. NUCL MED BIOL 26;1:91-98, 1999. © 1998 Elsevier Science Inc.

INTRODUCTION All the data from clinical and animal research clearly indicated that the estrogens affect the nigrostriatal dopamine (DA) function as well as behaviors mediated by striatal DA (see Van Hartesveld and Joyce, 1986, for review). So far, on the other hand, no consensus has been reached regarding either the locus, the direction or the mechanism of estrogen actions. Actually, depending on the dose of estrogen administered, the duration of treatment, the time interval between estrogen treatment and testing, the behavior measured and the part of the basal ganglia from which the behavior is elicited, estrogens appear either to enhance or to suppress striatal dopaminergic transmission. Thus, in an attempt to determine the nature of direct estrogen effects on the presynaptic component of the nigrostriatal dopamine system, the present studies were designed (1) to examine the effect of an acute physiological dose of estradiol (E2) on the in viva rate of DOPA accumulation in the striatum after i.p. administration of NSD 1015 and (2) to determine in viva whether E2 might act directly on the striatum to modulate DA synthesis and/or release, when delivered locally by means of a push-pull cannula.

The acute effect of physiological doses of estradiol (E2) on the dopaminergic activity in the striatum was studied. In a first series of experiments, ovariectomized rats were injected with 17 alpha or 17 beta E2 (125, 250, or 500 ng/kg of body weight, s.c.), and in situ tyrosine hydroxylase (TH) activity (determined by DOPA accumulation in the striatum after intraperitoneal administration of NSD 1015) was quantified. A dose-dependent increase in striatal TH activity was observed within minutes after 17 beta (but not 17 alpha) E2 treatment. To examine whether E2 acts directly on the striatum, in a second series of experiments, anesthetized rats were implanted in the striatum with a push-pull cannula supplied with an artificial CSF containing [3H]tyrosine. The extracellular concentrations of total and tritiated dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured at 20-min intervals. Addition of 10(-9) M 17 beta (but not 17 alpha) E2 to the superfusing fluid immediately evoked an approximately 50% increase in [3H]DA and [3H]DOPAC extracellular concentrations, but total DA and DOPAC concentrations remained constant. This selective increase in the newly synthesized DA and DOPAC release suggested that E2 affects DA synthesis rather than DA release. Finally, to determine whether this rapid E2-induced stimulation of DA synthesis was a consequence of an increase in TH level of phosphorylation, the enzyme constant of inhibition by DA (Ki(DA)) was calculated. Incubation of striatal slices in the presence of 10(-9) M 17 beta (but not 17 alpha) E2 indeed evoked an approximate twofold increase in the Ki(DA) of one form of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanism of the short-term activation by prolactin (PRL) of tyrosine hydroxylase (TH) in tuberoinfundibular dopaminergic neurons was examined in vitro on hypothalamic slices from ovariectomized rats. TH activity (determined by 3,4-dihydroxyphenylalanine accumulation in the median eminence after blockade of decarboxylase with NSD 1055) showed a dose-dependent increase within 2 h of incubation of the hypothalamic slices with PRL. To determine whether a phosphorylation process was involved in this increase in TH activity, we studied the sensitivity of the enzyme to dopamine (DA) feedback inhibition. In control median eminences, two kinetically different forms of TH coexisted, one exhibiting a Ki(DA) value of 29.92 +/- 0.49 microM, the other being approximately 15-fold more sensitive to DA inhibition with a Ki(DA) of 1.96 +/- 0.09 microM, likely corresponding to a phosphorylated and active form and to a nonphosphorylated and less active form, respectively. After PRL treatment, the TH form of low Ki(DA) remained unaffected, whereas the Ki(DA) of the purported active form of TH increased to 62.6 +/- 0.8 microM, suggesting an increase in the enzyme phosphorylation. This increase in the Ki(DA) of TH was selectively prevented by GF 109203X, a potent and selective inhibitor of protein kinase C, but not by a specific inhibitor of protein kinase A or calmodulin. Finally, this action of PRL could be mimicked by 12-O-tetradecanoylphorbol 13-acetate (a direct activator of protein kinase C). These results suggest that PRL, at the median eminence level, activates TH by increasing the enzyme phosphorylation and that this action may involve an activation of protein kinase C.

In vivo benzodiazepine receptor occupancy by increasing doses of CL 218,872 has been evaluated in the baboon Papio papio, using (11C) RO 15-1788 as specific radioligand and positron emission tomography as external detection system. Although BZR heterogeneity has been previously demonstrated in the brain of the living baboon using PET, we did not observe in our studies that CL 218,872 interacts preferentially with one of the BZR subtypes. The monophasic pattern of the dose dependent CL 218,872 displacement curve and the corresponding “in vivo Hill coefficient” near unity suggest that CL 218,872 binds in cerebral baboon cortex with a similar affinity with BZ1 as well as BZ2 subtypes. The anticon-vulsant properties of CL 218,872 against bicuculline and allylglycine-induced seizures were correlated with benzodiazepine receptor occupancy by assessment of electroencephalographic activity during positron emission tomography studies. Our data confirmed in vivo the hypothesis of a partial agonist anticonvulsant activity of CL 218,872. At the same time, the use of a GABAantagonist (bicuculline) or an inhibitor of the GABA synthesis (allylglycine) suggested the existence of an allosteric interaction between benzodiazepine receptors and GABA receptors.

Central type benzodiazepine receptors were studied in vivo by positron emission tomography in brain areas of 2 different groups of the baboon Papio papio: non-photosensitive (group 1) and those with an allylglycine-induced decrease in GABA-mediated inhibition (group 2). Further, a naturally photosensitive Papio papio (+3 level of photosensitive response) was compared to both groups. Regional brain binding of the specific benzodiazepine receptor ligand, [11C]Ro 15-1788, was not significantly different between groups 1 and 2. In addition, the data from the naturally photosensitive Papio papio did not seem to differ markedly from groups 1 and 2 either. Pharmacological effects of increasing doses of beta-CCM (0.05-3 mg/kg i.v.) and regional benzodiazepine receptor occupancy by the drug were simultaneously studied using electroencephalographic activity recording and positron emission tomography. A positive correlation was observed between the degree of photosensitivity of the baboon and sensitivity to the action of beta-CCM, with increasing convulsant efficacy of beta-CCM in going from group 1 to the naturally photosensitive baboon, then to group 2. Dose-related displacement curves of [11C]Ro 15-1788 binding by beta-CCM revealed that reduction in brain GABA concentration did not modify the inhibitory potency of beta-CCM on [11C]Ro 15-1788 binding in cerebral cortex. This suggests a lack of detectable in vivo allosteric effects of GABA on beta-CCM binding during beta-CCM-induced seizures. Thus, a given dose of beta-CCM displayed increasing pharmacological potency in going from baboons with the lowest photosensitivity to those with the highest, whereas benzodiazepine receptor occupancy by beta-CCM was similar in the cerebral cortex of the different baboons. Conversely, a given level of convulsant activity of beta-CCM was related to a different benzodiazepine receptor occupancy by the drug, depending on the photosensitivity of Papio papio. A given dose of a drug may, thus, have a different pharmacological potency when occupying the same number of receptors, depending on the physiopathological state of the subject.

An attempt was made to correlate the physiological or the dimethylbenz(a)anthracene (DMBA)-enhanced serum prolactin (PRL) surge, which occurs in the afternoon of proestrus in female Sprague-Dawley (SD) rats, with physiological or pathological changes in two biochemical estimates of the tuberoinfundibular dopaminergic (TIDA) neuron activity. Dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) concentrations as well as tyrosine hydroxylase (TH) activity were measured in the median eminence (ME) of control or DMBA-pretreated SD rats throughout the estrous cycle in relation to PRL secretion. In both groups of females, while the DA content was fairly constant, the DOPAC content and TH activity in the ME fluctuated markedly throughout the estrous cycle. Thus, in control animals, the DOPAC content, DOPAC/DA ratio and TH activity which were stable on the days of diestrus and morning of proestrus were markedly decreased at noon and early afternoon when serum PRL levels began to rise. Later in the afternoon of proestrus, when serum PRL levels were maximal, there was a marked but transient increase in the DOPAC content and DOPAC/DA ratio as well as a brief surge in TH activity. In the evening of the same day, when serum PRL returned to basal levels, the DOPAC content, DOPAC/DA ratio and TH activity were low. Finally on estrus morning, the DOPAC content, DOPAC/ DA ratio and TH activity increased again to reach the diestrus levels. In DMBA-pretreated females, similar fluctuations in TIDA neuronal activity occurred during the estrous cycle, but the dynamics of these changes was altered: the DOPAC/DA ratio and TH activity first showed a marked increase in the morning of proestrus day, before decreasing dramatically. No surge in TH activity was detectable in the afternoon of proestrus and the increase in the DOPAC/DA ratio was of lesser amplitude than that in the controls. In those females whose PRL levels were still higher than those of controls on the morning of estrus, the second increase in the DOPAC/DA ratio was not observed. These results suggest that the lowering in TIDA neuronal activity on the day of proestrus might explain the outset, but not the termination of the preovulatory PRL surge. The regulation involved in the latter process seems to be particularly impaired by DMBA pretreatment.

The release of newly synthesized [ 3 H]adenosine has been studied in vivo in cat caudate nucleus and substantia nigra, using a push pull cannula. In the presence of [ 3 H]adenosine as precursor, spontaneously released [ 3 H]adenosine was easily detectable in superfusates of the push pull cannula. In the caudate nucleus, potassium and veratridine caused a marked and reversible increase in [ 3 H]adenosine release. The effect of veratridine was completely blocked by tetrodotoxin (TTX) although TTX had no action by itself. Ouabain as well as glutamate, also markedly increased the release of [ 3 H]adenosine. The specific 5′ nucleotidase inhibitor α,β-methylene ADP, did not alter the increase in the amount of [ 3 H]adenosine obtained by veratridine, although it diminished the spontaneous release of [ 3 H]adenosine by about 20%. Push pull cannulae were also implanted simultaneously into the caudate nucleus and substantia nigra. Potassium applied into the caudate nucleus increased the local release of adenosine but did not change that observed in the substantia nigra. When potassium was applied into the substantia nigra, it also increased the local release of adenosine but did not change that observed in the caudate nucleus. The results are discussed in term of the possible existence of “purinergic neurons” and of the relation between the adenosine release and central nervous activity.

In order to study the mechanisms regulating the dopaminergic nigroamygdaloid cells, the release of dopamine was observed in the central nucleus of the amygdaloid complex. Halothane anesthetized rats were implanted, according to the experiment, with one or two push-pull cannulae in the central nuclei of the amygdala (ACE), the substantia nigra (SN) and/or the caudate nucleus (CN). Cannulae were supplied with artificial cerebrospinal fluid (CSF) containing tritiated tyrosine, and labeled dopamine [3H]DA was evaluated in successive superfusate fractions. Electrical stimulation of the medial forebrain bundle with an implanted bipolar electrode induced an increase of the [3H]DA release in the ipsi- and contralateral ACE. Electrical stimulation of the SN produced only a very delayed effect in the ipsilateral ACE but an immediate and large increase of [3H]DA release in the contralateral structure. Superfusion of unlabeled DA and α-methyl-p-tyrosine in the SN remained ineffective on the [3H]DA release in the ipsilateral ACE. In this structure the release of [3H]DA was, however, decreased by nigral superfusion with γ-amino-butyric acid (GABA). d -(+)-Amphetamine (1 μM), when superfused in the CN, induced a large enhancement of the [3H]DA release in the ipsilateral ACE simultaneously with the local increase of [3H]DA release. The results presented here are in agreement with the previous studies concerning the anatomical organization of the dopaminergic nigroamygdaloid pathway. The DA cell bodies located in the SN appear insensitive to a local action of DA, perhaps due to a lack of autoreceptors. They are, however, powerfully inhibited by GABA and the relation observed between the [3H]DA release in the CN and ACE support the hypothesis that the SN can act as a relay between the extrapyramidal and limbic systems.

The release of dopamine in the substantia nigra and striatum was investigated in halothane anaesthetized rats by means of the pushpull cannula method. Electrical stimulation of the subthalamic nucleus produced a marked enhancement of dopamine release in the ipsilateral substantia nigra. This effect is likely to be mediated by subthalamic efferent neurons since the application of acetylcholine in the subthalamic nucleus produced a similar effect. A later decrease of dopamine release was always observed in the ipsilateral striatum and was attributed to the autoregulation mechanisms of nigro-striatal dopaminergic neurons.

Intravenous administration of 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) leads to the progressive development of a model of Parkinson's disease in the primate. The development of damage occuring in the striatal area during MPTP-treatment was followed “in vivo” in a baboon by positron emission tomography (PET). Spiperone labelled with a positron emitter 76Br (76Br-BSP) was used for the quantitative “in vivo” imaging of D2 dopamine receptors. The decrease in the striatal binding of 76Br-BSP measured “in vivo”, after three series of MPTP injections, paralleled the increase in the severity of behavioral symptoms seen immediately after administration of the neurotoxin. At the end of the MPTP-treatment when neurological symptoms were the most important, a 36 % decrease in the 76Br-BSP specific binding was measured. Between the series of MPTP injections a partial recovery in the quantitative measurement of the 76Br-BSP specific binding occuring in the striatum was well correlated with the disappearance of the neurological syndrome. Post-mortem histological and biochemical studies in nigro-striatal anatomical structures of MPTP-intoxicated primates compared with control animals showed a 80 % loss of neuronal cell bodies in the substantia nigra compacta and a 42 % decrease in the density (Bmax) of D2 receptors (in vitro 3H-spiperone binding). All these results showed that the use of PET and 76Br-BSP allow to follow in a noninvasive way both the degenerative processes and the subsequent partial recovery which occur in dopaminergic striatal receptor function during MPTP-treatment.

An in vivo characterization of specific central type benzodiazepine (BZD) binding sites, labelled with [11C]Ro 15-1788 was performed, using positron emission tomography. After i.v. injection of 10 mCi [11C]Ro 15-1788 (corresponding to 1 nmol/kg), sequential quantitative tomographic slices of the brain were obtained during 80 min. In some experiments various doses of different cold drugs (BZD agonist or antagonist) were injected i.v. subsequently in order to explore the specificity of the binding of the radioligand in brain structures. The main criteria usually utilized in vitro to demonstrate a specific binding to receptors, such as regional distribution, stereospecificity and saturability of the binding and pharmacological effect linked to the receptor's occupancy, were demonstrated in the brain of a living baboon.