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V Leviel

Publications and source records attributed to V Leviel.

At least 55 records · Page 3Linked to original sources
PubMed1986

Nigroamygdaloid dopamine neurons: nigral modulation of their 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). Canulae 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 alpha-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 gamma-amino-butyric acid (GABA). D-(+)-Amphetamine (1 microM), 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.

Amygdala↗
PubMed1986

A single RNA species injected in Xenopus oocyte directs the synthesis of active tyrosine hydroxylase.

Tyrosine hydroxylase, the rate limiting enzyme in the biosynthesis of catecholamine, is a tetramer composed of four subunits of the same molecular mass. A full length cDNA clone encoding tyrosine hydroxylase has been inserted into the SP6 expression system. Translation of the corresponding RNA in Xenopus oocyte results in enzymatic activity, demonstrating that a single gene contains all the necessary genetic information to code for a functional enzyme. The potential of this system in the analysis of posttranslational tyrosine hydroxylase modifications is discussed.

Animals↗
PubMed1986

Stimulation of the subthalamic nucleus enhances the release of dopamine in the rat substantia nigra.

The release of dopamine in the substantia nigra and striatum was investigated in halothane anaesthetized rats by means of the push-pull 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.

Animals↗
PubMed1985

Spontaneous and evoked release of endogenous Zn2+ in the hippocampal mossy fiber zone of the rat in situ.

In rats anaesthetized with urethane, push pull cannulae were stereotaxically introduced in the hippocampus (bilaterally) and Zn2+ assayed in the perfusate by atomic absorption spectrophotometry. When the cannula was located in the immediate vicinity of the mossy fiber zone, both spontaneous and K+ evoked release of Zn2+ were observed, this release was associated with a reduction in the histologically demonstrable Zn2+ as assessed by means of the Timm's stain. Neither spontaneous nor evoked release of Zn2+ was observed when the cannula was located in the medial part of CA1, the fimbria or the thalamus. These observations suggest that Zn2+ is released in the mossy fiber zone.

Animals↗
PubMed1984

Intracerebroventricular apomorphine alleviates spontaneous forgetting and increases cortical noradrenaline.

Rats were trained in a 6 unit spatial discrimination maze for food reinforcement; they were then implanted with intracerebroventricular (i.c.v.) cannulae and tested 25 days after training. Control animals displayed significant forgetting; 10 micrograms apomorphine alleviated this forgetting, while a higher dose did not. A hole board activity study revealed that i.c.v. Apomorphine does not produce the shaped dose-response activity curve found with systemic injections. Neurochemical analysis of forebrain structures after injections showed that the dose which facilitated memory retrieval also increased cortical and hippocampal noradrenaline, while the larger dose did not.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1984

Blockade by frontocortical lesion of reciprocal regulation between the two nigrostriatal dopaminergic pathways.

Tritiated dopamine synthesized from tritiated tyrosine was estimated simultaneously in the two caudate nuclei and the two substantia nigra of cats anaesthesized with halothane. In control animals, the electrical stimulation of the right forelimb enhanced dopamine release in the right caudate nucleus and decreased dopamine release in the right substantia nigra. Opposite effects were observed in the contralateral structures. Left nigral application of d-amphetamine produced the same effect. However in cats with extensive lesions of the left pericruciate cortex, an increase in the release of dopamine in the left substantia nigra was the only detectable effect of these two treatments. These results suggest that the cortical structures are involved not only in the transfer of information between the two dopaminergic pathways but are also involved with regulation of the release of dopamine in the striatum originating in the substantia nigra. With regard to the role of the thalamic structures in this transfer of information, it is proposed that the thalamostriatal control of the release of dopamine previously suggested is closely dependent on cortical activity.

Animals↗
PubMed1983

Effects of naloxone on dopamine release in the nigrostriatal system.

Simultaneously with a systemic injection of naloxone (NAL), the effects of the nigral application of the d(+)-amphetamine (AMPH) or of right forepaw stimulation on the release of [3H]dopamine [( 3H]DA) in the two caudate nuclei (CN) and the two substantia nigrae (SN) were examined in halothane-anesthetized cats. These experiments were carried out using four push-pull cannulae implanted bilaterally in the CN and SN and continuously supplied with [3H]tyrosine [( 3H]Tyr), the metabolic precursor of dopamine. Nigral AMPH application (1 muM) produced a local increase of the [3H]DA in spite of the NAL injection (5 mg/kg) but the presence of this drug prevented the expected effect of AMPH in the three other structures. Furthermore, the effects of electrical forepaw stimulation (EPS) were abolished by injection of NAL. NAL alone had no effect on the spontaneous release of [3H]DA. It is concluded that antagonism between NAL and AMPH could be due: (1) to enkephalinergic control of dopamine regulated nigral efferents, (2) to an action on the thalamic structures responsible for the reciprocal control of the two nigrostriatal dopaminergic pathways.

Animals↗
PubMed1983

Release of adenosine in vivo from cat caudate nucleus.

A push-pull perfusion technique was used to study the release of endogenously synthesized [3H]-adenosine from caudate nucleus in the anaesthetized cat. The spontaneous release of [3H]adenosine newly synthesized from [3H]adenine reached a steady state level 40 min after the beginning of superfusion and continued for 4 h. Potassium and veratridine increased the release of newly synthetized [3H]-adenosine. The action of veratridine was completely blocked by tetrodotoxin. We conclude that spontaneous and evoked release of adenosine occurs in the cat striatum and might potentially affect central nervous function.

Adenosine↗
PubMed1983

Effects of unilateral electrical stimulation of various thalamic nuclei on the release of dopamine from dendrites and nerve terminals of neurons of the two nigrostriatal dopaminergic pathways.

The role of several motor and intralaminar thalamic nuclei in the regulation of dopamine release from terminals and dendrites of the nigrostriatal dopaminergic neurons was investigated in halothane-anaesthetized cats. For this purpose, the effects of the unilateral electrical stimulation of various thalamic nuclei on the release of newly synthesized [3H]dopamine were simultaneously determined in both substantiae nigrae and caudate nuclei using the push-pull cannula method. The electrical stimulation of the motor nuclei was the only one to induce asymmetric changes in the four structures since [3H]dopamine release was enhanced in the ipsilateral caudate nucleus and reduced in the contralateral structure while opposite responses were observed in the corresponding substantiae nigrae. A reduction of [3H]dopamine release occurred in the four structures or only in the contralateral substantia nigra and caudate nucleus following the stimulation of the parafascicularis nucleus and the adjacent posterior part of the nucleus centrum medianum or of the nucleus centralis lateralis and the adjacent paralaminar part of the nucleus medialis dorsalis, respectively. The stimulation of the anterior part of the nucleus centrum medianum, which in contrast to other thalamic nuclei examined, receives few nigral inputs, selectively enhanced [3H]dopamine release in the contralateral substantia nigra. No significant changes in [3H]dopamine release were seen either in the substantiae nigrae or in the caudate nuclei following the stimulation of midline thalamic nuclei. These results indicate that the motor and intralaminar thalamic nuclei exert multiple and selective influences on the release of dopamine from terminals and/or dendrites of the dopaminergic neurons. They also further support a role of thalamic nuclei in the transfer of information from one substantia nigra to the contralateral dopaminergic neurons. The possible involvement of connections between paired thalamic nuclei was underlined by the observations of evoked potentials in contralateral homologous nuclei following unilateral stimulation of motor, or some intralaminar, nuclei. The present report provides new insights on the mechanisms contributing to the reciprocal and/or bilateral regulations of nigrostriatal dopaminergic pathways.

Animals↗
PubMed1981

Involvement of the thalamus in the asymmetric effects of unilateral sensory stimuli on the two nigrostriatal dopaminergic pathways in the cat.

The effects of unilateral sensory stimuli on dopamine (DA) release from nerve terminals and dendrites of the two nigrostriatal dopaminergic pathways were estimated in halothane-anaesthetized cats without or with sagittal transections. In control animals, the electrical stimulation of the right forelimb enhanced DA release in the right caudate nucleus (CN) and decreased DA release in the right substantia nigra (SN). Opposite effects were observed in the contralateral structures. Sagittal transections of the corpus callosum and commissura anterior, or of the mesencephalic decussations or of the thalamic massa intermedia were made to investigate mechanisms involved in the reciprocal regulation of the two dopaminergic pathways. These sections were without effect on the spontaneous release of DA from nerve terminals and dendrites. The transection of the thalamic massa intermedia was the only one which interrupted the asymmetric changes in DA release induced by unilateral sensory stimuli; an increased dendritic release of DA was only seen in the left SN but it was significantly less pronounced than that observed in control cats. The other transections did not prevent the asymmetric changes in DA release evoked by the sensory stimulation. However, the mesencephalic sagittal transection significantly reduced the stimulatory effect on DA release induced in the left SN. These results suggest that the thalamus is involved in the transfer of information implicated in the reciprocal regulation of the two dopaminergic pathways. In the light of electrophysiological data, the role of nigrothalamic neurones in this phenomenon is discussed.

Animals↗
PubMed1981

Dendritic release of dopamine in the substantia nigra.

Dopamine can be released in the substantia nigra for the dendrites of nigrostriatal dopaminergic neurones, to be involved there in the self-regulation of the dopaminergic cells, to control the release of neurotransmitters from nigral afferent fibres and to influence the activity of nigral non-dopaminergic cells.

Afferent Pathways↗
PubMed1979

Symmetric bilateral changes in dopamine release from the caudate nuclei of the cat induced by unilateral nigral application of glycine and GABA-related compounds.

The release of [3H]DA synthesized from [3H]tyrosine was estimated in the two caudate nuclei (CN) during the unilateral nigral application of glycine and GABA-related compounds in 'encéphale isolé' cats using push-pull cannulae. Glycine (10(-5) M) reduced the release of [3H]DA in both CN and these effects were antagonized by strychnine (10(-5) M). A decrease in [3H]DA release was also seen in both CN during the unilateral nigral application of diazepam (10(-5) M). In contrast, muscimol (10(-6) M) and GABA (10(-5) M) stimulated [3H]DA release on both sides. The effect of GABA was blocked by picrotoxin (10(-5) M). Picrotoxin alone stimulated the release of [3H]DA in the ipsilateral CN and was without effect in the contralateral side. Bicuculline (10(-5) M) stimulated [3H]DA release only in the contralateral CN. A symmetric increase in [3H]DA release in both CN was also observed during the unilateral nigral application of potassium (30 mM). A model involving a facilitatory polysynaptic pathway originating from the substantia nigra (SN) and acting presynaptically on ther terminals of the contralateral DA neurons is proposed to explain the changes in [3H]DA release induced in the contralateral CN in these various situations. The results are discussed taking into account previous data on the reciprocal control of the two dopaminergic pathways induced by the unilateral nigral application of dopaminergic drugs.

Animals↗
PubMed1979

Effects of the unilateral nigral application of dopaminergic drugs on the in vivo release of dopamine in the two caudate nuclei of the cat.

The effects of the unilateral application of d-amphetamine, benztropine, haloperidol and thioproperazine to one substantia nigra on the release of 3H-dopamine (3H-DA) in the two caudate nuclei were examined in halothane-anesthetized cats. For this purpose animals were implanted with push-pull cannulae and 3H-DA was estimated in superfusates during the continuous delivery of L-3,5-3H-tyrosine. The nigral application of d-amphetamine (10-6 M) or benztropine (10-6 M) reduced the release of 3-H-DA in in the ipsilateral caudate nucleus and induced an opposite effect in the contralateral side. In contrast, the nigral application of haloperidol (10-6 M) or thioproperazine (10-6 M) slightly increased the release of 3H-DA in the ipsilateral caudate nucleus and induced a reduction of 3H-transmitter release in the contralateral side. These results emphasize the role of the dendritic release of DA in the control of the activity of dopaminergic neurons and confirm our previous findings concerning the existence of a reciprocal control in the activity of the two dopaminergic pathways.

Animals↗