Cat Caudate Research Articles

Effects of l-cysteine-sulphinate and l-aspartate, mixed excitatory amino acid agonists, on the membrane potential of cat caudate neurons

Responses evoked by l-cysteine-sulphinate ( l-CSA) and l-aspartate ( l-Asp) were recorded with intracellular electrodes from caudate neurons in halothane anesthetized cats. l-CSA and l-Asp were applied microiontophoretically to caudate cells and their effects on membrane and action potentials, as well as on cortically evoked synaptic potentials were evaluated. l-CSA and l-Asp induced depolarizations accompanied by regular firing resembling kainate (KA)- or quisqualate (QUIS)-induced excitation patterns (type 1) in 82% and 72% of the recorded neurons, respectively, and a mixed pattern consisting of a N-methyl- d-aspartate (NMDA)-like excitation (type 2) followed by a regular type 1 pattern in the remaining cells. In about a quarter of the cells the effects of l-CSA and l-Asp, but not those of KA or QUIS, were partially antagonized by 2-amino-7-phosphonoheptanoate (AP-7), a specific NMDA receptor antagonist. Kynurenate, a broad spectrum excitatory amino acid antagonist, blocked responses elicited by either l-CSA or QUIS. The actions of l-CSA and l-Asp on the firing pattern and membrane potential of cat caudate neurons in situ provide evidence in favor of their mixed agonist nature with respect to NMDA and non-NMDA excitatory amino acid receptors.

Dopamine neuron transplants: Electrophysiological unit activity of intrastriatal nigral grafts in freely moving cats

Fetal transplants of substantia nigra dopamine (DA)-containing neurons into the caudate nucleus in cats produced functional synaptic connections, as measured by behavioral analysis. Electrophysiological activity of single units from the intrastriatal nigral grafts revealed that these neurons displayed some of the characteristic electrophysiological parameters of DA neurons, i.e., long duration action potentials and tri-phasic waveform. However, these neurons discharged at a faster rate and never displayed the characteristic decremental burst pattern seen in intact, non-grafted animals. These data are the first electrophysiological recordings of grafted DA neurons in freely moving animals.

Characterization of substance P- and [MET]enkephalin-immunoreactive neurons in the caudate nucleus of cat and ferret by a single section golgi procedure

Modifications of the single-section Golgi-impregnation procedure of Gabbott and Somogyi 23 are described. The modifications allow easier and more rapid preparation of the sections for Golgi-impregnation and easier handling of large numbers of serial sections. The technique consists of placing a section that has been treated with osmium tetroxide and potassium dichromate on a microscope slide and “sandwiching” it with a second microscope slide. The two slides are held together at one end by tape and the assembly is dipped into a solution of silver nitrate. Golgi-impregnation of neurons occurs within a few hours and is generally complete within 12h. The technique has been applied to sections through the caudate nucleus of the cat and ferret in order to define the morphological characteristics of striatal substance P- and methionine enkephalinimmunoreactive neurons. Sections were first incubated to reveal the immunoreactive structures and then subjected to the Golgi method. Golgi-impregnated neurons that were immunoreactive for either substance P or methionine enkephalin had medium-size perikarya from which several dendrites emerged. The dendrites branched close to the perikaryon; secondary and higher order dendrites were densely laden with spines, as many as 15 spines per 10 μm of dendrite. It is concluded that both striatal substance P-containing and methionine enkephalin-containing neurons are of the medium-size densely spiny type. Medium-size densely spiny neurons may be homogeneous with respect to their somatodendritic morphology but heterogeneous with respect to their chemical characteristics and axonal morphology.

Ingestion-related activity of caudate and entopeduncular neurons in the cat

Single-unit activity was recorded in the caudate nucleus and entopeduncular nucleus in cats during ingestion. In both nuclei, ingestion-related neurons were of two types: those with no facial somatosensory receptive field and an ingestion-related response, and those with a facial somatosensory field and an ingestion response. Neurons in both regions contained cells with conditioned responses to the noise produced by the solenoid that delivered milk. No caudate neurons and only 3% of entopeduncular neurons were phasically related to jaw muscle activity. These results indicate that neurons in both input and output regions of the basal ganglia in the cat have complex ingestion-related response characteristics with little relationship to specific orolingual movements.

Morphological evidence for increased protein synthesis in CNS neurons after soman exposure

Fine structural changes in neurons of the dorsal hippocampus, caudate nucleus, supraoptic nucleus (SON), and ventral horn of the spinal cord of adult male or spayed female cats were studied after single and multiple doses (dose range 1.0–20.0 μg/kg sc) of the organophosphonate, pinacolyl methylphosphonofluoridate (soman). Increases in amounts of rough endoplasmic reticulum (rER) and polyribosomes, proliferation of Golgi complexes, as well as indentations of nuclear membranes occur after single and multiple exposures. The degree of change is dependent on dose, duration of exposure, and time of survival after exposure. The cell organelles affected are essential for protein synthesis and changes in their quantities are morphological indicators for changes in protein synthesis. The data presented in this study suggest an initial increase in protein synthesis after soman exposure, followed by early signs of degeneration. Soman (10 μg/kg iv) inhibition of cholinesterases of whole blood, spinal cord, and caudate nucleus of control and cats from which electrophysiological recordings of Renshaw cell field potentials were taken show significant differences. Moreover, while blood values are unmeasurable, spinal cord and caudate nucleus values are 42.21 and 53.6% those of controls at 30 min after injection and 63.41 and 50.75% those of controls after 240 min, respectively. No differences are noted between Renshaw cell field potentials after treatment and controls. Similarly, no changes in gross behavior are noted after 10 μg/kg sc. Yet, morphological signs of increases in protein synthesis are present. It is concluded that soman induces increased protein synthesis in many areas studied and that this increase is not dependent on inhibition of cholinesterase to a degree that affects gross behavior of evoked potentials from a CNS cholinergic-transmitting synapse—the motoneuron axon collateral and Renshaw cell ( J. C. Eccles, P. Fatt, and K. Koketsu (1954), J. Physiol. 126, 524–562).

Morphological Evidence for Increased Protein Synthesis in CNS Neurons after Soman Exposure

Fine structural changes in neurons of the dorsal hippocampus, caudate nucleus, supraoptic nucleus (SON), and ventral horn of the spinal cord of adult male or spayed female cats were studied after single and multiple doses (dose range 1.0-20.0 micrograms/kg sc) of the organophosphonate, pinacolyl methylphosphonofluoridate (soman). Increases in amounts of rough endoplasmic reticulum (rER) and polyribosomes, proliferation of Golgi complexes, as well as indentations of nuclear membranes occur after single and multiple exposures. The degree of change is dependent on dose, duration of exposure, and time of survival after exposure. The cell organelles affected are essential for protein synthesis and changes in their quantities are morphological indicators for changes in protein synthesis. The data presented in this study suggest an initial increase in protein synthesis after soman exposure, followed by early signs of degeneration. Soman (10 micrograms/kg iv) inhibition of cholinesterases of whole blood, spinal cord, and caudate nucleus of control and cats from which electrophysiological recordings of Renshaw cell field potentials were taken show significant differences. Moreover, while blood values are unmeasurable, spinal cord and caudate nucleus values are 42.21 and 53.6% those of controls at 30 min after injection and 63.41 and 50.75% those of controls after 240 min, respectively. No differences are noted between Renshaw cell field potentials after treatment and controls. Similarly, no changes in gross behavior are noted after 10 micrograms/kg sc. Yet, morphological signs of increases in protein synthesis are present. It is concluded that soman induces increased protein synthesis in many areas studied and that this increase is not dependent on inhibition of cholinesterase to a degree that affects gross behavior of evoked potentials from a CNS cholinergic-transmitting synapse--the motoneuron axon collateral and Renshaw cell (J. C. Eccles, P. Fatt, and K. Koketsu (1954), J. Physiol, 126, 524-562).

The relative roles of neuronal activity and direct presynaptic mechanisms in controlling the release of dopamine from the cat caudate nucleus.

Annals of the New York Academy of SciencesVolume 473, Issue 1 p. 80-91 The Relative Roles of Neuronal Activity and Direct Presynaptic Mechanisms in Controlling the Release of Dopamine from the Cat Caudate Nucleusa ANDRE CHERAMY, ANDRE CHERAMY Chaire de Neuropharmacologie INSERM U.114, College de France 75231 Paris cedex 05, FranceSearch for more papers by this authorRANULFO ROMO, RANULFO ROMO Chaire de Neuropharmacologie INSERM U.114, College de France 75231 Paris cedex 05, FranceSearch for more papers by this authorJACQUES GLOWINSKI, JACQUES GLOWINSKI Chaire de Neuropharmacologie INSERM U.114, College de France 75231 Paris cedex 05, FranceSearch for more papers by this author ANDRE CHERAMY, ANDRE CHERAMY Chaire de Neuropharmacologie INSERM U.114, College de France 75231 Paris cedex 05, FranceSearch for more papers by this authorRANULFO ROMO, RANULFO ROMO Chaire de Neuropharmacologie INSERM U.114, College de France 75231 Paris cedex 05, FranceSearch for more papers by this authorJACQUES GLOWINSKI, JACQUES GLOWINSKI Chaire de Neuropharmacologie INSERM U.114, College de France 75231 Paris cedex 05, FranceSearch for more papers by this author First published: December 1986 https://doi.org/10.1111/j.1749-6632.1986.tb23606.xCitations: 5 a Supported by grants from Rhône-Poulenc, DRET (83.084), INSERM, and CNRS (ATP). A. Chéramy is a research fellow of Rhone-Poulenc Sané. R. Romo is an IMSS fellow from Mexico. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume473, Issue1Neurochemical Analysis of the Conscious Brain: Voltammetry and Push‐Pull PerfusionDecember 1986Pages 80-91 RelatedInformation

In vivo presynaptic control of dopamine release in the cat caudate nucleus—I. Opposite changes in neuronal activity and release evoked from thalamic motor nuclei

Halothane-anaesthetized cats implanted with three push pull cannulae were used to estimate the effects of γ-aminobutyric acid (GABA) application (either 10 −3 M or 10 −5 M ) into the left motor nuclei of the thalamus (either ventralis medialis, or ventralis lateralis) on the firing rate of dopamine cells in the left substantia nigra (caudomedial part) and on the release of [ 3H]dopamine continuously synthesized from [ 3H]tyrosine, in the left substantia nigra (caudomedial part) and the left caudate nucleus. Preliminary experiments were performed to establish the electrophysiological characteristics of dopamine cells and non-dopamine cells in the pars compacta (mediocaudal part of substantia nigra) in groups of animals with the electrode inserted within the nigral push pull cannula or with the electrode inserted in the absence of a push-pull cannula. Dopamine and non-dopamine cells were distinguished according to several criteria (shape of the spike, duration of spike, frequency of discharge, conduction velocity estimated following antidromic activation from the caudate nucleus for dopamine cells or from the ventralis medialis for non-dopamine cells). Data obtained from recordings made within the push pull cannula were identical to those obtained in the absence of the cannula. In addition both the intravenous injection of amphetamine or its local application (10 −6 M) in the substantia nigra inhibited the firing rate of dopamine cells. When GABA was applied at 10 −3 M for 30 min into the ventralis medialis ventralis lateralis the multi-unit activity of thalamic cells recorded within the push pull cannula was inhibited. Single unit activity of dopamine cells was also inhibited and [ 3H]dopamine release was reduced in the caudate nucleus and increased in the substantia nigra. These results suggest that under these conditions, dopamine release from nerve terminals depended upon nerve activity and that dopamine released from dendrites inhibited the activity of dopamine cells. When GABA was applied at 10 −5 M for 30 min into the ventralis medialis-ventralis lateralis, multi-unit activity of thalamic cells was increased, single-unit activity of dopamine cells was inhibited and [ 3H]dopamine release was enhanced in the ipsilateral caudate nucleus and not affected in the left substantia nigra, demonstrating that in this situation the release of dopamine from nerve terminals was not dependent on the firing rate of dopamine cells. In addition, these results indicated that the activity of dopamine cells was not always dependent on the dendritic release of dopamine. Further experiments performed in cats with an acute hemi-transection (left side) made just in front of the substantia nigra to cut through all dopamine fibres confirmed that the GABA (10 −5 M )-evoked release of [ 3H]dopamine in the caudate nucleus was mediated by a presynaptic regulation triggered from thalamic-motor nuclei. Indeed, [ 3H]dopamine release was still enhanced by GABA (10 −3 M) application into the ventralis medialis-ventralis lateralis of such animals. In contrast the application of GABA (10 −3 M) into the ventralis medialis-ventralis lateralis was without effect on [ 3H]dopamine release; n the caudate nucleus of the hemi-transected animals. Results are discussed in the light of the respective contributions of nerve activity and presynaptic regulation in the control of dopamine transmission in the caudate nucleus.

In vivo presynaptic control of dopamine release in the cat caudate nucleus—II. Facilitatory or inhibitory influence of l-glutamate

The local effects of various concentrations of l-glutamate (from 10 −8 M up to 10 −8 M) on the release of [ 3H]dopamine synthesized continuously from [ 3H]tyrosine were examined in the caudate nucleus of halothane-anaesthetized cats implanted with push-pull cannulae. When used at a concentration of 10 −8 M or 10 −7 M, l-glutamate stimulated the release of [ 3H]dopamine from nerve terminals of the nigrostriatal dopamine neurons. This effect was still observed in the presence of tetrodotoxin (5 × 10 −7 M) but it was antagonized by 2-amino 6-trifluoromethoxy benzothiazole (PK 26124) (10 −5 M), an antagonist of glutamatergic transmission suggesting that the glutamatergic receptors involved were located on dopamine nerve terminals. While no significant change in the release of [ 3H]dopamine was observed with 10 −6 M l-glutamate, higher concentrations (from 10 −5 M to 10 −3 M) of the amino acid produced a longlasting reduction in the [ 3H]transmitter release. This latter effect was also antagonized by PK 26124 (10 −5 M) but, unlike that observed with 10 −8 M l-glutamate, it did not persist in the presence of tetrodotoxin (5 × 10 −7 M). On the contrary, a marked stimulation of the release of [ 3H]dopamine was seen in the presence of this neurotoxin. The reduction in the release of [ 3H]dopamine produced by 10 −4 M l-glutamate was also antagonized by bicuculline (10 −5M) and moreover a marked stimulation of [ 3H]dopamine release took place in the presence of this γ-aminobutyric acid (GABA) antagonist. Therefore, high concentrations of l-glutamate exerted an inhibitory presynaptic control on [ 3H]dopamine release which seemed to be indirect and mediated partly by GABAergic neurons. Since a sustained reduction in the spontaneous release of [ 3H]dopamine was seen in the presence of PK 26124, the corticostriatal glutamatergic neurons appeared to exert a tonic facilitatory presynaptic influence on dopamine release. This effect was important since it represented 40% of the tetrodotoxin-sensitive release of the [ 3H]transmitter. The direct (stimulatory) and indirect (inhibitory) presynaptic controls on dopamine release mediated by corticostriatal glutamatergic fibres are discussed in light of previous findings and of the anatomical organization of the caudate nucleus.

In vivo presynaptic control of dopamine release in the cat caudate nucleus—III. Further evidence for the implication of corticostriatal glutamatergic neurons

In confirmation of previous results, experiments in halothane-anaesthetized cats implanted with push-pull cannulae showed that the unilateral application of GABA (10 −5M for 30 min) into the left thalamic motor nuclei (either ventralis medialis, or ventralis lateralis) markedly stimulated the release of [ 3H]dopamine continuously synthesized from [ 3H]tyrosine in both caudate nuclei and in the contralateral substantia nigra. Three types of experiments confirmed that the changes in [ 3H]dopamine release evoked in both caudate nuclei resulted from a presynaptic facilitation mediated by the bilateral corticostriatal glutamatergic projection: (1) The constant delivery of 2-amino 6-trifluoromethoxy benzothiazole (PK 26124) (10 −5 M) to the left caudate nucleus prevented the increased release of [ 3H]DA evoked by application of γ-aminobutyric acid (GABA) (10 −5M) into ventralis medialis-ventralis lateralis while an enhanced release of [ 3H]dopamine still occurred in the contralateral caudate nucleus. Since PK 26124 is an antagonist of glutamatergic transmission, the presynaptic facilitation may involve glutamatergic neurons. (2) Single unit recordings of dopamine cells in the contralateral substantia nigra indicated that the increased release of [ 3H]dopamine from dendrites evoked by the application of GABA (10 −5M) into ventralis medialis ventralis lateralis was associated with a reduction in the firing rate of dopamine cells. Thus, the enhanced release of [ 3H]dopamine in the contralateral caudate nucleus may involve a presynaptic facilitatory process. (3) Finally, the unilateral lesion of the sensory motor cortex made prior to the superfusion of caudate nucleus with [ 3H]tyrosine prevented the responses evoked in the two caudate nuclei by the application of GABA (10 −5M) into ventralis medialis ventralis lateralis. Taken together, these results suggest that a thalamo-cortico-striatal neuronal loop involving the bilateral corticostriatal glutamatergic projection is responsible for the bilateral presynaptic facilitation of [ 3H]dopamine release induced in both caudate nuclei by the application of GABA (10 −5M) into ventralis medialis ventralis lateralis.

Immunohistochemical demonstration of neurotensin in striatal neurons of the cat, with particular reference to coexistence with enkephalin

Neurotensin-like immunoreactivity (NT-LI) was visualized in medium-sized, spiny neurons of the caudate nucleus (Cd) and putamen (Put) in colchicine-treated cats by the immunoperoxidase method. In serial sections alternately immunostained for NT and enkephalin (Enk), coexistence of NT-LI and Enk-LI was revealed in about 50% of NT-neurons and about 50% of Enk-neurons in Cd and Put.

In vitro release and electrophysiological effects in situ of homocysteic acid, an endogenous N-methyl-(D)-aspartic acid agonist, in the mammalian striatum

A potassium-induced, calcium-dependent release of endogenous homocysteic acid (HCA) from rat striatal slices was demonstrated. A precolumn derivatization high-performance liquid chromatography method was developed that allowed quantitative determination of sulfur-containing amino acids at the picomole level. Intracellular recordings from cat caudate neurons during simultaneous microiontophoretic application of drugs and electrical stimulation of the corticocaudate pathway showed that (L)-HCA evoked a depolarization pattern similar to that induced by N-methyl-(D)-aspartic acid (NMDA), and both these depolarizations could be selectively inhibited by a specific NMDA antagonist, (D)-2-amino-7-phosphonoheptanoic acid [(D)-AP-7]. A selective antagonism of (L)-HCA-induced depolarizations by (D)-AP-7 was confirmed in quantitative experiments with the frog hemisected spinal cord in vitro. Small quantities of iontophoretically applied (L)-HCA, but not of quisqualate, potentiated cortically evoked EPSPs in cat caudate neurons. These observations suggest that (L)-HCA might be a candidate as an NMDA-receptor-preferring endogenous transmitter in the caudate nucleus. One possible function for such transmitter systems could be the enhancement of EPSPs.

Quantitative morphology of medium-sized caudate spiny neurons in aged cats

These studies were designed to assess some of the morphological alterations that occur in medium-sized spiny neurons of the caudate nucleus in aged cats. Computer assistance was used to quantify in three dimensions the extent of the dendritic trees of 164 neurons from 11 cats (5 1–3 years and 6 over 10 years of age) stained by the rapid Golgi technique. In all animals beyond 10 years of age there was a decrease in the density of spines on distal dendritic segments. This decrease was moderate (16%) in 13 year old cats and reached about 50% in 15 and 18 year old animals. In addition, there was an increase in the frequency of occurrence of spines with enlarged heads in all aged cats. In cats over 13 years there was a marked loss of portions of distal dendritic segments. All measures of dendrite length displayed statistically significant decreases of 30–40% in cats 15 and 18 years of age. There were no significant age-related alterations in numbers of dendrites, number of branches per dendrite or soma diameter. These morphological results indicate that there is a sequence of age-related changes that occurs in caudate medium-sized spiny neurons and provides a basis from which to assess functional alterations.

The projection pattern of the suprageniculate nucleus to the caudate nucleus in cats

The suprageniculate nucleus of the posterior thalamus is a source of non-intralaminar thalamic nucleus which projects selectively to the medial and intermediate regions of the caudate nucleus in cats.

Caudate neuronal activity in cats during head turning: Selectivity for sensory-triggered movements

Units were recorded extracellularly from the caudate nucleus (CN) of cats during movement. The majority of CN units fired during sensory-triggered movements rather than movements in general. However, sensory stimulation was a necessary but not a sufficient condition for CN unit responding; stimuli caused unit responses only when movements were evoked. Additionally, only movements triggered by particular stimuli were associated with unit responding. These unit responses were not sensory because neural activity changes were associated with movement onset rather than stimulus presentation. These data are in accord with recent suggestions of a sensory-based motor function for the basal ganglia.

Conditionability of caudate dopamine activity in the caudate nucleus of cats demonstrated by in vivo electrochemistry

An in vivo electroanalytic method was used to measure dopamine and dopamine metabolite levels in the anterior caudate of freely behaving cats. Food reinforcement was made contingent on either increasing or decreasing dopamine metabolite levels. The cats were found to be capable of contingent metabolite level variation in accord with reinforcement contingency. The metabolite variations were observed as both short-term and long-term changes, and were significantly different than variations obtained during random reinforcement. No distinctive overt behavioral responses were observed to accompany any of the reinforcement conditions. These results indicate that central dopaminergic activity can be significantly altered through extrinsic control and further imply that specific stimulus environments may contribute to the regulation and/or disregulation of neurochemical brain systems.

Postnatal development of identified medium-sized caudate spiny neurons in the cat

The morphology of intracellularly recorded neurons in the cat caudate nucleus (Cd) was studied during postnatal development. After intracellular recording of evoked responses in these neurons, horseradish peroxidase (HRP) was injected iontophoretically through the recording micropipette. Fifty-eight Cd neurons in cats ranging from 6 days of age through adulthood were identified morphologically. All of the recovered Cd cells were medium-sized spiny neurons. The basic somatodendritic morphology of these neurons was evident in the youngest kittens. The most striking morphological change was the postnatal formation of an extensive local axonal collateral plexus. The development of these local axonal collaterals was also quantified with computer assistance in medium-sized Cd spiny neurons selected from silver-impregnated material. This analysis showed that the major development of the branches of this local plexus occurred between birth and 3–4 months of postnatal age. Data from both the HRP-filled and silver-stained axons indicated that the postnatal growth of the local axonal collaterals of the medium spiny cells was associated with the elaboration and increasing prevalence of evoked inhibitory postsynaptic potentials in Cd neurons.

Efferent connections of the cat caudate nucleus studied by retrograde axonal transport of horseradish peroxidase

A well-developed descending efferent system of the caudate nucleus has been revealed by retrograde axonal transport of horseradish peroxidase. It consists of numerous projections into the thalamus. A topical differentiation of the connections between the caudate nucleus and the paleostriatum and substantia nigra was found. It was established that the main source of efferent connections of the caudate nucleus were small and medium-sized neurons. It was demonstrated that the subthalamic nucleus has a special role in the descending efferent system of the caudate nucleus. In addition to the direct connections into the caudate nucleus itself the subthalamic nucleus has direct connections with the main output structures of the caudate nucleus, the paleostriatum, and the substantia nigra. The concept that the descending and ascending connections are interlinked in the mammalian central nervous system is supported by the results of this investigation into the caudate nucleus.

Local and remote effects of intra-caudate administration of GABA-related drugs on met-enkephalin release in the basal ganglion

The possible influence of GABAergic systems on the activity of enkephalinergic neurones within the basal ganglia was examined by measuring the release of Met-enkephalin in the caudate nuclei and pallida of halothane-anesthesized cats treated by intra-caudate applications of GABA-related drugs. Depending on the concentration used, GABA exerted local stimulatory (at 10 μM of the amino acid) or inhibitory (at 0.5 mM) action on Met-enkephalin release in the cat caudate nucleus. Only the inhibition was reproduced by the GABA agonists muscimol (1 μM) and (−)-baclofen (10 μM) and by diazepam (10 μM). Conversely, the intra-caudate application of the GABA antagonist bicuculline enhanced markedly the local release of the pentapeptide. Complementary studies using slices of the rat straitum (caudate nucleus + putamen) revealed that a low concentration of GABA (10 μM) tended to increase the K +-evoked efflux of Met-enkephalin, whereas a high concentration of the amino acid exerted a strong inhibitory effect on the peptide release. Such in vivo and in vitro findings suggest that the GABA-induced inhibition of Met-enkephalin release took place via the stimulation of specific GABA A and GABA B receptors within the caudate nucleus, whereas the GABA-induced increase of the peptide release might involve some intracellular regulatory processes in striatal neurones containing both GABA and enkephalins. In addition to altering the local release of Met-enkephalin, intra-caudate applications of GABA-related drugs affected the peptide release in the ipsilateral globus pallidus and contralateral basal ganglia. The observed changes suggest that GABA A, but not GABA B, receptors participated in some tonic inhibitory influence of striatal GABAergic neurones on the striato-pallidal enkephalinergic system. Furthermore, the present results confirmed previous studies (Bourgoin et al. 2) showing that GABAergic neurones can contribute to some bilateral modulation of enkephalinergic neurones within the basal ganglia.

Acetylcholine release in the cat caudate nucleus measured with the choline oxidase method

A chemiluminescent assay for the estimation of acetylcholine (ACh) was used to measure ACh release in caudate nuclei (CN) of halothane-anaesthetized cats implanted with push-pull cannulae. The validity of the entire experimental approach used was shown by the fact that ACh release was calcium-dependent and was increased by depolarizing agents (potassium ions, veratridine) as well as by atropine. The effects of GABA (10 −5 M, 30 min) unilateral application into the ventralis medialis and ventralis lateralis thalamic nuclei on ACh release in both CN were then examined. This treatment, known to increase DA release bilaterally, decreased ACh release in both CN. These data further reveal the role of thalamic nuclei in the bilateral regulation of the activity of neurons identified within the basal ganglia and are discussed in the light of the well-known inhibitory influence of nigrostriatal DA neurons on striatal cholinergic neurons.