The effect of acetylcholine and dopamine on the caudate spindle in cats

Electrocortical activity was reacorded in cats whose caudate nuclei were perfused and electrically stimulated using a push-pull cannula. Electric stimulation invariably induced spindles (10-14 Hz) in the ipsilateral frontal cortex. Perfusions of acetylcholine together with physostigmine reduced the number of spontaneous spindles, the response to electric stimulation and induced behavioural arousal. This effect was atropine-sensitive. Perfusions of dopamine with or without tranylcypromine had no significant effect on the number of spontaneous spindles or the response to electric stimulation. Injections of both acetylcholine and dopamine into the cuadate nucleus invariably induced spontaneous spindles and slow waves. The significance of acetylcholine and dopamine in the caudate nucleus intiating caudate spindles and their significance in controlling arousal is discussed.     

Excitatory and inhibitory effects of dopamine on neuronal activity of the caudate nucleus neurons in vitro

Effects of dopamine on the rat caudate nucleus neurons were examined in a slice preparation using an intracellular recording technique. Perfusion of the bath with a low concentration (1 μM) of dopamine produced a depolarization concomitant with an increase in the spontaneous firing and the number of action potentials evoked by a depolarizing pulse applied into the cells. In contrast, higher concentrations (100–500 μM) of dopamine inhibited the spontaneous and current-induced firings without apparent effects on the resting membrane potential. In addition, during application of a high concentration (100 μM) of dopamine there was a marked elevation of the threshold potential of the action potential elicited by a higher depolarizing current. Simultaneous application of haloperidol (0.5–5 μM) antagonized both excitatory and inhibitory effects induced by the low and high concentrations of dopamine, respectively. In addition, the excitatory effect induced by a low concentration (1 μM) of dopamine was antagonized by domperidone (0.5 μM), a selective D₂ receptor antagonist, while the inhibitory effect by a high concentration (100 μM) was blocked by SCH 23390, a selective D₁ receptor antagonist. These results strongly suggest that the postsynaptic sites of caudate nucleus neurons have at least two subtypes of dopamine receptors (D₁ and D₂ receptors) that mediate inhibitory and excitatory responses of the neuron to dopamine, respectively.     

Peptide-induced grooming behavior and caudate nucleus dopamine release

We simultaneously measured the display of grooming behavior and, by monitoring the extracellular dopamine concentration via transversal microdialysis, the release of dopamine in the caudate nucleus in freely moving rats after i.c.v. administration of 1 μg adrenocorticotropic hormone-(1–24) (ACTH-(1–24)). During a period of 1 h after administration of the peptide, the incidence of excessive grooming behavior was increased. Concomitantly, the concentration of dopamine in the caudate nucleus dialysates was significantly increased (maximal effect 151% of basal release) whereas that of its metabolite DOPAC was unchanged. The potent α-melanocyte stimulating hormone (α-MSH) receptor agonist, [Nle⁴,D-Phe⁷]α-MSH, induced grooming behavior and stimulated caudate nucleus dopamine release (maximal effect 148% of basal release) whereas ACTH-(7–16)-NH₂ did neither induce grooming behavior nor cause an increase in caudate nucleus dopamine release. Single-dose tolerance was observed for ACTH-induced grooming but not for ACTH-induced dopamine release. These data are in support of the proposed involvement of brain dopamine systems in grooming behavior of the rat but at the same time suggest that the effect of ACTH/MSH-like peptides on dopaminergic transmission in the caudate nucleus is proximal to the final neural pathway involved in ACTH-induced grooming behavior.     

Muscarinic receptors on dopamine terminals in the cat caudate nucleus: Neuromodulation of [H]dopamine release in vitro by endogenous acetylcholine

The directly acting muscarinic receptor agonist oxotremorine (1.8–10 μM) produced an increase in electrically evoked [³H]dopamine release from slices of the cat caudate. The maximal increase caused by oxotremorine was 40%, and was antagonized by the muscarinic receptor blocking agent atropine (0.1 μM). Exposure to the acetylcholinesterase (AChE) inhibitor physostigmine (1 μM) resulted in a 50% increase in electrically evoked [³H]dopamine release. The increase caused by physostigmine was also antagonized by atropine (0.1 μM).Atropine did not, however, alter the modulations in [³H]dopamine release mediated by the dopamine autoreceptor: the increase in electrically evoked [³H]dopamine release caused by the dopamine receptor antagonist S-sulpiride (0.1 μM) and the decrease caused by the dopamine receptor agonist pergolide (30 nM) were unaffected by atropine (0.1 μM). These results indicate that the muscarinic receptor-mediated and dopamine autoreceptor-mediated presynaptic effects on [³H]dopamine release are independent.The present results suggest that in the electrically depolarized caudate slice in vitro, released endogenous acetylcholine may interact with muscarinic receptors faciliting depolarization-evoked [³H]dopamine release,ifAChE is inhibited. These muscarinic receptors may be located on dopamine nerve terminals. In the context of present neuroanatomical knowledge, the action of released endogenous acetylcholine on dopamine terminals may be a non-synaptic neuromodulation.     

Nicotinic effect of acetylcholine on the release of newly synthesized (3H)dopamine in rat striatal slices and cat caudate nucleus.

The effect of acetylcholine (ACh), carbachol and nicotinic blocking agents on the release of newly synthesized [3H]dopamine ([3H]DA) was studied in vitro on rat striatal slices and in vivo on the cat caudate nucleus. In the latter case, the animals were anaesthetized with halothane; in some experimetns an 'encéphale isolé' preparation was used to eliminate anaesthesia. Rat striatal slices placed in a superfusion chamber were continuously superfused with L-[3,5-3H]tyrosine. A cup placed on the ventricular surface of the cat caudate nucleus similarly allowed a continuous superfusion of the structure with the 3H amino acid. In both cases the quantities of [3H]DA contained in serial superfusate fractions were estimated; the drugs were always added in superfusing medium. In vitro ACh (10(-5) M) and carbachol (10(-5) M) enhanced the release of [3H]DA (90%). Similar results were obtained in vivo in anaesthetized cats. The effect of ACh (10(-5) M) was more pronounced (125%) in presence of eserine (10(-4) M) than with ACh alone (65%). ACh was also effective in unanaesthetized cats. The ACh effect on [3H]DA release was reproducible within the same experiment both in vitro and in vivo. This allowed to test the effect of anticholinergic agents on the ACh induced release of [3H]DA. In vivo hexamethonium (10(-4) M, 10(-5) M) partially blocked the release of [3H]DA induced by ACh (10(-5) M) alone; the effect was not seen when ACh was added in the presence of eserine (10(-4) M). Both in vivo and in vitro the prior introduction of mecamylamine into the superfusing medium antagonized the stimulating effect of ACh (10(-5) M) on [3H]DA release. The effects of this nicotinic blocking agent were seen with various concentrations (10(-6); (10(-5) 10(-4) in the in vitro experiments.     

Muscarinic receptors on dopamine terminals in the cat caudate nucleus: neuromodulation of [3H]dopamine release in vitro by endogenous acetylcholine

The directly acting muscarinic receptor agonist oxotremorine (1.8-10 microM) produced an increase in electrically evoked [3H] dopamine release from slices of the cat caudate. The maximal increase caused by oxotremorine was 40%, and was antagonized by the muscarinic receptor blocking agent atropine (0.1 microM). Exposure to the acetylcholinesterase (AChe) inhibitor physostigmine (1 microM) resulted in a 50% increase in electrically evoked [3H]dopamine release. The increase caused by physostigmine was also antagonized by atropine (0.1 microM). Atropine did not, however, alter the modulations in [3H]dopamine release mediated by the dopamine autoreceptor: the increase in electrically evoked [3H]dopamine release caused by the dopamine receptor antagonist S-sulpiride (0.1 microM) and the decrease caused by the dopamine receptor agonist pergolide (30 nM) were unaffected by atropine (0.1 microM). These results indicate that the muscarinic receptor-mediated and dopamine autoreceptor-mediated presynaptic effects on [3H]dopamine release are independent. The present results suggest that in the electrically depolarized caudate slice in vitro, released endogenous acetylcholine may interact with muscarinic receptors facilitating depolarization-evoked [3H]dopamine release, if AChE is inhibited. These muscarinic receptors may be located on dopamine nerve terminals. In the context of present neuroanatomical knowledge, the action of released endogenous acetylcholine on dopamine terminals may be a non-synaptic neuromodulation.     

Effects of electrical stimulation on acetylcholine synthesis in cat caudate nucleus

The concentration of endogenous- and deuterium-labeled acetylcholine (ACh) in the cat caudate nucleus was determined after stimulation of either the substantia nigra or the precruciate cortex. In this procedure the caudate nucleus is exposed surgically, and a coring device is used to obtain biopsy specimens which are immediately frozen in liquid nitrogen. Samples are collected at rest, 5 min after stimulation, and again 5 min after a resting period. An infusion of 2H9-choline is maintained during these manipulations to provide a label for ACh synthesis. Electrical stimulation of the substantia nigra, which increases the release of dopamine, produced a decrease in endogenous ACh and the newly synthesized deuterium-labeled ACh. Stimulation of the precruciate cortex produced no significant effect on the levels or synthesis of ACh, but attenuated the effect of subsequent nigral stimulation. These preliminary results indicate that stimulation of the substantia nigra has a net excitatory effect on ACh synthesis in the caudate. This stimulation apparently is modulated by input from the cortex.     

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.     

Contrasting effects of 5-hydroxytryptamine on the release of dopamine and acetylcholine in the nucleus accumbens of rat

Summary The interaction between 5-hydroxytryptamine (5-HT) and the release of dopamine and acetylcholine in the nucleus accumbens of rat was investigated. 5-HT (20M) significantly decreased levels of [³H]-dopamine synthesized from [³H]-tyrosine. 5-HT also enhanced the release of [¹⁴C]-dopamine at all concentrations of K⁺ tested (up to 34 mM). The maximal effect of 5-HT occurred at 15 mM K⁺ and was reversed by methysergide (3M). Increasing concentrations of Ca²⁺ facilitated the releasing effect of 5-HT up to 1.2 mM Ca²⁺. In contrast, 5-HT had an inhibitory effect on the K⁺-evoked release of [³H]-acetylcholine synthesized from [³H]-choline. 5-HT was not effective at non-depolarizing concentrations of K⁺. Increasing the external Ca²⁺ concentration to 2.5 mM overcame the inhibition of [³H]-acetylcholine release due to 5-HT. These results indicate that 5-HT has at least two actions in the nucleus accumbens, one which is a methysergidesensitive facilitatory action on dopamine release promoted by Ca²⁺ entry and a second, inhibitory effect on the K⁺-evoked release of acetylcholine, which is not blocked by methysergide and appears to operate by reducing Ca²⁺ influx.     

Effect of cholecystokinin-octapeptide on dopamine release from slices of cat caudate nucleus

The cat caudate nucleus has been reported to possess a rich and fairly even distribution of nerve endings, containing both dopamine- and cholecystokinin-like peptides. In this study, the effect of cholecystokinin-octapeptide (CCK-8) on basal and electrically evoked tritium outflow from slices of cat caudate nucleus previously labeled with [3H]dopamine was examined. Evoked tritium outflow from slices of cat caudate nucleus was Ca2+ dependent and abolished by tetrodotoxin, suggesting that it reflects action potential-induced [3H]dopamine release. In the presence of bovine serum albumin and bacitracin, the sulfated but not the unsulfated form of CCK-8 inhibited both basal and electrically evoked tritium outflow from slices of cat caudate nucleus at very low concentrations. CCK-8 sulfate was efficient in causing this effect in concentrations down to 10(-14) M, and the maximum effect was obtained with 10(-11) M. In contrast, without bovine serum albumin and bacitracin, no inhibitory effect of CCK-8 sulfate was seen, but instead, a marked enhancement of tritium outflow at 10(-7) M was observed. The findings suggest that CCK-8 sulfate in dopamine/CCK coexistence regions is involved in regulating dopamine release.     

Spontaneous blink rates correlate with dopamine levels in the caudate nucleus of MPTP-treated monkeys.

Previous studies have suggested a dopaminergic regulation of eye blink rates in human and nonhuman primates. Blockade of either dopamine (DA) D1 or DA D2 receptors or DA depletion induced by the dopaminergic neurotoxin MPTP both decrease spontaneous eye blink rates in monkeys. MPTP-induced decreases in blink rates can be reversed by administration of the full efficacy D1 agonist dihydrexidine, which has also been found to have dramatic antiparkinsonian effects in MPTP-treated animals. Increases in blink rates can also be induced by D1 and D2 agonists in normal animals. In the current study, we have investigated whether blink rates correlate with concentrations of DA or HVA and/or HVA:DA ratios in specific brain regions in MPTP-treated monkeys. Furthermore, the potential relationship between the severity of behavioral indices of parkinsonism and blink rates were examined. We found that (1) blink rates significantly correlate positively with concentration of DA and inversely with HVA:DA ratios in the rostral portion of the ventromedial body of the caudate nucleus (CD), but not other subcortical regions, and (2) that severity of parkinsonism was inversely correlated with blink rate. These data support a dopaminergic regulation of blink rate and suggest that the ventromedial region of the body of the CD may be critically involved in regulation of blink rate.     

Gene variants of brain dopamine pathways and smoking-induced dopamine release in the ventral caudate/nucleus accumbens

CONTEXT: Preclinical studies demonstrate that nicotine administration leads to dopamine release in the ventral striatum. However, human studies reveal considerable interindividual variability in the extent of smoking-induced dopamine release. OBJECTIVE: To determine whether common gene variants of the brain dopamine pathway explain this observed phenotypic variability in humans. DESIGN: Blood samples were drawn to determine gene variants of dopamine system components, and positron emission tomography scanning with the radiotracer raclopride labeled with radioactive carbon (11C) was performed to measure smoking-induced dopamine release. SETTING: Academic brain imaging center. PARTICIPANTS: Forty-five tobacco-dependent smokers. INTERVENTIONS: Subjects either smoked a cigarette (n = 35) or did not smoke (n = 10) during positron emission tomography scanning. MAIN OUTCOME MEASURES: Gene variants of dopamine system components (the dopamine transporter variable nucleotide tandem repeat, D2 receptor Taq A1/A2, D4 receptor variable nucleotide tandem repeat, and catechol-O-methyltransferase Val158Met polymorphisms) and change in [11C]raclopride binding potential in the ventral caudate/nucleus accumbens on positron emission tomography scans. RESULTS: For subjects who smoked during scanning, those with at least one 9 allele of the dopamine transporter variable nucleotide tandem repeat, fewer than 7 repeats of the D4 variable nucleotide tandem repeat, and the Val/Val catechol-O-methyltransferase genotype had greater decreases in binding potential (an indirect measure of dopamine release) with smoking than those with the alternate genotypes. An overall decrease in ventral caudate/nucleus accumbens binding potential in those who smoked compared with those who did not smoke was also found but was smaller in magnitude than previously reported. CONCLUSIONS: Smokers with genes associated with low resting dopamine tone have greater smoking-induced (phasic) dopamine release than those with alternate genotypes. These findings suggest that dopamine system genotype variabilities explain a significant proportion of the interindividual variability in smoking-induced dopamine release and indicate that smoking-induced dopamine release has a genetic predisposition.