Effect of several dopaminergic drugs and trihexyphenidyl on cholinergic parameters in the rat striatum

Non-VMAT2 inhibitor treatments for the treatment of tardive dyskinesia

Although VMAT2-inhibitors are now established as first-line treatment for tardive dyskinesia, not all patients respond to, or tolerate them. Numerous other agents have been adopted to treat tardive dyskinesia, but with variable results and generally lower quality methodologic reports. Amantadine is the most promising but benzodiazepines, branched chain neutral amino acids, Vitamin B6, several nutraceuticals, and botulinum toxin injections might help some patients. In all cases, better placebo controlled trials are needed before definitive recommendations can be made.

Influence of NOS inhibitors on changes in ACH release and NO level in the brain elicited by amphetamine neurotoxicity

We studied the possible role of neurotoxicity in the d,l-amphetamine (AMPH)-induced release of acetylcholine (ACH) in the nucleus accumbens (Nac) and the involvement of endogenous NO in this process. For determination of ACH release the Nac was superfused using the push-pull-technique. NO was directly measured using the electron paramagnetic resonance technique. Repeated administration of AMPH increased ACH release by about 400%. N-nitro-L-arginine (L-NNA) and 7-nitroindazole (7-NI) nearly abolished the AMPH-induced increase in ACH release. AMPH increased NO as well as lipid peroxidation (LPO) products in the cortex. L-NNA and 7-NI substantially diminished NO increase. AMPH-evoked LPO was only slightly reduced by these compounds. It is concluded that AMPH enhances ACH release through increased NO synthesis and induces neurotoxicity via NO and by LPO independent NO generation.

Comparative dopaminergic and muscarinic antagonist activity of clozapine and haloperidol

Clozapine is an atypical antipsychotic drug, and its dopamine and muscarinic antagonist activity has been compared with haloperidol in rodents. Elevation in rat striatal acetylcholine (ACh) and mice cerebellar cGMP has been used as an agonist response for oxotremorine and quinpirole. Pretreatment with clozapine significantly blocked oxotremorine-induced elevation in striatal ACh (p<0.01) and cerebellar cGMP(p<0.05). At the same doses, clozapine had no significant effect on quinpirole-induced increases in ACh and cGMP levels. Pretreatment with haloperidol significantly antagonized quinpirole-induced elevation in striatal ACh (p<0.01) and cerebellar cGMP(p<0.05), and haloperidol had no significant effect on oxotremorine-induced agonist responses. Thus, clozapine is antimuscarinic at a dose level that lacks dopamine antagonist properties, whereas haloperidol is a dopamine antagonist and lacks antimuscarinic activity. The atypical neuroleptic profile of clozapine may be due to its high antimuscarinic and low antidopaminergic activity.

Mechanism of the galanin induced increase in acetylcholine release in vivo from striata of freely moving rats

Galanin (GAL) administered intracerebroventricularly (i.c.v.) induced a strong and long-lasting increase in the basal acetylcholine (ACh) release from striata of freely moving rats only when the excitatory corticostriatal input was removed, while its effect was transient in striata of sham-operated rats. This effect was dose-dependent (0.78, 1.56 and 3.12 nmol) and was completely prevented by the GAL receptor antagonist, galantide. GAL injected locally (3.12 nmol) in deafferented striata also induced a persistent increase in ACh release although to a lower extent. The impairment of monoaminergic neurotransmission caused by alpha-methylparatyrosine or p-chlorophenylalanine, respectively inhibitors of catecholamine and serotonin synthesis, completely prevented the rise in ACh output from deafferented striata while the muscarinic antagonist, scopolamine (0.5 mg/kg, s.c.), failed to do it. The data suggest that GAL in the deafferented striatum facilitates basal ACh release through an indirect mechanism. The effect seems to be at least partly mediated by an action of GAL on specific receptors in the striata.

alpha-Methyl analogues of acetylenic amines as striatal muscarinic antagonists

The effect of acetylenic amines, with or without alpha-methyl substitution, on striatal acetylcholine (ACh) concentration in rats was investigated. Oxotremorine, oxotremorine-1, and U-77053 (trimethyl (4-(1-pyrrolidinyl)-2 butynyl)-urea), the unsubstituted amines, increased striatal ACh concentration. On the other hand, the corresponding alpha-methyl substituted analogues, alpha-methyl-oxotremorine, BM-5, and alpha-methyl U-77053, decreased the concentration of ACh in the striatum. The results indicate that substitution of alpha-methyl in acetylenic amines converts compounds from agonists to antagonists for striatal muscarinic receptors.

The effects of intraperitoneally administered phencyclidine on the central nervous system: behavioral and neurochemical studies

The effects of intraperitoneally (IP) injected phencyclidine (phencyclohexyl piperidine; PCP) on the metabolism of dopamine (DA) and cholecystokinin-like immunoreactivity (CCK-LI) in the rat brain were investigated in connection with PCP-induced behavioral changes. The predominant behavior change elicited by 2.5 mg/kg PCP was locomotion, while with higher doses (5 and 10 mg/kg) sniffing, swaying and falling were observed in addition to the enhanced locomotor activity. Backpedaling and rotation were observed in 10 mg/kg PCP-treated rats. IP injection of PCP caused a dose-related increase in the levels of DA and 3,4-dihydroxy-phenylacetic acid (DOPAC) in the medial frontal cortex (MFC) and anterior cingulate cortex (ant.CC) without any changes in the nucleus accumbens (NAc) or striatum. CCK-LI in the MFC, ant.CC and NAc was decreased in a dose-dependent manner following IP injection of PCP. These findings support the evidence that PCP selectively activates the mesocortical DA systems. Furthermore, our results indicate a functional relationship between the mesocortical DA neurons and intrinsic CCK containing cortical neurons, and the change in the activity of the intrinsic CCK-containing cortical neurons in these two areas, perhaps due to an alteration in DA transmission, might be involved in behavioral changes after PCP injection.

Contrasting neurochemical interactions of tiletamine, a potent phencyclidine (PCP) receptor ligand, with the N-methyl-D-aspartate-coupled and -uncoupled PCP recognition sites

Neurochemical interactions of tiletamine, a potent phencyclidine (PCP) receptor ligand, with the N-methyl-D-aspartate (NMDA)-coupled and -uncoupled PCP recognition sites were examined. Tiletamine potently displaced the binding of [3H]1-(2-thienyl)cyclohexylpiperidine with an IC50 of 79 nM without affecting sigma-, glycine, glutamate, kainate, quisqualate, or dopamine (DA) receptors. Like other PCP ligands acting via the NMDA-coupled PCP recognition sites, tiletamine decreased basal, harmaline-, and D-serine-mediated increases in cyclic cGMP levels and induced stereotypy and ataxia. Tiletamine was nearly five times more potent than PCP at inhibiting the binding of 3-hydroxy[3H]PCP to its high-affinity NMDA-uncoupled PCP recognition sites. However, following parenteral administration, dizocilpine maleate (MK-801), ketamine, PCP, dexoxadrol, and 1-(2-thienyl)cyclohexylpiperidine HCl, but not tiletamine, increased rat pyriform cortical DA metabolism and/or release, a response modulated by the NMDA-uncoupled PCP recognition sites. Pretreatment with tiletamine did not attenuate the MK-801-induced increases in rat pyriform cortical DA metabolism, a result suggesting that tiletamine is not a partial agonist of the NMDA-uncoupled PCP recognition sites in this region. However, following intracerebroventricular administration (100-500 micrograms/rat), tiletamine increased pyriform cortical DA metabolism with a bell-shaped dose-response curve. These data indicate a differential interaction of tiletamine with the NMDA-coupled and -uncoupled PCP recognition sites. The paradoxical effects of tiletamine suggest that tiletamine might activate receptor(s) or neuronal pathways of unknown pharmacology.

D1 and D2 dopaminergic regulation of acetylcholine release from striata of freely moving rats

The effects of selective D1 and D2 dopaminergic agents on the extracellular acetylcholine (ACh) content in striata of freely moving rats were determined by the microdialysis technique. LY 171555, a selective D2 agonist, reduced ACh output by approximately 30% within 20 min at the dose of 0.2 mg/kg, i.p., whereas the D2 antagonists (-)-remoxipride (10 mg/kg, s.c.) and L-sulpiride (50 mg/kg, i.p.) induced maximal increases of approximately 50% within 10 and 20 min, respectively. In contrast, the D1 antagonist SCH 23390 (0.25 mg/kg, s.c.) decreased the extracellular ACh content by approximately 30% in 20 min, but lower doses--0.025 and 0.05 mg/kg--had no such effect. The stimulation of ACh release by LY 171555 was prevented by (-)-remoxipride but not by SCH 23390 (0.25 mg/kg, s.c.). In addition, the D1 agonist SKF 38393 failed to modify the ACh increasing effect of (-)-remoxipride. Thus, the D1 and D2 receptors subserve opposing functions on ACh release. The D1/D2 dopaminergic agonist R-apomorphine, at the does of 1 mg/kg, i.p., reduced ACh output by approximately 35% only when D1 receptors were blocked by SCH 23390 (0.025 mg/kg, s.c.). The results provide clear in vivo evidence of the tonic inhibition exerted by dopaminergic nigrostriatal input on the cholinergic system of the basal ganglia through D1 and D2 receptors.

Anaesthesia effects on in vivo acetylcholine transmission; comparisons of radioenzymatic and HPLC assays

The effect of general anaesthesia on extracellular levels of acetylcholine (ACh) in the caudate-putamen of freely moving rats was studied by microdialysis. ACh concentrations were determined in the same perfusate samples by radioenzymatic and HPLC/electrochemical procedures in order to compare the assays. The concentration of ACh in perfusate samples was estimated to be 0.30 microM in conscious unrestrained rats. However, when these rats were administered chloral hydrate (400 mg/kg i.p.), the level of ACh was decreased immediately by 50%, attaining a value of 0.06 microM within 20-40 min following the injection. Upon recovery of the righting reflex, ACh levels were once again re-elevated. The levels of choline (Ch), the precursor of ACh, were unaffected by anaesthesia. It was apparent that the level of consciousness (i.e. awake vs. anaesthetized) is an important factor determining ACh overflow. Radioenzymatic and HPLC assays proved to give identical results for the analysis of ACh and Ch.

Effects of the l isomer of fenfluramine on dopamine mechanisms in rat brain: further studies

Experiments were carried out to gain additional evidence that l-fenfluramine reduces the dopamine-mediated effects in intact animals. l-Fenfluramine 5 and 10 mg/kg i.p. dose dependently raised the levels of homovanillic acid in the striatum and nucleus accumbens of rats 1 h after injection. The effect of 5 mg/kg l-fenfluramine disappeared and was actually reversed 4 and 8 h after injection. The effect of 10 mg/kg l-fenfluramine, administered 48 h after the last haloperidol dose, was completely antagonized in both striatum and nucleus accumbens of animals made tolerant to the effect of haloperidol on homovanillic acid levels (through repeated treatment with 1 mg/kg haloperidol i.p. twice daily for 11 days). Unlike haloperidol (0.25 mg/kg), l-fenfluramine in various doses (2.5-20 mg/kg i.p.) did not modify the levels of striatal 3-methoxytyramine or change the decrease induced by a s.c. injection of 0.5 mg/kg apomorphine. The effect of apomorphine was not antagonized by 10 or 20 mg/kg l-norfenfluramine, an active metabolite of l-fenfluramine but 20 mg/kg l-norfenfluramine significantly raised striatal 3-methoxytyramine levels. l-Fenfluramine 20 mg/kg (but not 10 mg/kg) significantly enhanced the output of striatal acetylcholine assessed by trans-striatal microdialysis, for 60 min after injection. Apomorphine 1 mg/kg i.p. completely antagonized the increase of acetylcholine caused by 1 mg/kg haloperidol or 20 mg/kg l-fenfluramine. The results confirm that the l isomer of fenfluramine produces effects on the responses to dopamine and acetylcholine similar to those of neuroleptics by a mechanism not involving direct blockade of receptors.

Differential effects of phencyclidine (PCP) and ketamine on mesocortical and mesostriatal dopamine release in vivo

The interactions of phencyclidine (PCP) with the mesocortical dopaminergic system were of interest because of the putative role of this pathway in the etiology of schizophrenia. In the present investigation we examined the effects of PCP, and PCP-receptor agonist, ketamine, on dopamine (DA) release by measuring the levels of 3-methoxytyramine (3-MT), the only DA metabolite which is a reliable indicator of DA release in vivo. PCP increased DA release in the amygdala, pyriform and prefrontal cortices, while ketamine was less potent than PCP in this respect. In contrast to the changes in DA release in the cortical regions, ketamine decreased DA release in striatum, while PCP did not change DA release.

Dual effect of N-methyl-N-(1-methyl-4-pyrolidino)-2-butyl)acetamide on release of (3H)-acetylcholine from the rat hippocampal slices

The effect of muscarinic cholinergic drugs on (3H)-acetylcholine [3H)-Ach) release from slices of rat hippocampus was investigated either in the presence of eserine or hemicholinium-3 (HC-3), 10 microM each. BM-5 (N-methyl-N-(1-methyl-4-pyrolidino-2-butyl)acetamide) is a partial muscarinic cholinergic agonist. Like oxotremorine, BM-5 significantly (p less than 0.012) decreased the release of (3H)-Ach in the presence of HC-3. In the presence of eserine, (3H)-Ach release was significantly (p less than 0.001) enhanced both by atropine and BM-5. The decrease or increase in release of (3H)-Ach by BM-5, in the presence of HC-3 or eserine, respectively, may be due to its partial agonist effect on hippocampal muscarinic cholinergic receptors.

Mesolimbic and mesocortical dopamine activation induced by phencyclidine: contrasting pattern to striatal response

The effects of acute administration of phencyclidine, an indirect dopamine agonist, on biochemical indices of dopaminergic activation were examined in mesocortical, mesolimbic and nigrostriatal regions of the rat. High doses (10 mg/kg) of phencyclidine resulted in a marked increase in levels of the dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid in all mesolimbic and mesocortical sites examined, as well as in the ventral tegmental area, source of the dopaminergic innervation of mesolimbic/cortical sites. In contrast, levels of both metabolites decreased in the striatum and tended to decrease in the substantia nigra, source of the striatal dopaminergic innervation. The metabolite response to phencyclidine was dose-related. These data indicate that the mesolimbic and mesocortical dopaminergic neurons are activated by phencyclidine. Since the firing rate of both A10 (ventral tegmental area) and A9 (substantia nigra) dopamine neurons has previously been shown to be increased by phencyclidine, these data suggest that phencyclidine results in a differential regulation of presynaptic release of dopamine in mesolimbic/cortical as opposed to nigrostriatal dopaminergic regions.

Differential effects of striatal injections of dopaminergic, cholinergic and GABAergic drugs upon swimming behavior of rats

The present study provides a detailed report about similarities and dissimilarities between the effects of neostriatally applied dopaminergic (apomorphine, 250-300 ng; haloperidol, 250-500 ng), cholinergic (carbachol, 50-100 ng; scopolamine, 200-500 ng), and GABAergic (muscimol, 1-2 ng; bicuculline, 5-35 ng) drugs upon swimming of rats. The used swimming test consisted of 4 parts: (a) open-field test for analyzing drug-induced changes in normal behavior; (b) 'swimming without escape' test for analyzing drug-induced changes in the ability to switch from one type of behavior to another; (c) 'swimming with escape' test for analyzing drug-induced changes in the ability to switch from ongoing swimming behavior to climbing behavior by allowing the rats to escape via a rope; and (d) 'rope' test for analyzing drug-induced changes in the kind of contact behaviors needed to switch to the latter climbing behavior. In the open-field test the drugs produced neither abnormal behavior nor motor disturbances, which prevented the display of normal behavior in the remaining tests. Both apomorphine and carbachol produced identical effects in all tests. Muscimol produced overall effects which were not only opposite to those of apomorphine and carbachol, but also comparable to those of scopolamine. All effects elicited by apomorphine, carbachol and muscimol were antagonized by their corresponding antagonists: haloperidol, scopolamine and bicuculline respectively, whereas the effects of the latter were suppressed by their corresponding agonists. These data globally show that dopamine and acetylcholine act in the same direction but opposite to that of GABA as far as it concerns the regions investigated. The finding that haloperidol injected into the GABA target area produced effects which were not only similar to those of haloperidol injected into the dopamine target area, but also dissimilar to those of muscimol and bicuculline injected into the GABA target area, shows that the effects were drug-specific rather than region-specific. Though 3 distinct cholinergic regions were investigated, cholinergic-specific effects could only be elicited from one region, suggesting that the neostriatum is heterogeneous in this respect. Finally, well-delineated dissimilarities between haloperidol-, scopolamine-, and muscimol-treated rats were found in the rope test. These data show that behavior-relevant information transmitted by GABAergic drugs surmounted that transmitted by cholinergic drugs which, in turn, surmounted behavior-relevant information transmitted by dopaminergic drugs.

Frontal decortication and adaptive changes in striatal cholinergic neurons in the rat

Interruption of the corticostriatal pathway by undercutting the cortex resulted in a reduction of glutamate uptake by 55% and in a depression of acetylcholine (ACh) synthesis by 30% in striatum after two postlesion weeks without affecting the content of ACh and choline, the specific binding of [3H]dexetimide to muscarinic receptors, the activity of choline acetyltransferase and the levels of noradrenaline, serotonin, dopamine and 3,4-dihydroxyphenylacetic acid. The influence of this excitatory pathway on striatal cholinergic neuropharmacology was investigated. It was found that the effect of a number of agonists (R-apomorphine, bromocriptine, lisuride, quinpirole, JL-14389, 2-chloroadenosine, oxotremorine and methadone), capable of depressing cholinergic activity in the striatum through receptor-mediated responses--reflected as an increase in ACh content--is operative only when the corticostriatal pathway is intact. By contrast, antagonists capable of decreasing ACh content, i.e. the typical neuroleptics pimozide, haloperidol and the atypical ones clozapine, L-sulpiride, as well as the anti-muscarinic agent scopolamine, were not influenced by the lesion. The possibility that the lesion non-specifically damaged striatal cells on which the agonists, but not the antagonists acted was excluded by results showing, firstly, that the increase in striatal ACh elicited by the ACh precursor, choline, was not blocked by decortication, and secondly, that the degeneration of the corticostriatal neurons did not prevent the ACh-increasing effect of bromocriptine, a long-acting ergot alkaloid, when sufficient time was allowed for the drug to act. It was furthermore possible to restore the inhibitory action of apomorphine on cholinergic neurons either by short-term chemical lesion of the nigrostriatal dopaminergic input or by the administration of choline.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dopaminergic drugs on striatal acetylcholine concentration

Striatal acetylcholine concentration was determined after administration of varying doses of apomorphine, (+)-PPP and (-)-PPP to rats. (+)-PPP at 3 and 10 mg kg-1 is a dopamine agonist, whereas (-)-PPP at 0.3 and 3 mg kg-1 is a dopamine antagonist in the striatum.

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.

Increased striatal acetylcholine after 14 months cis-flupenthixol treatment in rats suggests functional supersensitivity of dopamine receptors

Rats received continuous administration of cis-flupenthixol (0.8-1.2 mg/kg/day) or trans-flupenthixol (0.9-1.2 mg/kg/day) in drinking water for 14 months. The administration of cis-flupenthixol, but not trans-flupenthixol, caused apparent cerebral dopamine receptor supersensitivity. Thus, animals receiving cis-flupenthixol, but not trans-flupenthixol, showed enhanced apo-morphine-induced stereotyped behaviour. Dopamine concentration in striatum was not altered by drug treatment but striatal HVA and DOPAC concentrations were reduced in animals receiving cis-flupenthixol, but not trans-flupenthixol. No consistent change in Bmax of KD for specific striatal 3H-spiperone binding was observed after 14 months drug intake. However, in cis-flupenthixol treated animals a 40% increase in Bmax was observed following 2 weeks drug withdrawal. Continuous cis-flupenthixol intake increased striatal acetylcholine concentrations; trans-flupenthixol was without effect. This suggests the apparent increase in cerebral dopamine receptor supersensitivity caused by continuous long-term cis-flupenthixol administration is of functional importance in the intact animal.

Effect of dimethylamino-2-ethoxyimino-2-adamantane (CM 54903), a non-polar dimethylaminoethanol analog, on brain regional cholinergic neurochemical parameters

CM 54903, a new psychotropic drug with a particular pharmacological profile, produced a widespread but short-lasting decrease in acetylcholine content in rat brain hemispheric regions but not in the midbrain-hindbrain or cerebellum at the dose of 40 mg/kg, i.p. The decrease was most conspicuous in the striatum. Brian regional choline contents were unaltered as were the acetylcholine turnover rates in the striatum and hippocampus. Neither choline acetyltransferase nor acetylcholinesterase activities were altered after the in vitro incubation or the in vivo administration of high amounts of the drug. CM 54903 was found to be a competitive, reversible inhibitor of the sodium-dependent high affinity uptake of choline by crude hippocampal and striatal synaptosomal preparations showing an IC50 of 10 microM in vitro. Despite the fact that the drug readily crosses the blood-brain barrier and achieves brain concentrations several-fold greater than its in vitro IC50, CM 54903 did not inhibit choline uptake in vivo although it was capable of preventing the pentylenetetrazol-stimulated choline uptake by hippocampal synaptosomes. The changes in striatal acetylcholine content induced by the blockade or the stimulation of muscarinic cholinergic receptors or dopaminergic receptors did not interfere with the effect of CM 54903 on striatal acetylcholine content while pentylenetetrazol completely prevented the decrease. The results taken together indicate that the major effect of CM 54903 on the cholinergic neurons is at the presynaptic level to compete with choline at its uptake sites.

Neurochemical effects of buspirone, a novel psychotropic drug, on the central cholinergic system

Buspirone, a novel psychotropic anxioselective agent, produced a dose-dependent decrease in the level of acetylcholine in the striatum of the rat. The maximum effect of about 25-30% was produced at the dose of 20 mg kg-1. A smaller decrease of 10% was also found in the n. accumbens-olfactory tubercle while other brain regions were unaffected. The drug did not alter striatal choline acetyltransferase or acetylcholinesterase activities and was feeble in displacing [3H]dexetimide from its specific muscarinic binding sites. The effect of buspirone in lowering acetylcholine content was more marked and longer lasting in the striatum of female than male rats. Buspirone proved to be weak as a blocker of the dopamine receptor agonist, apomorphine, and it appears that only a small proportion of the decrease in striatal acetylcholine content can be attributed to the blockade of dopamine receptors. Rapid homologous tolerance to an acute challenge with buspirone on striatal acetylcholine was achieved within seven days of its chronic administration, and, unlike clozapine, a cross tolerance of buspirone to chronic haloperidol treatment was also observed. Other data indicating that the drug differed from haloperidol both qualitatively and quantitatively on dopaminergic neurochemical parameters, and the fact that it is not cataleptogenic, suggest that buspirone cannot be considered a typical neuroleptic agent. The possibility that buspirone may act as an agonist at certain presynaptic dopamine receptors, which could translate into a fall in striatal acetylcholine content, is discussed.

Effects of GABAergic drugs on brain stimulation reward as assessed by a 'threshold' method

Rats were trained in a two-lever intracranial self-stimulation (ICSS) paradigm. Responses at the first lever delivered brain stimulation which was decreased in magnitude after every 5 responses. Responses at the second re-set the available current to its original value. The current level at which the re-set responses occurred was defined as the 'reward threshold'. The rate of responding at each current level during the stimulate-re-set sequence was also determined. This paradigm, therefore, allowed simultaneous rate-independent and rate-dependent assessment of ICSS. Decreased reward, as demonstrated by an elevated 'reward threshold', was produced in a dose-related manner by the GABA antagonist picrotoxin. Similar effects could be produced by making each stimulation train less rewarding, i.e. by reducing the amount of charge delivered per stimulation. Conversely, increased reward, as indicated by a lower 'reward threshold', was produced in a dose-related manner by the GABA-mimetic muscimol, or by increasing the amount of charge delivered by each stimulation. Response rats were not significantly changed at any stimulation intensity following treatment with either drug. These data suggest that the effects of picrotoxin and muscimol on ICSS are due to changed perception of reward and not to altered performance of the lever pressing task. An important role for GABA in the mediation of reward needs, therefore, to be considered.

Evidence of the modulatory role of serotonin in acetylcholine release from striatal interneurons

The release of acetylcholine was studied in isolated striatal slices of the rat. The spontaneous and ouabain-stimulated release of acetylcholine was higher in those slices where serotonergic input was somehow impaired: raphe nuclei lesion or p-chlorophenylalanine pretreatment or 5, 7-dihydroxytryptamine pretreatment resulted in a higher release. L-(m-chlorophenyl)-piperazine, a pure serotonin receptor stimulant and D-fenfluramine, a serotonin releaser significantly reduced the release of acetylcholine evoked by ouabain. Serotonin antagonists (cyproheptadine, mianserine and methysergide) prevented the effect of serotonin agonists. When the serotonergic neurons were destroyed either by p-chlorophenylalanine or by 5, 7-dihydroxytryptamine pretreatment D-fenfluramine had no inhibitory action; however, the effect of L-(m-chlorophenyl)-piperazine was not affected. It is suggested that there is a link between serotonergic and cholinergic neurons in the striatum: serotonin released from raphe-striatal neurons is able to inhibit the release of acetylcholine from striatal interneurons.

Is dopamine-sensitive adenylate cyclase involved in regulating the activity of striatal cholinergic neurons?

The dopamine (DA)-receptor mediated changes in striatal acetylcholine (ACh) levels have been studied to determine if this effect involves a D1-(adenylate cyclase dependent) or D2-(not linked to an adenylate cyclase) type of DA-receptor, Various DA-agonists (apomorphine, N-diphenethylamine derivatives) increased striatal ACh levels in both intact and 6-OHDA lesioned rats whereas only apomorphine stimulated the adenylate cyclase activity of striatal homogenates. The N-diphenethylamine compounds (RU 24213, RU 24926 and RU 26933) were without effect either on basal or DA-stimulated activities of this enzyme. In contrast, D-LSD (which acts as a partial agonist of the striatal DA-sensitive adenylate cyclase) did not modify the striatal ACh content. More interestingly, an intrastriatal injection of cholera toxin greatly stimulated striatal adenylate cyclase without altering ACh concentrations. Both haloperidol and methergoline antagonized the DA stimulation of adenylate cyclase, but only haloperidol decreased striatal ACh levels. These results indicate that the DA receptor involved in regulating the activity of striatal cholinergic neurons is of the D2-type.

Alterations in neurotransmitter activity after acute and chronic ethanol treatment: studies of transmitter interactions

Acute and chronic ethanol treatment has multiple effects on the neurotransmitter systems in the nigrostriatal complex. A single dose of ethanol increases striatal dopamine release at low doses, but depresses it at high doses. In ethanol-dependent rats, dopamine release is accelerated during intoxication, but is reduced during a withdrawal syndrome. Concomitantly, high-affinity choline uptake, an index of cholinergic activity, is elevated at times when dopamine release is depressed. Changes in dopaminergic or cholinergic receptor activity do not induce or result from these effects. Neither has a role for GABA or substance P yet been implicated. The data suggest that interactions between at least two trasmitters in the caudate nucleus may occur after acute and chronic ethanol treatment.

Effects of diethylcholine in two animal models of Parkinsonism tremors

(2-Hydroxyethyl) methyldiethylammonium iodide (diethylcholine; DEC) was tested against trihexyphenidyl for its ability to block tremors in two animal models of Parkinsonism tremors. Both DEC (75 mg/kg) and trihexyphenidyl (10 mg/kg) antagonized physostigmine tremors in mice. Both drugs also blocked tremors in rats which received intracaudate injections of carbachol. DEC was more efficacious than trihexyphenidyl in the rat model. No dose-related inhibition of tremors was seen for trihexyphenidyl (5--20 mg/kg) but inhibition by DEC was dose-related (25--50 mg/kg). The ED50 for tremor inhibition in the rat model by DEC was 33 mg/kg. DEC was also shown to cross the blood-brain barrier in mice. The probable mechanism of action of DEC is discussed.

Computer analysis of interacting dopaminergic and cholinergic control mechanisms in the extrapyramidal system

The experimental results of many authors suggest that the output activity of the extrapyramidal motor control system depends on a balance between the levels present of the chemical transmitters dopamine and acetylcholine. In this paper it is proposed that these results are best explained by two feedback regulatory systems interconnected with positive interaction--in the sense of the relative gain array (Bristol, 1966). Using the computer-aided design procedure CAIAD, a simple two-input two-output model is simulated so as to give responses similar to those observed when dopaminergic or cholinergic drugs are applied. The effect of reducing the gain in one control loop corresponds to the effect of lesioning part of the extrapyramidal system in the brain. In addition, the effect of an anti-schizophrenic drug such as haloperidol is interpreted as a disturbance input on one of the interacting paths.

Regional differences in the sensitivity of cholinergic neurons to dopaminergic drugs and quipazine in the rat striatum

Marked differences were found in the activity of choline acetylase (ChAc) in various discrete areas of the rat striatum. The richest cholinergic innervation was observed in the centrolateral part of the structure. A similar distribution was obtained by measuring acetycholine (ACh) levels in punches taken from frozen frontal serial slices. As revealed by the analysis of the topographical distributions of ChAc activity, ACh, 5-HT and DA, the regional cholinergic innervation differed markedly from that of aminergic terminals. Changes in ACh levels induced by drugs could be estimated in microdiscs of tissues punched from frozen slices. Apomorphine and haloperidol, which increased and decreased ACh levels respectively, induced similar effects in the various striatal areas examined. By contrast quipazine, a drug acting on 5-HT uptake and release and on serotoninergic receptors, selectively increased ACh levels in some areas of the striatum but not in others. The regional changes in ACh levels induced by quipazine were satisfactorily correlated with the regional distribution of 5-HT but not with that of DA. These results suggest that a limited population of striatal cholinergic neurons is under the inhibitory control of serotoninergic neurons. They also indicate that some striatal cholinergic neurons influenced by dopaminergic neurons are not controlled by serotoninergic neurons.

Apparent lack of a dopaminergic-cholinergic link in the rat nucleus accumbens septi-tuberculum olfactorium

The nucleus accumbens septi and tuberculum olfactorium (NAS-TO), which from part of the mesolimbic dopaminergic system, and the striatum, which is part of the nigrostriatal dopamingeric system, contain high levels of both dopamine (DA) and acetylcholine and resemble each other in some other biochemical properties. We determined whether blockade or stimulation of DA receptors by agonists or antagonists affects the cholinergic neurons in this brain structure. The DA receptor antagonists haloperidol, pimozide, chlorpromazine and clozapine had no effect on the acetylcholine level in the NAS-TO even at 2-8 times the minimum dose required to maximally decrease striatal acetylcholine. Similarly, D-amphetamine and bromocriptine (CB 154), DA receptor stimulating drugs, had no effect on the acetylcholine level in this brain area at doses up to 3 times higher than those that produced a maximum increase in the striatum. Piribedil (15-120 mg/kg) and apomorphine (4 mg/kg) did increase acetylcholine in the NAS-TO but the action was not blocked by pimozide and is therefore not attributable to DA receptor action. The data thus indicate an apparent lack of a dopaminergic-cholinergic link in the NAS-TO.

Effect of quipazine, a serotonin-like drug, on striatal cholinergic interneurones

Quipazine (30 mg/kg i.p., 60 min), a serotonin-like drug increased ACh levels in the striatum (37%) but was without effect on the transmitter content in the hippocampus and the parietal cortex of the rat. Added in vitro(10(-5) M) or injected in vivo, quipazine did not affect choline acetylase and cholinesterase activities in striatal tissue. The drug effect on striatal ACh levels did not appear to be related to an interaction with dopamine metabolism. Indeed quipazine still increased striatal ACh levels after degeneration of the dopaminergic neurons had been induced by local injection of 6-OH-DA. p-Chlorophenylalanine (PCPA) pretreatment (300 mg/kg, 48 and 24 h before the experiment) definitely prevented the quipazine effect on ACh levels. This result suggested that the drug may partially act by its interference with 5-HT metabolism. 5-Methoxy-N,N-dimethyltryptamine (10 mg/kg, i.p., 30 min), a serotonergic agonist, induced a weak but significant increase in ACh levels. These data provide some preliminary evidence for the existence of an inhibitory control of the cholinergic interneurones by the serotonergic neurones projecting to the striatum. However, the lack of effect of 5-hydroxytryptophan (100 mg/kg i.p.), PCPA (2 x 300 mg/kg i.p.) and of Lilly 110 140 (10 mg/kg i.p.) and chlorimipramine (10 mg/kg i.p.), two potent inhibitors of 5-HT uptake, on striatal ACh levels indicate that further experiments are required to retain this hypothesis.

Phencyclidine-induced rotational behavior in rats with nigrostriatal lesions and its modulation by dopaminergic and cholinergic agents

The peripheral administration of the psychotomimetic drug phencyclidine (1-(phenylcyclohexyl) piperidine hydrochloride) (PCP) induces a dose-related ipsilateral rotation in unilateral substantia nigra electrolytically-lesioned rats. The intensity of this rotation can be modulated by administration of various dopaminergic and cholinergic agents. Injection of alpha-methylparatyrosine methylester (125 mg/kg) or haloperidol (1 mg/kg) inhibited the ipsilateral circling behavior. Pimozide (1 mg/kg) also inhibitied the rotation, but to a lesser extent. The injection of the anticholinergic agent trihexyphenidyl (5 mg/kg) potentiated, and the cholinomimetic drug arecoline (5 mg/kg), depressed the rotation induced by PCP (7.5 mg/kg), It is probable that PCP possesses significant dopaminergic and anticholinergic properties. The capacity of PCP to induce rotation in this model may be related to its effects on dopaminergic and cholingergic neurons in the rat striatum. Thus, PCP may induce rotational behavior by potentiating dopaminergic transmission, by blocking cholinergic activity, or both; both of these effects have been demonstrated to be important in the generation of circling behavior in rats with nigrostriatal lesions.

Increase in striatal acetylcholine by picrotoxin in the rat: evidence for a gabergic-dopaminergic-cholinergic link

Picrotoxin, 2 mg/kg i.p., a GABA receptor blocking agent, increased rat striatal acetylcholine content by approximately 70% without altering the levels of this amine in the cerebral hemispheres, mesencephalon, diencephalon, hippocampus and cerebellum. Striatal choline levels were concomitantly decreased by about 25%. This dose of picrotoxin also increased striatal homovanillic acid levels by about 30%, an effect which was not antagonized by pretreatment with the dopamine receptor stimulating agent, piribedil. Picrotoxin did not affect striatal choline-O-acetyltransferase or cholinesterase activity after in vitro incubation. The action of picrotoxin on striatal acetylcholine levels was partially antagonized by pimozide and completely blocked by alpha-methyl-para-tyrosine pretreatment while the intraventricular injection of 6-hydroxydopamine was without effect. Convulsions were not prevented by any of these treatments. The results are interpreted as follows: picrotoxin released dopamine through disinhibition of the dopaminergic neurons as a result of blockade of gabergic receptors. The increased dopaminergic activity inhibited cholinergic neurons and lead to an increase in acetylcholine content. The data thus provide evidence for a possible gabergic (inhibitory)--dopaminergic (inhibitory)-cholinergic link terminating in the striatum.

Effects of tandamine and pirandamine, new potential antidepressants, on the brain uptake of norepinephrine and 5-hydroxytryptamine and related activities

Two novel agents, tandamine (TA; a thiopyrano (3,4-b) indole) and pirandamine (PA; an indeno (2,1-c)pyran), and the tricyclic antidepressants desimipramine (DMI), imipramine (I) and amitriptyline (A) were compared in various in vivo pharmacological tests and for norepinephrine (NE) and 5-hydroxytryptamine (5-HT) neuronal uptake inhibition. TA was found to be equivalent, or greater, in activity to DMI in blocking brain NE uptake, antagonizing reserpine-induced effects and potentiating the behavioural effects of l-Dopa. Similarly to DMI, TA did not appreciably block brain 5-HT uptake; unlike DMI, TA did potentiate central 5-HT activity at high doses. PA exerted an opposite profile to TA, being equivalent to A and greater than I as a 5-HT uptake blocker and central 5-HT potentiator; PA was not effective as a NE uptake blocker or potentiator. Neither TA or PA exhibited in vivo MAO inhibition, and in contrast to DMI, I and A, exhibited no central anticholinergic effects. TA, but not PA, potentiated apomorphine-induced gnawing. These findings indicate that TA is a relatively specific blocker of neuronal NE uptake and PA is a selective 5-HT uptake blocker.