Peripheral and central muscarinic receptor affinity of psychotropic drugs

Antagonism of oxotremorine-induced behavioral suppression by antimuscarinic drugs

The effects of benztropine, scopolamine, atropine, methylatropine, amitriptyline, phencyclidine, and meperidine were determined alone and in conjunction with a behaviorally suppressing dose (0.05 mg/kg IM) of oxotremorine in pigeons responding under a multiple fixed-ratio 30 fixed-interval 5-min schedule of grain presentation. Benztropine, scopolamine, atropine, and amitriptyline antagonized the behavioral suppressing effects of oxotremorine at doses that alone decreased responding. In contrast, methylatropine, phencyclidine, and meperidine did not antagonize the effects of oxotremorine. These results suggest that benztropine, scopolamine, atropine, and amitripytline decrease responding due to an action at central muscarinic receptors, whereas the behavioral effects of methylatropine, phencyclidine, and meperidine are due to actions other than at central muscarinic receptors.

Effects of the specific serotonin reuptake inhibitor, citalopram, upon local cerebral blood flow and glucose utilisation in the rat

The effects of the potent selective 5-HT reuptake blocking agent, citalopram (10 mg/kg, i.v.), on local cerebral blood flow (lCBF) and local cerebral metabolic rate of glucose (lCMRglu) were measured using [14C]iodoantipyrine (IAP) and [14C]2-deoxyglucose (2-DG) autoradiography, respectively. Significant decreases in lCBF were observed in nine of the 27 brain areas analysed, with significant decreases in lCMRglu observed in 17 areas. While decreases in blood flow were observed, it cannot be concluded that these were in fact the result of a direct action of 5-HT upon serotonergic receptors in cerebrovascular smooth muscle, since the dynamic relationship between flow and metabolism remains largely intact. The reductions in lCBF may be explained entirely by the secondary effects of depressed cerebral metabolic demand induced by citalopram which would, once again, question the role of specifically perivascular serotonergic nerve activity in the tonic control of cerebral blood flow.

Muscarinic antagonists attenuate neurotensin-stimulated accumbens and striatal dopamine metabolism

The effect of scopolamine and atropine upon the increase in extracellular 3,4-dihydroxyphenylacetic acid induced by central injection of neurotensin was examined in the nucleus accumbens and the striatum of anaesthetized rats using in vivo differential pulse voltammetry with carbon fibre electrodes. Scopolamine (1 and 3 mg/kg, i.p.) and atropine (20 micrograms, i.c.v.) did not alter the 3,4-dihydroxyphenylacetic acid level in the nucleus accumbens or the striatum, measured for 60 min after administration. Neurotensin (10 micrograms, i.c.v.) increased the 3,4-dihydroxyphenylacetic acid peak height in both regions. Pretreatment with scopolamine (1 mg/kg) 15 min before neurotensin injection blocked the increase in extracellular 3,4-dihydroxyphenylacetic acid in the striatum but not in the nucleus accumbens whilst scopolamine (3 mg/kg) partially attenuated the effect of neurotensin in the nucleus accumbens and blocked the increase in 3,4-dihydroxyphenylacetic acid in the striatum. Atropine partially attenuated the effect produced by neurotensin in the nucleus accumbens and blocked the increase in 3,4-dihydroxyphenylacetic acid induced by the peptide in the striatum. However, the increase in extracellular 3,4-dihydroxyphenylacetic acid induced by haloperidol (1 mg/kg, s.c.) was not altered by scopolamine (1 mg/kg) or atropine. Also, the increase in dopamine metabolism in the nucleus accumbens and the striatum after centrally injected haloperidol (10 micrograms, i.c.v.) was not altered by atropine (20 micrograms, i.c.v.). Together, the results demonstrate a functional interaction between muscarinic antagonists and neurotensin on in vivo dopamine metabolism in the nucleus accumbens and the striatum but with a greater effect in the latter region.

Muscarinic antagonists attenuate the increase in accumbens and striatum dopamine metabolism produced by clozapine but not by haloperidol

1. The effect of the muscarinic antagonists, scopolamine and atropine, were examined on the increase in extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens and the striatum induced by haloperidol and clozapine by use of in vivo differential pulse voltammetry with carbon fibre electrodes in anaesthetized rats. 2. Animals received saline (1 ml kg-1, s.c.), scopolamine (1 mg kg-1, o.p.) or atropine (20 micrograms, i.c.v.) followed 15 min later by saline (10 microliters, i.c.v.), haloperidol (1 mg kg-1, s.c.) or clozapine (30 mg kg-1, i.p.) and extracellular DOPAC was simultaneously recorded in the nucleus accumbens and the striatum every 5 min for 60 min after drug administration. 3. Scopolamine or atropine alone had no effect on the DOPAC peak height but attenuated the increase in extracellular DOPAC induced by clozapine in both brain regions. Neither scopolamine nor atropine altered the haloperidol-induced increase in accumbens or striatal extracellular DOPAC. 4. The present results demonstrate that muscarinic antagonists attenuate the increase in accumbens and striatal dopamine metabolism in vivo produced by the atypical neuroleptic clozapine but not the haloperidol-induced increase in dopamine metabolism. The results indicate that central muscarinic receptors are involved in the actions on dopaminergic function of clozapine but not haloperidol.

Effect of imipramine in the "learned helplessness" model of depression in rats is not mimicked by combinations of specific reuptake inhibitors and scopolamine

Administration of imipramine, which blocks noradrenergic, serotonergic and cholinergic reuptake, to rats for 4 days counteracts the shuttlebox escape failures otherwise seen in rats which have been exposed to inescapable shock (the "learned helplessness" model of depression). The effects of the more selective reuptake inhibitors talsupram (noradrenergic), citalopram (serotonergic) and the anticholinergic compound scopolamine were assessed alone and in combination after acute or 4 days' administration on escape behavior. Their possible synergistic effects when combined with imipramine were also assessed. Talsupram and citalopram were ineffective, whereas scopolamine counteracted the escape failures. Combinations of talsupram, citalopram and a subeffective dose of scopolamine were ineffective. A synergistic effect was only seen when scopolamine was combined with a suboptimal dose of imipramine. Thus, the effect of imipramine on "learned helplessness" might rely partly on its anticholinergic component. However, as an acute high dose of imipramine (25 mg/kg) was ineffective [unlike the acute administration of scopolamine (0.12 mg/kg)], this drug retains a pharmacological effect which is not mimicked by scopolamine alone or by combining the specific reuptake inhibitors with scopolamine.

The recovery of maturing brain from acute citalopram exposure

At various ages between birth and adulthood mice were exposed to the specific 5-HT uptake inhibitor citalopram. Their brains were assayed for indoleamine stores and turnover during the period of recovery from the drug's action. Young brain lacks the ability to fine tune its return to normal following citalopram action.

Effects of a selective 5-HT reuptake blocker, citalopram, on the sensitivity of 5-HT autoreceptors: electrophysiological studies in the rat brain

Citalopram (CIT), is a selective serotonin (5-HT) reuptake blocker and a clinically effective antidepressant. The present electrophysiological studies were undertaken to investigate in vivo the acute and long-term effects of CIT administration on 5-HT neurotransmission. In a first series of experiments, a single dose of CIT (0.05-0.5 mg/kg) was administered intravenously to naive rats while recording the activity of a 5-HT-containing neuron in the nucleus raphe dorsalis. A dose-response relationship of the inhibitory effect of CIT on the firing activity of 5-HT neurons was obtained with an ED50 of 0.23 +/- 0.03 mg/kg. In a second series of experiments, rats were treated with CIT (20 mg/kg/day, i.p.) for 2, 7 and 14 days. In rats treated for 2 days, there was a marked reduction in the firing activity of 5-HT neurons in the nucleus raphe dorsalis; there was a partial recovery after 7 days and a complete recovery after 14 days of treatment. The response of 5-HT neurons to intravenously administered LSD was decreased in rats treated for 14 days with CIT, indicating a desensitization of the somatodendritic 5-HT autoreceptor. In a third series of experiments, carried out in rats treated with CIT (20 mg/kg/day, i.p.) for 14 days, the suppression of firing activity of CA3 hippocampal pyramidal neurons produced by microiontophoretically-applied 5-HT and by the electrical activation of the ascending 5-HT pathway was measured. Long-term treatment with CIT did not modify the responsiveness of these neurons to microiontophoretically-applied 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor binding of N-(methyl-11C) clozapine in the brain of rhesus monkey studied by positron emission tomography (PET)

By means of positron emission tomography the uptake and kinetics of N-(methyl-11C)clozapine in different brain regions have been studied in Rhesus monkeys. 11C-clozapine rapidly entered the brain and maximum radioactive uptake was seen 5-12 min after administration. Highest uptake was measured in the striatum. Other regions with an uptake higher than in the cerebellum were thalamus and mesencephalon. The radioactivity from different brain regions decreased with an elimination half-life of about 5 h and parallelled the plasma kinetics of unlabelled clozapine. The striatum/cerebellum ratio of 11C-clozapine-derived radioactivity remained constant during the period studied and did not change after pretreatment with atropine. In contrast, the striatum/cerebellum ratio was somewhat lower after pretreatment with N-methylspiperone (NMSP), indicating competition for the same binding sites in the striatum. After pretreatment with increasing doses of clozapine, a dose-dependent protection of binding sites in the striatum for 11C-NMSP was seen. It is concluded that clozapine is more loosely bound to dopamine receptors in the striatum than N-methylspiperone and that the kinetics of clozapine in the brain parallel that in the plasma. The binding properties of clozapine within the brain may explain some of the clinical properties of the drug.

Neurochemical profile of Lu 19-005, a potent inhibitor of uptake of dopamine, noradrenaline, and serotonin

The neurochemical profile of a new compound, Lu 19-005 [(+/-)trans-3-(3,4-dichlorophenyl)-N-methyl-1-indanamine hydrochloride], has been investigated. Lu 19-005 is a potent inhibitor of the synaptosomal uptake of 3,4-dihydroxyphenylethylamine (dopamine, DA), noradrenaline (NA), and 5-hydroxytryptamine (5-HT, serotonin). In this respect it resembles diclofensine, whereas compounds such as GBR 13.069 and bupropion are more selective DA-uptake inhibitors. Although Lu 19-005 releases DA in in higher concentrations it must be considered as an uptake inhibitor, as the accumulation of DA is inhibited in much lower concentrations. Lu 19-005 attenuates the DA and NA depletion caused by 6-hydroxydopamine in mouse brain. These properties confirm the DA- and NA-uptake-inhibitory properties of the compound. In receptor-binding models and functional in vitro tests Lu 19-005 is devoid of dopaminergic-, serotonergic-, noradrenergic-, histaminergic-, and cholinergic-inhibiting properties. Since DA, NA, and 5-HT seem to be involved in depression, the profile of Lu 19-005--with equally potent activity on the three neuronal systems--makes it an interesting experimental tool and a potential new antidepressant agent.

Comparison of the effects of binodaline and amitriptyline on peripheral autonomic functions in healthy volunteers

Twelve healthy male volunteers participated in five experimental sessions separated by weekly intervals. At the beginning of each session the subjects received one single oral dose of the following drugs, according to a double-blind, balanced cross-over design: binodaline hydrochloride (50 mg or 100 mg); amitriptyline hydrochloride (50 mg or 100 mg); lactose placebo. Salivation and resting pupil diameter were assessed before and 2 h after the ingestion of the drugs; baseline sweating, carbachol- or phenylephrine-evoked sweating were measured 2 h following drug taking. Binodaline, like placebo, had little effect on salivary output, whereas amitriptyline caused a dose-dependent decrease in salivation. None of the drugs caused any significant change in resting pupil diameter or in baseline sweating. Carbachol-evoked sweating did not differ significantly following the ingestion of binodaline or placebo; on the other hand responses to carbachol were significantly reduced following amitriptyline. Phenylephrine-evoked sweating was reduced by both binodaline and amitriptyline. The lack of effect of binodaline on salivation, resting pupil diameter, baseline and carbachol-evoked sweating is in agreement with the results of animal experiments indicating the lack of an interaction of this drug with cholinergic mechanisms. The reduction in phenylephrine-evoked sweating would be indicative of an alpha-adrenoceptor blocking property of this drug.

Release of human neurophysin I during insulin-induced hypoglycemia in depressed patients is abolished after recovery with clomipramine treatment

Release of human neurophysin I (hNp I) and neurophysin II (hNp II) during insulin-induced hypoglycemia was studied in 10 unipolar depressed women before and after 4-5 weeks of standard antidepressant drug treatment with daily intravenous infusions of clomipramine. Before treatment, a significant increase of hNp I but not of hNp II serum levels in response to hypoglycemia was observed. At retest during clomipramine administration, a marked clinical amelioration occurred in all patients as determined with the Hamilton Rating Scale for Depression; the hNp I response to insulin was abolished, but no effect on hNp II concentration could be demonstrated. No correlation was found between the degree of the depression score decrease and the amplitude of the inhibition of hNp I release or serum levels of clomipramine or its metabolite, desmethylclomipramine. The meaning of this difference in reactivity of the neurohypophyseal system in the course of depressive illness, based on the pharmacological and biochemical profiles of clomipramine action, is discussed.

Comparison of affinities of muscarinic antagonists to pre- and postjunctional receptors in the guinea-pig ileum

The myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum was preincubated with [3H]choline, then superfused and stimulated electrically (1 Hz 120 pulses). Oxotremorine reduced the evoked outflow of [3H]acetylcholine in a concentration-dependent manner. Each of the six antagonists (scopolamine, methylatropine, trihexyphenidyl, 4-DAMP, clozapine, pirenzipine) produced parallel shifts of the concentration-response curves for the prejunctional effects of oxotremorine. Similarly, in contraction experiments, the antagonists competitively antagonized the postjunctional responses to oxotremorine. The pre- and postjunctional pA2 values did not differ significantly for any of the antagonists. It is concluded that pre- and postjunctional muscarinic receptors in the guinea-pig ileum are pharmacologically similar.

Sulpiride: assessment of a pharmacologically and chemically distinct neuroleptic

The substituted benzamide sulpiride is considered an "atypical" neuroleptic and antipsychotic in that its pharmacology and clinical effects differ significantly from "classical" dopamine antagonists such as the butyrophenones and phenothiazines. Sulpiride increases dopamine turnover, elevates prolactin release, inhibits emesis, and is an effective antipsychotic. Sulpiride does not affect other transmitters, requires sodium for binding, does not induce catalepsy in rats or strong sedation and extrapyramidal side effects in humans. Compared to the butyrophenone and phenothiazine neuroleptics sulpiride is chemically distinct because it lacks certain properties associated with other dopamine antagonists. Poor blood-brain barrier penetration and preferential receptor affinities in different brain regions are the most probable reasons for sulpiride's effects in vivo. Nevertheless, the atypical conformation of sulpiride merits study of its structure-activity relationships. Experimental determination of specific pharmacophores could provide the data necessary for a computer analysis of structure. Comparison of relative orientation of sulpiride's pharmacophores with similar data on classical neuroleptics is suggested for study of structural requirements for dopamine antagonism.

Effects of dopamine and dopamine antagonists on postprandial release of pancreatic polypeptide in dogs and in healthy volunteers

The effect of dopamine, 0.006, 0.12, 1.2, and 2.4 mg X kg-1 X h1, and the dopamine antagonist sulpiride on postprandial pancreatic polypeptide (PP) release has been studied in dogs. Dopamine reduced PP release, the reduction ranging between 28% and 97% of the integrated PP response after food. The inhibition obtained with dopamine, 0.12 and 2.4 mg X kg-1 X h-1, could be partly reversed (p less than 0.05) by sulpiride, 7.5 mg X kg-1. The concomitant administration of phentolamine, 1.0 mg X kg-1, and propranolol, 0.5 mg X kg -1, partly reversed the inhibition obtained with dopamine, 2.4 mg X kg-1 X h-1 (p less than 0.05). In healthy volunteers basal PP concentration and postprandial PP release were diminished by dopamine, 0.12 mg X kg-1 X h-1 (p less than 0.02). Sulpiride in dogs and haloperidol in volunteers reduced PP release when given without concomitant administration of dopamine. It is concluded that dopamine inhibits postprandial PP release via both dopaminergic and adrenergic receptors.

Chronic antidepressant therapy and associated changes in central monoaminergic receptor functioning

Acutely administered antidepressants possess a multiplicity of pharmacological actions. However, the fact that agents possessing similar pharmacological actions are devoid of antidepressant activity, together with the lack of correlation between doses required for acute pharmacological effects and clinical efficacy, suggest that the mechanism(s) of action of antidepressants cannot be directly attributed to the acute pharmacological properties of the drugs. The lag phase in onset of clinical effectiveness emphasizes the importance of adaptive changes following chronic antidepressant administration. A rapidly accelerating trend in attempting to delineate the precise molecular mechanisms of action of antidepressants is the shift in emphasis following chronic antidepressant therapies from alterations in uptake, storage, synthesis and release of neurotransmitters to adaptive changes in receptor functioning. These adaptations occur both pre- and postsynaptically. Examples of the former are alpha 2 and DA presynaptic receptors, both being down-regulated by certain forms of chronic antidepressant therapy. The fact that the NE-coupled adenylate cyclase system in rat brain slices is down-regulated by tricyclics, atypical antidepressants, MAO inhibitors and ECT emphasizes the importance of the system. Electrophysiological and behavioral studies point to the up-regulation of central alpha 1 and 5-HT receptor functioning following long-term antidepressant therapy. In contrast to the beta-adrenoceptor, these findings cannot be correlated with data from radioligand binding studies. In general central alpha 1-adrenoceptor binding remains unaltered. This is also true for 5-HT1 binding whereas cortical 5-HT2 binding is both increased and decreased depending on the type of antidepressant therapy being investigated. The relationship of these adaptive changes to the clinical efficacy of antidepressants in man is not clear since there is generally a lack of good models for studying human central receptor functioning. A review of current data from animal studies would tend to disfavour the view that all forms of antidepressant therapy possess a common mechanism of action. Perhaps multiple intervention sites exist. The introduction and evaluation of agents possessing a specificity of pharmacological action will undoubtedly aid psychotherapeutic research. The knowledge that peptides and 'classical' neurotransmitters can co-exist in the same neurone will undoubtedly generate studies of the significance and importance of the co-transmitter function of peptides in the mechanisms of action of antidepressant therapies.

Dopamine involvement in ACTH-induced grooming behavior

Low doses of dopamine agonists and antagonists were tested for their effects on the excessive grooming behavior induced by intracerebroventricular (ICV) injections of ACTH1-24. Grooming scores were significantly depressed at doses of haloperidol, metoclopramide, pimozide, and butaclamol that did not decrease locomotor activity. In fact at two doses of haloperidol (0.067 and 0.10 mg/kg), grooming scores were decreased while locomotor activity was increased significantly. Metoclopramide increased grooming scores at a dose reported to block presynaptic dopamine receptors. Apomorphine potentiated the grooming induced by low doses of ACTH. These data support the hypothesis that dopaminergic neurotransmission is necessary for the display of ACTH-induced grooming behavior.

Citalopram--pharmacological profile of a specific serotonin uptake inhibitor with antidepressant activity

1. Citalopram (Lu 10-171), a new bicyclic phthalane derivative, is an extremely potent inhibitor of neuronal serotonin (5-HT) uptake but has no effect on the uptake of noradrenaline (NA) and dopamine (DA). 2. Citalopram has no antagonistic activity towards DA, NA, 5-HT, histamine, gamma aminobutyric acid (GABA), acetylcholine, and morphine receptors. In this way it clearly deviates from many old and new antidepressant drugs which have antagonistic effects towards some of these transmitters. 3. In contrast to many tricyclic antidepressants citalopram is devoid of cardiotoxic effects, even when animals are exposed to concentrations far above the therapeutic level. 4. In man citalopram is metabolized to compounds which are also potent 5-HT-uptake inhibitors without effect of NA uptake and which are found in lower concentrations than citalopram itself. 5. In account of its extreme specificity as a 5-HT-uptake inhibitor citalopram should be considered as an experimental tool of the utmost importance. In preliminary clinical experiments citalopram has shown a clear antidepressant effect. This property together with the absence of troublesome anticholinergic adverse effects and cardiotoxic effects also make citalopram a most promising antidepressant drug.

The effects of the specific uptake inhibitor Lu 10-171 (citalopram) upon brain indoleamine stores in the maturing mouse

1. The specific 5-HT uptake inhibitor Lu 10-171 (Citalopram) was used to test uptake inhibition and reduced turnover in maturing mouse brain. 2. All ages showed 5-hydroxyindole acetic acid (5-HIAA) elevation indicative of inhibition and reduced turnover. Enzymatic blockade in conjunction with Lu 10-171 supported the evidence for reduced turnover. 3. The significance of early serotonergic maturation is discussed.

A quantitative assessment of CNS sympatho-inhibition produced by psychotropic drugs

As one index of sympathetic reactivity, electrodermal responses (EDR) were evoked from central (hypothalamic) and peripheral (ulnar nerve) sites in pentobarbital-anesthetized cats. When compared with intravenous chlorpromazine (ED50 approximately 1.0 mg/kg), only thioridazine, trifluoperazine, and pimozide were less potent than chlorpromazine in reducing the amplitude of these centrally-evoked sympathetic-cholinergic responses. Perphenazine and methotrimeprazine (a non-neuroleptic phenothiazine) were about twice as potent as chlorpromazine. Haloperidol and triflupromazine were about 5 times as potent and chlorprothixine was more than 10 times as potent. None of these agents reduced the peripherally-evoked electrodermal response, indicating a CNS mode of action. Diazepam was without effect at either site. In addition, pretreatment with yohimbine (0.5 mg/kg. i.v.) did not significantly alter the ED50 for any of the above drugs. These results demonstrate that all of the phenothiazines and non-phenothiazine neuroleptics tested produce a dose-dependent central sympatho-inhibition and that diazepam does not. The results also suggest that there is no significant correlation between central sympatho-inhibition and the antipsychotic potency of these compounds and that their depression of central sympathetic outflow is independent of alpha-adrenergic mechanisms in the CNS.

The effects of several muscarinic antagonists on pre- and postsynaptic receptors in the isolated rabbit heart

In order to reveal possible differences between pre- and postsynaptic muscarine receptors, seven antagonists were tested for their affinities on these receptor sites in the rabbit isolated perfused heart. Methacholine was used as an agonist to inhibit the noradrenaline overflow evoked by electrical stimulation (3 Hz, 3 min) of the sympathetic nerves (presynaptic parameter) and to decrease the systolic tension development of the right atrium (postsynaptic parameter). The affinity of an antagonist was expressed as pA2. A decreasing order of potency was obtained with ipratropium, scopolamine, atropine, trihexyphenidyl, amitriptyline, and gallamine, both for pre- and postsynaptic responses. The antagonists acted competitively and their effects were reversible. Furthermore, for none of the drugs did the pA2 (pre) differ from the pA2 (post). With QNB (3-quinuclidinyl benzilate) a pA2 (post) of 11.65 was obtained. However, the affinity to presynaptic receptors could not be determined as a pA2 value due to the very prolonged exposure time required for the equilibrium with QNB and for that with methacholine in the presence of QNB. It is concluded that the antagonists employed do not reveal differences between pre- and postsynaptic muscarine receptors of the rabbit heart, in spite of their greatly varying chemical structure and their individual affinities ranging over 5 orders of magnitude. The findings confirm the view of a homogeneous muscarine receptor population characterized by functional parameters.

Differential reversal by scopolamine and THIP of the antistereotypic and cataleptic effects of neuroleptics

Scopolamine reversed the neuroleptic-induced catalepsy and neuroleptic blockade of amphetamine-induced stereotypies in rats. The effect on catalepsy was the most pronounced. Butyrophenones were mainly sensitive to scopolamine reversal whereas the thioxanthenes cis-Z-flupentixol and piflutixol were not significantly influenced. THIP did not change the effects of cis-Z-flupentixol, fluphenazine and haloperidol. The relevance of these findings for the use of stereotypy and catalepsy tests as screening for antiscizophrenic and extrapyramidal side-effects, respectively, is discussed.

The effects of some dopamine antagonists on cholinergic mechanisms in the guinea-pig ileum

1. Activation of prejunctional muscarinic and opiate receptors on cholinergic neurones of the guinea-pig ileum by acetylcholine (ACh) or morphine was seen as an inhibition of twitch responses to transmural electrical stimulation. These inhibitory responses were antagonised by metoclopramide and DL308-IT but no other antagonist used blocked the morphine responses apart from sulpiride in very high concentrations (100 muM and above). 2 Prejunctional and postjunctional responses to ACh on the guinea-pig ileum were measured in the presence of increasing concentrations of some muscarinic and dopamine antagonists. Atropine, hyoscine, chlorpromazine, cis-flupenthixol and thioridazine showed no selectivity in their antagonism of either response to ACh. Benzhexol selectivity antagonised the postjunctional response whereas metoclopramide and DL308-IT showed greater selectivity for the prejunctional effect which they antagonised competitively. Sulpiride, a compound chemically related to metoclopramide, blocked neither the prejunctional nor postjunctional ACh responses. Clozapine antagonised the postjunctional ACh responses whilst apparently potentiating the prejunctional inhibition by ACh. 3 It was concluded that pharmacological differences may exist between prejunctional and postjunctional muscarinic receptors for ACh and that the antipsychotic actions of dopamine antagonists are unlikely to involve blockade of prejunctional ACh or opiate receptors.

The peripheral anticholinergic activity of tricyclic antidepressants: comparison of amitriptyline and desipramine in human volunteers

The effects of three single oral doses (25 mg, 50 mg and 100 mg) of amitriptyline and desipramine, and of placebo, were compared on a range of cholinergic functions (resting pupil diameter, pilocarpine-evoked miosis, baseline-sweating, carbachol-evoked sweating, salivation, heart rate) in eight healthy volunteers. Three measures (pilocarpine-evoked miosis, carbachol-evoked sweating and salivation) reflected the antimuscarinic property of the antidepressants; in two tests (pilocarpine-evoked miosis and salivation) amitriptyline appeared to be more potent than desipramine. Resting pupil diameter was not affected by amitriptyline, whereas desipramine caused mydriasis, indicating that pupil size is not a reliable measure of anticholinergic activity in the case of drugs which also affect adrenergic mechanisms. Baseline-sweating and heart rate were not affected by the antidepressants.

Neuropharmacological properties of amitriptyline, nortriptyline and their metabolites

Amitriptyline, nortriptyline and their metabolites, desmethylnortriptyline, cis and trans 10-hydroxyamitriptyline, cis and trans 10-hydroxynortriptyline and amitriptyline-N-oxide, have been tested for inhibitory effect on the uptake of serotonin (rabbit thrombocytes in vitro) and noradrenaline (mouse atria in vitro and mouse heart in vivo), for anticholinergic activity (guinea-pig ileum in vitro) and for antagonism against tetrabenazine induced inactivity as well as apomorphine and 5-hydroxytryptophan potentiating effect in mice. Amitriptyline inhibits serotonin and noradrenaline uptake equally, whereas nortriptyline is a more potent inhibitor of noradrenaline than of serotonin uptake. The metabolites resemble nortriptyline in this respect. The 10-hydroxylated metabolites are equipotent with amitriptyline as regards noradrenaline uptake inhibition. All the metabolites are less anticholinergic than amitriptyline and nortriptyline. The in vitro results are reflected in the in vivo behavioural tests, although some discrepancies are found, probably due to differences in absorption, distribution, metabolism and excretion. The importance of knowledge concerning pharmacological properties of the metabolites in comparison with amitriptyline and nortriptyline for correlating plasma levels of these and their metabolites to clinical outcome is discussed.

The binding of some antidepressant drugs to brain muscarinic acetylcholine receptors

1 The binding of some antidepressant drugs, including some new drugs of atypical structure (flupenthixol, iprindole, maprotiline, mianserin, nomifensine, tofenacine and viloxazine) to muscarinic acetylcholine receptors in the brain has been studied by displacement of [3H]-atropine. 2 Many of the drugs are potent muscarinic antagonists. 3 Some correlation can be made between the affinity for binding to the muscarinic acetylcholine receptor and the incidence of anticholinergic side effects in clinical usage.

Analysis of the activation of dopamine metabolism by a serotonin uptake inhibitor

The potentiation of the effect of haloperidol on rat striatal homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) by a serotonin (5-HT) uptake inhibitor, CGP 6085 A, has been further investigated. The evidence that this effect of CGP 6085 A is related to its 5-HT uptake inhibitory properties is discussed. The potentiation was antagonized by scopolamine and baclofen, and disappeared more rapidly than the uptake inhibitory effects of CGP 6085 A, presumably because the effects of uptake inhibition were counteracted by a reduction in 5-HT synthesis. CGP 6085 A also potentiated the effects of fluphenazine and pimozide, but not those of a number of other neuroleptics. It also failed to restore the effect of haloperidol in animals treated chronically with the neuroleptic. These results appear to indicate that CGP 6085 A can only stimulate DA neurons if their activity is already above the resting level. The antagonism of this effect by scopolamine suggests that the site of action of the 5-HT uptake inhibitor is before a cholinergic neuron.

Meperidine does not block the cholinergic effects of oxotremorine

Meperidine (20 and 40 mg/kg, IP) did not block the cholinergic effects (tremor, salivation, and tearing) produced by oxotremorine (0.4 mg/kg, SC) in rats, whereas atropine blocked these three effects (10 mg/kg, 2.5 mg/kg and 0.08 mg/kg, respectively.