Effect of apomorphine and pimozide on synthesis and turnover of labelled catecholamines in mouse brain

TH protein and mRNA in nigrostriatal dopaminergic neurons are down-regulated by continuous but not intermittent apomorphine

Levels of tyrosine hydroxylase (TH) and TH mRNA were measured after administration of dopamine agonists for a long period of time to elucidate the long-term feedback inhibition of dopamine synthesis in nigrostriatal dopaminergic neurons. Continuous infusion, which desensitized presynaptic dopamine receptors, but not repeated administration, down-regulated TH and TH mRNA levels. This suggests levels of TH protein and mRNA are only feedback inhibited by the continuous stimulation of postsynaptic dopamine receptors.

The distribution of alterations in energy metabolism in the rat brain produced by apomorphine

The effects of the putative dopaminergic agonist, apomorphine (0.15-5 mg/kg, i.v.), on glucose utilization in 43 anatomically discrete regions of the rat brain have been examined by the quantitative autoradiographic 2-deoxyglucose technique. Apomorphine failed to alter the rates of glucose utilization in 25 of these regions (for example, primary auditory areas, regions of white matter, hippocampal areas, nucleus accumbens and caudal regions of the neocortex). Dose-dependent alterations in glucose utilization were observed following apomorphine administration in a number of regions known to contain dopaminergic receptors (viz: caudate nucleus, substantia nigra, amygdala, subthalamic nucleus and anterior cingulate cortex). Moreover, dose-dependent alterations in glucose utilization were produced by apomorphine in a number of regions thought to contain few specific dopaminergic receptors (e.g., cerebellar hemisphere and vermis, lamina VI of rostral neocortical areas, and ventral nucleus of the thalamus). The distribution of alterations in glucose utilization following apomorphine administration are considered to reflect the functional involvement of the region in the overall response to apomorphine, and not simply the topography of dopaminergic receptor mechanisms.

Double-blind comparative clinical trial of pimozide and chlorpromazine in mania. A test of the dopamine hypothesis

Pimozide (PMZ), a relatively specific dopamine (DA) receptor blocking drug, was compared to chlorpromazine (CPZ) in a double-blind, between-patient clinical trial in mania. The trial lasted 14 days. Twenty-three patients who fulfilled Feighner's criteria for mania entered the trial (one patient entering on two separate occasions). Both drugs led to clinical improvement, with a significant effect being noted within 24 hours. According to one of the two rating scales used, initial improvement was greater with chlorpromazine, probably due to its greater sedative effect. By 7 days both drugs were equally effective. Sedative side effects were more frequent in patients on CPZ; extrapyramidal side effects were more frequent with PMZ. The finding that the relatively specific DA receptor blocking drug PMZ was as effective as CPZ in the treatment of mania is consistent with the view that hyperactivity of central DA pathways is involved in the pathogenesis of this condition.

Chronopharmacological studies of neuroleptics

Studies were carried out to clarify the mechanism of appearance and the laws controlling the appearance of such phenomena as circadian fluctuation in the effects of neuroleptics. A detailed review was initially made of previous studies on drugs closely related to neuroleptics; then data obtained by the authors was analyzed. Significant circadian fluctuation was found in the effect of chlorpromazine, haloperidol, and tetrabenazine, varying with the time of administration, with the kind of drug, and even with the dose of the same drug. There was also circadian fluctuation in lethality rate, which was seen to be a phenomenon controlled by a law different from that controlling circadian fluctuation in the effect of a drug. Circadian fluctuation in the effect of a drug was regulated externally by clock time, setting the light-dark rhythm of the raising environment. Different times of administration of a drug did not affect chronological changes in the blood level or intracerebral concentration of a drug after administration. From these results, it was assumed that this phenomenon might be induced by the circadian rhythm of drug sensitivity of a brain where the drug acts.

Behavioral and neuroendocrine effects of low dose ET-495: antagonism by haloperidol

Low doses of the dopamine agonist ET-495 were administered to nonpsychotic volunteer subjects by slow intravenous infusion, followed by a bolus of 1.5--2.5 mg haloperidol. ET-495 caused progressive dysphoria and sedation (in some cases, light sleep), effects believed to be mediated by dopaminergic inhibition. However, ET-495 also elevated growth hormone and suppressed prolactin, typical responses to dopamine agonist activity. Haloperidol reversed both the sedation and prolactin suppression induced by ET-495. These findings suggest: (1) that the sedation and hormonal responses were produced by stimulation of dopamine receptors; (2) that neurotransmitter systems mediating behavioral and neuroendocrine regulation may have differential neuropharmacological characteristics.

d-Amphetamine-induced increase in catecholamine synthesis in the corpus striatum of the rat: persistence of the effect after tolerance

The effect of d-amphetamine on in vivo catecholamine synthesis in four regions of rat brain was determined by measuring the accumulation of dopa after inhibiton of dopa decarboxylase. In doses up to 2.5 mg/kg, d-amphetamine caused dose-dependent increases in striatal dopa accumulation to a maximum of 280% of control; further increases in dose resulted in smaller effects until 10 mg/kg d-amphetamine was not significantly different from control. d-Amphetamine did not alter dopa accumulation in telencephalon, in diencephalon-mesencephalon, or in pons-medulla oblongata. d-Amphetamine did not affect either dopamine levels in striatum or NE levels in pons-medulla oblongata; at high doses, d-amphetamine did reduce norepinephrine levels in telencephalon and in diencephalon-mesencephalon. Daily administration of pre-session but not of post-session d-amphetamine produced tolerance to the effects of d-amphetamine on milk consumption in rats. The ability of d-amphetamine to increase striatal catecholamine synthesis was not altered by the development of tolerance to d-amphetamine. These results suggest that tolerance to d-amphetamine is not related to its effect on catecholamine synthesis but instead occurs via changes in aspects of catecholamine metabolism other than synthesis via change in catecholamine release, reuptake, or receptor sensitivity, or via changes in non-catecholaminergic mechanisms.

Brain dopamine receptor stimulation and the relief of Parkinsonism: relationship between bromocriptine and levodopa

The relationship between dopamine receptor stimulation by bromocriptine or levodopa and the relief of parkinsonism was studied in 24 patients with Parkinson disease. Bromocriptine, 30 mg daily for 20 weeks, elicited an improvement in the parkinsonian clinical features, but this was less than the subsequent improvement with levodopa and benserazide, 800 mg and 200 mg daily, respectively. There was a negative correlation between the pretreatment severity of the disease or changes in cerebrospinal fluid homovanillic acid (HVA) and improvement in parkinsonian disability during bromocriptine treatment. Futhermore, it was found that clinical improvement and HVA responses in the cerebrospinal fluid after dopamine receptor stimulation by bromocriptine may predict the clinical response to levodopa.

Effect of lergotrile on 3,4-dihydroxyphenylacetic acid (DOPAC) concentration and dopamine turnover in rat brain

Lergotrile, a dopamine agonist, lowered whole brain DOPAC (3,4-dihydroxyphenylacetic acid) concentration in rats. At low doses down to 0.5 mg/kg of lergotrile mesylate, this effect occurred within 30 min, whereas at higher doses (20 mg/kg) the decline in DOPAC was delayed. The decrease in DOPAC persisted for several hours and presumably resulted from a compensatory decrease in brain dopamine turnover secondary to receptor stimulation by lergotrile. Other indications of decreased brain dopamine turnover after lergotrile included (a) a slower decline in dopamine concentration after synthesis inhibition by alpha-methyltyrosine, (b) a slower decline in alpha-methyl-m-tyramine, a false transmitter that is stored and released by dopamine neurons, and (c) a decreased accumulation of dopamine in response to gamma-butyrolactone, an agent that blocks firing and dopamine release by dopamine neurons. Lergotrile mesylate (20 mg/kg) also increased brain levels of 5-hydroxyindoleacetic acid and of 3-methoxy-4-hydroxyphenylethylene glycol sulfate, metabolites of serotonin and norepinephrine, respectively, and these increases were not antagonized by spiperone, a dopamine receptor antagonist.

Dopaminergic agonist properties of ephedrine--theoretical implications

Reports of ephedrine-induced psychoses resembling amphetamine psychosis prompted studies of this classic sympathomimetic agent in systems that indicate central dopaminergic actions. Ephedrine induced dose-related stereotyped behavior in rats. This behavior was antagonized by haloperidol, but not by alpha- or beta-adrenergic blockers. Pretreatment with AMPT, but not reserpine, attenuated the stereotypy induced by ephedrine under one of two sets of conditions. Consistent prolactin suppression in humans was not seen. These findings are discussed in the context of clinical and pharmacologic data regarding other dopamine agonist drugs (the central nervous system stimulants, apomorphine, ET 495). These data suggest the possibility that synergistic noradrenergic and dopaminergic facilitation may be important in the induction of the stimulant psychoses.

The effects of psychotropic drugs on exploratory and stereotyped behaviour of rats studied on a hole-board

Exploratory and stereotyped behaviour of Male Wistar rats was studied on a hole-board. The two forms of behaviour were differentiated according to the pattern of hole-dipping activity. Increasing doses of dl-amphetamine stimulated both forms of behaviour with stereotyped behaviour becoming predominant particularly at the higher dose levels. At the highest dose of amphetamine used (16 mg/kg) a gradual transition from exploratory to stereotyped behaviour was observed with time. As the drug wore off this transition was reversed. Haloperitol at a dosage of 0.1 and 0.05 mg/kg blocked the response to a high dose of amphetamine whereas a lower dose (0.02 mg/kg) blocked the stereotyped response to amphetamine while some exploratory behaviour still took place. Apomorphine inhibited hole-dipping but at lower doses another form of exploratory behaviour was induced, this behaviour becoming stereotyped as the dose was increased. It is concluded that there is a close relationship between exploratory and stereotyped behaviours. Monoamine systems appear to play a significant role in the regulation of both forms of behaviour.

Effects of pimozide on noradrenergic transmission in rabbit isolated ear arteries

In the rabbit ear artery both dopamine and noradrenaline inhibit stimulation-induced (S-I) transmitter noradrenaline efflux. Pimozide, which is reported to be a specific dopamine receptor antagonist, was used to further study the effects of dopamine on transmitter efflux. In a concentration of 0.2 micrometer pimozide blocked the inhibition of S-I efflux produced by 0.5 micrometer dopamine but not that produced by 0.5 micrometer noradrenaline. In a concentration of 10 nM, pimozide enhances transmitter release and vasoconstrictor responses to sympathetic nerve stimulation; this may be due to blockade of feedback inhibition of transmitter release by endogenous dopamine. In a concentration of 1 micrometer, pimozide reduced transmitter release and vasoconstrictor responses to sympathetic nerve stimulation. Vasoconstrictor responses to noradrenaline and histamine are antagonized by pimozide in a noncompetitive manner.

Single and repeated administration of neuroleptic drugs to rats: effects on striatal dopamine-sensitive adenylate cyclase and locomotor activity produced by tranylcypromine and L-tryptophan or L-Dopa

Injection of tranylcypromine and L-tryptophan results in rats displaying behavioural changes including hyperactivity, probably due to stimulation of post-synaptic 5-hydroxytryptamine (5-HT) receptors. Increased locomotor activity of a different type is elicited by injection of tranylcypromine and L-dopa, a procedure which increased dopaminergic function in the brain. It has now been demonstrated that the neuroleptic drugs, chlorpromazine, alpha-flupenthixol, haloperidol and spiroperidol block both syndromes. The inhibition produced by these drugs on 5-HT-induced hyperactivity is probably because a dopaminergic system is involved in the behavioural expression of the 5-HT induced hyperactivity. The structurally related drugs with no neuroleptic activity (ethopropazine, promethazine and beta-flupenthixol)are without effect on thses hyperactivity syndromes. Also ineffective were the neuroleptics pimozide and clozapine. Striatal dopamine sensitive adenylate cyclase activity in vitro was inhibited by the administration of chlorpromazine (100 mg/kg) in vivo. Rats treated for 4 or more days with chlorpromazine, alpha-flupenthixol, spiroperidol and haloperidol subsequently showed enhanced locomotor activity in response to tranylcypromine and L-Dopa. Administration of those drugs which did not block hyperactivity acutely did not result in enhancement. Only chlorpromazine, when given for 4 days, enhanced the hyperactivity response following tranylcypromine and L-tryptophan, probably because the drug also blocks 5-HT receptors. In rats displaying enhanced behavioural responses no evidence was found for enhanced sensitivity of striatal adenylate cyclase to dopamine.

Brain dopamine receptors and sleep in the rat: effects of stimulation and blockade

A high dose of apomorphine, a stimulator of brain dopamine receptors, caused a reduction in total sleep, intermediate sleep and a delayed appearance of paradoxical sleep. With a lower dose, a small and not significant trend toward an increase of paradoxical sleep was observed. Spiroperidol, considered as a specific blocker of dopamine receptors, produced a dose-dependent increase of total sleep and a decrease of paradoxical sleep. Chlorpromazine induced a different effect, that is a clear enhancement of paradoxical sleep. Taken together, these results indicate that an activation of dopamine systems in the brain is partly involved not only in behavioral activation, but also in cortical activation of waking and paradoxical sleep. The effect of chlorpromazine on paradoxical sleep cannot be attributed to the antidopaminergic properties of this drug.

Influence of pheniramine and chlorpheniramine on apomorphine induced compulsive gnawing in mice

In mice, apomorphine (10 mg/kg s.c.) does not induce a compulsion to gnaw, but pretreatment with antihistamines, viz. pheniramine, chlorpheniramine and mepyramine, in doses ranging from 30 to 60 mg/kg i.p. caused gnawing activity. Mepyramine showed significantly less effect when compared to the other two agents. Antihistamines are known to influence the activity of biogenic amines in central nervous system. The potentiation of apomorphine-induced gnawing by antihistamines might depend upon the reciprocal balance between dopaminergic and cholinergic systems. This was tested by blocking biosynthesis of biogenic amines or by blocking their receptors. The potentiation of gnawing was antagonised by physostigmine (0.25 mg/kg) or blocked by pretreatment with alpha-methyl-p-tyrosine (alpha-MPT) (4 X 150 mg/kg) and bis-(4-methyl-1-homopiperazinylthiocarbonyl)-disulphide (FLA) (40 mg/kg), while p-chlorophenyl alanine (p-CPA) (3 X 100 mg/kg) had no effect. Similarly, phenoxybenzamine (30 mg/kg) and haloperidol (1.0 mg/kg) inhibited gnawing activity, but methysergide (10 mg/kg) had no effect. Furthermore, pretreatment with tetrabenazine (20 mg/kg) and L-Dopa (200 mg/kg) did not affect gnawing activity. It is concluded that both pheniramine and chlorpheniramine potentiate apomorphine gnawing by upsetting the cholinergic and dopaminergic balance in favour of dopaminergic dominance.

Apomorphine self-injection is not affected by alpha-methylparatyrosine treatment: support for dopaminergic reward

Pretreatment with AMPT at doses which markedly altered the self-injection or amphetamine did not affect the self-injection of apomorphine. These data support the idea that the self-injection of apomorphine is produced via the direct activation of dopamine receptors rather than by the release of either norepinephrine or dopamine.

Possible role for cyclic nucleotides and phosphorylated membrane proteins in postsynaptic actions of neurotransmitters

The postsynaptic actions of some neurotransmitters may be mediated through cyclic nucleotides and cyclic nucleotide-dependent phosphorylation of specific membrane proteins in postsynaptic cells. In addition to providing a molecular basis for the actions of several neurotransmitters and of certain drugs affecting behaviour, the model suggests a mechanism by which neurotransmitter signals may be converted into electrophysiological responses in postsynaptic cells.

Pimozide: a review of its pharmacological properties and therapeutic uses in psychiatry

Pimozide 1-(1-[4,4-bis(4-fluorophenyl)butyl]-4-peperidinyl)-2-benzimidazolone, is the first of a new series of psychotropic drugs, the kiphenylbutylpiperidines. It is advocated for once-daily use as maintenance therapy in chronic schizophrenia and for the treatment of psychic and functional disorders induced by personality traits. Published data suggest that in chronic schizophrenia, pimozide 4 to 6mg daily is indistinguishable from maintenance doses of chlorpromazine, fluphenazine, flupenthixol, perphenazine, or thioidazine. Patient groups have usually been to small to allow statistically significant differences to be apparent, but in some trials pimozide was significantly superior to trifluoperzine and to haloperidol. On present evidence, pimozide has no place in the hyperactive, aggressive type of patient or in treating the acute phase of schizophrenia, probably because of its relative lack of sedative properties compared with many antipsychotic drugs. The incidence and severity of extrapyramidal reactions with pimozide are low, but suitably designed controlled studies are needed to determine whether its use leads to a reduction in the requirement for antiparkinsonian medication. In anxious patients, pimozide seems to offer no advantages over currently available anxiolytic agents, either in terms of efficacy or incidence of side-effects. Claims for a specific effect against anxiety associated with psychosis or disturbed personality traits remain unproven.

Clinical pharmacokinetics of levodopa in parkinson's disease

Although levodopa has provided a major advance in the treatment of parkinsonism, its maximum benefits have not yet been realised, in part because of its complicated pharmacokinetics. This review summarises that available pharmacokinetic data involving levodopa, especially as it relates to therapeutic response of parkinsonian patients. A large number of factors, including protein intake, gastric emptying time, pyridoxine ingestion, and dopa decarboxylase activity, affect plasma levels of levodopa attained following oral administration of this drug. Other variables influence the rate of brain uptake of levodopa from the blood. Even so, plasma levodopa concentration correlates significantly with dosage size in a large parkinsonian population and also coincides with therapeutic response in many, but not all, patients. Therefore, in certain instances, valuable information may be derived by correlating clinical response with plasma levodopa concentration. Cerebrospinal fluid levels of homovanillic acid, a major metabolite of dopamine, may have some value in predicting clinical response to levodopa. This relationship, however, has not been firmly established. Concentration of homovanillic acid or levodopa in body fluids may also be closely related to certain adverse side-effects, including abnormal involuntary movements, gastric discomfort and psychiatric disturbances. Evidence indicates that a clearer understanding of levodopa pharmacokinetics may improve the clinical management of parkinsonism.

Neuroendocrine effects of haloperidol therapy in chronic schizophrenia

The neuroendocrine effects of haloperidol therapy have been examined in 62 male chronic schizophrenic patients, aged 16-62 years. The duration of the disease varied between 2 and 29 years. The patients were divided into 48 hebephrenics with onset of the disease at puberty, or immediately after puberty, and 14 paranoids with onset of the disease in adulthood. They received 6 mg i.m.p.d. of haloperidol, for 30 days, up to a total dose of 180 mg. The following hormonal variables were examined before therapy and at 10-20 and 30 days of treatment: total urinary gonadotropins, serum FSH and LH, GH response to insulin stimulation, ACTH reserve (Metyrapone test), total urinary 17-ketosteroids and 17-hydroxycorticoids before and after an ACTH stimulation test, serum testosterone, insulin response to glucose load, plasma thyroxine before and after a TSH stimulation test. The basic hormonal values revealed decreased secretion of total gonadotropins, FSH, LH, ACTH and testosterone, and increased insulin secretion. The haloperidol therapy seemed to stimulate the secretion of FSH, LH, total gonadotropins, ACTH and testosterone, up to normal or low-normal levels. No modifications were observed in the other hormonal variables. The significance of these results is discussed.

Drugs modifying dopaminergic activity and behaviour, the EEG and epilepsy in Papio papio

Acute changes in spontaneous motor activity, the EEG and photically induced epileptic responses have been observed in baboons (Papio papio) following the i.v. injection of drugs acting on dopaminergic transmission. Apomorphine hydrochloride, 0.5-1.0 mg/kg, produced a phase of acute excitement with accentuated vigilance and abnormal buccal motor activity lasting 30-40 min; during this phase myoclonic responses to intermittent photic stimulation were absent. After piribedil (ET 495, 1,2'' -pyrimidyl-4-piperonylpiperazine), 2-10 mg/kg, acute excitement was not seen. Intermittent delta activity was prominent in the EEG for 1-3 hr, and was associated with a slight reduction in photically induced epileptic responses. Haloperidol 0.6-1.2 mg/kg, produced a long-lasting reduction in spontaneous motor activity with an increased incidence of spontaneous EEG spikes and waves and a great enhancement of paroxysmal EEG activity during photic stimulation. Pimozide, 0.5-2.5 mg/kg, normally produced mild sedation and some EEG slowing. 2 animals responded idiosyncratically to both haloperidol and pimozide, displaying intermittent dystonic episodes with bucco-facial dyskinesia. These findings suggest that activation of dopaminergic receptors can lead to a reduction in myoclonic responses to photic stimulation.

Cholinergic-dopaminergic interaction in the striatum: the effect of 6-hydroxydopamine or pimozide treatment on the increased striatal acetylcholine levels induced by apomorphine, piribedil and d-amphetamine

Apomorphine (1 and 2 mg/kg), piribedil (15 and 60 mg/kg) and d-amphetamine (5 and 10 mg/kg) increased rat striatal acetylcholine levels without affecting choline. Pretreatment with pimozide (0.5 mg/kg) completely antagonized the effect of apomorphine and piribedil and by itself markedly decreased striatal acetylcholine levels. d-Amphetamine signigicantly antagonized the effect of pimozide. Nine days after pretreatment with 6-hydroxydopamine plus pargyline, striatal dopamine was decreased by 78% while acetylcholine and choline levels remained unaltered. Under these conditions, the effect of d-amphetamine was completely abolished while apomorphine and piribedil were just as active as in the vehicle-treated group. The results suggest that d-amphetamine acted indirectly to increase striatal acetylcholine levels probably through the release of dopamine and/or noradrenaline, while apomorphine and piribedil acted directly at dopamine receptor sites.

Dopamine-sensitive adenylate cyclase in mammalian brain: a possible site of action of antipsychotic drugs

Adenylate cyclase (EC 4.6.1.1), selectively stimulated by low concentrations of dopamine, has been found in the olfactory tubercle, the nucleus accumbens, and the caudate nucleus of several mammalian species. Several different classes of drugs effective in the treatment of schizophrenia (antipsychotic drugs) were potent inhibitors of the stimulation by dopamine of the enzyme from these various regions. The drugs studied included representatives of the phenothiazine, butyrophenone, and dibenzodiazepine classes. The inhibition by these antipsychotic drugs was competitive with respect to dopamine. The most potent of the antipsychotic agents tested was fluphenazine, which had a calculated inhibition constant (K(i)) of about 5 x 10(-9) M. For each of several drugs tested, the K(i) for the enzyme from the olfactory tubercle was similar to that for the enzyme from the caudate nucleus. Several compounds closely related structurally to the psychoactive phenothiazines, but which have little or no antipsychotic or extrapyramidal actions clinically, had low relative potencies as inhibitors of dopamine-stimulated adenylate cyclase activity. The results, considered together with other data, raise the possibility that the therapeutic effects, as well as the extrapyramidal side effects, of these antipsychotic agents may be attributable, at least in part, to their ability to block the activation by dopamine of specific dopamine-sensitive adenylate cyclases in the human brain.

Localization of ( 3 H)pimozide in the rat brain in relation to its anti-amphetamine potency

The pharmacological activity of the neuroleptic agent pimozide is well correlated with the concentration of [3H]pimozide in the brain of the Wistar rat. There is an enhanced uptake and retention of [3H]pimozide in the caudate nucleus, an area in which amphetamine and apomorphine act. Its concentration in the caudate nucleus is not correlated with its anti-apomorphine and anti-amphetamine potency. There are, however, significant shifts in the subcellular distribution of [3H]pimozide in the caudate nucleus, from the mitochondrial fraction to the fraction consisting mainly of submicroscopic nerve endings. These shifts correlate well with its pharmacological activity. This points to the small nerve-endings as being the site of action of pimozide. The drug does not influence either the penetration of (+)-[14C]amphetamine into the brain, or its metabolism, indicating that the anti-amphetamine action cannot be due to a decreased penetration of amphetamine into the brain, although a subcellular redistribution of amphetamine induced by pimozide cannot be excluded.