Drugs, neurotransmitters, and schizophrenia

Intracellular and extracellular electrophysiology of nigral dopaminergic neurons--3. Evidence for electrotonic coupling

Using three independent in vivo methods, we have obtained evidence for electrotonic coupling between sets of rat zona compacta dopaminergic neurons: (1) Lucifer yellow injection into single dopamine neurons resulted in labeling of two to five dopamine neurons in 18 out of 33 injections. Similar injections into reticular formation or nigral reticulata cells did not demonstrate multiple labeling. (2) Intracellular recording revealed spontaneously occurring small (3-15 mV) fast potentials that often triggered action potentials in dopamine neurons when the membrane potential was close to firing threshold. These fast potentials had a firing rate and pattern similar to that reported previously for extracellularly recorded dopamine neurons. Fast potentials were activated antidromically from the caudate nucleus at a latency similar to that reported for dopamine neurons, followed high frequency antidromic stimulation at a constant latency, and collided with spontaneously occurring fast potentials. However, directly elicited action potentials would not collide reliably with antidromically activated fast potentials. Intracellular injection of depolarizing or hyperpolarizing current increased and decreased, respectively, the rate of occurrence of these potentials. The firing rate of fast potentials could be increased and decreased by the intravenous administration of dopamine antagonists and agonists, respectively. (3) Simultaneous extracellular recording from pairs of DA neurons revealed numerous instances of synchronized action potentials. This was observed more frequently following intravenous haloperidol administration. Sets of burst firing dopamine neurons recorded simultaneously consistently demonstrated a decrease in the interspike interval as the burst progressed; a phenomenon commonly reported in other electrically coupled systems. Electrical coupling has been suggested to be present in sets of identified nigrostriatal dopamine neurons. Electrical communication between these neurons could be involved in modulating burst firing and in synchronizing dopamine release.

Coupling of dopamine D1 recognition sites with adenylate cyclase in nuclei accumbens and caudatus of schizophrenics

Sodium fluoride, guanylimidodiphosphate, and the D1 dopamine receptor agonist SKF 38393 elicited a greater activation of adenylate cyclase in homogenates of caudate nucleus in schizophrenic than in nonschizophrenic subjects used as controls. Similarly, a greater activation of adenylate cyclase by sodium fluoride was observed in the nucleus accumbens of schizophrenics. These findings suggest that the coupling of dopamine D1 recognition sites with adenylate cyclase is more efficient in the brain of the schizophrenic, presumably because of an increased affinity of the G/F protein for guanosine 5'-triphosphate.

Endogenous inhibitors of monoamine oxidase present in human cerebrospinal fluid

Inhibitory activity against the enzyme monoamine oxidase is present in low molecular weight fractions (less than 100,000) of human cerebrospinal fluid. These endogenous substances of different molecular weights (3000 to more than 35,000) act like monoamine oxidase inhibitor drugs to inhibit both type A and type B monoamine oxidase.

Chronic D-amphetamine and phencyclidine: effects on dopamine agonist and antagonist binding sites in the extrapyramidal and mesolimbic systems

Dopamine agonist and antagonist binding to rat striatal and mesolimbic region tissue was examined in rats chronically treated with D-amphetamine or phencyclidine. In striatum, D-amphetamine produces a down-regulation of [3H]spiroperidol binding but an increase in [3H]ADTN bound (measured in the absence of ascorbate). This suggests that [3H]spiroperidol and [3H]ADTN bind to distinct, separate sites which can be independently regulated.

Effects of retinal and pineal low molecular weight fractions and antipsychotic drugs on hydroxyindole-O-methyltransferase

Fractions from bovine retinas and sheep pineals of low molecular weight decrease the activity of purified hydroxyindole-O-methyltransferase (HIOMT). The antipsychotic drugs chlorpromazine and haloperidol show a similar effect under the same experimental conditions. It is suggested that they may imitate the effect of (an) unknown natural suppressor(s) of HIOMT-activity, present in retina and pineal, decreasing the biosynthesis of methoxyindoles.

Selective effects of buspirone and molindone on dopamine metabolism and function in the striatum and frontal cortex of the rat

The hypothesis that the nerve endings of the dopamine projection of the frontal cortex lack autoreceptors for regulation of tyrosine hydroxylase was tested by using the preferential inhibitors of dopamine autoreceptors, molindole and buspirone. In contrast to haloperidol, which elevates dopamine metabolism in the striatum and frontal cortex, both molindone and buspirone elicited little change in dopamine metabolism in the frontal cortex at doses up to 3.0 mg/kg, which cause the same maximal response in the corpus striatum as does haloperidol. Thus, the lack of autoreceptors in the frontal cortex is of pharmacological importance. That preferential inhibition of striatal dopamine autoreceptors may reverse catalepsy by enhancing synthesis and release of dopamine was tested by first inducing catalepsy with different drugs and then administering molindone or buspirone. Only buspirone (1.0 mg/kg) reversed catalepsy. This effect does not require presynaptic dopamine as catalepsy was reversed by buspirone in the dopamine-depleted rat (with 2.0 mg/kg R04-1284) as well as after postsynaptic dopamine receptor blockade by haloperidol of cis-flupenthixol. Thus, the mechanism for the reversal of catalepsy appears to be located efferent from the dopamine neuron. Buspirone, a non-benzodiazepine anti-anxiety drug, may prove useful for treatment of extrapyramidal motor disorders of either iatrogenic or idiosyncratic origin.

Sedative effects and prolactin response to single oral doses of melperone

The pharmacokinetics of melperone and the relationship between plasma concentration and the effect on arousal and prolactin secretion after single oral doses (10, 25, 50 and 100 mg) was studied in normal subjects. Dose-dependent kinetics were indicated by the fact that higher plasma concentrations than expected were demonstrated after the 100-mg dose. Melperone decreased arousal and increased prolactin secretion in a dose-dependent manner. The level of arousal was correlated to melperone plasma concentration over the entire dose range. Prolactin secretion was also correlated to melperone plasma concentration, provided the relationship was studied separately for the individual melperone doses. Thus at higher doses, higher plasma concentrations are needed to elicit the same prolactin outflow. The possibility that reduced arousal reactions might contribute in the antipsychotic action of neuroleptic drugs was discussed.

Kinetics of rat brain soluble catechol-O-methyltransferase and its inhibition by substrate analogues

1. The initial rates and inhibition of rat brain catechol-O-methyltransferase were studied. Double reciprocal plots of initial rates versus either S-adenosyl-L-methionine or 3,4-dihydroxybenzoic acid, in the absence of product, gave a series of lines intersecting to the left of the ordinate. 2. Inhibition in the presence of S-adenosyl-L-homocysteine was competitive but in the presence of vanillic acid was non-competitive if S-adenosyl-L-methionine was the varied substrate. 3. When 3,4-dihydroxybenzoic acid was the varied substrate, both S-adenosyl-L-homocysteine and vanillic acid gave rise to a non-competitive inhibition. 4. The initial rate and product inhibition patterns were consistent with an ordered BiBi mechanism with S-adenosyl-L-methionine being the first substrate and 3,4-dihydroxybenzoic acid the second substrate to combine with the enzyme. 5. In addition, these results suggest that vanillic acid is the first product and S-adenosyl-L-homocysteine the second product to dissociate from the enzyme. 6. The substrate analogues salsolinol and 3-carboxysalsolinol were competitive inhibitors with respect to 3,4-dihydroxybenzoic acid but were non-competitive with respect to S-adenosyl-L-methionine. For enzymes with an ordered mechanism an uncompetitive inhibition would be expected. 7. A possible explanation is that both substrate analogues can combine with either free enzyme with lower affinity or with an intermediary enzyme form with much greater affinity. 8. A scheme which is consistent with the data is presented.

Dopamine-receptor-stimulating autoantibodies: a possible cause of schizophrenia

Schizophrenia shares several genetic features with diseases known to be autoimmune and could therefore be an autoimmune disease itself. Antipsychotic drugs, which are effective in treating the psychotic symptoms of schizophrenia, have one property in common--they block dopamine receptors in the central nervous system. This observation has led to the hypothesis that overactivity of dopaminergic pathways is the cause of the psychotic symptoms, but a seeming anomaly is that the turnover of dopamine is not increased in schizophrenia. Dopamine-receptor-stimulating autoantibodies are postulated to cause the dopaminergic hyperactivity, thereby accounting for the anomaly.

The late stage following continuous amphetamine administration to rats is correlated with altered dopamine but not serotonin metabolism

In previous experiments rats pretreated with slow-release d-amphetamine (d-Amp) pellets for 4 1/2 days, given a 12-hr drug-free period, and then injected with d-Amp have been found to show a behavioral syndrome which has similarities to that induced by acute injections of the hallucinogens LSD and mescaline. The present results indicate that rats administered this same drug regimen have large decreases in Dopamine (DA), dihydroxyphenyl acetic acid (Dopac), and homovanillic acid (HVA) in caudate nucleus, smaller decreases in DA with no changes in Dopac and HVA levels in nucleus accumbens, but no alterations in 5-hydroxytryptamine (5HT) and 5-hydroxyindole acetic acid (5HIAA) levels in caudate, accumbens, brainstem and hippocampus. Increased 5HIAA levels are found in rats sacrificed with pellets intact following 3 days of continuous d-Amp administration, while sleep deprived and in motor stereotypies. The late and hallucinatory stage following continuous d-amp is correlated more closely with alterations in dopamine than of 5HT.

Serum prolactin level increase in normal subjects following administration of perphenazine oral dosage forms: possible application to bioavailability testing

Two pilot studies were performed to determine if oral phenothiazine products could generate a significant increase in serum levels of the hormone prolactin. The two studies employed three and four healthy normal male subjects, respectively. In the first study the subjects received a screening dose, a placebo, one 8-mg perphenazine tablet, and two 8-mg perphenazine tablets. In the second study, the subjects were dosed with two 10-mg amitriptyline tablets, one 10-mg amitriptyline tablet with one combination tablet containing 10 mg of amitriptyline and 4 mg of perphenazine, and two combination tablets, each containing 10 mg of amitriptyline and 4 mg of perphenazine. In both cases the drug treatments produced a significant rise in the serum prolactin levels versus a placebo or control. This increase was defined as a prolactin response. The possible utility of this response in bioavailability testing is discussed.

The effects of chlorpromazine and phenobarbital on cerebellar Purkinje cells

The morphological effects of two chemically different neuroactive drugs (chlorpromazine and phenobarbital) on developing Purkinje cells in the rat cerebellum were examined to determine the presence of cytological alterations. Therapeutic dosages of both drugs were chronically administered to separate groups of maternal rats beginning on day 18 postcoitus. Entire litters were sacrificed on postnatal days 13, 15, 18, and 21. Light microscopic quantitation of Purkinje cells demonstrated a statistically significant reduction in total numbers below control levels at all ages examined for both drugs. Pyknotic Purkinje cells, which appeared more numerous in the drug tested groups, had a paucity of synaptic contacts on both the soma and dendritic branches. Both drugs tested produced similar results within the parameters examined. These alterations have been discussed in relation to possible mechanisms and sites of action.

The projections of the ventral tegmental area and adjacent regions: a combined fluorescent retrograde tracer and immunofluorescence study in the rat

The organization of projection neurons in the ventral tegmental area (VTA), and in adjacent parts of the raphe nuclei medial to it (the central and rostral linear, and interfascicular nuclei), the mammillary body (the supramammillary region and the tuberomammillary nucleus), and the substantia nigra have been examined in the rat with Kuypers' retrograde double labeling method, and with a combined retrograde labeling (with true blue)-immunohistochemical method for the demonstration of dopaminergic neurons. First, the distribution, within the VTA and adjacent regions, of dopaminergic and non-dopaminergic cells that project to terminal fields in the telencephalon (nucleus accumbens, lateral septum, pre- and supragenual fields of the anterior limbic cortex, amygdala, dorsal hippocampus, and entorhinal area), in the diencephalon (lateral habenula), and in the brainstem (locus coeruleus, and parabrachial nucleus) was determined. Then, 15 different combinations of injections of the tracers bisbenzimide and true blue into different terminal fields were made to determine whether individual cells in the region of the VTA send collaterals to more than one site. Taken together, the results indicate that essentially separate groups of cells in the VTA and adjacent regions of the raphe project to each terminal field. In addition, each group can be further divided into dopaminergic and non-dopaminergic components, although the proportion of dopaminergic cells in each group can vary from over 80% (e.g., to the nucleus accumbens) to less than 1% (to the lateral habenula and to the locus coeruleus). In addition, it was found that the supramammillary region, which contains a dense extension of the A10 cell group in its medial part, and the tuberomammillary nucleus, project to, or through, most of the regions injected with retrograde tracers. Virtually all of the projections from the VTA and adjacent regions are partially crossed, the percentage of cells on the uninjected side ranging from over 40% (e.g., for locus coeruleus injections) to only about 2% (e.g., for amygdalar injections). Most of the groups of projection neurons in the region of the VTA are considerably intermixed with the exception of those that project to the lateral septum, to the lateral habenula, and to the hippocampal formation, which are concentrated in ventral and medial parts of the VTA, and in the raphe nuclei medial to the VTA. It was concluded that in the ventral part of the midbrain, essentially separate groups of aminergic and non-aminergic neurons in both the reticular formation (VTA) and in the adjacent nuclei of the raphe project bilaterally to a variety of similar terminal fields in the telencephalon, diencephalon, and brainstem. Further work at the single cell level is needed to determine whether these cell groups are differentially innervated by known inputs to the VTA and adjacent regions, most of which appear to descend through the medial forebrain bundle from sites in the limbic system and hypothalamus.

Effects of clozapine in a selective muscarinic bioassay and on single cells of the rat hippocampus

Acetylcholine was applied to isolated crayfish hindguts and caused dose-dependent increases in its contractile force. These effects were blocked by muscarinic but not by nicotinic antagonists. Dopamine, noradrenaline, enkephalin or GABA agonists had either no effect or one distinct from the action of acetylcholine. Of a number of antischizophrenic drugs, clozapine had the strongest antimuscarinic action with a pA 2 value of 7.5, followed by thioridazine with a pA 2 value of 6.7. All other drugs of the phenothiazine, butyrophenone or benzamide type were ineffective. From these results, it was concluded that the crayfish hindgut is a very reliable and simple bioassay for muscarinic actions of drugs. Clozapine was also applied by microiontophoresis to cat hippocampal neurons and its effects on carbachol-, acetylcholine- and glutamate-induced excitations was assessed. It displayed an inhibitory action on excitations induced by the cholinergic agents, but did not visibly affect those induced by glutamate. The fact that clozapine had strong antimuscarinic effects on the crayfish hindgut as well as on hippocampal neurons of a mammalian indicates a similarity between the muscarinic receptors in both tissues.

Effect of sulpiride, an atypical neuroleptic, on apomorphine-induced growth hormone secretion

Sulpiride (100 mg IM), an atypical neuroleptic, which does not block dopamine (DA) receptors that are linked to adenylate cyclase, abolished the growth hormone (GH) response to the DA receptor agonist, apomorphine (Apo) HCl (0.5 mg SC) in seven healthy male subjects. These results suggest that Apo increases GH secretion in man by an effect on DA receptors that are not linked to adenylate cyclase.

Simultaneous determination of monoamine transmitters, precursors and metabolites in a single mouse brain

A simple and sensitive procedure for simultaneous determination of monoamine transmitters and related substances including precursors and metabolites has been developed for a single mouse brain. The proposed procedure involves (1) primary butanol extraction, (2) separation of the substances into either acid or alkaline aqueous layers according to their physicochemical properties, and (3) determination by means of high-performance liquid chromatography with electrochemical detection. Three transmitters (noradrenaline, dopamine and 5-hydroxytryptamine) and their precursors (tyrosine, 3,4-dihydroxyphenylalanine and tryptophan) and major metabolites (normethanephrine, 3-methoxy-4-hydroxyphenylethylene glycol, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylacetic acid and 5-hydroxyindoleacetic acid) were selectively separated and sensitively detected in mouse whole brain sample. Although 3-methoxy-4-hydroxymandelic acid was also separated from other substances by authentic chromatography, the substance was not detected in mouse brain. Changes in levels of these substances were examined for drugs whose effects had been previously confirmed. These changes reflected putative effects of the drugs and confirmed that the procedure is effective for neurochemical research into the transmitter system.

6-Hydroxydopamine lesions of dopaminergic A10 neurons. Long-term effects on the urinary excretion of free and conjugated catecholamines and their metabolites in the rat

Free and conjugated catecholamines (dopamine, noradrenaline, adrenaline) and their methoxylated and/or deaminated metabolites were studied in rat urine after the bilateral destruction of the A10 dopaminergic cell group. Two months after the lesion, dopamine (DA) loss reached 91% in the nucleus accumbens, and was greater than 80% in olfactory tubercles, lateral septum and frontal cortex. At the same time urinary conjugated dihydroxyphenylacetic acid (DOPAC) was decreased by 45% whilst homovanillic acid (HVA) was increased only in its sulfated form (+62%). In contrast, no changes were observed in the free and conjugated forms of urinary DA, 3-methoxytyramine noradrenaline, normetanephrine, adrenaline, vanylmandelic acid, 3-methoxy-4-hydroxyphenylglycol and in the free forms of DOPAC and HVA. The present report confirms and extends our previous findings on the relationships between central dopaminergic activity and urinary deaminated metabolites of DA in the rat. It emphasizes the interest of urinary assays which could provide in vivo information on CNS functions.

Effects of amphetamine and amfonelic acid on the disposition of striatal newly synthesized dopamine

A comparison of the in vivo biochemical actions of the psychotomimetic central stimulants, d-amphetamine (d-AMPH) and amfonelic acid (AFA), on the metabolism of rat striatal newly synthesized [3H]dopamine (DA) was made by pulse labeling with [3H]tyrosine. No evidence for the formation of the alcoholic DA metabolites [3H]3-methoxy-4-hydroxyphenylethanol (MOPET) or [3H]3,4-dihydroxyphenylethanol (DOPET) was found in control or drug-treated animals. Both [3H]3,4-dihydroxyphenylacetic acid (DOPAC) and [3H]homovanillic acid (HVA) concentrations were increased by AFA in the presence of haloperidol, while [3H]DA content was decreased. In contrast, d-AMPH, in the presence of haloperidol, decreased [3H]DOPAC and increased [3H]DA, even in monoamine oxidase-blocked rats. Thus monoamine oxidase inhibition did not appear to be a major factor in the action of amphetamine to increase [3H]DA, but cannot be excluded as a contributing factor to the lowering of [3H]DOPAC. Similar actions of d-AMPH were seen on preformed DA. Amphetamine may release newly synthesized DA in such a way that some of the released DA enters the neuronal storage system.

Genetic regulation of neurotransmitter enzymes and receptors: relationship to the inheritance of psychiatric disorders

This report begins with a summary of the evidence for genetic involvement in certain major psychiatric syndromes. The relation of these disorders to deficits in central nervous system neurotransmitters is also summarized. These reviews serve as an introduction to our studies on the genetic regulation of neurotransmitters and their enzymes and receptors in inbred mice. The steady-state levels of the adrenal catecholamine biosynthetic enzymes are controlled genetically; not only is each enzyme regulated by a single locus, but also there is statistical evidence that the phenotypic expression of the entire pathway is regulated by a single gene. Studies on the biochemical mechanism of gene action suggest that genetic regulation is exerted on proteolysis of the enzymes, rather than their synthesis. In addition, we have examined the genetic control of dopamine receptors in inbred mice. Dopaminergic receptors in the nigrostriatal and mesolimbic pathways are under genetic control. Preliminary evidence suggests that the pathways are regulated by different genetic systems. If this early speculation proves true, it would have important clinical implications.

Monoamine oxidase (MAO) activity as a determinant in human neurophysiology

Several lines of evidence indicate that monoamine oxidase (MAO) activity can regulate levels of biogenic amines and neuronal activity in the nervous system. The two types of MAO activity, A and B, appear to have different domains of activity in the body. Brain tissue has both types of activity, although adrenergic neurons are thought to contain exclusively MAO-A. MAO activity can also be measured in peripheral tissues: MAO-A in cultured skin fibroblasts and placenta, and MAO-B in platelets and lymphocytes. These two types of activity are mediated by different enzyme molecules and are regulated independently by endogenous and exogenous factors including genetic determinants, hormones, and aging. In humans, inhibition of MAO-A activity leads to mood elevation in depressed patients; in contrast, low MAO-B activity in platelets has been associated with an increased susceptibility to psychopathology. In order to assess further the role of MAO activity in human mood and behavior, it will be important to measure both forms of the enzyme independently and to establish correlations between levels of activity and discrete phenotypic traits.

Behavioural effects of electrolytic and 6-hydroxydopamine lesions of the accumbens and caudate-putamen nuclei

Selective bilateral destruction of dopaminergic neuronal terminals in the accumbens nuclei with 6-hydroxydopamine reduced spontaneous and amphetamine-induced locomotor and exploratory behaviour and sniffing activity; amphetamine-induced stereotyped behaviour appeared to be mildly potentiated. Similarly induced bilateral destruction of dopaminergic nerve endings in the caudate-putamen reduced spontaneous activity; amphetamine-induced stereotyped behaviour was abolished. Some animals with severe degrees of neostriatal dopamine depletion were completely unresponsive to amphetamine, apart from intense sniffing activity. Bilateral electrolytic lesions of the accumbens nuclei did not alter spontaneous or amphetamine-induced activity.

Central nervous system receptors in neuropsychiatric disorders

1. Introduction of radioligand binding techniques has opened new possibilities in the study of the biological basis of psychiatric disorders. 2. The possible role of CNS receptors in schizophrenia, depression, anxiety, Huntington's disease and Alzheimer's dementia is discussed. 3. Data are presented in a systematic manner starting with the identification of receptors which appear to be the primary locus of action of drugs currently used in the treatment of these disorders. 4. A review of the data on the changes in receptor levels and/or affinity that might be associated with the respective disease follows. 5. Changes in receptor number and/or affinity after chronic drug therapy are outlined and the possible utilization of radioligand binding techniques in drug plasma level determination is discussed.

Effect of chlorpromazine on H-reflex recovery curves in normal subjects and schizophrenic patients

This study sought to determine the effect of chlorpromazine (CPZ) on a physiological measure, the H-reflex recovery curve (HRRC) and to determine whether the effect is different in normal subjects and schizophrenic patients. Eleven normal control subjects and 14 patients were administered 12.5 and 25.0 mg CPZ by IM injection. On the average. HRRCs measured 90 min after the injections were lower compared to pre-injection levels in both groups, at both doses. In general, the higher dose was more effective in both groups. Half of the patients, however, failed to respond to 12.5 mg, indicating that some schizophrenics are less sensitive than normals to CPZ. These results indicate that excessive dopamine activity or sensitivity may underlie abnormally high HRRCs in unmedicated psychotic patients.

The effects of chlorpromazine and phenobarbital on vasculogenesis in the cerebellar cortex

The morphological effects of two chemically different neuroactive drugs (chlorpromazine and phenobarbital) on vasculogenesis in rat cerebellum were examined to determine the presence of vascular alterations. Therapeutic dosages of both drugs were chronically administered to separate groups of maternal rats beginning on days 10, 13, 15, 18, and 21. In chlorpromazine-treated animals the specific length of blood vessels was most severely reduced in the Purkinje cell layer. Animals treated with phenobarbital demonstrated an initial reduction in specific length in the Purkinje cell layer but returned to control values by day 21 postnatal (p.n.). Blood vessels in the molecular and granular layers showed little change. The observed changes have been discussed in relation to possible mechanisms and their relationship to neurogenesis.

Postmortem stability of dopamine-sensitive adenylate cyclase, guanylate cyclase, ATPase, and GTPase in rat striatum

The stability of dopamine-sensitive adenylate cyclase, guanylate cyclase, ATPase, and GTPase was measured in homogenates of rat striatal tissue frozen from 0 to 24 h postmortem. ATPase, GTPase, and Mg2+-dependent guanylate cyclase activities showed no significant change over this period. Mn2+-dependent guanylate cyclase activity was stable for 10 h postmortem. Basal and dopamine-stimulated adenylate cyclase activity decreased markedly during the first 5 h. However, when measured in washed membrane preparations, these adenylate cyclase activities remained stable for at least 10 h. Therefore, the postmortem loss of a soluble activator, such as GTP, may decrease the adenylate cyclase activity in homogenates. These results are not consistent with an earlier suggestion that there is a postmortem degradation of the enzyme itself. Other kinetic parameters of dopamine-sensitive adenylate cyclase can also be measured independently of postmortem changes. Thus, it is possible to investigate kinetic parameters of dopamine-sensitive adenylate cyclase, guanylate cyclase, ATPase, and GTPase in human brain obtained postmortem.

Amphetamine psychosis and schizophrenia: a dual model

Several of the behavioral consequences of acute and chronic amphetamine treatment were evaluated and related to the underlying neurochemical correlates of drug treatment. It was suggested that decreased noradrenergic activity after long-term amphetamine treatment influences stimulus sampling, whereas enhanced dopaminergic activity was responsible for the progressive augmentation of stereotypy and self-stimulation behavior observed after long-term exposure to amphetamine. It was hypothesized that amphetamine-induced psychosis and the symptomatology associated with schizophrenia are related to alterations in both norepinephrine and dopamine activity.

Cardiac conduction and rhythm disturbances following suicidal ingestion of mesoridazine

The phenothiazine derivatives, particularly chlorpromazine and thioridazine, are known to produce significant electrocardiographic abnormalities. Until now, documented life-threatening arrhythmias have not been reported following large doses of mesoridazine, the besylate salt of a metabolite of thioridazine and a relatively recent addition to the phenothiazine group. We describe such a case in which alterations in both impulse conduction (first-degree atrioventricular block, prolonged QRS duration, and right axis deviation) and impulse formation (supraventricular and ventricular tachycardia) were noted following a suicidal ingestion of mesoridazine. The electrophysiologic mechanisms underlying phenothiazine-induced arrhythmogenesis are reviewed.

Behavioural effects of acute and chronic beta-phenylethylamine administration in the rat: evidence for the involvement of 5-hydroxytryptamine

The behavioural consequences of daily beta-phenylethylamine (PEA) administration for a period of 6 weeks have been examined. Rats first showed signs of the 5-HT behavioural syndrome after a single injection of PEA (50mg/kg) or 7 daily injections of PEA (25mg/kg). The syndrome reached peak intensity after 3 weeks treatment and was prevented by pre-treatment with 5-HT antagonists mianserin and methysergide or the neuroloptic clozapine but relatively unaffected by pre-treatment with haloperidol. These data provide strong evidence for an effect of PEA on brain 5-HT mechanisms. Because of the similarity between PEA and amphetamine and the suggestion that PEA may be involved in the aetiology of schizophrenia, it is proposed that the mechanisms of action of PEA be reassessed taking into account its ability to affect 5-HT systems in addition to catecholaminergic systems.

Dopamine-like properties of ephedrine in rat brain

1 Ephedrine (3.1-50 mg/kg) was given intraperitoneally to rats and was found to cause a marked increase in spontaneous locomotor activity. 2 In rats with a unilateral lesion in the substantia nigra made by stereotaxic injections of 6-hydroxydopamine, ephedrine (12.5-150 mg/kg i.p.) caused a dose-dependent turning towards the lesioned side. 3 Turning behaviour and increase in locomotion produced by ephedrine were antagonized by pretreatment of the animals with pimozide, amino-oxyacetic acid or reserpine plus alpha-methyl-p-tyrosine, but not by pretreatment with phenoxybenzamine, propranolol or methergoline. 4 In in vitro studies with synaptosomes prepared from rat brain, ephedrine blocked the uptake and caused the release of [3H]-dopamine. 5 Similar results with regard to locomotion and turning behaviour were obtained with (+)-amphetamine. 6 It is concluded that the increase in locomotion and turning behaviour produced by ephedrine is mediated through an indirect dopaminergic mechanism.

Effect of intramuscular chlorpromazine on serum prolactin levels in schizophrenic patients and normal controls

Serum prolactin levels were monitored for 2 hours after injection of chlorpromazine (CPZ) 50 mg intramuscularly (i.m.) in 6 male normal controls and 14 newly admitted male chronic schizophrenics. The increase in serum prolactin levels in the male normal controls was not significantly different from that in patients. Serum prolactin levels were compared in 18 male and 22 female psychotic patients of various psychiatric diagnoses who received 50 mg of CPZ i.m., and 7 male and 6 female patients who received 25 mg CPZ i.m. No significant sex or dose differences were seen in the magnitude of the prolactin response after i.m. CPZ. These results suggest that doses of CPZ 25 or 50 mg i.m. may result in maximal prolactin secretion in most subjects and that lower doses are needed to test the hypothesis that dopamine receptors are supersensitive in schizophrenia or the affective psychoses. In six patients with mixed diagnoses, serum levels of CPZ and other active metabolites were determined by radioreceptor binding assay; peak serum drug levels were highly correlated with peak serum prolactin levels (4 = 0.92) during the first 2 hours following CPZ 50 mg i.m.

Rapid decline of stereotyped behavior in rats during constant one week administration of amphetamine via implanted ALZET osmotic minipumps

Groups of rats were subcutaneously implanted with ALZET 2001 type osmotic minipumps containing d-amphetamine. Three doses of amphetamine (calculated as 0.47, 0.94 and 1.41 mg/kg/hour; measured values were approximately 50% lower), continuously released for 7 days, initially produced locomotor stimulation and stereotyped behavior slightly increasing over the first few days. During the later days, however, locomotor stimulation and stereotyped behavior markedly declined indicating tolerance development. These results contrast the often reported development of sensitization to the behavioral effect of amphetamine observed with repeated injections.

Response artifact in the measurement of neuroleptic-induced anhedonia

Systemic administration of the neuroleptic drug alpha-flupenthixol attenuated lever-pressing behavior in rats responding for rewarding brain stimulation. The magnitude of this attenuation was dose-dependent and resembled the effects of reward reduction and termination. However, when the operant response requirements of the same rats were changed to nose poking, identical drug treatments produced relatively little attenuation in performance. These data do not support the belief that neuroleptics produce a general state of anhedonia. Rather, the apparent suppression of reinforced behaviors depends at least in part on the kinetic requirements of the response.

Reward-induced stereotypy: modulation by the hippocampus

In animals with hippocampal damage, the signaled administration of reward is sufficient to induce the sort of behavioral sterotypy and locomotion that heretofore has been observed only after drug administration. Haloperidol returns these behaviors to normal. The interaction of the hippocampus with reward helps to explain many well-known characteristics of animals with lesions in the hippocampus and may have relevance for catecholamine-based clinical disorders.

Postsynaptic pharmacology of psychoactive substances in Aplysia californica

The effects of antidepressants and neuroleptics on postsynaptic iontophoretic responses to acetylcholine and dopamine have been examined in identified neurons of the central nervous system of Aplysia californica. The results demonstrate an antidopaminergic action of neuroleptics in accordance with in vivo and in vitro results in higher animals. Some of the antidepressant drugs tested also caused a blockade of dopamine hyperpolarizing responses. The incidence of anticholinergic activity of both antidepressants and neuroleptics also correlates well with other systems. The results furthermore suggest that the psychoactive drugs tested behave as antagonists for the neurotransmitter postsynaptic receptor sites.

Biochemical genetics of neurotransmitter enzymes and receptors: relationships to schizophrenia and other major psychiatric disorders

Genetic control of catecholamine biosynthetic enzymes and dopamine receptors is described. The steady-state levels of each of the catecholamine biosynthetic enzymes in the adrenal is regulated by a single genetic locus. The entire biosynthetic pathway gives the appearance of concerted inheritance under the control of a single locus. Mesolimbic and nigrostriatal dopamine receptors are also genetically regulated. Preliminary evidence suggests that agonist binding sites differ from antagonist sites in both brain regions, and that the genetic controls, which are expressed on receptor site number, are independent in the two brain regions.

Central and peripheral effects of lithium on amphetamine-induced hyperactivity in rats

Rats received 0.15 M LiCl either as a central treatment in the lateral cerebroventricles (2x20 microliter/rat) or as a peripheral treatment in the peritoneal cavity 15 ml/kg). The central treatment produced high lithium concentrations (1-1.2 mmol/kg) in the brain while peripheral treatment produced high lithium levels (1-2 mmol/1) in the blood at convenient times for behavioral tests. The central treatment antagonized amphetamine-induced hyperactivity but failed to affect open field behavior in otherwise untreated rats. In contrast, the peripheral treatment suppressed open field activity in otherwise untreated rats but failed to influence behavioral effects of amphetamine. The findings demonstrate differences between central and peripheral actions of LiCl on behavior in rats and show lithium to have central actions on hyperactivity induced by amphetamine.