ON THE RELEVANCE OF PREFERENTIAL INCREASES OF MESOLIMBIC VERSUS STRIATAL DOPAMINE TURNOVER FOR THE PREDICTION OF ANTIPSYCHOTIC ACTIVITY OF PSYCHOTROPIC DRUGS

Abstract— Drugs possessing (chlorpromazine, haloperidol, clozapine, thioridazine and sulpiride) or lacking (benzoctamine and perlapine) antipsychotic activity were compared with respect to their ability to enhance x-methyl-p-tyrosine-induced dopamine disappearance from the mesolimbic area and corpus striutum of rat brain. In addition, their effects on the endogenous concentrations of homovanillic (HVA) and 3.4-dihydroxyphenylacetic (DOPAC) acids in these two brain areas were determined. Some of the drugs enhanced dopamine disappearance in the mesolimbic area more than in the striatum. The most active in this respect were sulpiride. perlapine and chlorpromazine. By contrast, haloperidol was slightly more active in the striatum than in the mesolimbic area. None of the drugs was more efficient in elevating HVA levels in the mesolimbic area than in the striatum. However, there were large differences in the relative extent of the HVA increases in the two regions. Benzoctamine, perlapine and chlorpromazine increased HVA concentrations in the mesolimbic area nearly as much as in the striatum. Thioridazine and haloperidol, however, elevated striatal HVA much more effectively. Haloperidol and clozapine increased the DOPAC concentration in both areas to about the same extent. The other drugs were more active in the striatum. The largest difference between both regions was shown by chlorpromazine. Perlapine and benzoctamine, both lacking antipsychotic activity, produced much larger increases of HVA than of DOPAC. This is in contrast to the results obtained with true neuroleptics and may reflect an involvement of release phenomena in the action of these two drugs on dopamine metabolism. These results suggest that a preferential increase of dopamine turnover in the mesolimbic area is not necessarily linked to a better ratio of antipsychotic activity vs. extrapyramidal side effects. Moreover, an antiacetylcholine component of dopamine receptor blocking drugs does not seem to be a prerequisite for preferential activity on dopamine turnover in the mesolimbic system.     

Effects of phenothiazine and dibenzazepine derivatives on the muscarinic cholinergic system]

Interactions of some dialkylaminoalkyl (DAL) and dialkylaminoacyl (DAC) derivatives of phenothiazine and dibenzazepine with muscarinic cholinergic receptors (MR) of rabbit striatum and heart and rat brain were investigated. DAC derivatives were more active at brain and heart MR in some cases. The most active preparation was G-512, DA-analogue of chlorpromazine. Some cardiotropic properties of antianginal preparation nonachlazine may be connected with its central antimuscarinic activity.     

Clozapine increases rat serum prolactin levels.

Clozapine differs from other anti-psychotic drugs in that is produces little or no extrapyramidal side effects. The effects of clozapine on rat brain dopamine differ markedly from those of the neuroleptic drugs. The neuroleptics increase rat serum prolactin levels which has been attributed to their dopamine receptor blocking properties. We found that clozapine markedly increased serum prolactin levels in male rats when injected intraperitoneally in doses of 5, 10, 50 and 100 mg/kg. Serum prolactin levels after 5 mg/kg clozapine were significantly less than in rats given 10, 50 and 100 mg/kg which did not significantly differ from each other. Serum prolactin after 10 mg/kg clozapine was significantly greater than after chlorpromazine, 5 mg/kg and haloperidol, 0.5 mg/kg. The increases in serum prolactin are attributed to clozapine's ability to produce dopamine blockade or to inhibit nerve impulse-dopamine release, or both. The capacity of clozapine to affect brain serotonin and norepinephrine metabolism and its strong anti-cholinergic properties are probably not involved in its ability to increase serum prolactin.     

Comparison of the effects of substituted benzamides and standard neuroleptics on the binding of 3H-spiroperidol in the rat pituitary and striatum with in vivo effects on rat prolactin secretion.

The abilities of sulpiride, metoclopramide, clozapine, loxapine, chlorpromazine, thioridazine, fluphenazine, haloperidol, (+)-butaclamol and RMI 81,582 to displace ³H-spiroperidol from rat pituitary and striatal membranes in vitro were compared to their abilities to stimulate rat prolactin secretion in vivo. There was a significant correlation between the abilities of clozapine, chlorpromazine, thioridazine, fluphenazine, RMI 81,582, haloperidol and (+)-butaclamol to bind to pituitary and striatal spiroperidol binding sites and to stimulate rat prolactin secretion. Loxapine was somewhat more potent and sulpiride and metoclopramide were markedly more potent in their abilities to stimulate prolactin secretion than would be predicted on the basis of their abilities to bind to pituitary dopamine receptors as measured by antagonism of ³H-spiroperidol binding. The abilities of metoclopramide and sulpiride to increase prolactin secretion and to produce anti-psychotic and extrapyramidal effects may be mediated by action at dopamine receptors which differ from those at which classical neuroleptics act, and they may also be mediated by non-dopaminergic mechanisms. Potency as inhibitors of ³H-neuroleptic binding in the rat pituitary or striatum appears to have heretofore unappreciated limitations to predict physiological functions such as prolactin stimulation and anti-psychotic activity.     

Specificity of the dopamine sensitive adenylate cyclase for antipsychotic antagonists

Chlorpromazine, haloperidol and clozapine are approximately equipotent in antagonizing dopamine sensitive adenylate cyclase activity in homogenates of rat brain striatum, in contrast to the differences in clinical antipsychotic potencies reported by others. The antagonism appeared to occur at a structurally specific dopamine site, as inhibition by a series of chlorpromazine analogues of similar hydrophobicity exhibited a structural specificity similar to that found for their neuroleptic and cataleptic activities. Sulpiride, a dopamine antagonist with antipsychotic activity, and metoclopramide, a structurally related central dopamine antagonist, failed to inhibit the dopamine sensitive adenylate cyclase. Pre-treatment of rats with haloperidol (3 mg/kg per day) for 6 or 28 days did not induce a supersensitive response of the adenylate cyclase to stimulation by dopamine or apomorphine or inhibition by clozapine. It was concluded that the dopamine sensitive adenylate cyclase may not be the site of action of all anti-psychotic agents.     

Effects of acute and long-term treatment with neuroleptics on regional telencephalic neurotensin levels in the male rat

By means of radioimmunoassay measurements of regional neurotensin (NT) levels in the forebrain of the male rat it was shown that selective D2 DA receptor antagonists, such as haloperidol and sulpiride, and unselective D1 and D2 antagonists such as thioridazine, flupenthixol clozapine and fluperlapine, can acutely increase NT levels in the striatum and the nucleus accumbens without affecting NT levels in the amygdaloid or anteromedial frontal cortex. Conversely, acute treatment with the D1 DA receptor antagonist Schering 23390 (SCH 23390) produced a selective reduction of striatal NT levels. After long-term treatment clozapine, fluperlapine or SCH 23390, tolerance developed with regard to their ability to modulate striatal and accumbens levels. No tolerance occurred after chronic haloperidol, chlorpromazine and sulpiride. The results indicate that the acute administration of D1 and D2 DA receptor antagonists differentially modifies NT levels in the striatum and nuc. accumbens, and that antipsychotic drugs showing a relative lack of extrapyramidal side effects may be characterised by a failure to maintain increased NT levels in the basal ganglia upon long-term treatment.     

Aging and monoamine receptors in brain.

Biochemical evidence is presented for selective decreases in biogenic amine receptor systems with age in the rabbit. Dopamine-stimulated adenylate cyclase activity in striatum, hypothalamus, frontal cortex, and anterior limbic cortex declined by about 50% as rabbits aged from less than 1 to 5 years of age. Similar decreases were found for histamine-stimulated activity in hypothalamus and the cortical regions. These changes were in maximal response rather than in affinity for amine. In contrast, dopamine-stimulated adenylate cyclase of retina and both basal and Gpp(NH)p-stimulated activity in these regions were not altered with age. In addition, with age the number of binding sites for [3H]spiroperidol, a dopamine antagonist, decreased by 30--40% without change in ligand affinity in striatum and limbic cortex. These changes in striatum and cortex occurred in the absence of decreases in either dopamine concentration or choline acetylase activity. It is proposed that selective age-dependent decreases in the functional number of biogenic amine receptors occur in the absence of, or independent from neuronal cell loss, possibly by a mechanism of desensitization. These changes occurred in brain regions that in man are thought to be of importance in the age-related loss of cerebral function.     

THE EFFECT OF BROMOCRIPTINE ON RAT STRIATAL ADENYLATE CYCLASE AND RAT BRAIN MONOAMINE METABOLISM

In slices and homogenate from rat brain striatum bromocriptine in marked contrast to DA. NA and apomorphine. had no stimulatory effect on adenylate cyclase activity, but antagonised the stimulatory effects of both NA and DA. Bromocriptine (10 mg/kg s.c.) decreased the turnover of DA in striatum and limbic structures 3h after drug administration. However, an increase in the turnover of NA in the brain stem and that of 5-HT in the cortex was observed 4h following treatment with bromocriptine. Possible modes of action of bromocriptine are discussed.     

Typical and Atypical Neuroleptics Induce Alteration in Blood-Brain Barrier and Brain 59FeCl3 Uptake

Abstract: Long-term neuroleptic medication of schizophrenic patients induces extrapyramidal motor side effects, of which tardive dyskinesia (TD) is the most severe. The etiology of TD is still obscure. Recently, it was suggested that abnormal iron metabolism may play a crucial role in neuroleptic-induced dopamine D₂ receptor super-sensitivity. The apparent relationship between neuroleptics and iron is further supported by the increase of iron in the basal ganglia of patients with TD. We now report on the ability of neuroleptics to alter the blood-brain barrier in the rat and to potentiate the normally limited iron transport into the brain. Thus, chronic treatment of rats with chlorpromazine and haloperidol facilitated ⁵⁹Fe³⁺ uptake into brain cells. In contrast, clozapine, an atypical antipsychotic neuroleptic with little extrapyramidal motor side effects, caused iron sedimentation in brain blood vessels with no sign of detectable iron in the cells. Moreover, chronic treatment with chlorpromazine and haloperidol caused a 43% and 24% reduction, respectively, in liver nonheme iron, whereas clozapine induced an 81% increase. The apparent different potentials of chlorpromazine, haloperidol, and clozapine to increase iron transport into the brain from its peripheral stores may be linked to the severity of extrapyramidal motor side effects they induce and to the pathophysiology of TD.     

Influence of sexual differentiation on striatal and limbic catecholamines

The influence of sexual differentiation of the brain on catecholamine content in the corpus striatum and limbic system was studied. Our results suggest that circulating ovary hormones during the critical period play an important role in the sexual differentiation of dopaminergic neurons in the corpus striatum and limbic system. Absence of androgenic steroids in the critical period leads to permanent alterations in the DA content of the limbic system in the male rat. Gonadectomy does not significantly alter NA levels in either of the two studied brain areas.     

Effects of neuroleptics on glutaminase from rat synaptosomes

Phosphate-activated glutaminase was isolated from synaptosomes from three areas of rat brain. Glutamine utilization phosphate activation and inhibition by glutamate or ammonia were assessed in the absence or presence of haloperidol, chlorpromazine, or clozapine. All three drugs (at 1 micromolar concentration) elevated theK _m for glutamine using preparations from the amygdala, hippocampus, or striatum. They interfered with phosphate activation only in the amygdala preparation. No drug affected end-product inhibition. The data suggest that neuroleptics may depress the release of glutamic acid from synaptosomes by interfering with the activation of glutaminase by phosphate.     

Monoamine oxidase -A and -B activity in the rat brain after hemitransection

The activity of MAO-A and MAO-B in four different brain regions (striatum, limbic system, occipito-temporal cortex and hemispheres) was determined after hemitransection of the left side. There was no difference in the MAO-A activities of either the left or right sides of the brain in either control or hemitransected rats. The activity of MAO-B was the same for both sides in control rats, but there was an increased MAO-B activity in the left side of the hemitransected rats with respect to the right side in all brain regions investigated, with the possible exception of the limbic system. The increase was due to a change in the V_max rather than to a changed K_m of the MAO-B. The interaction of the MAO-B with oxygen was unchanged after hemitransection.     

Histotopography of changes in the enzyme activity of rat brain exposed to fluorophenazine]

The influence of fluorophenazine on succinic-, citric acid-, NAD-H2-and NADP-H2-dehydrogenases in different structures of rat brain was investigated by histochemical methods.Three hours after a single subcutaneous injection of fluorophenazine (1 and 5 mg/kg) the enzymatic activity was the greatest in the limbic and the frontal regions of the cortex. The inhibitory effects of fluorophenazine in these structures were greater than those of the neuroleptics trifluoroperazine, chlorpromazine.     

Atypical properties of several classes of antipsychotic drugs on the basis of differential induction of Fos-like immunoreactivity in the rat brain

Acute administration of typical and atypical antipsychotics has been reported to induce regionally distinct patterns of c-Fos expression in the rat forebrain. Furthermore, atypical index, the difference in the extent of increased Fos-like immunoreactivity (Fos-LI) in the nucleus accumbens (NAc) shell versus the dorsolateral striatum (DLSt), has been proposed to classify antipsychotics into typical or atypical antipsychotics. The present study was conducted to investigate the atypical properties of 24 antipsychotics that are used in Japan and blonanserin, a novel 5-HT2A and D2 receptor antagonist. We systematically examined the effects of the drugs on Fos-LI in the NAc and DLSt in the rat brain using immunohistochemistry and calculated the atypical index, comparing with those of haloperidol and clozapine. Floropipamide, oxypertine, nemonapride, pimozide and mosapramine, as well as clozapine, olanzapine, quetiapine and risperidone, showed high positive atypical index. Zotepine, perospirone, sulpiride, moperone, sultopride, thioridazine, carpipramine, clocapramine and blonanserin showed moderate ones. In contrast, fluphenazine, bromperidol, timiperone, spiperone, propericiazine, perphenazine, chlorpromazine and levomepromazine had negative atypical index like haloperidol. These results suggest that not only so-called atypical antipsychotics, but also several conventional drugs, possess atypical properties.     

Neuroleptics-induced changes of tyrosine hydroxylase activity in rat striatum in vitro and in vivo.

The potency of haloperidol and chlorpromazine, but not clozapine, for increasing homovanillic acid and activating tyrosine hydroxylase in the striatum was significantly weakened after the repeated administration in rats. These findings suggest that clozapine could supply enough dopamine to surmount the blockade of dopamine receptors in the striatum even after the repeated administration. This property of clozapine seems to be the cause of low incidence of extrapyramidal side effects in clinical use.     

Effect of neuroleptic drugs on prostaglandin synthetase activity

The effects of neuroleptic drugs (chlorpromazine, trifluperazine, fluphenazine, benperidol, bromperidol, flupentixol, clozapine, reserpine, RO-4-1284) on the activity of prostaglandin synthetase were studied in the microsomes of the seminal vesicles of the bull. The activity of prostaglandin synthetase was determined in the microsomes of bull brain (cortex, striatum, hippocampus, thalamus, hypothalamus) and the effect of the neuroleptic drugs was determine on the activity of prostaglandin synthetase in the thalamus, where the activity of this enzyme was highest. It was found that the experimental model of seminal vesicles was unsuitable for evaluating the effects of neuroleptic drugs on the central nervous system. It was demonstrated that prostaglandin synthetase activity differed in different parts of the brain and this activity was highest in the thalamus. The obtained results indicate that inhibition of prostaglandin synthetase activity seems to have no significant importance in the mechanism of the neuroleptic action of these drugs.     

Enzymatic lipid peroxidation and oxidative metabolism of aminazine in brain microsomal fractions]

NAD (P) H-dependent enzymic systems, both of lipid peroxidation and chlorpromazine oxidative metabolism are shown to be localized in the microsomal fractions from human and rat brain. Hydroxy-derivatives of chlorpromazine (e.g. 7-OH-chlorpromazine) formed in the course of enzymic NADPH-dependent metabolism possess antioxidant activity and inhibit lipid peroxidation in the brain microsomes. The properties of enzymic NAD (P) H-dependent oxigenase systems in the membranes of the microsomal reticulum of the liver and brain are compared.     

Effects of isomers of apomorphines on dopamine receptors in striatal and limbic tissue of rat brain

The optical isomers of apomorphine (APO) and N-propylnorapomorphine (NPA) were interacted with three biochemical indices of dopamine (DA) receptors in extrapyramidal and limbic preparations of rat brain tissue. There were consistent isomeric preferences for the R(-) configuration of both DA analogs in stimulating adenylate cyclase (D-1 sites) and in competing for high affinity binding of 3H-spiroperidol (D-2 sites) and of 3H-ADTN (DA agonist binding sites) in striatal tissue, with lesser isomeric differences in the limbic tissue. The S(+) apomorphines did not inhibit stimulation of adenylate cyclase by DA. The tendency for greater activity or higher apparent affinity of R(-) apomorphines in striatum may reflect the evidently greater abundance of receptor sites in that region. There were only small regional differences in interactions of the apomorphine isomers with all three receptor sites, except for a strong preference of (-)NPA for striatal D-2 sites. These results do not parallel our recent observations indicating potent and selective antidopaminergic actions of S(+) apomorphines in the rat limbic system. They suggest caution in assuming close parallels between current biochemical and functional, especially behavioral, methods of evaluating dopamine receptors of mammalian brain.     

Comparative neurochemical changes associated with chronic administration of typical and atypical neuroleptics: implications in tardive dyskinesia

An important goal of current neuroleptic research is to develop antipsychotic compounds with the low incidence of extrapyramidal side effects. The therapeutic success and less side-effect of atypical anti-psychotics such as clozapine and risperidone has focused the attention on the role of receptor systems other than dopaminergic system in the pathophysiology of neuroleptics-associated extrapyramidal side effects. The present study compares the effect of chronic administration of typical and atypical antipsychotics on neurochemical profile in rat forebrain. The study was planned to study changes in extracellular levels of norepinephrine, dopamine and serotonin in forebrain region of brain and tried to correlate them with hyperkinetic motor activities (vacuous chewing movements (VCM's), tongue protrusions and facial jerking) in rats, hall mark of chronic extrapyramidal side-effect of neuroleptic therapy tardive dyskinesia. Chronic administration of haloperidol (1 mg/kg) and chlorpromazine (5 mg/kg) resulted in significant increase in orofacial hyperkinetic movements where as clozapine and risperidone showed less significant increase in orofacial hyperkinetic movements as compared to control. There were also significant decrease in the extracellular levels of neurotransmitters dopamine, norepinephrine and serotonin in fore-brain as measured by HPLC/ED after chronic administration of haloperidol and chlorpromazine. Chronic administration of atypical neuroleptics clozapine and risperidone resulted in the decrease in extracellular concentration of dopamine and norepinephrine but the effect was less significant as compared to typical drugs. However, treatment with atypical neuroleptics resulted in 3 fold increase in serotonin levels as compared to forebrain of control rats. Typical and atypical neuroleptics showed varying effects on neurotransmitters, especially serotonin which may account for the difference in their profile of side effects (Tardive dyskinesia).     

Differences in effects of sultopride and sulpiride on dopamine turnover in rat brain

Sultopride and sulpiride are both chemically similar benzamide derivatives and selective antagonists of dopamine D2 receptors. However, these drugs differ in clinical properties. We compared the effects of sultopride and sulpiride on dopamine turnover in rats following the administration of these drugs alone or in combination with apomorphine. The administration of sultopride or sulpiride markedly accelerated dopamine turnover in the rat brain. The increase in the level of dopamine metabolites in the striatum was more marked in the sultopride-treated rats. Sulpiride affected the limbic dopamine receptors preferentially, whereas sultopride affected the striatal and the limoic dopamine receptors equally. A low dose of apomorphine induced a reduction in the concentration of dopamine metabolites in the striatum and the nucleus accumbens by approximately 55%, but not in the medial prefrontal cortex. Sultopride was more effective in preventing an apomorphine-induced reduction in dopamine metabolite levels. These results from rat experiments would model the pharmacological differences observed between sultopride and sulpiride in clinical use.