Stimulation by sulpiride, chlorpromazine and haloperidol of dopamine turnover in the cerebral cortex of the rat

BRL 20596, a novel anilide with central dopamine antagonist activity

BRL 20596 (N-(4-amino-5-chloro-2-methoxyphenyl)-1-phenylmethyl-4-piperidine-carbox amide) is a novel anilide related to clebopride (a gastric prokinetic benzamide) in which the sole change is reversal of the amide bond. Previous studies have shown conformational and electronic differences between these molecules which result in the anilide losing its gastric prokinetic activity, whilst retaining its central nervous system activity. Pharmacological and biochemical properties of BRL 20596 are compared here in animals with chlorpromazine, clebopride, haloperidol and sulpiride. BRL 20596 potently inhibited a number of behaviours, such as conditioned avoidance, amphetamine-induced stereotypy and turning, and apomorphine-induced climbing. Homovanillic acid (HVA) levels in the striatum and nucleus accumbens were raised at similar dose levels to those which inhibited these behaviours, whilst sedative activity was only exhibited at much higher dose levels. Haemodynamic changes were only observed with high IV doses of BRL 20596. Much lower doses of sulpiride were needed to raise prolactin levels than to raise HVA levels. This was not the case with BRL 20596 and the other drugs, where the doses needed for the two effects were similar. The results suggest that BRL 20596 is a central dopamine antagonist, with low sedative and haemodynamic activity.

Multiple dopamine receptors in brain and the pharmacological action of substituted benzamide drugs

Neuroleptic drugs are believed to control schizophrenia by blocking brain dopamine receptors, although most act also on a number of other neuronal systems in brain. Substituted benzamide drugs in general, are more specific for the dopamine system. Brain dopamine receptors, however, are not a single entity. They can be divided on the basis of their linkage to adenylate cyclase. Substituted benzamide drugs are selective antagonists of the adenylate cyclase independent dopamine receptor population. They may be selective antagonists of one sub-population of these adenylate cyclase independent receptors, for unlike typical neuroleptics the receptor interaction of substituted benzamide drugs with brain dopamine receptors depends upon the presence of sodium ions. The specificity of substituted benzamide drugs for brain dopamine receptors is reflected in their behavioural profile. Typical substituted benzamide drugs do not cause catalepsy and, in general, only weakly inhibit motor phenomena. This inability to act in vivo cannot be entirely explained by the poor penetration of these drugs into brain. The unique properties of the substituted benzamide drugs might explain their clinical value in the treatment of schizophrenia and in the treatment of dyskinesias.

Relationship between prolactin in the serum and cerebrospinal fluid of ovariectomized female rhesus monkeys

The entry of prolactin into the cerebrospinal fluid from the blood, and the relation between levels in the two compartments were studied under a variety of conditions in ovariectomized rhesus monkeys. Prolonged treatment with either domperidone or sulpiride, both dopamine-receptor blockers, elevated prolactin levels in serum and cerebrospinal fluid proportionally equally, so that the cerebrospinal fluid serum ratio was unchanged from controls (circa 12-20%). Gel filtration showed that only 'little' (monomeric) prolactin entered the cerebrospinal fluid in such monkeys. Following acute elevations of blood prolactin after a single injection of either sulpiride or ovine prolactin, cerebrospinal fluid levels increased linearly over a 90 min sampling period, despite falling serum levels. The rate of entry of prolactin into the cerebrospinal fluid was similar after either procedure, and was independent of absolute serum or cerebrospinal fluid levels, suggesting a rate-limiting mechanism. Furthermore, retrograde portal blood flow from the pituitary is not necessary to account for these results. Clearance of prolactin from the third ventricle was studied following intraventricular injection of prolactin. Prolactin was removed from the cerebrospinal fluid by a mechanism whose efficiency compares with that in serum, so that the half-life of prolactin in either compartment is about the same. Measurement of sodium, potassium and calcium in the cerebrospinal fluid during prolonged hyperprolactinaemia showed no change, indicating that the central effects of prolactin are not due to alteration of these electrolytes. These results show that cerebrospinal fluid levels of prolactin, and hence, those surrounding the brain, can be inferred accurately from those in the blood, and suggest that there may be a selective mechanism regulating the entry of prolactin into the cerebral compartment.

The pharmacology of sulpiride--a dopamine receptor antagonist

1. The clinical and experimental pharmacology of sulpiride, its effects on the CNS, gastrointestinal tract and cardiovascular system have been reviewed. 2. The majority of its actions are attributable to blockade of dopamine receptors. 3. Although sulpiride has a high affinity for dopamine receptors involved in emesis and prolactin secretion, it lacks part of the behavioural and biochemical profiles of the classical dopamine receptor antagonist neuroleptics. 4. In the cardiovascular system, sulpiride is a potent prejunctional dopamine receptor antagonist but has variable effectiveness in postjunctional dopamine receptor models. 5. These properties are discussed with reference to the mechanisms of action of sulpiride and the classification of dopamine receptors.

Suppression of REM and delta sleep by apomorphine in man: a dopamine mimetic effect

Apomorphine, a direct stimulant of dopamine receptors, was given in nonemetic doses by continuous IV infusion for 180-240 min during night sleep in normal subjects. During apomorphine infusion, a significant reduction of stage (S)4 and an abolition of rapid eye movement (REM) sleep occurred. The percent duration of S2 was significantly increased. In the 240 min following interruption of 240-min infusion of apomorphine, a significant increase of S4 and REM percent duration was observed. The effect of apomorphine infusion on sleep was prevented by the administration of haloperidol or sulpiride, two dopamine receptor blocking agents. This suggests that it is due to a dopamine mimetic action.

Comparison of sulpiride and chlorpromazine in psychoses. A double-blind multicentre study

In a material of 71 patients admitted because of acute or chronic psychoses, 32 were treated with sulpiride (up to 1,800 mg per day) and 39 with chlorpromazine (up to 675 mg). Duration of treatment was from 4 to 8 weeks. The effect of the two preparations was very similar as were the type and frequency of side effects, except that sulpiride did not cause sunrash.

The effects of intraperitoneal injection of 6-hydroxydopamine on the turnover and the levels of the brain catecholamines and the levels of plasma corticosterone in rats

1. The effects of intraperitoneal injection of 6-hydroxydopamine (6-OHDA) on the levels and the turnover of brain catecholamines and the levels of plasma corticosterone were studied in rats. 2. Two weeks after intraperitoneal injection of 6-OHDA (150 mg/kg) a virtually complete disappearance of cardiac noradrenaline was observed. 3. An increment and an accelerated turnover of noradrenaline in the hypothalamus was observed 2 weeks after peripheral administration of 6-OHDA (150 mg/kg). 4. There was no change in the levels and the turnover of noradrenaline in the cortex of the rats so treated. 5. There was not change in the levels and the turnover of dopamine in either the hypothalamus or the cortex of the 6-OHDA-treated rats. 6. An increment and an accelerated turnover of hypothalamic noradrenaline were not associated with any change in plasma corticosterone.

Inhibition of saline-induced diuresis in the rat by sulpiride

Sulpiride (120 mg/kg, i.p.) inhibited saline-induced diuresis in the rat, an effect not observed with haloperidol, clozapine, pimozide or chloromazine. The antidiuretic effect of sulpiride also occurred in hypophysectomized rats suggesting that the response was not prolactin-mediated.

Electrically induced release of [3H]dopamine from slices obtained from different rat brain cortex regions. Evidence for a widespread dopaminergic innervation of the neocortex

Slices obtained from the deeper layers of the rat dorsal frontal, parietal and occipital brain cortex were incubated in vitro with 6.25 X 10-7 M [3H]dopamine (DA), and subsequently superfused and electrically stimulated, while held on quick transfer electrodes, and changes in the efflux of 3H and of the individual amines measured. The separation of the amines, with quantitative recoveries, was performed by chromatography on cation-exchange resins eluted sequentially with water, 1 N HCL AND 6 M urea i 1 N HCl. When no drugs were used, the prestimulation efflux was entirely formed by deaminated metabolites, while following stimulation there was an increase in the efflux of deaminated metabolites, and considerable amounts of [3H]-noradrenaline (NA) now appeared. No DA was present in the pre- or poststimulation medium. Similar results were obtained in all the regions studied. When the slices were incubated with 10-5 M desmethylimipramine (DMI), 10-4 Mnialamide and 10-4 M tropolone, before and during incubation with [3H]DA, it was observed that, prior to stimulation, the efflux was composed of deaminated metabolites, DA and 3-methoxytyramine (MTA), and following the electrical stimulus there was an increased release of DA, NA and deaminated compounds (in order of decreasing release), while no change in that of MTA was evident. The stimulus-induced release of DA was greatest from frontal slices, intermediate from parietal, and lowest from occipital ones. DMI-resistant uptake of [3H]DA also diminished when passing from frontal to occipital. These findings are interpreted as due to the presence of dopaminergic axon terminals in all the regions studied, but with a density that diminishes in a rostrocaudal direction.