Nils-Erik Andén

Receptor activity and turnover of dopamine and noradrenaline after neuroleptics.

Abstract Fifteen neuroleptics of the phenothiazine, thioxanthene, dibenzazepine, butyrophenone or diphenylbutylamine type were studied in rats. The dopamine (DA) receptors in the corpus striatum were blocked by all the drugs. The effects on noradrenaline (NA) receptors in the spinal cord varied. Chlorpromazine blocked the two receptors about equally. Haloperidol, perphenazine, clothiapine and particularly spiroperidol had a greater effect on DA receptors. Pimozide and fluspirilene blocked only DA receptors. Turnover of DA and NA was studied using biochemical and histochemical techniques, after tyrosine hydroxylase inhibition. Perphenazine and clothiapine accelerated turnover of both amines whereas spiroperidol only accelerated that of DA. Pimozide and fluspirilene increased turnover of DA and, at higher doses, NA. The high doses usually reduced the endogenous DA and NA levels. Thus, the most potent and specific neuroleptics seemed to influence mainly the brain DA mechanisms, both functionally and chemically.

Evidence for dopamine receptor stimulation by apomorphine

Sm,-Recently, Ernst (1967) has reported that the apomorphine-induced compulsive gnawing in rats is not mediated via the release of catecholamines, since it is not reduced by the catecholamine synthesis inhibitors a-methyl-3,4dihydroxyphenylalanine and a-methyltyrosine. On the other hand, the gnawing seen after treatment with (+)-amphetamine is blocked by these synthesis inhibitors. Since the apomorphine-induced gnawing requires an intact corpus striatum and gnawing can also be produced by the catecholamine precursor dihydroxyphenylalanine, Ernst (1967) suggested that apomorphine acts on the dopamine receptors whereas amphetamine acts by releasing dopamine. In the present paper supporting evidence for this view is given by further functional, biochemical and histochemical studies. The functional influence of apomorphine on dopamine neurotransmission in the corpus striatum was examined after unilateral removal of the corpus striatum of adult hooded rats weighing about 200 g (And& Dahlstrom & others, 1966a). A possible action of apomorphine on the noradrenaline receptors of the spinal cord was tested in acutely spinalized adult hooded rats by evaluating the changes in the flexor reflex evoked by pinching the hind limbs. The effect of apomorphine on the dopamine and noradrenaline levels of the brain and spinal cord was determined biochemically (Bertler, Carlsson & Rosengren, 1958; Carlsson & Waldeck, 1958) and histochemically (Falck, Hillarp & others, 1962; Dahlstrom & Fuxe, 1964; Hamberger, Malmfors & Sachs, 1965). Function. These studies were made mainly on rats which had been pretreated with reserpine (10 mg/kg i.p., 3 hr) plus a-methyltyrosine methylester (H 44/68, 500mg/kg, i.p., 2 hr) after removal of the left corpus striatum by suction. After this treatment all the operated animals turned towards the unoperated side (cf. And6n & others, 1966a). After injection of apomorphine (1-25 mg/kg s.c.) these rats changed their position and turned or rotated towards the operated side. This effect began about 5 min after the injection and was evident for about 45-60 min. If apomorphine was given to operated rats not pretreated with reserpineH 44/68 combination, this action of apomorphine, like the gnawing, seemed to be less pronounced. If haloperidol (5 mg/kg i.p.) was given 15-20 min after apomorphine all the rats turned from the operated towards the unoperated side in about 15 min and the gnawing ceased. (+)-Amphetamine (0.5-25 mg/kg s.c.), like apomorphine, made the rats turn or rotate towards the operated side. In contrast to apomorphine, however, this action of amphetamine was not seen after pretreatment with reserpine plus H 44/68 (cf. Weissman, Koe & Tenen, 1966; Hanson, 1967; Ernst, 1967). Apomorphine (25 mg/kg s.c.), in contrast to (+)-amphetamine (05-25 mg/kg s.c.) and ~-3,4-dihydroxyphenylalanine (50-75 mg/kg i.v. 2 hr after nialamide 50 mg/kg i.p.), did not cause a definite increase of the flexor reflex in spinalized rats. Chemistry. The biochemical results obtained in unoperated adult hooded rats are presented in Table 1. Apomorphine caused a retardation of the depletion in brain dopamine produced by H 44/68. The difference between the dopamine levels in the apomorphine-H 44/68 group and in the H 44/68 group is statistically significant (P < 0.001, Student’s r-test). This action of apomorphine on the brain dopamine was blocked by haloperidol. The disappearance of noradrenaline from the brain and the spinal cord after H 44/68 did not seem to be influenced by apomorphine. (+)-Amphetamine did not cause any significant retardation of the dopamine and noradrenaline loss after H 44/68.

Demonstration and mapping out of nigro-neostriatal dopamine neurons

Abstract In normal rats dopamine-storing nerve terminals are found in the neostriatum (= the caudate nucleus + putamen) and dopamine-containing nerve cells in the substantia nigra, mainly in the pars compacta. After electrolytic lesions in the substantia nigra or the internal capsule the histochemical fluorescence and the dopamine content of the neostriatum were markedly reduced. Removal of the neostriatum produced an increased fluorescence of the dopamine nerve cells of the substantia nigra and of their axons central to the lesion. These axons ascend as a nerve tract in the internal capsule towards the neostriatum. The data give strong evidence for the existence of nigro-neostriatal dopamine neurons, which probably contain most or all of the dopamine present in the neostriatum.

Evidence for a central noradrenaline receptor stimulation by clonidine

Abstract Clonidine increased the flexor reflex of spinal rats also after depletion of all known noradrenaline stores, indicating a stimulation of also central noradrenaline receptors. No stimulation of 5-hydroxytryptamine or dopamine receptors was observed. The motility of reserpine treated animals was enhanced by clonidine provided that the DA receptors were stimulated. Clonidine reduced the disappearance of noradrenaline and also that of 5-hydroxytryptamine after synthesis inhibition. The chemical effects might be due to a negative feedback mechanism, evoked by the noradrenaline receptor stimulation. Both the functional and chemical changes were reduced by the noradrenaline receptor blocking agents haloperidol and phenoxybenzmine.

Different alpha-adrenoreceptors in the central nervous system mediating biochemical and functional effects of clonidine and receptor blocking agents

SummaryThe influence of clonidine on α-adrenoreceptors in the central nervous system of rats and mice has been investigated. Both functional events due to postsynaptic receptor stimulation (flexor reflex activity, motor activity) and biochemical changes have been considered.1.Clonidine was less potent in stimulating the hindlimb flexor reflex activity of spinal rats than in inhibiting the α-methyltyrosine-induced disappearance of noradrenaline in the spinal cord and in the whole brain of rats.2.The increase in flexor reflex activity due to clonidine (0.4 mg/kg) was virtually completely inhibited by phenoxybenzamine (20 mg/kg) and haloperidol (10 mg/kg), was partially inhibited by yohimbine (10 mg/kg) and piperoxan (60 mg/kg) and was not significantly inhibited by yohimbine (3 mg/kg) and tolazoline (50 mg/kg).3.The potentiation by clonidine of the apomorphine-induced locomotor stimulation of reserpinetreated mice was almost completely inhibited by phenoxybenzamine (20 mg/kg) but was not significantly affected by yohimbine (10 or 3 mg/kg) and only slightly inhibited by tolazoline (50 mg/kg).4.Clonidine (0.1 mg/kg) caused a considerable inhibition of the α-methyltyrosine-induced disappearance of noradrenaline in the spinal cord and brain of rats and in the brain of mice. This effect of clonidine was completely antagonized by yohimbine (10 mg/kg). It was markedly antagonized by yohimbine (3 mg/kg), piperoxan (60 mg/kg) or tolazoline (50 mg/kg) but not by phenoxybenzamine (20 mg/kg) or haloperidol (10 mg/kg).5.Clonidine (0.1 mg/kg) caused an inhibition of the accumulation of Dopa after decarboxylase inhibition in the noradrenaline-rich regions of the rat central nervous system. This effect was counteracted by yohimbine (10 mg/kg), piperoxan (60 mg/kg) or tolazoline (50 mg/kg) but not by phenoxybenzamine (20 mg/kg).6.The postsynaptic functional effects and the biochemical effects of clonidine may be due to stimulation of different α-adrenoreceptors since the two effects were inhibited differently by various α-adrenoreceptor blocking agents and since the two effects were produced by different doses of clonidine. The α-adrenoreceptors mediating the biochemical changes might be located on the noradrenergic neurones.

A functional effect of dopamine in the nucleus accumbens and in some other dopamine-rich parts of the rat brain

Dopamine (5 to 50 Μg) applied bilaterally to the nucleus accumbens of reserpine-nialamide pretreated rats produced a marked dose-dependent rise in coordinated locomotor activity, devoid of stereotypies such as gnawing, rearing and licking seen after dopamine application (50 Μg) to the neostriatum. The locomotor activity was completely blocked by pimozide, but not by phenoxybenzamine. The effects of apomorphine or d-noradrenaline were similar to those of dopamine. In contrast, l-noradrenaline produced a “convulsive” syndrome devoid of coordinated locomotor activity, and this convulsive syndrome could be completely blocked by phenoxybenzamine but not by pimozide. Release of endogenous dopamine by d- or l-amphetamine (10 and 50 Μg) in the nucleus accumbens produced a rise in coordinated activity, the d-isomer was about 4 times as potent as the l-isomer, and the effect of the d-isomer was blocked completely by α-methyltyrosine. Bilateral application of trifluoperazine (2.5 Μg) to the nucleus accumbens completely blocked the effect of systemically administered d-amphetamine (1.5 and 3.0 mg/kg), but similar application to the area of the central nucleus of the amygdala or the neostriatum was much less effective. Partial protection of the endogenous dopamine stores against the depleting action of reserpine by local application of metatyramine to the nucleus accumbens resulted in a higher level of basal activity than in control animals. Application of dopamine or noradrenaline to the area of the central nucleus of the amygdala or to the olfactory tubercles did not lead to any consistent changes in locomotor activity.The nucleus accumbens and olfactory tubercles contained most of the dopamine in the limbic forebrain, with noradrenaline more evenly distributed.These data suggest that the nucleus accumbens plays an important role in the locomotor activity in rats.

Evidence for a central 5-hydroxytryptamine receptor stimulation by lysergic acid diethylamide

1 Lysergic acid diethylamide (LSD) and the 5‐hydroxytryptamine (5‐HT) precursor, 5‐hydroxytryptophan produced similar functional effects in rat spinal cord and brain to the 5‐hydroxytryptamine precursor 5‐hydroxytryptophan, which indicates that LSD stimulates central 5‐HT receptors. 2 By means of combined histochemical and biochemical techniques it was found that LSD reduced the turnover rate of brain and spinal cord 5‐HT, studied after inhibition of the tryptophan hydroxylase by α‐propyldopacet‐amide. The turnover of brain noradrenaline but not dopamine was somewhat accelerated. 3 The functional and chemical effects by LSD were related to dose and to time. They were not observed after the LSD analogues 2‐bromo‐LSD and methysergide. 4 The retardation of the 5‐HT turnover by LSD may be due to negative feed‐back mechanisms evoked by direct stimulation of the central 5‐HT receptors.

Effects of tyrosine hydroxylase inhibition on the amine levels of central monoamine neurons

Abstract As shown by both histochemical and biochemical methods, the methyl ester of α-methyl- p -tyrosine (H 44/68, 500 mg/kg i.p.), an inhibitor of the tyrosine hydroxylase, causes the catecholamines but not the 5-hydroxytryptamine in rat brain and spinal cord to disappear almost completely in 24 hours. There were no significant differences between the various regions in rate and degree of the depletion of the terminals and cell bodies. After transection the loss of noradrenaline from the spinal cord was prevented below but not above the lesion showing the importance of the impulse flow for the disappearance of the transmitter. A marked recovery was seen in all terminals and cell bodies after 48 hours. The reappearance was somewhat faster in the cell bodies suggesting that the tyrosine hydroxylase is formed in them.

Inhibitory effect of gammahydroxybutyric acid and gammaaminobutyric acid on the dopamine cells in the substantia nigra

SummaryInjections of gammahydroxybutyric acid or gammaaminobutyric acid (GABA), but not betahydroxybutyric acid or carnitine, into the substantia nigra induced increases in brain dopamine of rats. No effect was found after injections into the neostriatum. The noradrenaline in the forebrain was unchanged after all the treatments. Gammahydroxybutyric acid may act by directly or indirectly mimicking an inhibitory GABA mechanism on the dopamine cells in the substantia nigra.

Selective stimulation of dopamine and noradrenaline autoreceptors by B-HT 920 and B-HT 933, respectively

Summary1.The azepine derivatives B-HT 920 and B-HT 933 did not increase the motor activity of mice pretreated with reserpine or reserpine plus apomorphine, indicating that they do not stimulate postsynaptic dopamine receptors or noradrenaline α1-receptors in the brain.2.The motor activity of mice not pretreated with reserpine was reduced by a low dose of B-HT 920 and by B-HT 933. The α1-adrenoceptor antagonist yohimbine reversed the sedation induced by B-HT 933, but not that induced by B-HT 920.3.B-HT 933 and a high dose of B-HT 920 retarded the α-methyltyrosine-induced disappearance of noradrenaline in the mouse brain by a yohimbine-sensitive mechanism.4.The α-methyltyrosine-induced disappearance of dopamine in the mouse brain was decelerated by a low dose of B-HT 920 and to a smaller degree by B-HT 933. The effects were inhibited by the dopamine receptor antagonist haloperidol. The effect of B-HT 933, but not that of B-HT 920, was partly antagonized by yohimbine.5.The enhanced synthesis of dopamine in the corpus striatum of mice following treatment with gammabutyrolactone was completely antagonized by B-HT 920, but not by B-HT 933, via a haloperidol-sensitive mechanism. The synthesis of noradrenaline in the brain stem and in the hemispheres was reduced by B-HT 933 via a yohimbine-sensitive mechanism.6.The results indicate that B-HT 920 can selectively and potently stimulate dopamine autoreceptor and that B-HT 933 can preferentially stimulate noradrenaline autoreceptors (α2-adrenoreceptors). These actions might cause the decreases in motor activity observed in mice not pretreated with reserpine.