Evidence for a noradrenergic and dopaminergic mechanism in the hyperactivity produced by 4, alpha-dimethyl-m-tyramine (H 77-77) in rats

Differences in the content and turnover of noradrenaline in rat heart atria and ventricles and circadian-phase-dependency

In light-dark-synchronized male rats the levels of noradrenaline in heart atria were about 3 times that found in heart ventricles. Noradrenaline turnover rate which were about 8-9 fold greater for the atria than for the ventricles displayed a circadian-phase-dependency with increased rates in the dark period in both parts of the rat heart.

Diurnal variations in the motor activity of the rat: effects of inhibitors of the catecholamine synthesis

The effects of the inhibitor of the tyrosine-hydroxylase H 44/68 and the inhibitor of the dopamine-beta-hydroxylase FLA 63 on the diurnal variations of the motor activity was studied in male Wistar rats, which were kept under standardized conditions of light and darkness (L:D = 12:12 h). The motor activity was continuously registered in groups of 5 rats using a two-channel Animex motimeter. During light FLA 63 (40 mg/kg, s.c.) greatly increased motor activity on acute application and during darkness the physiological elevation in motor activity was further but slightly increased. H 44/68 (200 mg/kg, i.p.) also increased motor activity during light, but in contrast to FLA 63 greatly reduced motor activity during darkness. The results indicate that though dopamine and noradrenaline are involved in the regulation of behavioural components, one or the other catecholamine may play a predominant role at different times of the day. Thus, it seems worthwhile to study the effects of drugs separately during light and during darkness.

Influence of the new 5-HT-uptake inhibitor paroxetine on hypermotility in rats produced by p-chloroamphetamine (PCA) and 4,alpha-dimethyl-7-tyramine (H 77/77)

Two different forms of hypermotility produced by the amphetamine derivatives PCA and H 77/77, 5 mg/kg of each, was studied in rats treated s.c. with the new 5-HT uptake inhibitor paroxetine. The substance inhibited the effect of PCA but did not influence that of H 77/77. The 5-HT-uptake inhibitors paroxetine, imipramine, and chlorimipramine were also administered p.o. at various times before PCA. The three substances inhibited PCA-induced hypermotility. Paroxetine 0.5-2 mg/kg, was active at intervals of 1-4 h and 4 mg/kg was active at 18-h interval. Imipramine and chlorimipramine 25-30 mg/kg showed PCA inhibition at treatment intervals of 1-2h, but 80-100 mg/kg or more was required to inhibit PCA at intervals of 4 and 18 h. Previous results have shown that PCA-induced hypermotility is antagonized by substances inhibiting 5-HT synthesis and uptake, whereas H 77/77-induced hypermotility is inhibited by substances blocking NA synthesis, uptake, and receptors. The previous and present results indicate that paroxetine is a selective 5-HT-uptake inhibitor. After oral administration paroxetine presumably produces a more potent and long-lasting 5-HT-uptake inhibition than imipramine and chlorimipramine.

Piperoxane reduces the effects of clonidine on aggression in mice and on noradrenaline dependent hypermotility in rats

Aggression in isolated male mice and hypermotility in rats produced by the noradrenaline releaser H 77/77 were studied after the s.c. administration of the alpha-adrenergic agonist clonidine and the alpha-antagonist piperoxane. Clonidine 0.005--0.5 mg/kg inhibited both behaviours while piperoxane showed a weak and short-lasting antiaggressive effect and no H 77/77 antagonism. Inactive doses of piperoxane reduced the inhibitory effects of clonidine. The results indicate that isolation-induced aggression in mice and H 77/77-induced hypermotility in rats are behavioural signs related to the availability of noradrenaline at the receptor.

Evidence for a noradrenergic mechanism in the grooming produced by (+)-amphetamine and 4, alpha-dimethyl-m-tyramine (H 77/77) in rats

Rats were kept on a 12-h light-dark cycle. One hour after the light was switched on, physiological saline, (+)-amphetamine 1 mg/kg, and H 77/77 5 mg/kg were injected s.c.; the number of groomings was counted 1-2 h after the treatments. (+)-Amphetamine and H 77/77 produced increased grooming which was antagonized by the tyrosine hydroxylase inhibitor H 44/68 (250 mg/kg), the dopamine-beta-hydroxylase inhibitor FLA 63 (40), the neuroleptics haloperidol (0.1 and 0.5), and clozapine (1 and 5). The (+)-amphetamine-induced grooming was also antagonized by the NA-receptor blocker aceperone (10) but not by the sedative phenothiazines mepazine (10) and diphenhydramine (20) nor diazepam (1). These results indicate that NA-release is involved in the mediation of (+)-amphetamine- and H 77/77-induced grooming. The inhibition of haloperidol and clozapine is presumably due to NA-receptor blockade.

Inhibition and potentiation of apomorphine-induced hypermotility in rats by neuroleptics

The effect of apomorphine (ap) was investigated in rats kept in a familiar cage; 0.25-5 mg/kg s.c. produced a short-lasting, abnormal hypermotility consisting mainly of locomotion and sniffing without grooming. Ap was administered to rate pretreated s.c. with various drugs. Ap hypermotility was antagonized by 12 neuroleptics from different chemical groups. The ap inhibitory effect of 5 neuroleptics was decreased when the interval between pretreatment and ap administration was increased from 0.5 to 4 hr. Clozapine was the only neuroleptic showing no inhibition but potentiation at 4 hr. Mepazine, a phenothiazine lacking antipsychotic effects, as well as the NA receptor blockers aceperone and phenoxybenzamine, did not inhibit ap hypermotility. Ap was also given 24 hr after haloperidol and clozapine. At this time both neuroleptics showed ap potentiation. The ap inhibition and potentiation after a single administration of the neuroleptics is presumable due to selective blockade and subsequent supersensitivity of some DA receptors.

Evaluation of the antinociceptive effects of 4, alpha-dimethyl-m-tyramine (H 77/77) in the rat

4, alpha-Dimethyl-m-tyramine (H 77/77) has been shown to induce dose dependently antinociceptive activity against 3 parameters: (1) the motor (M), (2) the vocalisation during stimulation (V) and (3) the vocalisation after withdrawal of stimulation (VA) responses. The effect of H 77/77 upon the V and VA pain responses was abolished or reduced by prior treatment with phenoxybenzamine, chlorpromazine, H 44/68, FLA 63, reserpine and protriptyline, and was potentiated by atropine sulphate. It is suggested that H 77/77 may exert is inhibitory effect on painful stimulation predominantly by inhibiting spinal sensory input.

Inhibition of 4,alpha-dimethyl-m-tyramine (H 77/77)-induced hypermotility in rats by single and repeated administration of chloropromazine, haloperidol, clozapine and thioridazine

The effect of H 77/77 (5 mg/kg s.c.) on motility of rats kept in a familiar cage was investigated. H 77/77 produced hypermotility, which was reduced by oral pretreatment with chlorpromazine, haloperidol, clozapine and thioridazine. The 4 neuroleptics were administered acutely and for a 14 day period. H 77/77 was given 30 min after the single or last dose of neuroleptc (chronic treatment) condition. After both single and repeated administration the neuroleptics showed H 77/77-antagonism in doses ranging from 0.1-2.0 mg/kg. The effect on H 77/77 activity did not change significantly after repeated treatment. Clozapine and thioridazine, which clinically produce only minor extrapyramidal side effects, exert a weak effect or none at all in tests commonly used for neuroleptic activity. These 2 neuroleptics were potent H 77/77-antagonists. Inhibition of H 77/77-hypermotility may possibly be used as a test for neuroleptics.

Neurochemical and pharmacological studies on a new 5HT-uptake inhibitor, FG4963, with potential antidepressant properties

A new phenylpiperidine derivative, FG4963, and several tricyclic antidepressants were compared in various in vitro and in vivo tests for central 5HT- and NA-uptake inhibition. FG4963 was found to be a 5HT-pump blocker with activity similar to that of chlorimipramine. FG4963 inhibited NA-uptake less than the most potent tricyclic thymoleptics. In contrast to imipramine derivatives FG4963 was a weak inhibitor of peripheral NA-uptake. FG4963 seems to produce central 5HT-potentiation without affecting organ functions regulated by the autonomic nervous system as much as tricyclic antidepressants.