Anna L. Renyi

Inhibition of the uptake of tritiated 5-hydroxytryptamine in brain tissue

Abstract The uptake of tritialted 5-hydroxytryptamine (5-HT) in slices of mouse brain was examined in vitro. A part of this uptake was inhibited by cocaine and was limited to concentrations of 5-HT below 3 × 10−6 M. This had the nature of an active uptake process. The other part was linear with the 5-HT concentration and had the nature of a partitions of 5-HT between the solution and the tissue. Reserpine reduced the accumulation of 5-HT but did not influence the rate of the initial uptake, which was strongly reduced by cocaine, imipramine and tryptamine derivatives. In vitro, the tertiary tricyclic antidepressant agents imipramine and amitriptyline were more active than their secondary analogues desipramine and nortriptyline in inhibiting the uptake of 5-HT. In vivo, this difference was further accentuated, probably because the tertiary amines reach a higher brain concentration, this being shown to apply for imipramine compared with desipramine.

Inhibition of the uptake of tritiated catecholamines by antidepressant and related agents

The inhibitory effects of desipramine and some related agents on the uptake of tritiated noradrenaline in slices of cerebral cortex of the mouse and the uptake of tritiated dopamine in slices of the corpus striatum of the rabbit were investigated. The effect of the drugs, administered in vivo, on the uptake of noradrenaline was compared with their antagonizing effect on the decrease of motor activity (sedation), ptosis and hypothermia produced by reserpine and tetrabenazine. In vitro, all the agents with the exception of UCB 6249 inhibited the uptake of the catecholamines. Lu 3-010, desipramine and imipramine were considerably more powerful in inhibiting the uptake of noradrenaline than of dopamine. In vivo, only these compounds and (±)-amphetamine inhibited the uptake of noradrenaline and antagonized the ptosis and hypothermia produced by reserpine, and the ptosis induced by tetrabenazine. UCB 6249 antagonized sedation and ptosis produced by tetrabenazine but not by reserpine.

Inhibition of the neuronal uptake of 5-hydroxytryptamine and noradrenaline in rat brain by (Z)- and (E)-3-(4-bromophenyl)-N,N-dimethyl-3-(3-pyridyl) allylamines and their secondary analogues.

(Z)-3-(4-Bromophenyl)-N,N-dimethyl-3-(3-pyridyl)allylamine (H ) and the secondary amine analogue (A 24356) were about 10 times more potent in inhibiting the uptake of [14C]-hydroxytryptamine than the uptake of [3H]-(−)noradrenaline in homogenate and slices of the rat hypothalamus in vitro, whereas the corresponding tertiary (E)-isomer (A 23140) had the same activity on both uptake mechanisms and the secondary (E)-derivative (A 23889) was much more potent in inhibiting the noradrenaline uptake. All four amines had rather low activity on the dopamine uptake in homogenate of rat striatum. After oral administration in vivo, H and A 24356 were about equally potent in inhibiting the 5-hydroxytryptamine uptake in slices of rat hypothalamus and were much less active on the noradrenaline uptake. On the other hand, A 23889 and A 23140 were very active inhibitors of the noradrenaline uptake but poor inhibitors of the 5-hydroxytryptamine uptake after administration in vivo. It was found that H was rapidly transformed to A 24356 in vivo and that the main effect in vivo was caused by the secondary amine derivative.

The pharmacology of zimelidine: A 5-HT selective reuptake inhibitor

Zimelidine (ZIM) and its main active metabolite norzimelidine (NZIM) have been shown to preferentially inhibit 5‐hydroxytryptamine (5‐HT) neuronal uptake both in vitro and in vivo while having much less effect on noradrenaline (NA) uptake. ZIM in vivo blocked the 5‐HT uptake mechanism in the cerebral cortex, hippocampus, striatum, hypothalamus and spinal cord, thus indicating effects on both the ascending and descending 5‐HT pathways. ZIM is devoid of a 5‐HT releasing action, MAO‐inhibitory properties and effects on dopamine (DA) uptake. ZIM failed to reduce NA turnover even in high doses, but markedly reduced 5‐HT turnover in very low doses in the rat. ZIM also enhanced 5‐HT mediated behaviours in mice in doses related to the inhibition of 5‐HT uptake. In contrast to amitriptyline (AMI) and mianserin (MIAN), ZIM only in extremely high doses displayed a 5‐HT receptor blocking action in vitro and failed to block 5‐HT mediated behaviour. ZIM was practically devoid of action on histamine H1 and H2 receptors, and had also a neglible action on noradrenergic α1‐ and α2‐receptors, and on β‐receptors. Unlike the tricyclic antidepressants (TADs) ZIM had a negligible action on muscarinic receptors and failed to affect cholinergic induced activity. Long‐term treatment with ZIM did not result in any attenuation of the 5‐HT uptake blocking potency or the reduction of 5‐HT turnover. This long‐term treatment slightly reduced the number of β‐receptors in the brain. However, repeated ZIM‐treatment induced a new 5‐HT receptor binding site characterized by a low affinity and with a high number of binding sites and decreased the number of high affinity 5‐HT receptor binding sites. Unlike the TADs zimelidine failed to block the action of reserpine. Metabolic and behavioural interaction studies in mice showed that ZIM was devoid of any significant interactions with ethanol, barbiturates and benzodiazepines. It is concluded that ZIM markedly differs front both the TADs and new antidepressants such as mianserin and nomifensine. ZIM seems preferentially to effect the presynaptic 5‐HT reuptake mechanism while having a negligible action on noradrenergic, 5‐HT, acetylcholine and histamine receptors in the brain.

A comparison of the inhibitory activities of iprindole and imipramine on the uptake of 5-hydroxytryptamine and noradrenaline in brain slices

Abstract Iprindole, an active antidepressant agent of the tricyclic class, was shown to be a very weak inhibitor of the uptake of noradrenaline (IC50 = 9 × 10−6M) and 5-HT (IC50 = 5 × 10−5M) in brain slices of mice in vitro , being over 100 times less active than imipramine (IC50 = 8 × 10−8M and 2 × 10−7M). In vivo iprindole inhibited the uptake reactions by less than 50 % at 100 mg/kg i.p. in mice and rats, whereas imipramine produced 50 % inhibition of the uptake of noradrenaline at 10 mg/kg i.p. and of that of 5-HT at 30 mg/kg i.p. In spite of weak uptake inhibition, iprindole potentiated the awakening effect of 1-dopa in reserpinized mice. The relationship between the antidepressant action of the tricyclic agents and the inhibition of the neuronal uptake of the biogenic amines is discussed.

Effects of zimelidine on serotoninergic and noradrenergic neurons after repeated administration in the rat

The effects of prolonged treatment of rats with zimelidine, 5, 12.5, and 25 μmol/kg PO twice daily for 2 weeks, on the accumulation of 14C-5-hydroxytryptamine (14C-5-HT) and 3H-noradrenaline (3H-NA) in hypothalamic slices were studied. The concentrations of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in whole brain, the concentration of 5-HT in whole blood and the in vitro labelling of receptors in cerebral cortex with 3H-5-HT, 3H-dihydroalprenolol (3H-DHA) and striatum with 3H-spiroperidol were also determined, and the concentrations of zimelidine and its demethylated metabolite norzimelidine in plasma and hypothalamus were analysed. The degree of inhibition of the accumulation of 14C-5-HT and 3H-NA was not changed or only slightly increased by prolonged treatment as compared to acute treatment with zimelidine, i.e. the 5-HT accumulation was more inhibited than the NA accumulation. The inhibition of 14C-5-HT accumulation was significantly correlated to the plasma and hypothalamic concentration of norzimelidine 14 h after the last repeated administration. The 5-HT concentration in whole blood was markedly reduced at the same doses which produced inhibition of 5-HT uptake in brain, which indicates that the inhibition of 5-HT uptake in platelets and in neurons are similarly affected. The concentration of 5-HIAA in whole brain was reduced by both single and repeated administration of zimelidine, whereas the concentration of 5-HT was decreased only after prolonged treatment. The density of β-adrenoceptors (binding of 3H-DHA) was significantly reduced by zimelidine, whereas 5-HT receptor binding (3H-5-HT) and dopamine receptor binding (3H-spiroperidol) were unchanged. It is concluded that the effects on 5-HIAA and 5-HT levels in brain and on the β-adrenoceptors in cerebral cortex reflect pre-and post-synaptic regulation resulting from the uptake inhibition.

Inhibition of the uptake of noradrenaline and 5-hydroxytryptamine by chlorphentermine and chlorimipramine

Abstract The inhibition of the simultaneous uptake of 3H-noradrenaline and 14C-5-hydroxytryptamine (5-HT) by chlorphentermine and chlorimipramine in slices of mouse midbrain was examined and compared with the potentiation of the responses of L-dopa and 5-hydroxytryptophan in mice. Uptakes of the two amines into the slices were inhibited equally by chlorphentermine (EC5 0 = 3 × 10−6 M) whereas chlorimipramine was about ten times more active in inhibiting the uptake of 5-HT (EC5 0 = 7 × 10−8 M) than that of noradrenaline (EC5 0 = 8 × 10−7 M). After administration of chlorphentermine in vivo 50% of the noradrenaline and 5-HT uptake was inhibited at 6 and 10 mg/kg, i.p., respectively. The corresponding values for chlorimipramine were 35 and 6 mg/kg, i.p., respectively. Both potentiated L-dopa and 5-HT in doses producing uptake inhibition although potentiation of L-dopa by chlorimipramine was greater than expected from its inhibition of the uptake of noradrenaline.

Cocaine-sensitive uptake of sympathomimetic amines in nerve tissue

The uptake of [3H]octopamine, [3H]norephedrine and [3H]phenylethanolamine in slices of cerebral cortex and heart of the mouse was investigated. Cocaine inhibited the uptake of octopamine but had no effect on that of the other two amines, whose uptake seems to be a pure physico‐chemical partition between the tissue and the solution. Together with previous results, these indicate that the cocaine‐sensitive uptake is linked with the hydroxyl groups in the benzene nucleus and particularly with that in the meta position. The results bear out the view that the potentiating effect of cocaine on the direct effect of sympathomimetic amines is due to inhibition of the uptake of the amines in sympathetic nerves, but they contradict the assumption that the antagonizing effect of cocaine on the indirect action of the amines is due to inhibition of the amine uptake.

In vivo inhibition of 3H-noradrenaline uptake by mouse brain slices in vitro.

In viuo inhibition of 3H-noradrenaline uptake by mouse brain slices in vItro SIR,-Pretreatment of animals with reserpine decreases the capacity of tissues to accumulate tritiated noradrenaline in vitro (Dengler, Spiegel & Titus, 1961a ; Ross & Renyi, 1966). Several other psychoactive compounds added to brain slices in vitro are known to inhibit the uptake of noradrenaline (Dengler, Spiegel & Titus, 1961b). However, pretreatment of mice with these compounds does not seem to decrease the noradrenaline uptake by subsequently prepared brain slices. In contrast to reserpine, most of these compounds seem to act reversibly and are probably loosely bound to the tissues. The tissue contents of these substances may therefore decrease during the in vitro incubation procedure by diffusion of the compounds into the incubation medium. We have tried to avoid this diffusion by using a briefer incubation period than was used in the aerlier experiments. Mice were injected intraperitoneally with the compounds and they were killed at the time noted in Table 1. The incubation of the brain cortex slices with the tritiated noradrenaline and the extraction of the amine taken up was as previously described (Ross & Renyi, 1964), with the exception that the incubation time was only 5 min. Four animals were used for each compound. The content of the amine in the slices was expressed as nmol/g. The statistical significance was calculated according to the Student’s t-test. Compounds supposed to inhibit the noradrenaline uptake at the cell membrane level (Carlsson & Waldeck, 1965), namely, desipramine, imipramine or amitriptyline, were strong inhibitors of the uptake of tritiated noradrenaline under the conditions used. But cocaine, which when added in vitro is a powerful inhibitor of the noradrenaline uptake by brain slices, had only a slight effect when injected in vivo. This finding would seem to suggest that too small amounts of cocaine reach the mouse brain in vivo. The large dose of chlorpromazine strongly inhibited the noradrenaline uptake, but the smaller dose had no effect although the animals were strongly tranquillised. This result may indicate that the phenothiazine class of tranquillisers

Uptake and metabolism of β-phenethylamine and tyramine in mouse brain and heart slices

Tritium labelled β‐phenethylamine and tyramine were incubated with slices of mouse brain and heart. Cocaine (3 × 10−5M) caused a reduction of 30% in the uptake of tyramine as well as in the formation of its metabolite 4‐hydroxyphenylacetic acid. Cocaine had no effect on either the uptake of phenethylamine nor its deamination to phenylacetic acid.