Biochemical observations on LSD-25 and Deseril

A review and reevaluation of the role of serotonin in the modulation of lordosis behavior in the female rat

The role of serotonin (5-HT) in the modulation of sexual receptivity (lordosis) in the female rat is reviewed and reevaluated. The effects on lordosis of drug treatments that decrease or increase the activity and availability of central 5-HT are first discussed, and this is followed by an evaluation of the effects of drugs that act directly at 5-HT receptors. In order to shed light on the physiological significance of effects of serotonergic drugs on lordosis, there is also a review of what is known of changes in levels of serotonergic activity and densities of 5-HT receptors in the female rat brain that take place through the estrous cycle and in response to administration of behaviorally effective doses of gonadal steroids. Serotonin has generally been thought to have a tonic, inhibitory effect on lordosis. However, it is concluded that 5-HT can either inhibit or facilitate lordosis depending on which subtypes of central 5-HT receptors become activated. Because of a lack of consistent or compelling evidence of effects of ovarian hormones on serotonergic activity or 5-HT receptors in critical areas of the brain, it is stated that there is at present no basis to conclude that the effects of pharmacological manipulations of serotonergic activity on lordosis reflect an important, physiological role of 5-HT in the modulation of lordosis behavior in the female rat.

Effects of xylamidine on peripheral 5-hydroxytryptamine-induced anorexia

Rats injected peripherally with 5-hydroxytryptamine (5-HT) showed a dose-dependent decrease in food intake following overnight fasting. The peripheral 5-HT-2 antagonist xylamidine had no effect on food intake when administered alone, but antagonised 5-HT-induced anorexia. However, at the highest dose of 5-HT (5 mg/kg), both doses of xylamidine (1.0 and 2.0 mg/kg) displayed the same degree of antagonism to the anorectic effect, but failed to block it completely. The results are discussed in terms of 5-HT receptor subtypes, and it is suggested that non-5-HT-2 receptors may be partially responsible for the mediation of peripheral 5-HT-induced anorexia.

Involvement of serotonin in prolactin release induced by electrical stimulation of the hypothalamus of the turkey (Meleagris gallopavo)

In anesthetized female turkeys electrical stimulation of the ventromedial nucleus (VMN) for 30 min caused increases in plasma prolactin (Prl); with maximum increase above the prestimulation level being 33.6 +/- 5.7 ng/ml for laying hens and 768.1 +/- 187.6 ng/ml for incubating hens. The possibility that serotonin (5-HT) plays a role in electrical stimulation-induced Prl release was investigated after administration of methysergide, a 5-HT receptor blocker (20 mg/kg), and stimulation in either the VMN or the infundibular nuclear complex-median eminence (INF-ME) region. Electrical stimulation in both the VMN and INF-ME region caused increases (P less than 0.05) in plasma Prl. Pretreatment with methysergide prevented the increase in plasma Prl that follows electrical stimulation in the VMN but had no effect on electrical stimulation-induced Prl release in the INF-ME region. We conclude that Prl release in the female turkey requires the functional integrity of serotonergic neurons within the VMN.

Correlation of [3H]5-hydroxytryptamine (5HT) binding to brain stem preparations and the production and prevention of myoclonus in guinea pig by 5HT agonists and antagonists

In guinea pig brain stem preparations [3H]5-hydroxytryptamine (5HT) bound specifically to both high and low affinity sites, but specific [3H]spiperone binding was low and could not be consistently detected. This indicates a prevalence of 5HT-1 type receptors in this tissue. High affinity-specific [3H]5HT binding was more potently displaced by indole-containing 5HT agonists than by piperazine-containing 5HT agonists. This agreed with the observation that indole-containing, but not piperazine-containing compounds induced dose-dependent myoclonus in guinea pigs which originates from brain stem. The capacity of indoleamine antagonists to displace [3H]5HT-specific binding from guinea pig brain stem was similar to their reported potency in displacing [3H]5HT from 5HT-1 receptors. The [3H]5HT-labelled binding site in guinea pig brain stem is a 5HT-1 receptor and appears to be responsible for the induction of indoleamine-dependent myoclonus.

Methysergide releases locomotion without support in lateral hypothalamic akinesia

Rats made profoundly akinetic by large bilateral electrolytic partial transections of the lateral hypothalamus were released from their akinesia by methysergide maleate (45 mg/kg, IP). When tested as soon as 24 hr postoperatively, lateral hypothalamic rats treated with methysergide displayed vigorous forward locomotion without postural support for as long as an hour and a half. By postoperative day 5, the locomotion elicited by methysergide was integrated with postural support to produce a more normal form of walking. Although atropine sulfate (50 mg/kg, IP) releases excessive walking in akinetic rats treated with 6-hydroxydopamine [53] it did not release locomotion lateral hypothalamic rats. Similarly, apomorphine, clonidine and phentolamine did not do so. Assuming that methysergide in the dose used exerts its effects primarily via the blockade of serotonin systems, we suggest that, in addition to an inhibitory cholinergic system, an independent inhibitory serotonergic system may also exaggerate the akinesia seen following treatments that diminish the action of brain catecholamine systems. Furthermore, the type of locomotion released by methysergide is a fractional form not previously isolated.

Effects of the interaction between methysergide and clonidine on growth hormone and prolactin secretion in normal man

The effects of methysergide (1 mg, p.o.), clonidine (50 micrograms, i.m.) and methysergide plus clonidine on growth hormone (GH) and prolactin (PRL) secretion in 8 normal male volunteers have been studied. Both methysergide and clonidine were found to enhance GH and to lower PRL plasma levels. The effects of methysergide are explained on the basis of a preferential action of methysergide metabolites on dopamine receptors, whereas the effects of clonidine are attributed to a stimulatory action on adrenaline receptors. The combined treatment methysergide plus clonidine resulted in a potentiation of the effects caused by the drugs when administered alone.

Quantitative determination of ergot alkaloids in biological fluids by radioimmunoassay

1 Cross-reactivity of ergot alkaloids with an antiserum produced against lysergic acid conjugated with human serum, albumin was utilized to develop a radioimmunoassay for ergotamine, dihydroergotamine, dihydroergotoxine, ergometrine and methylergometrine in biological fluids. The antisera showed no cross-reactivity with simpler indole structures. 2 A procedure for extraction and concentration of alkaloids in biological fluids was developed. 3 The assay is sensitive for 1.8 ng/ml ergotamine, 1.5 ng/ml dihydroergotamine, 2.2 ng/ml dihydroergotoxine, 0.7 ng/ml ergotmetrine and 0.5 ng/ml methylergometrine. 4 The assay is sufficiently sensitive to permit the measurement of urine and plasma ergot alkaloid levels and it is suitable for determination in cases where a known ergot alkaloid is used.

Ergot alkaloids as dopamine agonists: comparison in two rodent models

A series of ergot alkaloids, together with the DA agonists apomorphine and piribedil, were tested for protective effects against audiogenic seizures in an inbred strain of mice (DBA/2) and for induction of circling behaviour in mice with unilateral destruction of one nigrostriatal DA pathway. The order of potency against audiogenic seizures was apomorphine greater than ergocornine greater than bromocryptine greater than ergometrine greater than LSD greater than methysergide greater than piribedil while that observed in the rotating mouse model was apomorphine greater than ergometrine greater than ergocornine greater than bromocryptine greater than piribedil. LSD caused only weak circling behaviour even when administered in high doses (greater than 1 mg/kg). Methysergide was ineffective. Prior administration of the neuroleptic agent haloperidol blocked the effect of DA agonists and of ergot alkaloids in both animal models. The possible action of ergot alkaloids as DA agonists is discussed.

Effects of drugs acting on cerebral 5-hydroxytryptamine mechanisms on dopamine-dependent turning behaviour in mice

1. The effects of drugs acting on cerebral 5-hydroxytryptaminergic mechanisms on drug-induced turning behaviour in mice with unilateral destruction of nigro-striatal dopaminergic nerve terminals have been studied. 2. Administration of L-tryptophan (400 mg/kg) or 5-hydroxytryptophan (200 mg/kg) increased brain 5-hydroxytryptamine and decreased the turning induced by both apomorphine (2 mg/kg) and amphetamine (5 mg/kg). 3. Parachlorophenylalanine (3 X 500 mg/kg) decreased brain 5-hydroxytryptamine and increased both apomorphine and amphetamine-induced circling behaviour. 4. Varying the protein content of dietary intake significantly altered brain 5-hydroxytryptamine and tryptophan levels, spontaneous locomotor activity and amphetamine-induced circling behaviour in these mice. 5. Systemic administration of methysergide (0.5-4 mg/kg), lysergic acid diethylamide (0.025-0.2 mg/kg), cyproheptadine (2.5-20 mg/kg) or clomipramine (0.6-20 mg/kg) produced no consistent effect on drug-induced turning behaviour. 6. The results suggest that circling behaviour due to striatal dopamine receptor stimulation is depressed by an elevation of brain 5-hydroxytryptamine and enhanced by a reduction in brain 5-hydroxytryptamine. 7. The possible physiological relationship between dopamine and 5-hydroxytryptamine neurones in the basal ganglia is discussed.

Suppression of sleep-related prolactin secretion and enhancement of sleep-related growth hormone secretion

Methysergide, a clinically-used blocker of serotonin receptors, was administered to 10 normal young men at a dose of 2 mg every 6 h for 48 h. After drug treatment, serum levels of growth hormone during sleep were 41.9% higher than placebo values (less than 0.001). In contrast, drug treatment was associated with a 36.4% decrease in stimulated growth hormone secretion during insulin tolerance testing (P less than 0.01). These opposite effects of methysergide suggest that different mechanisms are responsible for sleep-related and insulin-induced growth hormone secretion. Accordingly, data obtained with pharmacologic stimuli may lead to erroneous inferences regarding physiologic growth hormone control mechanisms. Administration of methysergide profoundly suppressed sleep-related prolactin secretion; overall nocturnal mean prolactin fell by 70.3% from 4.30+/-0.19 to 1.28+/-0.06 ng/ml (P less than 0.0001). It appears that serotonin may be significant modulating neurotransmitter for the control of growth hormone secretion, limiting sleep-related release, and enhancing insulin-induced release. It seems likely from these data that the role of serotonin in the control of prolactin secretion is relatively more important, since serotonin receptor blockade dramatically reduced sleep-related prolactin secretion.

Failure of antiserotonergic agents to modify levallorphan-induced stereotypy in rats

The possibilty that the stereotypic behaviour induced by levallorphan, a narcotic antagonist, might be influenced by a serotonergic system was examined. Two antiserotonergic agents, methysergide and parachlorophenylalanine, failed to modify such stereotypy implying that serotonin is not involved. It is suggested that dopamine might be the principle mediator of this behaviour.

Monoamine mediation of the morphine-induced activation of mice

1. The dose-response relationship for hyperactivity in grouped mice following the injection of morphine sulphate has been established.2. The activation response can be modified by drugs which affect either catecholamines or indoleamines.3. The monoamine precursors L-DOPA and 5-hydroxytryptophan potentiate the response.4. The monoamine synthesis inhibitors alpha-methyl-p-tyrosine and p-chlorophenylalanine reduce the response.5. Inhibition of monoamine oxidase activity by pargyline caused a great increase in the response. The simultaneous administration of reserpine resulted in a further potentiation.6. Reserpine blocked the response whenever it was given alone, either before, with or after the injection of morphine.7. Blockade of alpha-adrenoceptors with phentolamine or phenoxybenzamine reduced the response.8. Blockade of tryptaminergic receptors with methysergide or cinanserin also antagonized the response.9. The major tranquillizers haloperidol and chlorpromazine reduced the response. Haloperidol was especially effective in this regard.10. The tricyclic antidepressant drug imipramine potentiated the response.11. The morphine antagonist nalorphine completely prevented the response.12. The anticholinergic agent atropine and the antihistaminic drug mepyramine did not affect the response.13. We conclude that dopamine, noradrenaline and 5-hydroxytryptamine are all involved in the normal activation response of grouped mice to morphine, with dopaminergic mechanisms being of primary importance.

Some experiments in the chemistry of normal sleep

Sleep is essential for physical and mental health. In the last 15 years there has grown up the concept of the brain stem reticular activating system. Electroencephalographic studies have shown two qualitatively different and alternating kinds of sleep, the orthodox (“slow wave”, or “forebrain“) and the paradoxical (”hind-brain“, “rapid eye movement”, “activated“, or “dreaming”) phases (Akertet al., 1965). It may be predicted that in the next decade attention will turn increasingly to the chemical basis of sleep. If a man is deprived of sleep for 100 hours, it is extremely difficult to keep him awake and one may suppose that an abnormal biochemical state exists within his central nervous system.