Nicotine-induced salivation in cats: effects of various drugs

Tail-tremor induced by exposure to cigarette smoke in rats

Tremors appearing only in the tail (tail-tremor) induced by cigarette smoke and subcutaneous nicotine were investigated using a smoking machine and Wistar rats. Daily exposure (twice a day) to smokes of two commercial cigarettes (Mild-Seven Select for the first 7 days and Long-Peace for the next 6 days) caused the tail-tremor to appear even if it was slight. A single subcutaneous nicotine (0.5 mg/kg) administration to rats exposed to the cigarette smokes for 13 days markedly caused the tail-tremor. On the other hand, daily subcutaneous injection of nicotine (0.5 mg/kg/day) also caused the tail-tremor to appear beginning on the 4th day and the incidence of tremor increased to 100% by the 12th day. These results indicate that tail-tremor can be caused not only by daily subcutaneous administration of nicotine but also by daily exposure to cigarette smoke.

Nicotine-induced tail-tremor and drug effects

Tail-tremor induced by repeated and daily administration (0.5 mg/kg SC x 6 times/day) of nicotine as well as effects of various drugs on this response were investigated in Wistar strain male rats. Daily administration of nicotine in doses of 0.5 mg/kg SC caused tail-tremors to appear beginning on the 3rd day. Tail-tremor induced by the first injection of each day gradually increased with the daily injections, however, the heightened effect of this first injection at the beginning of each day decreased during the day upon repeated administration of 6 times/day at 2-hr intervals. Basically, tail-tremor appeared about 5 min after SC administration of nicotine and reached a peak approximately 7-9 min after injection, declining to zero afterwards. Different drugs showed various effects on this response. While mecamylamine (0.5 and 1.0 mg/kg IP) abolished nicotine-induced tail-tremor, arecoline (0.5 and 1.0 mg/kg IP), atropine (2.5 and 5.0 mg/kg IP), scopolamine (1.0 and 2.0 mg/kg IP) and hexamethonium (0.5 and 1.0 mg/kg IP) showed no such effects. Furthermore, physostigmine (0.1 mg/kg IP) actually potentiated this action. These results suggest that tail-tremor induced by nicotine may be mediated through central nicotine receptor system.

Suncus murinus: a new experimental model in emesis research

Effects of various emetic and antiemetic drugs were studied using Suncus murinus for its potential use as an experimental model in emetic research. Subcutaneous injection of nicotine bitartrate (10-15 mg/kg), veratrine sulfate (0.5-1.0 mg/kg), emetine dihydrochloride (40-80 mg/kg) and oral administration of copper sulfate (20-100 mg/kg) caused dose-dependent emesis in suncus. The ED50 of nicotine, veratrine, emetine and copper sulfate were 7.9, 0.4, 47.6 and 21.4 mg/kg, respectively. However, subcutaneously injected apomorphine hydrochloride (0.1-100 mg/kg), digitoxin (0.5-1.0 mg/kg) and orally administered emetine dihydrochloride (10-80 mg/kg) did not induce the vomiting. Chlorpromazine and promethazine decreased the emetic effect of nicotine, veratrine and copper sulfate, but scopolamine hydrobromide was not effective. These results indicate that the Suncus murinus is sensitive to various emetic and antiemetic drugs and can be used as a new experimental animal model for the emesis. Emetic behavior of suncus was discussed in comparison with other animals.

Nature of salivation produced by thyrotropin-releasing hormone (TRH)

In the unanesthetized cat, TRH was injected into the cerebral ventricles (ICV) through chronically implanted cannulae and the nature of the evoked salivation was investigated. TRH injected in doses from 0.1 to 1.0 mg evoked salivation which was not dose-dependent. The antimuscarinic drug atropine as well as the ganglionic blocking agent mecamylamine injected also ICV prevented the salivation induced by ICV TRH. On the other hand, virtually no effect on the TRH-salivation was induced by the following drugs injected ICV: alpha and the beta adrenergic blocking agents, yohimbine and propranolol; dopamine antagonist, chlorpromazine; 5-hydroxytryptamine antagonist, methysergide; and the antihistamine, antazoline. Further, in cats pretreated with ICV reserpine and 6-hydroxydopamine, but not with ICV 5,6-dihydroxytryptamine and hemicholinium, the salivation caused by ICV TRH was abolished. It is concluded that central cholinoceptive and catecholaminergic mechanisms are involved in the salivation induced by ICV TRH.

Further studies on nicotine-induced emesis: nicotinic mediation in area postrema

In unanesthetized cats the emetic action of an injection of nicotine into the cerebral ventricle through chronically implanted cannulae was investigated. Nicotine injected in doses of 0.02-1.0 mg produced dose-dependent vomiting, which was abolished after ablation of the area postrema. However, copper sulfate given intragastrically evoked vomiting in cats with an ablated area postrema. The emetic response to intracerebroventricular (ICV) nicotine as well as the vomiting produced by intragastric copper sulfate was depressed or abolished in cats pretreated with ICV reserpine. On the other hand, the emetic response to ICV nicotine and to intragastric copper sulfate was virtually unchanged in cats pretreated with ICV 6-hydroxydopamine and 5,6-dihydroxytryptamine. The duration of vomiting produced by intragastric copper sulfate, but not that of ICV nicotine, was potentiated in cats pretreated with hemicholinium-3. Ganglionic blocking agents, mecamylamine and hexamethonium, injected ICV prevented the vomiting elicited by ICV nicotine. On the other hand, selected anti-muscarinic drugs, alpha and beta adrenergic receptor antagonists, dopamine antagonists, antihistamines and a 5-hydroxytryptamine antagonist all injected into the cerebral ventricle had virtually no effect on the vomiting induced by ICV nicotine. It is postulated that nicotine evokes vomiting by its action on nicotinic receptors within the area postrema but not on catecholaminergic or serotonergic neurones. Finally, acetylcholine could also be involved in the inhibition of the complex mechanisms underlying the central regulation of vomiting.

Nicotine-induced convulsions in cats and central nicotinic receptors

The effects were investigated of intracerebroventricular (ICV) injections in the cat of ganglionic blocking agents, antimuscarinic drugs, alpha and beta adrenergic blocking substances, dopamine antagonists, an antihistamine, reserpine and a 5-hydroxytryptamine antagonist as well as the inhibitors of catecholamines, 5-hydroxytryptamine and acetylcholine synthesis upon convulsions produced by nicotine, which was similarly injected. Mecamylamine and hexamethonium but not atropine, scopolamine, yohimbine, phenoxybenzamine, tolazoline, propranolol, practolol, chlorpromazine, haloperidol, antazoline and methysergide abolished the convulsions evoked by nicotine. Furthermore, reserpine, but not 6-hydroxydopamine, as well as 5,6-dihydroxytryptamine and hemicholinium blocked the convulsions caused by nicotine. It appears, therefore, that the convulsions produced by nicotine are mediated through central nicotinic receptors. However, the depressed catecholaminergic, 5-hydroxytryptaminergic and histaminergic mechanisms induced by reserpine can also suppress the convulsions evoked by nicotine.

Dimethylphenylpiperazinium-induced vomiting: nicotinic mediation in area postrema

In unanesthetized cats the emetic action of dimethylphenylpiperazinium (DMPP) was investigated, after it was injected into the cerebral ventricles through chronically implanted cannulae. DMPP injected in 0.2-2.0 mg doses into the cerebral ventricle produced dose-dependent vomiting, which was abolished after ablation of area postrema. However, copper sulfate given intragastrically evoked vomiting in cats with an ablated area postrema. Further, the emetic response to ICV DMPP and to intragastric copper sulfate was depressed or abolished in cats pretreated with ICV reserpine. The emetic response to ICV DMPP, but not that caused by intragastric copper sulfate, was potentiated in cats pretreated with ICV 5,6-dihydroxytryptamine. Ganglionic blocking agents, mecamylamine and hexamethonium, injected ICV prevented the vomiting elicited by ICV DMPP. On the other hand, selected anti-muscarinic drugs, alpha and beta adrenergic antagonists, dopamine antagonists, antihistamines and a 5-hydroxytryptamine (5-HT) antagonist all injected into the cerebral ventricles had virtually no effect on the vomiting induced by DMPP. It is postulated that DMPP evokes vomiting by its action on nicotinic receptors of nerve cells within the area postrema but not on catecholaminergic, serotonergic, or cholinergic receptors. Finally, 5-HT and acetylcholine could also be involved in the inhibition of the complex mechanisms underlying the central regulation of vomiting.