Sleep induced by drugs injected into the inferior horn of the lateral cerebral ventricle in dogs

Pilocarpine-induced Salivation and Thirst in Conscious Rats

The muscarinic receptor agonist pilocarpine is widely used as a sialogogue. It has been well-established that it also induces water intake in animals. However, the mechanisms underlying the relationships between these events are unknown. To address this problem, we examined water intake and parotid salivary secretion in conscious rats. Intraperitoneally injected pilocarpine increased both water intake and salivary secretion. Intracerebroventricularly injected pilocarpine also induced water intake, but not salivary secretion. Intracerebroventricularly applied atropine, a muscarinic receptor antagonist, suppressed the water intake produced by pilocarpine applied intraperitoneally and intracerebroventricularly. However, it did not affect the salivary secretion induced by pilocarpine applied peripherally. We conclude that peripherally applied pilocarpine affects the parotid glands and the thirst center in the central nervous system, while it may induce salivary secretion mainly via peripheral responses, but water intake mainly via the central nervous system.

Fourth ventricle effects of nicotine, 2-methylpiperidine and cytisine in dogs

Four distinguishable nicotinic binding sites have been identified as well as four nicotinic ligands with different specificities: (+/-)-2-methylpiperidine which binds to a very high affinity site (Site 1) and produces up-regulation of the high affinity site (Site 2); (-)-nicotine which binds to Site 1 and Site 2 as well as to a low affinity site (Site 4); (+)-nicotine which binds to Site 1, Site 4 and Site 3 which is also a high affinity site; and (-)-cytisine which binds to Sites 1 and 2. These drugs were injected into the 4th ventricle of 5 dogs in graded concentrations (12.5 to 400 micrograms) and their effects on the EEG, skin twitch reflex latency, heart rate, rectal temperature, pupillary diameter, blood pressure and the amplitude of the flexor reflex were measured. Drugs which act predominantly on Site 1 [(+/-)-2-methylpiperidine and (+)-nicotine] produced EEG synchronization and hyperalgesia while drugs which interact with Sites 2 and 4 produce EEG desynchronization, analgesia and tachycardia. These data indicate that nicotinic ligands which have different binding specificities have different actions in medullary function and support the hypothesis that the different binding sites have different pharmacologic significance.

Interaction between nicotine and endogenous opioid mechanisms in the unanesthetized dog

Nicotine produced a distinct reproducible syndrome in the conscious dog when injected intravenously or intracerebroventricularly. Intravenously administered nicotine (40 micrograms/kg/min for 20 minutes) increased cardiac and respiratory rates and produced analgesia, miosis, hypothermia, behavioral restlessness and emesis. When microinjected into the third cerebral ventricle, nicotine (100-200 micrograms) similarly increased cardiac and respiratory rates and pupillary diameter; and produced behavioral restlessness, emesis, erratic analgesia and maintained wakefulness and a desynchronized EEG. Microinjection of nicotine (5-25 micrograms) into the periaqueductal gray failed to alter any of the parameters studied. Intravenous pretreatment with the opioid antagonist naltrexone (2 mg/kg) influenced the action of intravenous nicotine on certain physiological systems. While naltrexone alone produced a significant degree of tachycardia, miosis, and analgesia, it potentiated the tachypnea and antagonized the miotic response evoked by nicotine. Methionine-enkephalin was detected in perfusates obtained from the lateral cerebral ventricles of conscious dogs. Nicotine produced a non-significant decrease in enkephalin levels. These observations suggest that there are interactions between endogenous opioid and nicotinic processes. However, they are complex and may differ from one functional system to another.

Effects of cholinomimetic drugs and their antagonists injected into vertebral artery of unanaesthetized dogs

In unanaesthetized dogs, cholinomimetic drugs and their antagonists, catecholamines and 5HT were injected into vertebral artery placed in a skin loop. Acetylcholine (1 mg), pilocarpine (1-2 mg), nicotine (250-500 microng), eserine (100 microng) and neostigmine (250 microng) produced sleep apart from a few other peripheral effects. Sleep for longer periods followed injections of tubocurarine (1 mg), atropine (50 microng) and hexamethonium (500 microng). Adrenaline (50 microng) and noradrenaline (50-250 microng) did not produce significant effects on behaviour and sleep. 5HT (250-500 microng) also caused sleep.