Effects of Nicotine Given Into the Brain of Fowls

Abstract

IThe effects of nicotine, given into the IlIrd ventricle of adult conscious fowls (Gallus domesticus) or infused into various brain regions of conscious young chicks, were tested on behaviour, electrocortical activity, respiratory rate and body temperature. Its effects given intraventricularly or applied externally to the brain-stem of anaesthetized fowls were also examined. 2 After intraventricular nicotine, fowls squatted for 3 to 5 min with eyes closed, electrocortical activity resembling that during sleep but with superimposed spike activity. Following this, fowls reawakened and tachypnoea developed, together with partial abduction of the wings from the trunk, the back becoming horizontal and the tail flexed. These effects were prevented by pempidine. 3 Intraventricular nicotine suppressed or, less commonly, reduced operant key-pecking, an effect unrelated linearly to dose. 4 Intraventricular nicotine given to fowls anaesthetized with chloralose produced brief apnoea, followed by increased amplitude of respiratory excursion for about 5 minutes. Respiratory rate accelerated slightly but tachypnoea did not develop. Nicotine applied directly to the ventral brain-stem increased respiratory amplitude in three out of seven fowls. 5 In anaesthetized fowls, intraventricular nicotine raised blood pressure for 2 to 3 min, an effect prolonged up to 70 min by acute bilateral vagotomy, whereas pressor effects of intravenous nicotine were extended merely two to three fold. Dividing the spinal cord at C2 prevented pressor effects of intraventricular nicotine; those of intravenous nicotine were unaltered. 6 In young chicks, nicotine infused into the diencephalon, telencephalon and myelencephalon induced effects similar to those observed immediately after intraventricular nicotine, i.e. chicks squatted with closed eyes but recovered within 3 to 5 minutes. Simultaneously, electrocortical activity changed from an alert to the sleep pattern, usually with superimposed 'spike' activity. Tachypnoea and associated postural changes did not develop. Pempidine prevented the behavioural and electrocortical effects of nicotine.

Effects of Cholinomimetic Agents Given Into the Brain of Fowls

“…Such problems arose in explaining prolongation by physostigmine of sleep-like behavioural and electrocortical activity induced by nicotine (Marley & Seller, 1974) when, not only did acetylcholine under similar circumstances evoke arousal, but the response was difficult to attenuate with cholinoceptive antagonists given singly or in combination.…”

“…Cholinomimetic substances, three aliphatic (acetylcholine, acetyl43-methacholine (methacholine), carbamylcholine (carbachol)) and two alicyclic (benzoylcholine and pilocarpine), were given into the IlIrd cerebral ventricle or infused into the hypothalamus of adult fowls to ascertain whether their central mode of action was muscarinic or nicotinic. Such categorization depended on whether their effects resembled those of muscarine or nicotine (see Marley & Seller, 1972, 1974 and whether these effects were prevented by hyoscine or by pempidine. Classification according to the pharmacological antagonist proved to be more practicable.…”

“…Such categorization depended on whether their effects resembled those of muscarine or nicotine (see Marley & Seller, 1972, 1974 and whether these effects were prevented by hyoscine or by pempidine. Classification according to the pharmacological antagonist proved to be more practicable.…”

Central Effects of Clonidine 2‐(2,6‐dichlorophenylamino)‐2‐imidazoline Hydrochloride in Fowls

“…Since noradrenaline was also hypothermic in fowls at or below thermoneutrality, it was scarcely surprising that blockade of its receptors elevated body temperature. Intraventricular atropine also elevated body temperature, a finding more difficult to interpret since acetylcholine and other cholinomimetics infused intraventricularly or into the hypothalamus of chickens at thermoneutrality, lacked temperature effects (Marley & Seller, 1972, 1974a; a hypothermic action of these substances did emerge when chickens were tested below thermoneutrality (Stephenson & Marley, unpublished). It seems therefore that metabolic processes in the fowl maintain a high body temperature, exceeding that in mammals, which is kept within physiological limits at thermoneutrality by hypothalamic release of noradrenaline and possibly of acetylcholine.…”