Effects of muscarine given into the brain of fowls

Abstract

Summary1. The effects of muscarine, given intraventricularly, in adult conscious fowls (Gallus domesticus) or microinfused into various brain regions of conscious young chicks, were tested on behaviour, electrocortical activity and respiratory rate. Its effects given intraventricularly or intravenously to anaesthetized fowls were also examined. 2. After intraventricular injection, muscarine elicited immediate behavioural and electrocortical arousal; body temperature was unaffected. After a delay of 3040 min, tachypnoea developed together with postural changes which included partial abduction of the wings away from the trunk, the back and tail becoming horizontal. These effects were prevented by intravenous or intraperitoneal atropine or hyoscine, but not by pempidine or methylatropine, and were potentiated by physostigmine. Hyoscine given intraventricularly or intravenously did not affect electrocortical activity. 3. Intraventricular muscarine given to anaesthetized adult fowls produced brief apnoea. On return of respiration, amplitude of respiratory excursion was diminished for about 5 min; tachypnoea did not develop. Blood pressure also rose briefly. With larger doses of intraventricular muscarine, large amplitude electromyographic potentials developed in the dorsal neck muscles followed later by side-to-side neck movements. 4. Muscarine given intravenously to anaesthetized adult fowls, raised blood pressure and perfusion pressure in a perfused hind limb, an effect most likely due to secretion of adrenal medullary catecholamines; these pressor effects were prevented by pempidine and phenoxybenzamine. Given directly to the perfused hind limb, muscarine lowered perfusion pressure. 5. In young chicks, muscarine microinfused into the diencephalon or myelencephalon elicited intense bilateral electrocortical alerting associated with periods of alternating violent motor activity and quiescence. Microinfusion of muscarine into the telencephalon induced ipsilateral electrocortical desynchronization without affecting behaviour. These effects of muscarine were prevented by intravenous, intraperitoneal or intracerebral hyoscine, but once its effects were established could be antagonized only with difficulty; pempidine did not prevent these effects. Microinfusions of muscarine into the brain did not affect posture, respiration or temperature.

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.…”

Effects of Cholinomimetic Agents Given Into the Brain of Fowls

“…Details of other techniques and recording methods used are given by Marley & Seller (1972). Experiments were performed at thermoneutrality, water and weight of food in the test chamber were recorded before and after infusing carbachol into the hypothalamus.…”

“…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.…”

Effects of Nicotine Given Into the Brain of Fowls

“…Stereotactic implantation of intraventricular and intracerebral cannulae, anaesthesia (halothane for recovery anaesthesia, chloralose for non-recovery experiments), postoperative care, methods for recording and integrating electrocortical activity, for recording blood pressure, body temperature and respiration, for injections via implanted cannulae, for histological preparation of the brain, were as described previously (Marley & Seller, 1972 11, 36, 44, 71, 173, 198, 206 and 231 pecks, at which time the cycle recommenced.…”

“…This paper presents results with fowls in which nicotine was infused into discrete areas of the brain and injected into the IlIrd cerebral ventricle; a brief account has been published (Marley & Seller, 1970a). The results indicate that not only can the central effects of nicotine be distinguished from those of muscarine but the selective antagonists for the substances differ, that for nicotine being pempidine whereas those for muscarine were atropine or hyoscine (Marley & Seller, 1970a,b;1972).…”