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Summary. The midbrain areas that yielded calling with the smallest currents were within the nucleus intercollicularis and isthmi complex. Natural calls were evoked, but they could not be localized. Rather, some calls were more easily evoked than others.Calling has been elicited with small currents from the midbrain of a variety of birds such as redwinged blackbirds J 4A getaius phoeniceus , chickens, Java sparrows Padda oryzivora 5 and in Japanese quail Coturnix coturnix japonica 6'7. However, a detailed threshold survey of the midbrain of the latter species is lacking. To date, there is general

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.

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