Neuropharmacological profile of the young chick

Abstract

The EEG and behavioral effects of diverse centrally active pharmacological agents were studied in unrestrained, unanesthetized, 5–14 day old white Leghorn cockerels. Effective doses of the barbiturates, alpha chloralose, chlorpromazine, reserpine, and morphine, produced behavioral depression and associated slow wave EEG activity. The hallucinogenic compounds, lysergic acid diethylamide, psilocybin, harmine, and mescaline, induced behavioral excitation, EEG arousal activity and abnormal body postures; the initial effects were often followed by behavioral depression. Caffeine produced no apparent alteration of either the EEG or the behavior of the young chick. Atropine induced an EEG arousal pattern, locomotor ataxia, and later a perceptible increase in normal motor activities. Amphetamine produced desynchronized EEG patterns characteristic of arousal, increased vocal activity, abnormal postures, and increased locomotor activities. Drug interactions with the unique amphetamine chick response revealed that atropine was the most effective amphetamine potentiating agent examined; while diphenhydramine and related agents were the most effective blocking agents of amphetamine induced behavior, that by themselves did not produce behavioral depression. Subconvulsant doses of metrazol produced slow wave EEG activity and behavioral quiescence; while convulsant doses induced clonus and diffuse, high voltage, spiking waves in the EEG. Strychnine produced tonic convulsions while the EEG demonstrated only a desynchronized pattern and not a pattern of spikes. The few differences in drug responses between avian and mammalian species appeared to be related to the absence of an avian functional cerebral cortex and a neothalamo-cortical anatomical complex. These anatomical differences in the bird result in: the absence of myoclonic jerking following alpha chloralose; the apparent lack of a caffeine stimulatory effect; the association of the atropine-induced EEG and behavioral effects; and the absence of strychnine-induced spikes in the cerebral hemisphere EEG. The many similarities in responsiveness between avian and mammalian species were more striking than the few differences. Especially prominent was the demonstration that the chick responses to those agents that effect mechanisms underlying the states of wakefulness and sleep, i.e. the barbiturates, chlorpromazine, reserpine, and amphetamine, were comparable to the responses reported for mammalian species. This suggested that there are a number of fundamental central nervous system mechanisms controlling EEG and behavioral activities, and originating in subcortical brain areas that appear to share common properties and presence in the homeothermal vertebrates.