SKIN-COLOUR CHANGES IN THE LIZARD, ANOLIS CAROLINENSIS, IN RESPONSE TO LOCALIZED ELECTRICAL STIMULATION AND LESIONS IN THE DIENCEPHALON

Abstract

A study was made of changes in skin colour in the lizard, Anolis carolinensis, in response to deep electrical stimulation at 0·2 mm intervals throughout the periventricular region of the diencephalon and the anterior brain stem. Double-barrelled glass microelectrodes with tip diameters of 3 μm were used. A 20 μA pulse-train consisting of a 500 Hz signal lasting for 1 s yielded localized responses. Skin darkening occurred only in response to stimulation delivered in the anterior and dorsal region of the diencephalon and skin lightening only in response to stimulation in a small area in the posterior and ventral region of the hypothalamus. Electrical lesions in the latter region resulted in permanent skin darkening. Surgical interruption of the hypothalamo–hypophysial neurosecretory tract did not block skin-colour change in response to dark or light backgrounds. It was concluded that MSH release is under tonic inhibitory control by hypothalamic neurones in Anolis. Both inhibitory and stimulatory neurones can be localized stereotaxically in the diencephalon and neither type corresponds with the neurosecretory neurones of the hypothalamo–hypophysial tract. The functional relationship between the stimulatory neurones and the inhibitory neurones and pars intermedia remains unclear.