Neurochemical and Behavioural Factors Affecting the Sensitive Period for Imprinting

Abstract

An investigation of the neurochemical properties underlying the sensitive period for imprinting was undertaken by exploring the action of a mixture of an N-methyl-Daspartate (NMDA) receptor antagonist ketamine (55 mg/kg) and an ∝₂-aradrenergic agonist, xylazine (6 mg/kg) (KX) on the ability of dark-reared chicks to imprint on day 8 posthatching. Chicks treated with this mixture at 10, 20 or 40 h after hatching and which were reared in the dark were able to imprint on day 8. Controls treated with saline were unable to imprint on day 8. Similarly, chicks treated with the KX mixture or with saline on day 4 or day 7 were not able to imprint on day 8. Two stimuli were used to imprint the chicks; a rotating stuffed hen, and a rotating red and black box. While day 2 chicks were able to imprint on the hen or the box, groups of day 8 chicks that had been treated with KX at 10, 20 or 40 h after hatching only imprinted if they had been exposed to the hen. Box-exposed groups did not imprint. This is not a predisposition-like effect because KX-treated chicks showed a preference for the hen only if they had previously been exposed to it.