NEWLY LEARNED AUDITORY RESPONSES MEDIATED BY NMDA RECEPTORS IN THE OWL INFERIOR COLLICULUS

Alignment of auditory and visual receptive fields in the optic tectum of the barn owl (Tyto alba) is maintained through experience-dependent modification of auditory responses in the external nucleus of the inf erior colliculus (ICX), which provides auditory input to the tectum. N ewly learned tectal auditory responses, induced by altered visual expe rience, were found to be pharmacologically distinct from normal respon ses expressed at the same tectal sites. N-methyl-D-aspartate (NMDA) re ceptor antagonists administered systemically or applied locally in the ICX reduced learned responses more than normal responses. This differ ential blockade was not observed with non-NMDA or broad-spectrum antag onists. Thus, NMDA receptors preferentially mediate the expression of novel neuronal responses induced by experience during development.