POSTNATAL-DEVELOPMENT OF FUNCTIONAL-PROPERTIES OF VISUAL CORTICAL-CELLS IN RATS WITH EXCITOTOXIC LESIONS OF BASAL FOREBRAIN CHOLINERGIC NEURONS

In the rat, visual cortical cells develop their functional properties during a period termed as critical period, which is included between e ye opening, i.e. postnatal day (PD) 15, and PD40. The present investig ation was aimed at studying the influence of cortical cholinergic affe rents from the basal forebrain (BF) on the development of functional p roperties of visual cortical neurons. At PD15, rats were unilaterally deprived of the cholinergic input to the visual cortex by stereotaxic injections of quisqualic acid in BF cholinergic nuclei projecting to t he visual cortex. Cortical cell functional properties, such as ocular dominance, orientation selectivity, receptive-field size, and cell res ponsiveness were then assessed by extracellular recordings in the visu al cortex ipsilateral to the lesioned BF both during the critical peri od (PD30) and after its end (PD45). After the recording session, the r ats were sacrificed and the extent of both cholinergic lesion in BF an d cholinergic depletion in the visual cortex was determined. Our resul ts show that lesion of BF cholinergic nuclei transiently alters the oc ular dominance of visual cortical cells while it does not affect the o ther functional properties tested. In particular, in lesioned animals recorded during the critical period, a higher percentage of visual cor tical cells was driven by the contralateral eye with respect to normal animals. After the end of the critical period, the ocular dominance d istribution of animals with cholinergic deafferentation was not signif icantly different from that of controls. Our results suggest the possi bility that lesions of BF cholinergic neurons performed during postnat al development only transiently interfere with cortical competitive pr ocesses.