Cholinergic and noradrenergic afferents influence the functional properties of the postnatal visual cortex in rats

Based on previous evidence that acetylcholine (ACh) and noradrenaline (NA) play a permissive role in developmental plasticity in the kitten visual cor tex, we reinvestigated this topic in the postnatal Visual cortex of rats wi th normal vision. In rats, the functional properties of visual cortical cel ls develop gradually between the second and the sixth postnatal week (Fagio lini et al., 1994). Cortical cholinergic depletion, by basal forebrain (BF) lesions at postnatal day (PD) 15 (eye opening), leads to a transient distu rbance in the distribution of ocular dominance (Siciliano et al., 1997). In the present study, we investigated the development of visual cortical resp onse properties following cytotoxic lesions of the locus coeruleus (LC) alo ne or in combination with lesions of cholinergic BE The main result is that early NA depletion impairs the orientation selectivity of cortical neurons , causes a slight increase of their receptive-field size, and reduces the s ignal-to-noise ratio of cell responses. Similar effects are obtained follow ing NA depletion in adult animals, although the effects of adult noradrener gic deafferentation are significantly more severe than those obtained after early NA depletion. Additional cholinergic depletion causes an additional transient change in ocular-dominance distribution similarly to that obtaine d after cholinergic deafferentation alone. Comparisons between depletion of NA on the one hand and depletion of both NA and ACh on the other suggest t hat the effects of combined deafferentation on the functional properties st udied result from simple linear addition of the effects of depleting each a fferent system alone.