CHOLINGERGIC DEPLETION REDUCES PLASTICITY OF BARREL FIELD CORTEX

This experiment examines the impact of the cholinergic input from the basal forebrain on the plasticity of the vibrissa related somatosensor y cortex. Newborn rat pups received intraventricular injections of the cholinergic immunotoxin IgG192-saporin, after bilateral removal of th e C-line whisker follicles. Compared with saline-injected control anim als, unilateral injections of 0.1 mu g IgG192-saporin decreased the nu mber of cholinergic neurons on the toxin injected side by 78% in the b asal nucleus of Meynert and the vertical limb of the diagonal band of Broca, 80% in the magnocellular preoptic nucleus and the horizontal li mb of the diagonal hand of Broca, and 54% in the medial septal nucleus . Neuronal loss contralateral to the toxin was approximately half that on the ipsilateral side. The size of the C and D row barrels were com pared from tangential sections through the barrel field. In control an imals, D row barrels expanded into C row territory, giving a ratio of areas for D/C barrels of 2.03. Depletion of the cholinergic neurons re duced the expansion of D row barrels and hence decreased the D/C ratio , with a greater reduction on the toxin-treated side (1.43, P < 0.005) compared with the contralateral side (1.64, P < 0.05). This study imp licates the basal forebrain cholinergic projection in somato-sensory c ortical plasticity.