The cholinergic nuclei of the basal forebrain of the rat: hypertrophy following contralateral cortical damage or section of the corpus callosum.

After damage of the neocortex of one hemisphere by removal of the pia-arachnoid mater, the cholinergic cells of the basal nucleus of the unoperated hemisphere show a marked increase in their cross-sectional areas. This hypertrophy reaches a maximum of 25% by 3 weeks after operation and persists indefinitely. The cell bodies appear normal in shape, are often paler-staining and the hypertrophy includes the proximal dendrites. The hypertrophy is confined to the part of the basal nucleus corresponding to that which shows shrinkage on the operated side. The enlargement is greatest in animals operated upon on the first day after birth (+31%), is less in adult animals (mean +22%) but occurs at all ages up to 496 days, the oldest animal used. After unilateral removal of the hippocampus or section of the fimbria there is hypertrophy of the cholinergic neurones of the contralateral medial septal nucleus (+24%) and vertical nucleus of the diagonal band (+18%). Removal of the olfactory bulb on one side had no apparent effect upon the cholinergic neurones in the contralateral horizontal nucleus of the diagonal band. Damage of the neocortex by exitotoxic amino acids did not result in hypertrophy of the cholinergic cells of the contralateral basal nucleus despite marked shrinkage of the neurones in the basal nucleus on the operated side. After section of the corpus callosum the neurones throughout the basal nucleus of both sides are significantly larger than in the normal animal; the hypertrophy has occurred by 20 days after operation and persists indefinitely.(ABSTRACT TRUNCATED AT 250 WORDS)