Basal forebrain projections to somatosensory cortex in the cat.

1. This investigation was designed to identify the source of cholinergic basal forebrain projections to somatosensory cortex in the cat. 2. Injections of horseradish peroxidase (HRP) into cortical areas 3a, 3b, and 1 after a 36 to 48-h survival period, labeled neurons in the basal forebrain. The distribution of retrogradely labeled neurons was compared with the distribution of cells labeled by choline acetyltransferase immunocytochemistry. Most retrogradely labeled neurons in the basal telencephalon were found on the border between the globus pallidus and adjacent structures. Sometimes labeled neurons were also found in both limbs of the diagonal band of Broca. 3. Excitotoxin lesions of these regions of the basal telencephalon led to a profound depletion of acetylcholinesterase-containing axons in primary somatosensory cortex. 4. These data lay necessary groundwork for tests of the hypothesis that the cholinergic projection modulates experience-dependent modifications in adult cat somatosensory cortex.