Sex differences in the ventral paleostriatum of the zebra finch: origin of the cholinergic innervation of the song control nuclei.

The two main song control nuclei in the forebrain of zebra finches, the higher vocal center (HVC) and the robust nucleus of the archistriatum (RA), are sexually dimorphic at many levels of their neural circuitry. These nuclei receive their cholinergic innervation from the ventral paleostriatum (VP), which is homologous to portions of the mammalian basal forebrain. We compared the cholinergic neurons in the VP between the sexes using choline acetyltransferase (ChAT) immunohistochemistry. Both the size and density of the ChAT-immunoreactive somata in areas of the VP that project to the HVC or RA in males were significantly larger than those in females. These sex differences in the VP may be reflected in the sex differences of behaviors such as song perception and production.