Development and adult organization of the lateral part of the bed nucleus of the stria terminalis in the chicken

The lateral part of the bed nucleus of the stria terminalis (BSTL) is a component of the subpallial amygdala located near the ventral sulcus of the lateral ventricle, but its limits have not been well defined in birds. In this study, we analyzed the expression patterns of a number of neurochemical markers: GABA, calbindin (CB), calretinin (CR), or neuronal nitric oxide synthase (nNOS), in the embryonic and adult chicken brain, to further characterize the organization of the avian BSTL. From embryonic day 16, it was possible to distinguish three different regions within BSTL on the basis of cytoarchitectonic and immunohistochemical features. A central region, referred to as lateral bed nucleus of the stria terminalis pars densocellularis (BSTLdc), is characterized by numerous tightly packed cell bodies, most of which are GABA-immunoreactive (ir), and two peripheral regions with lower cellular density displaying a moderate GABA expression, referred to as lateral bed nucleus of the stria terminalis, plexiform part 1 (BSTLp1) and plexiform part 2 (BSTLp2), respectively. In contrast to BSTLdc, both plexiform parts are characterized by the presence of many fibers and terminals immunoreactive for nNOS and CR, as well as some CR-ir scattered cells. A distinctive feature of BSTLp2 is a population of CB-ir cells embedded in a slightly CB-ir neuropil. Comparison of our immunohistochemical data with gene expression data suggests that BSTLdc and BSTLp1 are pallidal in nature, whereas BSTLp2 receives important contributions from the entopeduncular/preoptic area.