The posterior division of the bed nuclei of the stria terminalis has three major nuclei: principal, interfascicular, and transverse, which receive topographically ordered inputs from the medial amygdalar nucleus. The overall pattern of axonal projections from each nucleus was determined in male rats with the Phaseolus vulgaris-leucoagglutinin method. Together, these nuclei project topographically back to the medial amygdalar nucleus, to the adjacent lateral septal nucleus, to the nucleus accumbens and substantia innominata, to hypothalamic parts of the behavior control column, and to the hypothalamic periventricular region, which controls patterned neuroendocrine and autonomic responses. The principal nucleus preferentially innervates septal and hypothalamic regions that control reproductive behavior and visceromotor responses, confirming a similar analysis by Gu et al. (J Comp Neurol  460:542-562). In contrast, the interfascicular and transverse nuclei differentially innervate septal and hypothalamic regions that control defensive as well as reproductive behaviors. In addition, the transverse nucleus projects significantly to midbrain parts of the behavior control column concerned with foraging/exploratory behavior. All three posterior division nuclei also project to thalamocortical feedback loops (by means of the nucleus reuniens and paraventricular nucleus). These structural data may be interpreted to suggest that the bed nuclei posterior division forms part (pallidal) of a corticostriatopallidal system involved in controlling two major classes of social (defensive and reproductive) behavior.
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