The anatomical organization of the macaque pregeniculate complex

Saccade-related activity recorded in the primate pregeniculate nucleus, and its anatomical connections with the pretectal nucleus of the optic tract (NOT) and superior colliculus (SC), suggest that it plays a role in visual-ocular motor integration. To study this role, a clearer understanding of pregeniculate organization is required. Based on its connectivity and neurotransmitter immunocytochemistry, we demonstrate that this nucleus is composed of several subnuclei, suggesting the term, pregeniculate complex (PrGC). The PrGC includes a weakly developed dorsal lamina, rostrally, and a well-developed ventral lamina. The ventral lamina includes the retinorecipient and superior sublayers, rostrally, and the medial division, caudally. A thin lamina of cells lateral to the dorsal lateral geniculate nucleus is contiguous with the PrGC; we term this the lateral division. The PrGC and the lateral division each project to the SC/NOT; the superior sublayer and medial division of the PrGC are connected reciprocally to the SC/NOT. Immunocytochemistry for gamma-aminobutyric acid (GABA) and substance P (SP) further delineate the PrGC subnuclei. The retinorecipient sublayer stains most intensely for GABA and SP. The superior sublayer and medial division also stain strongly for GABA and SP. Essentially all neurons in the lateral division are GABA-positive. The combination of tract tracing and immunocytochemistry demonstrate differences in the connectivity of the PrGC subnuclei and the lateral division with the SC/NOT. This, combined with the differential localization of GABA in the PrGC, provides a basis for further study of its functional role.