A segmental map of architectonic subdivisions in the diencephalon of the frog Rana perezi: Acetylcholinesterase-histochemical observations

This work examines frog diencephalic subdivisions from a segmental viewpoint and adds a number of details to the atlas of the bullfrog diencephalon reported by Neary and Northcutt [1983]. Acetylcholinesterase histochemistry was performed on brains of Rana perezi, sectioned either sagittally or in a plane roughly parallel to the optic tract to optimize detection of segmental landmarks. This material provided a very detailed picture of individual neurons, neuropils and some fiber tracts expressing the enzyme in diverse patterns characteristic for each diencephalic region. The main diencephalic areas previously recognized in the bullfrog appeared subdivided into smaller AChE-chemoarchitectonic units. Modified subdivisions are proposed for several entities: preoptic, suprachiasmatic, entopeduncular, ventral thalamic, anterior thalamic, pretectal, hypothalamic and tuberculum posterior regions. A number of cell groups are described for the first time in frogs. This mapping is expected to be useful for the interpretation of immunocytochemical and experimental hodologic results in the diencephalon of frogs and opens new possibilities for comparative analysis.