CYTOARCHITECTURE OF THE MEDIAL GENICULATE-BODY IN THE MOUSTACHED BAT (PTERONOTUS-PARNELLII)

The cytoarchitectonic organization of the medial geniculate body and a djoining thalamic nuclei was analyzed in the mustached bat (Pteronotus parnellii). These subdivisions provide a reference for structural, ph ysiological, connectional, and neurochemical work. Most nuclei recogni zed in other mammals exist in the mustached bat, although the relative volume of the three divisions was species specific. The ventral divis ion contains medium-sized neurons and a few smaller cells and is well developed. Neurons in the lateral part lie in regularly aligned rows c orresponding to the laminae in Golgi material; in the medial part, the se laminae are obscured by fibers. The dorsal division has at least fo ur nuclei, each with a unique cytoarchitecture and myeloarchitectonic organization. The suprageniculate nucleus is prominent and has many la rge radiate neurons. Cells in the superficial dorsal nucleus have weak ly laminated dendrites, while dorsal nucleus neurons have spherical de ndritic fields. There is a wide range of neuropil patterns within the dorsal division. The suprageniculate nucleus has thick myelinated axon s, while the fibers in the superficial and dorsal nuclei are much thin ner. The rostral pole nucleus becomes prominent in the anterior one-ha lf of the auditory thalamus; its architectonic affiliation is equivoca l, and connectional and immunocytochemical studies suggest that it may belong to the dorsal division. The medial division is one nucleus wit h many types of neurons, and it has coarse axons without laminar orien tation. It is the smallest of the divisions and is present throughout the medial geniculate complex, except at the caudal tip and at the ros tral pole. Many features of medial geniculate body organization eviden t in other mammals are recognized in the mustached bat. These include a prominent ventral division, some of whose neurons have a laminar org anization, and a comparatively small medial division that is devoid of fibrodendritic laminae. Other features, such as the presence of a lar ge rostral pole nucleus, whose homologue in other species is uncertain , or the sparse number or small cells that may participate in local ci rcuits, set it apart from carnivores and primates and suggest that the re are species specific patterns of medial geniculate body organizatio n. (C) 1994 Wiley-Liss, Inc.