Fiber connections of the corpus glomerulosum pars rotunda (GR) in a teleost
tilapia Oreochromis niloticus
were studied by biotinylated dextran amine injections into the GR and inferior lobe. After tracer injections into the GR
major groups of labeled somata were found bilaterally in the cortical nucleus and ipsilaterally in the nucleus intermedius. Numerous labeled terminals were found ipsilaterally in the central nucleus
nucleus of lateral recess
and diffuse nucleus (NDLI) of the inferior lobe. Some other connections were also elucidated in the present study
although these were less abundant. Notably
efferent projections to the inferior lobe were not evenly distributed within each lobar nucleus. Labeled terminals were confined to the cell body zone of central nucleus and the outer cell-sparse layer of the nucleus of lateral recess. The rostrolateral portion of NDLI and ventrolateral portion of middle to caudal NDLI received few GR fibers
the rostromedial portion of NDLI a moderate density of fibers
and the rest of the nucleus numerous fibers. These different portions of the NDLI
to some extent
also differed in other afferent and efferent connections
suggesting regional specialization of the nucleus. Furthermore
restricted injections to the lobar nuclei suggest different efferent projections of the component cells of the GR: large and small cells. The large cells project only to the central nucleus
whereas the small cells project to the NDLI and nucleus of lateral recess. Therefore
the two types of GR cells appear to constitute parallel pathways from the pretectum to the inferior lobe. c 2007 Wiley-Liss
Inc.
