POSTNATAL CYTOARCHITECTURE OF THE RAT MEDIAL GENICULATE-BODY

The medial geniculate body (MGB) is a thalamic structure that provides vital information flow to the forebrain for complex acoustic processi ng. The development of cytoarchitectural features of the MGB was exami ned in rat to identify age-related patterns of growth in major genicul ate compartments that have been described previously (Clerici and Cole man [1990] J. Comp. Neurol. 297:14-31; Clerici et al. [1990] J. Comp. Neurol. 297:32-54): the ventral (MGv), dorsal (MGd), and medial (MGm) divisions. Results show that, on the day of parturition, all major nuc lei of each division are characterized, including the ovoid (OV) and v entral (LV) nuclei of MGv; the dorsal, deep dorsal (DD), caudodorsal, limitans, and suprageniculate nuclei of MGd; and the MGm. The MGv and MGd, which display comparable areas at birth, show rapid growth to pos tnatal day 7 (PND7), which then slows until PND11, around the time of ear canal opening; subsequently, MGv accelerates growth to reach large r adult size. From PND11 to PND16, thionin facilitates parcellation by extensive staining of dendritic processes of MGd, MGm, and lateral po sterior nucleus neurons but not neurons of the MGv or the dorsal later al geniculate nucleus. Golgi stains after birth reveal restricted dend ritic arborizations in MGv cells and dichotomous branching patterns of MGd neurons. Somal size in MGB increases dramatically subsequent to a fferent innervation and again following onset of auditory function. So mal growth occurs between all postnatal age groups tested for OV, LV, and DD nuclei, although LV segments related to high and low frequencie s do not differ. Cell packing density predicts the expanse of major MG B divisions better than somal size. These results demonstrate the inte grity and growth patterns of MGB nuclei and divisions from nascence an d provide a substrate for subsequent study of anatomical and physiolog ical development of the MGB. J. Comp. Neurol. 399:110-124, 1998. (C) 1 998 Wiley-Liss, Inc.