COMPARISON OF PROJECTION NEURONS IN THE PONTINE NUCLEI AND THE NUCLEUS-RETICULARIS TEGMENTI PONTIS OF THE RAT

Dendritic features of identified projection neurons in two precerebell ar nuclei, the pontine nuclei (PN) and the nucleus reticularis tegment i pontis (NRTP) were established by using a combination of retrograde tracing (injection of fluorogold or rhodamine labelled latex microsphe res into the cerebellum) with subsequent intracellular filling (lucife r yellow) in fixed slices of pontine brainstem. A multivariate analysi s revealed that parameters selected to characterize the dendritic tree such as size of dendritic field, number of branching points, and leng th of terminal dendrites did not deviate significantly between differe nt regions of the PN and the NRTP. On the other hand, projection neuro ns in ventral regions of the PN were characterized by an irregular cov erage of their distal dendrites by appendages while those in the dorsa l PN and the NRTP were virtually devoid of them. The NRTP, dorsal, and medial PN tended to display larger somata and more primary dendrites than ventral regions of the PN. These differences, however, do not all ow the differentiation of projection neurons within the PN from those in the NRTP. They rather reflect a dorso-ventral gradient ignoring the border between the nuclei. Accordingly, a cluster analysis did not di fferentiate distinct types of projection neurons within the total samp le. In both nuclei, multiple linear regression analysis revealed that the size of dendritic fields was strongly correlated with the length o f terminal dendrites while it did not depend on other parameters of th e dendritic field. Thus, larger dendritic fields seem not to be accomp anied by a higher complexity but rather may be used to extend the reac h of a projection neuron within the arrangement of afferent terminals. We suggest that these similarities within dendritic properties in PN and NRTP projection neurons reflect similar processing of afferent inf ormation in both precerebellar nuclei. (C) 1996 Wiley-Liss, Inc.