CONVERGENT PREFRONTAL CORTEX AND MAMILLARY BODY PROJECTIONS TO THE MEDIAL PONTINE NUCLEI - A LIGHT AND ELECTRON-MICROSCOPIC STUDY IN THE RAT

To study the convergence of medial prefrontal cortex and mamillary bod y projections to the medial pontine nuclei, light and electron microsc opic, neuroanatomical, tract-tracing experiments were performed. Injec tions of horseradish peroxidase conjugated to wheat germ agglutinin (W GA-HRP), biotin conjugated to dextran (BD), or rhodamine conjugated to dextran (RD) were made individually or in combinations into the cereb ral cortex, hypothalamus, or pens. In addition, injections of WGA-HRP into the medial prefrontal cortex and electrolytic lesions of the mami llary body were made to study the synaptology of afferent projections to the pontine nuclei. In the light microscopic studies, injections of WGA-HRP into the rostromedial pontine nuclei produced dense, retrogra de labeling both in the dorsal peduncular area of the medial prefronta l cortex and in the medial mamillary nucleus, pars medialis. Injection s of the anterograde tracers BD and RD into the medial prefrontal cort ex and the medial mamillary nuclei, respectively, resulted in partiall y overlapping terminal fields in the rostromedial pontine nuclei. In t he electron microscopic studies, injections of WGA-HRP into the dorsal peduncular area and electrolytic lesions of the mamillary body produc ed anterogradely labeled axon terminals and degenerating axon terminal s that synapsed on the same dendrites or neuronal somata in the rostro medial pontine nuclei. The results demonstrate that the medial prefron tal cortex and the medial mamillary nuclei have partially overlapping projections to the rostromedial pontine nuclei and implicate precerebe llar relay nuclei in the integration of limbic and/or autonomic functi ons mediated by convergent projections from the cerebral cortex and th e hypothalamus. J. Comp. Neurol. 398:347-358, 1998. (C) 1998 Wiley-Lis s, Inc.