ORGANIZATION OF DIRECT HIPPOCAMPAL EFFERENT PROJECTIONS TO THE CEREBRAL-CORTEX OF THE RHESUS-MONKEY - PROJECTIONS FROM CA1, PROSUBICULUM, AND SUBICULUM TO THE TEMPORAL-LOBE

This study investigates direct hippocampal efferent projections to the temporal lobe of the rhesus monkey. Tritiated amino acid injections w ere placed into the hippocampal formation to identify terminal fields, and complementary fluorescent retrograde tracer injections were place d into the cortex to identify the cells of origin. Tritiated amino aci d injections into CA1, prosubicular or subicular subfields produced an terograde label over parts of the parahippocampal gyrus and temporal p ole Injections of fluorescent retrograde tracers demonstrated that the se projections originate from longitudinal strips of neurons that occu py part of the CA1 subfield as well as from strips of neurons in adjac ent prosubicular and subicular subfields. Thus, an injection into area TH of the posterior parahippocampal gyrus labeled neurons in a longit udinal strip of proximal CA1 (i.e., near CA2) as well as a strip in th e subiculum; injections into areas TF, TL, 35, or Pro labeled neurons in a longitudinal strip of distal CA1 (i.e., near the prosubiculum) as well as one in the prosubiculum; and an injection into al ea TFO labe led neurons in a longitudinal strip in the middle of CA1. These strips of neurons extended longitudinally throughout the entire rostrocaudal length of the hippocampus. These results demonstrate that, in the mon key, CA1 projections to cortex arise topographically from longitudinal ly oriented strips of neurons that occupy only a part of the transvers e extent of CA1 but that cover most of the anteroposterior extent of t he hippocampus. Thus, in the monkey, CA1 is not a single uniform entit y and may have a unique role as a source of direct hippocampal project ions to the cerebral cortex. (C) 1998 Wiley-Liss, Inc.