Abstract
The neuroanatomical connections in the nonhuman primate of the brainstem structures to the Hippocampal Formation (HF, which includes the dentate gyrus -DG-, CA3, CA2, CA1, subiculum, pre-parasubiculum and the entorhinal cortex -EC-) are still unclear. Previous tracer studies in nonhuman primates show retrogradely labeled neurons in the brainstem including the Ventral Tegmental Area (VTA), Locus Coeruleus (LC) and Raphe Nuclei (RN), after deposits in the hippocampus (Amaral and Cowan, 1980), as well as in the EC (Insausti et al., 1987). In order to characterize the neurotransmitters associated to those projections (presumably dopaminergic -DA, VTA-, noradrenergic -NA, LC-, and serotoninergic -5-HT, RN-, respectively), and the topographic and laminar differences, we studied comparatively the innervation in the HF using immunohistochemical techniques.
Inmunohistochemistry for DA (Tirosine Hidroxilase, TH), NA (Dopamine Beta Hidroxilase, DBH), and 5-HT showed: a) The DG molecular layer had TH-immunoreactive fibers, while the polymorphic layer contained positive 5-HT fiber labeling, b) CA3 pyramidal layer showed denser 5-HT labeling than TH, c) CA1 had scattered TH and 5-HT fibers, d) The superficial layer of the rostral EC (I and II) had TH- and 5-HT-labelled processes, e) TH and DBH positive cells were primarily found in the lateral subdivisions of the EC (ELR/ELc). The preferential location of these positive fibers in ELR/ELc, is significant, as this portion of the EC receives abundant unimodal and polymodal sensory input and innervates the body and tail of the hippocampus, and therefore it might be a crucial link in the consolidation of memory through the monoaminergic modulation of the HF.
