Catecholaminergic innervation of the hippocampus in the cynomolgus monkey

We studied the immunocytochemical distribution of catecholaminergic fibers in the hippocampal formation from two cynomolgus monkeys by using phenylethanolamine‐N‐methyltransferase, dopamine‐beta‐hydroxylase, and tyrosine‐hydroxylase antibodies. There were no phenylethanolamine‐N‐methyltransferase immunoreactive fibers suggesting the lack of epinephrine containing fibers. In order to compare the distributions of tyrosine‐hydroxylase and dopamine‐beta‐hydroxylase immunoreactive fibers, we counted fibers in four hippocampal regions, the dentate gyrus, CA3, CA1, and the subiculum at three different rostrocaudal levels. The distributions of dopamine‐beta‐hydroxylase and tyrosine‐hydroxylase immunoreactive fibers were overlapping but clearly different, suggesting that the hippocampus receives both noradrenergic and dopaminergic inputs in primates. Dopamine‐beta‐hydroxylase‐immunoreactive fibers were present in moderate density and roughly evenly distributed throughout the hippocampus. Tyrosine‐hydroxylase immunoreactive fibers were found in high density in the dentate gyrus, in the stratum lacunosum‐moleculare, and in the molecular layer of the subiculum. There were only minor side‐side and rostrocaudal differences in the distribution of tyrosine‐hydroxylase and dopamine‐beta‐hydroxylase immunoreactive fibers. The identification of a putative dopaminergic projection to primate hippocampus, which is more dense and widely distributed than in the rodent, parallels similar increases in dopaminergic projections reported for primate cerebral neocortex.