A reduction of nonpyramidal cells in sector CA2 of schizophrenics and manic depressives

Background: Recent studies have suggested that there may be a preferential decrease of “nonpyramidal” neurons (NPs) in several corticolimbic regions of schizophrenic (SZ) brain. The current study was undertaken to determine whether a change in the density of pyramidal neurons (PNs) and NPs might be present in the hippocampal formation (HIPP) of SZ brain. Methods: A spatial counting approach in which the location of each and every PN and NP in the stratum pyramidale of sectors CA1–4 was applied to 11 normal control (CONs) and 10 SZs matched for age and postmortem interval, as well as 4 manic depressive (MD) subjects matched for age. Results: The data indicate that the CONs had approximately 10–20 times as many PNs than NPs in the various HIPP subfields. When the CON data were compared to those for the SZs, both the total number and density of PNs were found to be similar in all four sectors, while NPs were found to be selectively reduced by approximately 40% in CA2 of the SZ group. When the data were broken down according to patients with and without neuroleptic exposure, drug-free SZs showed a significant reduction in the density of NPs in CA2. The 4 MD cases both with and without neuroleptic exposure also showed a similar reduction of NPs in sector CA2. Conclusions: Taken together, the results of this study suggest that there may be a highly selective decrease in the number of NPs in sector CA2 that could play a contributory role in the pathophysiology of the major psychoses.