SEPTOTEMPORAL DISTRIBUTION OF [H-3]MK-801, [H-3]AMPA AND [H-3]KAINATEBINDING-SITES IN THE RAT HIPPOCAMPUS

The distribution of glutamate receptors in transverse hippocampal sect ions has been well investigated. However, in spite of the known septot emporal gradients of hippocampal connectivity no systematic studies ex ist about the distribution of glutamate receptors along the septotempo ral (longitudinal) hippocampal axis. Therefore, in the present study t his issue was investigated using receptor autoradiography for the [H-3 ]MK-801, [H-3]AMPA and [H-3]Kainate binding sites. Hippocampi from 30- day-old rats were sectioned perpendicularly to their longitudinal axis , yielding a total of 25-30 equidistantly spaced autoradiographs for e ach hippocampus. For each section layer-specific concentrations of bin ding sites were calculated by the aid of a computerized image analysin g system. The dependency of concentrations of binding sites on the sep totemporal position was evaluated by regression analysis. Gradients of binding were confined to distinct hippocampal layers. Significant sep totemporal gradients of [H-3]MK-801 binding were observed in selected layers of CA1 and the dentate gyrus, a septal to temporal decrease of binding in the oriens and radiatum layers of CA1 being most prominent. For [H-3]AMPA, significant septotemporal gradients of binding were re stricted to layers of CA3, CA4 and the dentate gyrus, with values gene rally increasing from septal to temporal levels. The observed septotem poral gradients possibly reflect functional segregations along the lon gitudinal hippocampal axis and could be important for the comparabilit y of ligand binding studies using transverse hippocampal sections or h ippocampal slice cultures.