Septohippocampal connections to field CA1 of the rat identified with field potential analysis and retrograde labeling by horseradish peroxidase.

Electrical stimulation of the medial septal nucleus produced field potentials in the hippocampal CA1 region of the rat. The laminar field-potential analysis suggested that the electromotive force of the septum-induced responses might be attributable mainly to excitatory postsynaptic potential currents generated in the stratum oriens (layer of distribution of basal dendrites of hippocampal pyramidal cells). Neural cell bodies in the medial septum-diagonal band complex were retrogradely labeled with horseradish peroxidase (HRP) injected into the stratum oriens of CA1, but not with HRP injected into other CA1 strata. Thus the medial septal nucleus was indicated to send excitatory inputs to basal dendrites of CA1 pyramidal cells.