A monosynaptic fiber track studied in vitro: evidence of a hippocampal CA1 associational system?

An excitatory afferent system previously undescribed in the in vitro slice was found to be present in the hippocampal CA1 stratum oriens. Evidence was provided that the system makes monosynaptic, en passage contact with CA1 pyramidal cells in the region of their basal dendrites. Slices from partially deafferented hippocampai were used in evaluating the possibility that the s. oriens pathway originated in the contralateral hippocampus. This possibility was not confirmed and the results were discussed in terms of an ipsilateral associational system in CA1 s. oriens.