Time course of changes in long-term potentiation of synaptic transmission following subcortical deafferentation on the rat hippocampus.

Brief tetanic stimulation potentiates synaptic transmission both in the CA1 and dentate area of slices cut from normal rats. This long-term potentiation (LTP) was assayed in slices made at various times from rats subjected to complete bilateral sectioning of all subcortical afferents which enter the hippocampus. Over about one week survival time, LTP is present in the CA1 region of all and also in the fascia dentata of about 50% of slices. We found no signs of LTP in the dentate area of slices cut over 8 weeks after deafferentation, while the responses were clearly potentiated in the CA1 area of the same slices. Four week was the longest period when a somewhat modified version of LTP could be produced in the subcortically deafferented dentate area. The results confirm previous reports that subcortical afferents mediate some unknown factors essential for maintenance of long-term plasticity of intrinsic synapses in the fascia dentata. This unidentified, perhaps trophic influence diminishes in about 4 weeks after severing the subcortical fibers. In contrast, maintenance of subcortical inputs are apparently not required for the LTP in the intrinsic CA1 synapses.