Date of Award
Doctor of Philosophy (PhD)
Professor R.J. Racine
Cooperative interactions between the septal (septo-dentate; SD) and perforant path (PP) inputs to the dentate gyrus granule cells (GCs) of the rat were examined to determine the effect on long-term potentiation (LTP). Tetanization of SD afferents produced LTP of the SD-GC response but not of the PP-GC response, and PP tetanization produced LTP of the PP-GC response but had no effect on SD-GC responses. Despite this specificity, concurrent SD and PP tetanization produced significantly greater LTP of the PP-GC population spike than was produced following PP-only trains. In addition to increasing its magnitude, concurrent trains also increased the duration of LTP. Concurrent SD and PP tetanization had no additional effect on SD-GC responses.
The heterosynaptic cooperativity effect depended on both the temporal interval between application of the SD and PP trains and on their order of activation. When the SD trains were applied less than 100 ms prior to the PP trains there was a large additional increment in LTP magnitude. Intertrain intervals between 100 and 1000 ms produced significantly smaller increments. Beyond 1000 ms, no interaction effects were observed. If the PP trains preceded the SD trains there was little or no evidence of a cooperativity effect. The PP-SD sequence actually appeared to inhibit the appearance of a cooperativity effect when the trains were subsequently applied concurrently.
Paired-pulse tests, designed to examine the effect of the SD trains on recurrent inhibition, raised the possibility that the SD trains may reduce the strength of the GC's recurrent inhibitory circuits and thereby increase the postsynaptic effect of each PP train.
These results increase the attractiveness of the LTP phenomenon as a candidate neural mechanism for learning and memory. The possible role of the heterosynaptic interactions in classical conditioning were discussed.
Robinson, Gilbert Bradley, "Associative Interactions Between Septo-Dentate and Perforant Path Afferents to the Rat Dentate Gyrus" (1984). Open Access Dissertations and Theses. Paper 1277.