The effects of long-term potentiation of the perforant path-dentate gyrus synapses on tone evoked potentials in the outer molecular layer of the dentate gyrus

Moore, Karen-Ann (1986) The effects of long-term potentiation of the perforant path-dentate gyrus synapses on tone evoked potentials in the outer molecular layer of the dentate gyrus. Masters thesis, Memorial University of Newfoundland.

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Abstract

The effects of potentiation of the perforant path-dentate gyrus synapses on tone evoked potentials in the outer molecular layer of the dentate granule cells were examined in rats. 3 control groups and an experimental group participated in 2 testing sessions (M1 and M2), in which 300 tones (70dB, 10 msec in duration) were presented every 10 seconds against a background noise of 60 dB. Control Group 1 did not receive any experimental manipulations of the perforant path between the 2 sessions. The experimental group received high frequency stimulation of the perforant path (10 trains, 20 msec in duration at a frequency of 100 Hz. every 15 seconds) between the 2 tone presentation sessions. To control for perforant path stimulation, two further control groups were used. Control 2 received low frequency, low intensity stimulation of the perforant path and Control 3 underwent the same high frequency stimulation as the experimental group but did not exhibit EPSP potentiation of the perforant path evoked (PPEP). -- Over time, from M1 to M2, the auditory evoked potential (AEP) increased in size. Potentiation inhibited the growth of the AEP during M2. The results suggested that a third variable may have a modulating influence over the AEP at the level of the molecular layer. A theoretical model, implicating feed-forward and recurrent inhibitory interneurons is presented. This model suggests that presynaptic habituation and postsynaptic potentiation are the processes by which these interneurons exert an influence over the cellular response to a tone. It is further postulated that learning may not only involve direct activation of granule cells, but also active potentiation of inhibitory interneurons.

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