Elsevier

Neuroscience Letters

Volume 70, Issue 1, 25 September 1986, Pages 132-137
Neuroscience Letters

Long-term potentiation of guinea pig mossy fiber responses is not blocked by N-methyl d-aspartate antagonists

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Abstract

Receptors preferentially activated by the excitatory amino acid N-methyl-d-aspartate (NMDA) do not mediate synaptic transmission in the hippocampus but are involved in initiating long-term potentiation (LTP) in hippocampal region CA1. We have examined the role of NMDA receptors in LTP of the commissural/associational and mossy fiber pathways to region CA3 pyramidal neurons. In the commissural/associational pathway, NMDA receptor blockers did not reduce synaptic responses but reversibly blocked the induction of LTP. In contrast, NMDA receptor blockers had no effect on mossy fiber LTP. These results suggest that induction of commissural/associational LTP differs from mossy fiber LTP, although the mechanisms underlying expression of LTP along these pathways could be similar. Kynurenate and l-2-amino-4-phosphonobutyrate, which potently reduce mossy fiber responses, also did not block induction of mossy fiber LTP.

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    Early work showed that activation of group III mGluRs with L-AP4 suppress both the excitability of CA3 PCs and the MF–CA3 synaptic transmission. The inhibitory effect was consistently observed with extracellular field potentials (Lanthorn et al., 1984; Harris and Cotman, 1986; Manzoni et al., 1995) and intracellular recordings (Yamamoto et al., 1983; Cotman et al., 1986). Interestingly, the inhibitory effect of L-AP4 was restricted to guinea pig hippocampus, and it was absent in the rat hippocampus.

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