Stimulation of the perforant path alters hippocampal levels of opioid peptides, glutamine and GABA

Abstract

This investigation demonstrates that stimulation of the perforant path under conditions which elicit wet dog shakes in rats produces a significant decrease in hippocampal levels of methionine-enkephalin, dynorphin A(1-8) and glutamine, and an increase in gamma-aminobutyric acid (GABA). Levels of these substances are not altered by stimulus parameters insufficient to elicit wet dog shakes. These results lend support to the notion that endogenous opioid peptides play a role in regulation of hippocampal excitability but may only be released under relatively intense stimulus conditions. The increase in GABA levels could be due to an increase in synthesis, an increase in reuptake or a reduction in release. The latter possibility is consistent with reports that iontophoretically applied enkephalin exerts its apparent excitatory effects via an inhibitory action on inhibitory neurons in the hippocampus.