Kainic acid depresses the ex vivo release of dynorphin B and glutamate from rat hippocampal mossy fiber synaptosomes

Abstract

This experiment examined the effects of intracerebroventricularly (i.c.v.) administered kainic acid (KA) on the subsequent ex vivo release of l-glutamate (Glu) and dynorphin B-like immunoreactivity (Dyn B-LI) from isolated rat hippocampal mossy fiber (MF) synaptosomes at 4.5 h, 20 h or 48 h after administration of 0.5 μg/μl KA. The Dyn B-LI content in the synaptosomal fraction initially decreased at 4.5 h and then rebounded and remained elevated above control levels at 20 h and 48 h. The K +-evoked release of Dyn B-LI from the synaptosomes was markedly depressed at 4.5 h after KA and remained significantly below control levels at 20 h and 48 h. In contrast, KA caused no change in the K +-evoked release of Glu at 4.5 h as compared to control levels, but did result in a significant decrease in Glu release at 20 h and 48 h. These data indicate a persistent effect of i.c.v. KA on neurotransmission at MF-CA3 synapses in rat hippocampus, resulting in a suppression of the release of Glu as well as the opioid peptide, Dyn B.