Abstract
We have previously demonstrated that nociceptin/orphanin FQ (N/OFQ), inhibits K + depolarisation-evoked glutamate release from rat cerebrocortical slices. In this study we have examined the effects of N/OFQ on glutamate release from rat cerebellar and brain stem slices as there are regional differences in nociceptin/orphanin FQ receptor (NOP) expression. Slices were depolarised with two pulses of 46 mM K + (S 1 and S 2) with N/OFQ added after S 1. Glutamate (non-radioactive) was measured using a fluorescence-based assay. N/OFQ effects were assessed by measuring area under S 1 and S 2 release curves and calculation of S 2/S 1 ratios. In cerebellar slices K + evoked S 2/S 1 ratio was 1.17±0.10 ( n=28). This was reduced in a concentration dependent (EC 50 22 nM; E max 46%) and naloxone (10 μM) insensitive manner by N/OFQ. In the brain stem K + evoked glutamate release was considerably reduced compared to cerebellum. In several preparations K + failed to evoke a significant release. In those that did K + evoked S 2/S 1 ratio was 1.03±0.07 ( n=13). A total of 100 nM N/OFQ reduced this by 38±12% and this response was naloxone insensitive. Due to this small response and its variability we could not construct a full concentration response curve. In conclusion we have demonstrated a functional NOP in rat cerebellum and brain stem that inhibits the release of glutamate.
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