Nociceptin/orphanin FQ inhibits glutamate release from rat cerebellar and brain stem slices

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 microM) 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.