Neuropeptide FF receptors couple to a cholera toxin-sensitive G-protein in rat dorsal raphe neurones

Abstract

In rat dorsal raphe neurones, nociceptin (300 nM) reduced the peak [Ca 2+] i transient, triggered by depolarization, by 36.7±1.8% ( n=46). This effect of nociceptin decreased to 16.7±2.9% ( n=18) after pre-treatment of the neurones with pertussis toxin (5 μg/ml, 2–6 h) but was unchanged (37.4±2.1%, n=44) after pre-incubation with cholera toxin (5 μg/ml, 2–6 h). This suggests that, in dorsal raphe neurones, the ORL1 receptor couples to inhibitory (G i/o) G-proteins. The neuropeptide FF analogue, [ d-Tyr 1, (N-Me)Phe 3]neuropeptide FF (10, 100, 1000 nM), acted as an anti-opioid and reduced the effect of nociceptin (300 nM, 30 s) by 62.0±3.3% ( n=28). Following pre-incubation with cholera toxin (5 μg/ml, 2–6 h) [ d-Tyr 1, (N-Me)Phe 3] neuropeptide FF was unable, at the three concentrations tested, to block nociceptin activity. We conclude that, in rat dorsal raphe neurones, neuropeptide FF receptors couple to stimulatory G-proteins (G s).