Opioids activate G proteins in REM sleep-related brain stem nuclei of rat

MU opioid receptors within the pontine reticular formation contribute to opioid-induced rapid eye movement (REM) sleep inhibition. Mu receptors are coupled to guanine nucleotide binding (G) proteins and this study tested the hypothesis that th μ opioid agonist [D-Ala,N-Me-Phe,Gly-ol]enkephalin (DAMGO) would activate G proteins in rat brain stem nuclei known to regulate REM sleep. In vitro autoradiography of DAMGO-stimulated [S]GTPγS binding showed that, compared with basal [S]GTPγS binding, DAMGO significantly increased G protein activation in the nucleus pontis oralis (56.2%), nucleus pontis caudalis (57.3%), laterodorsal tegmental nucleus (75.8%), pedunculopontine tegmental nucleus (72.4%), nucleus locus coeruleus (77.2%) and dorsal raphe nucleus (73.4%). DAMGO stimulation of [S]GTPγS binding in nuclei regulating REM sleep suggests that opioid-induced REM sleep inhibition involves activation of G proteins.