Evidence of the synthesis of opioid receptor like 1 receptor in nociceptinergic neurons in rat brain suggests the existence of autoreceptor: a confocal double staining study

Opioid receptor like 1 (ORL1) receptor is a novel mem ber of the opioid rec eptor family, wh ich was not bound by any of the typical opioid receptor li gands but bound by the recently discovered nociceptin (also termed orphanin FQ) with high affinity. By using double staining of fluorescent in situ hy bridization and immunohistochemistry, we observed the expression of ORL1 re ceptor mRNA in nociceptin-like immunoreactive neurons in multiple areas in rat brain including the hippocampus, arcuate nucleus in the hypothalamus, v entralateral periaquiductal gray (PAG) and raphe nuclei in brain stem. The expression of ORL1 mRNA in nociceptinergic neurons suggests that these rece ptors mediate, at least in part, the presynaptic autoreceptor functions. Fu rther anatomical and functional significance of the autoreceptor of nocicep tinergic neurons remain to be elucidated. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.