Estrus phase differences in female rats in morphine antinociception elicited from the ventrolateral periaqueductal gray.

Male rodents display greater systemic morphine antinociception than females which show their most marked effects during late diestrus or proestrus. Morphine (1-2.5 mug) antinociception on the tail-flick test elicited from the ventrolateral periaqueductal gray was examined across estrus phases in female relative to male rats.

Reciprocal interactions between the amygdala and ventrolateral periaqueductal gray in mediating of Q/N(1-17)-induced analgesia in the rat.

The opioid peptide, Orphanin FQ/nociceptin (OFQ/N(1-17))(,) its active fragments, and a related precursor peptide each produce analgesia following microinjection into the amygdala of rats. OFQ/N(1-17)-induced analgesia elicited from the amygdala is blocked by amygdala pretreatment of either general, mu, kappa, or delta-opioid antagonists even though OFQ/N(1-17) binds poorly to these receptor subtypes, and the antagonists bind poorly to the ORL-1/KOR-3 receptor. Agonists at mu and kappa opioid receptors as well as beta-endorphin each produce analgesia elicited from the amygdala that is blocked by opioid antagonist pretreatment in the ventrolateral periaqueductal gray (vlPAG) of rats.

Characterization of rat prepro-orphanin FQ/nociceptin((154-181)): nociceptive processing in supraspinal sites.

Orphanin FQ/nociceptin (OFQ/N), the endogenous ligand for the orphan receptor-like/kappa(3)-like opioid receptor clone, produces a variety of behavioral responses, including those associated with pronociception and antinociception. The OFQ/N precursor rattus-proOFQ (rppOFQ/N) contains several paired basic amino acids, which raises the possibility that post-translational processing can be responsible for the production of a number of additional biologically active peptide fragments. One of these putative peptides, rppOFQ/N (rppOFQ/N(154-181)), was examined for antinociceptive and pronociceptive processes in four brain sites involved in pain inhibition: the ventrolateral periaqueductal gray (vlPAG), the amygdala, the locus coeruleus (LC), and the rostroventromedial medulla (RVM).