Role of amygdaloid nuclei in the anxiolytic-like effect of nociceptin/orphanin FQ in rats.

We investigated the mechanism underlying the anxiolytic actions of the neuropeptide nociceptin/orphanin FQ (N/OFQ) using the elevated plus-maze test and T-maze test. Microinfusions of N/OFQ (10 or 32pmol) into the central amygdala (ACE) increased the time spent in the open arms of the elevated plus-maze (anxiolytic-like effects), whereas microinfusions of N/OFQ (10, 32 or 100 pmol) into the basolateral amygdala (ABL) did not affect the time spent in the open arms. Moreover, microinfusions of N/OFQ (32 pmol) into the ACE impaired escape performance from the open arms of the elevated T-maze (anxiolytic-like effects), but did not change inhibitory avoidance of the open arms. A non-peptidyl N/OFQ receptor (NOP) antagonist, J-113397(1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one) (10 mg/kg, s.c.), blocked the anxiolytic-like effects induced by N/OFQ. These results indicate that the anxiolytic-like effects of N/OFQ might be due to impaired escape performance from the open arms and it implicates the N/OFQ system within the ACE in the mediation of panic action.