Parsing the hedonic and motivational influences of nociceptin on feeding using licking microstructure analysis in mice

Abstract

Opioid peptides are implicated in processes related to reward and aversion; however, how specific opioid peptides are involved remains unclear. We investigated the role of nociceptin (NOC) in voluntary licking for palatable and aversive tastants by studying the effect of intracerebroventricularly (i.c.v.) administered NOC on licking microstructure in wild-type and NOC receptor knockout (NOP KO) mice. Compared to wildtypes, NOP KO mice emitted fewer bouts of licking when training to lick for a 20% sucrose solution. Correspondingly, i.c.v. administration of NOC increased the number of licking bouts for sucrose and sucralose in wildtype, but not NOP KO mice. The ability of NOC to initiate new bouts of licking for sweet solutions suggests that NOC may drive motivational aspects of feeding behavior. Conversely, adulterating a sucrose solution with the aversive tastant quinine reduced licking bout lengths in wildtype and NOP KOs, suggesting that NOC signaling is not involved in driving voluntary consumption of semi-aversive tastants. Interestingly, when consuming sucrose following 20 hours of food deprivation, NOP KO mice emitted longer bouts of licking than wildtypes, suggesting that under hungry conditions NOC may also contribute to hedonic aspects of feeding. Together, these results suggest differential roles for NOC in the motivational and hedonic aspects of feeding.