Behavioral and endocrine changes following antisense oligonucleotide-induced reduction in the rat NOP receptor

Rationale. Compared with the use of classic receptor ligands, antisense oligonucleotides (ASO) targeted at specific central nervous system receptors are an effective alternative in experiments designed to examine the behavioral role of such systems. Objectives. The nociception/orphaninFQ (N/OFQ) system has been implicated in mediating endocrine function, feeding, stress, pain, anxiety, and the rewarding effects of drugs of abuse. The objective of the current study was to examine whether long-term ASO-induced downregulation of N/OFQ's receptor (NOP) produced changes in endocrine, anxiety, nociception and ethanol's (EtOH's) locomotor activating properties. Methods. Male Long Evans rats were implanted with osmotic mini-pumps containing ASO for the NOP receptor. ASO was chronically infused for 26 days and, during this time, multiple behavioral and physiological measurements were conducted. Results. ASO infusion significantly reduced expression of the NOP receptor in brain, confirmed by significant reductions of OFQ-stimulated [S-35]-GTPgammaS binding in the paraventricular nucleus, prefrontal cortex, and septum. Behavioral changes were observed in ASO-treated animals including higher body temperature, increased water intake, decreased corticosterone (CORT) levels, decreased grooming in the open field, increased tail-flick latency, shorter durations on the open arms of the elevated plus maze, and heightened locomotor activity following EtOH. Conclusions. These behavioral, physiological and endocrine changes are relatively consistent with previous findings with agonists and antagonists for the NOP receptor and, taken together, suggest that ASO-induced downregulation of the NOP receptor is an effective method for studying the N/OFQ system.