Nucleus incertus Orexin2 receptors mediate alcohol seeking in rats

• Published in: Neuropharmacology 2016-11, Vol.110 (Pt A), p.82-91
• Main Authors: Kastman, Hanna E., Blasiak, Anna, Walker, Leigh, Siwiec, Marcin, Krstew, Elena V., Gundlach, Andrew L., Lawrence, Andrew J.
• Format: Article
• Language: English
• Subjects: Alcohol; Animals; Drug-Seeking Behavior - drug effects; Drug-Seeking Behavior - physiology; Ethanol - administration & dosage; Male; Microinjections; Nucleus incertus; Orexin; Orexin Receptor Antagonists - administration & dosage; Orexin Receptors - physiology; Raphe Nuclei - drug effects; Raphe Nuclei - physiology; Rats; Rats, Wistar; Reinstatement; Relaxin-3; Self Administration; Stress; Yohimbine - administration & dosage
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/j.neuropharm.2016.07.006

Alcoholism is a chronic relapsing disorder and a major global health problem. Stress is a key precipitant of relapse in human alcoholics and in animal models of alcohol seeking. The brainstem nucleus incertus (NI) contains a population of relaxin-3 neurons that are highly responsive to psychological stressors; and the ascending NI relaxin-3/RXFP3 signalling system is implicated in stress-induced reinstatement of alcohol seeking. The NI receives orexinergic innervation and expresses orexin1 (OX1) and orexin2 (OX2) receptor mRNA. In alcohol-preferring (iP) rats, we examined the impact of yohimbine-induced reinstatement of alcohol seeking on orexin neuronal activation, and the effect of bilateral injections into NI of the OX1 receptor antagonist, SB-334867 (n = 16) or the OX2 receptor antagonist, TCS-OX2-29 (n = 8) on stress-induced reinstatement of alcohol seeking. We also assessed the effects of orexin-A on NI neuronal activity and the involvement of OX1 and OX2 receptors using whole cell patch-clamp recordings in rat brain slices. Yohimbine-induced reinstatement of alcohol seeking activated orexin neurons. Bilateral NI injections of TCS-OX2-29 attenuated yohimbine-induced reinstatement of alcohol seeking. In contrast, intra-NI injection of SB-334867 had no significant effect. In line with these data, orexin-A (600 nM) depolarized a majority of NI neurons recorded in coronal brain slices (18/28 cells), effects prevented by bath application of TCS-OX2-29 (10 μM), but not SB-334867 (10 μM). These data suggest an excitatory orexinergic input to NI contributes to yohimbine-induced reinstatement of alcohol seeking, predominantly via OX2 receptor signalling. •Yohimbine-induced reinstatement of alcohol seeking activates orexin neurons in rats.•Microinjection of an OX2 receptor antagonist into the nucleus incertus attenuates alcohol seeking in rats.•Orexin-A induced depolarization of nucleus incertus neurons is prevented by an OX2, but not OX1 receptor antagonist.