Role of NOS‐NO signaling in clonidine‐ethanol evoked synergistic behavioral impairment

Abstract

Clonidine‐ethanol combination induces synergistic behavioral impairment in rats as measured by rotorod performance and loss of righting reflex (LORR) duration. We tested the hypothesis that NOS‐NO signaling in the locus ceruleus (LC) is implicated in this interaction. Pretreatment (i.c.) with non‐selective NOS inhibitor (L‐NAME) or nNOS‐selective inhibitor (NPLA) enhanced the impairment of rotorod performance caused by clonidine‐ethanol combination. Prolongation of behavioral impairment was caused by L‐NAME enhancement of the effect of ethanol, not clonidine. LORR caused by clonidine‐ethanol combination was abolished by eNOS‐selective inhibition (L‐NIO), but not nNOS inhibition. Western blot analyses complemented the pharmacological evidence by demonstrating that clonidine‐ethanol combination inhibits phosphorylation (activation) of nNOS (p‐nNOS) and increases levels of phosphorylated eNOS (p‐eNOS) in the LC; the change in p‐nNOS, but not p‐eNOS, was paralleled by similar change in LC p‐ERK1/2. Therefore, NOS‐derived NO in the LC is differentially involved in underlying mechanisms for clonidine‐ethanol induced behavioral impairment. A decrease in nNOS‐derived NO contributes to impaired rotorod performance, while an increase in eNOS‐derived NO contributes to LORR duration elicited by clonidine‐ethanol combination. [Supported by NIH grants 5F31AA015472 (TSB) and 2R01AA07839 (ARA)]