A comparison of the effects of clonidine and CNQX infusion into the locus coeruleus and the amygdala on naloxone-precipitated opiate withdrawal in the rat

Abstract

 Both the locus coeruleus (LC) and the amygdala have been implicated in aspects of opiate dependence and withdrawal. The LC is known to be one of the most sensitive sites for precipitating withdrawal behaviors after local opiate antagonist infusions in morphine-dependent subjects. The amygdala is also known to mediate antagonist-induced withdrawal behaviors and aversive motivational states. The goal of the present study was to evaluate directly the ability of noradrenergic agonists and glutamatergic antagonists to attenuate naloxone-precipitated withdrawal behaviors when infused into the LC or the central nucleus of the amygdala (CeA). The alpha-2-noradrenergic agonists clonidine or ST-91 were infused into the CeA to compare the effects of noradrenergic activation in the CeA to the attenuation of withdrawal previously observed in rats infused with clonidine into the LC, since the LC and CeA are known to contain co-localized opiate and noradrenergic receptors. The effects of microinfusions of the non-NMDA excitatory amino acid antagonist 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX) were also infused into the LC and CeA since opiate withdrawal is associated with increased glutamatergic transmission. Intra-CeA clonidine or ST-91 (2.4 µg/0.5 µl or 1.0 µl) produced significant reductions primarily in the occurrence of irritability. Conversely, intra-CeA or intra-LC infusions of CNQX (2.5 µg/0.5 µl) significantly attenuated naloxone-precipitated withdrawal, an effect similar to the attenuation previously observed after intra-LC clonidine infusions. These data demonstrate the specific behavioral effects of altering glutamatergic and noradrenergic neurotransmission in the LC or CeA during naloxone-precipitated opiate withdrawal. Elucidation of the neuroanatomical circuitry involved in opiate withdrawal should increase our understanding of the neuroadaptations associated with drug dependence and subsequent withdrawal behavior.