Lack of intersite GABA receptor subtype antagonist effects upon μ opioid receptor agonist-induced feeding elicited from either the ventral tegmental area or nucleus accumbens shell in rats

Pretreatment with the GABA_A receptor antagonist, bicuculline or the GABA_B receptor antagonist, saclofen, into the nucleus accumbens (Nacc) shell, respectively, potentiates and reduces feeding elicited by the μ opioid agonist, [D-Ala², Nme⁴, Gly-ol⁵]-enkephalin (DAMGO), administered into the same site. DAMGO-induced feeding elicited from the ventral tegmental area (VTA) region is significantly reduced by pretreatment with saclofen into the same site indicating local GABA mediation of opioid-induced feeding in each site. Given the neuroanatomical and functional connections between the two sites, the present study evaluated the dose-dependent actions of bicuculline and saclofen pretreatment in one site upon DAMGO-induced feeding elicited from the second site. Pretreatment of either bicuculline (7.5-75 ng) or saclofen (1.5-10 μg) into the Nacc shell failed to alter the time course or magnitude of DAMGO-induced feeding elicited from the VTA region. DAMGO-induced feeding elicited from the Nacc shell was unaffected by VTA region pretreatment with either bicuculline (7.5-75 ng) or saclofen (1.5-5 μg). A higher (10 μg) saclofen dose prevented significant DAMGO-induced feeding after 1 and 4 h. Thus, although GABA receptor subtype antagonists are capable of differentially modulating DAMGO-induced feeding when both drugs are applied locally in either the VTA region or the Nacc shell, it appears that any effects between the VTA region and the Nacc shell in modulating DAMGO-induced feeding do not depend upon a GABAergic synapse in the other site.