Nucleus accumbens dopamine release modulation by mesolimbic GABAA receptors-an in vivo electrochemical study
by
Xi ZX, Stein EA
Neuroscience Graduate Program,
Medical College of Wisconsin,
Milwaukee, WI 53226, USA.
Brain Res 1998 Jul 6; 798(1-2):156-65


ABSTRACT

The role of GABA receptors in regulating the mesolimbic dopamine (DA) system and drug reinforced behaviors has not been well characterized. Using fast-cyclic voltammetry, the effects of specific GABA receptor modulation on DA release in the nucleus accumbens (NAcc) and heroin self-administration (SA) behavior was investigated. The GABAA agonist muscimol, administered either intravenously or directly into the ventral tegmental area (VTA), significantly increased DA release in the NAcc in 7 of the 10 rats tested. DA release decreased in the remaining three rats; both effects were blocked by pretreatment with the GABAA receptor antagonist bicuculline. In contrast, the GABAB agonist baclofen decreased, while 2-OH-saclofen (a GABAB antagonist) increased DA release in the NAcc. However, when VTA GABAB receptors were previously activated or inactivated by microinjections of baclofen or 2-OH-saclofen, systemic injections of muscimol caused an inhibition of NAcc DA release. These results suggest that GABAA receptors may be co-localized on both DA neurons and non-DA (GABAergic) interneurons in the VTA, with the effects of GABAA determined by the net effect of both direct inhibition and indirect disinhibition of DA neurons. Finally, although a DA releaser, muscimol was neither self-administered in drug naive rats, nor did it substitute for heroin in rats previously trained to self-administer heroin, suggesting that GABAA receptors appear to play a complex role in mediating drug reinforcement, depending upon the dynamic functional state of GABAA receptors on both tegmental DA and non-DA neurons.
Pain
Heroin
Fentanyl
G protein
Tramadol
The "rush"
Microflora
Tolerance
Heroin Inc
Nociceptin
Speedballs
Remifentanil
Endomorphins
Opiated worms
Monkeys on heroin
Intravenous heroin
Heroin maintenance
Heroin and nitric oxide
The extended amygdala
Baclofen, dopamine and heroin
Heroin and the pleasure centres