Gestational exposure to ethanol (ETOH) is associated with increased vulnerability of adolescents to dependence on cigarette smoking. Given the fact that 22% of women continue to consume ETOH during their pregnancies, the increased risk of adolescent nicotine dependence in ETOH-exposed offspring is a major concern. Our preliminary studies strongly suggest that gestational exposure to ETOH may predispose abstinent human cigarette smokers to relapse, since adolescent rats exposed to ETOH, in a 3- trimester human-equivalent model, exhibit markedly enhanced reinstatement of extinguished nicotine- seeking behavior compared to pair-fed rats. The primary goal of this project is to determine how the neuronal circuitry involved in nicotine reinstatement is altered by gestational exposure to ETOH. The final common circuit in reinstatement behavior involves glutamatergic pyramidal neuron projections from the dorsal-medial prefrontal cortex (dmPFC) to the nucleus accumbens (NAcc) core. Our preliminary data indicate that ETOH-exposed adolescent rats show increased glutamate neurotransmission in this circuit, potentially due to reduced GABAergic regulation of dmPFC pyramidal neurons.
Specific aim 1 will characterize the effects of gestational ETOH on glutamatergic and GABAergic regulation of dmPFC, using in vivo microdialysis to measure glutamate levels in the NAcc following intra-dmPFC administration of selective agonists and antagonists. Then, specific aim 2 will determine whether NAcc glutamate neurotransmission is enhanced in ETOH offspring by the cue-induced reinstatement of extinguished nicotine-seeking behavior. Lastly, based on data indicating that dysfunctional GABAB receptors disinhibit dmPFC pyramidal neurons, leading to increased glutamate neurotransmission in the NAcc, both GABAB receptor expression and G-protein coupling will be analyzed. Together, these studies will clarify the neural mechanisms and neurotransmitter systems mediating the vulnerability to reinstate extinguished nicotine- seeking behavior in adolescent offspring exposed to moderate levels of ETOH in a 3-trimester human- equivalent model of gestation.
Adolescence is a peak period during which nicotine dependence is prevalent and prenatal alcohol exposure has been shown to further increase the vulnerability of adolescents to cigarette dependence. Thus, there is a definite need to further understand the neural mechanisms that are altered by gestational exposure to ethanol and which mediate the increased risk of adolescent relapse to cigarette smoking. Understanding the neural mechanisms involved will allow for improved smoking prevention strategies in alcohol exposed offspring as well as further our understanding of the long-term effects of prenatal alcohol exposure.
