Michael E. Nizhnikov, Ph.D. - US grants

DESCRIPTION (provided by applicant): Fetal alcohol exposure in humans is recognized as a likely contributor to alcohol abuse during adolescence and adulthood. Exposure to ethanol in laboratory rodents during the first two postnatal weeks is widely used as an experimental model of human fetal alcohol exposure, given its accepted value as a neurological model for the third trimester of human fetal development. Such early exposure has been shown to significantly increase ethanol intake later in life. The neural mechanisms susceptible to early ethanol exposure and responsible for the reported increased propensity for ethanol intake are yet to be investigated. The endogenous dynorphin/kappa opioid receptor system is of great interest due to its possible involvement in diminishing ethanol intake through modulation of its aversive properties. There is some experimental evidence, although still limited, that motivational properties of the dynorphin/kappa opioid receptor system change across ontogeny, with newborn and infant rats finding activation of kappa opioid receptors appetitive and adult rats demonstrating aversive responding. These findings, in turn, suggest ontogenetic differences in the kappa opioid receptor involvement in ethanol intake and reinforcement based, presumably, on ontogenetic changes in motivational properties of the dynorphin/ kappa opioid receptor system. The present proposal will test the hypothesis that the motivational properties of the kappa opioid system switch from appetitive to aversive during the 2nd postnatal week, with this switch being parallel to an ontogenetic increase in sensitivity to the aversive properties of ethanol. Exposure to ethanol early in life, especially during the period when the dynorphin/kappa opioid receptor system functions to mediate appetitive reinforcement, alters the aversive motivational properties of this system, with this alteration contributing to the propensity to consume large amounts of ethanol without experiencing its aversive consequences later in ontogeny. PUBLIC HEALTH RELEVANCE: Exposure to alcohol early in life is a major contributing factor to future use and abuse of the drug. The kappa/dynorphin opioid system seems to be critically involved in modulating the aversive properties of ethanol during adulthood. The function of this system may change as a result of early alcohol exposure. The proposed experiments will dissect the changes in the motivational properties of ethanol and the kappa/dynorphin system across the first two weeks of life. Furthermore, these studies will investigate possible effect of early ethanol exposure on the motivational properties of ethanol and kappa opioid system.

Recent data implicate the K opioid system in ethanol acceptance and reinforcement during infancy and adulthood. Pharmacological blockade of K opioid receptors enhances ethanol intake and reinforcing properties in adult rodents, whereas endogenous activity at K receptors is essential for infants to find ethanol appetitive. Furthermore, activation of the K opioid system is aversive for adult rats. In contrast, in infant rats, central activation of this system is extremely reinforcing. The present proposal will test the hypothesis that the K opioid system switches from mediating appetitive to aversive properties of ethanol between the first and the second postnatal week and that this ontogenetic switch occurs when motivational properties of K opioid activation become aversive instead of appetitive. Finally, changes in the K opioid system following central ethanol administration will be assessed during the first two weeks of postnatal life.

? DESCRIPTION (provided by applicant): Prenatal alcohol exposure has been shown to increase the probability of use and abuse of ethanol later in life. One question remaining to be answered is, can it also be transmitted across generations? Our data suggest that low/moderate ethanol exposure results in increased ethanol intake and reduced sensitivity to ethanol's hypnotic effects during puberty not only in those infant rats exposed to ethanol in the womb but also in their offspring. Our central hypothesis is that inheritance of ethanol use/abuse liability s transgenerational and associated with variations in DNA methylation in specific brain regions known to be involved in alcohols rewarding proper- ties. The transformative objective of the present proposal is to identify the specific genes in these brain areas that are involved in ethanol programming as well as the lineage involved in transgenerational transmission of the ethanol-exposed phenotype. This project uses an animal model of prenatal ethanol exposure to investigate the transmission of increased liability for ethanol abuse in the offspring directly exposed to alcohol in the womb and their progeny. Specific Aim 1 will determine the contribution of maternal and paternal lineages in the effect of gestational ethanol exposure on ethanol sensitivity and consumption in three generation of off- spring. This will be achieved through testing prenatally exposed animals and breeding male and female rats prenatally exposed (F1) to 1) ethanol, 2) water, or 3) non-manipulated in all possible combinations (9; see table in approach) to determine the lineage involved in transmission. Our hypothesis, that inheritance is through paternal lineage, will be tested by examining ethanol intake at postnatal day (PD) 14 and in adolescence, and sensitivity to the hypnotic effects (loss of righting reflex test) of ethanl at PD 42. Specific Aim 2 will identify the effect of ethanol exposure during gestation on genome-wide DNA methylation of F1 and F2 of the extreme lineage (affected lineage and control), using a whole-genome bisulfate sequencing technique. Results obtained after completion of this work will allow us to direct future work towards target genes involved in the transmission of ethanol-exposed phenotype, and to better understand the mechanisms involved in transgenerational inheritance of increased risk for ethanol abuse.