Food restriction and amphetamine exposure synergistically enhance accumbal dopamine D1 receptor-mediated locomotor activity

Abstract

Natural rewards such as food and drugs of abuse share the mesolimbic dopamine system, including the nucleus accumbens (NAcc), as a common neural pathway that influences appetite and addictive behavior. Ghrelin, an orexigenic hormone, acts synergistically with mesolimbic dopamine in this process. In the present study, we examined the effects of food restriction (FR) on plasma ghrelin levels and amphetamine (AMPH)-induced locomotor activity. Chronic FR (cFR) significantly enhanced AMPH-induced locomotor activity compared to normal feeding and acute FR (aFR), which was associated with increased plasma ghrelin and dopamine D1 receptor (D1R) expression levels in the NAcc. These effects were inhibited by either systemic or NAcc-specific administration of D1R or ghrelin receptor antagonists. Furthermore, rats under the aFR condition showed enhanced locomotor activity in response to intra-accumbal microinjection of the D1R agonist when pre-exposed to AMPH, whereas rats in the cFR condition showed these effects regardless of pre-exposures to either AMPH or saline. These results demonstrate that FR conditions interact with drugs of abuse via the accumbal ghrelin and D1R systems, thereby contributing to the expression of addictive behaviors. Notably, these findings suggest that dietary status should be considered during addiction treatment.