Modulatory Effects of Food Restriction on Brain and Behavioral Effects of Abused Drugs

Abstract

Energy homeostasis is achieved, in part, by metabolic signals that regulate the incentive motivating effects of food and its cues, thereby driving or curtailing procurement and consumption. The neural underpinnings of these regulated incentive effects have been identified as elements within the mesolimbic dopamine pathway. A separate line of research has shown that most drugs with abuse liability increase dopamine transmission in this same pathway and thereby reinforce self-administration. Consequently, one might expect shifts in energy balance and metabolic signaling to impact drug abuse risk. Basic science studies have yielded numerous examples of drug responses altered by diet manipulation. Considering the prevalence of weight loss dieting in Western societies, and the anorexigenic effects of many abused drugs themselves, we have focused on the CNS and behavioral effects of food restriction in rats. Food restriction has been shown to increase the reward magnitude of diverse drugs of abuse, and these effects have been attributed to neuroadaptations in the dopamine-innervated nucleus accumbens. The changes induced by food restriction include synaptic incorporation of calcium-permeable AMPA receptors and increased signaling downstream of D1 dopamine receptor stimulation. Recent studies suggest a mechanistic model in which concurrent stimulation of D1 and GluA2-lacking AMPA receptors enables increased stimulus-induced trafficking of GluA1/GluA2 AMPARs into the postsynaptic density, thereby increasing the incentive effects of food, drugs, and associated cues. In addition, the established role of AMPA receptor trafficking in enduring synaptic plasticity prompts speculation that drug use during food restriction may more strongly ingrain behavior relative to similar use under free-feeding conditions.