AMPA receptor subunit GluR1 downstream of D-1 dopamine receptor stimulation in nucleus accumbens shell mediates increased drug reward magnitude in food-restricted rats

Abstract

Previous findings suggest that neuroadaptations downstream of D-1 dopamine (DA) receptor stimulation in nucleus accumbens (NAc) are involved in the enhancement of drug reward by chronic food restriction (FR). Given the high co-expression of D-1 and GluR1 AMPA receptors in NAc, and the regulation of GluR1 channel conductance and trafficking by D-1-linked intracellular signaling cascades, the present study examined effects of the D-1 agonist, SKF-82958, on NAc GluR1 phosphorylation, intracranial electrical self-stimulation reward (ICSS), and reversibility of reward effects by a polyamine GluR1 antagonist, 1-NA-spermine, in ad libitum fed (AL) and FR rats. Systemically administered SKF-82958, or brief ingestion of a 10% sucrose solution, increased NAc GluR1 phosphorylation on Ser845, but not Ser831, with a greater effect in FR than AL rats. Microinjection of SKF-82958 in NAc shell produced a reward-potentiating effect that was greater in FR than AL rats, and was reversed by co-injection of 1-NA-spermine. GluR1 abundance in whole cell and synaptosomal fractions of NAc did not differ between feeding groups, and microinjection of AMPA, while affecting ICSS, did not exert greater effects in FR than AL rats. These results suggest a role of NAc GluR1 in the reward-potentiating effect of D-1 DA receptor stimulation and its enhancement by FR. Moreover, GluR1 involvement appears to occur downstream of D-1 DA receptor stimulation rather than reflecting a basal increase in GluR1 expression or function. Based on evidence that phosphorylation of GluR1 on Ser845 primes synaptic strengthening, the present results may reflect a mechanism via which FR normally facilitates reward-related learning to re-align instrumental behavior with environmental contingencies under the pressure of negative energy balance.