Involvement of nucleus accumbens AMPA receptor trafficking in augmentation of D- amphetamine reward in food-restricted rats.

RATIONALE: Chronic food restriction (FR) increases behavioral responsiveness to drugs of abuse and associated environments. Pre- and postsynaptic neuroadaptations have been identified in the mesoaccumbens dopamine pathway of FR subjects but the mechanistic basis of increased drug reward magnitude remains unclear.
OBJECTIVES: Effects of FR on basal and D-amphetamine-induced trafficking of AMPA receptor subunits to the nucleus accumbens (NAc) postsynaptic density (PSD) were examined, and AMPA receptor involvement in augmentation of D-amphetamine reward was tested.
MATERIALS AND METHODS: FR and ad libitum fed (AL) rats were injected with D-amphetamine (2.5 mg/kg, i.p.) or vehicle. Brains were harvested and subcellular fractionation and Western analyses were used to assess AMPA receptor abundance in NAc homogenate and PSD fractions. A follow-up experiment used a curve-shift protocol of intracranial self-stimulation to assess the effect of 1-naphthylacetyl spermine (1-NASPM), a blocker of Ca(2+)-permeable AMPA receptors, on rewarding effects of D-amphetamine microinjected in NAc shell.
RESULTS: FR increased GluA1 in the PSD, and D-amphetamine increased p-Ser845-GluA1, GluA1, GluA2, but not GluA3, with a greater effect in FR than AL rats. D-amphetamine lowered reward thresholds, with greater effects in FR than AL rats, and 1-NASPM selectively reversed the enhancing effect of FR.
CONCLUSIONS: Results suggest that FR leads to increased synaptic incorporation of GluA1 homomers to potentiate rewarding effects of appetitive stimuli and, as a maladaptive byproduct, D-amphetamine. The D-amphetamine-induced increase in synaptic p-Ser845-GluA1, GluA1, and GluA2 may contribute to the rewarding effect of D-amphetamine, but may also be a mechanism of synaptic strengthening and behavior modification.