Involvement of the Cannabinoid CB1 Receptor in Modulation of Dopamine Output in the Prefrontal Cortex Associated with Food Restriction in Rats

Increase in dopamine output on corticolimbic structures, such as medial prefrontal cortex (mPFC) and nucleus accumbens, has been related to reward effects associated with palatable food or food presentation after a fasting period. The endocannabinoid system regulates feeding behavior through a modulatory action on different neurotransmitter systems, including the dopaminergic system. To elucidate the involvement of type 1 cannabinoid receptors in the regulation of dopamine output in the mPFC associated with feeding in hungry rats, we restricted the food availability to a 2-h period daily for 3 weeks. In food-restricted rats the extracellular dopamine concentration in the mPFC increased starting 80 min before food presentation and returned to baseline after food removal. These changes were attenuated in animals treated with the CB1 receptor antagonist SR141716. To better understand how food restriction can change the response of mesocortical dopaminergic neurons, we studied several components of the neuronal circuit that regulates dopamine output in the mPFC. Patch-clamp experiments revealed that the inhibitory effect of the CB1 receptor agonist WIN 55,212-2 on GABAergic sIPSC frequency was diminished in mPFC neurons of FR compared to fed ad libitum rats. The basal sIPSC frequency resulted reduced in mPFC neurons of food-restricted rats, suggestive of an altered regulation of presynaptic GABA release; these changes were accompanied by an enhanced excitability of mPFC and ventral tegmental area neurons. Finally, type 1 cannabinoid receptor expression in the mPFC was reduced in food-restricted rats. Together, our data support an involvement of the endocannabinoid system in regulation of dopamine release in the mPFC through changes in GABA inhibitory synapses and suggest that the emphasized feeding-associated increase in dopamine output in the mPFC of food-restricted rats might be correlated with an altered expression and function of type 1 cannabinoid receptor in this brain region.