Abstract
The medial prefrontal cortex (mPFC) is a key brain region for the control of consummatory behavior. Neuronal activity in this area is modulated when rats initiate consummatory licking and reversible inactivations eliminate reward contrast effects and reduce a measure of palatability, the duration of licking bouts. Together, these data suggest the hypothesis that rhythmic neuronal activity in the mPFC is crucial for the control of consummatory behavior. The muscarinic cholinergic system is known to regulate membrane excitability and control low-frequency rhythmic activity in the mPFC. Muscarinic receptors (mAChRs) act through KCNQ (Kv7) potassium channels, which have recently been linked to the orexigenic peptide ghrelin. To understand if drugs that act on KCNQ channels within the mPFC have effects on consummatory behavior, we made infusions of several muscarinic drugs (scopolamine, oxotremorine, physostigmine), the KCNQ channel blocker XE-991, and ghrelin into the mPFC and evaluated their effects on consummatory behavior. A consistent finding across all drugs was an effect on the duration of licking bouts when animals consume solutions with a relatively high concentration of sucrose. The muscarinic antagonist scopolamine reduced bout durations, both systemically and intra-cortically. By contrast, the muscarinic agonist oxotremorine, the cholinesterase inhibitor physostigmine, the KCNQ channel blocker XE-991, and ghrelin all increased the durations of licking bouts when infused into the mPFC. Our findings suggest that cholinergic and ghrelinergic signaling in the mPFC, acting through KCNQ channels, regulates the expression of palatability.
Highlights
Consummatory behavior modulates neuronal activity in the medial prefrontal cortex of rats and primates (Petykó et al, 2009, 2015; Bouret and Richmond, 2010; Horst and Laubach, 2012, 2013)
As reversible inactivations of the agranular insular cortex (AIC) and medial prefrontal cortex (mPFC) have comparable effects on palatability driven feeding (Baldo et al, 2015), we propose that the two areas work together with basolateral amygdala (BLA) to regulate consummatory behavior, by enabling the conversion of reward values into control signals that guide action selection
As the orexigenic peptide ghrelin has recently been shown to act on the same KCNQ channels (Shi et al, 2013), we evaluated its actions within the medial prefrontal cortex (mPFC) in some of the same animals, and found similar behavioral effects to the drugs that enhanced cholinergic tone and blocked KCNQ channels
Summary
Consummatory behavior modulates neuronal activity in the medial prefrontal cortex (mPFC) of rats and primates (Petykó et al, 2009, 2015; Bouret and Richmond, 2010; Horst and Laubach, 2012, 2013). A recent study from our group (Horst and Laubach, 2013) found that population activity in the rostral prelimbic cortex was strongly modulated at the moment when rats initiated licking. These changes in spike activity were coterminous with 4–8 Hz phase locking in simultaneously recorded field potentials. Following inactivation of the mPFC, animals responded as if they were naive to the task We interpreted these findings as evidence for the rostral mPFC being crucial for the expression of incentive contrast and for the deployment of learned feeding strategies
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