The medial prefrontal cortex is crucial for the maintenance of persistent licking and the expression of incentive contrast

Abstract

We examined the role of the medial prefrontal cortex (mPFC) in reward processing and the control of consummatory behavior. Rats were trained in an operant licking procedure in which they received alternating access to solutions with relatively high and low levels of sucrose (20 and 4%, w/v). Each level of sucrose was available for fixed intervals of 30 s over 30 min test sessions. Over several days of training, rats came to lick persistently when the high level of sucrose was available and suppressed licking when the low level of sucrose was available. Pharmacological inactivations of the mPFC, specifically the rostral part of the prelimbic area, greatly reduced intake of the higher value fluid and only slightly increased intake of the lower value fluid. In addition, the inactivations altered within-session patterns and microstructural measures of licking. Rats licked equally for the high and low levels of sucrose at the beginning of the test sessions and “relearned” to reduce intake of the low value fluid over the test sessions. Durations of licking bouts (clusters of licks with inter-lick intervals <0.5 s) were reduced for the high value fluid and there were many more brief licking bouts (<1 s) when the low value fluid was available. These effects were verified using an alternative approach (optogenetic silencing using archaerhodopsin) and were distinct from inactivation of the ventral striatum, which simply increased overall intake. Our findings suggest that the mPFC is crucial for the maintenance of persistent licking and the expression of learned feeding strategies.

Feeding-modulatory effects of mu-opioids in the medial prefrontal cortex: a review of recent findings and comparison to opioid actions in the nucleus accumbens

“…For each orexigenic manipulation of the Acb, it was found that reducing neural activity in the hypothalamus (via either glutamate blockade or GABA stimulation) eliminated the Acb-mediated hyperphagia, indicating that intact hypothalamic function is necessary for the expression of Acb-driven hyperphagia. This conclusion is further bolstered by recent optogenetic studies showing that silencing the Acb shell increases consumption, stimulating that region decreases consumption, and that these effects are mediated through projections of D1-bearing Acb neurons projecting to the hypothalamus (O’Connor et al 2015; Parent et al 2015). Further work indicated that either GABA receptor or μ-OR stimulation in the Acb shell provoked expression of the immediate-early gene, Fos, in several hypothalamic regions, including the LH-PeF (Baldo et al 2004; Stratford and Kelley 1999; Zhang and Kelley 2000).…”

“…The precise mechanisms underlying these effects are unclear, but a number of possibilities come to mind. For example, because electrophysiological studies have suggested that units in vmPFC encode information regarding food-associated taste characteristics (including taste hedonics) and reward valuation (Jezzini et al 2013; Parent et al 2015), the intra-PFC μ-OR-mediated increase in food intake could reflect an enhancement of the hedonic properties of the food. Nevertheless, the μ-OR stimulation-induced pattern of bout initiation coupled with the shortening of individual bouts indicates that commerce with the food does not sustain the relatively longer periods of consumption that might be expected with increased gustatory reward (Davis and Smith 1992; Ostlund et al 2013; Spector et al 1998).…”

“…In a general sense, medial PFC plays a prominent role in modulating ongoing behavior, and inhibiting disadvantageous behavior, to match prevailing (and often changing) contingencies; examples include the regulation of set-shifting (Birrell and Brown 2000; Dalley et al 2004; Floresco et al 2008; Ragozzino et al 1999) and the expression of extinction learning (Eddy et al 2016; Peters et al 2008; Quirk et al 2006; Rhodes and Killcross 2007). With regard to ingestive behaviors, recent findings that inhibition of ventromedial PFC disturbs the temporal distribution of licking bouts in an incentive-contrast paradigm, ‘misaligning’ licking bout durations to high and low concentrations of sucrose (Parent et al 2015). This finding suggests a PFC-based operation that matches the temporal duration of licking bouts with the reward value of the food.…”

Dorsal Anterior Cingulate Cortex: A Bottom-Up View

“…One theory is that the dACC carries a value signal that allows decision makers to overcome a tendency to succumb to temptation (Blanchard et al 2015, Hillman & Bilkey 2010). (For related ideas, see Parent et al 2015, Passetti et al 2002, and Rushworth et al 2003.) Another complementary idea is that the dACC encodes the cost of failing to persist, thereby recruiting self-control (Blanchard & Hayden 2014, Kurzban et al 2013).…”

Cumulative effects of social stress on reward-guided actions and prefrontal cortical activity

“…Self-paced, instrumental sucrose preference task. The task design was inspired by prior studies involving ratio schedules (23), incentive contrast (24,25), and head fixation for awake, mobile mice (26). For the behavioral setup, the mouse was head-fixed but could move its body freely on a treadmill, either a skewered Styrofoam ball or a 7"-diameter plexiglass running disk, to reduce the stressful effect of restraint.…”