Extinction of cue-evoked food-seeking recruits a GABAergic interneuron ensemble in the dorsal medial prefrontal cortex of mice

After a period of forced abstinence, rats treated with the norepinephrine neurotoxin DSP-4 still exhibit preserved food-seeking behavior and prefrontal cortex fos-expressing neurons

Aims

Relapse is a common characteristic of compulsive behaviors like addiction, where individuals tend to return to drug use or overeating after a period of abstinence. PFC (prefrontal cortex) neuronal ensembles are required for drug and food-seeking behaviors and are partially regulated by Norepinephrine (NE). However, the contributions of neuromodulators, such as the adrenergic system, in food-seeking behavior are not fully understood.

Main methods

To investigate this, we trained male and female rats to press a lever in an operant chamber to obtain banana-flavored food pellets for ten days. We then administered DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride), a neurotoxin that diminishes norepinephrine levels in the brain. The rats were kept in their home cages for ten more days before being returned to the operant chambers to measure food-seeking behavior.

Key findings

Despite receiving DSP-4, the PFC neuronal ensembles measured by Fos and food-seeking behavior did not differ between groups, but rather sex.

Significance

Although both NE and Fos expressing neurons are implicated in food-seeking, they do not seem to be involved in a cue-contextual induced re-exposure response.

Extinction of Cocaine Memory Depends on a Feed-Forward Inhibition Circuit Within the Medial Prefrontal Cortex

BACKGROUND

Cocaine-associated environments (i.e., contexts) evoke persistent memories of cocaine reward and thereby contribute to the maintenance of addictive behavior in cocaine users. From a therapeutic perspective, enhancing inhibitory control over cocaine-conditioned responses is of pivotal importance but requires a more detailed understanding of the neural circuitry that can suppress context-evoked cocaine memories, e.g., through extinction learning. The ventral medial prefrontal cortex (vmPFC) and dorsal medial prefrontal cortex (dmPFC) are thought to bidirectionally regulate responding to cocaine cues through their projections to other brain regions. However, whether these mPFC subregions interact to enable adaptive responding to cocaine-associated contextual stimuli has remained elusive.

METHODS

We used antero- and retrograde tracing combined with chemogenetic intervention to examine the role of vmPFC-to-dmPFC projections in extinction of cocaine-induced place preference in mice. In addition, electrophysiological recordings and optogenetics were used to determine whether parvalbumin-expressing inhibitory interneurons and pyramidal neurons in the dmPFC are innervated by vmPFC projections.

RESULTS

We found that vmPFC-to-dmPFC projecting neurons are activated during unreinforced re-exposure to a cocaine-associated context, and selective suppression of these cells impairs extinction learning. Parvalbumin-expressing inhibitory interneurons in the dmPFC receive stronger monosynaptic excitatory input from vmPFC projections than local dmPFC pyramidal neurons, consequently resulting in disynaptic inhibition of pyramidal neurons. In line with this, we show that chemogenetic suppression of dmPFC parvalbumin-expressing inhibitory interneurons impairs extinction learning.

CONCLUSIONS

Our data reveal that vmPFC projections mediate extinction of a cocaine-associated contextual memory through recruitment of feed-forward inhibition in the dmPFC, thereby providing a novel neuronal substrate that promotes extinction-induced inhibitory control.