Chemogenetic modulation of the medial prefrontal cortex regulates resistance to acute stress-induced cognitive impairments

Abstract

The medial prefrontal cortex (mPFC) has been implicated in regulating resistance to the effects of acute uncontrollable stress. We previously showed that mPFC-lesioned animals exhibit impaired object recognition memory after acute exposure to a brief stress that had no effect in normal animals. Here, we used designer receptors exclusively activated by designer drugs to determine how modulating mPFC activity affects recognition-memory performance under stressful conditions. Specifically, animals with chemogenetic excitation or inhibition of the mPFC underwent either a brief ineffective stress (20-min restraint + 20 tail shocks) or a prolonged effective stress (60-min restraint + 60 tail shocks). Subsequent recognition memory tests showed that animals with chemogenetic mPFC inhibition exposed to brief stress showed impairment in an object recognition memory task, whereas those with chemogenetic mPFC excitation exposed to prolonged stress did not. Thus, the present findings the decreased mPFC activity exacerbates acute stress effects on memory function whereas increased mPFC activity counters these stress effects provide evidence that the mPFC bidirectionally modulates stress resistance.

Keywords: acute stress; chemogenetic; medial prefrontal cortex; recognition memory; stress resistance.

Fig. 1

G_i-DREADD expression in the mPFC. (A, B) Representative photomicrograph and histological reconstruction of the mPFC of rats expressing virally transduced hM4Di, detected by monitoring mCherry fluorescence (red). (C, D) Representative images of hM4Di-mCherry (red) and c-Fos (green) expression in VEH- and CNO-administered rats exposed to a 20-min stress or control (unstressed) conditions. (E) Quantification of c-Fos⁺ cells in the mPFC of VEH- and CNO-administered rats. Scale bar = 200 μm. Data are presented as means ± SEM (error bars) (^*P < 0.05). (F, G) Representative images of hM4Di and EGFP expression in the mPFC of VEH- and CNO-administered rats that were exposed to 20-min or 60-min stress. Right: magnified images of areas in dotted rectangles at left. Scale bar = 500 μm.

Fig. 2

An ineffective brief (20-min) stress impairs recognition memory in rats with DREADD-mediated inhibition of mPFC activity. (A) Experimental procedure. (B–D) Time spent exploring 2 identical objects placed at left (L) and right (R) sides (counterbalanced) of the open-field box during the familiarization phase, and time spent exploring a novel (N) versus familiar (F) object during the test phase in VEH- and CNO-administered rats with mPFC-infused hM4Di-AAV or EGFP–AAV. (E–G) Preference percent for the novel object in VEH- and CNO-administered rats infused with hM4Di-AAV or EGFP–AAV. ^*, Significantly greater time spent exploring the novel object than the familiar object; ^**, CNO-administered rats with 20-min stress showed a significantly lower preference for the novel object than rats in other groups. Error bars represent SEM.

Fig. 3

Gq-DREADD expression in the mPFC. (A, B) Representative photomicrograph and histological reconstruction of the mPFC of a rat expressing virally transduced hM3Dq, detected by monitoring mCherry fluorescence (red). (C, D) Representative images of hM3Dq-mCherry (red) and c-Fos (green) expression in VEH- and CNO-administered rats exposed to a 60-min stress or control (unstressed) conditions. (E) Quantification of c-Fos⁺ cells in the mPFC of VEH- and CNO-administrated rats. Scale bar = 200 μm. (F) Representative images of EGFP expression in the mPFC of VEH- and CNO-administered rats with 60-min stress exposure. Right: magnified images of areas in dotted rectangles at left. Scale bar = 500 μm. Data are presented as means ± SEM (error bars) (^*P < 0.05).

Fig. 4

DREADD-mediated mPFC excitation counteracts acute stress effects on memory. (A) Experimental procedure. (B, C) Exploration time for 2 identical objects placed at left (L) and right (R) sides of an open-field box during the familiarization phase, and exploration time for a novel (N) versus familiar (F) object during the test phase, in VEH- and CNO-administered rats with mPFC-infused hM3Dq-AAV or EGFP–AAV. (D) Preference for the novel object by VEH- and CNO-administered rats infused with hM3Dq-AAV. (E) Preference percentage for the novel object by VEH- and CNO-administered rats infused with EGFP–AAV. ^*, Significantly greater time spent exploring the novel object than the familiar object; ^**, rats in the CNO group exposed to a 60-min stress had significantly higher preference percent for the novel object than equivalently stressed rats in the VEH-administered group.