Differential dendritic remodeling in prelimbic cortex of male and female rats during recovery from chronic stress

Abstract

Chronic stress produces differential dendritic remodeling of pyramidal neurons in medial prefrontal cortex of male and female rats. In males, this dendritic remodeling is reversible. However, the timeline of recovery, as well as the potential for reversibility in females, is unknown. Here, we examined dendritic recovery of pyramidal neurons in layer II-II of prelimbic cortex in male and female rats following chronic restraint stress (3h/day for 10days). Dendritic morphology and spine density were analyzed immediately following the cessation of stress, or following a 7- or 10-day recovery period. Chronic stress produced apical dendritic retraction in males, which was coupled with a decrease in the density of stubby spine on apical dendrites. Further, following a 10-day recovery period, the morphology of neurons from stressed rats resembled that of unstressed rats. Male rats given a 7-day recovery period had apical dendritic outgrowth compared to unstressed rats. Immediately after cessation of stress, females showed only minimal dendritic remodeling. The morphology of neurons in stressed females resembled those of unstressed rats following only 7days of recovery, at which time there was also a significant increase in stubby spine density. Males and females also showed different changes in baseline corticosterone concentrations during recovery. These findings not only indicate that dendritic remodeling in prelimbic cortex following chronic stress is different between males and females, but also suggest chronic stress induces differential hypothalamic-pituitary-adrenal axis dysregulation in males and females. These differences may have important implications for responses to subsequent stressors.

Keywords: corticosterone; dendritic morphology; prefrontal cortex; sex differences; spine density.

FIG. 1

(A) Schematic depiction of experimental timeline for assessing dendritic morphology in chronically stressed males and females during a post-stress recovery period. Arrow represents tissue collection. (B) Schematic diagram of coronal sections through rat prefrontal cortex. The portions of prelimbic cortex from which neurons were sampled is shown (shaded areas). Coordinates indicate position relative to bregma (Paxinos and Watson, 1998). (C) Digital micrograph of Golgi-stained neuron in layer II–III of mPFC. Scale bar = 50 μm. (D) Digital micrograph demonstrating different spine types on a pyramidal neuron in layer II–III of mPFC. M, mushroom; S, stubby; T, thin. Scale bar = 5 μm.

FIG. 2

(A) Mean weight change in unstressed versus stressed male and female rats receiving a 0d, 7d, or 10d recovery. Stress attenuated weight gain in 0d Rec male and female rats. (B) Mean adrenal-weight-to-body- weight ratios (adrenal weight/100 g body weight) in unstressed versus stressed male and female rats receiving a 0d, 7d, or 10d recovery. Stress increased relative adrenal weight in 0d Rec male and female rats. Error bars represent SEM. * p < 0.05 compared to same-sex controls; † p < 0.10 compared to same-sex controls; # p < 0.05 compared to same-sex 0d Rec rats; a p < 0.05 compared to male rats.

FIG. 3

Mean serum CORT at perfusion in unstressed versus stress male and female rats receiving a 0d, 7d, or 10d recovery. While 7d Rec male rats tended to have suppressed baseline CORT, stressed females had elevated CORT at all times post-stress. Error bars represent SEM. Inset: Scatterplot of individual datapoints. Stressed female rats have a high degree of individual variability. * p < 0.05 compared to same-sex controls; † p < 0.10 compared to same-sex controls; a p < 0.05 compared to male rats.

Fig. 4

(A) Computer-assisted reconstruction of apical arbors of Golgi-stained neurons in layer II–III of PL in unstressed, 0d, 7d, and 10d Rec male and female rats. Neurons are at or near the mean for each group. Scale bar = 50 μm. (B) Mean length of apical branches in unstressed, 0d, 7d, and 10d Rec male rats with 10-μm concentric circles summed across the proximal, middle, and distal third of the arbor. 0d Rec male rats have decreased dendritic length in the middle third of the arbor, while 7d Rec male rats have increased dendritic length in the distal third. (C) Mean length of apical branches in unstressed, 0d, 7d, and 10d Rec females with 10-μm concentric circles summed across the proximal, middle, and distal third of the arbor. Stressed females have no changes in dendritic length across the apical arbor at any time post-stress. * p < 0.05 Unstressed vs 0d Rec males; † p < 0.10 Unstressed vs 0d Rec females; ‡ p < 0.05 0d Rec vs 7d Rec of same sex; # p < 0.05 0d Rec vs 10d Rec of same sex.

Fig. 5

(A) Mean length of basilar branches per tree in unstressed, 0d, 7d, and 10d Rec male rats with 10-μm concentric circles summed across the proximal, middle, and distal third of the arbor. (B) Mean length of basilar branches per tree in unstressed, 0d, 7d, and 10d Rec female rats with 10-μm concentric circles summed across the proximal, middle, and distal third of the arbor. Overall basilar branch length did not vary across stress condition or sex. Error bars represent SEM.

Fig. 6

(A) Linear regression for average PL apical branch length in unstressed female rats vs. serum CORT. (B) Linear regression for average PL apical branch length in 10d Rec female rats vs. serum CORT. Apical branch length is negatively correlated with serum CORT un unstressed females. This correlation is reversed in 10d Rec female rats.

Fig. 7

(A) Total apical spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. (B) Apical stubby spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. Chronic stress decreased stubby spine density in 0d Rec male rats, but increase spine density in 7d Rec females. (C) Apical thin spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. (D) Apical mushroom spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. Error bars represent SEM. * p < 0.05 Unstressed vs 0d Rec males; † p < 0.05 Unstressed vs 7d Rec females; a p < 0.05 0d Rec females vs 0d Rec males.

Fig. 8

(A) Estimated number of spines on apical terminal dendrites in unstressed 0d, 7d, and 10d Rec male and female rats. Chronic stress decreased the total number of terminal spines in both male and female 0d Rec rats compared to unstressed rats. (B) Estimated number of stubby spines on apical terminal dendrites in unstressed 0d, 7d, and 10d Rec male and female rats. In males, chronic stress decreased estimated stubby spine number in 0d Rec rats compared to both unstressed and 10d Rec rats, and this decrease approached significance compared to 7d Rec rats. (C) Estimated number of thin spines on apical terminal dendrites in unstressed 0d, 7d, and 10d Rec male and female rats. Chronic stress decreased the estimated number of thin spines in both male and female 0d Rec rats compared to unstressed rats. (D) Estimated number of mushroom spines on apical terminal dendrites in unstressed 0d, 7d, and 10d Rec male and female rats. Chronic stress decreased the estimated number of mushroom spines in both male and female 0d Rec rats compared to unstressed rats. # p < 0.05 0d Rec vs all other groups; * p < 0.05 0d Rec vs Unstressed and 10d Rec males; ^ p < 0.07 0d Rec vs 7d Rec males; † p < 0.05 Unstressed vs 7d Rec females; ‡ p < 0.07 7d Rec vs 10d Rec females.

Fig. 9

(A) Total basilar spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. Chronic stress decreased basilar spine density in 0d and 7d Rec male rats. (B) Basilar stubby spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. (C) Basilar thin spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. (D) Basilar mushroom spine density in unstressed, 0d, 7d, and 10d Rec male and female rats. Chronic stress decrease mushroom spine density in 0d and 7d Rec rats. Error bars represent SEM. * p < 0.05 Unstressed vs 7d Rec males; † p < 0.10 Unstressed vs 0d Rec males; a p < 0.05 7d Rec females vs 7d Rec males; ‡ p < 0.05 Unstressed vs 0d Rec; # p < 0.10 Unstressed vs 7d Rec.

Fig. 10

(A) Estimated number of total basilar terminal spines in unstressed 0d, 7d, and 10d Rec male and female rats. (B) Estimated number of stubby basilar terminal spines in unstressed 0d, 7d, and 10d Rec male and female rats. (C) Estimated number of thin basilar terminal spines in unstressed 0d, 7d, and 10d Rec male and female rats. (D) Estimated number of mushroom basilar terminal spines in unstressed 0d, 7d, and 10d Rec male and female rats.