Brain region-specific expression of genes mapped within quantitative trait loci for behavioral responsiveness to acute stress in Fisher 344 and Wistar Kyoto male rats

Abstract

Acute stress responsiveness is a quantitative trait that varies in severity from one individual to another; however, the genetic component underlying the individual variation is largely unknown. Fischer 344 (F344) and Wistar Kyoto (WKY) rat strains show large differences in behavioral responsiveness to acute stress, such as freezing behavior in response to footshock during the conditioning phase of contextual fear conditioning (CFC). Quantitative trait loci (QTL) have been identified for behavioral responsiveness to acute stress in the defensive burying (DB) and open field test (OFT) from a reciprocal F2 cross of F344 and WKY rat strains. These included a significant QTL on chromosome 6 (Stresp10). Here, we hypothesized that the Stresp10 region harbors genes with sequence variation(s) that contribute to differences in multiple behavioral response phenotypes between the F344 and WKY rat strains. To test this hypothesis, first we identified differentially expressed genes within the Stresp10 QTL in the hippocampus, amygdala, and frontal cortex of F344 and WKY male rats using genome-wide microarray analyses. Genes with both expression differences and non-synonymous sequence variations in their coding regions were considered candidate quantitative trait genes (QTGs). As a proof-of-concept, the F344.WKY-Stresp10 congenic strain was generated with the Stresp10 WKY donor region into the F344 recipient strain. This congenic strain showed behavioral phenotypes similar to those of WKYs. Expression patterns of Gpatch11 (G-patch domain containing 11), Cdkl4 (Cyclin dependent kinase like 4), and Drc1 (Dynein regulatory complex subunit 1) paralleled that of WKY in the F344.WKY-Stresp10 strain matching the behavioral profiles of WKY as opposed to F344 parental strains. We propose that these genes are candidate QTGs for behavioral responsiveness to acute stress.

Fig 1. Behavioral responses to footshock of F344 and WKY adult male rats.

(A) WKY adult male rats froze longer (freezing duration in seconds) following the footshocks in the CFC conditioning chamber. (B) Number of rears are significantly lower for WKYs compared to F344s. (C) F344s move around the chamber after the footshock significantly more than WKYs measured by distance traveled in cm. Data are presented as mean ± standard error of mean. N = 16 per group. ** P < 0.01 by Student’s t-test.

Fig 2. Phenotypic differences between the F344, WKY, and F344.WKY-Stresp10 strains in the defensive burying and open field tests.

(A, B) Both WKY and F344.WKY-Stresp10 adult male rats exhibited significantly longer latency to bury and shorter duration of burying the electrified prod compared to the F344s. (C, D) Both WKY and F344.WKY-Stresp10 rats groomed less (time spent grooming in seconds) and reared less compared to the F344s in the DB paradigm. (E) WKYs also rear significantly less than F344s in the OFT, while the number of rearing of F344.WKY-Stresp10 did not differ significantly from either parental strain. Data are presented as mean ± standard error of mean. N = 13–18 per group. ** P < 0.01 by two-way ANOVA followed by Bonferroni’s multiple comparisons test.

Fig 3. Expression analyses of candidate quantitative trait genes in the hippocampus, amygdala, and frontal cortex of F344, WKY, and F344.WKY-Stresp10 adult male rats.

(A) Candidate genes with similar expression between the WKY and F344.WKY-Stresp10 strains, but different from the F344, in two or more brain regions. (B) Genes that express a similar pattern in only one brain region. Data are presented as mean ± standard error of mean. N = 5–7 per group. * P < 0.05 and ** P < 0.01 by two-way ANOVA followed by Bonferroni’s multiple comparisons test. # P < 0.05 and ## P < 0.01 by Student’s t-test.