Effects of maternal behaviors in rats with neuropathic pain on emotions of offspring rats and the relationship with DNA methylation in amygdala

Abstract

Objective To investigate the effects of maternal behaviors in the rats with neuropathic pain (NP) on emotions of offspring rats and the relationship with DNA methylation in the amygdala. Methods Forty-eight healthy adult Sprague-Dawley rats (24 males and 24 females), weighing 200-250 g, were used in the study.Twelve female and 12 male rats were randomly selected, and NP was induced by chronic constriction injury (CCI). Each female rat was mated with one male rat at 10 days after CCI.Forty-eight F1 generation rats of maternal rats with NP were randomly divided into 2 groups (n=24 each) using a random number table: NP1 group and NP2 group.Forty-eight F1 generation rats of normal maternal rats were randomly divided into 2 groups (n=24 each) using a random number table: S1 group and S2 group.The F1 generation rats were cross-fed immediately after birth between group NP2 and group S2, and fed by their own mother rats in NP1 and S1 groups.All the offspring rats were fed to 21 days after birth by the maternal rats selected, and separately fed to 30 days after birth, and then subjected to behavioral testing.Retrieving and licking pups were recorded after delivery in maternal rats to evaluate the maternal behaviors.The mechanical and thermal paw withdrawal thresholds were measured in the offspring rats.Elevated plus maze and open field tests were conducted to detect anxiety and depression behaviors in the offspring rats.At 1 day after completion of behavioral testing, the expression of DNA methyltransferase 1 (DNMT1) and DNA methyltransferase 3a and 3b in the amygdala was detected by Western blot analysis. Results Compared with S1 or S2 groups, the latency to lick pups, latency to retrieve pups, and total retrieval time were significantly prolonged, and the total time spent licking pups was significantly shortened in NP1 group or NP2 group(P 0.05). Compared with group S1, the ratios of time spent in the open arm to the closed arm and of time spent in the central square to the peripheral square were significantly decreased, DNMT1 expression in the amygdala was significantly up-regulated, and the total DNA methylation was increased in the offspring rats in S2 and NP1 groups (P<0.05). Compared with group NP2, the ratios of time spent in the open arm to the closed arm and of time spent in the central square to the peripheral square were significantly decreased, DNMT1 expression in the amygdala was significantly up-regulated, and the total DNA methylation was increased in the offspring rats in S2 and NP1 groups (P<0.05). Conclusion Decreased maternal behaviors in the rats with NP results in negative emotions including anxiety and depression in the offspring rats, and the mechanism is related to increased DNA methylation in the amygdala of the offspring rats. Key words: Neuralgia; Maternal behavior; Amygdala; DNA methylation