Maternal separation in rats induces neurobiological and behavioral changes on the maternal side

Abstract

The time after parturition is a sensitive period for mothers where they are prone to develop psychopathological symptoms. Studies investigating dams after separation from their pups (maternal separation, MS) showed that MS induces alterations similar to postpartum depression. This study aims to give further details on affected behavior and neurobiology of dams after MS. MS in rats from postnatal day 2-20 over four hours daily was performed. Upon reunion, maternal behavior, and ultrasonic vocalization (USV) of dams were measured. On the day of weaning, dams were tested for anxiety-like behavior in the elevated-plus-maze and marble burying test. Then Morc1 mRNA in the medial prefrontal cortex and Nr3c1 encoding the glucocorticoid receptor mRNA in the hippocampus were measured using real-time PCR to examine possible neurobiological correlates in psychopathology and social behavior. GABA and glutamate serum levels were analyzed by high-performance liquid chromatography as peripheral markers for stress-induced psychopathology. MS in dams increased maternal care towards pups even though both groups show high levels of maternal behavior even in late lactation. Furthermore, the emission of 50-kHz and 22-kHz USVs increased significantly. No differences in anxiety-like behavior were detected. MS further reduced Morc1 but not Nr3c1 expression. Serum GABA but not glutamate levels were significantly increased in separated dams. This study reinforces the benefit of investigating dams after MS for studying postpartum stress. Subclinical markers mainly connected to depression, namely Morc1 and GABA, proved to be useful allowing for earlier detection of symptoms of critical postpartum stress.

Figure 1

Licking and grooming (A) and arched-back nursing (B) behavior at PD2, PD6, PD14, and PD20 in separated (black) and unseparated (grey) dams. Separated dams were expressing significantly higher licking and grooming behavior. Amount of 50-kHz (C) and 22-kHz (D) frequencies calls: Separated dams (black) vocalized significantly more at 50-kHz and 22-kHz frequencies at the last day measured compared to control dams (grey). Mean number of 50-kHz and 22-kHz USV calls ± SEM are presented for n = 8 controls and n = 8 separated dams. Data were analyzed by student’s t-test.

Figure 2

(A) Delta CT values of Morc1 mRNA analyzed in mPFC brain region. Separated dams were expressing significantly lower levels of Morc1 mRNA as shown in significant higher CT values. Means ± SEM are presented for n = 15 controls and n = 13 separated dams. *P < .01. (B) Delta CT values of Nr3c1 mRNA analyzed in hippocampus brain region. Means ± SEM are presented for n = 8 controls and n = 8 separated dams. (C, D) Serum analyses of neurotransmitters glutamate for n = 14 controls and n = 15 separated dams and GABA for n = 15 controls and n = 14 separated dams after MS. Separated dams showed higher concentrations of both neurotransmitters but only GABA demonstrating significant differences. Means ± SEM are presented. Data was analyzed using a One-Way ANOVA.