Dataset Information

Unstable maternal environment, separation anxiety, and heightened CO2 sensitivity induced by gene-by-environment interplay.

ABSTRACT:

Background

In man, many different events implying childhood separation from caregivers/unstable parental environment are associated with heightened risk for panic disorder in adulthood. Twin data show that the occurrence of such events in childhood contributes to explaining the covariation between separation anxiety disorder, panic, and the related psychobiological trait of CO(2) hypersensitivity. We hypothesized that early interference with infant-mother interaction could moderate the interspecific trait of response to CO(2) through genetic control of sensitivity to the environment.

Methodology

Having spent the first 24 hours after birth with their biological mother, outbred NMRI mice were cross-fostered to adoptive mothers for the following 4 post-natal days. They were successively compared to normally-reared individuals for: number of ultrasonic vocalizations during isolation, respiratory physiology responses to normal air (20%O(2)), CO(2)-enriched air (6% CO(2)), hypoxic air (10%O(2)), and avoidance of CO(2)-enriched environments.

Results

Cross-fostered pups showed significantly more ultrasonic vocalizations, more pronounced hyperventilatory responses (larger tidal volume and minute volume increments) to CO(2)-enriched air and heightened aversion towards CO(2)-enriched environments, than normally-reared individuals. Enhanced tidal volume increment response to 6%CO(2) was present at 16-20, and 75-90 postnatal days, implying the trait's stability. Quantitative genetic analyses of unrelated individuals, sibs and half-sibs, showed that the genetic variance for tidal volume increment during 6%CO(2) breathing was significantly higher (Bartlett χ = 8.3, p = 0.004) among the cross-fostered than the normally-reared individuals, yielding heritability of 0.37 and 0.21 respectively. These results support a stress-diathesis model whereby the genetic influences underlying the response to 6%CO(2) increase their contribution in the presence of an environmental adversity. Maternal grooming/licking behaviour, and corticosterone basal levels were similar among cross-fostered and normally-reared individuals.

Conclusions

A mechanism of gene-by-environment interplay connects this form of early perturbation of infant-mother interaction, heightened CO(2) sensitivity and anxiety. Some non-inferential physiological measurements can enhance animal models of human neurodevelopmental anxiety disorders.

SUBMITTER: D'Amato FR

PROVIDER: S-EPMC3072999 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Depression is a heterogeneous disorder characterized by a wide range of symptoms, including but not restricted to increased anxiety-like behavior, altered stress responsivity, increased depressive like behavior, decreased pleasure seeking, and altered susceptibility to drugs of abuse. Adding another level of complexity to the disease is the fact that individuals differ in their susceptibility to depression. Research done over the past decade has highlighted the contribution of early life adverse experience to this individual differences in vulnerability to depression. Such studies have been done at the clinical as well as the preclinical level, where rodent and primate models of adverse postnatal environment such as Maternal Separation (MS) are used. MS involves separation of the pup from the dam for 3h every day for the first two weeks of postnatal life. The MS model has been characterized to produce long lasting anxiety-like behavior, depressive behavior and altered stress responsivity in adulthood. While several molecular mechanisms have been hypothesized to mediate the long lasting effects of MS, the serotonin 2a receptor is an attractive candidate, given its role in regulating anxiety-like behavior. So we set out to ask if Maternal Separation alters the 5HT2a responses. In order to assay if MS alters the transcriptional targets of the 5Ht2a receptor, we use a drug that stimulates the 5Ht2a receptor, DOI. The experiment involves injecting both control and MS animals with DOI and looking at the transcriptome induced by DOI under control and MS conditions. This would help understand how the adverse early life experience MS, alters the transcriptional response of an adult rat to stimulation at the 5HT2a receptor, which is physiologically seen in conditions of stress. Maternal Separation (MS) was carried out according to standard protocol. Briefly, upon birth the litters were assigned to either the control or the maternal separation group. Pups from the maternal separation litters were separated from their mother every day for a period of 3 hours from postnatal day 2 (p2) to postnatal day 14 (p14) while the control litters were left undisturbed. After p14, the maternally separated pups were left undisturbed and all litters were weaned at postnatal day 30. Experiments on adult control and MS rats were performed at postnatal day 60. We wanted to ask if a history of adverse experience in early life like MS would alter the transcriptional response of the adult rat to the 5Ht2a agonist DOI. In order to measure the transcriptional changes induced by DOI in control and maternally separated animals, 15 rats (7 - Control and 8 - Maternally Separated) were injected i.p. with either saline or 8 mg/kg DOI. The groups included Control (Control rats injected with saline; n=3), DOI (control rats injected with 8 mg/kg DOI; n=4), MS (MS rats injected with saline, n=4) and MS+ DOI (MS rats injected with 8 mg/kg DOI, n=4). Rats were sacrificed 2 hours after the injection by decapitation. The prefrontal cortex was quickly dissected out and stored at -70 till further use. Total RNA from each rat was extracted, labeled with Cy3 and hybridized onto Agilent Custom Rat Array 8X15K (AMADID: G2509F_16352). Each biological replicate was hybridized onto one array making the total number of arrays 15.