| Abstract No.: | A-E1170 |
| Country: | Canada |
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| Title: | THE ROLE OF THE ESTROGEN RECEPTOR ON MATERNAL SENSITIZATION IN POST-PARTUM SPRAGUE-DAWLEY RATS |
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| Authors/Affiliations: | 1 Natalia Pinzon*; 1 Alison Fleming;
1 University of Toronto, ON, Canada
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| Content: | Objective: Mother rats first engage in maternal behaviour under the influence of hormones. However, once they have exhibited maternal behaviour, this behaviour is sustained through exposure to sensory cues from the pups (“Maternal Experience Effect”). The present project investigated whether the maternal experience effect is mediated through activation of estrogen receptors by administering post-partum maternally experienced and inexperienced dams the anti-estrogen PSK 3668 at the time of retention.
Methods: Sixty-four 60-90 day old pregnant Sprague Dawley rats were monitored around the time of parturition at 20-minute intervals between 0800h and 2000h. Following parturition (post-natal day 0, PND 0), rats received 48 hours of exposure to pups (EX) or no exposure (NOEX). The NOEX group had their newborn pups removed at 15-minute intervals until the entire litter had been delivered. All animals were then pup-deprived for 8 days and tested for maternal retention (i.e, pup retrieval, pup licking, hovering, and nest building) with donor pups starting on PND 10 for 10 consecutive days or until maternal behaviour was displayed. The foster pups were left with the dam overnight and then replaced with new foster pups the following morning.
Twenty-four hours prior to each retention test, half of the rats within each group received a sub-cutaneous injection of the antiestrogen (AE) PSK 3668 while the other half received an oil vehicle (Veh) injection. One hour after the last behavioural retention test, rats were given an overdose of Sodium Pentobarbital (approx. 1.0cc) and perfused intracardially with 0.9% Phosphate Buffered Saline and 4% Paraformaldehyde. Brains were extracted and processed for estrogen receptor (ER) immunohistochemistry.
Results: Results from the current study showed that EX animals had significantly shorter latencies to become maternal compared to their NOEX counterparts. In addition, AE animals displayed longer latencies to become maternal compared to Veh animals but only in the NOEX condition. Differences in the percentage of animals that reached maternal criterion on each of the testing days were also found, with EX animals having higher percentage to become maternal compared to NOEX; and Veh animals also having higher percentage to become maternal compared to AE animals.
Conclusion: It appears that the estrogen receptor is more involved in the mediation of the initial expression and sensitization of maternal behaviour. Once a mother establishes a brief maternal experience with her young, the ER does not appear to influence maternal retention upon reinstatement of pups. However, if a mother is not allowed to interact with her young following parturition, as in the NOEX group, then blocking the ER appears to delay maternal sensitization. These results may suggest that activation of the ER during during mother-litter interactions might be the result of ligand independent activation through somatosensory input provided by the pups.
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