| Abstract No.: | B-G2198 |
| Country: | Canada |
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| Title: | THE EFFECTS OF EARLY LIFE PAIN EXPERIENCES AND MATERNAL CARE ON ADULT PERCEPTION OF PAIN IN RATS. |
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| Authors/Affiliations: | 2 Cynthia de Medeiros*; 2 Alison Fleming; 1 Celeste Johnston; 1 Claire-Dominique Walker;
1 McGill University, Montreal, QC, Canada; 2 University of Toronto at Mississauga, ON, Canada.
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| Content: | Objectives: Preterm neonates receive many untreated painful procedures, particularly during the first weeks of life. Evidence suggests that long-term negative consequences result from this early exposure to repeated pain and that maternal care may help reduce these effects. Using an animal model to mimic early exposure to pain in preterm infants, we tested whether maternal stimulation (licking) plays a key role in determining pain threshold responses later in adulthood.
Methods: To isolate the effects of maternal licking from other maternal influences, we used the “pup in a cup” artificial rearing paradigm. Animals were reared either without (artificially reared [AR]) or with (maternally reared [MR]) their mothers. All AR animals received a cheek cannulation to allow for automated feeding of artificial rat milk. AR animals received either a ‘minimal’ amount of tactile stimulation (AR-MIN; 2 anogenital stimulations per day) or a ‘maximal’ amount of tactile stimulation (AR-MAX; 2 anogenital stimulations and 5 body stimulations per day). MR animals were either shams (MR-SHAM; received cheek cannulation) or controls (MR-CON; no cannulation). Both AR and MR groups were subdivided into 3 treatment groups either receiving no injection, formalin (0.5%-1.0%), or saline injections twice daily from postnatal day (PND) 4-14. In adulthood, animals were tested for their threshold latency to paw withdrawal in the Hargreaves Test (PND 70-74) and response to an acute injection of formalin (2.5%) in the hind paw (PND 77-87). Each animal was injected with formalin and saline on two separate test days and their pain behavior was scored every minute for 1-hour.
Results: Hargreaves Test: On both active intensities (30% and 50%) of thermal sensitivity, animals injected with formalin postnatally displayed the shortest latency to lift the paw when compared to animals in the saline and no injection groups. MR-CON animals consistently exhibited a higher pain threshold compared to the two AR groups, suggesting that the AR procedure might have interacted with the neonatal treatment to reduce pain threshold.
Formalin Test: Area under the curve was calculated for Phase 1 (1-4 minutes) and Phase 2 (5-60 minutes). All groups exhibited the typical biphasic response following the formalin injection. In our preliminary experiments, the amount of stimulation received by pups did not affect behavioral pain scores. However, in the no injection condition, AR-MAX animals displayed an increased pain score compared to MR-CON animals in Phase 2 of the response.
Conclusion: Our preliminary results suggest that both being reared artificially and experiencing early repeated pain decreased thermal pain threshold in adulthood and that the combined effect was more pronounced for the paw latency reflex than the acute formalin pain response. Pain scores following adult formalin injections were lowest in maternally reared non-injected animals, demonstrating the potent effect of maternal care to help reduce pain sensitivity. Thus, early pain experiences may result in greater sensitivity to pain in adulthood, an effect that can, however, be attenuated by maternal care. Supported by CIHR.
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