| Abstract No.: | A-G1202 |
| Country: | Canada |
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| Title: | NATURALLY OCCURRING VARIATIONS IN MATERNAL CARE MODULATE THE EFFECTS OF REPEATED NEONATAL PAIN ON BEHAVIORAL SENSITIVITY TO THERMAL PAIN IN THE ADULT OFFSPRING. |
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| Authors/Affiliations: | 1 Claire-Dominique Walker*; 1 Zhifang Xu; 1 Joseph Rochford; 2 Celeste Johnston;
1 Douglas Mental Health University Institute, McGill University; 2 School of Nursing, McGill University, Montreal, QC, Canada.
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| Content: | Preterm neonates subjected to several painful procedures in the NICU experience long-term behavioral and physiological consequences and in particular display changes in pain thresholds and decreased stress responsiveness later in life. Recent studies have determined that maternal comfort measures can reduce the acute and long-term effects of pain in preterm infants. Using an animal model of repeated mild neonatal pain (needle prick), we demonstrated earlier that maternal behavior was significantly modified by the state of the pup, leading to increased licking and grooming (LG) of the pups subjected to pain. Objectives: in this study, we tested 1) whether repeated inflammatory pain during the first 2 weeks of postnatal life had a significant effect on pain behavior and stress responses in the adult offspring and 2) whether naturally occurring variations in maternal care (amount of licking & grooming, LG) could modulate these responses.
Methods: repeated scoring of maternal behavior during the first 6 days of life allowed to divide mothers into either high (H), middle (M) or low (L) LG mothers. Offspring from the 3 maternal groups were either unhandled (UH) or injected twice daily with formalin (0.5-1%, F) or saline (SAL) in the hind paw between PND3-14. As adults, male rats were tested for their pain sensitivity in the Hargreaves and the formalin (2.5%) tests as well as hormonal responses to restraint stress.
Results: we confirmed that the phenotype of the mother (LG scores) in the 45 min following daily injections of her pups remained the same as that observed under basal resting conditions. Maternal phenotype had a significant effect on the latency to withdraw the paw in the Hargreaves test (p<0.002), as rats from the L mothers showed reduced latencies compared to those from H or M mothers, irrespective of neonatal treatment. Thus, provision of greater sensory stimulation to the pups by the mother reduces thermal pain sensitivity. In contrast, neonatal repeated exposure to formalin significantly (p<0.001) increased pain scores to an acute injection of formalin in adulthood compared to SAL or UH rats, an effect that was observed for rats originating from either H, L or M maternal groups. Integrated pain score for the second phase of the formalin response and the minimum reached between the 2 phases of the response were significantly higher in the F (p<0.001) compared to SAL or UH group, suggesting a long-term effect of early inflammatory pain on adult pain responsiveness. Corticosterone responses of adult offspring to restraint stress were not influenced by neonatal treatment or maternal phenotype.
Conclusions: together, these results suggest that 1) natural variations in maternal care can affect some, but not all modalities of pain responses in the adult offspring and 2) early inflammatory pain during a critical period of pain pathways development could lead to enduring consequences on pain behavior in adulthood. Supported by CIHR. |
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