Repeated neonatal needle-prick stimulation increases inflammatory mechanical hypersensitivity in adult rats

•Neonatal repetitive pain in rats did not change maternal behavior.•Neonatal repetitive pain did not affect basal thresholds to mechanical stimuli.•Male and female offspring had a reduction in mechanical threshold after CFA challenge.•Female animals showed higher formalin-induced hypersensitivity co...

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Published in:	International journal of developmental neuroscience Vol. 78; no. 1; pp. 191 - 197
Main Authors:	de Carvalho, Ravena Carolina, Prado, Lara, Rissardo Oliveira, Naynne Cristina, Vilela Giusti, Fabiana Cardosos, Santos Vieira, Jádina, Giusti-Paiva, Alexandre, da Silva, Josie Resende Torres, da Silva, Marcelo Lourenço
Format:	Journal Article
Language:	English
Published:	United States Elsevier Ltd 01-11-2019 Elsevier BV
Subjects:	Animal behavior Animals Behavior, Animal - physiology Critical period Evaluation Exposure Female Formaldehyde Hyperalgesia - physiopathology Hypersensitivity Infants Inflammation Inflammation - physiopathology Litter Male Maternal Behavior Neonatal pain Neonates Newborn Offspring Organic chemistry Pain Pain - physiopathology Pain Measurement Pain perception Pain sensitivity Pain Threshold - physiology Physical Stimulation Rat pups Rats Rats, Wistar Repetitive pain Rodents Sensitivity analysis Stimulation Stimuli Weight Repetitive pain Pain Newborn Rat pups Neonatal pain
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Summary:	•Neonatal repetitive pain in rats did not change maternal behavior.•Neonatal repetitive pain did not affect basal thresholds to mechanical stimuli.•Male and female offspring had a reduction in mechanical threshold after CFA challenge.•Female animals showed higher formalin-induced hypersensitivity compared to males. Newborn infants are vulnerable to procedural stress and pain exposure on the first weeks of life that represents a critical period for the development of nociceptive, sensory, emotional, and social functions. We evaluated the nociceptive behavior of adult male and female rats that were submitted to nociceptive experience in the neonatal period and the maternal behavior in the postnatal period. The animals were submitted to repetitive needle pricking from the second to the fifteenth postnatal day (PND 2–15). Maternal behavior and litter weight were evaluated during this period. Mechanical sensitivity to pain was assessed in offsprings during the adulthood by exposing them to inflammatory stimuli, including formalin test or the Freund’s complete adjuvant (CFA) injection followed by the electronic von Frey test at 0, 3, 6 and 24 h later. Maternal behavior and litter weight were not altered by pinprick stimuli during PND 2–15. Additionally, pinprick stimulation reduced the paw withdrawal threshold in CFA-injected animals compared to control. In the formalin test, there was a difference between the genders. Female rats are statically more sensitive to formalin stimulation and showed an increased licking time in both the first and second phases and increased number of flinches in second phase. Experiencing early life repetitive pain exposure increased inflammatory pain sensitivity in adult offspring rats and female rats are more sensitive to chemical stimulation. Future investigations of the mechanisms involved in this effect may contribute to the improvement of the understanding of inflammatory pain sensitivity differences.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0736-5748 1873-474X
DOI:	10.1016/j.ijdevneu.2019.02.004