Неонатальная воспалительная боль, когнитивная и стресс-реактивная функции у взрослых самцов и самок крыс

Abstract

Repetitive neonatal pain may cause central nervous system disorders. Existing clinical data on the effect of neonatal pain on learning, memory and stress-reactivity of the hypothalamic-pituitary-adrenal axis (the HPA axis) are limited to adolescence and have mostly been obtained for male individuals. The mechanism of neonatal pain effect has not yet been researched. Ontogenetic studies carried out on different-sex specimen are crucial for prediction, prevention and treatment of adaptive behavioural disorders caused by neonatal pain stress. Lately, this has become even more relevant due to COVID-19 affecting new-borns in need of intensive therapy. In this study, the impact of neonatal inflammatory pain on adult cognition and hormonal stress response was investigated in male and female rats. Continuous neonatal pain was induced by hindpaw formalin injections on days one and two from birth. In adult rats, we assessed spatial learning and memory using the Morris water maze and evaluated HPA reactivity in response to the formalin test. No significant cognitive function differences were found between the experimental group of rats subjected to neonatal pain and the control group. Within the experimental group subjected to neonatal pain, males showed better long-term spatial memory than females. After testing the long-term memory, we evaluated HPA reactivity by corticosterone levels in response to a formalin test. This parameter was higher in males. Only females with neonatal pain showed differences between short-term and long-term memory, with poorer long-term memory. Possible causes of sex differences in the cognitive function and hormonal stress response in adult rats exposed to neonatal inflammatory pain are discussed.