Does Pain in the Neonatal Period Influence Motor and Sensory Functions in a Similar Way for Males and Females During Post-Natal Development in Rats?

OBJECTIVE : Early pain experiences can lead to disruption in the long-term responses to pain and in abnormal development and behavior in rodents. We evaluated the sensory and motor development of Wistar rats after exposure to painful stimulation (repetitive needle prickling) immediately after birth. METHODS : Male and female rats were followed up to 6 months of life, and sensory and motor functions were investigated by testing paw withdrawal with von Frey filaments, calibrated forceps (CF), and grip strength (GS) tests. RESULTS : Body weight increased with age and tended to be smaller in pain groups compared with their controls of the same sex. GS values also increased with age in controls but were stable and even decreased in pain groups from 120 up to 180 days. The von Frey filaments test showed higher values on the nonstimulated paws in male and female pain groups, with no differences between sides on the controls. The CF test showed smaller values on the stimulated paws in the pain group, with no differences between sides on the controls. CONCLUSIONS : Pain in the neonatal period influences sensory and motor functions negatively during development in male and female rats, even long term after the painful stimulus is ceased. The neonatal injury-induced hypersensitivity is persistent, and male and female rats respond similarly to the stimulus.