QUANTIFICATION OF SUBSTANCE P IN DORSAL ROOT GANGLION NEURONS IN YOUNG AND ADULT RATS, AFTER NOCICEPTIVE STIMULATION DURING THE NEONATAL PERIOD

Substance P (SP) is widely used as a marker for peripheral neurons with unmyelinated fibers. Understanding the plasticity in peripheral pain pathways, even before the stimulus reach the central nociceptive areas is crucial, particularly when noxious stimuli are applied to neonates, when the nervous system is still under remodeling process. We quantified SP immunostained neurons in the dorsal root ganglion (DRG) of male and female Wistar rats 15 and 180 days after nociceptive stimulation [1] during the neonatal period. Right and left L5 DRG were removed, frozen and 8 μm thick criossections were incubated in rabbit polyclonal anti‐substance P antibody (1:5.000; 24hr). Immunostaining protocol was used as described [2]. Labeled neurons were counted and compared between ages, genders and groups. Differences were considered significant if p<0.05. Gender differences were present in both ages, being the number of SP positive neurons in the DRG larger in males on both sides, in animals 15 days old. After 6 months, males showed a larger number of SP positive neurons only on the right side that received the nociceptive stimulus, compared to females. An increased number of SP positive neurons in the DRG of the stimulated side in females was present, immediately after nociceptive stimulation but not after 6 months. In conclusion, neonatal noxious stimulation caused a permanent increase in the SP positive neurons in males that was not observed in females, suggesting that differences in pain sensitivity between genders could be related to morphological alterations of the nervous system.Support or Funding InformationFAPESP, CNPq, CAPES and FAEPA