Abstract
The effect of age on pain thresholds has not been fully explained in both human and animal research. Several studies described pain threshold increase in older adults compared to young adults in men, however, reduction of noxious inhibitory system was revealed during aging.
The aim of the present study was to determine nociceptive threshold in rats during their development and aging. Nociceptive thresholds were evaluated using the paw and tail withdrawal latencies to thermal stimulation (plantar test).
The thresholds were evaluated on postnatal day 7, 16, 23 (weaning), and at the age of 1, 2, 3, 6, 9, 12, 15 and 18 months in forelimbs, hind limbs and tail. Nociceptive thresholds were lowest at PD 7 and then increased to maximum at weaning period.
Since the age of 1 month the thresholds remained unchanged but with one decrease at the age of 9 months for tail. Comparing withdrawal latencies of different body parts, it was found that the latency was shortest in tail and longest in forelimbs at PD7, during weaning it was opposite (the shortest latency was in forelimbs and longest in tail), and in the adults, latencies of forelimbs and hind limbs remained unchanged but tail latency shortened to the level of the forelimbs.
It is suggested that nociceptive threshold depends on age until the age of 1 month, while in adult animals the withdrawal latency to thermal stimulation depends rather on external factors like season, air temperature and/or humidity.