A study on the development of nociceptive responses in pre- and postweanling rats: the tail electric stimulation test...

The development of nociceptive responses to the tail electric stimulation test was investigated. Male Wistar albino rats were used for studies on adult and pre- and postweanling rats of 20 and 25 days of age, respectively. The thresholds for the motor response (tail withdrawal), vocalization during stimulus and vocalization afterdischarge were assessed. These responses are considered to be integrated at spinal, medulla oblongata and diencephalon-rhinencephalon levels, respectively. Adult animals showed significantly higher thresholds for the three responses when compared to the neonates, while 25-day old rats showed significantly higher thresholds for the vocalization afterdischarge than the 20-day old pups. Although the effect of age cannot be ruled out, these latter results might indicate that the weaning process is critical in the development of the mechanisms related to the emotional/affective component of pain. The results also indicate the suitability of the nociceptive test employed for these kinds of studies.