Treadmill Stepping in Newborn Rats

The purpose of this study was to investigate the influence of treadmill belt speed on mechanically-induced (tail-pinch) and pharmacologically-induced (quipazine, a 5HT _2A agonist) stepping behavior in one-day old rats. On postnatal day 1 (P1), male rat pups were tested on one of four moving treadmill belt speeds. Stepping was induced using a tail-pinch and quipazine administration to examine real-time adaptations on belt speeds. For tail-pinch-induced stepping in the forelimbs and hindlimbs, there was a significant effect of time but not belt speed. Step cycle duration was significantly shorter for both forelimbs and hindlimbs on the fast belt speed compared to all other belt speeds. For the forelimbs, this effect was driven by changes in stance phase duration. Compared to control the speed, step area was significantly larger on medium and fast speeds for forelimbs and slow and fast speeds for hindlimbs. For quipazine-induced stepping, forelimbs and hindlimbs showed significantly more steps across slow, medium, and fast belt speeds compared to the control speed. The forelimbs showed significantly shorter step cycle durations on the fast belt speed compared to the control belt speed. Again, this difference was driven by changes in the stance phase. There were no significant differences in step cycle duration, stance and swing phase durations, or step area between speeds for the hindlimbs. Overall, we showed that both mechanical and pharmacological stimulation is reliable at inducing stepping on a moving treadmill belt in neonatal rats, and P1 rats show real-time adaptations in response to a moving treadmill belt.