Sensory feedback modulates quipazine-induced stepping behavior in the newborn rat

Abstract

Research has shown that sensory feedback modulates locomotor behavior in intact as well as spinal adult animals. Here we examined if locomotor activity ("stepping") in newborn rats is influenced by cutaneous and proprioceptive feedback. One-day-old rats were treated with the serotonergic receptor agonist quipazine (3.0mg/kg) to induce air-stepping behavior or with saline (vehicle control). During stepping, a substrate/floor (elastic, stiff, or none) was placed beneath their limbs so that the feet could make plantar surface contact with a substrate. Pups treated with quipazine showed significantly more alternated fore- and hindlimb steps and plantar paw contact with the substrate, compared to pups treated with saline. Pups also made proportionately less contact with the stiff substrate versus the elastic substrate during stepping. Different types of movements made on the substrate (paw pushes, taps, swipes, and stances) were also characterized. These results indicate that sensory feedback modulates locomotor mechanisms and behavior in perinatal rats.

Figure 1

Illustration of a P1 rat pup interacting with the elastic substrate. (Top panel) The pup is suspended in the air by a sling, with the elastic substrate placed beneath the limbs. Notice that the forelimbs are slightly flexed and not touching the substrate. (Bottom) In the next video frame, the forelimbs are extending and pressing down on the elastic substrate using the plantar side of the foot, thus exhibiting what was called a forepaw push.

Figure 2

Alternated forelimb stepping by drug treatment and substrate condition. (Top panel) The mean number and (Bottom) the mean percentage of alternated forelimb steps during the 5-min Baseline and 45-min Test period. Immediately after Baseline, subjects were treated with quipazine or saline, and an elastic, stiff, or no substrate was placed below their feet for the remainder of the Test session. Points show means; vertical lines depict SEM.

Figure 3

Effect of drug treatment and substrate on the percentage of alternated steps made in contact with the elastic or stiff substrate. (Top panel) The mean percentage of forelimb and (Bottom) hindlimb steps made in contact with the substrate during the 5-min Baseline and 45-min Test period. Points show means; vertical lines depict SEM.

Figure 4

Alternated hindlimb stepping by drug treatment and substrate condition. (Top panel) The mean number and (Bottom) the mean percentage of alternated hindlimb steps during the 5-min Baseline and 45-min Test period. Points show means; vertical lines depict SEM.

Figure 5

Paw-substrate interactions by drug treatment and substrate condition. The mean number of (A) paw pushes, (B) taps, (C) swipes, and (D) stances in the forelimbs and hindlimbs during the 45-min Test period for subjects in the elastic or stiff substrate conditions. Bars show means; vertical lines depict SEM.

Figure 6

Paw touches by drug treatment and substrate condition. (Top panel) The mean number of substrate touches and (Bottom) the percentage of plantar paw touches in the forelimbs and hindlimbs during 45-min Test period for subjects in the elastic or stiff substrate conditions. Bars show means; vertical lines depict SEM.