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 (3.0 mg/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.

Range of motion (ROM) restriction influences quipazine-induced stepping behavior in postnatal day one and day ten rats

“…To start the test session, subjects were secured in the prone posture to a vinyl-coated horizontal bar using a jacket with adjustable straps across the neck and abdomen [16]. The jacket was fitted so that it did not impede limb movement.…”

“…Volume of injection was based on body weight (i.e., 25 μl/5 g). Quipazine is a 5-HT receptor agonist that has been shown in previous studies to induce stepping behavior in fetal and newborn rats [12, 15], at the dose used in this study (3.0 mg/kg) [11, 15, 16]. Immediately following the injection, a 15-min ROM (range of motion) restriction was imposed for half of the subjects.…”

“…Frequencies of alternated, synchronized, and non-stepping limb movements (e.g., twitches and unilateral steps) were scored. Alternated steps were defined as occurring when the pup’s homologous limbs exhibited sequential extension and flexion in one limb immediately followed by sequential extension and flexion in the other limb [15, 16]. Synchronized steps were defined as occurring when the pup’s homologous limbs exhibited simultaneous flexion and extension in both legs.…”

“…Common methods for evoking air-stepping in developing rats in vivo include presentation of olfactory stimuli, tail pinch, or treatment with pharmacological agents such as quipazine [10-14]. Quipazine is a 5-HT receptor agonist that has been shown to induce locomotor behavior in prenatal [15] and postnatal rats [11, 12, 16]. It is thought to act at 5-HT 2A receptors [17].…”

“…However, few studies have investigated the role of sensory feedback on motor behavior, particularly locomotion, during early development. Some methods used to investigate the effects of sensory feedback during early motor development include: limb weighting [18-26], interlimb yoking [19, 27, 28], treadmill training [25, 29], and responses to different substrates [16]. Together, these studies provide compelling evidence that early motor systems can adapt to sensory changes both during the sensory experience (real-time) and after the stimulus is removed (persistent effects).…”