Spontaneous and NMDA evoked motor rhythms in the neonatal mouse spinal cord: an in vitro study with comparisons to in situ activity

Abstract

The current paper presents our initial efforts to establish an in vitro spinal preparation for investigating locomotor pattern generation in mice. We have characterized the step cycle timing from EMG activity in the gastrocnemius (G) and tibialis anterior (TA) muscles of freely moving intact adult as well as neonatal mice and then compared those data with rhythmic EMG activity in an isolated spinal cord-hindlimb preparation. The motor output during the first four days of life was evaluated in an effort to identify the optimal post-partum period for in vitro locomotor studies. The in vitro pattern generating capabilities of the lumbosacral region were tested in both nonhemisected and hemisected preparations. Spontaneous as well as NMDA evoked in vitro activity in the antagonist set of hindlimb muscles included sequences of: 1) synchronous bursting; 2) mixed synchrony and alternation; and/or 3) irregular alternations. The alternating bursting observed in vitro was more often an alternation of sequences rather than a cycle-to-cycle phasing between G and TA muscles. In summary, while there was evidence of reciprocal inhibition in neonates, the circuitry for cycle-to-cycle alternation between antagonists was found to be labile.

NMDA Receptor Activation Triggers Voltage Oscillations, Plateau Potentials and Burstinq in Neonatal Rat Lumbar Motoneurons ln Vitro

“…During neurochemically induced rhythmic motor activity in the in vitro neonatal rat spinal cord, high frequency packets of discharge (4-8 Hz) have been observed within the main envelopes of alternating slow discharge recorded via electroneurograms or electromyograms (Cazalets et al, 1990a;Cowley and Schmidt, 1995). Similar high frequency packets of discharge have also been recorded in the in vitro neonatal mouse spinal cord (Hernandez et al, 1991) and within hindlimb discharge episodes during rhythmic activity in the adult cat (Noga et al, 1993). The role and exact mechanism of these high frequency events remains unknown (Cowley and Schmidt, 1995).…”

Characteristics of the developing human locomotor system: Similarities to other mammals

“…The ability to walk soon after birth is important for survival in many mammals, and is one of the rhythmic behaviors that develop very early in life. Indeed, long before the behavior is manifest, the circuitry for rhythmic stepping is functional in quadrupeds (Brown, 1915;Cazalets, Menard, Cremieux, & Clarac, 1990;Hernandez, Elbert, & Droge, 1991;Kudo & Yamada, 1987;Smith & Feldman, 1987;Windle, 1931). These circuits reside in the spinal cord, with autonomous rhythm generating ability (Brown, 1915), and are called central pattern generators (CPGs) (Grillner & Zangger, 1975).…”

A synaptic mechanism for network synchrony

“…The details of synaptic connectivity responsible for this phenomenon have been substantially explored in the lamprey (Wallén and Grillner, 1987; Grillner et al, 2001; Grillner, 2006) and the Xenopus embryo (Dale and Roberts, 1984, 1985). More recently, work in higher vertebrates (Masino et al, 2012) has emphasized how well conserved this network motif is throughout the vertebrate subphylum including lampreys, fishes, amphibians, chelonids and mammals (Dale and Roberts, 1984; Sigvardt et al, 1985; Kudo and Yamada, 1987; Hernandez et al, 1991; Guertin and Hounsgaard, 1998; Gabriel et al, 2009; Masino et al, 2012). After complete spinal transection (Cohen and Wallén, 1980; Brodin et al, 1985), the lamprey swimming network can still generate the electrophysiological correlates of swimming.…”