Specificity of Intramuscular Activation During Rhythms Produced by Spinal Patterning Systems in the In Vitro Neonatal Rat With Hindlimb Attached Preparation

Abstract

Klein DA, Tresch MC. Specificity of intramuscular activation during rhythms produced by spinal patterning systems in the in vitro neonatal rat with hindlimb attached preparation. J Neurophysiol 104: 2158 -2168, 2010. First published July 21, 2010 doi:10.1152/jn.00477.2010. In intact adult vertebrates, muscles can be activated with a high degree of specificity, so that even within a single traditionally defined muscle, groups of motor units can be differentially activated. Such differential activation might reflect detailed control by descending systems, potentially resulting from postnatal experience such that activation of motor units is precisely tailored to their mechanical actions. Here we examine the degree to which such specific activation can be seen in the rhythmic patterns produced by isolated spinal motor systems in neonates. We examined motor output produced by the in vitro neonatal rat spinal cord with hindlimb attached. We recorded the activity of different regions within the posterior portion of biceps femoris (BFp; i.e., excluding the anterior/vertebral head). We found that in the rhythms evoked by bath application of serotonin/N-methyl-D-aspartate (5-HT/ NMDA), all regions of BFp were active during extension. However, the regions of BFp were activated in a specific sequence, with the activation of rostral regions consistently preceding those of more caudal regions in both afferented and deafferented preparations. In the rhythms evoked by cauda equina (CE) stimulation, rostral and middle regions of BFp remained active in extension, but the caudal region of BFp was usually active in flexion. Stimulation of L5 and S2 dorsal roots typically evoked rhythms with all regions of BFp active during extension; although the same rostral to caudal sequence of activation observed in 5-HT/NMDA evoked rhythms could also be observed in these rhythms, we also observed cases with reversed sequences, with activity proceeding from caudal to rostral. S2 dorsal root stimulation occasionally evoked rhythms with flexor activity in caudal BFp, similar to CE-evoked rhythms. Taken together, these results suggest a high degree of individuated control of muscles by spinal pattern generating networks, even at birth.

Spontaneous locomotor activity in late-stage chicken embryos is modified by stretch of leg muscles

“…Centrally generated two-burst patterns also occur during fictive locomotion in the neonatal rat, and recruitment varies with the form of network activation, i.e. pharmacologic, electrical currents (Klein and Tresch, 2010). Thus, we interpret our findings as significant evidence that proprioceptive input produced by limb movement can modulate centrally generated RLM patterns prior to hatching.…”

Force‐sensitive afferents recruited during stance encode sensory depression in the contralateral swinging limb during locomotion

“…The spinal cord is positioned dorsal‐up so that stepping can be activated by bath application of neurochemicals (Fig. D–E) to generate coordinated muscle activity patterns with limb kinematics that compare well to what is seen in the adult …”

“…1D-E) to generate coordinated muscle activity patterns with limb kinematics that compare well to what is seen in the adult. [12][13][14][15][16] We have since incorporated ventral and dorsal root recordings, as well as intracellular recordings, to relate neural function and behavior in ways not typically possible in vitro. 17 A particularly exciting observation regarding afferent feedback concerned the control of transmission in contralateral afferents by a distinctive form of presynaptic inhibition (PSI), called primary afferent depolarization (PAD).…”

Ascending pathways that mediate cholinergic modulation of lumbar motor activity

“…; Whelan et al . ; Strauss and Lev‐Tov ; Klein and Tresch ; Taccola ) potently activate the hindlimb and body‐stabilizing CPGs in rodents in the absence of supraspinal control. Our studies of the isolated spinal cord of the newborn rat revealed that the sacrocaudal afferent‐induced locomotor rhythm could be blocked by bathing the sacral segments in low‐calcium high‐magnesium Kreb's saline, to suppress synaptic transmission, or by selective application to these segments of the non‐NMDA receptor blocker CNQX (Strauss and Lev‐Tov ) or the mu‐opioid agonist DAMGO (Blivis et al .…”