The effect of dorsal root transection on the efferent motor pattern in the cat's hindlimb during locomotion

Abstract

Mesencephalic cats can walk on a treadmill if the midbrain locomotor region is stimulated. The motor pattern of different hindlimb muscles is similar to that of th intact cat. The present experiments in the mesencephalic preparation test if the complex motor pattern in one hindlimb is causally dependent on the afferent signals arising in the same limb during walking. The electromyographical activity and the movement pattern during locomotion were compared before and after transecting all dorsal root fibres originating from one hindlimb. Flexor and extensor muscles at different joints may retain their general pattern after the dorsal root transection. This applies also to muscles such as the knee flexors, which have a short and early flexor burst and a second burst during the extension phase, and the short toe dorsiflexor , which has an early burst in the transition between flexor and extensor activity. After the dorsal root transection the pattern of activity may become more variable and it can even break down altogether. The present results demonstrate that the central nervous system devoid of phasic afferent inflow from one hindlimb can produce a complex motor output to this limb rather than a motor pattern degraded to a simple alternation between flexors and extensors.

Organization of mammalian locomotor rhythm and pattern generation

“…While afferent input plays a critical role in controlling and shaping CPG operation, it is also clear that the spinal cord circuitry can generate specific profiles of motoneuron activity in the absence of sensory input (Grillner and Zangger, 1984). Such observations led to suggestions for more complicated architectures for the locomotor CPG.…”

Neural control of locomotion; Part 1: The central pattern generator from cats to humans

“…However, transection of the dorsal roots docs not eliminate all afferent input to the spinal cord be cause afferent information can reach the spinal cord by means of unmyelinated [15] and myelinated [16] sensory fibers in the ventral (motor) roots. As pointed out by Grillner and Zangger (1984), many of these afférents come from visceral regions [17]. Furthermore, no ap parent sensation is evoked after ventral root stimula tion [18].…”

“…Forelimb movements may induce hindlimb stepping in forward gait. Grillner and Zangger (1984) claimed that interlimb coordination during hindlimb walking deteriorated fol lowing deafferentation in the 'mesencephalic' cat [17], This is a decerebrated cat (obtained after intercollicular transection at the level of the brain stem) in which complete quadrupedal stepping can be evoked by elec trical stimulation of a specific brainstem site below the transection (the mesencephalic locomotor region (MLR), [19]). Depending on the strength of the stimu lus, different gait patterns could be produced (walking» trotting, galloping).…”

“…In the cat several authors have suggested that the activity of hamstrings at end swing could originate from stretch reflexes [2][3][4]. To shed light on this type of question, transection of the dorsal roots was used and it was shown that a seemingly normal locomotor outputs could remain in acute spinal cats [14,17,40]. Although indeed, a striking similarity exists with the normal pattern it has been argued that the stability of the pattern and some of the details of the activation pattern requires the presence of intact afferents [41].…”

Modeling discrete and rhythmic movements through motor primitives: a review

“…Brown (1912) showed that cats with transected spinal cord and with cut dorsal roots showed rhythmic pattern of muscle activation. Even if, in the initial experiments, the transection of the dorsal roots does not exclude the influence of sensory feedback as pointed out by Grillner and Zangger (1984), there is now very clear evidence that rhythms can be generated centrally without requiring sensory information. Indeed, experiments on lampreys (Cohen and Wallen (1980), Grillner (1985)), on salamanders (Delvolvé et al (1999)) and on frog embryos (Soffe and Roberts (1982)) have shown that when the spinal cord is isolated from the body, electrical or chemical stimulations activate patterns of activity, called fictive locomotion, very similar to the ones observed during intact locomotion.…”