Stimulation of the group I extensor afferents prolongs the stance phase in walking cats

Abstract

Group I afferents in nerves innervating the lateral gastrocnemius-soleus (LG-Sol), plantaris (Pl), and vastus lateralis/intermedius (VL/VI) muscles were stimulated during walking in decerebrate cats. The stimulus trains were triggered at a fixed delay following the onset of bursts in the medial gastrocnemius muscle. Stimulation of all three nerves with long stimulus trains (> 600 ms) prolonged the extensor bursts and delayed the onset of flexor burst activity. LG-Sol nerve stimulation had the strongest effect; often delaying the onset of flex- or burst activity until the stimulus train was ended. By contrast, flexor bursts were usually initiated before the end of the stimulus train to the Pl and VL/VI nerves. The minimum stimulus strength required to increase the cycle period was between 1.3 x threshold and 1.6 x threshold for all three nerves. Simultaneous stimulation of the Pl and VL/VI nerves produced a larger effect on the cycle period than stimulation of either nerve alone. The spatial summation of inputs from knee and ankle muscles suggests that the excitatory action of the group I afferents during the stance phase is distributed to all leg extensor muscles. Stimulation of the group I afferents in extensor nerves generally produced an increase in the amplitude of the heteronymous extensor EMG towards the end of the stance phase. This increase in amplitude occurred even though there were only weak monosynaptic connections between the stimulated afferents and the motoneurones that innervated these heteronymous muscles. This suggests that the excitation was produced via oligosynaptic projections onto the extensor motoneuronal pool. Stimulation with 300 ms trains during the early part of flexion resulted in abrupt termination of the swing phase and reinitiation of the stance phase of the step cycle. The swing phase resumed coincidently with the stimulus offset. Usually, stimulation of two extensor nerves at group I strengths was required to elicit this effect. We were unable to establish the relative contributions of input from the group Ia and group Ib afferents to prolonging the stance phase. However, we consider it likely that group Ib afferents contribute significantly, since their activation has been shown to prolong extensor burst activity in reduced spinal preparations. Thus, our results add support to the hypothesis that unloading of the hindlimb during late stance is a necessary condition for the initiation of the swing phase in walking animals.

Modulation of cutaneous reflexes by load receptor input during human walking

“…This gives more stability of the step cycle with both feet on the ground. The fact that the stance phase did not alter is at variance with findings in children (Yang et al 1998) and animals (Conway et al 1987;Duysens and Pearson 1980;Fouad and Pearson 1997;Gossard et al 1994;McCrea 1998;Pearson et al 1992;Whelan 1996;Whelan et al 1995). These studies indicate that body loading results in an increase in step cycle duration as a result of prolongation of the stance phase.…”

“…For example, in the cat and rat, unloading of the leg is essential for the onset of the swing phase (Duysens and Pearson 1980;Fouad and Pearson 1997;Whelan 1996; for review, see Duysens et al 2000;Pearson et al 1998;Whelan et al 1995). Recently, similar effects were observed in humans, especially under conditions when supraspinal control mechanisms were impaired or incapable to regulate reflexes, for example in newborn with immature pyramidal tracts (Yang et al 1998) or in patients with spinal cord lesions (Harkema et al 1997).…”

“…First, from animal studies, it is known that the load-related input, derived from proprioceptive and cutaneous afferents, can induce reflexes, some of which act directly on the central pattern generator (Conway et al 1987;Duysens and Pearson 1980;Gossard et al 1994;McCrea 1998;Pearson 1995;Pearson et al 1992;Whelan 1996). Proprioceptive influences, for example body loading and unloading, have strong facilitatory effects on the electromyographic activity (EMG) of extensor muscles such as the gastrocnemius (GM) and soleus (SO), but only marginal effect on the flexor muscles both in cats (Gossard et al 1994;Pearson et al 1998;Whelan et al 1995) and humans (Clement et al 1984;Dietz and Colombo 1998;Dietz et al 1992).…”

Control of obstacle climbing in the cockroach, Blaberus discoidalis . I. Kinematics

“…Pearson (1972) recorded from Periplaneta americana walking horizontally while dragging a weight, and found that for a given leg cycle time the greater load produced higher Ds frequency than when the animal was unimpeded. In the decerebrate cats, stimulation of group 1 afferents prolongs stance phase (Whelan et al 1995), and removal of proprioceptive feedback from leg loading, by the leg stepping into a hole, reduces stance phase extensor activity (Hiebert and Pearson 1999).…”

Loading the Limb During Rhythmic Leg Movements Lengthens the Duration of Both Flexion and Extension in Human Infants

“…Direct or indirect activation of extensor muscle afferents that detect stretch and load during the extension period of walking enhances the amplitude of the muscle activity, prolongs ipsilateral extension and inhibits the transition to flexion (Conway et al 1987;Duysens and Pearson 1980;Guertin et al 1995;Ivanenko et al 2002;Pang and Yang 2000;Pearson et al 1992;Whelan et al 1995). A similar phenomenon is seen when the period of flexion is loaded during walking.…”