The effect of selective brainstem or spinal cord lesions on treadmill locomotion evoked by stimulation of the mesencephalic or pontomedullary locomotor regions

Abstract

The descending pathways from the brainstem locomotor areas were investigated by utilizing reversible cooling (to block synaptic or fiber transmission) and irreversible subtotal lesions of the brainstem or spinal cord (C2-C3 level). Experiments were conducted on decerebrate cats induced to walk on a treadmill by electrical stimulation of the brainstem. Locomotion produced by stimulation of the mesencephalic locomotor region (MLR) was not abolished by caudal brainstem lesions that isolated the lateral tegmentum or by extended rostral/caudal dorsal hemisections of the spinal cord. These results demonstrate that the MLR does not require a pathway projecting through the lateral tegmentum of the brainstem or the dorsal half of the spinal cord, as previously suggested (Mori et al., 1977, 1978b; Shik and Yagodnitsyn, 1978; Shik, 1983). Rather, the results indicate that the descending pathway originating from the MLR projects through the medial reticular formation (MedRF) and the ventral half of the spinal cord. Locomotion produced by stimulation of the pontomedullary locomotor region (PLR) was blocked by reversible cooling of either the MedRF or the ventrolateral funiculus of the spinal cord. In some cases, locomotion could be produced by stimulation of the PLR following extended dorsal hemisections of the spinal cord. These results demonstrate that the PLR can also produce locomotion by activation of cells in the MedRF that project caudally through the ventral half of the spinal cord. Stimulation of the PLR could also elicit locomotion following its surgical isolation from the MedRF of the brainstem. Furthermore, lesions of the dorsal spinal cord resulted in the loss of PLR-evoked locomotion in some, but not all, cases. Thus, an alternative projection of the PLR through the dorsal half of the spinal cord (Kazennikov et al., 1980, 1983a,b; Shik, 1983) cannot be ruled out. Overall, these results demonstrate that the PLR is not an essential component of the motor pathway originating from the MLR. The organizational scheme of "brainstem locomotor regions" is discussed in the context of recent information demonstrating a link between the sensory component of the trigeminal system and locomotor pathways (Noga et al., 1988).

Temporal and Spatial Profiles of Pontine-Evoked Monoamine Release in the Rat's Spinal Cord

“…The presently reported dynamics of extrajunctional concentration after locus ceruleus stimulation suggest that paracrine noradrenergic modulation of locomotion can operate on a time scale of ϳ1 s. Preliminary evidence shows that extrajunctional monoamine concentrations rapidly increase during mesencephalic locomotor region-evoked fictive locomotion in the cat (Noga et al 1999), beginning a few seconds prior to the onset of locomotion. Thus spinal monoamines seem to be partly modulatory, and it is likely that they preset the gain and quality of locomotion that is subsequently activated by fast reticulospinal command fibers (Jordan 1991;Noga et al 1995a). The extrajunctional levels observed in the present study are well within the physiological range for receptor-mediated effects (Allgaier et al 1992;Zoli et al 1998), and a high proportion of spinal noradrenergic synapses are remote from synaptic contacts (Ridet et al 1993).…”

“…One of these was ϳ1 mm dorsal and 0.4 mm rostral to the locus ceruleus target, near the caudal and medial edges of the nucleus cuneiformis, a component of the mesencephalic locomotor region (Noga et al 1991). However, this site showed high variability in its effectiveness, as depicted by standard error bars of the graph in Fig.…”

Aspiration of a cervical spinal contusion injury in preparation for delayed peripheral nerve grafting does not impair forelimb behavior or axon regeneration

“…In the present study a single exposure to GDNF at 28d after injury probably was not involved in limiting behavioral changes associated with cavity manipulation, since neuroprotective features (sparing of white matter and overall decrease in lesion volume) of GDNF which might contribute to a behavioral effect appear to transpire only after acute treatment (Iannoti et al, 2004). Promoting regeneration of chronically injured reticular formation neurons, as well as rubrospinal, vestibulospinal, and raphespinal tract neurons, is potentially clinically important because of their prominent role in rat locomotor activity (Jordan, 1991;Loy et al, 2002;Martin et al, 1985;Muir and Whishaw, 2000;Noga et al, 1991).…”

International spinal research trust research strategy. III: A discussion document

“…In animal models, fibres passing through the ventrolateral funiculi, including reticulospinal axons, appear to be important for functional recovery of hindlimb locomotor function. 31 In humans, the importance of the ventrolateral systems is less clear, while damage to corticospinal fibres has more serious effects. 32 The minimal sparing of white matter, in terms of either area or axonal number, that is compatible with locomotion is B10% for cats, 33 o25% for non-human primates 34 and o10% for humans.…”