Brainstem control of locomotion and muscle tone with special reference to the role of the mesopontine tegmentum and medullary reticulospinal systems

Abstract

The lateral part of the mesopontine tegmentum contains functionally important structures involved in the control of posture and gait. Specifically, the mesencephalic locomotor region, which may consist of the cuneiform nucleus and pedunculopontine tegmental nucleus (PPN), occupies the interest with respect to the pathophysiology of posture-gait disorders. The purpose of this article is to review the mechanisms involved in the control of postural muscle tone and locomotion by the mesopontine tegmentum and the pontomedullary reticulospinal system. To make interpretation and discussion more robust, the above issue is considered largely based on our findings in the experiments using decerebrate cat preparations in addition to the results in animal experimentations and clinical investigations in other laboratories. Our investigations revealed the presence of functional topographical organizations with respect to the regulation of postural muscle tone and locomotion in both the mesopontine tegmentum and the pontomedullary reticulospinal system. These organizations were modified by neurotransmitter systems, particularly the cholinergic PPN projection to the pontine reticular formation. Because efferents from the forebrain structures as well as the cerebellum converge to the mesencephalic and pontomedullary reticular formation, changes in these organizations may be involved in the appropriate regulation of posture-gait synergy depending on the behavioral context. On the other hand, abnormal signals from the higher motor centers may produce dysfunction of the mesencephalic-reticulospinal system. Here we highlight the significance of elucidating the mechanisms of the mesencephalic-reticulospinal control of posture and locomotion so that thorough understanding of the pathophysiological mechanisms of posture-gait disorders can be made.

Serotonin controls initiation of locomotion and afferent modulation of coordination via 5‐HT7receptors in adult rats

“…; Takakusaki et al . ). Once a low threshold site for MLR‐evoked locomotion was identified, repeated stimuli over a prolonged period in the experiments described here produced consistent responses (Figs and ).…”

Lesions causing freezing of gait localize to a cerebellar functional network

“…Stimulation of this region can induce locomotion in experimental animals. 21,23,24 Neuroimaging studies suggest that a similar CLR may exist in humans. Prior studies have used mental imagery of gait 25 or special foot pedals that allow for active stepping in the MRI scanner.…”

Midbrain circuits that set locomotor speed and gait selection

“…Yet, the commands for initiation and gait selection may originate in different supraspinal structures. The most important neuronal structure that has been implicated in these functions is a region in the midbrain named the mesencephalic locomotor region or MLR 7,8,9 .…”

“…Analogues of MLR have been observed in many vertebrates including fish, rodents, primates and humans 8,9,11,12 but with conflicting results as to its anatomical location. In addition to CnF the more ventrally located pedunculopontine nucleus (PPN) has been implicated.…”