Kazuya Yoshimura

The neural control of orienting: role of multiple-branching reticulospinal neurons

This chapter emphasizes the functional significance of the multiple-branching patterns of descending axons implicated in the control of movement. The example provided concerns orienting head movements, which are controlled by pathways from the superior colliculus (SC). Such control is mediated via cervical reticulospinal neurons (C-RSNs), which take origin in the nucleus reticularis pontis caudalis and nucleus reticularis gigantocellularis, and give off multiple collaterals along the full length of their axonal trajectory. Their projection is not only to lamina IX neck motor nuclei in upper cervical segments, but also to laminae VII-VIII in lower cervical segments. Thus, SC commands for head orienting are transmitted to both neck motoneurons and lower cervical spinal circuitry, which latter network controls appropriate postural adjustments by the coordinated control of motoneurons supplying the four limbs.

1505 Effects of gap stimulation on orienting and pontomedullary reticular nerons in cats

MATSUO MATSUSHITA The dorsal spinocerebellar tract (DSCT) of the thoracic cord originates from Clarke’s column, marginal neurons of Clarke’s column, and lamina V neurons (uncrossed), and neurons in lamina VIII (crossed). We examined whether the thoracic DSCT projects to the cerebellar nuclei. Following injections of biotinylated dextran into two-four segments between the T4 and T9 segments in the rat, anterogradely labeled terminals were bilaterally seen , but predominantly ipsilaterally in the cerebellar nuclei. They were distributed in medial and ventral parts of the middle and caudomedial subdivisions of the medial nucleus, rostromedial parts of the anterior interpositus nucleus, and medial to caudal parts of the posterior interpositus nucleus. Labeled terminals were consistently seen in the ventral part of the lateral nucleus and the dorsolateral hump region. The present study demonstrates that the thoracic DSCT projects mainly to the medial nucleus, and the anterior and posterior interpositus nuclei.

Load Changes in Limbs during Orienting in Non-Restrained Cats

We simultaneously investigated eye and head movements and postural adjustment during orienting by measuring load force exerted by four limbs in cats. When light is moved from the fixation point to the target position, the head first begins moving towards the target position, and the eye moves in the opposite direction due to the vestibulo-ocular reflex (VOR). Later, the eye moves quickly in the target direction by saccade, synchronous with the remaining rapid head orientation movement. Head movement is classified as either ‘head rotation’ or ‘head translation’. During head rotation, the load force in ipsilateral limb to the target position decreased, and that in the contralateral limb increased. During head translation, on the contrary, load force in the ipsilateral limb increased and that in the contralateral limb decreased. This phenomenon was observed in fore- and hindlimbs. The latencies of head movement are very similar with those of the load force change in many trials, and in case in which the head movement has short latency, the amount of load force change is larger. In contrast, when head movement has long latency, the amount of load force change is smaller. In a previous study, we recorded two types of neurons from ponto-medullary reticular formation. The firing of these neurons was related with head movement. The cervical reticulospinal neuron (C-RSN) in ponto-medullary reticular formation got off collateral to both neck and forelimb motoneurons. These types were named phasic neuron (PN) and phasic sustained neuron (PSN). We discuss the relation between load changes and the two types of neurons and postural adjustment during orienting.

Pathways controlling head orienting and their function in the cat and monkey

The basal ganglia-a higher center of motor control-are known to receive inputs from multiple motor-related areas of the frontal lobe, including the primary motor cortex, the premotor cortex, the supplementary motor area, the pre-supplementary motor area, and the cingulate motor area. In order to understand the mechanism of motor information processing of the basal ganglia, it is important to clarify the distribution patterns of these cortical motor inputs in the basal ganglia, especially in the striatum that is the major input station of the basal ganglia. Employing a combination of electrophysiological mapping and anatomical tract-tracing, the segregation-overlap relationship of corticostriatal input zones from the motor-related areas has systematically been analyzed in the macaque monkey.