The internal lateral (IL) subnucleus of the parabrachial nucleus (PB), which is one of the seven lateral subnuclei of the PB, receives information from the spinal cord. The IL subnucleus perhaps relays nociceptive signals to the intralaminar nuclei of the thalamus, apparently being implicated in the motivational-affective component of pain reaction. However, cells of origin of spinal fibers to the IL subnucleus have not been investigated sufficiently. We intended to clarify these cells by injection of fast blue or wheat germ agglutinin-conjugated horseradish peroxidase into the IL subnucleus and/or other lateral subnuclei in the rat. When the tracer was injected into the IL subnucleus, many cells were labeled bilaterally in laminae I, V, and VII, and in the dorsolateral and dorsomedial parts of the lateral funiculus throughout the entire length of the spinal cord. A small number of labeled cells appeared ipsilaterally in laminae II-IV and VI in the upper cervical segments and contralaterally in laminae VIII and X throughout the spinal cord. Labeled cells in lamina I were more numerous ipsilaterally than contralaterally in the first two cervical segments but were more numerous contralaterally than ipsilaterally in the remaining spinal segments. Labeled cells were seen with a contralateral predominance in lamina VII, but with an ipsilateral predominance in lamina V and in the dorsolateral and dorsomedial parts of the lateral funiculus. With tracer injected into the lateral subnuclei of the PB, excluding the IL subnucleus, labeled cells were found primarily in lamina I throughout the entire length of the spinal cord. These results show that cells giving rise to spinoparabrachial fibers were more numerous and more widely distributed than previously reported.

The course of spinocerebellar fibers in the rat spinal cord was investigated by injecting horseradish peroxidase into the cerebellar anterior vermis after complete transection of the left inferior and right superior cerebellar peduncles. By this procedure, fibers passing via the inferior cerebellar peduncles (icp-fibers) were labeled retrogradely on the right side of the spinal cord, whereas fibers passing via the superior cerebellar peduncles (scp-fibers) were labeled on the left side. Crossed icp-fibers were located diffusely in the anterior and lateral funiculi in the sacral to lower lumbar segments. They gradually migrated laterally and dorsally in these funiculi and received many uncrossed icp-fibers moving laterally in the lateral funiculus from the gray substance in the upper lumbar to lower thoracic segments. These mixed fibers shifted more dorsally and laterally in the anterior and lateral funiculi to aggregate in the narrow peripheral zone of the lateral funiculus in the upper thoracic and lower cervical segments, and received many crossed fibers in the upper cervical segments. There were more icp-fibers than scp-fibers through the spinal cord. However, the extent of scp-fibers in the anterior and lateral funiculi was essentially the same as that for icp-fibers, except that a few scp-fibers were found in the dorsolateral marginal zone of the lateral funiculus. It has been generally accepted that the dorsal spinocerebellar tract ascends in the dorsal half of the lateral funiculus and enters the cerebellum via the inferior cerebellar peduncle, whereas the ventral spinocerebellar tract ascends in the ventral half of it and takes the superior cerebellar peduncle route. The results of this study suggest that it is necessary to revise this concept.

Potential sources of cerebellar cortical afferent fibers were identified in the vestibular ganglion, medulla oblongata, pons, and cerebellar nucleus of seven anesthetized Macaca fuscata after local injections of wheat germ agglutinin-conjugated horseradish peroxidase or Fast Blue into the flocculus (FL) or ventral paraflocculus (VP). There were differences in the sources of mossy fibers to the FL and VP. Labeled neurons, after injections into the FL, were located mainly in the ipsilateral vestibular ganglion, bilaterally in the vestibular and prepositus hypoglossal nuclei, nucleus reticularis tegmenti pontis, and the central part of the mesencephalic reticular formation including the raphe nuclei. Labeled neurons were rarely seen in the pontine nuclei after injections into the FL. By contrast, after injections into the VP, numerous labeled neurons were located in the contralateral pontine nuclei, but relatively few in the vestibular nuclei bilaterally. Sources of climbing fibers to the FL and VP were completely contralateral to the injection side. After the injection into the FL and VP, labeled neurons were located in the dorsal cap, ventrolateral outgrowth, and ventral part of the medial accessory olivary nucleus. The projections from these three olivary areas were generally consistent with a zonal pattern of terminations in the FL and VP. The present results are consistent with a hypothesis that the FL is mainly involved in the control of vestibulo-ocular reflex and that the VP is mainly involved in the control of smooth pursuit eye movements.

. The anatomical connection between the frontal eye field and the cerebellar hemispheric lobule VII (H-VII) suggests a potential role of the hemisphere in voluntary eye movement control. To reveal the involvement of the hemisphere in smooth pursuit and saccade control, we made a unilateral lesion around H-VII and examined its effects in three Macaca fuscata that were trained to pursue visually a small target. To the step (3°)-ramp (5-20°/s) target motion, the monkeys usually showed an initial pursuit eye movement at a latency of 80 -140 ms and a small catch-up saccade at 140 -220 ms that was followed by a postsaccadic pursuit eye movement that roughly matched the ramp target velocity. After unilateral cerebellar hemispheric lesioning, the initial pursuit eye movements were impaired, and the velocities of the postsaccadic pursuit eye movements decreased. The onsets of 5°visually guided saccades to the stationary target were delayed, and their amplitudes showed a tendency of increased trial-to-trial variability but never became hypo-or hypermetric. Similar tendencies were observed in the onsets and amplitudes of catch-up saccades. The adaptation of open-loop smooth pursuit velocity, tested by a step increase in target velocity for a brief period, was impaired. These lesion effects were recognized in all directions, particularly in the ipsiversive direction. A recovery was observed at 4 wk postlesion for some of these lesion effects. These results suggest that the cerebellar hemispheric region around lobule VII is involved in the control of smooth pursuit and saccadic eye movements.

Using the retrograde horseradish peroxidase (HRP) method, we determined whether axons of the spinocerebellar tract (SCT) neurons pass through the superior (SCP) or the inferior (ICP) cerebellar peduncle in rats. Following bilateral section of either the SCPs or the ICPs, HRP was injected into the cerebellar anterior lobe and lobule VI, and the resulting labeled neurons were quantitatively examined throughout the length ofthe spinal cord. Almost all SCT neurons in the central cervical nucleus, Clarke''s column and lamina VII of the third cervical (C3) to third thoracic (T3) segments and the T11 to fifth lumbar (L5) segments, and the majority of SCT neurons in the ventrolateral part of the anterior horn of the L6 to caudal (Ca) segments and laminae V of the C8-L5 segments and VII of the L6-Ca segments project their axons through the ICPs. The majority of spinal border cells (T11–L5) and a large number of SCT neurons in lamina VII of the C3-T3, T11–L5 and L6–Ca segments project their axons through the SCPs. A nearly equal number of SCT neurons in lamina VIII (C1-L6) send axons through the SCPs or the ICPs. The proportion of SCT neurons projecting via the SCPs versus those projecting via the ICPs was approximately 1:5.

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