Alan R. Gibson

Activation of climbing fibers.

Cells in the inferior olive are the sole source of climbing fibers to the cerebellum. In this article, we review some of the discharge properties of olivary cells that are important for understanding its functional role in cerebellar processing. It is generally believed that climbing fiber input supplies the cerebellum with information related to movement errors in order to improve motor performance. As a whole, olivary properties are not consistent with this function. The properties are consistent with the hypothesis that the olive is important for associating arbitrary sensory stimuli with somatosensory events. Although such associations would not be useful for improving the accuracy of motor commands, they may be useful for organizing appropriate behaviors to cope with the predicted event.

Functional Relations of Cerebellar Modules of the Cat

The cerebellum consists of parasagittal zones that define fundamental modules of neural processing. Each zone receives input from a distinct subdivision of the inferior olive (IO)—activity in one olivary subdivision will affect activity in one cerebellar module. To define functions of the cerebellar modules, we inactivated specific olivary subdivisions in six male cats with a glutamate receptor blocker. Olivary inactivation eliminates Purkinje cell complex spikes, which results in a high rate of Purkinje cell simple spike discharge. The increased simple spike discharge inhibits output from connected regions of the cerebellar nuclei. After inactivation, behavior was evaluated during a reach-to-grasp task and during locomotion. Inactivation of each subdivision produced unique behavioral deficits. Performance of the reach-to-grasp task was affected by inactivation of the rostral dorsal accessory olive (rDAO) and the rostral medial accessory olive (rMAO) and, possibly, the principal olive. rDAO inactivation produced paw drag during locomotion and a deficit in grasping the handle during the reach-to-grasp task. rMAO inactivation caused the cats to reach under the handle and produced severe limb drag during locomotion. Inactivation of the dorsal medial cell column, cell group β, or caudal medial accessory olive produced little deficit in the reach-to-grasp task, but each produced a different deficit during locomotion. In all cases, the cats appeared to have intact sensation, good spatial awareness, and no change of affect. Normal cerebellar function requires low rates of IO discharge, and each cerebellar module has a specific and unique function in sensory–motor integration.

Cat visual corticopontine cells project to the superior colliculus

Abstract Antidromic stimulation was used to study corticopontine visual axons and their tectal collaterals in cats. Sixty-seven cortical cells were activated antidromically by electrical stimulation of the rostral pontine visual area, 38 in area 18, and 29 in lateral suprasylvian cortex. Two thirds of these corticopontine cells (46 cells) could also be antidromically activated by stimulation of the superior colliculus, demonstrating that they gave rise to a tectal collateral.

Consensus paper: current views on the role of cerebellar interpositus nucleus in movement control and emotion.

In the present paper, we examine the role of the cerebellar interpositus nucleus (IN) in motor and non-motor domains. Recent findings are considered, and we share the following conclusions: IN as part of the olivo-cortico-nuclear microcircuit is involved in providing powerful timing signals important in coordinating limb movements; IN could participate in the timing and performance of ongoing conditioned responses rather than the generation and/or initiation of such responses; IN is involved in the control of reflexive and voluntary movements in a task- and effector system-dependent fashion, including hand movements and associated upper limb adjustments, for quick effective actions; IN develops internal models for dynamic interactions of the motor system with the external environment for anticipatory control of movement; and IN plays a significant role in the modulation of autonomic and emotional functions.

Pathways for control of face and neck musculature by the basal ganglia and cerebellum

The basal ganglia are believed to influence movement via thalamo-cortical projections. However, the basal ganglia may also affect brainstem areas involved in movement control such as the red nucleus. The red nucleus receives input from the cerebellum and projects to motor neurons and premotor neurons in the contralateral brainstem and spinal cord. Are there pathways that allow output from the basal ganglia to influence processing in the red nucleus? This study uses the bidirectional tracer, WGA-HRP, to demonstrate that regions of the cat red nucleus receive input from the basal ganglia as well as from the cerebellum. Output from the entopeduncular nucleus, the feline equivalent of the internal segment of the globus pallidus, provides a modest direct input to the red nucleus as well as a more substantial indirect input via projections to the zona incerta and the fields of Forel. Regions of the red nucleus with input from the basal ganglia also receive input from the cerebellar dentate nucleus and lateral regions of interpositus. The regions of the red nucleus receiving basal gangliar input project to the contralateral facial nucleus and upper segments of the cervical spinal cord. Therefore, the red nucleus provides a junction where output from the basal ganglia can interact with output of the cerebellum for movement control of the head and face. The pathway may provide a substrate for a variety of movement disorders that are seen with diseases of the basal ganglia such as cervical dystonia and Parkinsons facies.

Activated autologous macrophage implantation in a large-animal model of spinal cord injury.

OBJECT Axonal regeneration may be hindered following spinal cord injury (SCI) by a limited immune response and insufficient macrophage recruitment. This limitation has been partially surmounted in small-mammal models of SCI by implanting activated autologous macrophages (AAMs). The authors sought to replicate these results in a canine model of partial SCI. METHODS Six dogs underwent left T-13 spinal cord hemisection. The AAMs were implanted at both ends of the lesion in 4 dogs, and 2 other dogs received sham implantations of cell media. Cortical motor evoked potentials (MEPs) were used to assess electrophysiological recovery. Functional motor recovery was assessed with a modified Tarlov Scale. After 9 months, animals were injected with wheat germ agglutinin-horseradish peroxidase at L-2 and killed for histological assessment. RESULTS Three of the 4 dogs that received AAM implants and 1 of the 2 negative control dogs showed clear recovery of MEP response. Behavioral assessment showed no difference in motor function between the AAM-treated and control groups. Histological investigation with an axonal retrograde tracer showed neither local fiber crossing nor significant uptake in the contralateral red nucleus in both implanted and negative control groups. CONCLUSIONS In a large-animal model of partial SCI treated with implanted AAMs, the authors saw no morphological or histological evidence of axonal regeneration. Although they observed partial electrophysiological and functional motor recovery in all dogs, this recovery was not enhanced in animals treated with implanted AAMs. Furthermore, there was no morphological or histological evidence of axonal regeneration in animals with implants that accounted for the observed recovery. The explanation for this finding is probably multifactorial, but the authors believe that the AAM implantation does not produce axonal regeneration, and therefore is a technology that requires further investigation before it can be clinically relied on to ameliorate SCI.