Changes in Excitability of Ascending and Descending Inputs to Cerebellar Climbing Fibers during Locomotion

Abstract

The inferior olive climbing fiber projection plays a central role in all major theories of cerebellar function. Therefore, mechanisms that control the ability of climbing fibers to forward information to the cerebellum are of considerable interest. We examined changes in transmission in cerebro-olivocerebellar pathways (COCPs) and spino-olivocerebellar pathways (SOCPs) during locomotion in awake cats (n ϭ 4) using low-intensity electrical stimuli delivered to the contralateral cerebral peduncle or the ipsilateral superficial radial nerve to set up volleys in COCPs and SOCPs, respectively. The responses were recorded as evoked extracellular climbing fiber field potentials within the C1 or C3 zones in the paravermal cerebellar cortex (lobule Va-Vc). At most C1 and C3 zone sites, the largest COCP responses occurred during the stance phase, and the smallest responses occurred during the swing phase of the ipsilateral forelimb step cycle. In marked contrast, SOCP responses recorded at the same sites were usually largest during the swing phase and smallest during the stance phase. Because substantial climbing fiber responses could be evoked in all phases of the step cycle, the results imply that olivary neurons remain excitable throughout, and that the differences between SOCPs and COCPs in their pattern of step-related modulation are unlikely to have arisen solely through inhibition at the level of the inferior olive (e.g., by activity in the inhibitory cerebellar nucleo-olivary pathway). The different patterns of modulation also suggest that climbing fiber signals conveyed by COCPs and SOCPs are likely to affect information processing within the cerebellar cortical C1 and C3 zones at different times during locomotion.

Electrophysiological Localization of Eyeblink-Related Microzones in Rabbit Cerebellar Cortex

“…As has been established previously, a number of criteria allow climbing fiber-evoked potentials to be distinguished from those generated by mossy fiber activity, in particular, the following: (1) the onset latency of climbing fiber field potentials (CFPs) are always Ͼ9 ms and therefore longer than those dependent on most direct pathways terminating as mossy fibers (Ekerot and Larson, 1973); and (2) CFPs are depressed after a second stimulus delivered 40 ms after the first, whereas mossy fiber field potentials (MFPs) are usually unchanged or facilitated ( Fig. 1 A, B) (Armstrong and Harvey, 1968;Apps and Lee, 1999;Pardoe et al, 2004). As verification, we recorded single-unit Purkinje cells (in both awake and anesthetized animals) in which the evoked complex spike activity mirrored components of the field potential ascribed to climbing fiber activity at the same location (Fig.…”

Pontine Maps Linking Somatosensory and Cerebellar Cortices Are in Register with Climbing Fiber Somatotopy

“…Second, studies in which mapping of cerebellar cortical zones in the barbiturate-or propofolanesthetized cat have been used to guide the insertion of recording microwires into the cerebellar cortex have found that the climbing fiber responses obtained from individual microwires in the awake animal displayed the same pattern of peripheral input as the zone in which they were implanted (Pardoe et al, 2004). Together, these findings suggest that the cerebellar cortical territory in which particular climbing fiber responses occur is not constrained by the choice of anesthetic and that the degree of segregation of climbing fiber inputs is maintained in the awake animal.…”

Organization of Cerebral Projections to Identified Cerebellar Zones in the Posterior Cerebellum of the Rat

“…For example, it seems remarkable that climbing fiber responses in vermal lobule VII may be triggered from the prelimbic cortex (Watson et al, 2009) which does not qualify as a major disynaptic source to this region. Of course, although to some extent the cerebro-olivo-cerebellar pathway is disynaptic (Lee and Kim, 2012), it usually involves more synapses (Baker et al, 2001;Pardoe et al, 2004).…”