Somatotopical organisation within the climbing fibre projection to the paramedian lobule and copula pyramidis of the rat cerebellum

Abstract

The climbing fibre projection to the paramedian lobule (lobule VII) and the copula pyramidis (lobule VIII) in the posterior lobe of the rat cerebellum was investigated in pentobarbitone-anaesthetised animals. Percutaneous electrical stimulation generated climbing fibre field potentials on the cerebellar surface that indicated a somatotopical organisation into five distinct cortical areas. Each area was identified by the site(s) of peripheral stimulation that evoked the largest response within that area, and from medial to lateral the cortex was subdivided as follows [principal site(s) of stimulation in parentheses with corresponding range of onset latencies]: in the paramedian lobule, area 1 (contralateral face, 17-18 ms), area 2 (ipsilateral forelimb, 10-15 ms) and area 3 (ipsi- and contralateral forelimbs, 16-26 ms and 15-30 ms, respectively); and in the copula pyramidis, area 4 (tail, 17-21 ms) and area 5 (ipsilateral hindlimb, 13-19 ms). In additional retrograde tracer experiments, small volumes of fluorescent-tagged beads were injected into each of the different areas and the location of retrogradely labelled olive cells was mapped. By comparison with other species, the results indicate that in the paramedian lobule area 1 corresponds to zone A2; area 2 corresponds, at least in part, to medial C1; and area 3 corresponds to C2; in addition, farther laterally, a C3 zone may be present. In the copula pyramidis, areas 4 and 5 correspond to subzones of medial C1. Overall, the results support the view that a general principle of cerebellar cortical organisation is a division into parasagittal zones, each characterised by its somatotopically organised climbing fibre input that arises from a specific, rostrocaudally oriented column of cells within the inferior olivary nucleus.

Selective Impairment of the Cerebellar C1 Module Involved in Rat Hind Limb Control Reduces Step-Dependent Modulation of Cutaneous Reflexes

“…This module is present as the C1 zone in the copula pyramidis (COP) and has related regions in the C1 and C3 zones of lobules II-V of the anterior lobe (Atkins and Apps, 1997;Voogd et al, 2003;Pijpers et al, 2005). Indeed, we show that a small targeted injection of CTb-S into C1 of COP results in degeneration within well circumscribed regions of the precerebellar nuclei.…”

“…A small quantity of CTb-S (30 -50 nl) at full concentration was pressure injected into either the C1 zone of COP or paramedian lobule (PMD) of the right cerebellar hemisphere (for surgical procedure, see below). Electrophysiological mapping of climbing fiber receptive fields enabled targeting of the injections at the center of cortical zones (Atkins and Apps, 1997). Animals were killed at various time intervals after injection to establish a time course of the resultant CTb labeling.…”

“…Bottom, Three three-dimensional representations of precerebellar nuclei: from top to bottom, the basal pontine nuclei , the lateral reticular nuclei , and the left inferior olivary complex (Ruigrok, 2004). Purkinje cells of the C1 and C3 zones (middle, blue stripes) of the anterior lobe and of the C1 zone of lobule VIII (COP) are believed to be involved in processing hindlimb information and to project to the medial part of the AIN (Atkins and Apps, 1997;Voogd et al, 2003;Pijpers et al, 2005). To study the function of the related module, all blue areas would need to be affected simultaneously.…”

“…In addition, supplementary doses were given intraperitoneally to maintain deep levels of anesthesia. This anesthetic was chosen because it allows the identification of cortical zones by extracellular recording of evoked climbing fiber field potentials while reducing mossy fiber responses (Atkins and Apps, 1997). The rats of experimental group 3 were anesthetized with isoflurane (5% initially, 0.5-2% maintenance in 0.5 L/min oxygen and 1 L/min nitrous oxide).…”

“…In group 1 and 2 animals, evoked field potentials were recorded on the right cerebellar surface with glass-coated tungsten microelectrodes (tip, ϳ50 m; impedance, 50 -140 k⍀) as the result of brief (0.1 ms) electrical percutaneous stimulation of the ipsilateral or contralateral forelimb or hindlimb with pairs of needle electrodes (Atkins and Apps, 1997). In this way, the location of the C1 zone of the COP or PMD was identified by their relatively short latency field potential that was triggered from ipsilateral hindlimb or ipsilateral forelimb stimulation, respectively.…”