Climbing fiber coupling between adjacent Purkinje cell dendrites in vivo

Fredrik Bengtsson

doi:10.3389/neuro.03.007.2009

Abstract

Climbing fiber discharges within the rat cerebellar cortex have been shown to display synchrony, especially for climbing fibers terminating in the same parasagittal bands. In addition, Purkinje cells which have the smallest rostrocaudal separation also seem to have the highest degree of synchrony. But this has so far only been investigated for distances down to 250 μm. In the present study, we wanted to investigate whether Purkinje cells that are located immediately next to each other display a particularly pronounced synchrony in their climbing fiber discharges. To this end, we used a previously undescribed type of electrophysiological recording, a single electrode, loose patch, dual dendritic recording, from pairs of adjacent Purkinje cells in the decerebrated, non-anesthetized cat. From each recorded dendrite, this technique provided well isolated, unitary calcium spikes, which we found to have a spontaneous activity that was essentially identical with the pattern of spontaneous climbing fiber discharges. By calculating the coupling in firing between the adjacent dendrites, we found that most climbing fiber responses occurred independently of each other and that the probability of coupled discharges was less than 8%. These values are comparable to those obtained in previous studies for Purkinje cells located within the same parasagittal band and show that climbing fiber coupling within a microzone exists also in non-rodent mammalian species. However, since the degree of synchrony of climbing fiber discharge was not particularly pronounced in adjacent Purkinje cells, it seems unlikely that climbing fiber synchrony has pronounced systematic regional variations within the same microzone.

Highlights

Inferior olivary (IO) neurons are connected to each other with gap junctions (Llinas et al, 1974), which makes them electrotonically coupled (Devor and Yarom, 2002; Llinas and Yarom, 1981; Placantonakis et al, 2006)
This has been shown to occur in numerous studies in which the synchrony of climbing fiber (CF) discharges have been investigated with recordings of CF responses in Purkinje cells (PCs) of the cerebellar cortex (De Zeeuw et al, 1997; Flusberg et al, 2008; Lang et al, 1999; Ozden et al, 2008; Welsh et al, 1995)
In order to provide a more complete measure of coupling, where the discharge of one IO cell leads the discharge of an adjacent IO cell, we measured the probability with which the discharge of one IO cell was followed by a discharge in its DISCUSSION Using a not previously described type of recording, the singleelectrode double loose patch dendritic recording, we investigated the degree of CF coupling in pairs of adjacent PC dendrites

Summary

Introduction

Inferior olivary (IO) neurons are connected to each other with gap junctions (Llinas et al, 1974), which makes them electrotonically coupled (Devor and Yarom, 2002; Llinas and Yarom, 1981; Placantonakis et al, 2006). The coupling provides a mechanism by which IO neurons may become synchronized in their output This has been shown to occur in numerous studies in which the synchrony of climbing fiber (CF) discharges have been investigated with recordings of CF responses in Purkinje cells (PCs) of the cerebellar cortex (De Zeeuw et al, 1997; Flusberg et al, 2008; Lang et al, 1999; Ozden et al, 2008; Welsh et al, 1995). The synchronization has been reported to preferentially occur in narrow sagittal bands (De Zeeuw et al, 1997; Lang et al, 1999) suggesting that synchronization may primarily be a property of the IO neurons that project to the same microzone of the cerebellar cortex. The morphological underpinnings of the microzonal organization are that individual IO cells diverge to innervate 5–10 PCs which all are located in a very narrow sagittal band (Sugihara et al, 2001) and that different IO neurons projecting the same microzone can be found in the same small part of the IO (Garwicz et al, 1996; Sugihara et al, 2007)

Methods

Results

Conclusion