BioSystems 54 2000 141 – 149
Interrelated modification of excitatory and inhibitory synapses in three-layer olivary-cerebellar neural network
Isabella Silkis
Laboratory of
‘
Neurophysiology of Learning
’
, Institute of Higher Ner6ous Acti6ity and Neurophysiology of the Russian Academy of Sciences, Butlero6a
5
a street, Moscow
117865
, Russia Received 19 July 1999; accepted 20 October 1999
Abstract
The model of three-layer olivary-cerebellar neural network with modifiable excitatory and inhibitory connections between diverse elements is suggested. The same Hebbian modification rules are proposed for Purkinje cells, granule
input cells, and deep cerebellar nuclei output cells. The inverse calcium-dependent modification rules for these cells and hippocampalneocortical neurones or Golgi cells are conceivably the result of the involvement of cGMP and
cAMP in postsynaptic processes. The sign of simultaneous modification of excitatory and inhibitory inputs to a cell is opposite and determined by the variations in pre- andor postsynaptic cell activity. Modification of excitatory
transmission between parallel fibers and Purkinje cells, mossy fibers and granule cells, and mossy fibers and deep cerebellar nuclei cells essentially depends on inhibition effected by stellatebasket cells, Golgi cells and Purkinje cells,
respectively. The character of interrelated modifications of diverse synapses in all three layers of the network is influenced by olivary cell activity. In the absence presence of a signal from inferior olive, the long-term potentiation
depression in the efficacy of a synapse between input mossy fiber and output cell can be induced. The results of the suggested model are in accordance with known experimental data. © 2000 Elsevier Science Ireland Ltd. All rights
reserved.
Keywords
:
Olivary-cerebellar network; Excitatory synapse; Inhibitory synapse; Long-term potentiation; Long-term depression; Modification rules
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1. Introduction
Cerebellum is the one of a few structures in the central nervous system wherein neural intercon-
nections are known in detail De Zeeuw et al., 1998; Laine and Axelrad, 1998; Voogd and Glick-
stein, 1998. These connections are schematically shown in Fig. 1. Neurones at different cerebellar
layers receive information about peripheral events and central processes via mossy fibers MFs and
climbing fibers CFs Fig. 1. Output cerebellar elements, deep cerebellar nuclei cells DCNCs,
activate cerebral cortex via the thalamus. The
Tel.: + 7-95-334-4345; fax: + 7-95-338-8500. E-mail address
:
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PII: S 0 3 0 3 - 2 6 4 7 9 9 0 0 0 7 5 - 1
knowledge of the role of cerebellum in motor learning allowed elaboration of a neuronal model
of learning Ito, 1984; Houk et al., 1996; Clark et al., 1997; Kenyon, 1997; Mauk and Donegan,
1997; Raymond and Lisberger, 1997. The Marr – Albus – Ito model of cerebellum-dependent learn-
ing is based on only one type of synaptic plasticity: associative long-term depression of ex-
citatory transmission LTDe in synaptic path- ways between parallel fibers PFs and Purkinje
cells PCs Marr, 1969; Albus, 1971; Ito, 1984. The induction of this LTDe requires a pairing of
PFs and CF activation. Not only associative LTDe, but also homosynaptic LTDe and ho-
mosynaptic long-term potentiation of excitatory transmission LTPe have been recently found in
synapses formed by PFs on PCs Hartell, 1994. In addition, long-term depression of inhibitory
transmission LTDi between stellate or basket cells and PCs has been demonstrated Llano et al.,
1991; Kano et al., 1992. Only the mechanism of LTDe for PCs is described Linden, 1994; Daniel
et al., 1998; however, it is controversial. We have recently proposed the unitary postsynaptic mecha-
nism of excitatory and inhibitory synaptic plastic- ity
for the
neocortical, hippocampal
and cerebellar Purkinje cells Silkis, 1999. Using this
mechanism, one can predict the character of mod- ification of excitatory and inhibitory synapses on
diverse cells, if the types of postsynaptic recep- torschannels and second messenger are known.
Predicted results can be experimentally tested. The aim of this work has been to elucidate the
possible mechanisms and character of simulta- neous modifications in the efficacy of excitatory
and inhibitory synaptic inputs to different ele- ments of olivary-cerebellar neural network trig-
gered by rhythmic activation of MFs and CF.
2. The proposed mechanism of synaptic plasticity for Purkinje cells
