Two Types of Reactions of Glial Cells to the Stimulation of Parallel Fibers in the Presence of an NO-Generating Compound as a Morphological Expression of the Physiological Activity of Two Types of Astrocytes in the Frog Cerebellum

摘要

In our previous study [1] on the plasticity of cell interactions, we demonstrated the asymmetry of neuron-neuron and neuron-glia encapsulating reactions to the imbalance of glutamate (Glu) and nitric oxide (NO) in the synapse of parallel fibers (PFs)on the Purkinje cells (PCs) of the upper molecular layer of the frog cerebellum in vitro. The asymmetry of cell reactions at the level of neuron-glia interaction consisted in the following. In the case of Glu excess in vitro (1 mM), the amount of spinesencapsulated by glial cells was larger than the amount of glia-encapsulated boutons,, Glial wrappings [1], the most intense type of the glial encapsulation of neurons, were observed around vacant spines, which are the main source of NO in the upper molecular layer of the cerebellum. Conversely, in the case of NO excess (1 mM NaNO_2), the number of boutons encapsulated by glial cells was larger than the number of glia-encapsulated spines, and glial wrappings were observed around vacant boutons, which were the main sources of Glu in the upper molecular layer of the cerebellum [1]. These results not only demonstrate a close functional interaction between the neu-rotransmitter Glu/NO imbalance in the extracellular medium and the plastic reaction of glial cells, but also allow us to assume the existence of more than one type of glial cells near PF-PC synapses. However, these data are insufficient for judging on the number of glial cell types involved in the function of PF-PC synapses, which are the main synapses in the cerebellum that connect its input and output neurons (granular cells (GrCs) and PCs, respectively). The necessary information can be obtained if we analyze the data on two morphologically opposite reactions of glial cells interacting with boutons and spines in PF-PC synapses after the electric stimulation of PFs in the presence of excess NO in vitro [1]. These glial cells (normally indistinguishable morphologically) are astrocytes, which are known to be functionally active near PF-PC synapses and to prevent other types of glial cells from penetrating into the area influenced by astrocytes [2, 3]. We attempted to determine whether the frog cerebellum contained two types of astrocytes interacting with the polar terminals of PF-PC synapses (boutons and spines) and to estimate their role in the functioning of an information system such as the cerebellum [4, 5].