Plastic Rearrangements of Synapse Ultrastructure in the Cerebellum in Toxicity due to Glutamate and NO-Generating Compounds

Ultrastructural changes in synaptic boutons of parallel fibers (PF) and the spines of Purkinje cell dendrites (PCD) in the frog cerebellum were stdied on exposure to high concentrations (1 mM) of glutamate (Glu) and NO-generating compounds, creating a model of stroke. Exposure to Glu led to envelopment of terminal boutons by spines, while NO-generating compounds, conversely, led to envelopment of spines by boutons. Morphological studies showed that in Glu solution, there was a dominance of synapses in which glial cells were surrounded by spines, while boutons were dominant in the presence of NO. On electrical stimulation of PF, the relative content of synapses whose boutons were enveloped by glial cells was greater than the proportion of synapses in which glial cells were enveloped by spines, by a factor of 10. These morphological changes reflect the functional state of PF and PCD synapses in response to the harmful influences of excess Glu and NO, apparent as different forms of synaptic contacts and neuron-glial structures.

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