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Abstract
Optokinetic stimulation activates visual climbing fiber pathways that synapse upon
contralateral floccular Purkinje cells. Long-term horizontal optokinetic stimulation
causes a progressive decrease in gain of the optokinetic reflex and leads to the subsequent
genesis of a prolonged negative optokinetic afternystagmus. Since the flocculus is
involved in adaptation to optokinetic stimulation, we used the technique of differential
display reverse transcription-polymerase chain reaction to explore transcriptional
changes in the flocculus evoked by long-term optokinetically evoked climbing fiber
discharge. Several differentially transcribed gene products were isolated and sequenced.
One of these, calbindin mRNA, was expressed in relatively decreased abundance in the
flocculus that received increased climbing fiber input. Decreased transcription of
calbindin mRNA was confirmed by northern blots. Hybridization histochemistry was used
to localize calbindin mRNA to Purkinje cells and confirmed decreased transcription
of calbindin mRNA in Purkinje cells located in folium 1 of the flocculus. Western
blots and immunohistochemistry localized the climbing fiber-evoked decreased expression
of calbindin to Purkinje cells in folia 1 of the flocculus. The expression of four
other calcium-binding proteins in the flocculus was not influenced by optokinetic
stimulation. Changes in expression of calbindin could be evoked by decreases in intracellular
calcium associated with climbing fiber-evoked decreases in Purkinje cell simple spike
activity.The application of differential display reverse transcription-polymerase
chain reaction has provided a positive screen for several molecules in addition to
calbindin whose expression is affected by naturally evoked activity in a major synaptic
pathway to the cerebellum. Further experiments will be required to specify the functional
role of each of these molecules.