Stellate cell inhibition of Purkinje cells in the turtle cerebellum in vitro.

1. The stellate cell‐mediated inhibition of Purkinje cells was studied by intracellular recordings in an in vitro slice preparation of the turtle cerebellar cortex. A graded inhibitory postsynaptic potential (IPSP) was recorded in Purkinje cells upon stimulation of the parallel fibre‐stellate cell pathway. 2. The IPSP was abolished by bicuculline, and had a reversal potential around ‐75 mV, consistent with a GABAA receptor‐operated Cl‐ conductance dominating the response investigated here. 3. Paired recordings from synaptically coupled stellate cells and Purkinje cells demonstrated that the inhibitory input from a single stellate cell is sufficient to reduce the firing in a Purkinje cell. 4. The extracellular‐evoked IPSP interacted with the active postsynaptic membrane properties in the Purkinje cell. Interaction with both the Na+ plateau and the IA prolonged the responses to an IPSP, making the net effect of the inhibitory response dependent on the membrane potential in each postsynaptic neurone. 5. A precisely timed IPSP was particularly efficient in reducing dendritic Ca2+ influx. 6. The voltage‐dependent Ca2+ component of a climbing fibre response (CFR) as well as of a parallel fibre (PF) input was reduced by the IPSP. 7. It is suggested that Ca2+ spike‐mediated reduction in Purkinje cell excitability may be prevented by the stellate cell IPSP‐mediated reduction in Ca2+ influx.