Physiological and anatomical studies of the interactions between Purkinje cells and basket cells in the cat's cerebellar cortex: evidence for a unitary relationship.

Intracellular recordings have been obtained from neurons in lobule V of the cat's vermis, which were identified as basket cells following intracellular injections of HRP. Stimulation of the inferior cerebellar peduncle or peripheral nerves elicited an initial depolarizing and subsequent hyperpolarizing response. Neither potential could be graded with changes in stimulus intensity; both displayed all-or-none properties at threshold levels of stimulation. The depolarization and hyperpolarization were confirmed as an excitatory postsynaptic potential and an inhibitory postsynaptic potential (IPSP), respectively, on the basis of their response to intracellular injections of hyperpolarizing and depolarizing currents into the cell body. A possible source of the unitary IPSP is the Purkinje cell, via its recurrent axonal collaterals. To test this hypothesis, an electron microscopic analysis was carried out to define the synaptic relationships between the recurrent collaterals of an HRP-filled Purkinje cell and 3 basket cells. Serial section analysis reveals that collaterals from a single Purkinje cell contact several basket cells, but each basket cell received somatic input from only one Purkinje cell. These data provide an anatomical substrate for the unitary IPSP observed during intracellular recording from basket cells. The unitary nature of the Purkinje cell-basket cell interaction indicates that a very limited population of cortical neurons may be involved in local circuits that integrate afferent information in the cerebellar cortex.