INTRACELLULAR CORRELATES OF ACQUISITION AND LONG-TERM-MEMORY OF CLASSICAL-CONDITIONING IN PURKINJE-CELL DENDRITES IN SLICES OF RABBIT CEREBELLAR LOBULE HVI

Intradendritic recordings in Purkinje cells from a defined area in par asaggital slices of cerebellar lobule HVI, obtained after rabbits were given either paired (classical conditioning) or explicitly unpaired ( control) presentations of lone and periorbital electrical stimulation, were used to assess the nature and duration of conditioning-specific changes in Purkinje cell dendritic membrane excitability. We found a s trong relationship between the level of conditioning and Purkinje cell dendritic membrane excitability after initial acquisition of the cond itioned response. Moreover, conditioning-specific increases in Purkinj e cell excitability were still present 1 month after classical conditi oning. Although dendritically recorded membrane potential, input resis tance, and amplitude of somatic and dendritic spikes were not differen t in cells from paired or control animals, the size of a potassium cha nnel-mediated transient hyperpolarization was significantly smaller in cells from animals that received classical conditioning. In slices of lobule HVI obtained from naive rabbits, the conditioning-related incr eases in membrane excitability could be mimicked by application of pot assium channel antagonist tetraethylammonium chloride, iberiotoxin, or 4-aminopyridine. However, only 4-aminopyridine was able to reduce the transient hyperpolarization. The pharmacological data suggest a role for potassium channels and, possibly, channels mediating an I-A-like c urrent, in learning-specific changes in membrane excitability. The con ditioning-specific increase in Purkinje cell dendritic excitability pr oduces an afterhyperpolarization, which is hypothesized to release the cerebellar deep nuclei from inhibition, allowing conditioned response s to be elicited via the red nucleus and accessory abducens motorneuro ns.