Purkinje cell loss by OX7-saporin impairs acquisition and extinction of eyeblink conditioning.

The current study examined the effects of globally depleting Purkinje cells in the cerebellar cortex with the immunotoxin OX7-saporin on acquisition and extinction of delay eyeblink conditioning in rats. Rats were given OX7-saporin or saline 2 wk before the start of eyeblink conditioning. The rats that reached a performance criterion of two consecutive days with 80% or greater conditioned responses were given 5 d of extinction training followed by 2 d of reacquisition training. Rats that received infusions of OX7-saporin had 77.2%-97.9% Purkinje cell loss and exhibited impaired acquisition and extinction. The amount of Purkinje cell loss was correlated with the magnitude of the acquisition and extinction impairments. The highest correlations between Purkinje cell number and the rate of acquisition were in lobule HVI and the anterior lobe. The highest negative correlation between Purkinje cell number and the percentage of conditioned responses during extinction was in the anterior lobe. The results indicate that cerebellar Purkinje cells, particularly in the anterior lobe and lobule HVI, play significant roles in acquisition and extinction of eyeblink conditioning.