Effects of paired and unpaired eye-blink conditioning on Purkinje cell morphology

This experiment addressed (1) the importance of conjunctive stimulus presen tation for morphological plasticity of cerebellar Purkinje cells and inhibi tory interneurons and (2) whether plasticity is restricted to the spiny bra nches of Purkinje cells, which receive parallel fiber input, These issues w ere investigated in naive rabbits and in rabbits that received paired or un paired presentations of the conditioned stimulus (CS) and unconditioned sti mulus (US), To direct CS input to the cerebellar cortex, pontine stimulatio n served as the CS, Air puffs to the cornea served as the US, Paired condit ion rabbits received pontine stimulation for 350 msec paired with a cotermi nating 100-msec air puff, Unpaired condition rabbits received the same stim uli in a pseudorandom order at 1- to 32-sec intervals, Rabbits were trained for a mean of 12 days, Naive rabbits received no treatment, In Golgi-stain ed Purkinje neurons in lobule HVI, total dendritic length, main branch leng th, total spiny branch length, and number of spiny branch arbors were all g reater in the naive group than in the paired and unpaired groups, which did not differ, No differences were found between the hemispheres ipsilateral and contralateral to the trained eye, The dendritic length and number of br anches for inhibitory interneurons did not differ across groups, The Purkin je cell morphological changes detected with these methods do not appear to be uniquely related to the conjunctive activation of the CS and US in the p aired condition.