INCREASED ASTROCYTIC ENSHEATHEMENT OF RAT PARALLEL FIBER-
PURKINJE CELL SYNAPSES AFTER 20 DAYS OF ACROBATIC LEARNING IN
RATS EXPOSED TO NEONATAL ETHANOL
Anna Klintsova, Charles R. Goodlett, William T. Greenough
Increased synapse number in the cerebellar cortex has been demonstrated after complex motor skill learning but not after motor activity alone. It was separately demonstrated in cerebral cortex that experience-dependent synaptic changes are associated with an increase in the surface contact between astrocytes and synapses. The present study attempted to determine if complex motor skill learning (termed the “acrobatic condition”) would result in cerebellar astrocyte plasticity in normal rats (suckle control, SC), gastrostomy control (GC) rats and in animals that were exposed to ethanol (4.5 g/kg/day) on postnatal days 4-9 (alcohol-exposed, AE). When 6 months old, animals from all postnatal conditions were randomly assigned for 20 days either to an inactive cagehoused condition (IC) or to the acrobatic condition (AC). Both SC and AE rats were previously demonstrated to have an increased number of parallel fiber – Purkinje cell synapses after 20 days in AC. We used electron microscopy in combination with unbiased stereology to examine volume fraction (V v
) of astrocyte processes as well as total surface density (S v
) of glial membrane in the neuropil and S
Vapposed
of glial membrane apposed to synaptic elements in the cerebellar cortex of rats. There was an effect of neonatal condition on V v
(but not on S
Vapposed
) : AE animals had a higher glial volume fraction in the cerebellar molecular layer than SC and GC littermates. V v
of glia was significantly increased in both SC and AE animals after 20 days of acrobatic learning. There was also a significant increase in the S
Vapposed of glial processes with synapses in molecular layer of cerebellar cortex in AC animals from all three neonatal groups. Our data suggests that motor learning-associated synaptogenesis is supported by enhanced glial plasticity that persists in cerebellum of the alcohol-exposed rats. The combination of elevated astrocyte Vv in the AE group, where neuron loss has been previously reported, and astrocyte Vv and apposition changes in response to the AC training suggests that pathological and therapeutic changes in astrocytes can co-exist in the same tissue. (supported by…)