GLIAL HYPERTROPHY IS ASSOCIATED WITH SYNAPTOGENESIS FOLLOWING MOTOR-SKILL LEARNING, BUT NOT WITH ANGIOGENESIS FOLLOWING EXERCISE

Rats reared from weaning in a complex environment have an increase in 1) glial surface area, 2) capillary volume, and 3) the number of synap ses, per neuron. In that paradigm it has not been possible to determin e whether the glial increase more closely correlates with the increase in synaptic numbers or with angiogenesis. More recently we have found that rats that exercised had an increase in the density of capillarie s without an increase in the synaptic numbers, whereas rats that learn ed new motor skills had a greater number of synapses per neuron withou t an increase in the density of capillaries. Those findings provided t he opportunity to investigate whether changes in glial volume in the c erebellum correspond to changes in the number of synapses or in capill ary volume. Glial area fraction estimates were obtained using point co unts on electron micrographs from the previous studies. The skill lear ning group had a greater volume of molecular layer per Purkinje cell, and also a greater volume of glia per Purkinje cell, than rats in eith er an inactive group or rats in two exercise groups. No significant di fferences were found in glial volume per synapse and glial volume per capillary across groups, although there was a tendency for glial volum e per capillary to be lower in the exercise groups. The data indicate that glial volume correlates with synaptic numbers and not with capill ary density. (C) 1994 Wiley-Liss, Inc.