Early postnatal differentiation of granule cell dendrites in the olfactory bulbs of normal and unilaterally odor-deprived rats.

Unilateral naris closure in rat pups on the day after birth (P1) results in a substantial loss of synaptic targets for the late developing granule cell population, suggesting granule cell differentiation may be altered. However, dramatic reductions in granule cell numbers also occur in deprived bulbs. A loss of 'competitors' may therefore balance losses in synaptic availability. The issue was quantitatively addressed by analyzing granule cell dendritic development in both sham-operated and unilaterally deprived pups. The period between P10 and P30 was marked by significant developmental increases in dendritic height, length and numbers of branches in control subjects. Continued growth was virtually confined to the most distal processes. Spine number and density also increased, but subsequently decreased in all by sixth-order processes. Growth curves for normal and deprived conditions were virtually identical at all ages suggesting that deprivation-induced changes do not involve alterations in initial phases of granule cell dendritic elaboration.