Synaptophysin-like immunoreactivity in the rat olfactory bulb during postnatal development and after restricted early olfactory experience.

Synaptophysin is a synaptic vesicle protein that provides a marker of synaptic distribution in the brain. We used synaptophysin immunohistochemistry to detect changes in synaptic distribution in the main olfactory bulb during normal early postnatal development and following early olfactory restriction. Synaptophysin-like immunoreactivity appears early in the postnatal development of most bulbar laminae. In the first postnatal week, the entire glomerular neuropil is stained intensely, but by PND 19, the glomerular perimeter becomes more intensely stained than its core. This immunoreactivity is especially dense along that aspect of the perimeter facing the olfactory nerve layer. To determine if this developmental pattern could be affected by early olfactory experience, unilateral naris closure was performed on PND 1. In deprived bulbs at PND 19, the difference in staining between the glomerular border and the glomerular core is significantly less than in either contralateral glomeruli or glomeruli from unoperated animals. The difference between the glomerular border and the glomerular core is greater in bulbs contralateral to a closed naris than in bulbs from unoperated animals. Staining intensity measured over entire glomeruli is not altered by naris closure, nor is staining of other laminae. The changes detected after naris closure indicate that the glomerular distribution of synaptophysin may be particularly sensitive to early olfactory experience.