ACTIVITY-DEPENDENT REGULATION OF CALCIUM-BINDING PROTEINS IN THE DEVELOPING RAT OLFACTORY-BULB

Intracellular calcium, important in a variety of second messenger casc ades, is regulated in part by calcium-binding proteins such as calreti nin, parvalbumin, and calbindin. These proteins are highly concentrate d in the rat main olfactory bulb and are localized in distinct neurona l populations. In the present study, postnatal expression was characte rized immunohistochemically in normal rats and in rats with functional olfactory deprivation caused by unilateral naris closure, a manipulat ion that attenuates electrical activity in the bulb. Bulbs were examin ed from rats that had undergone naris closure or sham surgery on eithe r postnatal day 1 (P1) or P30 and were allowed varying subsequent surv ival times. Each of the calcium-binding proteins showed both distinct patterns of early expression and differential susceptibility to olfact ory restriction. For example, at P10, the densest immunoreactivity was observed for calretinin, a protein whose expression was the least aff ected by naris closure. After occlusion from P1-P30, there was a 30% r eduction in the density of calbindin-immunoreactive profiles in the gl omerular layer, and parvalbumin-immunoreactive profiles were reduced b y 64% in the external plexiform layer. Unlike many other changes induc ed by deprivation, the effects of olfactory restriction on calbindin a nd parvalbumin expression were not age dependent: naris closure from P 30-P60 caused similar substantial decreases in calbindin and parvalbum in immunoreactivities.These data demonstrate that the expression of ca lbindin and parvalbumin in rat bulb is regulated, in part, by afferent activity that is associated with full sensory experiences. The reduct ions of these calcium-binding proteins following olfactory deprivation are likely to be commensurate with altered control of intracellular c alcium. (C) 1997 Wiley-Liss, Inc.