Focal denervation alters cellular phenotypes and survival in the rat olfactory bulb: a developmental analysis

Our previous work (Couper Leo et al. [2000] J. Comp. Neurol. 417:325-336) introduced a technique for focally denervating the olfactory bulb soon after birth and described the pattern of changes incurred by this procedure by postnatal day (P) 30. The current study extends these findings with a developmental analysis of the effects of focal denervation in P10 and P20 rats. The results suggest that denervation begins to affect bulb architecture and cell survival soon after the procedure is performed, but that alterations within the bulb occur over an extended time period. For example, at P10, bulb and laminar sizes and mitral/tufted cell profile number had begun their decline, and nearly all measurements were significantly reduced by P20. Furthermore, a superficial-to-deep gradient of alterations in bulb architecture and a temporal separation of the effects on mitral/tufted cell dendrites vs. somata were observed. Immunohistochemical analyses of olfactory marker protein (OMP)-, calretinin- calbindin-, parvalbumin-, tyrosine hydroxylase-, and glutamic acid decarboxylase-stained sections indicated that: 1) denervation alters the interaction between olfactory axons and their targets in a developmentally significant manner; 2) the fine structure of denervated cells is altered; 3) cell phenotypes are differentially affected by loss of afferent contact, perhaps due to the age-dependent expression of their defining antigens; and 4) specific cell populations may be lost as a result of denervation.