Chemical Deafferentation of the Nasal Neuroepithelium Profoundly Reduces Cholecystokinin Gene Expression in the Mouse Olfactory Bulb

A denervation study was carried out to determine whether damage to the neuronal perikarya in the primary olfactory pathway alters the transneuronal level of cholecystokinin (CCK) mRNA expression. The time course study of denervation-induced change in CCK mRNA expression was done using northern blot and in situ hybridization methods. Northern blot analysis revealed a significant reduction in CCK mRNA expression. The quantified radioactive orbital densities in the olfactory bulb in the control at 48 hours, 7 days, and 14 days after the denervation were 1025 (100%), 743 (72%)/513 (50%), 358 (35%)/498 (49%) and 325 (32%)/338 (33%) photo-stimulated luminescence, respectively. In situ hybridization indicated that CCK expression in external tufted cells and middle tufted cells decreased time-dependently, reaching 76% of the control levels at 48 hours, 45% at 7 days, 26% at 14 days, and 15% at 30 days, respectively. CCK mRNA was expressed also in the deep tufted cells and mitral cells. Low-power darkfield photomicrography revealed that deep tufted cells and mitral cells did not undergo a profound decrease as seen in the external and middle tufted cells. These data suggest that CCK mRNA expression is differentially controlled by cell subpopulations in the olfactory bulb after deafferentation.