TERMINAL ARBORIZATIONS OF OLFACTORY NERVE-FIBERS IN THE GLOMERULI OF THE OLFACTORY-BULB

The glomerulus of the olfactory bulb may serve as a fundamental organi zational unit for odor representation. In this context, the axons of o lfactory receptor cells with similar response spectra may converge in specific glomerlui. While the topography between the olfactory epithel ium and the olfactory bulb glomeruli has been explored, the characteri stics of primary afferent terminal fields within glomeruli are poorly understood. To explore this issue, reconstructions of the terminal arb ors of single olfactory nerve (ON) fibers within glomeruli were carrie d out in the rat olfactory bulb at the light microscopic level. Tissue samples prepared with the Golgi-EM technique resulted in distinct imp regnation of limited subsets of individual ON fibers. Following camera lucida reconstruction, quantitative analyses were made on selected se ts of ON fibers and on the glomeruli they invaded. Most ON fibers bega n to arborize only after penetrating the glomeruli to a mean depth of approximately 35.9 mum. The fibers gave rise to a complex arbor of bra nches that was limited in total length (mean 157.7 mum) and the number of en passant varicosities or terminal enlargements (mean = 8.1). The number of varicosities and terminal boutons was proportional to the t otal length of branches. Also, there was a statistically significant c orrelation between the total branch length and the area (mum2) encompa ssed by the total arbor. The intraglomerular region supplied by the te rminal arbor of an individual ON fiber was generally restricted. Given the recent molecular specificity attributed to olfactory receptor cel ls, this may provide a morphological basis for selective processing of signals encoded by specific receptors in the olfactory epithelium. (C ) 1993 Wiley-Liss, Inc.