Variability of position of the P2 glomerulus within a map of the mouse olfactory bulb

Olfactory receptor neurons (ORNs) that express a common odorant receptor mo lecule target specific glomeruli in the olfactory bulb. We systematically a ssessed the location of the olfactory glomeruli that receive input from ORN s expressing P2 receptors in the P2-internal ribosome entry site-tau-lacZ m ouse. We present a new mapping method that includes an Internet-accessible computer program for generating two- and three-dimensional maps of the glom erular sheet in the olfactory bulbs of mice. Cylindrical coordinates were u sed to define glomerular location: The coordinates were given as the antero posterior (AP) distance parallel to the long axis of the bulb (rostrocaudal ; RC) and angular measurements with origin defined by the remnant ependymal layer in the center of the granule cell layer in the bulb. Using this meth od, we can apply rigorous statistical methods to give objective estimates o f position and variability. At the 95% confidence interval, the lateral P2 glomerulus lies at coordinates 1,008 mum +/- 306 mum AP x 146 degrees +/- 1 2 degrees, and the medial P2 glomerulus lies at 1,828 mum +/- 196 mum AP x 204 degrees + 8 degrees. We estimate that these coordinates encompass a dom ain containing 29 and 37 of the 1,800 glomeruli (similar to2%) for the late ral and medial glomeruli, respectively. Furthermore, the data reported here demonstrate that the rostrocaudal position of small P2 glomeruli is three times more variable than that of large glomeruli. (C) 2001 Wiley-Liss, Inc.