Abstract
It is generally believed that the main olfactory system processes common odors and the vomeronasal system is involved mainly in the detection of pheromones. The accessory olfactory bulb (AOB) is the first relay station in the vomeronasal system. To investigate how pheromonal information is processed in the rat AOB, we obtained high resolution mapping of pheromone-induced activation by optical imaging of intrinsic signals. Urine collected from male or female rats were used as test substances. Application of volatile components in the male urine (2-5%) with a syringe mainly activated the anterior AOB (aAOB), whereas female urine-induced activation was observed in both the aAOB and caudal part of the AOB in the male rats. In the female rats, urine-induced activation occurred mostly in the aAOB. Application of non-volatile urine components was performed by putting the nostrils contact with filter paper moistened with urine (3-5%). Either male or female urine induced mainly activation in the posterior AOB (pAOB) and to a lesser extent in the aAOB. In contrast, urinary responses were also observed in a few of glomeruli of the main olfactory bulb. The threshold for urine-induced activation in the glomeruli, however, was approximately 50%, which was higher than that obtained in the AOB (1%). These results provide the evidence that the aAOB is activated by volatile components in male or female urine, whereas the pAOB is activated by non-volatile components. [J Physiol Sci. 2006;56 Suppl:S185]
