Firing properties of accessory olfactory bulb mitral/tufted cells in response to urine delivered to the vomeronasal organ of gray short-tailed opossums.

In comparison with many mammals, there is limited knowledge of the role of pheromones in conspecific communication in the gray short-tailed opossum. Here we report that mitral/tufted (M/T) cells of the accessory olfactory bulb (AOB) of male opossums responded to female urine but not to male urine with two distinct patterns: excitation followed by inhibition or inhibition. Either pattern could be mimicked by application of guanosine 5'-O-3-thiotriphosphate and blocked by guanosine 5'-O-2-thiodiphosphate, indicating that the response of neurons in this pathway is through a G-protein-coupled receptor mechanism. In addition, the inhibitor of phospholipase C (PLC), U73122, significantly blocked urine-induced responses. Male and female urine were ineffective as stimuli for M/T cells in the AOB of female opossums. These results indicate that urine of diestrous females contains a pheromone that directly stimulates vomeronasal neurons through activation of PLC by G-protein-coupled receptor mechanisms and that the response to urine is sexually dimorphic.