Inositol-1,4,5-trisphosphate accumulation induced by urinary pheromones in female rat vomeronasal epithelium

Abstract

The mechanisms involved in pheromone-induced responses in the vomeronasal neurons, especially in mammals, are still unclear. In the present study, we examined the effects of rat urine samples containing various types of pheromones regulating gonadal functions on the accumulation of cAMP and inositol 1,4,5-trisphosphate (IP 3) in a vomeronasal membrane preparation from the female Wistar rat. Stimulation of the preparation with forskolin induced cAMP accumulation, but stimulation with urine samples excreted from the male Wistar rat, the female Wistar rat, and the male Donryu rat did not change cAMP levels. These results were consistent with the electrophysiological results showing that dialysis of a high concentration of cAMP into the vomeronasal neuron does not induce currents. Stimulation with the three urine samples induced the accumulation of IP 3 in the membrane preparation. These results are consistent with previous electrophysiological results [K. Inamura, M. Kashiwayanagi, K. Kurihara, Inositol-1,4,5-trisphosphate induces responses in receptor neurons in rat vomeronasal sensory slices, Chem. Senses 22 (1997) 93–103; K. Inamura, M. Kashiwayanagi, K. Kurihara, Blockage of urinary responses by inhibitors for IP 3-mediated pathway in rat vomeronasal sensory neurons, Neurosci. Lett. 233 (1997) 129–132]. After the treatment with Pertussis toxin (PTX), the male Wistar urine did not induce IP 3 accumulation significantly. Application of the male Wistar urine decreased ADP-ribosylation of G i with PTX, while that of the male Donryu urine decreased ADP-ribosylation of G o. Thus, the present results support a mechanism by which the responses of the rat vomeronasal neurons to urinary pheromones are mediated by IP 3, G i and/or G o.