Using the whole-cell mode of the patch-clamp technique, we recorded action potentials, voltage-activated cationic currents and putative second messenger-activated currents in receptor neurons in the vomeronasal sensory epithelium of female rats. The resting membrane potential and input resistance were -45.5 +/- 2.5 mV (mean +/- SEM, n = 39) and 1.5 +/- 0.2 G omega (mean +/- SEM, n = 37). Current injection of 1-3 pA induced overshooting action potentials. The firing frequency increased with increasing current injections linearly from 1 to 10 pA and reached a plateau at 30 pA, suggesting that rat vomeronasal receptor neurons sensitively elicit action potentials in response to a small receptor potential. Under voltage clamp, voltage-dependent Na+ inward current, inward Ca2+ current, sustained outward K+ current and Ca-(2+)-activated K(+)-current were identified. Dialysis of D-inositol-1,4,5-trisphosphate (D-IP3) induced inward currents with an increase in membrane conductance in approximately 54% of the cells and inward current fluctuations in 15% of the cell. L-IP3 also induced inward currents and current fluctuations in 53 and 13% of the cells respectively. The mean amplitude of inward currents induced by 100 microM D-IP3 and L-IP3 were 84.6 +/- 14.0 pA (SEM, n = 82) and 66.1 +/- 9.4 pA (SEM, n = 100) respectively. The IP3-induced responses were blocked by elimination of Na+ and Ca2+ in the external solution or application of 10 microM ruthenium red. The present study suggested that IP3-mediated transduction pathways exist in rat vomeronasal receptor neurons.

1. Responses of vomeronasal sensory neurons to urine excreted from rats, mice and hamsters were studied by the on-cell patch clamp method in slices of sensory epithelium from female Wistar rats. 2. The urine excreted from male and female Wistar rats, male Donryu rats and male C57BL/6 mice induced relatively large responses, while urine from male Sprague-Dawley rats and male Syrian hamsters induced small responses. 3. Of the 62 neurons responding to urine, 57 responded to only one of the urine preparations. 4. The sensory neurons that responded to the male Wistar urine were localized in the apical position of the epithelium where one type of GTP-binding protein, Gi2alpha, is selectively expressed. The neurons in the basal position of the epithelium, which express Goalpha, responded to urine from the other animals. 5. This study demonstrates that sensory neurons responsive to different urinary pheromones are localized in a segregated layer in the rat vomeronasal sensory epithelium.

The distribution of Fos-immunoreactive (Fos-ir) cells in the accessory olfactory bulb (AOB) of rats following vomeronasal organ exposure to urine was studied. Following exposure to male and female Wistar rat urine, Fos-ir cells were found in the mitral/tufted cell layer, granule cell layer and periglomerular cell layer of the AOB of female Wistar rat, with the highest number in the granule cell layer. Exposure to water or removal of the vomeronasal organ suppressed the expression of Fos-ir cells. These results suggest that female Wistar rats specifically detect urinary substances derived from male or female Wistar rats via the vomeronasal organ. Exposure of the vomeronasal organ of female Wistar rats to male Wistar urine induced the appearance of many more Fos-ir cells in all layers of the AOB than exposure to female Wistar urine. As for the mitral/tufted cell layer, the density of Fos-ir cells in the rostral portion (Gi2alpha-positive) of all regions of the AOB was about twice as high as that in the caudal portion when male urine was given. The distribution pattern of Fos-ir cells in response to female urine was not identical to that in response to male urine. That is, the density of Fos-ir cells in the caudal portion was slightly larger than that in the rostral portion in the lateral region, while in other regions the density in the rostral portion was higher than that in the caudal portion. It is likely that information from different pheromones is transmitted to the higher brain regions through the different regions of the AOB.

No abstract

No abstract