Search

Previous workers had identified the vomeronasal organ, on anatomical evidence, as an accessory olfactory organ, present in most terrestrial vertebrates. Lesion experiments had demonstrated its importance in sexual behaviour in the hamster. Howevever, the sequestered position of the vomeronasal receptor epithelium within the organ raised questions concerning the access of olfactory stimuli. Using electrophysiological and pharmacological methods we have now demonstrated the following. 1. A pumping mechanism exists, powered by vasomotor movements, which can suck stimulus substances into the vonmeronasal organ. 2. A mechanism also exists for the active expulsion of the contents of the vomeronasal organ. 3. These mechanisms are activated by fibres running in the nasopalatine nerve. 4. The suction mechanism is controlled by sympathetic, probably adrenergic, fibres from the superior cervical sympathetic ganglion. Control of the expulsion mechanism has not been definitely established but does not appear to be sympathetic. 5. The vomeronasal organ can be adequately stimulated by activation of the pumping mechanism in the presence of odour. 6. Odour responses of single units in the accessory olfactory bulb have been recorded for the first time. 7. The time course of neuronal response in the accessory olfactory bulb is more rapid than predicted by many authors. The response is sufficiently fast that the vomeronasal system cannot be ruled out as a possible sensory pathway in many odour related behaviours. Possible modes of action of the pumping mechanism in awake animals are discussed.

Explorations of the qualitative and quantitative differences between the odors of pemenone (PEM), androstenone (AND) and isovaleric acid (IVA) show that they share a number of common perceptual characteristics. Among these are similarities in their odor quality and relative intensity ratings. PEM is also an efficient cross-adaptor and modulator of a subject's AND sensitivity. Here we evaluate the reciprocal efficacy of AND adaptation to alter the perceived intensity and quality of PEM, IVA and AND. Twenty-three people, including both those osmic and allosmic (n = 11) for the putrid odor quality of PEM, were tested. Following training in odor quality and intensity rating techniques, subjects sampled a selected substance for 2 min to obtain adaptation and then reported quality and intensity ratings for the three test stimuli. There was significant self-adaptation by PEM and IVA in all subjects, but self-adaptation by AND was only observed in the PEM-osmic subjects. AND did not cross-adapt PEM or IVA to any significant extent. Collectively, these results contrast with our earlier study in which PEM was an efficient cross-adaptor of AND. Here, AND was no more efficient than the control as an adapting substance for PEM, despite significant self-adaptation of PEM by itself. This lack of reciprocity in the effectiveness of PEM and AND as cross-adapters is not related to differences in odor intensity, as the PEM and AND concentrations were adjusted for each subject to elicit comparable intensity reports. These results support the notion that PEM, AND and IVA share certain perceptual characteristics, but interact differentially with three or more sets of perceptual channels that are now thought to result in a putrid odor quality.

Electrical stimulation of nerve fibers emerging from different positions of the olfactory epithelium was used to determine the receptive fields for 52 olfactory bulb neurons in the hamster. The responses of olfactory bulb neurons were recorded extracellularly with metal-filled micropipettes. Suprathreshold stimuli (500 microA) were applied to each of eight standard epithelial positions spaced approximately 250 microns apart, and the position, or positions, which, when stimulated, produced a response in the bulb were taken as an index of the neuron's receptive field. The results indicate that most bulb neurons have very localized receptive fields limited to only one or two stimulating positions. Furthermore, there was a statistically significant correlation between the location of a neuron's receptive field in the olfactory epithelium and the recording depth of the neuron in the olfactory bulb (Spearman rank correlation coefficient, rs, 0.67, P < 0.001). These findings demonstrate that in the mammalian olfactory system there exists a topographical projection of input from localized regions in the epithelium onto the second-order neurons in the olfactory bulb.

Electrical responses of single olfactory receptor neurons of the male redbanded leafroller moth were elicited by each of the principle components of the sex pheromone and six other behaviorally active compounds. Response frequencies to equal intensities of each of these compounds and changes in response frequency with increasing amounts of any one compound, varied from receptor to receptor. These differences in response characteristics appear to be due to factors intrinsic to the olfactory recptor neuron and not to factors external to it. The encoding of odor quality by these receptor neurons cannot be in the simple presence or absence of activity in any one of them. Rather, odor quality may be encoded by the pattern of activity which invariably arises across an ensemble of receptor neurons, each having its own distribution of sensitivities.