An electrophysiological study of the accessory olfactory bulb in the rabbit--I. Analysis of electrically evoked potential fields.

Following electrical stimulation of the vomeronasal nerves, the primary olfactory nerves, the lateral olfactory tract and the corticomedial amygdala, we have made a study of evoked potentials in the rabbit accessory olfactory bulb. Vomeronasal nerve stimulation evoked a complex field potential consisting of a compound action potential followed by 4 negative waves (N1, N2, N3, N4). In contrast to the field potential elicited in the main olfactory bulb following primary olfactory nerve stimulation, there was either no evoked wave or only a weak positive component of the field in the accessory bulb. Amygdala stimulation caused a long latency, long duration negative-positive dipolar field potential in the accessory olfactory bulb. Both antidromic and orthodromic field potentials showed sign reversal when the electrode penetrated the bulb at a point corresponding to the lower border of the mitral cell band. Stimulation of the lateral olfactory tract elicited a weak, short-latency wave which did not show any sign reversal when the electrode was lowered into the accessory bulb. This wave was presumably due to fibres arising in the main bulb and projecting through the accessory bulb into the lateral olfactory tract. Electrical stimulation of the primary olfactory nerves did not induce any response in the accessory bulb neither did vomeronasal nerve stimulation evoke a response in the main olfactory bulb. The origin of these potential fields is discussed and it is concluded that the synaptic organization of the accessory olfactory bulb resembles that of the main olfactory bulb in lower vertebrates. There is no detectable communication between the two olfactory systems.