Electrographic recording from bovine vomeronasal capsule under spontaneous and stimulated conditions

Abstract

The vomeronasal organ (VNO) is an accessory olfactory system which in many vertebrates seems to be involved in reproductive behavior, particularly in permitting males to detect estrus in conspecific females. We postulated that EEG-like field potentials could be recorded from the VNO because the organ has a sensory epithelium that can discharge in response to odorants, and because VNO receptor cells are structurally similar to cells in the olfactory mucosa that produce field potentials (the “electro-olfactogram”). We examined this postulate in male cattle by surgically implanting recording/perfusion cannulae into the ducts leading to each VNO. Both bipolar (between VNOs) and reference recording revealed continuous spontaneous voltage fluctuations that were similar to an EEG, except that amplitudes were larger and frequencies slower. Simultaneous recording of the EEG and VNO, using the same nasal reference electrode revealed that neither signal was “contaminated” by voltages from the other. Perfusions of one VNO with whole urine, urine condensate, or aqueous reconstituted urine extracts, whether from females in estrus or in anestrus, produced massive transient electrical responses from both VNOs. Perfusion with penicillin or local anesthetics caused more sustained large electrical responses from both VNOs, except that activity became quiescent about 15 min after local anesthesia. These results suggest that it is feasible to use direct recording of VNO responses to stimulation to investigate the behavioral physiology of the VNO. The cellular origin of these potentials is not self-evident, inasmuch as there are several probable sources: VNO receptor cells, cells of origin of the nervus terminalis, trigeminal afferents, vasomotor fibers, vascular erectile tissue, and fluid motion in the VNO. The experimental approach that is presented here could provide an assay system for exploring comparative functions and the behavioral significance of the various cell types that are associated with the mammalian VNO.