Physiology & Behavior, Vol. 28, pp. 1011-1015. Pergamon Press and Brain Research Publ., 1982. Printed in the U.S.A. Autonomic Innervation of the Vomeronasal Organ of the Cat RONALD ECCLES Department of Physiology, University College, Cardiff, Great Britain CF1 1XL Received 13 November 1981 ECCLES, R. Autonomic innervation of the vomeronasal organ of the cat. PHYSIOL BEHAV. 28(6) 1011-1015, 1982.- Electrical stimulation of sympathetic fibres to the vomeronasal organ of the cat caused a suction of fluid into the lumen of the organ. A resting secretion was observed from the organ, and electrical stimulation of parasympathetic fibres caused secretion to drip from the vomeronasal duct. A model of a possible vasomotor pumping mechanism is discussed and the pathways taken by the autonomic fibres to the organ are described. Cat vomeronasal organ Autonomic innervation Stimulus access to vomeronasai organ Vomeronasal secretion THE vomeronasal organ or Jacobson's organ is an accessory olfactory organ present in most terrestrial vertebrates and there is much evidence based on behavioural and anatomical studies which indicates that the vomeronasal organ has an important role in sexual behaviour and reproduction [10,13]. A major problem concerning the physiology of the vom- eronasal organ is the determination of how substances gain access to the olfactory receptor epithelium sequestered within the organ. In the cat, the vomeronasal organ consists of a pair of tubular structures lying on either side of the nasal septum above the vomer bone. The organ is closed posteriorly and opens anteriorly by means of a fine duct (30-40/zm diameter) into the nasopalatine canal [12]. The nasopalatine canal, sometimes referred to as Stensen's canal, connects the nasal cavity with the oral cavity through the incisival foramen. The position of the vomeronasal organ in the cat is illustrated in Fig. 1. Because of the very small size of the vomeronasal duct, airborne and dissolved sub- stances would only enter the vomeronasal organ very slowly by diffusion and clearance from the organ would similarly be very slow. This problem of stimulus access has led some authors to conclude that the function of the vomeronasal organ is directed to the retention of odours, "giving an after smell" [12]. The vomeronasal organ may be involved in the detection of pheromones in urine as many male mammals respond to female urine by approach, sniffing, licking and the Flehmen response in which the mouth is opened by lift- ing the upper lip, with the nostrils closed [11]. The Flehmen response is generally believed to cause suction of fluid borne substances into the vomeronasal organ [9,13]. Several au- thors have suggested that there might be some vasomotor mechanism for presenting the chemical stimulus to the re- ceptor epithelium and that the vascular tissue around the vomeronasal organ may play a role in this mechanism [8, 10, 12]. There is some evidence in the hamster for a vasomotor pumping mechanism which sucks fluid into the vomeronasal organ, but the autonomic control of this mechanism is at present poorly understood [10]. In the present study experi- ments on the anaesthetized cat have demonstrated a vas- omotor pumping mechanism regulated by the sympathetic innervation of the vomeronasal organ and also shown that clear serous secretion may be elicited from the organ on parasympathetic stimulation. METHOD Cats of either sex weighing between 0.8-2 kg were anaes- thetized with sodium pentobarbitone (40 mg/kg IP and sub- sequently IV as required). Drugs were administered through a cannula inserted into the cephalic vein. The trachea was cannulated and the animals were allowed to breathe spon- taneously. The cats were placed supine and the jaws were fixed open. An incision was made in the mid line between the nasopalatine ducts extending from the incisor teeth posteriorly for about 1 cm. The sides of the incision were clamped back with arterial forceps and blunt dissection was used to expose the vomer bone and both vomeronasal ducts. An incision was made into the vomeronasal duct and the tip of a fine plastic cannula (0.55 mm diameter, 3-4 cm length) was carefully inserted 2-3 mm into the cut end of the duct towards the organ. The tip of the cannula was drawn out to a fine point to facilitate cannulation of the duct. Care was taken not to insert the pointed cannula too far into the organ, otherwise bleeding occurred. The cervical sympathetic nerve was exposed by an inci- sion in the neck and the cut peripheral end of the nerve was mounted on bipolar silver electrodes. In some experiments the Vidian nerve and sphenopalatine ganglion were exposed by displacement of the eye as previously described by Eccles and Wilson [6] and the cut peripheral end of the nerve was mounted on bipolar silver electrodes. Histology After sacrificing the animal the head was f'Lxed in 10% formal saline and whole sections of the nasal cavity were cut and observed under a x 10 binocular microscope. Some Copyright © 1982 Brain Research Publications Inc.m0031-9384/82/0601011-05503.00/0