ELECTRICAL ACTIVITY IN THE OLFACTORY 



SYSTEM OF RABBITS WITH INDWELLING 



ELECTRODES 



David G. Moulton 

 Division of Physiology, Florida State University, Tallahassee, Florida 



INTRODUCTION 



Attempts to determine how the olfactory bulb deals with the massive 

 input from its receptors, and what its discharges reveal about the way 

 odors are discriminated, have largely been restricted to studies on animals 

 immobilized by surgery or drugs ; or on the wave activity in the bulb of 

 chronically implanted animals (e.g. Adrian, 1950 ; 1956 ; Mozell and 

 Pfaffmann, 1954 ; Mozell, 1958 ; Hernandez-Peon et al., 1960). However, 

 for a fuller understanding of olfactory processes we must know more about 

 the behavior of the spike potentials of the bulb, and their relation to 

 events occurring more peripherally, in animals far removed from the effects 

 of surgical trauma, anesthetics or neuromuscular blocking agents. Not 

 only do such compounds profoundly influence central synaptic trans- 

 mission, but they may also restrict odorant access to the nasal chemore- 

 ceptors by altering the flow of nasal secretions, or the degree of vascular 

 engorgement of the nasal mucosa. A sensory system does not normally 

 function in isolation : its full exploitation demands a complex interplay 

 of activities in accessory structures; and using electrophysiological methods 

 we are hkely to learn more about its potentialities and its significance for 

 behavior when it is being actively focused by the animal, than when it is 

 being artificially stimulated by the experimenter. 



The approach to these problems through the use of animals with chronic- 

 ally implanted electrodes is particularly favored by the anatomy of the 

 olfactory system. In macrosmatic species, such as the rabbit, the large 

 bulbs and numerous receptor cell axons laced through the cribriform plate 

 allow activity to be recorded simultaneously from both primary and 

 secondary neurones, with little disruption of overlying tissue. In addition, 

 and despite their rich content of autonomic fibers, the nasal mucosa and 

 the ethmoidal nerve are also interesting targets, particularly in view of the 

 potential importance of trigeminal sensitivity in the discrimination of odors 

 (see Tucker, this symposium). We have recently begun to investigate the 



71 



