An electrophysiological study of the efferent olfactory system in the burbot.

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Abstract
Unitary activity was recorded from the central 1 stump of a cut olfactory tract in the burbot (Lota lota). The fibers recorded from were identified as axons of efferent neurons conducting impulses toward the olfactory bulb. The efferent neurons were found to be spontaneously active. Efferent impulses could be evoked by stimulation of the ipsi- and contralateral olfactory tracts. The velocity of impulse propagation indicated that the efferent fibers were myelinated. The sensitivity of the efferent responses to ischemia, and the post-tetanic potentiation of the response, together with other evidence, indicated that the efferent fibers had their cell bodies in the telencephalon. Those efferent neurons, which could be activated by both ipsi- and contralateral shocks, showed long periods of suppressed excitability when conditioning and test shocks were given to opposite tracts. In some efferent fibers, the spontaneous activity was inhibited by touch stimuli to the skin, which shows the possibility of extra-olfactory influence upon bulbar activity.