OLFACTORY BULB RESPONSE TO ANTIDROMIC OLFACTORY TRACT STIMULATION IN THE RABBIT

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Abstract
Antidromic olfactory tract stimulation in the rabbit evoked a response which was composed of an initial positive-negative spike, a second negative component and a slow negative wave in shallow layers. In deeper layers the two early components were followed by an initial negative spike and a slow positive wave, while the slow negative wave increased in size. The two early components had almost the same refractoriness; absolute refractory period was 4-6 msec, and relative refractory period was in the range of 30-60 msec. The slow positive wave had about 50 msec. refractoriness, while the slow negative wave had no definite refractoriness, but it was of a summating nature. The deep initial spike was an antidromic volley in mitral cell axons, and it became through the mitral cell bodies the shallower initial positive-negative spike, which was propagated at the conduction rate of about 0.5 m/sec. towards the apical dendrites. From the effects of asphyxia, topical curarization, and the behavior to repetitive stimulation of the anterior commissure and of the olfactory tract itself, the second negative component was revealed as activities of abundant basal dendrites activated synaptically through the recurrent axon collaterals of the mitral cells. During observation on unit discharges, double discharges were sometimes found The second spike of the double discharge behaved like the second negative component in some respects and appeared to be elicited synaptically through the recurrent axon collateral of a mitral cell. This finding gives a favorable support for the above interpretation of the second negative component. It was found, moreover, that the deep slow positive wave was the condensed "source" of the second positive negative component of the whole bulb cortex. Finally, the slow negative wave is considered as the activity of a large number of internal granular cells because of its similarity to the anterior commissure response. In addition, the depth relationship and interaction among the bulb surface response, the olfactory tract response and the anterior commissure response were examined.