Abstract
The olfactory bulb response to direct electrical stimulation was studied in succinylcholine-paralyzed rabbits. The following results were obtained.
1) The response set up by direct stimulation of the olfactory bulb is composed of two most stable components, i. e. spike and slow potentials. The response was compared with the findings of other investigators.
2) Regional difference of the response pattern is due to the thickness of the layer of olfactory nerve fibers. The spike is most prominent near the anterior portion of the bulb. In the hindmost portion, probably the accessory bulb, a complicated response was found.
3) Response amplitude-recording distance relation indicates that spike is rapidly decreased in amplitude, while slow potential does gradually. This depends mainly upon the lower threshold of slow potential than that of spike and also interglomerular transfer of activation.
4) Absolute and relative refractoriness of the spike was different from that of the slow potential. Absolute refractoriness of both potentials were respectively about 2 msec and 6 msec.
5) By means of the depth recording, element corresponding to the spike was discriminated from that generating the slow potential. It was found that the former is localized in superficial layer, while the latter in somewhat deeper one.
6) Gamma-aminobutyric acid and gamma-amino-beta-hydroxybutyric acid depressed the slow potential markedly while the spike remained unchanged. Close similarity of the slow potential to the cerebral dendritic potential was pointed out.
7) Procaine suppressed completely the spike, whereas the amplitude of slow potential was not markedly affected. Likewise strychnine abolished the spike but caused the slow potential to augment a little.
8) The spike and slow potentials were not significantly affected by curarine applied topically or intravenously.
The above evidences seem to offer further support for our hypothesis about origins of the spike and slow potentials: The former is due to the action potential of olfactory nerve fibers in the superficial layer, and the latter results largely from the activity of dendrites of mitral and tufted cells.
