CENTRIFUGAL REGULATION OF OLFACTORY BULB ACTIVITY AS STUDIED BY STIMULATION OF THE AMYGDALA AND THE ANTERIOR LIMB OF THE ANTERIOR COMMISSURE

Abstract

The influences of the activity of the amygdala, the anterior limb of the anterior commissure and the mesencephalic reticular formation of the activity of the olfactory bulb were studied in the rabbit by means of electrical stimulation. A potential wave evoked by electrical stimulation of the olfactory epithelium (A-wave) was inhibited considerably and for as long as 600 to 800 msec, when the lateral part of the amygdala was stimulated. But this phenomenon was not observed when the medial part was stimulated. The above inhibition was strikingly elongated when single or repetitive stimulation of the mesencephalic reticular formation was combined. The latter stimulation itself did not show any inhibitory effect upon the A-wave. From the shape of the evoked potential, the striking inhibitory phenomenon and the histological finding of the efferent fibers in the bulb, it was concluded that the lateral part of the amygdala sends inhibitory fibers to the olfactory bulb. The centrifugal inhibitory fibers from the lateral part of the amygdala were traced to the olfactory bulb. They were found in parallel with and slightly above the lateral olfactory tract. Any inhibitory effect was not found upon the A-wave when the anterior limb of the anterior commissure was stimulated singly or together with stimulation of the mesencephalic reticular formation.