Slow potentials in the turtle olfactory bulb in response to odor stimulation of the nose and electrical stimulation of the olfactory nerve

Abstract

Summary The olfactory bulb of the gopher tortoise and box turtle was investigated anatomically by the use of a silver technique and electrophysiologically by evoked responses from odor stimulation of the nose and electrical stimulation of the olfactory nerve. Anatomically the bulb in both species of turtle revealed the usual 7-layer structure, but considerable species differences existed in the distribution of the lamina. In particular, the dorsal hemisphere of the box turtle bulb was found to lack olfactory nerve input even anterior to the large accessory olfactory bulb. The bulbar evoked potential to odor stimulation was a series of 3 slow potentials: wave I, a monophasic event of about 150 msec duration; wave II, a non-oscillatory potential usually more than 1 sec duration; and wave III, an oscillatory potential superimposed on wave II. The electrically evoked response recorded at bulb surfaces with afferent input also consisted of 3 component potentials: N 1 appeared as a negative inflection on the ascending phase of N 2 , a larger amplitude negative wave of 40–50 msec duration, which was followed by a longer lasting positive wave. Bulb surface regions receiving olfactory nerve input were defined by surface negativity of N 2 and waves I and II. In the partially deafferented box turtle bulb, it was shown that olfactory nerve fibers from the lateral aspect of the nerve innervated lateral and ventrolateral bulb, while ventromedially situated fibers innervated ventromedial bulb.