Efferent evoked responses in the olfactory pathway of the cat

Abstract

Evoked potentials were recorded in the olfactory bulb, lateral olfactory tract, olfactory tubercle, prepyriform cortex and anterior commissure of curarized cats, after stimulation of various areas of bulbo-mesencephalic reticular formation. The potentials in all the recorded olfactory stations were bilateral, with identical peak latencies for homologous structures, but with shorter latencies for the olfactory tubercle (4.9 msec) than for the olfactory bulb (5.5 msec). The latency for the prepyriform cortex was 8.5 msec. The evoked potentials in the olfactory bulb were abolished by section of the lateral olfactory tract, and by electrolytic lesion or transient blockage of the olfactory tubercle by topoligically applied procaine. Section of the anterior commissure or prepyriform cortex did not abolish the evoked potentials in the olfactory structures; on the contrary, a slight enhancement of amplitude was usually found. The destruction of the olfactory tubercle abolished the potentials evoked in the prepyriform cortex. The conduction velocity of the efferent fibers in lateral olfactory tract ranged between 5 and 10 m/sec. These data point to the existence of a pathway from the bulbo-mesencephalic areas to the olfactory tract, the olfactory tubercle being the common structure influencing the olfactory bulb and olfactory cortex.