[Resistance of the slow potential and inhibition of afferent input of the frog olfactory bulb to hypoxia and blockade of synaptic transmission by manganese, cobalt and magnesium ions]

Abstract

The effects of hypoxia and Mn++, Co++ and Mg++ on the electrical responses of the olfactory bulb to natural stimulation and single direct electric stimulation of olfactory nerve were studied in a frog. The slow potential evoked by natural stimulation and related inhibition of afferent olfactory input proved to be much more resistant to depression of synaptic transmission in the olfactory bulb with any methods used than postsynaptic components of the olfactory bulb orthodromic potential and related postsynaptic inhibition. Slow potentials were recorded after total blockade of synaptic transmission by Mg++ ions. It is concluded that the slow potential and related inhibition of afferent olfactory input are mainly of nonsynaptic nature. It is suggested that the slow potential reflects the depolarization of glial cells in a glomerular layer evoked by accumulation of K+ ions. Possible mechanisms for inhibition of olfactory bulb afferent input are discussed.