Ultrastructural changes associated with reversible and irreversible suppression of electrical activity in olfactory cortex slices

Summary The fine structure and electrical activity were studied in thin brain sections prepared from the olfactory cortex of the guinea pig and incubated in vitro in standard and modified conditions. In the standard medium, the potential response was maintained with no marked changes for 4–5 hours and thereafter gradually decreased. The ultrastructure of the tissue was well preserved for the initial 2 hours of incubation. After incubation for 5 hours, many empty spaces were noted. Some dendritic stumps lost fine internal structure, but most of the synapses were apparently normal. Cyanide suppressed the potential response, and caused swelling of the nerve terminals and a decrease in the number of synaptic vesicles. The recovery of the response in the standard medium was not accompanied by a full restoration in the fine structure. If slices were incubated in the absence of glucose and oxygen, with cyanide in glucose-free medium, or at a low temperature, the potential response was irreversibly depressed. In these slices, numerous wide spaces of low electron density were noted which were concluded to have been derived, at least partly, from the swollen dendrites.Dedicated to Professor Toshihiko Tokizane on the occasion of his 60th birthday.