Pharmacological Studies on the Electrical Activities of the Olfactory Bulb

Abstract

During the experiments observing the drug effects on the steady potential of various brain structures, the authors (1) found that the steady potentials of certain subcortical structures such as the hypothalamus and hippocampus were more sensitively altered by psychopharmacological agents than the EEG activity in the same areas. Although many attempts (2-4) have been made to explain the steady potential, its physiological signi ficance has been still unknown. The authors have been interested in this electrical phenomenon from their belief that changes in the steady potential would indicate the CNS activity in some different way from EEG changes . In order to elucidate the cor relation between a steady potential and EEG in the various states of activity of the brain, the more primitive brain structure seemed desirable to persue . The authors thus selected the olfactory bulb, because this structure showed a distinct afferent activity in response to olfactory stimulation and its excitatory as well as inhibitory states could be easily demonstrated. Ottoson (5, 6) has observed a slow potential elicited by odori ferous stimulation in the olfactory epithelium as well as in the olfactory bulb . Ottoson's slow potential is regarded as a DC potential change in this structure . The present study was conducted to ascertain the effects of drugs on the DC potential , slow potential and EEG activity of the olfactory bulb, in the hope of elucidating if any mutual cor relations of these electrical phenomena exist. METHODSForty-three cats of either sexes weighing from 2 to 4 kg were used in this experi ments. As soon as possible after decamethonium bromide 0 .5 mg/kg was injected intra venously in unanesthetized animals , artificial respiration was started through tracheal cannulation. The animal was then placed on an stereotaxic instrument , the skull was exposed with a large skin incision under local anesthesia . Pain in the margins of the operative wounds and pressure points from the stereotaxic instrument was carefully controlled by topical application of 2% lidocaine, containing epinephrine in an ap propriate concentration, throughout the experiment. The frontal sinus was opened and the dorsal surface of the olfactory bulb was exposed . A fine silver-silver chloride wire

Olfaction

“…Ueki, Tanaka & Sugano (206) reported that the induced waves some times showed increases in amplitude following intravenous injections of epinephrine (5-10 p.g per kg) although a positive dc shift was occasionally seen in the bulbar slow potential. Penaloza-Rojas & Zeidenweber (207) found that 2-4 IJ,g of epinephrine injected directly into the bulbs of cats led to marked increases in the amplitude of induced activity reminiscent of that seen with increased respiration or arousal.…”