AN IN-VITRO PREPARATION OF FROG NOSE AND BRAIN FOR THE STUDY OF ODOR-EVOKED OSCILLATORY ACTIVITY

An in vitro preparation is described that consists of frog brain rostr al to the brainstem connected to the nasal epithelium by the olfactory nerves. Field potential and intracellular recordings from various bra in structures can be obtained while stimulating the nasal epithelium w ith air-borne odours for at least 12 h after removal of the brain. Pow er spectra, amplitude and duration of odour-evoked and spontaneous fie ld potentials in vitro are similar to those obtained from paralyzed, s pinal cord pithed frogs. A brief puff of odourant applied to the olfac tory epithelium produces a 1-2 s bout of 7-13 Hz oscillations in the f ield potential recorded from the ipsilateral bulb and various ventral, lateral and medial telencephalic structures. Odour evoked bulbar osci llations are maintained after removal of the telencephalon. Electrical stimulation of the olfactory nerves will not elicit oscillations like those evoked by odour stimulation. High-pressure puffs of non-odouris ed, moist air, elicit olfactory bulb oscillations similar to those evo ked by lower pressure puffs of odourised air. Intracellular recordings from most mitral cells reveal oscillations in membrane potential that are phase-locked to the field potential. The extent to which these ph ase-locked oscillations produce action potentials varies, apparently a s a function of the strength and duration of a long-lasting inhibitory potential that is superimposed upon the 7-13 Hz oscillations. This pr eparation is well-suited for the study of the cellular basis of oscill atory activity in vertebrate brain, and the function of sensory-evoked oscillatory responses in processing of sensory information.