Evoked potential and single unit responses to olfactory nerve volleys in the isolated turtle olfactory bulb.

An in vitro preparation of the whole olfactory bulb of the turtle has been investigated using extracellular evoked potentials and unitary spikes. The compound action potential has a slow conduction velocity (0.15 mm/msec), brief relatively refractory period (10 msec) and prolonged supernormality (several hundred msec). The evoked potentials undergo prolonged periods of partial and complete suppression, as tested by the responses to paired volleys in the olfactory nerves. The suppression has a complex temporal pattern, and lasts more than 4 sec. Similar periods were revealed by the unitary spike responses of presumed mitral cells to olfactory nerve volleys. The results are similar to those reported in in vivo studies of turtle and other species. They suggest that the basic properties of mitral cells and their synaptic interactions with local interneurons are maintained in this isolated olfactory bulb preparation.