Simultaneous recordings from two physiologically different types of relay neurons, mitral cells and ruffed cells, in the olfactory bulb of goldfish

Anatomical differences characterizing mitral cells and ruffed cells were pu blished by Kosaka and Hama in three teleost species. Physiological response s from both different types of relay neurons were recorded extracellularly and simultaneously in the plexiform layer using a single tungsten microelec trode. During interstimulus intervals mitral cells responded with higher, f requently burst-like impulse rates triggered by the activity of epithelial receptor neurons. The mitral cell activity could be totally suppressed duri ng local anesthesia of the olfactory epithelium. Puffed cell impulse rates were low and each action potential triggered a long-lasting (3-5 ms), conti nuously variable, summed up granule cell potential. In contrast to mitral c ells, blockade of epithelial receptor cells significantly increased the act ivity of ruffed cells. I.e,, the ruffed cells, which have no input from the olfactory epithelium, are spontaneously active, and are laterally inhibite d by granule cells activated by mitral cells.,During olfactory stimulation contrasting interactions between mitral cells and ruffed cells resulting in a drastic intensification of centrally transmitted information, frequently were recorded. An excitation of mitral cells activity via granule cells la terally inhibited the ruffed cells activity, and an inhibition of mitral ce lls activity simultaneously "released" an excitation of ruffed cells. This is the first physiological determination of different types of relay neuron s in the olfactory bulb of fish.