Mitral cells and ruffed cells. Two physiologically different types of relay neurons in the olfactory bulb of goldfish.

Abstract

Anatomical differences characterizing mitral cells (MC) and ruffed (RC) cells were published 10-15 years ago by Kosaka and Hama in three teleost species (goldfish, catfish and sea eel). Physiological responses from the two different types of relay neurons were recorded extracellularly and simultaneously in the plexiform layer using a single tungsten microelectrode electrode (A-M systems 5770; 10-12 MW). During interstimulus intervals MC responded with higher, frequently burst-like impulse rates (mean value 2.7 s-1) triggered by the activity of epithelial receptor neurons. The MC activity could be totally suppressed during anesthesia of the epithelium. RC impulse rates were low (mean value 0.75 s-1), and each potential triggered a long-lasting (3-5 ms), continuously variable, summed granule cells (GC) potential (approximately 3 ms peak to peak). MC activity via GC laterally inhibited RC potentials. In contrast to MC, blockade of epithelial receptor cells increased the activity of RC. During olfactory stimulation (nonfamiliar stimuli: amyl acetate, beta-ionone, 2-phenylethanol 10(-6) M; relevant natural stimuli: four amino acids 10(-6)-10(-10) M; preovulatory pheromone 17,20 beta-dihydroxy-4-pregnen-3-one 10(-9)-10(-13) M, bile acid taurolithocholic acid, 10(-6)-10(-10) M) contrasting interactions between MC and RC were present that even in the lowest concentration resulted in a drastic intensification of centrally transmitted information. More frequently an inhibition was recorded from MC, and decreasing lateral inhibition via GC resulted in an activation of RC. Activation of RC resulted in an activation of pools of GC via initial pedunculate protrusions from the long unmyelinated portion of their axons, laterally inhibiting pools of MC in their vicinity.