Temporal pattern analyses in pairs of neighboring mitral cells

1. Neighboring mitral cells in the rat olfactory bulb have been previously shown to give similar response profiles to a series of odorants. We now analyze their temporal patterns of activity before and during stimulation to evaluate to what extent soma proximity may act on their temporal correlation and to what extent olfactory stimulation may force two close cells to fire with similar patterns. 2. In anesthetized adult rats, we recorded simultaneously the extracellular single-unit activities of two mitral cells with the use of twin micropipettes with tips separated by less than 40 microns. These activities were recorded before and during stimulation by a series of five odorants. 3. Activities were classified into nine types according to their temporal pattern along the respiratory cycle. These types comprised nonrhythmic patterns and rhythmic ones, the latter being simple or complex. A phase parameter was also calculated to compare the positions of maximal activity within respiratory cycles of pairs of cells that had rhythmic activities. 4. All analyses were made by comparing data from pairs of close cells with data from pairs of control cells obtained by pairing each first cell of all recorded pairs with the second units of all other pairs. Results reveal a probability of similar activity types significantly higher in pairs of close cells than in control ones before stimulation. Odorant stimulation enhances this difference by reducing the probability of similar associations in control pairs. Close cells present similar patterns as frequently before, as during, stimulation; however, the probability of double nonrhythmic firings decreases whereas the probability of double rhythmic ones increases.(ABSTRACT TRUNCATED AT 250 WORDS)