Explaining 'sister' cells in and out of synch
They were able to target -- and record electrical signals (action potentials) -- from mitral cells that they call "sister cells," whose responses on average are quite similar. This stands to reason because sister cells, by definition, receive information via primary dendrites from the same glomerulus. The scientists were also able to identify and monitor activity of "non-sister" mitral cells, ones whose firing activity is fundamentally dissimilar because of the comparatively wide contrast in the odors that their glomeruli report.
Perhaps the most interesting and surprising finding of the electrical recordings obtained in this fashion is that sister mitral cells, although they are connected to the same glomerulus, do not respond redundantly when a mouse is presented with an odor to which the glomerulus is responsive. In fact, says Albeanu, "we observed that odors de-synchronize pairs of sister mitral cells. This is something we did not expect."
How to explain this? The team formed a hypothesis based on comparisons of recordings made of the activity of many pairs of sister and non-sister mitral cells. According to Albeanu, "We thought of two metrics of activity with which to compare sisters and non-sisters. One kind compares the number of times cells fire in a single respiratory cycle; the other compares the intervals between their firing 'spikes,' and more specifically the points at which they occur relative to the start of a respiratory cycle.
"In other words, we looked at the rate of their firing, and compared it, in the same cells, both sisters and non-sisters, to the timing of their firing," says Albeanu. The team found that in sister cells, when the rate of firing changed in one sister, it changed in a similar manner in the other sister. But the timing of their firing differed -- instead of firing at
|Contact: Peter Tarr|
Cold Spring Harbor Laboratory