The effect of sniff frequency on presynaptic inhibition of receptor input to the olfactory bulb

PÍREZ, N.; CAREY, R.M.; WACHOWIAK, M.

Sarasota, Florida, Estados Unidos

Conferencia; XXIX Reunion Anual de AChemS; 2007

Association for Chemoreception Sciences

Olfactory receptor neurons (ORNs) converge onto olfactory bulb (OB) glomeruli corresponding to individual odorant receptors. ORN input to a glomerulus is modulated via feedback presynaptic inhibition. Slice experiments using paired olfactory nerve stimulation have shown that this inhibition peaks 100-200 ms after a conditioning pulse and decays with a time-constant of ~500 ms. Sniffing in rodents varies between 2-10 Hz (intersniff intervals from 100-500 ms); thus, changes in sniff frequency could change the level of presynaptic inhibition of ORN input. We asked how sniff frequency modulates the level of presynaptic inhibition at the ORN synapse in vivo by imaging odorant-evoked input to the OBs of anesthetized mice. ORNs were loaded with calcium-sensitive dye and sniff frequency was controlled using an artificial sniff protocol. As reported previously (Vucinic et al. 2006), blocking GABAB-mediated presynaptic inhibition increased the amplitude of odorant-evoked calcium signals, but, contrary to that study, we observed no change in the relative amplitude of ‘surround’ signals. Surprisingly, the increase in ORN input was independent of sniff frequency, and was seen even during the first sniff after odorant onset. It is possible that each sniff (150-200 ms in duration) evokes sufficiently prolonged input to the glomerulus that feedback presynaptic inhibition is evoked by all sniffs regardless of intersniff interval. Alternatively, presynaptic inhibition may occur tonically in the anesthetized mouse but not in slice preparations. Experiments testing these two hypotheses are currently underway.