Modulation of receptor neuron input to the olfactory bulb mediated by feedback versus lateral presynaptic inhibition

MCGANN, J.P.; PÍREZ, N.; GAINEY, M.A.; MURATORE, C.; ELIAS, A.S.; WACHOWIAK, M.

Sarasota, Florida, Estados Unidos

Conferencia; XXVII Reunion Anual de AChems; 2005

Association for Chemoreception Sciences

Olfactory bulb afferents (ORNs) converge onto glomeruli that correspond to individual odorant receptors. Afferent input to a glomerulus can be modulated via mechanisms mediated, at least in part, by GABAB receptors. We asked how this presynaptic inhibition affects odorant-evoked input to glomeruli by imaging odor representations with an optical reporter of ORN transmitter release and blocking GABAB receptors in vivo. A GABAB antagonist greatly increased odorant-evoked transmitter release in each responsive glomerulus, but did not change the spatial distribution of responsive glomeruli. Co-activation of neighboring glomeruli with odorant mixtures did not suppress transmitter release relative to the corresponding single-odorant presentations. Experiments in olfactory bulb slices revealed that single olfactory nerve shocks profoundly inhibited subsequent transmitter release from all fibers innervating a responding glomerulus, including afferents entering the glomerulus from separate, unstimulated bundles. This intraglomerular feedback inhibition was long-lasting and reduced by glutamate receptor blockers and by GABAB antagonists. We also found lateral inhibition of transmitter release between neighboring glomeruli in slices, but this inhibition was much weaker than feedback inhibition and limited at physiological temperatures. We conclude that feedback inhibition of transmitter release from ORNs can strongly modulate the magnitude of afferent input to the bulb, but that lateral inhibition plays a relatively small role.