Pírez, N: Presynaptic control of sensory input on the mammal

Presynaptic inhibition modulates signal transmissionin the olfactory pathway by several mechanisms, amajor one being mediated by GABAB receptors, whichsuppress presynaptic calcium influx and subsequenttransmitter release from the receptor neuronterminal. Presynaptic inhibition could function tolimit the strength of olfactory input to the centralnervous system, as well as provide a substrate forcentrifugal control of odorant representations earlyin the olfactory system. Odorant and electricalstimulation combined with in vivo pharmacology wereused to characterize the functional determinants ofGABAB-mediated presynaptic. The results of this workshowed that tonic inhibition is a major determinantof receptor input strength; and were dependent onglutamatergic transmission from second-order neuronsin the glomerular layer. When the behavioral state ofthe awake animal was altered, odorant-evokedresponses were affected. Taken together these resultssuggest that tonic inhibition via top-down,centrifugal control plays a major role in modulatingthe magnitude of sensory input to the brain as afunction of behavioral state.