The effect of acetylcholine on rat olfactory bulb unit activity.

The olfactory bulb (OB) of the rat receives an extrinsic innervation from the most anterior part of the basal forebrain cholinergic complex. The effect of microiontophoretically applied acetylcholine (ACh) on OB unit activity was studied in 16 adult male rats. A total of 80 units was recorded and in 50% of the cases the cell layer where the recording was done was clearly identified. The results provide evidence for a particularly high level of sensitivity to ACh in the outer glomerular layer (73%). Both inhibitory and excitatory responses were found. These results are in agreement with histological studies indicating that this layer presents the highest density of cholinergic terminals. As a whole, present knowledge suggests the existence of a strong cholinergic control of the olfactory input at the level of the first synapse in the system.