CHOLINERGIC INNERVATION OF OLFACTORY GLOMERULI IN THE RAT - AN ULTRASTRUCTURAL IMMUNOCYTOCHEMICAL STUDY

The ultrastructural organization of cholinergic afferents to the rat o lfactory bulb (OB) was studied with the aid of choline acetyltransfera se (ChAT) immunocytochemistry in electron microscopy. Particular atten tion has been paid to a subset of glomeruli characterized by a remarka bly high density of cholinergic afferents. Numerous cholinergic termin als making symmetric or asymmetric synaptic contacts were observed in the periglomerular area. ChAT-labelled terminals have a diameter rangi ng from 0.3 to 1.5 mum and contain numerous clear agranular vesicles. Axo-somatic and axo-dendritic contacts were both observed in contact w ith several types of target neurons. Three types of cholinoceptive, no ncholinergic neurons could be identified: periglomerular cells, superf icial short-axon cells, and external tufted cells. Our results provide an anatomical substrate for the hypotheses concerning the complex eff ects of acetylcholine in the processing of sensory information in the olfactory bulb. (C) 1993 Wiley-Liss, Inc.