Developmental and aging aspects of the cholinergic innervation of the olfactory bulb

The olfactory bulb is a limbic paleocortex which receives monosynaptic sens ory afferents from the olfactory mucose, and a strong direct cholinergic in put from the basal forebrain. This review focuses on the rat olfactory bulb as a suitable model to study cholinergic involvements in cortical processi ng, during development, adulthood and aging. Anatomical and biochemical dat a show that cholinergic influences upon the bulbar neuronal network are exe rted through several types of target cells and receptors (muscarinic and ni cotinic). Functional data indicate that cholinergic afferents to the olfact ory bulb are involved in local events related to olfactory learning. Neurod egenerative disorders such as Alzheimer's disease involve early olfactory d eficits and typical histopathological lesions in the olfactory bulb. In sum mary, with its exclusively extrinsic cholinergic innervation and direct sen sory input, the rat olfactory bulb offers the opportunity to study the cell ular and molecular mechanisms of cholinergic influences on cortical process ing, in both normal and pathological conditions. (C) 1999 ISDN. Published b y Elsevier Science Lid. All rights reserved.