Chemical organization of the macaque monkey olfactory bulb: III. Distribution of cholinergic markers

Abstract

[EN]The distribution patterns of choline acetyltransferase (ChAT) and acetylcholinesterase(AChE) were studied in the olfactory bulb (OB) of three species of macaque. AChE wasdetected by a histochemical method and ChAT immunoreactivity by immunocytochemistry.Similar results were observed in all species analyzed. With the exception of the olfactorynerve layer, all layers of the macaque monkey OB demonstrated a dense innervation ofAChE- and ChAT-positive fibers. The distribution patterns of AChE- and ChAT-labeled fiberswere similar for both cholinergic markers, although the number of AChE-labeled fibers wasclearly higher than the number of ChAT-immunoreactive fibers. The highest density of AChEand ChAT-stained fibers was observed in the interface between the glomerular layer and theexternal plexiform layer and in the internal plexiform layer. Dense bundles of labeled fiberswere observed in the caudal OB, coursing from the olfactory peduncle. All ChAT-immunopositive elements were identified as centrifugal fibers, derived from neurons caudalto the OB. Neither olfactory fibers nor intrinsic neurons were observed after ChAT immu-nocytochemistry. However, a few AChE-positive cells were observed in the glomerular layerand in both external and internal plexiform layers. These neurons were presumably identi-fied as periglomerular cells, superficial short-axon cells, and/or external tufted cells and deepshort-axon cells. Contrary to other neurotransmitters and neuroactive substances, the dis-tribution patterns of ChAT and AChE activities in the macaque monkey OB closely resem-bled the patterns described in macrosmatic mammals and showed laminar differences withthe distribution pattern observed in humans.