SYNAPTOPHYSIN AND SYNAPTOPORIN EXPRESSION IN THE DEVELOPING RAT OLFACTORY SYSTEM

The expressions of two closely related synaptic vesicle antigens synap tophysin and synaptoporin were examined in the olfactory system of the adult rat and during pre- and postnatal development. In the adult, im munocytochemistry showed that the continuously regenerating olfactory receptor neurons (primary neurons) produce both synaptophysin and syna ptoporin which were localized in the cell bodies of the receptor neuro ns in the olfactory epithelium, their dendrites, axonal processes in t he olfactory nerve and their terminals in the olfactory bulb glomeruli . Furthermore, ultrastructural analysis revealed synaptophysin- and sy naptoporin-immunoreactivities associated with synaptic vesicles in mos t olfactory receptor axonal terminals impinging on dendrites of the mi tral and tufted neurons (secondary neurons in the olfactory bulb circu itry) in the olfactory glomeruli. In like manner, tufted neurons, gran ule and periglomerular neurons (interneurons in the olfactory bulb cir cuitry) express both synaptophysin and synaptoporin. In contrast, mitr al neurons expressed only the synaptophysin antigen which was likewise associated with mitral axonal terminals in their target the olfactory cortex. The patterns of synaptophysin and synaptoporin expressions in mitral neurons (synaptophysin only) and tufted neurons (synaptophysin and synaptoporin) were similar in prenatal, postnatal and adult rats as revealed by immunocytochemistry and in situ hybridization. However, the biosynthesis of synaptophysin and synaptoporin by granule and per iglomerular neurons, olfactory bulb interneurons, occurred mainly post natally.