Distribution and synaptic organization of nitric oxide synthase immunoreactive neurons in the rat olfactory

Lee, Nam Soo; Yoon, He Ro

Abstract

BACKGROUND AND OBJECTIVES: Nitric oxide (NO) has been reported to play important roles in the regulation of olfactory information in the mammarian olfactory bulb. Although the distribution of nitric oxide synthase (NOS)-immunoreactive neurons in the olfactory bulb in the rat and other animals have been investigated by light microscopy, ultrastructures of the synaptic organization between NOS-immunoreactive neurons have not been studied yet. This study was conducted in order to identify NOS- immunoreactive neurons in the rat olfactory bulb and to define their synaptic organizations under the electron microscope using the preembedding immunocytochemical method which utilizes anti-NOS antiserum.
MATERIALS AND METHODS
The olfactory bulbs of the rats were cut into 50 micromiter thick vertical sections and immunostained using the ABS method. Stained sections were observed under the light microscope. Some of the stained sections, additionally stained with uranyl acetate and dehydrated, were embedded in Epon 812 and prepared into 80 nm thick sections to be observed under the electron microscope. RESULT: NOS-immunoreactive neurons of the rat olfactory bulb made up 25.0% of periglomerular cells and 18.9% of granule cells. NOS-immunoreactive periglomerular cells received synaptic input from unlabeled axon terminals of the olfactory nerve and unlabeled periglomerular cells within the glomeruli. The output targets of NOS immunoreactive periglomerular cells were unlabeled axon terminals of the olfactory nerve and unlabeled periglomerular cells. NOS-immunoreactive granule cells received synaptic input from unlabeled processes of granule cells and axon terminals of mitral cells, and made output synapses onto the unlabeled axon terminals of mitral cells.
CONCLUSION
NOS-immunoreactive neurons are periglomerular cells and granule cells, and NO liberated from NOS cells may play important roles in the modulation of olfactory transmission.