LHRH and catecholamine neuronal systems in the olfactory bulb of the mouse

The luteinizing-hormone-releasing hormone (LHRH) components of the mouse olfactory system were studied by using the indirect immunohistofluorescence technique. LHRH-positive cell bodies were found in both the main olfactory bulb (MOB) and the accessory olfactory bulb (AOB); two distinct cell groups were found--one located adjacent to the AOB in the dorsal part of the MOB and a second in the superficial ventromedial aspect of the MOB. LHRH-positive fibers were found predominantly in the posterior half of the main olfactory bulb innervating the olfactory nerve layer, the glomerular layer, the external plexiform layer, and the mitral cell layer, and small numbers innervated the AOB. The greatest density of LHRH-immunoreactive fibers was seen adjacent to the AOB where one group of LHRH-positive cells was noted. Sections adjacent to those stained with LHRH antibody were analysed for tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). The TH staining was intense for both cells and fibers in the glomerular layer of the MOB. In the AOB lower numbers of cell bodies and fibers were seen in the glomerular layer. The internal granular layer and internal plexiform layers were both stained, the internal granular layer showing more intensely fluorescent fibers with a higher density. Since no overlapping DBH-positive fibers were found here, these TH-positive nerve endings may be dopaminergic. DBH staining was confined to sparse networks of weakly fluorescent fibers with the highest numbers in the internal plexiform layer of the AOB and fewer fibers in the external plexiform, rostral, and granular layers of the MOB. Elution-restaining experiments revealed that the LHRH-positive and TH-positive elements represent different cell populations.