Immunohistochemical and Ultrastructural characterization of the terminal nerve ganglion cells of the ayu, Plecoglossus altivelis (Salmoniformes, Teleostei).

Abstract

Little is known on the cytological properties of the terminal nerve ganglion (TNG) cells in teleosts (Demski, 1993. Acta Anat., 148:81-95). To characterize the TNG cells of a salmonoid fish, Plecoglossus altivelis, we adopted immunohistochemistry and transmission electron microscopy (TEM). The majority of the TNG cells formed a compact mass halfway between the olfactory sac and the olfactory bulb, whereas a few cells were scattered in the ventromedial region of the olfactory bulb. The cell had a voluminous perikaryon that was positive to antisera against gonadotropin-releasing hormone (GnRH), molluscan cardioexcitatory tetrapeptide (FM-RFamide), and neuropeptide Y (NPY). Immunostaining of consecutive sections with each antiserum showed the coexistence of these antigens in the same cells and their processes. Most of the processes originating from the cells projected centrally to the basal forebrain, including the optic nerve. With TEM, the cells revealed a peptidergic nature, i.e., the presence of abundant granular endoplasmic reticula and well-developed Golgi bodies in association with vesicles that were 70-100 nm in diameter. Occasionally, the cells adjoined one another directly without the intervention of glial sheets. Synaptic contacts were frequent in the proximal region of the processes, where thin lateral processes of the cells and axon terminals of unknown origin were intermingled with each other. Terminal buttons being engulfed by the soma were commonly seen. The TNG cells of the salmonoid fish share many cytological characteristics with the cells of the nucleus olfactoretinalis of advanced teleosts such as acanthopterygians.