Cytoarchitecture, synaptic organization and fiber connections of the nucleus olfactoretinalis in a teleost (Navodon modestus).

Cytoarchitecture, synaptic organization and fiber connections of the nucleus olfactoretinalis (NOR) in a teleost, Navodon modestus, have been studied light- and electron-microscopically using an HRP or HRP-degeneration combined method. Following HRP injections into the optic nerve, most contralateral and a few ipsilateral neurons in the NOR were labeled. There are two types of neurons in NOR. Type I neurons have a medium-sized spindle-shaped soma with a round nucleus, and type II neurons have a large oval soma with an invaginated nucleus and contain cored vesicles (80-130 nm in diameter). Afferent terminals which form synaptic contacts with cell bodies of NOR neurons were classified into 3 types according to their morphological characteristics; S, F1 and F2 terminals. S terminals originated in ipsilateral area ventralis telencephali pars supracommissuralis (Vs). These terminals contain both spherical and cored vesicles, and make synaptic contacts with both type I and type II neurons. F1 terminals, which originated in ipsilateral area dorsalis telencephali pars posterior (Dp), are large in profile, and contain flat vesicles and mitochondria with irregularly arranged cristae. These terminals make synaptic contacts only with type I neurons. F2 terminals are small in profile, and contain flat vesicles, cored vesicles and small mitochondria with regularly arranged cristae. F2 terminals make synaptic contacts with both type I and type II neurons. The functional significance of NOR and the relationship between NOR and the ganglion of the nervus terminalis are discussed.