Light- and electron microscopic localization of parvalbumin, calbindin D-28k and calretinin in the dorsal lateral geniculate nucleus of the rat.

The localization of parvalbumin, calbindin D-28k and calretinin have been investigated in the dorsal lateral geniculate nucleus (d lgn) of the rat at the light and electron microscopical level. Parvalbumin and calretinin positive sites are restricted to nerve fibres, whereas calbindin is present in fibres as well as in nerve cells showing morphological characteristics of interneurons. Ultrastructurally parvalbumin immunoreactivity is found in large terminals surrounded by glial lamellae containing round vesicles and making asymmetric contacts on dendrites. These morphological characteristics are typical for retinal endings of type 2a. Another kind of parvalbumin positive presynaptic terminals are seen on the surface of unstained nerve cell bodies and features symmetrical contacts. We conclude that this type represents axonal terminals of GABAergic neurons of the thalamic reticular nucleus. Calbindin positive nerve cells in the d lgn occur in the latero-dorsal part and according to morphological characteristics, belong to interneurons. Calbindin positive nerve cells receive synaptic terminals deriving from different kind of unstained presynaptic profiles. Calretinin immunoreactivity is localized in small to medium sized presynaptic endings with round vesicles, pale mitochondria and Gray-type 1 contacts on dendrites of relay- and interneurons. Some calretinin positive terminals are located in triads or in complex encapsulated regions. Therefore we identify calretinin positive terminals as the retinal inputs of type 2b. Our results demonstrate the expression of the three calcium binding proteins in morphologically, physiologically and biochemically different structures within the d lgn of the rat. The distribution differs from that found in the d lgn of the cat or monkey.