PHOSPHORYLATED NEUROFILAMENT EPITOPES IN NEURONAL PERIKARYA IN THE SEPTUM, MESENCEPHALON AND DORSAL-ROOT GANGLIA OF MAMMALS AND BIRDS

We and other researchers have previously described the presence of axo n-specific phosphorylated neurofilament epitopes in the cell bodies of three neuronal types in the rat: bipolar septofimbrial neurons and th e large light A-type cells in the dorsal root ganglia and the mesencep halic nucleus of the Vth nerve. This spontaneous presence of phosphory lated neurofilaments at the level of the perikaryon contrasts with the induced appearance of these epitopes in axotomized neurons. We have u ndertaken a study of this phenomenon in rat, mouse, gerbil, rabbit, pi g and chicken to analyse its species distribution. Phosphorylated neur ofilament positive perikarya could be detected in the dorsal root gang lia and mesencephalic nucleus of the Vth nerve in all analysed species . Although this labelling has been shown to be specific for A-type cel ls in rat, in pig small cells were preferentially labelled, whereas th e largest cells were mostly completely devoid of label. In the septofi mbrial nucleus, phosphorylated neurofilament positive perikarya were s een in rat, mouse, gerbil and rabbit. In the pig, only a phosphatase-i nsensitive neurofilament antibody labelled these neurons. In the chick en, the labelling was completely absent. These observations establish the widespread species distribution of perikaryal phosphorylated neuro filament epitopes in the dorsal root ganglia and mesencephalic nucleus of the Vth nerve. In the septofimbrial nucleus however, this phenomen on seems to be restricted to rodents and lagomorphs. We discuss possib le explanations for these cytoskeletal singularities in dorsal root ga nglia, the mesencephalic nucleus of the Vth nerve and septofimbrial ne urons.