EXPRESSION OF JUN, FOS AND ATF-2 PROTEINS IN AXOTOMIZED EXPLANTED ANDCULTURED ADULT-RAT DORSAL-ROOT GANGLIA

The expression of c-Jun, JunB, JunD, c-Fos and ATF-2 transcription fac tors was studied in L4/L5 dorsal root ganglion neurons of adult rats, in order to determine the extent to know to which extend the expressio n of transcription factors in vitro parallels the pathophysiological e xpression in vivo. First, dorsal root ganglia were dissociated and cul tured for up to 15 days in vitro (culture). Second, the dorsal root an d the peripheral nerve fibres were transected close at the dorsal root ganglia, and the completely axotomized dorsal root ganglia were kept in artificial cerebrospinal fluid for up to 24 h. This procedure (expl antation) preserves the intraganglionic morphology intact. Culture evo ked a persistent expression of c-Jun and JunD in the majority of small neurons independent on neurite extension. In contrast, the number of large neurons with c-Jun decreased and with JunD increased with incuba tion time. JunB and c-Fos, which were also visible in the majority of neurons, strongly decreased with culture time in both small and large neurons. ATF-2 was visible in the vast majority of neurons and did not change during the observation period. Incubation with brain-derived n eurotrophic factor for 15 days reduced JunB expression and raised c-Fo s expression, but did not affect c-Jun or JunD labellings. Explantatio n of dorsal root ganglia evoked a dramatic and rapid induction of c-Ju n in neurons located in the periphery of the ganglia, an area that sho wed prominent apoptosis as visualized by transferase dUTP nick end-lab elling, followed by a delayed increase in neurons of the central parts of dorsal root ganglia. Expression of JunB showed a dramatic increase within 2 h in the whole ganglion, but disappeared within the followin g hours. JunD dropped from its basal levels within 4 h and was almost absent after 8 h. c-Fos did not appear until 6 h, when transferase dUT P nick end-labelling also became detectable, and remained visible in a rather small number of neurons. As with culture, incubation of explan ted dorsal root ganglia with brain-derived neurotrophic factor prevent ed the initial rise in JunB, accelerated and enhanced c-Fos expression , but did not alter c-Jun and JunD expression. Immunoreactivity of ATF -2 declined or disappeared in those dorsal root ganglia compartments t hat showed a rise in c-Jun and transferase dUTP nick end-labelling. Th ese findings demonstrate that inducible transcription factors such as Jun and Fos proteins are differentially expressed in adult neurons in vitro when compared to pathophysiological conditions in vivo such as n erve fibre transection (axotomy or rhizotomy). Moreover, the compariso n between the explantation and culture experiments suggests that it is the complete axotomy of neurons that provokes those expression patter ns found in neuronal cultures of adult neurons. The rapid and persisti ng expression of c-Jun during neurite extension and apoptosis points a t the activation of a pivotal program that might be determined by the presence or absence of ATF-2 and that is involved in regeneration or d egeneration. (C) 1998 IBRO. Published by Elsevier Science Ltd.