Long-lasting expression of JUN and KROX transcription factors and nitric oxide synthase in intrinsic neurons of the rat brain following axotomy

Abstract

In adult rats, the medial forebrain bundle (MFB) and mammillothalamic tract (MI) were unilaterally transected, resulting in axotomy of neurons in numerous areas such as the substanta nigra (SN), ventral tegmental area (VIA), nucleus (ncl.) mammillaris (MnM), and ncl. parafascicularis of the thalamus (PE). In these areas, expression of the transcription factor proteins c-JON, JUN B, JUN D, c-FOS, FOS B, KROX-20, KROX-24, and CREB was investigated by immunocytochemistry up to 150 d. In parallel, the expression of nitric oxide synthase (NOS) was investigated both immunocytochemically and by the NADPH-diaphorase reaction (NDP), and the antibody against NOS was further characterized. The colocalization of c-JUN with NDP or NOS was also studied in the axotomized neurons. c-JUN and JUN D became visible in nuclei of many neurons of the ipsilateral MnM, PF, VIA, and SN (predominantly in the pars compacta and those double labeled by tyrosine hydroxylase, TH) after 36 hr, not after 24 hr, following transection of MFB and MT. In MnM, c-JUN and JUN D persisted at a nearly maximal level for up to 150 d. In PF, these proteins returned to control levels after 75 d. Expression of c-JUN and JUN D declined in the VIA after 30 d, but in the SN, it already declined after only 10 d. KROX-24 had a later onset of expression, being visible after 3 din all investigated areas, and its pattern was similar to that of JUN proteins, although labeling was visible in fewer nuclei and declined earlier. JUN B, c-FOS, FOS B, and KROX-20 were not expressed in these areas, and substantial alterations of CREB immunoreactivity (CREB-IR) could not be detected. A subset of SN neurons (predominantly in the pars reticularis and negative for TH) presented an early and transient expression of all studied JUN, FOS, and KROX-24 proteins within 3 hr of transection that declined between 24 hr and 48 hr to basal levels. This expression pattern is typical of that caused by transynaptic stimulation (probably due to excitation of descending striatal neurons running within the MFB) and was clearly distinct from that evoked by c-JUN, JUN D, and KROX-24 IRs after 36 hr (predominantly in the pars compacta). An ipsilateral increase in NOS and NDP became visible in many neurons of the MnM after 10 d, but not after 5 d, and this persisted up to 150 d. The temporospatial pattern of NDP was similar to the pattern of NOS-IR. In the MnM, 78-92% of neurons with NDP and 67-8 1 % of neurons with NOS-JR were also labeled for c-JUN. NOS-IR and NOP did not change in VIA and SN and remained absent in PP. These results indicate that axotomized intrinsic neurons of CNS show either individual transient or long-lasting changes of transcription factors that may underlie and mediate their different sprouting potencies. The particular persistence and lasting coexpression of c-JUN and NOS in MnM neurons indicate a protective role of NOS and c-JUN partnership for damaged neurons in the rat CNS.