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We present the first comparative investigation of the basal and transsynaptically induced expression of c-JUN, JUN B, JUN D, c-FOS, FOS B, and KROX-24 proteins in the spinal cord, using immunocytochemistry with specific antibodies. We demonstrate that electrical stimulation of the sciatic nerve at A delta/C-fiber (not A alpha/beta-fiber) intensity strongly induces the expression of these immediate-early gene-encoded proteins. Basal immunoreactivity was found for c-JUN in motoneurons, for JUN D in almost every cell of the gray matter, and for KROX-24 in the superficial dorsal horn. One hour after electrical stimulation of the sciatic nerve at A delta/C-fiber intensity, expression of all proteins except JUN D reached its maximum. Initially immunoreactivity was restricted to the ipsilateral dorsal horn, but after 4 hours appeared contralaterally. Expression of JUN D was increased only after 4 hours. Within the dorsal horn, the expression of c-JUN, JUN B, FOS B, and KROX-24 was mainly restricted to the superficial layers. Immunoreactivity decreased to basal levels between 8 and 16 hours. c-FOS and JUN D were expressed in both the superficial and deep dorsal horn; in the latter, c-FOS and JUN D persisted longer. Induced JUN D was present the longest and was still visible after 32 hours. In motoneurons of the ipsilateral ventral horn, c-JUN, JUN D, and c-FOS appeared after 8 hours. Surgical exposure of the sciatic nerve evoked a strikingly prolonged expression of all proteins compared to that following electrical stimulation of the sciatic nerve. Our results demonstrate that stimulation of nociceptive A delta- and C-fibers induces early and late expression of proteins encoded by immediate-early genes with a specific temporal and spatial distribution of the expression of each protein. Furthermore, the extent of protein expression reflects the intensity of noxious stimulation.

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In adult rats, the medial forebrain bundle (MFB) and mammillothalamic tract (MT) were unilaterally transected, resulting in axotomy of neurons in numerous areas such as the substantia nigra (SN), ventral tegmental area (VTA), nucleus (ncl.) mammillaris (MnM), and ncl. parafascicularis of the thalamus (PF). In these areas, expression of the transcription factor proteins c-JUN, 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, VTA, 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 VTA 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 d in 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.(ABSTRACT TRUNCATED AT 400 WORDS)

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