Differential expression of immediate early genes in the hippocampus and spinal cord

Hindbrain structures involved in pain processing as revealed by the expression of c-Fos and other immediate early gene proteins

We have used the evoked expression of the immediate early gene-encoded proteins (c-Fos, Fos B, Jun B, Jun D, c-Jun and Krox-24) to monitor sensory processing in the hindbrain structures of rats undergoing somatic inflammation. Experiments were performed on freely moving animals that did not experience constraints other than those imposed by the disease itself. Local injections of chemicals were used to cause subcutaneous inflammation of the plantar foot or monoarthritis by intracapsular injection. Labelling was studied at survival times that corresponded either to the time points of maximum labelling in the spinal cord (4 h for the subcutaneous model, 24 h and two weeks for the monoarthritis model) or at survival times that corresponded to the chronic phase of monoarthritis evolution (six, nine and 15 weeks). Controls consisted of freely moving, unstimulated animals. Basal expression was observed for all immediate early genes and in a variety of structures, but always remained moderate. All immediate early gene-encoded protein expressions except c-Jun were evoked, but except for c-Fos, and to a lesser extent Jun D, intensities of staining always remained faint. The following results will be mainly based on c-Fos expression, as this protein proved to be the most effective marker for all the survival times studied. Somatic pain evoked c-Fos expression in a subset of discrete subregions of both the caudal medulla oblongata and transitional areas of the pontomesencephalic junction. In the caudal medulla oblongata, structures involved were the caudal intermediate reticular nucleus, the subnucleus reticularis dorsalis, the ventrolateral reticular formation and the lateral paragigantocellular nucleus. Structures involved at the pontomesencephalic junction level mostly included the superior and dorsal lateral subnuclei of the parabrachial area, the nucleus cuneiformis and the most caudal portions of the lateral central gray, also including the laterodorsal tegmental nucleus; labelling in other lateral subnuclei of the parabrachial area always remained moderate. Staining in the caudal reticular areas was evident only at short survival times (4 and 24 h survival times in subcutaneous and monoarthritis models, respectively). Staining in nuclei of the pontomesencephalic junction was evident in all cases except for the very long survival periods (six to 15 weeks) of monoarthritis. In all cases staining was bilateral with contralateral predominance with regard to the stimulated limb. The present work demonstrates that hindbrain structures involved in somatic pain processing can be effectively identified in behaving animals and that c-Fos is the most reliable activity marker in this case.(ABSTRACT TRUNCATED AT 400 WORDS)

Application of morphine prior to noxious stimulation differentially modulates expression of Fos, Jun and Krox-24 proteins in rat spinal cord neurons

The expression of Fos, Jun and Krox-24 proteins was investigated in spinal cord neurons of the rat 2, 4 and 8 h following noxious thermal stimulation of one hind-paw and pre-treatment with morphine. The number of neurons expressing c-Fos, c-Jun, Jun B and Krox-24 were maximal after 2 h and thereafter declined. The number of Fos B and Jun D immunoreactive neurons increased constantly for up to 8 h with Jun D showing expression above baseline only after 4 h following stimulation. Intravenous application of morphine (5 and 10 mg/kg) 20 min before noxious heat stimulation decreased the expression of all six proteins at any time-point with a predilective effect on neurons of deeper laminae of the dorsal horn. The suppressive effects of morphine were more pronounced with the higher dose of morphine and completely reversed by intravenous naloxone (1 and 10 mg/kg). The temporospatial patterns of expression following morphine were similar to those seen without morphine, but in a much smaller number of neurons and with a shorter time-course. However, despite the high dose of morphine and continuous halothane anaesthesia during the whole experimental procedures, a considerable number of neurons expressing the various genes remained in all laminae of the spinal cord. At 2 h following noxious heat stimulation morphine had decreased the number of labelled neurons for c-Fos, Fos B, Krox-24, c-Jun and Jun B to 30-60% of control levels in laminae I-II and to 10-30% in laminae III-VII,X of the spinal cord. At 4 h the level of reduction had further increased while Jun D was only moderately reduced to 75% in all laminae of the spinal cord. Eight hours following noxious heat plus morphine application we did not detect noxious evoked immunoreactivity for c-Fos, Krox-24, c-Jun and Jun B, while there was residual labelling for Fos B in the superficial dorsal horn and for Jun D in laminae I-VII and X of the spinal cord. The different temporospatial pattern of immediate early gene expression in neurons of the spinal cord dorsal horn following noxious stimulation suggest that variable transcription complexes may interact with DNA regulatory sequences and could thus activate alternative secondary response genes, even under protection of a high dosage of morphine applied before noxious stimulation.

Protein kinase C and F1/GAP-43 gene expression in hippocampus inversely related to synaptic enhancement lasting 3 days

The mRNA levels of protein F1 (also known as GAP-43), and protein kinase C (PKC) subtypes were measured 3 days after the induction of long-term enhancement (also known as long-term potentiation) in the hippocampus of chronically prepared conscious rats by quantitative in situ hybridization. Altered mRNA levels correlated significantly with alternations in synaptic efficacy; such correlations have not been reported previously. Rats with greater synaptic enhancement had lower gene expression in the CA3 subfield of F1/GAP-43 and both beta-PKC and gamma-PKC, but not alpha-PKC. For microtubule-associated protein 2 (MAP-2), neurogranin, and the glutamate receptor subtype B-flip, no correlation was observed in any cell field between synaptic enhancement and hybridization to the mRNA. To our surprise, alterations in mRNA levels of F1/GAP-43 and gamma-PKC were highly correlated (r = +0.928, P < 0.001), suggesting coordinate regulation. Since F1/GAP-43 is associated with neurite growth, its lowered expression at 3 days would reduce potential growth, leading to synaptic stabilization. We propose that long-term synaptic change is mediated by gene expression of the very same proteins initially modified posttranslationally.

Opioid peptide gene expression in the nucleus tractus solitarius of rat brain and increases induced by unilateral cervical vagotomy: implications for role of opioid neurons in respiratory control mechanisms

Neurons expressing messenger RNA encoding the opioid peptide precursors, preproenkephalin and preprodynorphin were localized in the medulla oblongata of the rat by in situ hybridization of specific DNA oligonucleotide probes. Neurons containing preproenkephalin messenger RNA were found throughout the medullary reticular formation in the gigantocellular and paragigantocellular reticular nuclei, the parvicellular and lateral reticular nuclei; commissural, medial and ventrolateral subnuclei in the nucleus tractus solitarius and the nucleus of the spinal trigeminal tract. Labelled cells were also concentrated in the more medial regions of the area postrema. In contrast, neurons containing preprodynorphin messenger RNA had a more restricted distribution and were detected in the commissural and ventrolateral nucleus tractus solitarius and nucleus of the spinal trigeminal tract, especially in the more dorsal regions. Expression of preproenkephalin and preprodynorphin messenger RNA was also examined in the dorsal vagal complex of rats that had undergone a unilateral nodose ganglionectomy or cervical vagotomy. Twenty-four hours after both cervical vagotomy and nodose ganglionectomy, there was a specific 1.5-2-fold elevation in preproenkephalin and preprodynorphin messenger RNA levels in the ventrolateral subnucleus of the contralateral nucleus tractus solitarius relative to levels in the ipsilateral nucleus tractus solitarius and in the nucleus tractus solitarius of sham-operated animals. Previous immunohistochemical studies demonstrating the co-localization of enkephalin and dynorphin in the ventrolateral nucleus tractus solitarius suggest that these changes occurred in the same population of neurons. In light of the suggested role of the ventrolateral nucleus tractus solitarius as a central respiratory centre and the activation of the intact pulmonary afferents that innervate this area following a unilateral vagotomy (which increases inspiration volume and expiratory time by affecting the Hering-Breuer reflex), our results suggest a specific involvement of enkephalin- and dynorphin-containing neurons in the ventrolateral nucleus tractus solitarius in central respiratory control mechanisms.

Immediate early gene expression in the rat forebrain following striatal infusion of quinolinic acid

Expression in the rat forebrain of immediate early genes belonging to the fos and jun families was investigated at various time points following an intrastriatal infusion of quinolinic acid. Fos immunoreactivity was rapidly and transiently induced, exhibiting maximal intensity 2 h post-lesion, and was principally located in neuronal nuclei situated around the periphery of the lesioned straitum, in regions that subsequently show little, if any, neurodegeneration. Fos immunoreactivity was additionally expressed throughout the ipsilateral cortex. In contrast, Jun immunoreactivity, which remained undetectable for 12 h after the lesion, reached its maximal intensity 24 h post-lesion, at which time it was most densely distributed in neuronal nuclei found within the central lesioned areas of the striatum. In situ hybridization analysis using radiolabelled oligonucleotide probes confirmed this spatial and temporal separation between c-fos and c-jun expression within the striatum and extended it further, showing that, whilst jun mRNA displayed very similar expression characteristics to those of c-fos mRNA, both fos B mRNA and jun D mRNA exhibited induction patterns closely resembling those of c-jun mRNA. These results clearly suggest that two distinct programmes of immediate early gene expression can be induced in vivo. The rapid (2 h) and transient induction of c-fos/jun B may well be a response to NMDA receptor activation, whereas the molecular signal for the late (24 h) and sustained induction of c-jun/fos B/jun D is currently a focus for our investigations.

Immediate early gene activation during the initial phases of the excitotoxic cascade

Direct brain injections of the N-methyl-D-aspartate receptor agonist quinolinic acid (QA) trigger an excitotoxic cascade characterized by rapid neuronal death and glial/immune cell activation. The present study compared the timing of immediate early gene (IEG; c-fos, c-jun, jun-B, and zif/268) induction with the response of neuronal transcripts during the first 24 hr of a QA lesion within the rodent striatum. Following QA exposure, IEG mRNA induction periods extended from 30 min to 24 hr. Several characteristics of this prolonged transcriptional response suggest that separate cell populations (neuronal vs. glial) originate individual IEG phases during the first day of the lesion. The first IEG phase was rapid and peaked at 60 min. This initial IEG phase, likely neuronal in origin, was dominated by robust increases in the expression of c-fos, jun-B, and zif/268 mRNAs in contrast to small increases in c-jun expression. A second, delayed IEG phase was initiated after the first hour and extended to 24 hr. This IEG phase was more intense and continued beyond the period of neuronal survival as detected by the loss of neurotransmitter-specific mRNAs (preprotachykinin, preproenkephalin, and glutamic acid decarboxylase). During this phase, c-jun mRNA levels coordinately increased with c-fos. Interestingly, the transcriptional peak of the delayed IEG phase occurred between 4 and 12 hr, the time which corresponded to the rapid decline of neuronal transcripts.(ABSTRACT TRUNCATED AT 250 WORDS)

Compositional changes of AP-1 DNA-binding proteins are regulated by light in a mammalian circadian clock

Recent reports have shown that the nuclear phosphoprotein Fos is induced by light in a mammalian circadian clock, the suprachiasmatic nucleus. To learn how light and circadian phase affect the binding of Fos to DNA, we analyzed the photic and temporal regulation of immunoreactive Jun protein expression and AP-1 DNA-binding activity in the rat suprachiasmatic nucleus. Immunohistochemistry and gel mobility shift assays suggest that AP-1 activity during the night and after a light pulse consists of constant, as well as variable, protein components; JunD could be identified as a constituent of both dark- and light-activated binding complexes, whereas binding by JunB and Fos could be implicated only after photic stimulation. Since JunD or JunB could be colocalized with Fos in individual suprachiasmatic nucleus cell nuclei, light may be acting in at least some suprachiasmatic nucleus cells by altering AP-1 protein composition rather than binding site occupancy.

The KROX-20 transcription factor in the rat central and peripheral nervous systems: novel expression pattern of an immediate early gene-encoded protein

The KROX-20 protein (also termed EGR-2) is encoded by an immediate early gene cloned by cross-hybridization to the Drosophila melanogaster Krüppel gene. It belongs to a class of transcription factors with zinc finger motifs and binding activity to a transcriptional regulatory DNA element termed the early growth response consensus sequence. In the present study the temporospatial expression of KROX-20 was investigated in the central and peripheral nervous systems of normal rats and after various stimuli known to induce immediate early genes, including epileptic seizures, axotomy, pharmacological treatment with glutamate and alpha-adrenergic receptor antagonists, and peripheral noxious stimulation. Immunocytochemistry was performed with a specific polyclonal antiserum generated against a fusion protein containing KROX-20 sequences. In the central nervous system, KROX-20 protein demonstrated distinct constitutive nuclear expression in specific neuronal subpopulations of the cortex, septum, amygdala, olfactory bulb and hypothalamus. In addition, distinct cytoplasmic immunoreactivity was present in spinal and medullary motoneurons, dorsal root ganglion neurons and a few neuronal cell populations of midbrain and forebrain. In the CNS, KROX-20 was only induced by bicuculline-induced epileptic seizures. Topographically, the postictal increase of KROX-20 levels was restricted to areas with constitutive expression, such as cerebral cortex, fornix and amygdala. Induction of KROX-20 peaked at 4-8 h after onset of seizure activity. No increase in immunoreactivity was observed in the hippocampus, the brain region most severely affected by bicuculline-induced seizures. Transection of central and peripheral nerve fibers did not result in KROX-20 induction in axotomized neurons. However, KROX-20 was induced in Schwann-like cells after transection of the sciatic nerve. In contrast to KROX-20, KROX-24, a related transcription factor of the zinc finger family, was markedly induced in hippocampal and spinal neurons following seizures and peripheral noxious stimulation, respectively, as well as in CNS neurons following axotomy. Our data indicate that KROX-20 represents an immediately early gene product with basal expression in selected neuronal populations of the nervous system and a restricted inducibility after intentional stimuli.

Expression of immediate early gene proteins following axotomy and inhibition of axonal transport in the rat central nervous system

The expression of the immediate early gene-encoded proteins c-Jun, Jun B, Jun D, c-Fos, Fos B and Krox-24 in central neurons following transection of, or inhibition of, axonal transport in their axons was investigated in the rat using immunocytochemistry. Transection of the medial forebrain bundle, which produces an essentially complete axotomy of neurons in the ipsilateral mammillary nucleus, substantia nigra pars compacta, ventral tegmental area and parafascicularis, induced the expression of c-Jun, Jun D and, to a lesser extent, Krox-24, in these nuclei. Microinjection of colchicine into the medial forebrain bundle to chemically inhibit axonal transport similarly induced the expression of these proteins in these areas. The expression of the proteins was first evident 24 h after transection, reached a maximum at 48 h and was still present after 10 days. However, after 30 days the proteins were absent from the substantia nigra, ventral tegmentum and parafascicularis, and were still present only in the mammillary nuclei. The other immediate early genes, Jun B, c-Fos and Fos B, were never expressed above the basal levels seen in untreated rats. Transection of the corpus callosum and the hippocampal commissure, which produces only a partial axotomy of neurons in the cerebral cortex and hippocampus, respectively, did not induce the expression of any of the genes in these neurons. Microinjection of colchicine or vinblastine to produce a localized inhibition of axonal transport in the cerebral cortex, hippocampus, thalamus and cerebellum also induced the expression of c-Jun, Jun D and, again to a lesser extent, Krox-24, in neurons surrounding the injection site. In contrast to this selective expression, administration of the neuronal excitant metrazole induced the expression of all six immediate early gene proteins in central nervous system neurons. These results demonstrate that transection of, or inhibition of, transport in the axons of central neurons induces a particular pattern of expression of transcriptionally operating immediate early genes that may be related to the regenerative competency of the neurons.

Brain transcription factor expression: effects of acute and chronic amphetamine and injection stress

Amphetamine influences behaviors and the expression of transcription factor genes in the central nervous system (CNS). A single d-amphetamine dose (7.5 mg/kg, i.p.) enhances behavioral stereotypy and augments brain expression of c-fos, fos-B, fra-1, zif268, jun-B, and c-jun by 2-11 fold. When the single amphetamine dose is preceded by 28 saline injections over 14 days, it is half as effective in enhancing expression of these genes. Rats injected with 7.5 mg/kg i.p. twice daily for 2 weeks and sacrificed after the last injection reveal further attenuation or abolition of the amphetamine-induced mRNA upregulation. These stigmata of 'tolerance' in gene expression display partial overlap with behavioral tolerance, manifest as changes in locomotor activity. Rats receiving low (2 mg/kg) amphetamine challenge doses following the 2-week 7.5 mg/kg b.i.d. amphetamine treatment show tolerance to the locomotor activating effects of the drug; no tolerance is evident following a high (7.5 mg/kg) challenge dose. These data suggest that amphetamine-induced alterations in brain transcription factor gene expression can display 'tolerance' and possibly 'cross-tolerance' with the stress caused by i.p. injection.

Anticonvulsant agents, dizocilpine maleate, enadoline and HA 966 have different effects on N-methyl-DL-aspartate-induced immediate early gene induction in mice

Administration of N-methyl-DL-aspartate (85 mg/ml) was given by infusion (0.14 ml/min) until a clonic seizure was elicited. In situ hybridization was used to assess regional levels of four immediate early gene messenger RNA levels (c-fos, c-jun, junB, and a nerve growth factor induced gene, NGFI-A). Messenger RNA levels were highest at 25 min following infusion of N-methyl-DL-aspartate. c-jun messenger RNA levels remained elevated for over 2 h; however, c-fos, junB and, NGFI-A messenger RNA levels had returned to control levels by this time. Expression was detected in the hippocampus, hypothalamus and piriform cortex. Pre-treatment (30 min prior to N-methyl-DL-aspartate) with the anticonvulsant drugs dizocilpine maleate (1 mg/kg) and HA 966 (200 micrograms, i.c.v.) resulted in significantly reduced immediate early gene messenger RNA levels in the hypothalamus and piriform cortex, and attenuated levels in the hippocampus. Pre-treatment with the anticonvulsant agent enadoline (3 mg/kg), given at an anticonvulsant dose, did not result in reduced immediate early gene messenger RNA levels. These results suggest that monitoring immediate early gene expression may lead to advances in the understanding of the mechanism of action of many pharmacological agents, such as the kappa-opioid agonist enadoline.

Differential expression of immediate early genes in the superior cervical ganglion after nicotine treatment

We examined the effects of single and multiple systemic injections of nicotine on the expression of five immediate early genes in the rat superior cervical ganglion by in situ hybridization histochemistry. A single nicotine injection resulted in a rapid and transient activation phase of nerve growth factor I-A, c-fos and jun-B at 20 min, and a later and less prominent activation of c-jun, which stayed high from 20 to 60 min. there was a parallel slow and long-lasting activation of jun-D, which remained high 4 h after nicotine treatment. Tyrosine hydroxylase mRNA, but not neuropeptide Y mRNA, was also induced by nicotine. Denervation of the ganglion did not prevent the induction of immediate early genes, but the nicotine antagonists hexamethonium and mecamylamine completely blocked the induction of immediate early genes, indicating that nicotine acted directly on receptors present on ganglion cells. When repeated nicotine injections were given, there was a refractory period of 1-2 h for c-fos, nerve growth factor I-A and jun-B induction. Repeated nicotine injections at 1-h intervals prevented about 80% of c-fos, nerve growth factor I-A and jun-B mRNA induction seen after a single injection. Because nicotine is known to induce immediate early genes in the adrenal glands as well, we examined whether similar kinetics of the gene induction could be seen in the adrenal medulla. However, no refractory period for repeated nicotine treatment or down regulation of the induction of the immediate early genes could be demonstrated in the adrenal medulla. The results show that sympathetic neurons respond to nicotine with altered expression of immediate early genes. Nicotine-induced expression of immediate early genes may be mediated and regulated by different factors in neuronal and endocrine noradrenergic cells.

Immediate early gene expression in experimental epilepsy

Neuronal excitation by experimentally induced seizures elicits the rapid induction of a set of genes called immediate early genes (IEGs). The gene products of fos, jun and Krox, multimember gene families that belong to the class of IEGs, participate in a fundamental biological control mechanism, the regulation of gene transcription. IEG encoded proteins act as third messengers in an intracellular signal transduction cascade between neural cell surface receptors, cytoplasmic second messenger systems and specific target genes in the nucleus, a process for which the term 'stimulus transcription coupling' has been given. Almost all types of seizures cause dynamic alterations of IEG expression in neurons of the limbic system, but also in non-limbic areas, such as the cortex, striatum and thalamus. IEG encoded transcription factors are thought to up- or down-regulate effector genes with preferential expression in the central nervous system, including genes for neurotransmitters, growth factors, receptors, synaptic and axonal proteins. If the concept holds true that IEGs act as molecular switches converting epileptic short-term excitation of neurons into alterations of the molecular phenotype, future research may help to explain hitherto unexplained phenomena in epileptogenesis including changes of synaptic efficacy, kindling and sprouting.

Correlations between immediate early gene induction and the persistence of long-term potentiation

The duration of long-term potentiation in the dentate gyrus of awake rats was examined following systematic manipulation of the number of stimulus trains delivered. This was correlated with the induction of immediate early genes in separate groups of animals given identical stimulus regimes. Following 10 trains of stimulation, long-term potentiation decayed with a time constant of up to several days (long-term potentiation 2), and this correlated with the appearance of an increase in the messenger RNA and protein levels of zif/268. Increasing the number of stimulus trains resulted in a greater probability of eliciting long-term potentiation with a time constant of several weeks (long-term potentiation 3), as well as increasing the induction of zif/268, c-Jun, Jun-B, Jun-D and Fos-related proteins. When 10 trains were delivered repeatedly on up to five consecutive days, only the zif/268 protein levels showed associated changes. These data provide support for the hypothesis that long-term potentiation 3 involves mechanisms additional to those for long-term potentiation 2. One possible mechanism is altered gene expression, initiated by immediate early gene transcription factors such as zif/268 and possibly homo- or heterodimers of Fos and Jun family members, that then contributes to the stabilization or maintenance of long-term potentiation 3.

The effect of dizocilpine and enadoline on immediate early gene expression in the gerbil global ischaemia model

Increases in mRNA levels for c-fos, c-jun, junB, hsp70 and NGFI-A were observed in the dentate gyrus of the hippocampus following 7 min ischaemia in the Mongolian gerbil. The response was rapid and transient (30 min to 4 hr) for NGFI-A, junB and c-fos mRNA. In contrast c-jun mRNA remained increased for several hours. Hsp70 increased in the dentate gyrus 1 hr after the insult, returned to control values at 4 hr and showed a secondary increase at 24 hr. At 24 hr increased hsp70 mRNA was observed in other regions of the CNS, i.e. CA1, CA2, CA3 and cortex. The non-competitive NMDA receptor antagonist, dizocilpine, attenuated the increases in IEG expression and was neuroprotective. In contrast the kappa opiate receptor agonist, enadoline, protected the CA1 neurones from degeneration but did not inhibit the increased levels of IEG mRNA. Increases in hsp70 mRNA were reduced to baseline by both enadoline and dizocilpine. These results suggest that inhibition of IEG expression is not a prerequisite for neuroprotection. However, hsp70 was predictive of neuronal protection and may be a useful assay in this and related models.

Involvement of cholecystokinin receptor types in pathways controlling oxytocin secretion

1. Intravenous administration of cholecystokinin (CCK) results in a transient activation of oxytocin neurones in the rat, and hence to oxytocin secretion: this activation is followed by expression of c-fos mRNA and of Fos-like immunoreactivity (Fos-LI) in magnocellular oxytocin neurones. Fos-like immunoreactivity is also induced in the regions of the brainstem that are thought to relay information from the periphery to the hypothalamus. 2. Administration of the selective CCKA receptor antagonist MK-329, but not the CCKB receptor antagonist L-365,260, prior to CCK injection, prevented oxytocin release as measured by radioimmunoassay and oxytocin neuronal activation as measured by electrophysiology and by the lack of induction of c-fos mRNA. 3. MK-329 abolished the release of adrenocorticotrophic hormone (ACTH) following injection of CCK. 4. MK-329 prevented the expression of Fos-LI in the hypothalamic magnocellular nuclei and in the area postrema and dorsal vagal complex of the brainstem. 5. L-365,260 had no effect on the expression of Fos-LI in the brainstem, but attenuated that seen in the hypothalamic magnocellular nuclei. 6. We conclude that CCK acts on CCKA receptors, either in the area postrema or on peripheral endings of the vagus nerve, to cause the release of hypothalamic oxytocin and ACTH. Information may be carried to the hypothalamus in part by CCK acting at CCKB receptors.

The role of excitatory amino acid receptors and intracellular messengers in persistent nociception after tissue injury in rats

Increased pain sensitivity (hyperalgesia) and persistent nociception following peripheral tissue injury depends both on an increase in the sensitivity of primary afferent nociceptors at the site of injury (peripheral sensitization), and on an increase in the excitability of neurons in the central nervous system (central sensitization). We will review evidence that central sensitization, and the persistent nociception it leads to, are dependent on an action of glutamate and aspartate at excitatory amino acid (EAA) receptors. Additional evidence will be presented implicating a role of various intracellular second messengers that are coupled to EAA receptors (nitric oxide, arachidonic acid, and protein kinase C) to central sensitization and persistent nociception following tissue injury. Finally, we will examine the evidence for a contribution of molecular events, including noxious stimulus-induced expression of immediate-early genes such as c-fos to persistent nociception.

Basic fibroblast growth factor-induced increase in zif/268 and c-fos mRNA levels is Ca2+ dependent in primary cultures of hippocampal neurons

Basic fibroblast growth factor (bFGF) is present in the developing rat brain and has been shown to provide critical trophic support for hippocampal neurons in culture. The influence of bFGF on the expression of mRNAs encoding the transcription factors zif/268 and c-fos was studied in primary cultures of hippocampal neurons (derived from rat embryos) using reverse transcription-coupled PCR. In these cultures grown for 3 days in the absence of serum, bFGF causes a dramatic and transient increase in the levels of zif/268 and c-fos, within 15 and 30 min, respectively. A similar induction of these two early genes occurs following activation of protein kinase C (PKC). The bFGF-induced activation persists after PKC desensitization but is inhibited by chelation of intracellular Ca2+. These results suggest that in primary cultures of hippocampal neurons, bFGF induces the expression of immediate early genes through a pathway that requires Ca2+ mobilization.

Spinal and hindbrain structures involved in visceroception and visceronociception as revealed by the expression of Fos, Jun and Krox-24 proteins

We have used the evoked expression of the immediate early gene-encoded proteins (Krox-24, c-Fos, Fos B, Jun D, Jun B, c-Jun) to monitor visceral processing in both the spinal cord and hindbrain structures of rats undergoing either mechanical colorectal or chemical intraperitoneal stimulation. Experiments were conducted under controlled volatile anaesthesia to suppress affective reactions that visceral stimulations may induce. The results refer to the effects of anaesthesia alone, and of both innocuous and noxious stimulations. Non-nociceptive and nociceptive stimulation but not anaesthesia were effective in evoking c-Fos, c-Jun, Jun B and Krox-24 expressions in the spinal cord. Intraperitoneal injections labelled cells mostly at the thoracolumbar junction levels, while colorectal distension labelled cells mostly at the lumbrosacral junction levels. Labelling was widely distributed throughout the gray matter including superficial layers, deep dorsal horn, lamina X and sacral parasympathetic columns. Krox-24- and, to a lesser degree, c-Jun-labelled cells were quite numerous in the superficial layers of the dorsal horn; Jun B, and especially c-Fos, were very effective in demonstrating inputs to all parts of the spinal cord. Both anaesthesia and noxious visceral stimulation were effective in evoking c-Fos, Krox-24 and Jun B expressions in discrete hindbrain subregions. The structures which are primarily labelled under anaesthesia are the rostral ventrolateral medulla, the external medial and lateral nuclei of the parabrachial area, the medial and dorsal subnuclei of the nucleus of the solitary tract, the area postrema, the central gray including pars alpha and nucleus O, the nucleus beta of the inferior olive, the locus coeruleus, and the inferior colliculi and adjacent parts of central gray. The structures which are primarily labelled following noxious visceral stimulation are the caudal intermediate reticular nucleus as part of the caudalmost ventrolateral medulla and the superior lateral nucleus of the rostrolateral parabrachial area. Labelling in the caudal intermediate reticular nucleus was maximal for colorectal distension. Labelling in the superior lateral nucleus was specific to peritoneal inflammation. The Edinger-Westphal nucleus is a structure in which noxious-evoked labelling was superposed onto the anaesthesia-evoked labelling. Nociception-evoked overexpression in this nucleus was maximal for intraperitoneal inflammation. The present work demonstrates that the central effects induced by either anaesthesia or visceroception including pain can be effectively monitored through the induction of an array of immediate early genes.(ABSTRACT TRUNCATED AT 400 WORDS)

The pharmacology of pain signalling

Recent advances in pain research illustrate the analytical power of modern neurosciences in a field previously accessible only to methods of systems biology. Novel molecular and cellular biological techniques have changed the face of pain research by detailing the multiplicity of pain transducing and pain suppressive systems which involve neuronal and hormonal systems acting in concert to help the individual to cope with pain. The introduction of concepts of neuronal plasticity in this field has led to important therapeutical consequences. Novel compounds and new regimens for drug treatment to prevent activity-dependent long-term changes or to facilitate extinction in pain-related systems are emerging.

Early nerve growth factor-induced events in developing rat septal neurons

A culture system enriched for nerve growth factor (NGF) receptor bearing cells was developed to investigate signal transduction events activated by NGF in postmitotic central nervous system neurons. Cells from the septal region of embryonic rats at 16 days of gestation were grown on glass coverslips above a glial cell layer established from postnatal rat cortex. The separation of glial and neuronal planes in this "bilaminar" system permits the diffusion of glial-derived factors required by septal neurons for survival yet allows the investigation of NGF responses in a pure neuronal population. Approximately 15% of the neurons in this culture system were immunoreactive for the low affinity NGF receptor. NGF rapidly increased MAP kinase activity (2-5 min) and transiently induced expression of c-fos in septal neurons. NGF treatment also increased choline acetyltransferase activity, while the number of cholinergic neurons remained constant. Septal neuron survival depended on the presence of glial cells, but neuronal viability in the bilaminar system was unaffected by anti-NGF antiserum, indicating that glial-derived neurotrophic support is not mediated by NGF alone. These data suggest that the bilaminar culture system is a useful system for the study of early events in NGF-activated signal transduction and the nature of glial-derived trophic support of developing basal forebrain neurons.

JUN, FOS, KROX, and CREB transcription factor proteins in the rat cortex: basal expression and induction by spreading depression and epileptic seizures

The expression of the nuclear c-JUN, JUN B, JUN D, c-FOS, FOS B, KROX-24, and CREB transcription factors was investigated in the cortex of adult rats by immunocytochemistry. The expression patterns were studied in untreated rats and up to 24 hours following topical application of 1 M KCl to the cortical surface (KCl) or i.v. injection of bicuculline (BIC). Topical KCl induced cortical spreading depression and systemic injection of bicuculline evoked generalized tonic-clonic seizures. In untreated rats, JUN B, c-FOS, and FOS B were expressed in a small number of neurons in the piriform, perirhinal, entorhinal, and insular cortex and in layers II, III, and VI of all neocortical areas. In contrast, c-JUN, JUN D, and KROX-24 were expressed in all cortical layers but with different intensities of immunoreactivity (IR): c-JUN-IR was generally weak and predominantly present in layers II, III, and VI. JUN D-IR was equally strong in all layers. KROX-24 showed a prominent expression in layers II, IV, and VI. The CREB protein exhibited a slight preponderance in layer II and piriform cortex. Following KCl or BIC, a strong induction was seen for c-FOS, JUN B, and KROX-24, whereas c-JUN, JUN D, and FOS B showed only a moderate increase compared to basal levels. Changes of CREB-IR could not be detected. The localization of induced JUN, FOS, and KROX proteins reflected the pattern of labelling in untreated animals but demonstrated a higher intensity of labelling and an increased number of immunoreactive nuclei. The intensity and persistence of IR as well as the number of labelled cells following BIC exceeded those following KCl. Following BIC, increased levels of FOS B and JUN D were still present after 24 hours. Counterstaining with cresyl-violet and GFAP, a marker for astrocytes, revealed that JUN, FOS, and KROX proteins were expressed in neurons but not in glial cell populations. The present data demonstrate that CREB, JUN, FOS, and KROX transcription factors exhibit a layer-specific expression in the cerebral cortex with only slight area-specific differences both in untreated rats and following stimulation with KCl and BIC. The expression of transcription factor proteins indicate complex molecular genetic changes in cortical neurons due to pathophysiological events such as seizure activity and spreading depression.

Differential time course and spatial expression of Fos, Jun, and Krox-24 proteins in spinal cord of rats undergoing subacute or chronic somatic inflammation

We have used the evoked expression of both immediate early gene (IEG)-encoded proteins (Krox-24, c-Fos, Fos B, Jun D, Jun B, c-Jun), and dynorphin to monitor sensory processing in the spinal cords of rats undergoing subacute or chronic somatic inflammation (i.e., subcutaneous inflammation of the plantar foot and monoarthritis, respectively). Behavioral and immunocytochemical approaches were conducted in parallel up to 15 weeks postinjection in order to detect possible relationships between clinical evolution and spatiotemporal pattern of IEG-encoded protein expression. Each disease had specific characteristics both in terms of their clinical evolution and pattern of evoked protein expression. All IEG proteins were expressed in both cases. Most of the staining was observed in both the superficial layers of the dorsal horn and deep dorsal horn (laminae V-VII and X). Monoarthritis was distinguished by a high level of total protein expression. Staining was especially dense in the deep dorsal horn. More labelled cells were observed at 1-2 days and at 2 weeks postinjection, corresponding to the initiation and progressive phases of the disease, respectively. Subcutaneous inflammation was characterized by a moderate level of total IEG expression. More labelled cells were observed in the first day following injection. It is the relative degree of expression of each IEG-encoded protein with regard to the others that characterized the progression of the diseases. Early stages of the diseases coincided with the expression of all Fos and Jun proteins, while late stages showed an increase in Jun D and Fos B involvement; Krox-24 was induced mostly during the early phases and/or periods of paroxysm of the diseases. Persistent stimulation was characterized by a predominant expression in deep versus superficial layers of the dorsal horn. Evoked expression of c-Jun in motoneurons was only observed in monoarthritis. The peak of dynorphin expression was late in regard to both the induction of inflammation and period of maximal IEG-encoded protein expression. The present work indicates that the neural processing that takes place during progression of these diseases can be monitored well at the spinal cord level by using the expression of an array of IEG-encoded proteins. Study of long term evolutive diseases and especially those that evolve into chronicity can largely benefit from such an approach.

Induction of immediate early genes by cyclic AMP in primary cultures of neurons from rat cerebral cortex

In this paper, we tested whether physiological activators of the cAMP second messenger pathway in primary cultures of neurons from rat cerebral cortex directly induce c-fos and other immediate early gene (IEG) transcription factors. We have found that brief (30 s to 2 min) stimulation of neurons with vasoactive intestinal peptide (VIP) and SKF-38393, a D1-dopaminergic receptor agonist, potently increased mRNA levels for the IEGs c-fos, jun-B, and NGFI-A, with weaker increases for c-jun. This action was mimicked by forskolin and dibutyryl cAMP. IEG induction by VIP and dibutyryl cAMP was not blocked by excitatory amino acid receptor antagonists or by blockers of dihydropyridine-sensitive calcium channels. Moreover, calcium-free medium did not modify IEG induction by dibutyryl cAMP, suggesting that cAMP can directly regulate IEG expression in differentiated neurons independently of calcium.

Expression of c-Jun as a response to dorsal root and peripheral nerve section in damaged and adjacent intact primary sensory neurons in the rat

It was previously shown that the immediate early gene, c-jun, was highly expressed over long periods, in both peripheral sensory and motor neurons following axon damage or block of axoplasmic transport. Here we have examined the question of whether the expression of c-Jun protein is related to axon injury per se or to the process of axon growth. We have examined dorsal root ganglion (DRG) cells subjected to different manipulations which are associated with varying degrees of regrowth, as follows: (i) after peripheral nerve section, where it appears that all damaged neurons make some regenerative effort. 1-24 days after sciatic nerve section and ligation most cells in L4/L5 DRG were c-Jun-positive; (ii) after section of the central processes of the DRG cells, which then showed a slow and limited regrowth of their axons towards, but not into, the spinal cord. This resulted in a variable, but significant, expression of c-Jun in a small number of DRG cells; (iii) in intact sensory neurons that were offered the opportunity to sprout into adjacent denervated peripheral tissue. The sciatic nerve was ligated and the response of cells in the L3 ganglia (many of which project to the saphenous nerve) was measured. A small but significant number of cells were c-Jun-positive; (iv) in intact sensory neurons that were offered the opportunity to sprout centrally into partialy denervated neuropil of the spinal cord. We examined neurons in the L3 DRG after rhizotomy of the adjacent L4/L5 dorsal roots. Previous work suggests that sensory neurons show at best a very limited growth under these conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatotopic and laminar organization of fos-like immunoreactivity in the medullary and upper cervical dorsal horn induced by noxious facial stimulation in the rat

The distribution of fos-like-immunoreactivity (fos-LI) in the medullary and upper cervical dorsal horn was examined following noxious facial stimulation, in order to evaluate the use of fos as a marker for neuronal activation in trigeminal nociceptive pathways. Control animals that received urethane anesthesia and no facial stimulation showed substantial bilateral labeling in the trigeminal complex that was restricted to one rostrocaudal level, at the transition between the medullary dorsal horn (nucleus caudalis) and nucleus interpolaris. Noxious mechanical stimulation (pinch) of different facial sites produced labeling in the ipsilateral dorsal horn whose distribution varied predictably with the rostrocaudal and dorsoventral position of the facial stimulation site, such that rostral facial sites were represented rostrally in the dorsal horn and dorsal sites were represented ventrolaterally. The cornea was exceptional among the facial stimulation sites in that it had a specific representation at two distinct rostrocaudal levels, in C1 and the interpolaris-caudalis transition region; the position of the rostral peak was somatotopically inappropriate, based on the representation of other facial sites. The proportion of labelling in laminae III-IV relative to laminae I-II was higher with noxious mechanical stimulation than with noxious thermal (55 degrees C) or chemical (subcutaneous injection of capsaicin) stimulation. The proportion of labelling in laminae III-IV produced by electrical stimulation of the infraorbital nerve was no greater than that produced by pinch. The results suggest that fos-LI mapping can be a useful method for the investigation of somatotopy but is subject to serious limitations when used for the investigation of laminar organization. The results also suggest that the interpolaris-caudalis transition region may have properties that are distinct from those of the rest of the trigeminal complex, possibly related to an involvement in autonomic function.

Nitric oxide synthase is found in some spinothalamic neurons and in neuronal processes that appose spinal neurons that express Fos induced by noxious stimulation

To determine if nitric oxide (NO) and Fos immunoreactivity induced by noxious stimulation were colocalized in spinothalamic neurons, double-staining immunocytochemical techniques were combined with retrograde neuroanatomical tracing procedures. Initial studies on three rats demonstrated that Fos and nitric oxide synthase (NOS), the synthesizing enzyme for nitric oxide, did not coexist in spinothalamic tract neurons. However, some spinothalamic neurons were found to contain NOS and some NOS immunoreactive processes were found to appose Fos containing neurons. Thus the remainder of the study: (1) analyzed the relationship of NOS positive neuronal processes with Fos stained neurons using a Fos immunocytochemical technique in combination with either NOS immunofluorescence or NADPH-diaphorase histochemistry; and (2) quantitated the number of NOS containing cells that project to the thalamus using a combined immunofluorescent-retrograde tracing procedure. Both NOS-like immunoreactive (NOS IR) neuronal processes and NADPH-diaphorase positive neuronal processes in the dorsal horn of the lumbar spinal cord were found to appose Fos positive neurons located in laminae I and II of the dorsal horn. Approximately 40% of Fos-labeled cells in these superficial laminae were found to be in apposition to or in close proximity to NOS labeled neuronal processes. Examination of spinal cord sections for NOS-containing spinothalamic tract neurons revealed that lamina X was the only spinal cord region containing such double-labeled neurons. Further quantification revealed that approximately 10% of NOS positive neurons in lamina X were double-labeled with Fluorogold. These findings support the hypothesis that nitric oxide is involved in nociceptive events occurring in the spinal cord in response to a peripheral noxious stimulus and further indicate that nitric oxide may contribute to the central transmission of spinothalamic information.

Regulation of gene expression in hippocampal neurons by distinct calcium signaling pathways

Calcium ions (Ca2+) act as an intracellular second messenger and can enter neurons through various ion channels. Influx of Ca2+ through distinct types of Ca2+ channels may differentially activate biochemical processes. N-Methyl-D-aspartate (NMDA) receptors and L-type Ca2+ channels, two major sites of Ca2+ entry into hippocampal neurons, were found to transmit signals to the nucleus and regulated gene transcription through two distinct Ca2+ signaling pathways. Activation of the multifunctional Ca(2+)-calmodulin-dependent protein kinase (CaM kinase) was evoked by stimulation of either NMDA receptors or L-type Ca2+ channels; however, activation of CaM kinase appeared to be critical only for propagating the L-type Ca2+ channel signal to the nucleus. Also, the NMDA receptor and L-type Ca2+ channel pathways activated transcription by means of different cis-acting regulatory elements in the c-fos promoter. These results indicate that Ca2+, depending on its mode of entry into neurons, can activate two distinct signaling pathways. Differential signal processing may provide a mechanism by which Ca2+ controls diverse cellular functions.

C-fos expression in rat lumbar spinal cord following peripheral stimulation in adjuvant-induced arthritic and normal rats

Our previous data reported a maximal expression of the c-fos immediate-early gene in the lumbar spinal cord of the non-stimulated polyarthritic rat neurons, three weeks after Freund's adjuvant injection. The present study utilises c-fos expression to judge the reactivity of spinal neurons to calibrated mechanical pressure applied to the ankle joint, in both normal and arthritic rats under ketamine anesthesia. The results indicate that the number of Fos-like immunoreactive neurons (1) is slightly decreased in ketamine-anesthetized non-stimulated arthritic rats as compared to the non-anesthetized non-stimulated ones, (2) is significantly higher in both stimulated normal and arthritic animals as compared to non-stimulated animals, particularly in laminae I, II, V and VI of L3 and L4, and (3) is significantly increased in stimulated arthritic as compared to stimulated normal rats, in all laminae of lumbar spinal segments. The appearance of 'basal' Fos labeling during the adjuvant-induced arthritic disease and the increased number of Fos-like immunoreactive neurons in stimulated arthritic rats compared to stimulated normal animals indirectly suggests that these neurons are abnormally active and thus involved in the hyperalgesia of arthritic disease. Therefore the use of Fos-like immunoreactivity in the chronic pain model seems to be an appropriate tool to study possible effects of various pharmacological compounds, such as analgesics and anti-inflammatory drugs.

Induction of c-Fos-like protein in the lateral habenular nucleus by persistent noxious peripheral stimulation

Persistent noxious peripheral stimulation by formalin injection into the unilateral hindpad of anaesthetized rats induced c-Fos-like protein immunoreactivity (c-Fos-LI) in neurons within the lateral habenular nucleus (LHb) bilaterally. Formalin injection after the transection of spinal cords also induced c-Fos-LI in many neurons within the LHb, though the number of labeled cells changed depending on the post-transection period. These results suggest that the LHb modulates nociceptive information, but that it receives nociceptive information via extraspinal pathways as well as intraspinal ascending noxious pathways.

Contribution of central neuroplasticity to pathological pain: review of clinical and experimental evidence

Peripheral tissue damage or nerve injury often leads to pathological pain processes, such as spontaneous pain, hyperalgesia and allodynia, that persist for years or decades after all possible tissue healing has occurred. Although peripheral neural mechanisms, such as nociceptor sensitization and neuroma formation, contribute to these pathological pain processes, recent evidence indicates that changes in central neural function may also play a significant role. In this review, we examine the clinical and experimental evidence which points to a contribution of central neural plasticity to the development of pathological pain. We also assess the physiological, biochemical, cellular and molecular mechanisms that underlie plasticity induced in the central nervous system (CNS) in response to noxious peripheral stimulation. Finally, we examine theories which have been proposed to explain how injury or noxious stimulation lead to alterations in CNS function which influence subsequent pain experience.

Activation of cAMP-responsive genes by stimuli that produce long-term facilitation in Aplysia sensory neurons

One of the hallmarks of long-term memory in both vertebrates and invertebrates is the requirement for new protein synthesis. In sensitization of the gill-withdrawal reflex in Aplysia, this requirement can be studied on the cellular level. Here, long-term but not short-term facilitation of the monosynaptic connections between the sensory and motor neurons requires new protein synthesis and is reflected in an altered level of expression of specific proteins regulated through the cAMP second-messenger pathway. Using gene transfer into individual sensory neurons of Aplysia, we find that serotonin (5-HT) induces transcriptional activation of a lacZ reporter gene driven by the cAMP response element (CRE) and that this induction requires CRE-binding proteins (CREBs). The induction by 5-HT does not occur following a single pulse, but becomes progressively more effective following two or more pulses. Moreover, expression of GAL4-CREB fusion genes shows that 5-HT induction requires phosphorylation of CREB on Ser119 by protein kinase A. These data provide direct evidence for CREB-modulated transcriptional activation with long-term facilitation.

Molecular biology of vertebrate learning: is c-fos a new beginning?

An elevated expression of c-fos nuclear protooncogene (immediate early gene) has been shown repeatedly to correlate with long-term neuronal responses. This paper reviews recent data suggesting that neuronal plasticity, including learning and memory formation, may involve c-fos expression as well. On the basis of biological functions of the Fos protein, well known to be a component of a transcription factor, AP-1, (activator protein 1) a hypothesis suggesting a role of transcription factors in the integration of information during learning processes is proposed.

Additive induction of Egr-1 (zif/268) mRNA expression in neuroblastoma x glioma hybrid NG108-15 cells via cholinergic muscarinic, alpha 2-adrenergic, and bradykinin receptors

Administration of carbachol, noradrenaline, and bradykinin induced Egr-1 mRNA expression within 1 h in mouse neuroblastoma x rat glioma hybrid NG108-15 cells. With specific receptor antagonists, the Egr-1 inductions by carbachol and noradrenaline were shown to be mediated via cholinergic muscarinic and alpha 2-adrenergic receptors, respectively. At their saturation levels for Egr-1 induction, the two agonists had additive effects when added together, but no prolongation of the effect on Egr-1 induction was observed. Addition of carbachol or noradrenaline 6 h after primary stimulation with carbachol or noradrenaline did not result in secondary Egr-1 induction, probably because of receptor desensitization. On the other hand, bradykinin consistently had an additive effect on Egr-1 induction, irrespective of the time of its addition, suggesting that the signal pathways for Egr-1 induction by carbachol or noradrenaline and by bradykinin are different. Treatment of cells with pertussis toxin or cholera toxin strongly inhibited Egr-1 induction by carbachol or noradrenaline but only partially inhibited the induction by bradykinin. Thus, the signals transduced in NG108-15 cells by different neurotransmitter receptors appear to have different effects on Egr-1 induction, depending on the times of stimulation and the combinations of receptors stimulated.

Expression of Egr-1 in the brain of sleep deprived rats

In previous research, rats subjected to prolonged sleep deprivation have shown disturbances of thermoregulation, hormonal and metabolic changes in apparent response to the thermoregulatory problems, lesions on the tail and paws, and eventual death. To search for alterations of functional activity in brain, the expression of the immediate early gene Egr-1 was examined by immunocytochemistry and Northern blotting in rats subjected to total sleep deprivation (TSD) for 10 days. Controls included yoked stimulus-control (TSC) rats, surgically implanted but otherwise undisturbed control rats, and unoperated control rats. Photographs of immunoreacted coronal sections from four sets of rats were ranked blindly for 25 brain regions. TSD rats showed tendencies for regionally specific increases in Egr-1-like immunoreactivity in dorsal raphe, lateral habenula, superior colliculus, and ventral periaqueductal grey. However, most regions showed no differences in Egr-1-like immunoreactivity between TSD and control rats. Neither was there a difference in whole brain Egr-1 mRNA by Northern blot in two additional sets of rats. Thus, this study, like previous studies of brain histology, amines, adrenoceptors, and glucose utilization, does not provide positive support for the hypothesis that sleep protects the central nervous system against massive global damage, fatigue, or dysfunction.

Differential expression of immediate early genes after transection of the facial nerve

Facial motoneurons respond to peripheral transection of the facial nerve with a number of molecular changes. In order to obtain insight into the transcriptional mechanisms underlying the changes induced by axotomy, the expression of a number of immediate early genes was investigated after facial nerve lesion in the rat. Some immediate early genes (such as c-fos, c-jun or jun B) are known to encode transcription factors that bind to DNA at sites that regulate gene expression and they could therefore contribute to long-term changes in motoneurons. Northern blot analysis of RNA extracted from the facial nucleus from postoperative intervals covering hours and days revealed that axotomy results in a unique pattern of immediate early gene induction in the facial nucleus. c-Jun, jun B and 12-O-tetradecanoylphorbol-13-acetate-induced sequence (TIS) 11 messenger RNA, also present in low amounts in the unoperated nucleus, were strongly induced in a long-term fashion after nerve injury. Increased levels of these messenger RNAs were first detectable at 5 h, reaching a maximum (300-500% compared to control) within 24 h followed by a gradual decline during the following week. Elevated levels were maintained at least up to eleven days compared to the unoperated side. On the other hand, c-fos messenger RNA was neither expressed in the unoperated nucleus, nor was c-fos messenger RNA induced by axotomy at any of the time-points studied. Another member of the TIS family of immediate early genes TIS 7 (PC4), however, was detectable at low levels in normal facial nucleus, but its expression was unaffected by lesion. The three axotomy-induced messenger RNAs, c-jun, jun B and TIS 11, were all localized in the facial motoneurons by in situ hybridization histochemistry indicating that their induction occurs as part of the retrograde reaction of the motoneurons in response to lesion. These data suggest that c-jun, jun B and TIS 11 may play a role in triggering the regeneration programme of motoneurons.

Differential expression of immediate early genes in rubrospinal neurons following axotomy in rat

Many immediate early genes are rapidly and transiently expressed in the central nervous system following a variety of stimuli. Damage to the axons of peripheral and certain central neurons has been shown to result in a long-term increase in expression of c-Jun in the parent cell bodies. In the peripheral nervous system this increased expression of c-Jun protein and mRNA develops over 24 h following sciatic nerve section and is maintained if the damaged nerve is ligated, but returns to basal levels if the peripheral nerve is allowed to regenerate. Here, we report on the response of rubrospinal neurons to spinal cord hemisection at levels C3 and T10. c-Jun expression was first seen at 12 h post-lesion in a limited number of rubral neurons. The number of positively stained neurons increased up to 10 days post-lesion and then declined over the following weeks. By 7 weeks post-lesion there was still evidence of c-Jun immunoreactivity in both large and other clearly atrophic rubrospinal neurons. c-Fos immunoreactivity was seen only at 12-48 h in a small number of rubrospinal neurons. Evidence from retrograde tracing experiments following fluorogold application to the hemisected cord suggested that all c-Jun-positive neurons projected into the spinal cord. No c-Jun response was seen following a lesion at T10.(ABSTRACT TRUNCATED AT 250 WORDS)

[NSAIDS in postoperative pain?]

Postoperative pain arises largely from distension and sectioning of nerve fibers, which generate a short-lasting but enormous afferent impulse barrage. This causes a long-lasting enlargement of receptive fields and an increase in excitability of dorsal horn neurons sending their axons up to the brain. The central process set up by extreme afferent excitation can be prevented by local anesthetics that will block afferent impulse conduction, or by premedication with opioid analgesics that will reduce the massive synaptic activation of dorsal horn neurons. Several mechanisms cause hyperactivity in these nociceptive neurons, one being an abundant formation of prostaglandins. Prostaglandins in the spinal cord facilitate the synaptic transmission from nociceptive afferents. Nonsteroidal anti-inflammatory drugs (NSAIDs) produce relief from postoperative pain by blocking the formation of prostaglandins in the spinal cord, thus abolishing the facilitatory effect of these compounds.

Differential expression of immediate early genes after hippocampal long-term potentiation in awake rats

The pattern of expression of fos and jun family immediate early genes following the induction of long-term potentiation (LTP) was investigated in the dentate gyrus of awake rats. Rapid, transient increases in the levels of c-jun and jun-B mRNA and protein, and in the levels of Fos-related proteins (FRAs), occurred in the dentate gyrus after LTP-inducing tetanization of the perforant path. A delayed, and more prolonged induction occurred for jun-D mRNA and protein. The induction of c-Jun, Jun-B, Jun-D and Fos-related proteins was prevented by administration of an N-methyl-D-aspartate receptor antagonist, which also blocked LTP induction, and by pentobarbital, which reduced but did not block LTP. These findings show that differential expression of fos and jun gene family members occurs in a distinct pattern following LTP in awake rats. The responsive genes may participate in the biochemical cascade leading to the long-term stabilization of synaptic modifications.

c-jun expression in substantia nigra neurons following striatal 6-hydroxydopamine lesions in the rat

The proto-oncogene c-jun is thought to play a role in the control of growth and differentiation of many cell types. It has been demonstrated previously that damage to axons of peripheral motor or sensory neurons resulted within 24 h in substantially increased levels of the c-jun gene in the parent cell bodies. These increased levels of c-jun protein and messenger RNA are maintained if the damaged nerve is ligated, but return to basal levels if the peripheral nerve is allowed to regenerate. We have examined the expression of immediate early genes in central neurons of the rat and now show that a 6-hydroxydopamine-induced axotomy of the dopaminergic nigrostriatal pathway results in a substantial increase in the levels of c-jun (but not c-fos) messenger RNA and protein within neurons of the substantia nigra pars compacta. However, the central neuronal response differs from the peripheral nerve response in that it becomes maximal at four to eight days post-lesion and is transient, declining to control levels in nigral neurons by 14 days post-lesion. These expression patterns may be related to the differential capacity of central and peripheral neurons to regenerate. The precise role of c-jun in these processes, or in the regenerative response, is unclear but it remains possible that c-jun activation following axon damage leads to an increased expression of genes which are essential for the regenerative response. The nature of the mechanism by which c-jun levels are attenuated in central neurons is also unclear, but inhibitory factors, generated by the central environment, may play a role.

Tissue-plasminogen activator is induced as an immediate-early gene during seizure, kindling and long-term potentiation

The requirement of protein and messenger RNA synthesis for long-term memory suggests that neural activity induced by learning initiates a cascade of gene expression. Here we use differential screening to identify five immediate-early genes induced by neuronal activity. One of these is tissue-plasminogen activator (tPA), an extracellular serine protease, which is induced with different spatial patterns in the brain by three activity-dependent events: (1) convulsive seizure increases expression of tPA in the whole brain; (2) stimulation of the perforant path produces an epileptiform after-discharge that ultimately leads to kindling increases the levels of tPA throughout the hippocampus bilaterally; and (3) brief high-frequency stimulation of the perforant path that produces long-term potentiation (LTP) causes an NMDA (N-methyl-D-aspartate) receptor-mediated increase in the levels of tPA mRNA which is restricted to the granule cells of the ipsilateral dentate gyrus. As release of tPA is correlated with morphological differentiation, the increased expression of tPA may play a role in the structural changes that accompany activity-dependent plasticity.