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

Splicing factor transformer-2β (Tra2β) regulates the expression of regulator of G protein signaling 4 (RGS4) gene and is induced by morphine

Regulator of G protein signaling 4 (RGS4) is a critical modulator of G protein-coupled receptor (GPCR)-mediated signaling and plays important roles in many neural process and diseases. Particularly, drug-induced alteration in RGS4 protein levels is associated with acute and chronic effects of drugs of abuse. However, the precise mechanism underlying the regulation of RGS4 expression is largely unknown. Here, we demonstrated that the expression of RGS4 gene was subject to regulation by alternative splicing of the exon 6. Transformer-2β (Tra2β), an important splicing factor, bound to RGS4 mRNA and increased the relative level of RGS4-1 mRNA isoform by enhancing the inclusion of exon 6. Meanwhile, Tra2β increased the expression of full-length RGS4 protein. In rat brain, Tra2β was co-localized with RGS4 in multiple opioid action-related brain regions. In addition, the acute and chronic morphine treatment induced alteration in the expression level of Tra2β in rat locus coerulus (LC) in parallel to that of RGS4 proteins. It suggests that induction of this splicing factor may contribute to the change of RGS4 level elicited by morphine. Taken together, the results provide the evidence demonstrating the function of Tra2β as a new mediator in opioid-induced signaling pathway via regulating RGS4 expression.

Multiple neurotransmitter receptors contribute to the spinal Fos expression

The aim of this study is to identify the receptors which could potentially mediate the activation of c-Fos. Therefore, the effects of neurotransmitter receptor agonists in the activation of c-Fos in spinal neurons were studied by intrathecal injection of excitatory amino acid (EAA) receptor agonists: N-Methyl-D-Aspartate (NMDA), (S)-alpha-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic acid (AMPA), 2-Carboxyl-3-carboxymethyl-4-isopropenylpyMidine (Kainic acid, KA), (1S-3R)-1-Aminocyclopentane-1, 3-dicarboxylacid (ACPD), and substance-P receptor (neurokinin-1) agonist, [Sar9, Met (O2)11] SP (SarMet-SP). All drugs tested activated the production of c-Fos in spinal dorsal horn neurons. AMPA was found as the most potent agonist tested producing market production of c-Fos particularly in neurons of lamina II at doses of 10 pM per 10-microl injection. At this dose, other agonists were relatively ineffective. At higher doses, AMPA significantly increased the activated cells. NMDA significantly increased c-Fos production to a marked extent only at doses above 10 nM per 10-microl injection. KA and ACPD were least potent of the excitatory amino acid agonists. Injection of SarMet-SP at doses of 1 nM activated Fos selectively in neurons of lamina I. A dose-dependent increase in number of c-Fos-positive cells was observed for AMPA, KA, ACPD, and SarMet-SP, whereas NMDA gave a very strong expression after a high dose with no dose dependency. These finding suggest that multiple neurotransmitter receptors lead to c-Fos production in spinal neurons.

Endomorphins suppress nociception-induced c-Fos and Zif/268 expression in the rat spinal dorsal horn

We evaluated the potency of endomorphin-1 and -2 as endogenous ligands on c-Fos and Zif/268 expression in the spinal dorsal horn by formalin injection to the rat hind paw. Endomorphin-1, -2, or morphine was administered intrathecally or intracerebroventricularly 5 min before formalin injection (5%, 100 microl). All drugs produced marked reductions of formalin-induced c-Fos and Zif/268 immunoreactivity in laminae I and II, and laminae V and VI in the rat lumbar spinal cord. The reductions of Zif/268 expression by endomorphins were greater than those by morphine, while the reductions of c-Fos expression by endomorphins were smaller than those by morphine. These effects of endomorphins were attenuated by pretreatment with naloxone. These results indicate that endomorphin-1 and -2 act as endogenous ligands of mu-opioid receptor in neurons of the spinal dorsal horn and suppress the processing of nociceptive information in the central nervous system.

Differential effects of NMDA and AMPA/KA receptor antagonists on c-Fos or Zif/268 expression in the rat spinal dorsal horn induced by noxious thermal or mechanical stimulation, or formalin injection

The involvement of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate (KA) receptors in the induction of c-Fos and Zif/268 expression in spinal dorsal horn neurons following noxious thermal or mechanical stimulation, or formalin injection into the rat hind paw was examined by intrathecal administration of a competitive NMDA receptor antagonist, 2-amino-5-phosphonopentanoic acid (APV) or an AMPA/KA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), or both, 30 min prior to noxious stimulation. APV caused a significant reduction in the level of c-Fos expression in the superficial layer induced by each of these three noxious stimuli. The effects of APV on Zif/268 expression or of CNQX on c-Fos or Zif/268 expression in the superficial layer induced by these three noxious stimuli were dependent on the type of stimulus applied to the rat hind paw. The noxious thermal stimulus-evoked c-Fos expression level was reduced by APV and/or CNQX, while Zif/268 expression was hardly changed. Both c-Fos and Zif/268 expressions following formalin injection were reduced by APV alone and APV+CNQX, but not by CNQX alone. Zif/268 expression following noxious mechanical stimulation was significantly reduced only by APV+CNQX although APV or CNQX alone did not affect the expression, while c-Fos expression was reduced by APV and APV+CNQX but not by CNQX alone. These findings suggest that NMDA and AMPA/KA receptors are differentially involved in c-Fos and Zif/268 expression in the spinal dorsal horn following noxious thermal, formalin and mechanical stimulation.

Upregulation of the HLH Id gene family in neural progenitors and glial cells of the rat spinal cord following contusion injury

Spinal cord injury (SCI) leads to a complex sequence of cellular responses, including astrocyte activation, oligodendrocyte death, and ependymal cell proliferation. Inhibitors of DNA binding (Id1, Id2, Id3) belong to a helix-loop-helix (HLH) gene family. Id genes have been implicated in playing a vital role in the proliferation of many cell types, including astrocytes and myoblasts. In the present study, the expression of Id family members in spinal cord after contusion injury was investigated by in situ hybridization. Id1, Id2, and Id3 mRNA expression was upregulated 5 mm rostral and caudal to the lesion center, and reached maximal levels 3 days after SCI. In addition, cell populations expressing Id1, Id2, and Id3 mRNA were maximally increased 3 days after SCI. The increase in Id2 and Id3 mRNA expression and Id2 and Id3 mRNA+ cells was still observed at 8 days. The Id mRNA expressing cells were phenotyped by combining immunostaining of cell-specific markers with in situ hybridization. Glial fibrillary acidic protein (GFAP)+ astrocytes were found to express all three Id mRNA, whereas S-100alpha+ astrocytes only expressed high levels of Id2 and Id3 mRNA. Cells having a neural progenitor morphology and the marker nestin appeared after SCI and they expressed Id1, Id2, and Id3 mRNA. Interestingly, some Rip+ oligodendrocytes located in the areas close to the central canal expressed Id3 mRNA after injury. In conclusion, Id genes are upregulated in a time-dependent manner in astrocytes, oligodendrocytes, and neural progenitor subpopulations after SCI, suggesting that they play major roles in cellular responses following SCI.

Induction of glycerol phosphate dehydrogenase gene expression during seizure and analgesia

Using mRNA differential display, we found that the gene for NAD(+)-dependent glycerol phosphate dehydrogenase (GPDH; EC 1.1.1.8) is induced in rat brain following seizure activity. Northern blot and in situ hybridization analysis confirmed the differential display results; they also showed, in a separate model of neuronal activation, that after thermal noxious stimulation of the hind-paws, a similar increase in GPDH mRNA occurs in the areas of somatotopic projection in the lumbar spinal cord. Surprisingly, administration of analgesic doses of morphine or the nonsteroidal antiinflammatory drugs aspirin, metamizol (dipyrone), and indomethacin also increased GPDH mRNA levels in rat spinal cord. The opioid receptor antagonist naloxone completely blocked morphine induction of GPDH but had no effect on GPDH induction by noxious heat stimulation or metamizol treatment, implicating different mechanisms of GPDH induction. Nevertheless, in all cases, induction of the GPDH gene requires adrenal steroids and new protein synthesis, as the induction was blocked in adrenalectomized rats and by cycloheximide treatment, respectively. Our results suggest that the induction of the GPDH gene upon peripheral noxious stimulation is related to the endogenous response to pain as it is mimicked by exogenously applied analgesic drugs.

Changes in pain threshold and lumbar spinal cord immediate-early gene expression induced by paced and nonpaced mating in female rats

Vaginocervical stimulation (VCS) received during mating is known to induce analgesia and to suppress FOS-immunoreactivity (FOS-IR) in lumbar spinal cord. However, it is not known whether this suppression of FOS-IR reflects inhibition of afferent nociceptive input. The present studies examined whether two immediate-early gene (IEG) products, FOS and Egr-1, covary with nociception by comparing both responses in estrous females that received mating stimulation known to induce varying amounts of FOS-IR in brain. Ovariectomized steroid-treated rats were mated under conditions in which they paced or did not pace sexual contacts with males until receiving 5 or 15 intromissions. Control groups received mounts-without-intromission only from males or remained in their homecages. In experiment I, paced mating resulted in a significant overall suppression of FOS-IR in the lumbar 6 (L6) spinal segment compared to nonpaced and mounts only stimulation. This reduction occurred specifically among paced females receiving five intromissions. In contrast, significant elevations above homecage levels were seen in paced females given 15 intromissions, all nonpaced females, and mounts only animals. The numbers of Egr-1-immunoreactive (Egr-1-IR) cells increased equally above homecage levels in all male-exposed females. In experiment II, females that received five intromissions (paced or nonpaced) showed significant increases in tail-flick latency (TFL) within 5 s (time 0) after mating, while females receiving 15 intromissions showed hyperalgesia (15 nonpaced) or no change (15 paced) in TFL throughout 90 s postmating. Additional females tested immediately after receiving two ejaculations showed analgesia. Paced mating, though more effective than nonpaced mating in suppressing FOS-IR, did not influence the appearance of VCS-induced analgesia. We conclude that the suppression of FOS-IR by paced mating is not related to mating-induced analgesia.

Metabolic activity changes in the rat spinal cord during adjuvant monoarthritis

The development of chronic pain is associated with activity-dependent plastic changes in neuronal structures in the peripheral and central nervous system. In order to investigate the time-dependent processing of afferent noxious stimuli in the spinal cord we employed the quantitative autoradiographic 2-deoxyglucose technique in a model of chronic monoarthritic pain in the rat. Spinal metabolic activity was determined at various time-points (two, four and 14 days) after the injection of complete Freund's adjuvant into the left tibiotarsal joint. In addition, the effect of acute noxious mechanical stimulation of the arthritic joint was investigated at 14 days of monoarthritis. Local glucose utilization was determined in lumbar segments L2-L5, ipsi- and contralateral to the inflamed hindpaw, and compared with saline-injected controls. In general, monoarthritic animals had bilaterally increased metabolic activity in all laminae of the spinal cord. Detailing the time-course showed that in rats with two days of monoarthritis metabolic activity was significantly increased to a similar extent on both sides of all spinal laminae. In contrast, at four days, glucose utilization in deep laminae of the dorsal horn (laminae V-VI), the central gray area (laminae X) and the ventral horn (laminae VII-IX) tended to return to control levels. At 14 days of monoarthritis, however, metabolic activity showed a further increase in all laminae of the spinal cord. This increase was more pronounced on the side ipsilateral to inflammation, reaching 65% above corresponding control levels in laminae V, VI. Animals with 14 days of monoarthritis which were subjected to mechanical noxious stimulation of the arthritic joint displayed clear behavioral signs of acute pain. Although in this group metabolic activity was above control levels, it was lower than in animals with 14 days of monoarthritis that were not additionally stimulated. The data show not only a general increase of spinal cord metabolic activity during the time-course of the development of a chronic pain state, but also show a region-specific non-linear time profile. This may reflect the complexity of transducing and suppressive transmitter systems involved in the central processing of ongoing pain.

The effect of fentanyl on c-fos expression in the trigeminal brainstem complex produced by pulpal heat stimulation in the ferret

We have previously shown that Fos-like immunoreactivity (Fos-LI) is evoked in the brainstem of ferrets following stimulation of pulpal A delta and C fibers originating from the maxillary canine. This study evaluated the effects of the mu-opioid receptor agonist fentanyl on Fos expression evoked by noxious thermal stimulation of the right maxillary and mandibular canines in pentobarbital/chloral hydrate anesthetized adult male ferrets. Pulpal heating evoked Fos expression in two distinct regions of the spinal trigeminal nuclear complex: the transitional region between subnucleus interpolaris and caudalis (Vi/Vc) and within the subnucleus caudalis (Vc). More Fos positive cells were expressed in both regions ipsilateral to the site of stimulation compared with the contralateral side (P < 0.05, ANOVA). Pretreatment with fentanyl significantly and dose-dependently suppressed the number of Fos positive cells in both the Vi/Vc transitional region and Vc (P < 0.05, ANOVA). The suppressive effect of fentanyl on Fos expression was blocked by the intravenous administration of naloxone, an opioid antagonist, indicating a specific opioid receptor effect. In addition, opioid receptor antagonism with naloxone alone enhanced Fos expression in Vi/Vc and Vc in response to heat stimulation. The administration of naloxone without heat stimulation failed to evoke Fos expression in Vi/ Vc and Vc. These findings suggest that the activation of trigeminal Vi/Vc and Vc neurons by noxious dental heat stimulation is controlled by a naloxone sensitive endogenous opioid system as indicated by Fos expression. Collectively, these results suggest that neuronal populations in Vi/Vc and Vc regions may contribute to pain responses to noxious dental stimulation and these responses can be modulated by both endogenous and exogenous opioids.

Thymulin induces c-fos expression in the spinal cord of rats which is reversed by meloxicam and morphine

Intraplantar (i.pl.) injections of thymulin have been shown to produce hyperalgesia in rats through a prostaglandin E2-dependent mechanism. This study aimed at investigating if such injections can produce sustained activation of spinal neurons by mapping the fos-like-immunoreactivity (FLI) as a marker for this activation. Our results showed that thymulin produces significant and sustained FLI in neurons located in spinal laminae known to be involved in nociception. Pretreatment with either morphine or meloxicam (a cyclooxygenase inhibitor) revealed differential effects on FLI and the hyperalgesia induced by thymulin. These findings support the hypothesis that thymulin can affect central neurons either directly or through the peripheral nerve terminals.

Spinal section and opioid receptor blockade induce the appearance of Fos-like immunoreactivity in the spinal cord of the decerebrated rabbit

The expression of Fos-like immunoreactivity has been studied in spinal segments L5-S1 of decerebrated, unanaesthetized, but otherwise unstimulated rabbits. The aim of the study was to establish baseline levels of Fos in such preparations, and to examine how these might change after spinalization and opioid receptor blockade. In animals with an intact spinal cord, approximately 30 Fos-positive profiles per section were found in the superficial dorsal horns (i.e. laminae I and II) of each 40-microm section, while about 20 profiles per section were found immediately adjacent to the central canal (lamina X). Fos-like immunoreactive profiles were rare elsewhere in the gray matter. When the spinal cord was sectioned at L1 (after blockade with local anaesthetic), significantly more Fos-like immunoreactivity was found in superficial and central regions of the gray matter (approximately 90 profiles per section) in animals perfused 4 h after decerebration, but not when perfusion was performed 2 or 8 h after decerebration. The opioid antagonist naloxone (0.25 mg/kg/h) had little effect on expression of Fos-like immunoreactivity in spinalized preparations, but significantly increased the numbers of Fos-positive profiles in all but the ventral areas of the spinal gray matter in non-spinalized preparations. The present data show that spinal section induces a transient increase in expression of Fos in the superficial and central parts of the spinal gray matter. It appears that spinalization induces spontaneous activity in some neurons in these regions of the cord, presumably as a result of relief of descending inhibition. The effects of naloxone indicate that endogenous opioids exert tonic inhibition over Fos-expressing spinal neurons in non-spinalized rabbits.

Comparison of the expression of two immediate early gene proteins, FosB and Fos in the rat preoptic area, hypothalamus and brainstem during pregnancy, parturition and lactation

Medial preoptic area (MPA), supraoptic nucleus (SON), magnocellular (MaPVN) and parvocellular (PaPVN) paraventricular hypothalamic nuclei, and mesencephalic lateral tegmentum (MLT) are involved in maternal behavior, parturition and lactation. This study investigated the FosB and Fos immunoreactivity in these regions of virgin, pregnant, parturient, lactating, and lactating-arrested rats. The patterns of FosB and Fos expression were compared between the sections taken from the same animals. Quantitative immunohistochemistry revealed a significant increase in the numbers of FosB-positive neurons in the MPA, SON, MaPVN, and MLT of parturient and lactating females as compared with pregnant or virgin animals. In lactating rats, the numbers of FosB-positive neurons in the MPA, PaPVN, and MLT were increased, but the numbers in the SON and MaPVN were decreased as compared with parturient females. Many Fos-positive neurons were also seen in parturient and lactating rats, and the patterns of Fos expression in each region were quite similar to those of FosB. Moreover, double-labeling immunohistochemistry revealed that: (1) many FosB-positive nuclei were observed in oxytocin and vasopressin neurons of the SON and PVN in parturient rats; (2) within FosB-positive neurons, 89.5% in the MPA, 86.8% in the MLT of parturient rats, and 92% in the MPA and 90.8% in the MLT of lactating animals were also Fos-positive. Only a small number of FosB and Fos-positive neurons were seen in females that were killed in the early stage of parturition. Removal of the litters immediately after parturition completely eliminated FosB and Fos expression in each region in the dams. Taken together, the present results suggest that FosB expression is co-involved with Fos in the neural activation during parturition and lactation in rats.

Development of tolerance to the antinociceptive effect of systemic morphine at the lumbar spinal cord level: a c-Fos study in the rat

The development of tolerance to the antinociceptive effects of morphine was investigated in rats using carrageenin-induced spinal c-Fos expression. We took advantage of this technique to especially study, at the cellular level, in freely moving animals, the development of tolerance based on the visualization of dorsal horn spinal cord neurons which play a major role in nociceptive processes. Two hours after intraplantar injection of carrageenin (6 mg/150 microliter of saline), c-Fos-like immunoreactivity (FLI) was observed predominantly in the superficial and deep laminae of the dorsal horn in segments L4 and L5 of the spinal cord. In naive rats, acute intravenous morphine (3 mg/kg, i.v.) reduced the number of superficial and deep FLI neurons; 49% and 59% reduction respectively (p<0.0001 for both). In morphine-pretreated rats (daily administration of subcutaneous morphine: 1, 3, 5, 10, 20 or 40 mg/kg once a day for 4 days), antinociceptive tolerance tested on day 5 by acute morphine (3 mg/kg, i.v.) was manifest in those groups pretreated with the highest doses of morphine (10, 20 or 40 mg/kg). From regression analysis, it appeared that tolerance to the antinociceptive effect of morphine developed progressively as a function of the chronic morphine dose used on neurons involved in spinal nociceptive processes (superficial and deep dorsal horn neurons). Similarly, in rats pretreated with 10 mg/kg of morphine over 1, 2, 3 or 4 days, tolerance progressively developed, for both spinal neuronal populations, as a function of the duration of the pretreatment. These results are discussed in the context of the several possible sites of action of morphine.

Effects of halothane, ketamine and nitrous oxide on dynorphin mRNA expression in dorsal horn neurons after peripheral tissue injury

Peripheral tissue injury is known to induce changes in gene expression in spinal neurons and result in a prolonged alteration of neuronal excitability. The purpose of this study was to examine the effect of halothane on the dynorphin mRNA expression in spinal dorsal horn neurons after peripheral tissue injury by formalin injection and compare the effect to that of ketamine and nitrous oxide. Male Sprague-Dawley rats were anesthetized with 1.3% halothane, ketamine, or 67% nitrous oxide. Fifteen minutes after induction of anesthesia, rats received an intraplantar injection of 150 microliter 5% formalin into the unilateral hindpaw. General anesthesia was maintained for 8 h, and the expression of preprodynorphin (PPD) and preproenkephalin (PPE) mRNAs in the spinal cord (L4-5) was examined by in situ hybridization. The degree of edema of the inflamed foot was not different among the three anesthesia groups and the control (no anesthesia) group. The number of neurons expressing PPD mRNA dramatically increased in the superficial dorsal horn ipsilateral to the formalin injection in the control group compared to the contralateral side. The number of neurons labeled for PPD mRNA in the halothane group was significantly less than the control group. However, the number of PPD mRNA-expressing neurons in both the ketamine and nitrous oxide groups was significantly less than the halothane group. The expression of PPE mRNA was not influenced by these anesthetics. These data indicate that the suppressive effect of halothane anesthesia on the induction of PPD mRNA in dorsal horn neurons was smaller than those of ketamine and nitrous oxide, suggesting an important supplemental way to control the alteration of gene expression in spinal neurons for clinical settings.

Metamizol potentiates morphine effects on visceral pain and evoked c-Fos immunoreactivity in spinal cord

In a model of visceral pain consisting of intraperitoneal injection of acetic acid (writhing test), simultaneous administration of subanalgesic doses of metamizol (150 mg/kg) and morphine (0.2 mg/kg) resulted in a potent analgesia (19 +/- 1 vs. 2.3 +/- 0.8 writhes; P < 0.05). While the analgesic effect of morphine (2 mg/kg) was antagonized by naloxone (1 mg/kg), the opioid antagonist did not reverse the analgesia induced by the combination of metamizol and morphine. Potentiation by metamizol was also observed as a bilateral decrease in stimulus-evoked c-Fos induction in superficial laminas (I-II) of the dorsal spinal cord after drug combination compared to single administration (66.5 +/- 2.2 vs. 80.7 +/- 4.2; P < 0.05). Conversely, the number of nuclei immunostained with an antibody that recognizes all proteins of the Fos family was not modified by the same dose combination compared to single treatment (21.1 +/- 1.3 vs. 20.2 +/- 1.2). Furthermore, in a model of somatic pain consisting of peripheral thermal stimulation of the paws, simultaneous administration of metamizol (100-250 mg/kg) and morphine (0.5 mg/kg) failed to modify flexor reflex latency.

c-fos expression in isolated rat spinal cord

Expression of c-fos-immunoreactivity (c-fos-ir) has been demonstrated in the dorsal horn of lumbar segments of an isolated spinal cord preparation from 3 week old rats. The method of preparation generated a low level of c-fos-ir activity which was not significantly altered by low intensity (1.5 times threshold) dorsal root stimulation, but was significantly increased by high intensity (20 times threshold) stimulation. Replacement of the calcium in the bathing medium by 2 mM manganese suppressed all detectable c-fos-ir, whereas inclusion of 0.5 microM capsaicin caused intense c-fos-ir expression in the absence of stimulation. The number of dorsal horn cells exhibiting c-fos-ir increased between 0.5 and 1 h after stimulation, reaching a maximum at 2 h, with no further increase at longer intervals. Few positive cells were found when the incubation temperature was reduced from 27 to 20 degrees C. The strongest increase in c-fos-ir was found in the dorsal horn ipsilateral to the stimulated dorsal root and a smaller, but significant, increase was also seen in the contralateral dorsal horn. Cords obtained from animals treated at 1 day old with capsaicin to destroy afferent C fibres showed a reduction in the number of c-fos-ir positive cells induced by high intensity dorsal root stimulation. This preparation will aid detailed investigation of the pharmacology of nociceptive pathways.

Enhanced expression of metabotropic glutamate receptor 3 messenger RNA in the rat spinal cord during ultraviolet irradiation induced peripheral inflammation

Metabotropic glutamate receptors are thought to play a role in the development and maintenance of spinal hyperexcitability resulting in hyperalgesia and pain. In this study we have used in situ hybridization to investigate the distribution of metabotropic glutamate receptors mGluR1-7 messenger RNA in the rat spinal cord in a model of inflammatory hyperalgesia. Hyperalgesia was induced in nine-day-old rats by exposure of the left hindpaw to an ultraviolet light source. Lumbar portions of spinal cords were removed from control and ultraviolet-treated animals. In situ hybridization with specific oligonucleotide probes was used to localize metabotropic glutamate receptor messenger RNAs. mGluR1, 3-5 and 7 subtype messenger RNA was detected in the gray matter of the spinal cord with distribution being specific for the different subtypes. A significant increase in the expression of mGluR3 messenger RNA was seen in cells of the dorsal laminae in both sides of the lumbar spinal cord. This increase was most pronounced in laminae II, III and IV but gradually decreased and disappeared by the third day of inflammation. In parallel with this, behavioural experiments revealed mechanical hyperalgesia in both hindlimbs after ultraviolet irradiation. There was no change in mGluR3 messenger RNA expression in the thoracic segments. No changes have been detected in the levels of expression of mGluR 1,2,4,5,7 subtype messenger RNA in spinal cords taken from hyperalgesic animals. These observations show that during ultraviolet irradiation induced inflammation, the synthesis of mGluR3 messenger RNA is altered suggesting that regulation of metabotropic glutamate receptor expression may be instrumental in plastic changes within the spinal cord during the development of hyperalgesia and pain.

Egr transcription factors in the nervous system

The Egr proteins, Egr-1, Egr-2, Egr-3 and Egr-4, are closely related members of a subclass of immediate early gene-encoded, inducible transcription factors. They share a highly homologous DNA-binding domain which recognises an identical DNA response element. In addition, they have several less-well conserved structural features in common. As immediate early proteins, the Egr transcription factors are rapidly induced by diverse extracellular stimuli within the nervous system in a discretely controlled manner. The basal expression of the Egr proteins in the developing and adult rat brain and the induction of Egr proteins by neurotransmitter analogue stimulation, physiological mimetic and brain injury paradigms is reviewed. We review evidence indicating that Egr proteins are subject to tight differential control through diverse mechanisms at several levels of regulation. These include transcriptional, translational and post-translational (including glycosylation, phosphorylation and redox) mechanisms and protein-protein interaction. Ultimately the differentially co-ordinated Egr response may lead to discrete effects on target gene expression. Some of the known target genes of Egr proteins and functions of the Egr proteins in different cell types are also highlighted. Future directions for research into the control and function of the different Egr proteins are also explored.

Fos-like immunoreactivity induced by intraplantar injection of endotoxin and its reduction by morphine

C-Fos-like immunoreactivity (FLI) in the central nervous system, has been associated with the processing of nociceptive information in acute and chronic pain animal models. The aim of this study was to investigate whether intraplantar (i.pl.) injections of endotoxin (ET, 1.25 microg) can induce FLI in the lumbar spinal cord of rats and to assess the effects of morphine injection on c-fos expression. FLI was studied in various groups of rats at 2, 3, 4, 6, 9 and 24 h following ET injections. Labeled neurons were mainly detected in the lumbar segments ipsilateral to the ET-injected leg, with a major peak (71.01 +/- 4.79 positive neurons) at 4 h and a second peak (29.87 +/- 5.97 positive neurons) at 9 h followed by a recovery to the baseline at 24 h after ET injections. Within the laminae, the majority of positive neurons was observed at 2-3 h in laminae I and II and in deep laminae (V and VI mainly) starting at 4 h after ET injections. Rostrocaudally, labeled neurons were observed initially in L4-L5 segments (2-3 h post-ET) after which they extended to L2-L6 segments at 4 h after ET. Morphine injections either i.p. (1 or 2 mg/kg) or i.pl. (50 microg) significantly reduced ET-induced hyperalgesia and simultaneously the FLI. The maximum effect was observed on labeled neurons in the deep laminae (V and VI mainly). We conclude that local injections of ET can induce FLI in the lumbar spinal cord with a temporal and spatial patterns comparable to the described hyperalgesia, and that both FLI and hyperalgesia are reduced by morphine in a dose-dependent manner with a maximal effect shown by the local i.pl. morphine injections.

Induction of NGFI-A gene expression in the rat suprachiasmatic nucleus by photic stimulation

Photic induction of NGFI-A gene expression was investigated in the rat suprachiasmatic nucleus (SCN) using in situ hybridization histochemistry. Following light exposure for 30 min, NGFI-A mRNA appeared in the ventral portion of the rostral SCN, in the ventrolateral and in part of the dorsomedial portion at the middle level, and in the lateral portion of the caudal SCN. The distribution of NGFI-A mRNA was wider than that of c-fos mRNA which was confined to the ventrolateral portion at the middle level of the SCN. By double labeling in situ hybridization, approximately half of NGFI-A mRNA-positive cells in the SCN were shown to coexpress vasoactive intestinal peptide (VIP) mRNA, while 16% of cells positive for c-fos mRNA coexpressed VIP mRNA. These findings indicate that the broadness of NGFI-A mRNA and c-fos mRNA expression after photic stimulation are different. NGFI-A gene induced in these cells of the SCN including VIP neurons may be involved in circadian entrainment by light.

Activation by cutaneous or visceral noxious stimulation of spinal neurons projecting to the medullary dorsal reticular nucleus in the rat: a c-fos study

The involvement of spinal neurons in the transmission of cutaneous and visceral nociceptive input to the medullary dorsal reticular nucleus was studied. Rats were injected with cholera toxin subunit B in the left dorsal reticular nucleus and subjected 4 days later to noxious mechanical, thermal or chemical stimulation of the proximal internal aspect of the left thigh, or to chemical stimulation of the urinary bladder. Sections of spinal segments T13-L3 were processed immunocytochemically for cholera toxin subunit B and Fos protein. The percentage of double-labelled cells in the population of Fos-positive cells was higher in lamina I (1-4%) than in deeper laminae (0-0.7%) following all stimuli. The percentage of double-labelled cells in the population of retrogradely labelled cells was 30-53% in lamina I and 0-5% in laminae III-X. Visceral stimulation activated more retrogradely labelled lamina I cells than any kind of cutaneous stimulation. Pyramidal cells were activated in higher numbers than multipolar and flattened cells after thermal cutaneous or visceral stimulation, and in lower numbers than multipolar cells after mechanical stimulation. These results suggest that, in the experimental conditions used, spinal cord cells conveying noxious input to the dorsal reticular nucleus are concentrated in lamina I. They further indicate that the spinal-dorsal reticular nucleus pathway plays a major role in the transmission of nociceptive visceral input, and point to the preferential involvement of pyramidal cells in cutaneous thermal and visceral processing.

Inhalation anesthetics suppress the expression of c-Fos protein evoked by noxious somatic stimulation in the deeper layer of the spinal cord in the rat

The effects of inhalation anesthetics, nitrous oxide (N2O) and halothane, on the expression of c-Fos protein evoked by formalin injection were studied in the spinal cord in the rat. The expression of c-Fos protein was detected by immunocytochemistry following the injection of formalin (5%, 100 microliters) into the plantar surface of the left hindpaw. After 15 min of halothane (F) anesthesia, the anesthetics was switched to 40% or 70% of N2O, 0.5% or 1.5% of F or room air (for control) immediately following the formalin injection. Two hours later the rats were sacrificed and perfused. Sections of the L4 level of spinal cord were immunostained with anti c-Fos antibody. We counted the number of Fos-like immunoreactive (FLI) cells in every specific lamina as follows: superficial layer (laminae I and II), nucleus proprius (laminae III and IV), neck of the dorsal horn (laminae V and VI) and ventral gray (laminae VII-X). Then we compared the results of each category of sample. Both N2O and halothane suppressed the expression of c-Fos in the neck of the dorsal horn and ventral gray in a dose-dependent manner, but no effects were seen at the superficial layer or nucleus proprius. Suppression of c-Fos expression was greater under N2O than halothane anesthesia. This finding suggests that N2O had a stronger analgesic effect than halothane. The current study indicates that inhalation anesthetics do not act equally on every kind of spinal neurons. Both N2O and halothane have effects on spinal neurons in the deeper layers but not on the neurons existed in laminae I-II, some of which directly receive noxious inputs. Pretreatment with 2 mg/kg of naloxone, which completely reversed the effects of morphine, did not alter the effect of 70%N2O, suggesting that the analgesic effect of N2O is not mediated by an intrinsic opioid mechanism at the spinal cord level.

Differential c-fos expression in the nucleus of the solitary tract and spinal cord following noxious gastric distention in the rat

c-Fos has been used as a marker for activity in the spinal cord following noxious somatic or visceral stimulation. Although the viscera receive dual afferent innervation, distention of hollow organs (i.e. esophagus, stomach, descending colon and rectum) induces significantly more c-Fos in second order neurons in the nucleus of the solitary tract and lumbosacral spinal cord, which receive parasympathetic afferent input (vagus, pelvic nerves), than the thoracolumbar spinal cord, which receives sympathetic afferent input (splanchnic nerves). The purpose of this study was to determine the contribution of sympathetic and parasympathetic afferent input to c-Fos expression in the nucleus of the solitary tract and spinal cord, and the influence of supraspinal pathways on Fos induction in the thoracolumbar spinal cord. Noxious gastric distention to 80 mmHg (gastric distension/80) was produced by repetitive inflation of a chronically implanted gastric balloon. Gastric distension/80 induced c-Fos throughout the nucleus of the solitary tract, with the densest labeling observed within 300 microns of the rostral pole of the area postrema. This area was analysed quantitatively following several manipulations. Gastric distension/80 induced a mean of 724 c-Fos-immunoreactive nuclei per section. Following subdiaphragmatic vagotomy plus distention (vagotomy/80), the induction of c-Fos-immunoreactive nuclei was reduced to 293 per section, while spinal transection at T2 plus distention (spinal transection/80) induced a mean of 581 nuclei per nucleus of the solitary tract section. Gastric distension/80 and vagotomy/80 induced minimal c-Fos in the T8-T10 spinal cord (50 nuclei/section), but spinal transection/80 induced 200 nuclei per section. Repetitive bolus injections of norepinephrine produced transient pressor responses mimicking the pressor response produced by gastric distension/80. This manipulation induced minimal c-Fos in the nucleus of the solitary tract and none in the spinal cord. It is concluded that noxious visceral input via parasympathetic vagal afferents, and to a lesser extent sympathetic afferents and the spinosolitary tract, contribute to gastric distention-induced c-Fos in the nucleus of the solitary tract. The induction of c-Fos in the nucleus of the solitary tract is significantly greater than in the viscerotopic segments of the spinal cord, which is partially under tonic descending inhibition, but is not subject to modulation by vagal gastric afferents. Distention pressures produced by noxious gastric distention are much greater than those produced during feeding, suggesting that c-Fos induction in the nucleus of the solitary tract to noxious distention is not associated with physiological mechanisms of feeding and satiety. The large vagal nerve-mediated induction of c-Fos in the nucleus of the solitary tract following gastric distension suggests that parasympathetic afferents contribute to the processing of noxious visceral stimuli, perhaps by contributing to the affective-emotional component of visceral pain.

Sensitization of the tail-flick reflex following exposure to either a single prolonged test trial or behavioral testing under the analgesic influence of morphine

Although the tail-flick response to radiant heat is widely used in nociceptive research, there are indications that this benchmark test possesses some undesirable characteristics. Of present concern is the possibility that the supra-threshold stimuli associated with behavioral testing while under the influence of an effective hypoalgesic manipulation can alter subsequent tail-flick responses. To examine the effects of supra-threshold heating of the tail, we exposed anesthetized rats to either (1) manual restraint of the tail during a single tail-flick trial to a 5- or 7-sec cut-off, or (2) testing while under the analgesic effects of morphine (5 mg/kg/ml). A single prolonged trial produced hyperalgesia which lasted for 30 min. Following naltrexone injection, hyperalgesia was also found in animals that had been tested while under morphine analgesia. In contrast, animals that received morphine but were not tested under its influence did not exhibit hyperalgesia of similar magnitude. Analyses of tail temperature data in the second experiment indicate that these results are not dependent on shifts in tail temperature. These results suggest that, in anesthetized animals, exposure to prolonged tail-flick trials can produce hyperalgesia.

Chronic morphine administration enhances the expression of Kv1.5 and Kv1.6 voltage-gated K+ channels in rat spinal cord

Prolonged opiate administration leads to the development of tolerance and dependence. These phenomena are accompanied by selective regulation of distant cellular proteins and mRNAs, including ionic channels. Acute opiate administration differentially affects voltage-dependent K+ currents. Whereas, opiate activation of K+ channels is well established opioid-induced inhibition of K+ conductance has also been studied. In this study, we focused on the effect of chronic morphine exposure on voltage-dependent Shaker-related Kv1.5 and Kv1.6 K+ channel gene expression and on Kv1.5 protein levels in the rat spinal cord. Several experimental approaches including in-situ hybridization, RNAse protection, reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry were employed. We found that motor neurons are highly enriched in Kv1.5 and Kv1.6 mRNA and in Kv1.5 channel protein. Moreover, we found significant increases in the amount of mRNA encoding for these two K+ channels and in Kv1.5 channel protein in the spinal cord of morphine-treated rats, compared with controls. For example, quantitative in-situ hybridization, revealed a 2.1 +/- 0.15- and 2.3 +/- 0.5-fold increase in Kv1.5 and Kv1.6 channel mRNA levels, respectively. Similar results were obtained by semiquantitative RT-PCR analyses. Kv1.5 protein level was increased by 1.9-fold in the spinal cord or morphine-treated rats. Our results suggest that Kv1.5 and Kv1.6 Shaker K+ channels play an important role in regulating motor activity that increases in mRNA and protein levels of the spinal cord K+ channels after chronic morphine exposure could be viewed as a cellular adaptation which compensates for a persistent opioid-induced inhibition of K+ channel activity. These alterations may account, in part, for the cellular events leading to opiate tolerance and dependence.

Induction of c-fos expression in cervical spinal interneurons after kainate stimulation of the motor cortex in the rat

The expression of the immediate-early gene c-fos was used as a marker of neuronal activity to investigate the cervical spinal interneuron populations involved in the corticomotoneuronal pathway. Adult rats received unilateral kainate injections in the forelimb area of the primary motor cortex. After a survival period of 90 min, during which the animals showed vehement twitching of the contralateral forelimb, the rats were perfused and their brains and cervical spinal cords processed for Fos-like immunoreactivity. In the cervical spinal cord Fos-like immunoreactive neurons were found bilaterally in the dorsal horn and in the intermediate zone, though contralaterally significantly more labelled nuclei were encountered in two different areas. One area closely resembles the corticospinal terminal field as demonstrated with anterograde horseradish-peroxidase tract-tracing and the other reflecting primary afferent and noxious sensory neurons in the dorsal horn. Thus by monitoring the evoked expression of the immediate-early gene c-fos, structural components of the rat motor system can be identified.

Intraplantar morphine depresses spinal c-Fos expression induced by carrageenin inflammation but not by noxious heat

1. We have studied the effects of intraplantar administration of the same doses of morphine on intraplantar carrageenin (6 mg 150 microliters-1 of saline) and noxious heat (52 degrees C for 15 s) induced spinal c-Fos expression and inflammation. 2. Intraplantar carrageenin, in awake rats, induced numerous Fos-like immunoreactive (Fos-LI) neurones in the dorsal horn of L4-L5 lumbar segments of the spinal cord and extensive peripheral oedema. At 1 h 30 min, Fos-LI neurones were preferentially located in the superficial laminae (74 +/- 2%) whereas at 3 h, Fos-LI neurones were observed both in the superficial (45 +/- 2%) and deep (37 +/- 1%) laminae of the spinal dorsal horn. 3. Intraplantar morphine dose-dependently reduced c-Fos expression induced 1 h 30 min after carrageenin (r = 0.605, P < 0.02), these effects were completely blocked by intraplantar methiodide naloxone (20 micrograms) (121 +/- 22% of control carrageenin expression). The systemic injection of the highest dose of intraplantar morphine (50 micrograms) had no significant effect on the number of Fos-LI neurones (88 +/- 9% of control carrageenin expression). None of the drugs influenced unilateral peripheral oedema observed 1 h 30 min after carrageenin. 4. In the second series of experiments, intraplantar morphine dose-dependently reduced the number of superficial and deep Fos-LI neurones induced 3 h after carrageenin (r = 0.794, P < 0.0004 and r = 0.698, P < 0.004, respectively). Furthermore, the effects of the highest dose of intraplantar morphine were completely blocked by co-administration of intraplantar methiodide naloxone (20 micrograms). 5. In addition, intraplantar morphine dose-dependently reduced the ankle (r = 0.747, P < 0.002) and paw (r = 0.682, P < 0.005) oedema observed 3 h after carrageenin, with the effect of the highest dose of intraplantar morphine being completely blocked by co-administration of methiodide naloxone (98 +/- 4% and 102 +/- 8% of control paw and ankle oedema, respectively). 6. Brief noxious heat stimulation, in urethane anaesthetized rats, induced, 2 h after the stimulation, numerous Fos-LI neurones in the dorsal horn of L3-L4 lumbar segments of the spinal cord but no detectable peripheral oedema. Fos-LI neurones were preferentially located in superficial laminae (94 +/- 2%) of the spinal dorsal horn. None of the drugs influenced the noxious heat induced c-Fos expression. 7. Such results illustrate that peripheral effects of morphine preferentially occur during inflammatory states and outline the interest of extending clinical investigations of the possible use of local injection of morphine in various inflammatory pain states.

Differential distribution of Fos-like immunoreactivity in the spinal trigeminal nucleus after noxious and innocuous thermal and chemical stimulation of rat cornea

Corneal afferent nerves project to two spatially distinct sites within the spinal trigeminal nucleus: the subnucleus interpolaris/caudalis transition and the subnucleus caudalis/upper cervical spinal cord transition. The role of these two regions in processing corneal input is uncertain. To determine if neurons in these regions encode different features of an applied corneal stimulus, immunoreactivity for the immediate early gene protein product, Fos, was quantified in barbiturate-anesthetized rats. Intensity was varied across thermal (thermal probe 5, 35, 42, 52 degrees C; radiant heat of approximately 45 degrees C) stimuli and compared with that seen after mustard oil (5 microliters, 20%) or mineral oil application. All stimuli increased the number of Fos-positive neurons located at the ventrolateral pole of the subnucleus interpolaris/caudalis transition compared with unstimulated controls. By contrast, only 52 degrees C thermal probe and mustard oil produced an additional peak of Fos-positive neurons within the superficial laminae at the subnucleus caudalis/cervical cord transition. Further, the magnitudes of the bimodal peaks of Fos produced by 52 degrees C thermal probe and mustard oil stimuli were different quantitatively. Mustard oil caused a greater Fos response at the subnucleus interpolaris/caudalis transition than 52 degrees C thermal probe stimulation, whereas the opposite was true at the subnucleus caudalis/cervical cord transition. Double-labeling revealed that Fos immunoreactive neurons within the spinal trigeminal nucleus were restricted to regions densely labeled for calcitonin gene-related peptide. These results indicate that select features of corneal stimuli such as modality are encoded differently by neurons in the trigeminal subnucleus interpolaris/caudalis transition compared with those located in the subnucleus caudalis/cervical cord transition. It is likely that neurons in these two brainstem regions subserve different aspects of corneal sensation.

Enhanced effects of co-administered dexamethasone and diclofenac on inflammatory pain processing and associated spinal c-Fos expression in the rat

This study determines the effects of dexamethasone versus co-administered dexamethasone and diclofenac, on carrageenan-evoked spinal c-Fos expression and peripheral oedema in the freely moving rat. Drugs were administered intravenously 25 min before intraplantar injection of carrageenan (6 mg/150 microliters of saline). Three hours later the number of spinal c-Fos-LI neurones and peripheral oedema were assessed. The total number of control carrageenan-evoked c-Fos-LI neurones in the lumbar spinal cord was 121 +/- 5 labelled neurones per section, segments L4-L5, which were predominantly located in the superficial and deep laminae (41 +/- 3% and 40 +/- 2% of the total number of c-Fos-LI neurones per section, respectively) of the dorsal horn of the spinal cord. Pre-administered dexamethasone (0.05, 0.10 and 0.50 mg/kg i.v.) dose-dependently reduced the total number of c-Fos-LI neurones (30 +/- 4%, 52 +/- 3% and 58 +/- 2% reduction, respectively), with effects of the higher doses being strongest on the deep laminae c-Fos-LI neurones. The effects of dexamethasone on the total number of c-Fos-LI neurones and the peripheral oedema were positively correlated. Co-administration of low doses of dexamethasone and diclofenac (0.025 + 1.5 mg/kg i.v. respectively), which had negligible effects when administered separately, greatly reduced both the total number of carrageenan-evoked c-Fos-LI neurones (61 +/- 5% reduction as compared to control value) and the peripheral oedema (80 +/- 8% and 60 +/- 5% reduction for ankle and paw oedema, respectively). The attenuation by co-administered dexamethasone and diclofenac, of both c-Fos expression and the peripheral oedema, was significantly greater than the effect of dexamethasone alone (P < 0.001 for both) and diclofenac alone (P < 0.001 for both). Our study illustrates enhanced attenuating effects of co-administered dexamethasone and diclofenac on both inflammatory oedema and the associated spinal expression of c-Fos, an indicator of nociceptive transmission at the spinal level. The apparent interactions between the mechanisms of action of NSAIDs and steroids suggest that co-therapy may produce beneficial inflammatory and pain relief in the absence of excessive side effects.

Lasting reduction of severe spasticity after ending chronic treatment with intrathecal baclofen

OBJECTIVE

To investigate whether the dose of intrathecal baclofen necessary for a sufficient reduction of muscle tone and spasms changes during treatment of severe spasticity.

METHODS

A group of 27 patients received intrathecal baclofen for 61 (SD 18) months.

RESULTS

Spasticity remained absent or strongly reduced after stopping the intrathecal baclofen infusion in seven patients. The dose of baclofen could be reduced to 40% of that dose which was originally necessary in 10 patients. The dose remained the same or increased slightly in 10 patients. Possible reasons for the continuing reduction of spasticity after terminating long term intrathecal baclofen infusion in some patients could be: lasting morphological changes in spinal cord neurons by second messenger controlled modulation of gene expression, a toxic effect of baclofen on spinal neurons, muscular atrophy, inflammation due to the catheter, or progression of multiple sclerosis.

CONCLUSIONS

A higher initial daily dose of intrathecal baclofen might lead to a faster, lasting suppression of spasticity and the development of spastic symptoms might even be prevented by pre-emptive treatment with baclofen in patients with newly acquired lesions of the spinal cord.

When is the maximal effect of pre-administered systemic morphine on carrageenin evoked spinal c-Fos expression in the rat?

This study evaluated, in awake rats, the time course of the expression of c-Fos in spinal cord neurons, in the L4-L5 segments, at various time points after intraplantar carrageenin (0.5 h, 1 h, 1.5 h, 2 h and 2.5 h). In addition, the effects of pre-administered morphine (3 mg/kg, i.v.) on the c-Fos expression, at the various time points, were studied. Very few Fos-like immunoreactive (Fos-LI) neurons were observed 0.5 h after carrageenin. However, spinal c-Fos expression increased initially (at 1 h), in the superficial laminae (I-II) of the spinal dorsal horn, and incrementally increased both in the superficial and deep (V-VI) laminae at later time points after carrageenin. Systemic morphine did not significantly decrease the number of superficial Fos-LI neurons observed 1 h after carrageenin, whereas it significantly reduced the number of superficial Fos-LI neurons induced at 1.5 h and 2 h after carrageenin (58 +/- 3% and 57 +/- 10% reduction, P < 0.001, respectively). In addition, morphine reduced the number of deep Fos-LI neurons at 1.5 h and 2 h after carrageenin (86 +/- 4%, P < 0.01 and 82 +/- 8%, P < 0.001 reduction as compared to control carrageenin expression, respectively). In contrast, morphine was less efficacious in decreasing the number of Fos-LI neurons observed in the superficial and deep laminae at 2.5 h after carrageenin (34 +/- 6% and 59 +/- 6% reduction, P < 0.001, respectively). Thus, the peak effect of pre-administered morphine on carrageenin evoked c-Fos expression was observed 1.5 h and 2 h after intraplantar carrageenin, with a weaker effect observed at 2.5 h after carrageenin. The pharmacokinetic complications between the time course of the antinociceptive effects of morphine and c-Fos expression is discussed. These results clearly demonstrate that studies of c-Fos expression with pharmacological investigations should take into consideration this finding since one delay after the stimulation does not give a full indication of the full potential of the drug tested.

Aspirin and acetaminophen reduced both Fos expression in rat lumbar spinal cord and inflammatory signs produced by carrageenin inflammation

This study, performed in freely moving rats, evaluates the effects of the two most prescribed analgesics, aspirin and acetaminophen, on carrageenin inflammation and the associated c-Fos expression in the rat lumbar spinal cord. Maximal dorsal horn c-Fos expression is observed 3 h after carrageenin (6 mg/150 microliters of saline), with Fos-like (Fos-LI) neurones being predominantly located in laminae I-II and V-VI (41 +/- 3% and 39 +/- 5% of the total number of Fos-LI neurones per section for the control group, respectively) of the dorsal horn. Pretreatment with aspirin (75 or 150 mg/kg, i.v.) reduced the number of Fos-LI neurones induced by carrageenin-inflammation (28 +/- 2% and 45 +/- 1% reduction, respectively; P < 0.001 for both). Acetaminophen (75 or 105 mg/kg, i.v.) reduced the number of Fos-LI neurones (19 +/- 1% and 43 +/- 1% reduction, respectively; P < 0.001 for both). When considering the lower dose (75 mg/kg), the effects of aspirin were significantly more marked than those of acetaminophen (P < 0.001). There was a tendency for both aspirin and acetaminophen to have a more pronounced effect on the number of Fos-LI neurones located in deeper laminae, these differential effects being significant for 75 mg/kg of aspirin (P < 0.01) and 150 mg/kg of acetaminophen (P < 0.01). Both the two doses of aspirin and acetaminophen greatly reduced the inflammatory signs associated with the intraplantar injection of carrageenin. Furthermore there was a positive correlation between the effects of aspirin and acetaminophen on the number of Fos-LI neurones and the inflammatory signs which developed after carrageenin. Our results suggest that the effects of both drugs are mainly due to peripheral site of action without rejecting an additional central site of action of systemic non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen. In addition, our results suggest that the approach we used could be a useful tool to evaluate systematically and quantitatively the effects of NSAIDs. Finally, the effects obtained with the low dose of acetaminophen question the classical view of textbooks claiming that such a compound had no anti-inflammatory effect and are in agreement with previous observations in humans.

Attenuation of c-Fos expression in the rat lumbosacral spinal cord by morphine or tramadol following noxious colorectal distention

We have previously reported that repetitive, noxious colorectal distention (CRD) induces c-Fos in the lumbosacral spinal cord. This study examined the effects of the analgesics morphine and tramadol on c-Fos expression resulting from noxious CRD in the rat. Pre-treatment (30 min or 1 min, i.v.) with morphine (1.25 mg/kg-5.0 mg/kg) or tramadol (1 mg/kg-20 mg/kg) dose-dependently attenuated c-Fos expression to CRD in all areas of the L6-S1 spinal gray matter. The highest dose of morphine was equipotent to the highest dose of tramadol. Repetitive dosing (1/4 of the greatest dose every 30 min) was as effective as a single bolus dose for both drugs. The visceromotor response to CRD was dose-dependently attenuated by tramadol and was reversed by naloxone. However, the dose of tramadol that eliminated the visceromotor response (7% of control) reduced the c-Fos expression to 47% of control. These results demonstrate that these two analgesics attenuate immediate-early gene expression and the visceromotor response to a noxious visceral stimulus and suggest that complete attenuation of c-Fos expression is not necessary for these compounds to produce analgesia to a noxious visceral stimulus.

Effect of administration of high dose intrathecal clonidine or morphine prior to sciatic nerve section on c-Fos expression in rat lumbar spinal cord

The effects of moderate and high intrathecal doses of clonidine, an alpha 2 adrenoceptor agonist, or a high dose of morphine on sciatic nerve section-induced expression of c-Fos-like immunoreactivity was studied in laminae I and II of the dorsal horn and laminae VIII and IX of the ventral horn of rat lumbar spinal cord. c-Fos-like immunoreactivity was examined by immunohistochemistry in normal rats (group 1), rats implanted with an intrathecal catheter with its tip on the lumbar spinal cord (group 2), injected with 10 micrograms (group 3) or 50 micrograms (group 4) clonidine intrathecally 3 h before being killed. In other groups, saline, 10 or 50 micrograms clonidine or 30 micrograms morphine was injected 1 h before unilateral nerve section, and the expression of c-Fos-like immunoreactivity was examined 2 h after axotomy. Few labeled neurons were found in normal controls. The intrathecal catheter itself caused a significant increase in bilateral c-Fos-like immunoreactivity in spinal dorsal and ventral horn compared to normals. The level of c-Fos-like immunoreactivity after 10 or 50 micrograms intrathecal clonidine was similar as in the intrathecal catheter group. Sciatic nerve section caused a significant ipsilateral increase in c-Fos-like immunoreactivity in the dorsal horn compared to the intact side in rats injected with saline. Pretreatment with 10 or 10 micrograms clonidine did not reduce sciatic nerve section-induced expression of c-Fos-like immunoreactivity, but instead caused a significant bilateral increase in c-Fos-like immunoreactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin B receptor antagonism enhances the ability of a low dose of morphine to reduce c-Fos expression in the spinal cord of the rat

Three hours after intraplantar carrageenin (6 mg/150 microliters) Fos-like immunoreactivity was predominantly observed in the superficial and deep laminae of the L4-L5 segments of the dorsal horn of the spinal cord in the rat. The total number of Fos-like immunoreactive neurons was equally divided between the superficial (laminae I-II) and deep laminae (laminae V-VI), 99 +/- 3 and 102 +/- 7 Fos-like immunoreactive neurons per section, respectively. In the absence of carrageenin stimulation a negligible number of Fos-like immunoreactive neurons were observed. Pre-administered systemic morphine (0.3 mg/kg) did not significantly influence the total number of Fos-like immunoreactive neurons 3 h after carrageenin. However, pre-administration of a higher dose of morphine (3 mg/kg) significantly reduced the total number of Fos-like immunoreactive neurons (28 +/- 8% reduction, P < 0.001, as compared with control carrageenin Fos-like immunoreactive expression), with this effect being equally divided between the superficial and deep laminae (29 +/- 5 and 29 +/- 6% reduction, respectively, P < 0.001, as compared with control carrageenin Fos-like immunoreactive expression, for both). Pre-administration of the selective cholecystokinin B receptor antagonist, L-365-260 (0.2 mg/kg), alone did not influence the total number of Fos-like immunoreactive neurons 3 h after carrageenin.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient functional connections between the developing corticospinal tract and cervical spinal interneurons as demonstrated by c-fos immunohistochemistry

Previous research on the rat corticospinal tract (CST) which develops mainly postnatally revealed that some CST axons grow transiently into the spinal gray matter and are subsequently eliminated. In the present study the question was addressed whether these fibres also form transient functional connections. Rats aged 14 and 60 days postnatally received unilateral injections of the potent glutamate agonist kainate into the cerebral motor cortex. After a survival period of 90 min. the rats were perfused and their brains and spinal cords processed for the immediate early gene c-fos by immunohistochemistry. Increased levels of c-fos as opposed to sham-operated animals was observed in several brain nuclei as well as in the cervical spinal cord. In the spinal gray one population of labelled interneurons in particular appeared to correlate well with the CST projection field. A decrease was noted in the number of c-fos positive neurons from postnatal day 14 to 60, suggesting that during development transient functional connections are formed between the CST and its target.

Morphine, 5-HT2 and 5-HT3 receptor antagonists reduce c-fos expression in the trigeminal nuclear complex following noxious chemical stimulation of the rat nasal mucosa

Noxious chemical stimulation of the rat nasal mucosa induces the expression of the immediate early gene c-fos in trigeminal brainstem neurons. In the present study, we applied the irritant mustard oil (1%) into the left nostril of urethane anesthetized rats. Immunohistochemical methods were used to evaluate the expression of Fos protein in the trigeminal subnuclei interpolaris and caudalis and to test the effects of putative analgesics that might depress synaptic transmission in neurons related to nociception. For this purpose, morphine (3 mg/kg and 10 mg/kg), the 5-HT2 antagonist ketanserin (0.5 mg/kg and 5 mg/kg) and the 5-HT3 antagonist ICS 205-930 (0.1 mg/kg and 1 mg/kg) were administered intravenously prior to noxious stimulation. Pretreatment with any of the three compounds reduced Fos-like immunoreactivity. The effect of morphine was reversible with naloxone. The reduction of the expression of Fos-like immunoreactivity by exogenous morphine speaks in favour of an opioidergic link in the modulation of orofacial pain in the trigeminal nuclei. The effects of the 5-HT receptor antagonists are most likely mediated via 5-HT2 and 5-HT3 receptors located on primary afferent fibres.

Anticonvulsants suppress c-Fos protein expression in spinal cord neurons following noxious thermal stimulation

The expression of the nuclear immediate-early gene-encoded protein c-Fos in spinal cord dorsal horn neurons of the rat following noxious thermal stimulation was compared in carbamazepine-, valproate- and phenytoine-treated animals. Single intraperitoneal injection of carbamazepine (50 mg/kg), valproate (300 mg/kg) or intravenous injection of phenytoine (20 mg/kg) before noxious stimulation reduced the number of c-Fos immunoreactive neurons to 65-80% of control levels in superficial laminae and to 30-60% in deep laminae of the dorsal horn. Pretreatment with carbamazepine or valproate for 4 or 8 days combined with an injection immediately before noxious stimulation further significantly decreased the number of c-Fos neurons in the deep dorsal horn only in animals treated with valproate. The observation that activity-dependent gene expression in the spinal cord is effectively modulated by anticonvulsants discloses a novel therapeutic potential of these compounds. Presumably via an acute suppression of high-frequency repetitive firing and/or altered synaptic transmission of intraspinal or descending neurotransmitter systems these drugs gain access to neuroplastic mechanisms which might be relevant for the restoration of physiological levels of neuronal excitability in the central nervous system.

Indomethacin reduces both Krox-24 expression in the rat lumbar spinal cord and inflammatory signs following intraplantar carrageenan

This study evaluated the 'evoked' expression of Krox-24 protein in the lumbar spinal cord after peripheral carrageenan-induced inflammation and its modification by preadministration of indomethacin, a non-steroidal anti-inflammatory drug, in freely moving rats. Three h after intraplantar carrageenan (6 mg/150 microliters saline) a maximal 'evoked' Krox-24 expression was observed in L2-L6 segments of the dorsal horn ipsilateral to carrageenan inflammation. A maximal number of 'evoked' Krox-24 neurons was observed in L4-L5 segments, predominantly in the superficial laminae (I-II) and to a lesser extent in the medial part of neck (laminae V-VI) of the dorsal horn. Such an increase was not observed after an intraplantar injection of control vehicle saline. increase doses of carrageenan (1, 3 and 6 mg) induced a dose-dependent increase (r2 = 0.617, P < 0.0001) in the number of evoked' Krox-24 neurons observed in the superficial dorsal horn 3 h after carrageenan. Systemic preadministration of indomethacin (1, 2.5 and 5 mg/kg) dose-dependently reduced (r2 = 0.508, P < 0.0001) the total number of carrageenan (6 mg at 3 h)-'evoked' Krox-24 neurons (29 +/- 5, 45 +/- 4 and 57 +/- 2% reduction as compared with control, respectively). Systemic indomethacin dose-dependently reduced the inflamed paw and ankle diameter (16 +/- 8, 34 +/- 12, 54 +/- 6% and 48 +/- 14,. 75 + 16, 90 +/- 7% reduction as compared with the control carrageenan inflammation, respectively). There was a positive correlation between the effect of systemic indomethacin on both 'evoked' Krox-24 expression in superficial laminae and the inflammatory signs (r2 = 0.25, P < 0.01 for the paw diameter; r2 = 0.22, P < 0.05 for the ankle diameter). In addition, the total number of 'evoked' Krox-24 neurons was significantly reduced (43 +/- 5% reduction as compared with control) by an oral pretreatment of indomethacin (10 + 10 mg/kg). Oral indomethacin totally blocked the ankle diameter and reduced the paw diameter (100 + 14 and 30 +/- 6% reduction of the control carrageenan inflammation, respectively).

Carrageenin-evoked c-Fos expression in rat lumbar spinal cord: the effects of indomethacin

This study evaluated the effects of systemic indomethacin on carrageenin evoked c-Fos expression in rat lumbar spinal cord neurons. Fos-like immunoreactivity was not observed after the intraplantar injection of the control vehicle saline. 2 h after administration of carrageenin (6 mg/150 microliters) into the hind limb, Fos-like immunoreactive neurons were observed in the lumbar spinal cord (64 labelled neurons per L4-L5 sections) and were numerous in the superficial laminae (I-II), whereas at 3-4 h both superficial and deeper laminae (V, VI and ventral horn) were labelled. 3 h after carrageenin administration, maximal Fos-like immunoreactivity was observed (104 labelled neurons per L4-L5 sections). At later time points Fos-like immunoreactivity was observed predominantly in the deeper laminae. Fos-like immunoreactivity was rarely observed within laminae III-IV at any of the time points. At 24 h, the number of Fos-like immunoreactive neurons decreased (36 labelled neurons per L4-L5 sections). With increasing doses of carrageenin, an increase in the number of Fos-like immunoreactive neurons was observed. The number of Fos-like immunoreactive neurons induced by the carrageenin stimulation (6 mg, at 3 h) was clearly reduced by oral pretreatment with indomethacin (20 mg/kg). In addition, i.v. indomethacin (1, 2.5 or 5 mg/kg) dose dependently reduced the number of Fos-like immunoreactive neurons and the inflammation of the paw and the ankle of the injected foot. A strong relationship between the effect of indomethacin on c-Fos expression and its effect on inflammatory processes was observed. These results suggest that Fos-like immunoreactivity induced by carrageenin inflammation may be a very useful tool to study the effects of anti-inflammatory drugs, at both peripheral and central levels of inflammation.

Expression of nitric oxide synthase and colocalisation with Jun, Fos and Krox transcription factors in spinal cord neurons following noxious stimulation of the rat hindpaw

Expression of nitric oxide synthase (NOS) was investigated in neurons of lumbar spinal cord of adult rats following subcutaneous injection of formalin (FOR) in one hindpaw. NOS was visualized immunocytochemically using a specific antibody and by the NADPH-diaphorase reaction (NDP). In the untreated rat, NOS immunoreactivity (IR) and NDP were present in neurons of the superficial dorsal horn (sDH) predominantly in layers II-III, and in the deep dorsal horn (dDH) predominantly in layer X. Twenty-four hours following FOR, the numbers of neurons labelled for NOS and NDP and the density of NDP containing nerve fiber varicosities significantly increased in sDH of the ipsilateral L3-L4 segments. NOS-IR and NDP gave a rather congruent distribution of labelled neurons in the dorsal horn. In contrast, distinct NOS-IR but not NDP was visible in large diameter motoneurons and in the lateral spinal nucleus. Double labelling demonstrated that in sDH most of the NDP-reactive neurons show a close spatial relationship to fibers and varicosities immunoreactive for substance P and CGRP. These neuropeptides are considered mediators of synaptic input from nociceptive primary afferents. Colocalization of NDP with c-Jun, JunB, JunD, c-Fos, FosB and Krox-24 transcription factors was investigated in neurons of lumbar spinal cord. c-Jun, JunB, c-Fos and Krox-24 reached their maximal levels of expression 2 h after FOR and returned to basal levels after 10 h. FosB and JunD reached their maximal expression after 5 h, persisted up to 10 h and were still visible in 60%-70% of the maximal number of labelled nuclei after 24 h. This persistent expression of transcription factors might contribute to the up-regulation of NOS expression between 10 h and 24 h. In a low number of NDP neurons, suprabasal immunoreactivity of JunB, c-Fos and Krox-24 proteins was visible up to 10 h, and of JunD and FosB up to 24 h in sDH neurons; c-Jun was not expressed in NDP labelled neurons of sDH, but, similar as JunD, showed basal colocalization in preganglionic sympathetic and parasympathetic neurons. In dDH, colocalization of Jun, Fos and Krox-24 proteins in few neurons was only observed following a second FOR stimulus given 24 h after the first one. Double-staining also demonstrated that many Jun, Fos and Krox labelled neurons are in close proximity to NDP labelled nerve fibers suggesting a functional relationship between expression of immediate-early gene encoded transcription factors and presence of nitric oxide in the rat spinal cord.