Knee joint inflammation attenuates spinal FOS expression after unilateral paw formalin injection in rat

Acute Mono-Arthritis Activates the Neurohypophysial System and Hypothalamo-Pituitary Adrenal Axis in Rats

Various types of acute/chronic nociceptive stimuli cause neuroendocrine responses such as activation of the hypothalamo-neurohypophysial [oxytocin (OXT) and arginine vasopressin (AVP)] system and hypothalamo-pituitary adrenal (HPA) axis. Chronic multiple-arthritis activates the OXT/AVP system, but the effects of acute mono-arthritis on the OXT/AVP system in the same animals has not been simultaneously evaluated. Further, AVP, not corticotropin-releasing hormone (CRH), predominantly activates the HPA axis in chronic multiple-arthritis, but the participation of AVP in HPA axis activation in acute mono-arthritis remains unknown. Therefore, we aimed to simultaneously evaluate the effects of acute mono-arthritis on the activity of the OXT/AVP system and the HPA axis. In the present study, we used an acute mono-arthritic model induced by intra-articular injection of carrageenan in a single knee joint of adult male Wistar rats. Acute mono-arthritis was confirmed by a significant increase in knee diameter in the carrageenan-injected knee and a significant decrease in the mechanical nociceptive threshold in the ipsilateral hind paw. Immunohistochemical analysis revealed that the number of Fos-immunoreactive (ir) cells in the ipsilateral lamina I-II of the dorsal horn was significantly increased, and the percentage of OXT-ir and AVP-ir neurons expressing Fos-ir in both sides of the supraoptic (SON) and paraventricular nuclei (PVN) was increased in acute mono-arthritic rats. in situ hybridization histochemistry revealed that levels of OXT mRNA and AVP hnRNA in the SON and PVN, CRH mRNA in the PVN, and proopiomelanocortin mRNA in the anterior pituitary were also significantly increased in acute mono-arthritic rats. Further, plasma OXT, AVP, and corticosterone levels were significantly increased in acute mono-arthritic rats. These results suggest that acute mono-arthritis activates ipsilateral nociceptive afferent pathways at the spinal level and causes simultaneous and integrative activation of the OXT/AVP system. In addition, the HPA axis is activated by both AVP and CRH in acute mono-arthritis with a distinct pattern compared to that in chronic multiple-arthritis.

The analgesic efficacy of intra-articular acetaminophen in an experimental model of carrageenan-induced arthritis

BACKGROUND

Acetaminophen is one of the most common drugs used for the treatment of pain and fever.

OBJECTIVES

To examine the effects of intra-articular (IA) acetaminophen on carrageenan-induced arthritic pain-related behaviour and spinal c-Fos expression in rats.

METHODS

The present study was performed using 20 Sprague Dawley rats. Forty microlitres of IA 0.9% NaCl was injected in the control group, and 40 µL of IA carrageenan was injected in the carrageenan group. One hour after carrageenan injection, 400 µg of IA acetaminophen was injected in the IA acetaminophen group, and 400 µg of intraperitoneal (IP) acetaminophen was injected in the IP acetaminophen group. One day before injection, and 4 h and 8 h after injection, diameters of both knee joints, motility of the rat, paw loading and joint mobility were assessed. After the rats were euthanized, L3 and L4 spinal segments were excised for c-Fos assessment.

RESULTS

IA acetaminophen decreased both the severity and distribution of c-Fos expression. IP acetaminophen decreased only the distribution of c-Fos expression. IA acetaminophen decreased knee diameter at 8 h. IA and IP acetaminophen increased rat motility and paw loading scores. Joint mobility scores of IP acetaminophen were similar to saline at 8 h.

CONCLUSIONS

Results of the present study indicate an analgesic and⁄or possible anti-inflammatory effect of IA acetaminophen and provide further evidence on the efficacy of systemic acetaminophen injection in reducing arthritic pain.

THE EFFECT OF NORMOVOLEMIC HEMODILUTION ON C-FOS PROTEIN IMMUNOREACTIVITY IN THE POSTISCHEMIC RAT BRAIN CORTEX

The hemodilution effect was evaluated in the parietal, temporal, and basal regions of postischemic rat brain neocortex by the immunohistochemical detection of the c-Fos protein. Rats were subjected to the four-vessel-occlusion and the hemodilution was used in one group of animals. Coronal sections of rat brains were used for immunohistochemical processing of c-Fos protein after different postischemic reperfusion intervals. The number of c-Fos positive neuronal nuclei was significantly decreased in the hemodilution group after 4 h of reperfusion in the parietal and basal neocortex compared to the reperfusion without hemodilution.

TMJ inflammation increases Fos expression in the nucleus raphe magnus induced by subsequent formalin injection of the masseter or hindpaw of rats

The study was designed to examine the effect of persistent temporomandibular joint (TMJ) inflammation on neuronal activation in the descending pain modulatory system in response to noxious stimulus. Formalin was injected into the left masseter muscle or hindpaw of rats 10 days after injection of the left TMJ with saline or complete Freund's adjuvant (CFA). The results showed that 10-day persistent TMJ inflammation (induced by CFA) alone did not induce a significant increase in Fos-like immunoreactive (Fos-LI) neurons in the rostral ventromedial medulla (RVM) or locus coeruleus (LC), but that formalin injection of the masseter muscle or hindpaw induced a significant increase in Fos-LI neurons in the RVM and LC of rats with and without TMJ inflammation (P < 0.05). However, persistent TMJ inflammation significantly increased Fos-LI neurons in the nucleus raphe magnus (NRM) induced by subsequent formalin injection of the masseter muscle and hindpaw (70.2% increase and 53.8% increase, respectively, over the control TMJ-saline-injected rats; P < 0.05). The results suggest that persistent TMJ inflammation increases neuronal activity, in particularly in the NRM, by the plastic change of the descending pain modulatory system after ipsilateral application of a noxious stimulus to either orofacial area or a spatially remote body area.

Persistent monoarthritis of the temporomandibular joint region enhances nocifensive behavior and lumbar spinal Fos expression after noxious stimulation to the hindpaw in rats

Effects of persistent temporomandibular joint (TMJ) inflammation on nociceptive responses of remote bodily areas of the rat were investigated. Monoarthritis of the TMJ region was evoked by the injection of complete Freund's adjuvant (CFA) into the left TMJ region. Rats without injection of CFA into the TMJ region served as controls (non-CFA group). Time spent on licking behavior evoked by the injection of formalin into the left hindpaw and withdrawal thresholds of mechanical stimulation to both sides of the hindpaw were measured during TMJ inflammation for 3 weeks. Furthermore, expression of Fos protein in the lumbar dorsal horn was immunohistochemically investigated following the injection of formalin into the hindpaw during TMJ inflammation. Formalin-evoked nocifensive behavioral activities were significantly enhanced at 10 and 14 days after CFA injection in the late phase, while the withdrawal threshold to mechanical stimulation was significantly decreased bilaterally at 8, 10 and 14 days after CFA injection. Both formalin-evoked licking behavior and mechanical withdrawal thresholds to bilateral hindpaw at 21 days after CFA injection were similar to those in the non-CFA group. The number of Fos-positive neurons in the lumbar dorsal horn ipsilateral to the formalin injection at 1 and 7 days after CFA injection into the TMJ were similar to those in the non-CFA group; however, those were significantly increased in the laminae I-II and V-VI of the lumbar dorsal horn at 14 days after CFA injection. TMJ inflammation for 7 and 14 days alone produced a small number of Fos-expressing neurons in the lumbar dorsal horn. These results provide evidence that persistent unilateral inflammation of the TMJ region causes an increase in behavioral hyperalgesia of the hindpaw, which is attributed to the modulation of neural activities, in part, in the lumbar dorsal horn, likely mediated by supraspinal neural mechanisms.

Study of the inflammatory process induced by injection of carrageenan or formalin in the rat temporomandibular joint

The aim of this study was to evaluate the effects of the injection of two phlogistic agents, carrageenan and formalin, in the rat TMJ, and the inflammatory process induced by these substances. In this study, a total of 45 adult rats were distributed in two experimental groups and a control group. The animals were sacrificed after three hours, 24 hours, three days, seven days, and 15 days after a single injection of each substance. Histological data initially demonstrated an inflammatory process represented by acute infiltration, which later became mixed, and finally chronic in both experimental groups. Hyperplasia of the synovial membrane was observed after three days, being intense at seven days, and present after 15 days only in the formalin group. Local saline injection in the control group caused no inflammatory reaction. It was concluded that a single local injection of carrageenan or formalin was enough to induce inflammatory reaction in the TMJ and periarticular soft tissues, and that the resulting processes were similar, but more persistent in the formalin group.

Intraarticular Pretreatment with Ketamine and Memantine Could Prevent Arthritic Pain: Relevance to the Decrease of Spinal c-Fos Expression in Rats

To determine whether intraarticular pretreatment with N-methyl-D-aspartic (NMDA) receptor antagonist ketamine or memantine currently used in humans has prophylactic analgesia in arthritic pain, we examined the effects of their intraarticular injection before carrageenan injection into the knee joint on pain-related behavior and spinal c-Fos expression in rats. Injection of ketamine (0.2 mg and 1 mg) or memantine (0.1 mg, 0.2 mg, and 1 mg) into the knee joint, but not the abdominal cavity, immediately before carrageenan injection (2%, 40 microL) significantly prevented pain-related behavior. The intraarticular injection of ketamine (1 mg) or memantine (0.2 mg) also suppressed c-Fos expression in the laminae I-II and laminae V-VI at the L3-4 spinal level. Subsequent statistical analyses revealed that the degree of the spinal c-Fos expression was correlated with the extent of the pain-related behavior. These results suggest that peripheral administration of NMDA receptor antagonists has prophylactic analgesic effects in arthritic pain, which might be associated with the decrease of central nociceptive signaling. Because ketamine and memantine are currently used in humans and considered clinically safe, they may have therapeutic value in the treatment of joint pain.

Activation of p38 mitogen-activated protein kinase in spinal microglia is a critical link in inflammation-induced spinal pain processing

We examined the effect of p38 mitogen-activated protein kinase (MAPK) inhibitors in models of nociception and correlated this effect with localization and expression levels of p38 MAPK in spinal cord. There was a rapid increase in phosphorylated p38 MAPK in spinal cord following intrathecal administration of substance P or intradermal injection of formalin. Immunocytochemistry revealed that phosphorylated p38 MAPK-immunoreactive cells were predominantly present in laminae I-IV of the dorsal horn. Double-staining with markers for neurons, microglia, astrocytes and oligodendrocytes unexpectedly revealed co-localization with microglia but not with neurons or other glia. Pretreatment with p38 MAPK inhibitors (SB20358 or SD-282) had no effect on acute thermal thresholds. However, they attenuated hyperalgesia in several nociceptive models associated with spinal sensitization including direct spinal activation (intrathecal substance P) and peripheral tissue inflammation (intraplantar formalin or carrageenan). Spinal sensitization, manifested by enhanced expression of cyclo-oxygenase-2 and inflammation-induced appearance of Fos-positive neurons, was blocked by pretreatment, but not post-treatment, with p38 MAPK inhibitors. Taken together, these results indicate that spinal p38 MAPK is involved in inflammation-induced pain and that activated spinal microglia play a direct role in spinal nociceptive processing.

The behavioral and neuronal effects induced by repetitive nociceptive stimulation are affected by gonadal hormones in male rats

The role of gonadal hormones in inducing long-term modifications in response to transient nociceptive stimuli was investigated in adult male rats. Three weeks after gonadectomy or sham surgery, animals were randomly divided into groups to be exposed to sham (only a prick in the dorsal hind paw) or formalin treatment (50 microl, 5% s.c. in the dorsal hind paw) once a week for the following 3 weeks. In gonadectomized animals the formalin-induced responses (licking, flexing and jerking of the injected paw) did not differ from those of intact animals after the first formalin injection. However, their levels were higher after the second or third injections. Indeed, in intact animals the formalin-induced responses progressively decreased, being significantly lower after the third injection than after the first; in gonadectomized animals, the formalin-induced responses did not change with repetition of the formalin treatment. In intact rats, c-Fos expression in the paraventricular nucleus of the thalamus and arcuate nucleus of the hypothalamus remained at control levels or decreased in animals injected two or three times with formalin; in gonadectomized rats, c-Fos expression increased with repetition of the noxious stimulation, reaching the highest levels in animals injected three times with formalin. These results show that male gonadal hormones have an inhibitory, adaptive effect on the behavioral and neuronal responses to repeated nociceptive stimulation.

Spinal adenosine agonist reduces c-fos and astrocyte activation in dorsal horn of rats with adjuvant-induced arthritis

Adjuvant-induced arthritis (AIA) is a useful animal model of rheumatoid arthritis (RA). We have previously shown that stimulation of spinal adenosine A1 receptors decreases peripheral signs of AIA. In this study we show that when the final dose of adenosine A1 agonist is given 1 h prior to sacrifice the number of c-Fos positive cells evoked by the AIA in both the superficial and deep dorsal horns decreases by about 50%. In saline-treated AIA animals the increase in c-Fos expression seen in laminae I-IV was accompanied by an increase in glial fibrillary acidic protein immunoreactivity, indicative of astrocyte activation. Astrocyte activation was only partially attenuated by adenosine A1 receptor agonist treatment.

The thermal and mechanical anti-hyperalgesic effects of pre- versus post-intrathecal treatment with lamotrigine in a rat model of inflammatory pain

Intrathecal (IT) lamotrigine, a sodium channel blocker which suppresses neuronal release of glutamate, has been shown to produce a long-lasting antihyperalgesic effect in the neuropathic pain models. In the present study, we examined the anti-hyperalgesic effects of pre- versus post-treatment of IT lamotrigine in an animal inflammatory pain model, the inflamed knee joint model of the rat. Thermal and mechanical antinociception was assessed in rats using a modified Hargreaves box and von Frey hairs. Induction of tonic persistent inflammatory pain was induced by intra-articular injection (i.a.) of a carrageenan-kaolin mixture (CK) into the right knee-joint. Rats were randomly assigned to the groups receiving IT lamotrigine in distinct doses of 5, 50 or 100 ug either pre- (10 min before CK injection) or post-inflammation induction (4 h or 23 h). We observed that CK injection resulted in a significant thermal and mechanical hyperalgesia throughout a 24-h observation period. Pre-treatment with IT lamotrigine revealed a time and dose-dependent suppression of thermal and mechanical hyperalgesia, whereas the post-treatment with IT lamotrigine only showed an effect for mechanical nociception.

CONCLUSION

IT Lamotrigine is antihyperalgesic at a dose larger than 50 ug in the early phase of inflammatory pain model. It reverses tactile allodynia but not thermal hyperalgesia when given after the inflammation induction.

Effects of previous noxious stimulus applied to remote areas on noxious stimulus-evoked c-Fos expression in the rat trigeminal nucleus caudalis

Noxious stimulus-evoked c-Fos expression in the spinal dorsal horn is modulated by noxious stimuli applied previously to remote areas of the body. To confirm the existence of such modulation in c-Fos expression in the trigeminal system, changes in c-Fos expression in the trigeminal nucleus caudalis induced by formalin injection into the rat whisker pad were examined by previously injecting formalin into different areas (contralateral whisker pad, ipsilateral or contralateral forepaw) of the body. Formalin injection-evoked c-Fos expression in this nucleus was significantly reduced by previous formalin injection into the contralateral whisker pad or ipsilateral forepaw but not into the contralateral forepaw. The interval between the two injections of formalin that produced a maximal reduction of formalin injection-evoked c-Fos expression was 1 h, and the reduction of c-Fos expression was less when the interval of the two noxious stimuli was longer or shorter than 1 h. These results suggested that noxious stimulus-evoked c-Fos expression in the trigeminal nucleus caudalis is reduced by noxious stimulus applied previously to remote areas, and the reduction is dependent on the area of previous noxious stimulation and interval between the two noxious stimuli.

Transient spinal cord ischemia in rat: the time course of spinal FOS protein expression and the effect of intraischemic hypothermia (27 degrees C)

1. In the present study, we characterize the time course of spinal FOS protein expression after transient noninjurious (6-min) or injurious (12-min) spinal ischemia induced by inflation of a balloon catheter placed into the descending thoracic aorta. In addition, this work examined the effects of spinal hypothermia on FOS expression induced either by ischemia or by potassium-evoked depolarization (intrathecal KCl). 2. Short-lasting (6-min) spinal ischemia evoked a transient FOS protein expression. The peak expression was seen 2 hr after reperfusion in all laminar levels in lumbosacral segments. At 4 hr of reperfusion, more selective FOS expression in spinal interneurons localized in the central part of laminae V-VII was seen. At 24 hr no significant increase in FOS protein was detected. 3. After 12 min of ischemia and 2 hr of reflow, nonspecific FOS expression was seen in both white and gray matter, predominantly in nonneuronal elements. Intrathecal KCl-induced FOS expression in spinal neurons in the dorsal horn and in the intermediate zone. Spinal hypothermia (27 degrees C) significantly suppressed FOS expression after 6 or 12 min of ischemia but not after KCl-evoked depolarization. 4. Data from the present study show that an injurious (but not noninjurious) interval of spinal ischemia evokes spinal FOS protein expression in glial cells 2 hr after reflow. The lack of neuronal FOS expression corresponds with extensive neuronal degeneration seen in this region 24 hr after reflow. Noninjurious (6-min) ischemia induced a transient, but typically neuronal FOS expression. The significant blocking effect of hypothermia (27 degrees C) on the FOS induction after ischemia but not after potassium-evoked depolarization also suggests that simple neuronal depolarization is a key trigger in FOS induction.

Incipient cauda equina syndrome as a model of somatovisceral pain in dogs: spinal cord structures involved as revealed by the expression of c-fos and NADPH diaphorase activity

Segmental and laminar distribution of Fos-like immunoreactive, reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-exhibiting and double-labeled (Fos-like immunoreactive and NADPHd-exhibiting) neurons was examined in lower lumbar and sacral segments of the dog spinal cord using the model of multiple cauda equina constrictions. NADPHd histochemistry was used as marker of nitric oxide synthase-containing neurons. The appearance and the time-course of Fos-like immunoreactive, NADPHd and double-labeled neurons was studied at 2 h and 8 h postconstriction characterized as the incipient phase of cauda equina syndrome. The occurrence of Fos-like immunoreactive and NADPHd-exhibiting neurons in fully developed cauda equina syndrome was studied at five days postconstriction. An increase in Fos-like immunoreactivity in superficial laminae (I-II) and an enhanced NADPHd staining of lamina VIII neurons were found. A statistically significant increase in Fos-like immunoreactive neurons was found in laminae I-II and VIII-X 8 h postconstriction, and in contrast, a prominent decrease in Fos-like immunoreactive neurons was found in laminae I-II, accompanied by a statistically significant increase in Fos-like immunoreactive neurons in more ventrally located laminae VII-X at five days postconstriction. Quantitative analysis of laminar distribution of constriction-induced NADPHd-exhibiting neurons revealed a considerable increase in these neurons in laminae VIII-IX 8 h postconstriction and a statistically highly significant increase in NADPHd-exhibiting neurons in laminae VII-X five days postconstriction. Concurrently, the number of NADPHd-exhibiting neurons in laminae I-II was greatly reduced. While a low number of double-labeled neurons was found throughout the gray matter of lower lumbar and sacral segments at 2 h postconstriction, a statistically significant number of double-labeled neurons was found in lamina X 8 h and in laminae VII-X five days postconstriction. The course and distribution of anterograde degeneration resulting five days after multiple cauda equina constrictions are compared with segmental and laminar distribution of Fos-like immunoreactive and NADPHd-exhibiting neurons. Prominent involvement of the spinal cord neurons appearing in the lumbosacral segments at the early beginning and in fully developed cauda equina syndrome results in a Fos-like immunoreactivity and strongly enhanced NADPHd staining of some neuronal pools. Under such circumstances, an early cauda equina decompression surgery is advisable aimed at decreasing or preventing the derangement of the neural circuits in the lumbosacral segments.