Effect of circadian system disruption on the concentration and daily oscillations of cortisol, progesterone, melatonin, serotonin, growth hormone, and core body temperature in periparturient dairy cattle.

Metabolic, circadian, sleep, and reproductive systems are integrated and reciprocally regulated, but the understanding of the mechanism is limited. To study this integrated regulation, the circadian timing system was disrupted by exposing late pregnant nonlactating (dry) cows to chronic shifts in the light-dark phase, and rhythms of body temperature and circulating cortisol (CORT), progesterone (P4), serotonin (5HT), melatonin (MEL), and growth hormone (GH) concentrations were measured. Specifically, across 2 identical studies (1 and 2), at 35 d before expected calving (BEC) multiparous cows were assigned to control (CON; n = 24) and exposed to 16 h light and 8 h dark or phase shift (PS; n = 24) treatments and exposed to 6-h light-dark phase shifts every 3 d until parturition. All cows were exposed to control lighting after calving. Blood samples were collected in the first study at 0600 h on d 35 BEC, d 21 BEC, and 2 d before calving, and d 0, 2, 9, 15, and 22 postpartum (PP). A subset of cows (n = 6/group) in study 1 was blood sampled every 4 h over 48 h beginning on d 23 BEC, 9 BEC, and 5 PP. Body temperature was measured every 30 min (n = 8-16/treatment) for 48 h at 23 BEC and 9 BEC in both studies; and at 14 PP and 60 PP only in study 2. Treatment did not affect levels of CORT, GH, or P4 at 0600 h, but overall level of 5HT was lower and MEL higher in PS cows across days sampled. A 2-component versus single-component cosinor model better described [>coefficient of determination (R2);

Inclusion of Oat and Yeast Culture in Sow Gestational and Lactational Diets Alters Immune and Antimicrobial Associated Proteins in Milk.

Maternal diet supplementation with pro- and prebiotics is associated with decreased incidence of diarrhea and greater piglet performance. This study investigated the impact adding whole ground oat as a prebiotic, alone or in combination with a probiotic, yeast culture (YC) (Saccharomyces cerevisiae), to sow gestation and lactation rations had on milk protein composition, piglet growth, and incidence of post-weaning diarrhea (PWD). Diets: control (CON), CON + yeast culture (YC) [5 g/kg], CON + oat (15% inclusion rate) (Oat) or CON+ YC [5 g/kg] + Oat (15%) were fed the last 30 days of gestation and throughout lactation (18-21 days). Shotgun proteome analysis of day 4 and 7 postpartum milk found 36 differentially abundant proteins (P-adj < 0.1) in both Oat and YC supplemented sows relative to CON. Notable was the increased expression of antimicrobial proteins, lactoferrin and chitinase in milk of Oat and YC sows compared to CON. The levels of IgA, IgM (within colostrum and milk) and IgG (within milk) were similar across treatments. However, colostral IgG levels in Oat-supplemented sows were significantly lower (p < 0.05) than that of the control sows, IgG from Oat-supplemented sows displayed greater reactivity to E. coli-antigens compared with CON and YC. Piglets from sows that consumed Oat alone or in combination weighed significantly more (p < 0.05) at birth compared to CON and YC. However, piglets in the Oat + YC group weighed less at weaning and had the lowest weight gain (p < 0.05) postweaning, compared with CON. Taken together with the observation that piglets of either YC- or Oat-fed sows had less PWD compared to CON and YC+ Oat suggests that Oat or YC supplementation positively impacts piglets through expression of certain milk-associated immune and antimicrobial proteins.

Methacholine induced airway contraction in porcine precision cut lung slices from indoor and outdoor reared pigs.

Repetitive exposure to bioaerosols in swine production facilities (SPF) promotes respiratory dysfunction in workers and animals. An adequate understanding of the impact of the SPF environment on pulmonary physiology is needed. However, there is currently no sufficient ex vivo model to investigate the cause for agriculture-related lung disease. The precision cut lung slices (PCLS) technique represents a practical and useful procedure for ex vivo studies. Our goal was to use the PCLS technique to develop a model of agriculture-related lung diseases using a physiologically relevant animal model, the domesticated pig. Freshly prepared pig lung tissue cores were sectioned into 300 µm slices and viability was measured by lactate dehydrogenase activity and live/dead staining. Airway contractility in response to a methacholine (MCh) dose gradient (10-7-10-4 M) was measured. After the last MCh dose, PCLS were incubated with 1 mM chloroquine to allow airways to relax. Time-lapse images were taken every minute for 35 minutes and used to determine airway lumen area changes. Porcine PCLS remained viable and demonstrated metabolic activity for three days. PCLS from indoor and outdoor pigs contracted in response to MCh exposure and relaxed when incubated with chloroquine. Notably, PCLS of indoor pigs showed greater airway constriction in response to 10-5 M MCh exposure compared to outdoor pig PCLS (P<0.05). These data suggest that exposure to the indoor pig production environment may be associated with hyperresponsiveness in swine airways, and support future studies to investigate lung response to inflammatory substances using the porcine PCLS model.

Sorrel Extract Reduces Oxidant Production in Airway Epithelial Cells Exposed to Swine Barn Dust Extract In Vitro.

Exposure to hog barn organic dust contributes to occupational lung diseases, which are mediated by inflammatory and oxidative stress pathways. Isoprostanes-a family of eicosanoids produced by oxidation of phospholipids by oxygen radicals-are biomarkers of pulmonary oxidative stress. Importantly, 8-isoprostane has been implicated as a key biomarker and mediator of oxidative stress because it is a potent pulmonary vasoconstrictor. Antioxidants found in fruits and vegetables hold promise for preventing or reducing effects of oxidative stress-related diseases including chronic bronchitis and chronic obstructive pulmonary disease (COPD). Here, we investigated 8-isoP and oxidant production by organic dust-exposed airway epithelial cells and the inhibitory effects of an extract from calyces of the sorrel plant, Hibiscus sabdariffa, on oxidant-producing pathways. Confluent cultures of normal human tracheobronchial epithelial cells were pretreated or not with 1% sorrel extract prior to 5% dust extract (DE) exposure. Following DE treatments, live cells, cell-free supernatants, or cell extracts were evaluated for the presence of 8-isoprostane, superoxide, hydrogen peroxide, nitric oxide, hydroxyl radical, peroxynitrite, and catalase activity to evaluate sorrel's inhibitory effect on oxidative stress. The well-known radical scavenging antioxidant, N-acetyl cysteine (NAC), was used for comparisons with sorrel. DE exposure augmented the production of all radicals measured including 8-isoprostane (p value < 0.001), which could be inhibited by NAC or sorrel. Among reactive oxygen and nitrogen species generated in response to DE exposure, sorrel had no effect on H2O2 production and NAC had no significant effect on NO· production. The observations reported here suggest a possible role for sorrel in preventing 8-isoprostane and oxidant-mediated stress responses in bronchial epithelial cells exposed to hog barn dust. These findings suggest a potential role for oxidative stress pathways in mediating occupational lung diseases and antioxidants within sorrel and NAC in reducing dust-mediated oxidative stress within the airways of exposed workers.

Electrospun nanofibers of poly(ε-caprolactone)/depolymerized chitosan for respiratory tissue engineering applications.

Synthetic grafts comprised of a porous scaffold in the size and shape of the natural tracheobronchial tree, and autologous stem cells have shown promise in the ability to restore the structure and function of a severely damaged airway system. For this specific application, the selected scaffold material should be biocompatible, elicit limited cytotoxicity, and exhibit sufficient mechanical properties. In this research, we developed composite nanofibers of polycaprolactone (PCL) and depolymerized chitosan using the electrospinning technique and assessed the properties of the fibers for its potential use as a scaffold for regenerating tracheal tissue. Water-soluble depolymerized chitosan solution was first prepared and mixed with polycaprolactone solution making it suitable for electrospinning. Morphology and chemical structure analysis were performed to confirm the structure and composition of the fibers. Mechanical testing of nanofibers demonstrated both elastic and ductile properties depending on the ratio of PCL to chitosan. To assess biological potential, porcine tracheobronchial epithelial (PTBE) cells were seeded on the nanofibers with composition ratios of PCL/chitosan: 100/0, 90/10, 80/20, and 70/30. Transwell inserts were modified with the nanofiber membrane and cells were seeded according to air-liquid interface culture techniques that mimics the conditions found in the human airways. Lactase dehydrogenase assay was carried out at different time points to determine cytotoxicity levels within PTBE cell cultures on nanofibers. This study shows that PCL/chitosan nanofiber has sufficient structural integrity and serves as a potential candidate for tracheobronchial tissue engineering.

Direct writing of polymeric coatings on magnesium alloy for tracheal stent applications.

This paper investigates the direct-write inkjet method for depositing multi-layer coatings of biodegradable polymers on magnesium alloy surface. Immersion studies were conducted on Poly(lactic-co-glycolic) acid (PLGA), polycaprolactone (PCL), and poly-ester urethane urea (PEUU) coatings to determine the corrosion behavior of different samples based on their varying degradation properties. Using the inductively coupled plasma spectroscopy, a reduction in magnesium ion concentration was observed from the polymer-coated samples indicative of the lower corrosion rates as compared to the uncoated Mg substrate. Findings also showed correlation between the release of the magnesium ions and the health of fully differentiated normal human bronchial epithelial (NHBE) cells via evaluation of key biomarkers of inflammation and toxicity, cyclooxygenase-2 (COX-2) and lactate dehydrogenase (LDH), respectively. The induction of COX-2 gene expression was proportional to the increase in magnesium exposure. In addition, the release of higher magnesium content from uncoated and PCL polymer coated samples resulted in lower LDH activity based on the favorable response of the NHBE cells. PEUU and PLGA polymer coatings provided good barrier layer corrosion protection. This research evaluates candidate polymer coatings as a source for therapeutic agents and barrier layer to control the corrosion of magnesium alloys for tracheal applications.

5-alk(en)ylresorcinols as the major active components in wheat bran inhibit human colon cancer cell growth.

We and others have found that wheat bran oil is the active constituent in wheat bran for colon cancer prevention. However, the active components in wheat bran oil are still unknown. Using human colon cancer cells (HCT-116 and HT-29) as the guiding assays, we further purified the active components from wheat bran using column chromatography. In this study, we identified that a fraction containing 5-n-alk(en)ylresorcinols had the strongest inhibitory effect on the proliferation of human HCT-116 and HT-29 colon cancer cells. Further purification led to the identification of 14 5-alk(en)ylresorcinols. Among them, 7, (10'Z,13'Z,16'Z)-5-(nonadeca-10',13',16'-trienyl)resorcinol, is a novel compound and 5, 6, 9, 10, and 13 were purified as individual compounds for the first time. The identification and structural elucidation of these compounds were based on 1D and 2D NMR and tandem mass spectral analyses. All these compounds (1-14) except 10 were evaluated for growth inhibition of human colon cancer cell lines (HCT-116 and HT-29). Our results indicate that increasing the length of the side chain will diminish the inhibitory activity, and the existence of a double bond and a carbonyl group will strengthen such an activity.

Lactoferrin for the prevention of post-antibiotic diarrhoea.

Antibiotic-associated diarrhoea (AAD) is a common cause of morbidity and mortality. Older individuals in long-term care facilities are particularly vulnerable due to multisystem illnesses and the prevailing conditions for nosocomial infections. Lactoferrin, an antimicrobial protein in human breastmilk, was tested to determine whether it would prevent or reduce AAD, including Clostridium difficile in tube-fed long-term care patients. Thirty patients were enrolled in a randomized double-blind study, testing eight weeks of human recombinant lactoferrin compared to placebo for the prevention of antibiotic-associated diarrhoea in long-term care patients. Fewer patients in the lactoferrin group experienced diarrhoea compared to controls (p = 0.023). Based on the findings, it is concluded that human lactoferrin may reduce post-antibiotic diarrhoea.

Assessment of behavior during labor in rats and effect of intrathecal morphine.

BACKGROUND: Efficacy of analgesics varies with the type of pain. Little is known in this regard concerning labor pain, given the ethical barriers to study in humans and the lack of surrogate animal models. To address this, the authors classified and quantified spontaneous behaviors during labor and delivery in rats and examined the effects of a known analgesic, intrathecal morphine. METHODS: Pregnant rats were video recorded for 72 h surrounding the time of anticipated labor and delivery. Specific behaviors were identified and classified into general activities, phasic stretching behaviors, and maternal attention activities. Rats received intrathecal infusion of saline or morphine, 0.035-3.5 microg/h, beginning approximately 1 day before delivery, and effects on behaviors and response to noxious heating of the paw were quantified. RESULTS: Phasic stretching behaviors occurred with high frequency before delivery of the first pup and were rare after delivery of the last pup. Intrathecal morphine at infusion rates greater than 0.035 microg/h abolished these behaviors without affecting general or maternal behaviors or the timing or duration of labor and delivery. Morphine was also antinociceptive to noxious heat, but only at infusion rates of 1.0 microg/h or higher. CONCLUSIONS: Phasic stretching behaviors are observed after distension or inflammation of pelvic viscera in rats, and similar behaviors occur during labor and delivery. Selective and dose-related blockade by intrathecal morphine of only these behaviors suggests that they reflect nociception and that this simple monitoring method can be used to study therapies for the pain of labor and delivery.

A pain model after gynecologic surgery: the effect of intrathecal and systemic morphine.

BACKGROUND: Despite recent recognition that visceral pain differs from somatic pain in its neurophysiologic basis and treatment modalities, most laboratory studies of postoperative pain use a model of superficial somatic injury, and there is no model of postoperative pain after gynecologic surgery. We describe spontaneous behavior in rats after laparotomy with or without noxious stimulation of the uterus and cervix to more specially address pain after gynecologic surgery. METHODS: Female Sprague-Dawley rats received inhaled anesthesia only, anesthesia with laparotomy, or laparotomy plus 60 min of tonic distension of the lower uterine segment and cervix, followed by video observation of spontaneous behavior. RESULTS: Compared with anesthesia alone, laparotomy decreased some spontaneous behaviors (drinking water, grooming, and exploration). Laparotomy plus uterocervical manipulation further decreased these behaviors and increased abnormal behaviors (licking of the lower abdomen and squashing posture of the pelvis to the floor). Intrathecal and systemic morphine restored spontaneous behavior and reduced abnormal behaviors, with minor differences between routes of administration. CONCLUSIONS: These data suggest that specific behaviors may distinctly reflect somatic and visceral components of postoperative gynecologic pain, and that this model may be used to test novel therapies to relieve pain in this setting.

Uterine cervical afferents in thoracolumbar dorsal root ganglia express transient receptor potential vanilloid type 1 channel and calcitonin gene-related peptide, but not P2X3 receptor and somatostatin.

BACKGROUND: Little is known regarding the phenotype of afferents that innervate the uterine cervix. Chronic estrogen sensitizes uterine cervical afferents to mechanical distension, but whether this reflects changes in afferent neurotransmitter or excitatory ion channel expression is unknown. The authors used immunocytochemistry to characterize uterine cervical afferents and the effects of estrogen on them. METHODS: Fluorogold was injected into the uterine cervix of intact rats (n = 7) and those with ovariectomy alone (n = 9) or with estrogen supplementation (n = 8). Bilateral dorsal root ganglia at T12-L2 were removed and immunostained for transient receptor potential vanilloid type 1 (TRPV1), P2X3 receptor, calcitonin gene-related peptide, and somatostatin. The proportion of fluorogold-traced dorsal root ganglion neurons expressing each of these markers was compared with untraced neurons. RESULTS: Most fluorogold-traced cells were found at L1 (> 55%) and were of small diameter (24 microm). TRPV1 expression was similar between traced and untraced cells, except the estrogen treatment increased TRPV1 expression in traced cells. Calcitonin gene-related peptide expression was greater in traced than in untraced cells, with no effect of experimental treatment. No traced cells expressed the P2X3 receptor or somatostatin, although each of these was present in untraced cells. CONCLUSION: Uterine cervical afferents in the hypogastric nerve express TRPV1, an important nociceptive channel, which may play a role in estrogen-induced sensitization of cervical afferents. High expression of calcitonin gene-related peptide suggests a sensory and efferent role for this peptide. In contrast to other viscera, these afferents do not express somatostatin or P2X3 receptor, indicating a unique phenotype of these C fibers.

Preoperative inhibition of cyclooxygenase-1 in the spinal cord reduces postoperative pain.

Intrathecal administration of cyclooxygenase (COX)-1, but not COX-2, specific inhibitors given on postoperative day 1 has analgesic effects in an incisional model of postoperative pain. We investigated the effects of preoperative administration of intrathecal COX inhibitors in this model. Fifteen minutes before surgery, rats received intrathecally the COX-1 preferring inhibitor, ketorolac, the specific COX-1 inhibitor, SC-560, the COX-2 inhibitor, NS-398, or vehicle. A 1-cm longitudinal incision was then made through skin, fascia, and muscles of the plantar aspect of a left paw in male rats. Withdrawal threshold to von Frey filaments was measured at 2 h, 4 h, and at intervals up to 5 days later. Ketorolac and SC-560 increased withdrawal threshold to mechanical stimulation, but NS-398 had no significant effect. These results suggest that COX-1 plays an important role in spinal cord pain processing and sensitization after surgery and that preoperative intrathecal administration of specific COX-1 inhibitors may be useful to treat postoperative pain.

Intrathecal morphine reduces allodynia after peripheral nerve injury in rats via activation of a spinal A1 adenosine receptor.

BACKGROUND: The degree to which intrathecally administered morphine can alleviate hypersensitivity in animals after peripheral nerve injury is controversial, and the mechanisms by which morphine works in these circumstances are uncertain. In normal animals, morphine induces adenosine release, and in vitro data suggest that this link is disrupted after peripheral nerve injury. Therefore, using a controlled, blinded study design, the authors tested intrathecal morphine efficacy in rats with peripheral nerve injury and the role of spinal A1 adenosine receptors in the action of morphine. METHODS: Male rats underwent intrathecal catheter implantation and lumbar spinal nerve ligation, resulting in hypersensitivity to tactile stimulation of the paw. Intrathecal morphine alone or with naloxone or the specific A1 adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentyxanthine (DPCPX), was administered, and withdrawal threshold to von Frey filament application to the hind paw was determined. RESULTS: Intrathecal morphine (0.25-30 microg) dose-dependently reversed mechanical hypersensitivity after spinal nerve ligation, with an ED50 of 0.79 microg. The effect of morphine was blocked by intrathecal naloxone. Intrathecal DPCPX alone had no effect on withdrawal threshold after spinal nerve ligation but completely reversed the effect of morphine, with an ID50 of 5.6 microg. CONCLUSIONS: This study is in accord with two recent reports that support short-term efficacy of intrathecal morphine to reverse hypersensitivity to mechanical stimuli in animal models of neuropathic pain. Despite previous studies demonstrating that morphine releases less adenosine after peripheral nerve injury, the current study suggests that the antihypersensitivity effect of morphine in these conditions is totally reliant on A1 adenosine receptor activation.

Spinal noradrenaline transporter inhibition by reboxetine and Xen2174 reduces tactile hypersensitivity after surgery in rats.

Spinal noradrenaline (NA) released in response to noxious stimuli may play an important role in suppression of nociceptive transmission. Here, we investigated the efficacy of a competitive NA transporter inhibitor (reboxetine) and a noncompetitive NA transporter inhibitor peptide, Xen2174, isolated from the Pacific cone snail, to treat tactile hypersensitivity following paw incisional surgery. Male Sprague-Dawley rats were anesthetized, an incision of the plantar aspect of the hind paw was performed, and withdrawal threshold to von Frey filaments near the surgical site determined. Reboxetine (0.5-5 microg) and Xen2174 (0.3-100 microg) increased withdrawal threshold when injected 24h after paw incision, with a peak effect at 15-60 min, for Xen2174, an ED50 value of 0.64 microg. Administration of Xen2174 (3-30 microg) 15 min before incision also reduced hypersensitivity in a dose-dependent manner. Withdrawal threshold after the single 30 microg dose was greater than vehicle control even at 2, 3, and 5 days after incision. Doses

Intrathecal morphine and ketorolac analgesia after surgery: comparison of spontaneous and elicited responses in rats.

Pain after surgery results in significant morbidity, and systemic opioids often fail to provide adequate analgesia without marked sedation and respiratory depression. Intrathecal morphine provides better analgesia, but is limited by delayed respiratory depression. Intrathecal injection of the cyclooxygenase inhibitor, ketorolac, has recently entered clinical trials, and the current study examined the interaction between intrathecal morphine and ketorolac to treat postoperative pain. We also sought to compare these treatments on a commonly used assessment of withdrawal threshold and a new assessment of spontaneous behavior after surgery. Male Sprague Dawley rats and underwent hind paw incision or subcostal laparotomy surgery. Intrathecal morphine, ketorolac, or their combination were injected on the first postoperative day, with outcome measure being return to pre-surgery withdrawal threshold with von Frey filament testing of the paw after paw incision, or return to pre-surgery exploratory activity after laparotomy. Intrathecal morphine completely reversed the effects of surgery in both models, but intrathecal ketorolac only partially reversed them. Ketorolac enhanced the potency of morphine several fold in both models, and did so synergistically after paw incision. In all cases drug potency was greater for spontaneous than elicited responses. These data confirm that spinal opioid receptor and cyclooxygenase enzyme inhibition diminish elicited tactile hypersensitivity after surgery, and that they similarly return spontaneous behavior to normal. Differences in drug potency could reflect fundamental differences in outcome measures or in the surgical procedures themselves. These data support combination study of intrathecal morphine and ketorolac for postoperative pain.

Repeated dosing with oral allosteric modulator of adenosine A1 receptor produces tolerance in rats with neuropathic pain.

BACKGROUND: The positive allosteric adenosine receptor modulator, T62 (2-amino-3-(4-chlorobenzoyl)-5,6,7,8-tetrahydrobenzothiophene), has been shown to reduce mechanical allodynia in a rat model of neuropathic pain. However, whether chronic oral T62 retains efficacy in this pain model has not been examined. Therefore, the authors studied antiallodynic effects of chronic oral T62 in spinal nerved-ligated rats, as well as motor and sedative behavioral effects. METHODS: Oral T62, 100 mg/kg, or oral oil was applied daily to spinal nerve-ligated rats for 4 weeks, with rat weights examined daily. Sedation, placing and ambulation scores, and withdrawal threshold were observed for 3 h daily for the first 2 weeks and then once a week. At the end of observation, the animals were killed, and the spinal tissues were collected for radioligand binding. In addition, withdrawal thresholds were also observed in rats with 5 days of treatment with 50 mg/kg oral T62. Furthermore, the effects of intrathecal adenosine on rats with oral T62 or oil treatment were compared. RESULTS: Chronic oral T62, at 100 mg/kg, initially returned the withdrawal threshold to mechanical testing to preinjury levels, with minor or no sedative or motor effects. Tolerance was observed, with a 60% loss of most possible effects in antiallodynia within 5 days of daily administration. Similarly, tolerance also occurred with chronic oral T62 at 50 mg/kg but did not alter the effect of intrathecal adenosine. Furthermore, 4 weeks of exposure to 100 mg/kg T62 resulted in a small reduction in spinal cord A1 receptor number. CONCLUSION: The results imply that chronically administered A1 adenosine modulators lose efficacy over time, partly as a result of receptor down-regulation.

Cyclooxygenase-1 in the spinal cord plays an important role in postoperative pain.

Cyclooxygenase-2 (COX-2) activity in the spinal cord plays a key role in sensitization to sensory stimuli during acute inflammation. In contrast, intrathecal administration of COX-2 specific inhibitors has minimal analgesic effects in an incisional model of postoperative pain. We investigated the role of COX isoforms in this model by examining the expression of COX-1 and the effect of intrathecal COX inhibitors. A 1cm longitudinal incision was made through skin, fascia and muscles of the plantar aspect of the left paw in male rats, and withdrawal threshold to von Frey filaments measured. Rats were perfused at 1, 2, 3, 5, and 7 days after incision, and COX-1 immunohistochemistry was performed on L3 to S2 spinal cord and gracile nucleus sections. Other rats received intrathecally the COX-1 preferring inhibitor, ketorolac, the specific COX-1 inhibitor, SC-560, the COX-2 inhibitor, NS-398 or vehicle 1 day after surgery. Withdrawal threshold was measured at intervals up to 5 days later. COX-1 immunoreactivity increased in glia in the ipsilateral L4-L6 spinal dorsal horn and ipsilateral gracile nucleus after incision. Mechanical allodynia peaked on postoperative day 1, and COX-1 immunoreactivity increased on day 1, peaked on day 2, and declined thereafter. Ketorolac and SC-560 dose-dependently increased withdrawal threshold in this model, but NS-398 had no effect. These results suggest that COX-1 plays an important role in spinal cord pain processing and sensitization after surgery. Increased COX-1 activity could precede the up-regulation of COX-1 protein, and spinally administered specific COX-1 inhibitors may be useful to treat postoperative pain.

Plasticity in action of intrathecal clonidine to mechanical but not thermal nociception after peripheral nerve injury.

BACKGROUND: Intrathecal clonidine reduces tactile allodynia in animal models of neuropathic pain, and this effect is blocked by atropine. However, the role of tonic spinal cholinergic activity and its interaction with alpha2-adrenergic systems in normal and neuropathic conditions and to different sensory methods has not been systematically examined. The authors examined cholinergic receptor involvement in thermal and mechanical sensitivity in normal and neuropathic animals and its interaction with intrathecal clonidine. METHODS: Normal rats and rats that received L5/L6 spinal nerve ligation were tested with acute radiant heat, paw pressure, and punctate mechanical stimulation before and after the intrathecal administration of saline, the muscarinic receptor antagonist, atropine, or a toxin to destroy cholinergic neurons, and then after intrathecal clonidine. RESULTS: Atropine, the cholinergic neuronal toxin, and saline did not alter baseline withdrawal thresholds. In nerve-injured rats, neither saline nor atropine altered antinociception from clonidine to a thermal stimulus, but atropine reduced the effect of clonidine to von Frey filament withdrawal threshold (34 +/- 5.6 vs. 14 +/- 5.8 g [mean +/- SEM], saline vs. atropine; P < 0.05) and to withdrawal threshold to paw pressure after clonidine (174 +/- 18 g vs. 137 +/- 16 g, saline vs. atropine; P < 0.05). CONCLUSIONS: These data suggest that after nerve injury, mechanical but not thermal antinociception from intrathecal clonidine relies on a muscarinic interaction, because only mechanical antinociception was antagonized by atropine. These results do not favor a regulation of nociceptive transmission by a tonic release of acetylcholine in nerve-injured rats.

Spinal adrenergic and cholinergic receptor interactions activated by clonidine in postincisional pain.

BACKGROUND: Previous pharmacologic and molecular studies suggest that the alpha(2)-adrenoceptor subtype A is the target for spinally administered alpha(2)-adrenergic agonists, i.e., clonidine, for pain relief. However, intrathecally administered alpha(2) C antisense oligodeoxynucleotide was recently reported to decrease antinociception induced by clonidine in the rat, suggesting non-A sites may be important as well. The current study sought to determine the subtype of alpha(2) adrenoceptors activated by clonidine in a rodent model for human postoperative pain, and to examine its interaction with spinal cholinergic receptors. METHODS: Postoperative hypersensitivity was produced in rats by plantar incision of the hind paw and punctuate mechanical stimuli were applied around the wound 24 h after surgery. Effects of intrathecal clonidine and 2-(2,6-diethylphenylamino)-2-imidazoline (ST91) on withdrawal thresholds to the stimulus were determined. To examine the adrenoceptor subtype and its interaction with spinal cholinergic receptors, animals were intrathecally pretreated with vehicles BRL44408 (an alpha(2) A subtype-preferring antagonist), ARC239 (an alpha(2) non-A subtype-preferring antagonist), atropine (a muscarinic antagonist), and mecamylamine (a nicotinic antagonist). RESULTS: Intrathecal ST91 showed a significantly greater efficacy when compared with clonidine. The analgesic effect of clonidine was diminished by pretreatment with either adrenoceptor antagonist, whereas the effect of ST91 was solely blocked by ARC239 pretreatment. Atropine and mecamylamine abolished the effect of clonidine effect but not the effect of ST91. CONCLUSIONS: Both alpha(2) A and alpha(2) non-A adrenoceptors, as well as spinal cholinergic activation, are important to the antihypersensitivity effect of clonidine after surgery. ST91 is more efficacious in this model than clonidine and relies entirely on alpha(2) non-A adrenoceptors.

Allosteric adenosine receptor modulation reduces hypersensitivity following peripheral inflammation by a central mechanism.

Activation of adenosine A1 receptors by endogenous adenosine or synthetic agonists produces antinociception in animal models of acute pain and also reduces hypersensitivity in models of inflammatory and nerve-injury pain. Allosteric adenosine modulators facilitate and potentiate the action of adenosine agonists at the A1 receptors. The purpose of the current study was to examine the effect and site of action for an allosteric adenosine modulator, T62 [2-amino-3-(4-chlorobenzoyl)-5,6, 7,8-tetrahydrobenzothiophene], in rat models of acute pain and inflammation. Intrathecal (i.t.) T62 did not change the withdrawal latency or threshold of normal rats to acute heat or to acute paw pressure. In contrast, i.t. T62 reversed thermal hypersensitivity in carrageenin-inflamed rats. Subcutaneous (s.c.) injection of T62 into the inflamed paw had no such effect. To investigate a potential site of action on nociceptors, single-unit afferent activity to mechanical stimuli on A delta- and C-fibers was examined in normal or carrageenin-inflamed rats before and after intravenous (i.v.) T62 administration. Intravenous T62, 3 mg/kg, had no significant effect in either normal or inflamed conditions. These results support previous studies to suggest that adenosine receptor modulators lack efficacy to acute nociceptive stimuli in the normal condition, but reduce hypersensitivity during inflammation through a central mechanism.