Intrathecal adenosine analog administration reduces substance P in cerebrospinal fluid along with behavioral effects that suggest antinociception in rats

Caffeine and Primary (Migraine) Headaches-Friend or Foe?

Background: The actions of caffeine as an antagonist of adenosine receptors have been extensively studied, and there is no doubt that both daily and sporadic dietary consumption of caffeine has substantial biological effects on the nervous system. Caffeine influences headaches, the migraine syndrome in particular, but how is unclear. Materials and Methods: This is a narrative review based on selected articles from an extensive literature search. The aim of this study is to elucidate and discuss how caffeine may affect the migraine syndrome and discuss the potential pathophysiological pathways involved. Results: Whether caffeine has any significant analgesic and/or prophylactic effect in migraine remains elusive. Neither is it clear whether caffeine withdrawal is an important trigger for migraine. However, withdrawal after chronic exposure of caffeine may cause migraine-like headache and a syndrome similar to that experienced in the prodromal phase of migraine. Sensory hypersensitivity however, does not seem to be a part of the caffeine withdrawal syndrome. Whether it is among migraineurs is unknown. From a modern viewpoint, the traditional vascular explanation of the withdrawal headache is too simplistic and partly not conceivable. Peripheral mechanisms can hardly explain prodromal symptoms and non-headache withdrawal symptoms. Several lines of evidence point at the hypothalamus as a locus where pivotal actions take place. Conclusion: In general, chronic consumption of caffeine seems to increase the burden of migraine, but a protective effect as an acute treatment or in severely affected patients cannot be excluded. Future clinical trials should explore the relationship between caffeine withdrawal and migraine, and investigate the effects of long-term elimination.

Electroacupuncture inhibits visceral pain via adenosine receptors in mice with inflammatory bowel disease

To investigate the involvement of peripheral adenosine receptors in the effect of electroacupuncture (EA) on visceral pain in mice with inflammatory bowel disease (IBD). 2,4,6-Trinitrobenzene sulfonic acid (TNBS) was used to induce the visceral pain model. EA (1 mA, 2 Hz, 30 min) treatment was applied to bilateral acupoints "Dachangshu" (BL25) 1 day after TNBS injection once daily for 7 consecutive days. Von Frey filaments were used to measure the mechanical pain threshold. Western blot was used to detect the protein expression levels of adenosine 1 receptor (A1R), adenosine 2a receptor (A2aR), adenosine 2b receptor (A2bR), adenosine 3 receptor (A3R), substance P (SP), and interleukin 1 beta (IL-1β) in colon tissue. EA significantly ameliorated the disease-related indices and reduced the expression of SP and IL-1β in the colon tissues of mice with IBD. EA increased the expression of A1R, A2aR, and A3R and decreased the expression of A2bR in the colon tissue. Furthermore, the administration of adenosine receptor antagonists influenced the effect of EA. EA can inhibit the expression of the inflammatory factors SP and IL-1β by regulating peripheral A1, A2a, A2b, and A3 receptors, thus inhibiting visceral pain in IBD mice.

Adenosine for postoperative analgesia: A systematic review and meta-analysis

Purpose

Perioperative infusion of adenosine has been suggested to reduce the requirement for inhalation anesthetics, without causing serious adverse effects in humans. We conducted a meta-analysis of randomized controlled trials evaluating the effect of adenosine on postoperative analgesia.

Methods

We retrieved articles in computerized searches of Scopus, Web of Science, PubMed, EMBASE, and Cochrane Library databases, up to July 2016. We used adenosine, postoperative analgesia, and postoperative pain(s) as key words, with humans, RCT, and CCT as filters. Data of eligible studies were extracted, which included pain scores, cumulative opioid consumption, adverse reactions, and vital signs. Overall incidence rates, relative risk (RR), and 95% confidence intervals (CI) were calculated employing fixed-effects or random-effects models, depending on the heterogeneity of the included trials.

Results

In total, 757 patients from 9 studies were included. The overall effect of adenosine on postoperative VAS/VRS scores and postoperative opioid consumption was not significantly different from that of controls (P >0.1). The occurrence of PONV and pruritus was not statistically significantly different between an adenosine and nonremifentanil subgroup (P >0.1), but the rate of PONV occurrence was greater in the remifentanil subgroup (P <0.01). Time to first postoperative analgesic requirement in the adenosine group was not significantly difference from that of the saline group (SMD = 0.07, 95%CI: −0.28 to 0.41, P = 0.71); but this occurred significantly later than with remifentanil (SMD = 1.10, 95%CI: 2.48 to 4.06, P < 0.01). Time to hospital discharge was not significantly different between the control and adenosine groups (P = 0.78). The perioperative systolic blood pressure was significantly lower in the adenosine than in the control group in the mannitol subgroup (P < 0.01). The incidence of bradycardia, transient first- degree atrioventricular block, and tachycardia was not significantly different between the adenosine and control groups (P > 0.1).

Conclusion

Adenosine has no analgesic effect or prophylactic effect against PONV, but reduce systolic blood pressure and heart rates. Adenosine may benefit patients with hypertension, ischemic heart disease, and tachyarrhythmia, thereby improving cardiac function.

Ultrasound-guided continuous infraclavicular brachial plexus block using bupivacaine alone or combined with adenosine for pain control in upper limb surgery

Introduction:

The infraclavicular brachial plexus block (ICB) is designed to deposit anesthetic high in the plexus, achieving anesthesia of the hand, forearm, elbow, and distal arm. Adenosine is a metabolic intermediate that is involved in nearly all aspects of cell function, including neurotransmission and signal transduction.This study was aimed to show whether addition of adenosine to bupivacaine in ultrasound-guided ICB had an analgesic effect.

Methods:

Sixty adult patients were divided into two equal groups, each group included 30 patients. Group I received infraclavicular bupivacaine 0.325% in a volume of 30 ml. Group II received 30 ml of 0.325% bupivacaine + 12 mg adenosine. The block was maintained with an infusion of 10 ml/h. The following parameters were assessed: Success rate, time of the sensory onset, motor block, visual analog scale (VAS), and amount of i.v. pethidine needed.

Results:

This study showed an analgesic effect of infraclavicular adenosine as evidenced by a statistically significant shorter mean time of onset of the sensory block (16 vs. 20 min, P < 0.05), lower mean VAS score over 48 h (1.7 vs. 2.7, P < 0.05), longer mean time of first parenteral analgesic requirement (299 vs. 255 min, P < 0.05), and lower mean total dose of pethidine needed over 48 h after surgery (25.5 vs. 56.6 mg, P <0.05). All patients got successful infraclavicular block and recovered uneventfully without any sensory or motor deficit.

Conclusion:

Adenosine may provide valuable addition to the therapeutic options in anesthesia and pain management. Further research is required to figure out its exact role

Adenosine and ATP receptors

Adenosine and ATP, via P1 and P2 receptors respectively, can modulate pain transmission under physiological, inflammatory, and neuropathic pain conditions. Such influences reflect peripheral and central actions and effects on neurons as well as other cell types. In general, adenosine A1 receptors produce inhibitory effects on pain in a number of preclinical models and are a focus of attention. In humans, i.v. infusions of adenosine reduce some aspects of neuropathic pain and can reduce postoperative pain. For P2X receptors, there is a significant body of information indicating that inhibition of P2X3 receptors may be useful for relieving inflammatory and neuropathic pain. More recently, data have begun to emerge implicating P2X4, P2X7 and P2Y receptors in aspects of pain transmission. Both P1 and P2 receptors may represent novel targets for pain relief.

Roles of Adenosine Receptor Subtypes in the Antinociceptive Effect of Intrathecal Adenosine in a Rat Formalin Test

The contributions of adenosine receptor subtypes to antinociception produced by adenosine were determined at the spinal level. There are 4 types of adenosine receptors, namely A1, A(2A), A(2B) and A3. The authors investigated the properties of the subtypes of spinal adenosine receptors in terms of nociceptive modulation. The nociceptive state was induced by subcutaneously injecting formalin solution (5%, 50 microl) into the hind paws of male Sprague-Dawley rats. After observing the effect of intrathecal adenosine during the formalin test, the effects of intrathecal adenosine A1 (CPT), A(2A) (CSC), A(2B) (alloxazine) and A3 (MRS 1220) receptor antagonists on the action of adenosine were examined. Intrathecal adenosine inhibited phase 2 flinching response without affecting phase 1 response. CPT, CSC, alloxazine and MRS 1220 antagonized the antinociceptive action of adenosine during phase 2 of the formalin test. These results suggest that spinal adenosine A1, A(2A), A(2B) and A3 receptors may play an important role in the antinociception of adenosine in the formalin-induced facilitated state.

Evaluation of interaction between intrathecal adenosine and MK801 or NBQX in a rat formalin pain model

Adenosine and excitatory amino acids have been known to be involved in modulating nociceptive transmission at the spinal level. The authors assessed the characteristics of the interaction of the adenosine-excitatory amino acid antagonist combinations in the spinal cord of rats on the formalin-induced nociception. Intrathecal NMDA antagonist ((5R, 10S)-(+)-5-methyl-10,11-dihydro-(5)H-dibenzo[a[,]d]cyclohepten-5,10-imine hydrogen maleate, MK801, 30 microg) and AMPA antagonist (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[F]quinoxaline-7-sulfonamide, NBQX, 3 microg) decreased the total number of flinches during both phases in the formalin test. Intrathecal adenosine (300 microg) had little effect on the phase 1 flinching response, but decreased the phase 2 response. The fixed dose analysis and the isobolographic analysis revealed that adenosine interacts additively with MK801 and NBQX in the spinal cord.

Analysis of Interactions between Serotonin and Gabapentin or Adenosine in the Spinal Cord of Rats

We evaluated the nature of the pharmacologic interaction after concurrent administration of 5-HT-gabapentin and 5-HT-adenosine at the spinal level. Intrathecal catheters were placed in the subarachnoid space of male Sprague-Dawley rats. Nociception was induced by subcutaneous injection of formalin solution (5%, 50 microl) into the hind paw. A fixed dose analysis and an isobolographic analysis were used to determine the properties of interaction. Intrathecal 5-HT dose-dependently suppressed the flinching response during phase 1 of the formalin test, while neither gabapentin nor adenosine affected the phase-1 flinching response. All three intrathecal drugs attenuated the phase-2 flinching response in a dose-dependent manner. The intrathecal combination of 5-HT with a fixed dose of gabapentin or adenosine in phase 1 had little effect or increased the antinociception of 5-HT alone. Isobolographic analysis in phase 2 revealed an additive or a synergistic interaction after intrathecal delivery of 5-HT-gabapentin or 5-HT-adenosine mixture. Taken together, the combination of 5-HT with either gabapentin or adenosine may offer a potential remedy in the treatment of the facilitated state as well as acute pain in the spinal cord.

Interaction between intrathecal gabapentin and adenosine in the formalin test of rats

Spinal gabapentin and adenosine have been known to display an antinociceptive effect. We evaluated the nature of the interaction between gabapentin and adenosine in formalin-induced nociception at the spinal level. Male Sprague-Dawley rats were prepared for intrathecal catheterization. Pain was evoked by injection of formalin solution (5%, 50 microL) into the hindpaw. After examination of the effects of gabapentin and adenosine, the resulting interaction was investigated with isobolographic and fractional analyses. Neither gabapentin nor adenosine affected motor function. Gabapentin or adenosine decreased the sum of the number of flinches during phase 2, but not during phase 1 in the formalin test. Isobolographic analysis, in phase 2, revealed an additive interaction between gabapentin and adenosine. Taken together, intrathecal gabapentin and adenosine attenuated the facilitated state and interacted additively with each other.

Intrathecal adenosine A1 receptor agonist attenuates hyperalgesia without inhibiting spinal glutamate release in the rat

The analgesia effects of intrathecal adenosine A1 receptor agonist, R-PIA, on the hyperalgesia and CSF-glutamate release after formalin injection into the rat paw were evaluated. R-PIA significantly and dose-dependently attenuated increases in flinching behavior, and this attenuating effect was reversed by the adenosine A1 receptor antagonist, aminophylline. Morphine blocked flinchs, however MK-801 partially abolished. The increase in CSF-glutamate release evoked by formalin stimulation was inhibited by morphine but not by either R-PIA or MK-801. These findings suggest that the intrathecal adenosine A1 receptor agonist provokes analgesic effect via the postsynaptic action independent of an effect upon spinal glutamate release.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.