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Lumbosacral-bulbo-spinal loop relayed by RVM on-cells regulates visceral nociception and modulates inhibitory effects of pregabalin and ondansetron
Sikandar S, Dickenson AH (2008) Lumbosacral-bulbo-spinal loop relayed by RVM on-cells regulates visceral nociception and modulates inhibitory effects of pregabalin and ondansetron. Neuroscience 2008 Abstracts 269.4/GG19. Society for Neuroscience, Washington, DC.
Summary: Descending controls from brainstem nuclei including the rostral ventromedial medulla (RVM) have been shown to play an important role in visceral pain, and compounds modulating serotonergic receptor activity and compounds targeting the α2δ subunit of voltage-gated calcium channels have demonstrated clinical efficacy in providing symptomatic relief in patients with visceral hyperalgesia. We investigated the role of RVM on-cells and a serotonergic lumbosacral-bulbo-spinal loop in visceral hyperalgesia and examined the antihyperalgesic effects of ondansetron and pregabalin in modifying visceral pain responses to colorectal distension (CRD) in rats. An in vivo model of visceral pain was established involving CRD and a reliable EMG recording protocol for measuring activity in the external oblique muscle following CRD for quantifying evoked visceromotor responses (VMR) in Sprague-Dawley rats. Changes in VMR evoked by CRD in a range of 10-80 mmHg were recorded following administration of ondansetron (50 μg/kg i.t.) and pregabalin (30 mg/kg s.c.) in naïve rats and rats pretreated with 0.25% intracolonic mustard oil (MO) to induce colonic hyperalgesia. Moreover, RVM on-cells were selectively ablated with injection of the neurotoxin saporin conjugated to the μ-receptor agonist dermorphin (DermSAP) using stereotaxic techniques. Twenty-eight days post-injection, the VMR were compared between naïve, SAP and Derm-SAP rats in control conditions and following intracolonic MO. CRD produced graded VMR responses that were facilitated by intracolonic MO. Both ondansetron and pregabalin were shown to effectively reduce evoked VMR to CRD in naïve rats and MO pretreated rats by antagonizing spinal 5-HT3 receptors and by binding to the α2δ subunit of voltage-gated calcium channels, respectively. Moreover, DermSAP pretreatment was shown to reduce overall evoked VMR, and the antihyperalgesic efficacies of ondansetron and pregabalin were also shown to be modified by the loss of on-cells in DermSAP rats. Furthermore, we verified immunohistochemically RVM on-cell ablation in DermSAP rats and quantified RVM 5-HT cell intensity between naïve, SAP and DermSAP rats. This study illustrates the role of 5-HT3-mediated descending facilitatory controls in visceral pain as well as providing evidence for the antihyperalgesic efficacy of the second generation α2δ ligand pregabalin in the CRD model. Moreover, evidence is provided for a facilitatory serotonergic lumbosacral-bulbo-spinal loop relayed by RVM on-cells that is evoked by CRD and modulates efficacies of pregabalin and ondansetron.
Related Products: Dermorphin-SAP / MOR-SAP (Cat. #IT-12)
A brainstem generator for cutaneous allodynia associated with migraine headache
Edelmayer RM, Vanderah TW, Majuta L, Fioravanti B, De Felice M, Chichorro JG, Ossipov MH, King T,Lai J, Kori SH, Nelsen AC, Cannon KE, Heinricher MM, Porreca F (2008) A brainstem generator for cutaneous allodynia associated with migraine headache. Neuroscience 2008 Abstracts 171.15/LL16. Society for Neuroscience, Washington, DC.
Summary: Migraine patients often demonstrate cutaneous allodynia that begins unilaterally and intracranially and spreads, via unknown mechanisms, to contralateral and extracranial body regions. As cutaneous allodynia likely reflects the development of central sensitization, we hypothesized that descending facilitatory influences from the rostral ventromedial medulla (RVM) might underlie the generalized expression of this phenomenon. We employed a modified model of application of inflammatory mediators (IM) to the dura of unanesthetized animals and explored the possible requirement of a brainstem site for expression of generalized cutaneous allodynia. Rats were surgically implanted with two cannulas, one of which permitted the application of IM to the surface of the dura and the other for administration of compounds to the RVM, 7 days after surgery. Tactile withdrawal thresholds of the peri-ocular region of the face as well as the hindpaws were tested pre-surgery, post-surgery, and up to 6 hr after application of IM. Bupivacaine or YM022 (CCK2 receptor antagonist) were administered to the RVM at various times after IM. In some studies dermorphin-saporin was administered as a single microinjection to elicit a cytotoxic effect on presumed pain facilitation cells in the RVM; these rats were tested with IM after a further 28 days. Recordings of RVM “ON” and “OFF” cell activity were also performed in separate groups of naïve animals prior to, and after, IM application to the dura. Dural IM produced robust facial and hindpaw allodynia which peaked after approximately 3 hr and recovered to baseline thresholds by approximately 6 hr. RVM bupivacaine, YMO22, or cytotoxic destruction of pain facilitation cells had no effects on sensory thresholds alone, but prevented or significantly attenuated the expression of IM-induced cutaneous allodynia. In addition, IM applied to the dura produced a sustained increase in the discharge of RVM ON cells while transiently inhibiting OFF cells. Facial and hindpaw allodynia associated with dural stimulation may be a useful surrogate of migraine-associated pain which may be exploited mechanistically for the development of novel therapeutic strategies. The data demonstrate the requirement of descending facilitation from the RVM for the expression of cranial and extracranial cutaneous hypersensitivity and offer direct evidence of brainstem involvement in cutaneous allodynia associated with headache pain.
Related Products: CCK-SAP (Cat. #IT-31)
Descending facilitation from the brainstem determines behavioural and neuronal hypersensitivity following nerve injury and efficacy of pregabalin.
Bee LA, Dickenson AH (2008) Descending facilitation from the brainstem determines behavioural and neuronal hypersensitivity following nerve injury and efficacy of pregabalin. Pain 140:209-223. doi: 10.1016/j.pain.2008.08.008
Summary: Rostral ventromedial medulla (RVM) facilitatory On cells are thought to be involved in the mechanisms that control chronic pain. Dermorphin-SAP (Cat. #IT-12, 3 pmol injected into the RVM of rats) was used to examine how mu-opioid receptor expressing facilitatory cells fit into this circuit. Saporin (Cat. #PR-01) was used as a control. The results show that activity in the RVM may influence the outcome of nerve injury.
Related Products: Dermorphin-SAP / MOR-SAP (Cat. #IT-12), Saporin (Cat. #PR-01)
The p75 receptor is associated with inflammatory thermal hypersensitivity.
Watanabe T, Ito T, Inoue G, Ohtori S, Kitajo K, Doya H, Takahashi K, Yamashita T (2008) The p75 receptor is associated with inflammatory thermal hypersensitivity. J Neurosci Res 86:3566-3574. doi: 10.1002/jnr.21808 PMID: 18709654
Summary: Inflammation, which can lead to pain hypersensitivity, not only elevates NGF levels, but also can increase the sensitivity of high-threshold receptors. NGF is thought to be a major contributor to heightened pain states due to inflammation, and in this work the authors investigated the role that the p75 neurotrophin receptor might play in NGF-induced hyperalgesia. 30 minutes prior to injection with Freund’s adjuvant, mice received 10 μl of polyclonal anti-p75 (Cat. #AB-N01) into the plantar surface of the paw. The antibody administration blocked hyperalgesia, indicating that p75 plays an important role in inflammation-induced hyperalgesia.
Related Products: NGFr (mu p75) Rabbit Polyclonal (Cat. #AB-N01)
The neonatal injury-induced spinal learning deficit in adult rats: central mechanisms.
Young EE, Baumbauer KM, Hillyer JE, Patterson AM, Hoy KC, Jr., Mintz EM, Joynes RL (2008) The neonatal injury-induced spinal learning deficit in adult rats: central mechanisms. Behav Neurosci 122:589-600. doi: 10.1037/0735-7044.122.3.589
Summary: This report examined whether neonatal injuries had any contralateral effects in adult life, and evaluated the role of the NK1 receptor of adult animals that had been subjected to neonatal trauma. Rats were injected with 5 µl of SP-SAP (Cat. #IT-07, 30 ng/µl, 100 ng/µl, or 300 ng/µl) into the intrathecal space. Blank-SAP (Cat. #IT-21) was used as a control. The results indicate both that injury effects are isolated in the injured limb, and NK1 receptor-expressing cells are involved in processing this pain.
Related Products: SP-SAP (Cat. #IT-07), Blank-SAP (Cat. #IT-21)
Involvement of the basal cholinergic forebrain in the mediation of general (propofol) anesthesia.
Laalou FZ, de Vasconcelos AP, Oberling P, Jeltsch H, Cassel JC, Pain L (2008) Involvement of the basal cholinergic forebrain in the mediation of general (propofol) anesthesia. Anesthesiology 108:888-896. doi: 10.1097/ALN.0b013e31816d919b
Summary: The authors examined whether the basal forebrain cholinergic system is involved in mediating the effects of general anesthesia. Three different forms of 192-IgG-SAP (Cat. #IT-01) administration were used: intracerebroventricular injection of 2 µg, 0.4 µg injected into the nucleus basalis magnocellularis, and 0.8 µg into the medial septum/vertical diagonal band of Broca. The results suggest that loss of cholinergic neurons in the cortex and hippocampus leads to potentiation of the anesthetic effects of Propofol.
Related Products: 192-IgG-SAP (Cat. #IT-01)
Substance P receptor-expressing dorsal horn neurons: Lessons from the targeted cytotoxin, substance P-saporin.
Wiley RG (2008) Substance P receptor-expressing dorsal horn neurons: Lessons from the targeted cytotoxin, substance P-saporin. Pain 136:7-10. doi: 10.1016/j.pain.2008.03.010
Summary: This review covers some of the more recent work utilizing SP-SAP (Cat. #IT-07) and SSP-SAP (Cat. #IT-11) in the dorsal horn. Specific answers to experimental questions are discussed, as well as some of the questions generated by the research. The potential of SP-SAP and SSP-SAP as pain therapeutics is also explored, along with potential clinical applications of other targeted toxins in pain therapy.
Related Products: SP-SAP (Cat. #IT-07), SSP-SAP (Cat. #IT-11)
Oxaliplatin acts on IB4-positive nociceptors to induce an oxidative stress-dependent acute painful peripheral neuropathy.
Joseph EK, Chen X, Bogen O, Levine JD (2008) Oxaliplatin acts on IB4-positive nociceptors to induce an oxidative stress-dependent acute painful peripheral neuropathy. J Pain 9:463-472. doi: 10.1016/j.jpain.2008.01.335
Summary: Oxaliplatin is a platinum-based chemotherapy agent. Use of this reagent produces various pathological pain states, depending on the dosage site. The authors administered 3.2-µg intrathecal injections of IB4-SAP (Cat. #IT-10), using saporin (Cat. #PR-01) as a control. Lesioning IB4-binding neurons in the dorsal horn completely prevented oxaliplatin-induced hyperalgesia, indicating that the IB4-positive nociceptor neuronal subset is crucial to this type of neuropathy.
Related Products: Saporin (Cat. #PR-01), IB4-SAP (Cat. #IT-10)
Spinal mu-opioid receptor-expressing dorsal horn neurons: role in nociception and morphine antinociception.
Kline IV RH, Wiley RG (2008) Spinal mu-opioid receptor-expressing dorsal horn neurons: role in nociception and morphine antinociception. J Neurosci 28:904-913. doi: 10.1523/JNEUROSCI.4452-07.2008
Summary: The authors used Dermorphin-SAP (Cat. #IT-12) to investigate the function of spinal cord mu-opioid receptor (MOR)-expressing dorsal horn neurons in nociception and morphine analgesia. Rats were treated with 500 ng intrathecal injections of Dermorphin-SAP; 500 ng of Blank-SAP (Cat. #IT-21), and up to 1 µg of Saporin (Cat. #PR-01) were used as controls. The data indicate that MOR-expressing dorsal horn neurons are necessary for morphine action and play a role in nocifensive responses to persistent pain in the formalin test.
Related Products: Dermorphin-SAP / MOR-SAP (Cat. #IT-12), Blank-SAP (Cat. #IT-21), Saporin (Cat. #PR-01)
Lesioning mu opioid receptor-containing neurons in the ventrolateral periaqueductal gray attenuates morphine analgesia in male but not female rats
Loyd DR, Murphy AZ (2007) Lesioning mu opioid receptor-containing neurons in the ventrolateral periaqueductal gray attenuates morphine analgesia in male but not female rats. Neuroscience 2007 Abstracts 921.4/NN15. Society for Neuroscience, San Diego, CA.
Summary: Chronic pain will affect four out of five persons at some point across the lifespan. While the opioid-based narcotic morphine is the most prevalent treatment for chronic pain in clinical settings, it is becoming increasingly clear that morphine produces a significantly greater degree of analgesia in males compared to females. In both somatic and visceral pain models, the ED50 for morphine is generally two-fold higher for females than for males. The midbrain periaqueductal gray (PAG) and its descending projections to the rostral ventromedial medulla (RVM) is the primary circuit for opioid-based analgesia. We have recently shown that the PAG-RVM pathway is sexually dimorphic both in its anatomical organization and in its activation during persistent pain. Interestingly, while female rats have a greater number of PAG neurons that project to the RVM, inflammatory pain activates these cells to a greater degree in males. Additionally, systemic morphine inhibits the pain-induced activation of PAG neurons in males, but not females. Sex differences in neuronal activity during pain and morphine analgesia are prominent in the ventrolateral PAG, a region containing a large population of mu opioid receptor-containing neurons. We have recently shown that females have significantly lower levels of mu opioid receptors (MOR) in this region, however it is not known whether sex differences in MOR expression contribute to our observed sex differences in morphine analgesia. To test the role of ventrolateral PAG MOR in morphine analgesia, the cytotoxin saporin conjugated to the MOR agonist dermorphin (Der-Sap) was injected into the ventrolateral PAG to site-specifically lesion MOR-containing neurons. Twenty-eight days later, rats received an intraplantar injection of CFA to induce persistent pain and twenty-four hours later morphine was administered systemically using a cumulative dosing paradigm (1.8 -18mg/kg). Lesions of PAG MOR-containing neurons resulted in a two-fold rightward shift in morphine ED50 values in male rats compared to controls. Interestingly, in females no difference was noted in morphine ED50 for Der-Sap treated females versus controls suggesting that the PAG is not a critical site for morphine analgesia in females. Der-Sap treatment had no significant impact on baseline paw withdrawal latencies or CFA-induced hyperalgesia. These results indicate that the PAG is a primary locus for systemic morphine analgesia in males only and suggests the necessity for the development of sex-specific treatments for persistent pain in females.
Related Products: Dermorphin-SAP / MOR-SAP (Cat. #IT-12)