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The rostromedial tegmental nucleus: a key modulator of pain and opioid analgesia.

ABSTRACT: A recently defined structure, the rostromedial tegmental nucleus (RMTg; aka tail of the ventral tegmental area [VTA]), has been proposed as an inhibitory control center for dopaminergic activity of the VTA. This region is composed of GABAergic cells that send afferent projections to the ventral midbrain and synapse onto dopaminergic cells in the VTA and substantia nigra. These cells exhibit µ-opioid receptor immunoreactivity, and in vivo, ex vivo, and optogenetic/electrophysiological approaches demonstrate that morphine excites dopamine neurons by targeting receptors on GABAergic neurons localized in the RMTg. This suggests that the RMTg may be a key modulator of opioid effects and a major brake regulating VTA dopamine systems. However, no study has directly manipulated RMTg GABAergic neurons in vivo and assessed the effect on nociception or opioid analgesia. In this study, multiplexing of GABAergic neurons in the RMTg was achieved using stimulatory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) and inhibitory kappa-opioid receptor DREADDs (KORD). Our data show that locally infused RMTg morphine or selective RMTg GABAergic neuron inhibition produces 87% of the maximal antinociceptive effect of systemic morphine, and RMTg GABAergic neurons modulate dopamine release in the nucleus accumbens. In addition, chemoactivation of VTA dopamine neurons significantly reduced pain behaviors both in resting and facilitated pain states and reduced by 75% the dose of systemic morphine required to produce maximal antinociception. These results provide compelling evidence that RMTg GABAergic neurons are involved in processing of nociceptive information and are important mediators of opioid analgesia.

SUBMITTER: Taylor NE

PROVIDER: S-EPMC7343630 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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The rostromedial tegmental nucleus: a key modulator of pain and opioid analgesia.

Taylor Norman E NE Long Hu H Pei JunZhu J Kukutla Phanidhar P Phero Anthony A Hadaegh Farnaz F Abdelnabi Ahmed A Solt Ken K Brenner Gary J GJ

Pain 20191101 11

A recently defined structure, the rostromedial tegmental nucleus (RMTg; aka tail of the ventral tegmental area [VTA]), has been proposed as an inhibitory control center for dopaminergic activity of the VTA. This region is composed of GABAergic cells that send afferent projections to the ventral midbrain and synapse onto dopaminergic cells in the VTA and substantia nigra. These cells exhibit µ-opioid receptor immunoreactivity, and in vivo, ex vivo, and optogenetic/electrophysiological approaches ...[more]

PMID: 31246732

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Project description:BACKGROUND:This is an updated version of the original Cochrane review published in Issue 4, 2006. Patients may control postoperative pain by self administration of intravenous opioids using devices designed for this purpose (patient controlled analgesia or PCA). A 1992 meta-analysis by Ballantyne et al found a strong patient preference for PCA over non-patient controlled analgesia, but disclosed no differences in analgesic consumption or length of postoperative hospital stay. Although Ballantyne's meta-analysis found that PCA did have a small but statistically significant benefit upon pain intensity, a 2001 review by Walder et al did not find statistically significant differences in pain intensity or pain relief between PCA and groups treated with non-patient controlled analgesia. OBJECTIVES:To evaluate the efficacy and safety of patient controlled intravenous opioid analgesia (termed PCA in this review) versus non-patient controlled opioid analgesia of as-needed opioid analgesia for postoperative pain relief. SEARCH METHODS:We ran the search for the previous review in November 2004. For this update, we searched the Cochrane Central Register of Controlled Trials (CENTRAL 2014, Issue 12), MEDLINE (1966 to 28 January 2015), and EMBASE (1980 to 28 January 2015) for randomized controlled trials (RCTs) in any language, and reference lists of reviews and retrieved articles. SELECTION CRITERIA:We selected RCTs that assessed pain intensity as a primary or secondary outcome. These studies compared PCA without a continuous background infusion with non-patient controlled opioid analgesic regimens. We excluded studies that explicitly stated they involved patients with chronic pain. DATA COLLECTION AND ANALYSIS:Two review authors independently extracted data, which included demographic variables, type of surgery, interventions, efficacy, and adverse events. We graded each included study for methodological quality by assessing risk of bias and employed the GRADE approach to assess the overall quality of the evidence. We performed meta-analysis of outcomes that included pain intensity assessed by a 0 to 100 visual analog scale (VAS), opioid consumption, patient satisfaction, length of stay, and adverse events. MAIN RESULTS:Forty-nine studies with 1725 participants receiving PCA and 1687 participants assigned to a control group met the inclusion criteria. The original review included 55 studies with 2023 patients receiving PCA and 1838 patients assigned to a control group. There were fewer included studies in our updated review due to the revised exclusion criteria. For the primary outcome, participants receiving PCA had lower VAS pain intensity scores versus non-patient controlled analgesia over most time intervals, e.g., scores over 0 to 24 hours were nine points lower (95% confidence interval (CI) -13 to -5, moderate quality evidence) and over 0 to 48 hours were 10 points lower (95% CI -12 to -7, low quality evidence). Among the secondary outcomes, participants were more satisfied with PCA (81% versus 61%, P value = 0.002) and consumed higher amounts of opioids than controls (0 to 24 hours, 7 mg more of intravenous morphine equivalents, 95% CI 1 mg to 13 mg). Those receiving PCA had a higher incidence of pruritus (15% versus 8%, P value = 0.01) but had a similar incidence of other adverse events. There was no difference in the length of hospital stay. AUTHORS' CONCLUSIONS:Since the last version of this review, we have found new studies providing additional information. We reanalyzed the data but the results did not substantially alter any of our previously published conclusions. This review provides moderate to low quality evidence that PCA is an efficacious alternative to non-patient controlled systemic analgesia for postoperative pain control.

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The rostromedial tegmental nucleus: a key modulator of pain and opioid analgesia.

Publications

The rostromedial tegmental nucleus: a key modulator of pain and opioid analgesia.

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