Activation of spinal dorsal horn astrocytes by noxious stimuli involves descending noradrenergic signaling

Curcuma latifolia Roscoe extract reverses inflammatory pain in mice and offers a favorable CNS safety profile

ETHNOPHARMACOLOGICAL RELEVANCE

Curcuma latifolia Roscoe, a plant in the Curcuma genus, has been used as a food additive and folk medicine in Thailand to treat pelvic pain and improve premenstrual syndrome. Although it has been used for centuries, no scientific studies have proved its potential effects on inflammatory pain and central nervous system (CNS) safety profiles.

AIM OF THE STUDY

This study aimed to evaluate the potential effects of the ethanolic extract of C. latifolia rhizome on inflammatory pain in mice, together with its CNS safety profiles.

MATERIALS AND METHODS

First, network pharmacology was employed to identify the role of bioactive constituents in C. latifolia on inflammatory pain. In addition, in vitro pharmacology was also evaluated to confirm the anti-inflammatory activity of C. latifolia extract at cellular levels in activated macrophages and microglia. Furthermore, the efficacy of the plant extract in attenuating formalin-induced pain-like behaviors in mice was evaluated. Mice were orally administered the extract (125, 250, 500 mg/kg) followed by the measurement of formalin-induced pain-like behaviors. The LABORAS automated behavioral analysis and rotarod test were used to assess potential CNS side effects of C. latifolia extract (500 mg/kg) in mice.

RESULTS

The results demonstrated that major bioactive constituents present in C. latifolia have the ability to regulate multiple targets, biological processes and pathways associated with inflammatory pain as assessed by network pharmacology. C. latifolia modulated peripheral and central immune cells via reducing proinflammatory mediators (NO, TNF-α, and IL-6). C. latifolia extract improved formalin-induced pain-like behaviors in a dose-dependent manner during phase II of the formalin test. The efficacy of the plant extract at doses of 250 and 500 mg/kg was comparable to that of the positive control (indomethacin 10 mg/kg). Furthermore, the highest therapeutic dose of the extract did not affect motor coordination, exploratory behaviors, general behaviors, and overall well-being of mice, indicating no development of potential CNS adverse effects after administration of the extract.

CONCLUSION

These findings provide novel perspectives on using C. latifolia extract for pain management, considering its therapeutic efficacy and CNS safety.

Microglia and Astrocytes in Amyotrophic Lateral Sclerosis: Disease-Associated States, Pathological Roles, and Therapeutic Potential

Microglial and astrocytic reactivity is a prominent feature of amyotrophic lateral sclerosis (ALS). Microglia and astrocytes have been increasingly appreciated to play pivotal roles in disease pathogenesis. These cells can adopt distinct states characterized by a specific molecular profile or function depending on the different contexts of development, health, aging, and disease. Accumulating evidence from ALS rodent and cell models has demonstrated neuroprotective and neurotoxic functions from microglia and astrocytes. In this review, we focused on the recent advancements of knowledge in microglial and astrocytic states and nomenclature, the landmark discoveries demonstrating a clear contribution of microglia and astrocytes to ALS pathogenesis, and novel therapeutic candidates leveraging these cells that are currently undergoing clinical trials.

Spinal cord astrocytes regulate myocardial ischemia-reperfusion injury

Astrocytes play a key role in the response to injury and noxious stimuli, but its role in myocardial ischemia-reperfusion (I/R) injury remains largely unknown. Here we determined whether manipulation of spinal astrocyte activity affected myocardial I/R injury and the underlying mechanisms. By ligating the left coronary artery to establish an in vivo I/R rat model, we observed a 1.7-fold rise in glial fibrillary acidic protein (GFAP) protein level in spinal cord following myocardial I/R injury. Inhibition of spinal astrocytes by intrathecal injection of fluoro-citrate, an astrocyte inhibitor, decreased GFAP immunostaining and reduced infarct size by 29% relative to the I/R group. Using a Designer Receptor Exclusively Activated by Designer Drugs (DREADD) chemogenetic approach, we bi-directionally manipulated astrocyte activity employing GFAP promoter-driven Gq- or Gi-coupled signaling. The Gq-DREADD-mediated activation of spinal astrocytes caused transient receptor potential vanilloid 1 (TRPV1) activation and neuropeptide release leading to a 1.3-fold increase in infarct size, 1.2-fold rise in serum norepinephrine level and higher arrhythmia score relative to I/R group. In contrast, Gi-DREADD-mediated inhibition of spinal astrocytes suppressed TRPV1-mediated nociceptive signaling, resulting in 35% reduction of infarct size and 51% reduction of arrhythmia score from I/R group, as well as lowering serum norepinephrine level from 3158 ± 108 to 2047 ± 95 pg/mL. Further, intrathecal administration of TRPV1 or neuropeptide antagonists reduced infarct size and serum norepinephrine level. These findings demonstrate a functional role of spinal astrocytes in myocardial I/R injury and provide a novel potential therapeutic approach targeting spinal cord astrocytes for the prevention of cardiac injury.

Batatasin III, a Constituent of Dendrobium scabrilingue, Improves Murine Pain-like Behaviors with a Favorable CNS Safety Profile

Batatasin III is a stilbenoid compound present in a wide variety of Dendrobium species. Although the pharmacological efficacy of batatasin III has been reported in several disease models, its antinociceptive efficacy and central nervous system (CNS) side effects remain unknown. Thus, this study examined the effects of batatasin III on pain-like behaviors in mouse models of formalin- and lipopolysaccharide (LPS)-induced inflammatory pain. The results revealed a significant antinociceptive effect of batatasin III in both models, as 50 mg/kg batatasin III elicited comparable antinociception as 10 mg/kg indomethacin. Further, the anti-inflammatory effect of batatasin III was assessed in LPS-induced RAW 264.7 macrophages and BV-2 microglial cells. The compound significantly reduced the levels of inflammatory mediators (nitric oxide, TNF-α, and IL-6) in LPS-stimulated cells in a concentration-dependent manner. Following efficacy evaluations, the potential CNS side effects of batatasin III were evaluated using the rotarod test and the Laboratory Animal Behavior Observation, Registration, and Analysis System. Batatasin III-treated mice exhibited comparable forced, spontaneous, and general locomotive behaviors to vehicle-treated mice, indicating no potential CNS side effects. Overall, this study demonstrated the preclinical antinociceptive efficacy and CNS safety of batatasin III, suggesting its potential role in the development of new analgesics.

Activation of locus coeruleus-spinal cord noradrenergic neurons alleviates neuropathic pain in mice via reducing neuroinflammation from astrocytes and microglia in spinal dorsal horn

Background

The noradrenergic neurons of locus coeruleus (LC) project to the spinal dorsal horn (SDH), and release norepinephrine (NE) to inhibit pain transmission. However, its effect on pathological pain and the cellular mechanism in the SDH remains unclear. This study aimed to explore the analgesic effects and the anti-neuroinflammation mechanism of LC-spinal cord noradrenergic pathway (LC:SC) in neuropathic pain (NP) mice with sciatic chronic constriction injury.

Methods

The Designer Receptors Exclusively Activated by Designer Drugs (DREADD) was used to selectively activate LC:SC. Noradrenergic neuron-specific retro–adeno-associated virus was injected to the spinal cord. Pain threshold, LC and wide dynamic range (WDR) neuron firing, neuroinflammation (microglia and astrocyte activation, cytokine expression), and α2AR expression in SDH were evaluated.

Results

Activation of LC:SC with DREADD increased the mechanical and thermal nociceptive thresholds and reduced the WDR neuron firing. LC:SC activation (daily, 7 days) downregulated TNF-α and IL-1β expression, upregulated IL-4 and IL-10 expression in SDH, and inhibited microglia and astrocytes activation in NP mice. Immunofluorescence double staining confirmed that LC:SC activation decreased the expression of cytokines in microglia of the SDH. In addition, the effects of LC:SC activation could be reversed by intrathecal injection of yohimbine. Immunofluorescence of SDH showed that NE receptor α2B-AR was highly expressed in microglia in CCI mice.

Conclusion

These findings indicate that selective activation of LC:SC alleviates NP in mice by increasing the release of NE and reducing neuroinflammation of astrocytes and microglia in SDH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02489-9.

Spinally projecting noradrenergic neurons of the locus coeruleus display resistance to AAV2retro-mediated transduction

BACKGROUND

The locus coeruleus (LC) is the principal source of noradrenaline (NA) in the central nervous system. Projection neurons in the ventral portion of the LC project to the spinal cord and are considered the main source of spinal NA. To understand the precise physiology of this pathway, it is important to have tools that allow specific genetic access to these descending projections. AAV2retro serotype vectors are a potential tool to transduce these neurons via their axon terminals in the spinal cord, and thereby limit the expression of genetic material to the spinal projections from the LC. Here, we assess the suitability of AAV2retro to target these neurons and investigate strategies to increase their labelling efficiency.

RESULTS

We show that the neurons in the LC that project to the spinal dorsal horn are largely resistant to transduction with AAV2retro serotype vectors. Compared to Cholera toxin B (CTb) tracing, AAV2retro.eGFP labelled far fewer neurons within the LC and surrounding regions, particularly within neurons that express tyrosine hydroxylase (TH), the rate-limiting enzyme for NA synthesis. We also show that the sensitivity for transduction of this projection can be increased using AAV2retro.eGFP.cre in ROSA26^tdTom reporter mice (23% increase), with a higher proportion of the newly revealed neurons expressing TH compared to those directly labelled with AAV2retro containing an eGFP expression sequence.

CONCLUSION

These tracing studies identify limitations in AAV2retro-mediated retrograde transduction of a subset of projection neurons, specifically those that express NA and project to the spinal cord. This is likely to have implications for the study of NA-containing projections as well as other types of projection neuron in the central nervous system.