Modulation of brain networks by sumatriptan-naproxen in the inflammatory soup migraine model

Where do we stand on fMRI in awake mice?

Imaging awake animals is quickly gaining traction in neuroscience as it offers a means to eliminate the confounding effects of anesthesia, difficulties of inter-species translation (when humans are typically imaged while awake), and the inability to investigate the full range of brain and behavioral states in unconscious animals. In this systematic review, we focus on the development of awake mouse blood oxygen level dependent functional magnetic resonance imaging (fMRI). Mice are widely used in research due to their fast-breeding cycle, genetic malleability, and low cost. Functional MRI yields whole-brain coverage and can be performed on both humans and animal models making it an ideal modality for comparing study findings across species. We provide an analysis of 30 articles (years 2011-2022) identified through a systematic literature search. Our conclusions include that head-posts are favorable, acclimation training for 10-14 d is likely ample under certain conditions, stress has been poorly characterized, and more standardization is needed to accelerate progress. For context, an overview of awake rat fMRI studies is also included. We make recommendations that will benefit a wide range of neuroscience applications.

Electroacupuncture at Fengchi(GB20) and Yanglingquan(GB34) Ameliorates Paralgesia through Microglia-Mediated Neuroinflammation in a Rat Model of Migraine

Background: Multiple studies have suggested that paralgesia (hyperalgesia and cutaneous allodynia) in migraine reflects the activation and sensitisation of the trigeminovascular system (TGVS). In particular, it reflects the second-order and higher nerve centre sensitisation, which is caused and maintained by neuroinflammation. Microglia activation leads to the release of proinflammatory cytokines involved in inflammatory responses. Accumulating evidence indicates that electroacupuncture (EA) is effective in ameliorating paralgesia, but the underlying mechanisms of EA in migraine attacks caused by microglia and microglia-mediated inflammatory responses are still unclear. The purpose of this study was to explore whether EA could ameliorate the dysregulation of pain sensation by suppressing microglial activation and the resulting neuroinflammatory response, and to evaluate whether this response was regulated by Toll-like receptor 4 (TLR4)/nuclear factor-kappa B(NF-κB) in the trigeminal nucleus caudalis (TNC) in a rat model of migraine. Methods: Repeated Inflammatory Soup (IS) was infused into the dura for seven sessions to establish a recurrent migraine-like rat model, and EA treatment was administered at Fengchi (GB20) and Yanglingquan (GB34) after daily IS infusion. Facial mechanical withdrawal thresholds were measured to evaluate the change in pain perception, and plasma samples and the TNC tissues of rats were collected to examine the changes in calcitonin gene-related peptide (CGRP), the Ibal-1-labelled microglial activation, and the resulting inflammatory response, including interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and their regulatory molecules TLR4/NF-κB, via enzyme-linked immunosorbent assay (ELISA), real-time polymerase chain reaction (RT-PCR), immunohistochemistry (IHC) and Western blot analysis. Results: Repeated IS injections into the dura induced facial mechanical paralgesia, which is the manifestation of migraine attacks, and increased the expression of CGRP, Ibal-1, microglial mediated inflammatory cytokines (IL-1β, TNF-α, IL-6), and regulatory molecules TLR4/NF-κB. EA at GB20/34 significantly attenuated repetitive IS-induced pain hypersensitivity. This effect was consistent with decreased levels of CGRP and inflammatory cytokines in the plasma and the TNC via the inhibition of microglia activation, and this response may be regulated by TLR4/NF-κB. Conclusions: EA ameliorated paralgesia in repetitive IS-induced migraine-like rats, which was mainly mediated by a reduction in microglial activation and microglial-mediated inflammatory responses that could be regulated by TLR4/NF-κB.

OnabotulinumtoxinA effects on trigeminal nociceptors

BACKGROUND

OnabotulinumtoxinA (onabotA) is approved globally for prevention of chronic migraine; however, the classical mechanism of action of onabotA in motor and autonomic neurons cannot fully explain the effectiveness of onabotulinumtoxinA in this sensory neurological disease. We sought to explore the direct effects of onabotulinumtoxinA on mouse trigeminal ganglion sensory neurons using an inflammatory soup-based model of sensitization.

METHODS

Primary cultured trigeminal ganglion neurons were pre-treated with inflammatory soup, then treated with onabotulinumtoxinA (2.75 pM). Treated neurons were used to examine transient receptor potential vanilloid subtype 1 and transient receptor potential ankyrin 1 cell-surface expression, calcium influx, and neuropeptide release.

RESULTS

We found that onabotulinumtoxinA cleaved synaptosomal-associated protein-25 kDa in cultured trigeminal ganglion neurons; synaptosomal-associated protein-25 kDa cleavage was enhanced by inflammatory soup pre-treatment, suggesting greater uptake of toxin under sensitized conditions. OnabotulinumtoxinA also prevented inflammatory soup-mediated increases in TRPV1 and TRPA1 cell-surface expression, without significantly altering TRPV1 or TRPA1 protein expression in unsensitized conditions. We observed similar inhibitory effects of onabotulinumtoxinA on TRP-mediated calcium influx and TRPV1- and TRPA1-mediated release of calcitonin gene-related peptide and prostaglandin 2 under sensitized, but not unsensitized control, conditions.

CONCLUSIONS

Our data deepen the understanding of the sensory mechanism of action of onabotulinumtoxinA and support the notion that, once endocytosed, the cytosolic light chain of onabotulinumtoxinA cleaves synaptosomal-associated protein-25 kDa to prevent soluble N-ethylmaleimide-sensitive factor attachment protein receptor-mediated processes more generally in motor, autonomic, and sensory neurons.

Estradiol Treatment Enhances Behavioral and Molecular Changes Induced by Repetitive Trigeminal Activation in a Rat Model of Migraine

A migraine is a neurological condition that can cause multiple symptoms. It is up to three times more common in women than men, thus, estrogen may play an important role in the appearance attacks. Its exact pathomechanism is still unknown; however, the activation and sensitization of the trigeminal system play an essential role. We aimed to use an animal model, which would better illustrate the process of repeated episodic migraine attacks to reveal possible new mechanisms of trigeminal pain chronification. Twenty male (M) and forty ovariectomized (OVX) female adult rats were used for our experiment. Male rats were divided into two groups (M + SIF, M + IS), while female rats were divided into four groups (OVX + SIF, OVX + IS, OVX + E2 + SIF, OVX + E2 + IS); half of the female rats received capsules filled with cholesterol (OVX + SIF, OVX + IS), while the other half received a 1:1 mixture of cholesterol and 17β-estradiol (OVX + E2 + SIF, OVX + E2 + IS). The animals received synthetic interstitial fluid (SIF) (M + SIF, OVX + SIF, OVX + E2 + SIF) or inflammatory soup (IS) (M + IS, OVX + IS, OVX + E2 + IS) treatment on the dural surface through a cannula for three consecutive days each week (12 times in total). Behavior tests and immunostainings were performed. After IS application, a significant decrease was observed in the pain threshold in the M + IS (0.001 < p < 0.5), OVX + IS (0.01 < p < 0.05), and OVX + E2 + IS (0.001 < p < 0.05) groups compared to the control groups (M + SIF; OVX + SIF, OVX + E2 + SIF). The locomotor activity of the rats was lower in the IS treated groups (M + IS, 0.01 < p < 0.05; OVX + IS, p < 0.05; OVX + E2 + IS, 0.001 < p < 0.05), and these animals spent more time in the dark room (M + IS, p < 0.05; OVX + IS, 0.01 < p < 0.05; OVX + E2 + IS, 0.001 < p < 0.01). We found a significant difference between M + IS and OVX + E2 + IS groups (p < 0.05) in the behavior tests. Furthermore, IS increased the area covered by calcitonin gene-related peptide (CGRP) immunoreactive (IR) fibers (M + IS, p < 0.01; OVX + IS, p < 0.01; OVX + E2 + IS, p < 0.001) and the number of neuronal nitric oxide synthase (nNOS) IR cells (M + IS, 0.001< p < 0.05; OVX + IS, 0.01 < p < 0.05; OVX + E2 + IS, 0.001 < p < 0.05) in the caudal trigeminal nucleus (TNC). There was no difference between M + IS and OVX + IS groups; however, the area was covered by CGRP IR fibers (0.01 < p < 0.05) and the number of nNOS IR cells was significantly higher in the OVX + E2 + IS (p < 0.05) group than the other two IS- (M + IS, OVX + IS) treated animals. Overall, repeated administration of IS triggers activation and sensitization processes and develops nociceptive behavior changes. CGRP and nNOS levels increased significantly in the TNC after IS treatments, and moreover, pain thresholds and locomotor activity decreased with the development of photophobia. In our model, stable high estradiol levels proved to be pronociceptive. Thus, repeated trigeminal activation causes marked behavioral changes, which is more prominent in rats treated with estradiol, also reflected by the expression of the sensitization markers of the trigeminal system.

Modification of the resting-state network involved at different stages of neuropathic pain

Neuropathic pain (NeuP) is shown to be associated with abnormal changes in several specific brain regions. However, the large-scale interactivity of neuronal networks underlying the sensory and emotional abnormalities during NeuP remains unexplored. The present study aimed to explore the alterations in the relevant functional resting-state networks (RSNs) and their intra-networks at the different stages of NeuP based on resting-state functional magnetic resonance imaging (rs-fMRI). A NeuP rat model was established by chronic constriction injury (CCI). Three RSNs were identified to be associated with the NeuP, including the default mode network (DMN), sensorimotor network (SMN), and interoceptive network (IN). The functional connectivity (FC) of the left caudate putamen (CPu) within the DMN and the right piriform cortex within the IN were significantly reduced at the early stage of NeuP, when the maximum allodynia was apparent early, which reflected the suppressed function of the DMN and IN. At 4 weeks post-CCI, when negative emotions were present, the FC of the right insular cortex in the SMN and left visual cortex in the IN were significantly elevated, representing the increased excitability of both SMN and IN. Our study revealed the characteristic functional organization at the network level induced by NeuP and emphasized the role of SMN, DMN, and IN in the pathological mechanisms of NeuP.

Could Experimental Inflammation Provide Better Understanding of Migraines?

Migraines constitute a common neurological and headache disorder affecting around 15% of the world’s population. In addition to other mechanisms, neurogenic neuroinflammation has been proposed to play a part in migraine chronification, which includes peripheral and central sensitization. There is therefore considerable evidence suggesting that inflammation in the intracranial meninges could be a key element in addition to calcitonin gene-related peptide (CGRP), leading to sensitization of trigeminal meningeal nociceptors in migraines. There are several studies that have utilized this approach, with a strong focus on using inflammatory animal models. Data from these studies show that the inflammatory process involves sensitization of trigeminovascular afferent nerve terminals. Further, by applying a wide range of different pharmacological interventions, insight has been gained on the pathways involved. Importantly, we discuss how animal models should be used with care and that it is important to evaluate outcomes in the light of migraine pathology.

Applications in Awake Animal Magnetic Resonance Imaging

There are numerous publications on methods and applications for awake functional MRI across different species, e.g., voles, rabbits, cats, dogs, and rhesus macaques. Each of these species, most obviously rhesus monkey, have general or unique attributes that provide a better understanding of the human condition. However, much of the work today is done on rodents. The growing number of small bore (≤30 cm) high field systems 7T- 11.7T favor the use of small animals. To that point, this review is primarily focused on rodents and their many applications in awake function MRI. Applications include, pharmacological MRI, drugs of abuse, sensory evoked stimuli, brain disorders, pain, social behavior, and fear.

Determining 5HT7R's Involvement in Modifying the Antihyperalgesic Effects of Electroacupuncture on Rats With Recurrent Migraine

Electroacupuncture (EA) is widely used in clinical practice to relieve migraine pain. 5-HT₇ receptor (5-HT₇R) has been reported to play an excitatory role in neuronal systems and regulate hyperalgesic pain and neurogenic inflammation. 5-HT₇R could influence phosphorylation of protein kinase A (PKA)- or extracellular signal-regulated kinase_{1 / 2} (ERK_{1 / 2})-mediated signaling pathways, which mediate sensitization of nociceptive neurons via interacting with cyclic adenosine monophosphate (cAMP). In this study, we evaluated the role of 5-HT₇R in the antihyperalgesic effects of EA and the underlying mechanism through regulation of PKA and ERK_{1 / 2} in trigeminal ganglion (TG) and trigeminal nucleus caudalis (TNC). Hyperalgesia was induced in rats with dural injection of inflammatory soup (IS) to cause meningeal neurogenic inflammatory pain. Electroacupuncture was applied for 15 min every other day before IS injection. Von Frey filaments, tail-flick, hot-plate, and cold-plated tests were used to evaluate the mechanical and thermal hyperalgesia. Neuronal hyperexcitability in TNC was studied by an electrophysiological technique. The 5-HT₇R antagonist (SB269970) or 5-HT₇R agonist (AS19) was administered intrathecally before each IS application at 2-day intervals during the 7-day injection protocol. The changes in 5-HT₇R and 5-HT₇R-associated signaling pathway were examined by real-time polymerase chain reaction (RT-PCR), Western blot, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA) analyses. When compared with IS group, mechanical and thermal pain thresholds of the IS + EA group were significantly increased. Furthermore, EA prevented the enhancement of both spontaneous activity and evoked responses of second-order trigeminovascular neurons in TNC. Remarkable decreases in 5-HT₇R mRNA expression and protein levels were detected in the IS + EA group. More importantly, 5-HT₇R agonist AS19 impaired the antihyperalgesic effects of EA on p-PKA and p-ERK_{1 / 2}. Injecting 5-HT₇R antagonist SB-269970 into the intrathecal space of IS rats mimicked the effects of EA antihyperalgesia and inhibited p-PKA and p-ERK_{1 / 2}. Our findings indicate that 5-HT₇R mediates the antihyperalgesic effects of EA on IS-induced migraine pain by regulating PKA and ERK_{1 / 2} in TG and TNC.