Migraine-relevant sex-dependent activation of mouse meningeal afferents by TRPM3 agonists

Background Migraine is a common brain disorder that predominantly affects women. Migraine pain seems mediated by the activation of mechanosensitive channels in meningeal afferents. Given the role of transient receptor potential melastatin 3 (TRPM3) channels in mechanical activation, as well as hormonal regulation, these channels may play a role in the sex difference in migraine. Therefore, we investigated whether nociceptive firing induced by TRPM3 channel agonists in meningeal afferents was different between male and female mice. In addition, we assessed the relative contribution of mechanosensitive TRPM3 channels and that of mechanosensitive Piezo1 channels and transient receptor potential vanilloid 1 (TRPV1) channels to nociceptive firing relevant to migraine in both sexes. Methods Ten- to 13-week-old male and female wildtype (WT) C57BL/6 J mice were used. Nociceptive spikes were recorded directly from nerve terminals in the meninges in the hemiskull preparations. Results Selective agonists of TRPM3 channels profoundly activated peripheral trigeminal nerve fibres in mouse meninges. A sex difference was observed for nociceptive firing induced by either PregS or CIM0216, both agonists of TRPM3 channels, with the induced firing being particularly prominent for female mice. Application of Yoda1, an agonist of Piezo1 channels, or capsaicin activating TRPV1 channels, although also leading to increased nociceptive firing of meningeal fibres, did not reveal a sex difference. Cluster analyses of spike activities indicated a massive and long-lasting activation of TRPM3 channels with preferential induction of large-amplitude spikes in female mice. Additional spectral analysis revealed ​a dominant contribution of spiking activity in the α- and β-ranges following TRPM3 agonists in female mice. Conclusions Together, we revealed a specific mechanosensitive profile of nociceptive firing in females and suggest TRPM3 channels as a potential novel candidate for the generation of migraine pain, with particular relevance to females.

Noninvasive Near-Infrared Light Triggers Remote Activation of Thermo-Responsive TRPV1 Channels in Neurons Based on Biodegradable/Photothermal Polymer Micelles

In this study, we developed a novel biodegradable/photothermal polymer micelle-based remote-activation method for a temperature-sensitive ion channel, namely transient receptor potential cation channel subfamily V member 1 (TRPV1). Biodegradable/photothermal polymer...

Capsaicin and TRPV1 Channels in the Cardiovascular System: The Role of Inflammation

Capsaicin is a potent agonist of the Transient Receptor Potential Vanilloid type 1 (TRPV1) channel and is a common component found in the fruits of the genus Capsicum plants, which have been known to humanity and consumed in food for approximately 7000–9000 years. The fruits of Capsicum plants, such as chili pepper, have been long recognized for their high nutritional value. Additionally, capsaicin itself has been proposed to exhibit vasodilatory, antimicrobial, anti-cancer, and antinociceptive properties. However, a growing body of evidence reveals a vasoconstrictory potential of capsaicin acting via the vascular TRPV1 channel and suggests that unnecessary high consumption of capsaicin may cause severe consequences, including vasospasm and myocardial infarction in people with underlying inflammatory conditions. This review focuses on vascular TRPV1 channels that are endogenously expressed in both vascular smooth muscle and endothelial cells and emphasizes the role of inflammation in sensitizing the TRPV1 channel to capsaicin activation. Tilting the balance between the beneficial vasodilatory action of capsaicin and its unwanted vasoconstrictive effects may precipitate adverse outcomes such as vasospasm and myocardial infarction, especially in the presence of proinflammatory mediators.

A Comparison Study of the Effect on IBS-D Rats among Ginger-Partitioned Moxibustion, Mild Moxibustion, and Laser Moxibustion

Background. Diarrhea-predominant irritable bowel syndrome (IBS-D) is a functional gastrointestinal disorder that severely affects patients’ life. Moxibustion is believed to be an effective way to treat IBS-D. However, the therapeutic effects and the underlying mechanisms in symptom management of IBS-D by different moxibustion therapies remain unclear. Methods. IBS-D model rats were divided into groups and treated with ginger-partitioned moxibustion (GPM), mild moxibustion (MM), and laser moxibustion (LM) at a temperature of 43°C, respectively. The temperature curves of acupoints were recorded during interventions. The therapeutic effects were evaluated on the basis of general condition, stool, and hematoxylin-eosin staining of the colon tissue. Moreover, the expression of transient receptor potential vanilloid 1 (TRPV1) receptors in both acupoint tissue and colon tissue was analyzed by immunohistochemistry. Results. After moxibustion treatment, the symptoms were improved. The expression of TRPV1 was increased in acupoint tissue and decreased in colon tissue. GPM and MM showed a more significant influence on IBS-D rats compared with LM. The temperature profile of GPM and MM was wave-like, while LM had an almost stable temperature curve. Conclusion. GPM, MM, and LM could improve the symptoms in IBS-D rats. Moxibustion might activate TRPV1 channels in the acupoint tissue and induce acupoint functions, which in turn inhibit the pathological activation state of the colon’s TRPV1, followed by improvements in abdominal pain and diarrheal symptoms. LM with stable temperature might lead to the desensitization of TRPV1 receptors and the tolerance of acupoint. GPM and MM provided dynamic and repetitive thermal stimulations that perhaps induced acupoint sensitization to increase efficacy. Therefore, dynamic and repetitive thermal stimulation is recommended in the application of moxibustion.

Use of capsaicin as a model in the study of migraine: a literature review

Capsaicin is able to induce mast cell degranulation, an event probably related to the pathophysiologyof a migraine attack. The present review study aimed to address the mechanisms of action of capsaicin and other chemical inducers in mast cell degranulation and an interaction of nerves and events that happen in the dura mater with the activation of mast cells. A survey was carried out in the literature, from 1980 to 2019, in different databases, using the following terms: capsaicin, mast cell and dura mater. 36 articles were selected for this review. Studies indicate that the main mechanisms of action of capsaicin are chemical induction through the activation of TRPV1 channels,allowing calcium influx into neurons in the trigeminal ganglion of the dura mater, activating mast cell degranulation, releasing pro-inflammatory (e.g., histamine, oxide nitric) and vasoactive (e.g., CGRP and substance P) substances. Therefore, the use of capsaicin may be a tool to be used in an animal model to better understand the pathophysiology of migraine.

Abstract MP45: Deletion Of The Transient Receptor Vanilloid-1 (TRPV1) Channel In Rats Attenuates 2 Kidney 1 Clip Hypertension

Renal denervation lowers arterial blood pressure (ABP) in both clinical populations and multiple experimental models of hypertension. This therapeutic effect is partly attributed to the removal of overactive renal sensory nerves that increase sympathetic efferent activity and ABP. Renal sensory nerves highly express TRPV1 channels, and administration of the TRPV1 agonist capsaicin increases renal sensory nerve activity. However, the extent by which TRPV1 channels directly contribute to renal nerve dependent models of hypertension has not been tested. To test this hypothesis, we generated a novel TRPV1 -/- rat using CRISPR/Cas9 and deletion of exon 3. Male and female TRPV1 -/- and wild-type littermates (8-12 weeks) were instrumented with telemetry. At 2 weeks later, renovascular hypertension via renal stenosis was produced by placement of a PTFE cuff (0.16 x 0.22 inches, 1mm long) around the right renal artery. Male TRPV1 -/- and wild-type rats had no differences in baseline mean ABP (99±2 vs 98±3 mmHg, respectively; n=7-9) or heart rate (390±7 vs 400±8 bpm, respectively). Renal stenosis significantly increased mean ABP in both groups; however, mean ABP was significantly lower at Day 28 in male TRPV1 -/- versus wild-type rats (125±8 vs 155±2 mmHg, respectively: P<0.01). Ganglionic blockade with chlorisondamine (2.5mg/kg, sc) at Day 28 produced a smaller fall in mean ABP of male TRPV1 -/- versus wild-type rats (-53±4 vs -86±3 mmHg, respectively; P<0.001). On the other hand, female TRPV1 -/- and wild-type rats had no differences in baseline mean ABP (102±2 vs 104±1 mmHg, respectively; n=6-9) or heart rate (419±8 vs 410±7 bpm, respectively). Renal stenosis significantly increased mean ABP in both groups; however, there were no differences at Day 28 between female TRPV1 -/- versus wild-type rats (117±8 vs 122±6 mmHg, respectively). Moreover, the increase in mean ABP was smaller in females versus males. The ganglionic blocker chlorisondamine produced similar depressor responses in female TRPV1 -/- versus wild-type rats (-64±7 vs -65±7 mmHg, respectively). These findings illustrate a sex difference in renovascular hypertension in rats, but importantly indicate that TRPV1 channels contribute to the established phase of renovascular hypertension in male rats.

Abstract MP48: Crispr/cas9 Trpv1 Deletion In Rats Does Not Impair Mechano- And Chemo-sensory Renal Afferent Nerve Responses

Elevated renal afferent nerve activity (ARNA) or dysfunctional renal reflexes contributes to hypertension and chronic kidney disease. The transient receptor potential vanilloid type-1 (TRPV1) channel is expressed in renal sensory nerves, and intrarenal administration of the TRPV1 agonist capsaicin increases ARNA. Nonselective denervation of renal sensory nerves using high-concentration capsaicin reduces arterial blood pressure (ABP) in experimental models of hypertension. However, the role of TRPV1 channels in ARNA responses to chemo- and mechano-sensitive stimuli has not been directly tested. To test this hypothesis, we generated a novel TRPV1 rat knockout model (TRPV1 -/- ) using CRISPR/CAS9 to delete exon 3 . ARNA multifiber recordings were performed in male and female TRPV1 -/- and wild-type littermates (250-400g) after decerebration or Inactin anesthesia (data combined). Wild-type and TRPV1 -/- rats had no significant differences in baseline mean ABP (126±4 mmHg vs 138±5 mmHg, respectively; n=8-10) or heart rate (451±25 bpm vs 432±24 bpm, respectively; n=8-10). Baseline ARNA was not different between wild-type and TRPV1 -/- rats (16±3 Hz vs 28±6 Hz, respectively; n=8-10). Intrarenal artery infusion of the TRPV1 agonist capsaicin (0.1-10μM, 50μL per 15s) significantly increased ipsilateral ARNA in wild-type but not TRPV1 -/- rats (Δ discharge with 10μM: 65±3 Hz vs 6±1 Hz, respectively; n=5-7). As a second chemosensitive stimulus, intrarenal artery infusion of bradykinin (0.1-10μM, 50μL per 15s) produced similar increases in ipsilateral ARNA between wild-type and TRPV1 -/- rats (Δ discharge with 10μM: 52±6 Hz vs 73±18 Hz, respectively; n=5-6). Finally, elevated renal pelvic pressures (0-20mmHg; 30s) significantly increased ipsilateral ARNA in both wild-type and TRPV1 -/- rats; however, the ARNA response was significantly greater in TRPV1 -/- versus wild-type rats (Δ discharge with 20mmHg: 47±14 Hz versus 18±6 Hz, respectively; n=5-8). In conclusion, mechanosensitive and chemosensitive ARNA responses remain intact in TRPV1 -/- rats. The mechanisms responsible for renal sensory nerve activation remain unidentified and the impact of TRPV1 deletion in rat models of hypertension and kidney disease remains to be tested.

Abstract P197: Increased Serotonin In Visceral Adipose Tissue May Contribute To Stimulate Sensory Neurons Mediating Obesity Hypertension In Mice Exposed To Early Life Stress

Male C57BL/6J mice exposed to maternal separation and early weaning (MSEW), a mouse model of early life stress, display increased blood pressure (BP) and sympathetic activation compared to obese controls when fed a high fat diet (HF). Moreover, HF-fed MSEW males display exacerbated BP responses to the acute stimulation of the adipose afferent reflex (AAR) in epididymal white adipose tissue (eWAT). The aim of this study was to investigate the contribution of endogenous factors that could stimulate fat sensory neurons. MSEW and control (C) mice (n=8/group) were placed on a LF or HF (10% and 60% Kcal from fat, respectively) for 16 weeks. Then, serum obtained by decapitation and adipose tissue samples were collected to measure mRNA and protein expression of 15 factors and receptors known to activate sensory neurons. No differences were found across measurements on LF. Plasma AGT and AngII were decreased in HF-fed MSEW compared to C (AGT: 760±48 vs. 1267±161 ng/ml, p<0.05; AngII; 413±57 vs. 1082±340 pmol/l, p<0.07, Attoquant) and no differences were found in leptin (103±6 vs. 104±4 ng/ml, p<0.87). In eWAT, MSEW and C showed similar AGT (2.1±0.4 vs. 1.9±0.3 ng/ml per g tissue), AngII (1.7±0.2 vs. 2.3±0.5 pg AngII/mg tissue), ACE 1 activity (21.5±1.2 vs. 20.0±0.9 RFU/min/μg protein, p<0.33) and leptin (102.8±6.1 vs. 104.5±6.8 ng/mg of tissue, p<0.87). However, HF-fed MSEW showed increased eWAT mRNA expression of tryptophan hydroxylase 1 (Tph1), the rate limiting enzyme in serotonin (5-HT) synthesis (10.2±2.9 vs. 1.6±0.3 2 -ΔΔct , p<0.03). SERT-Tph1-MAO signaling pathway protein expression was activated, and fat serotonin concentration was also increased in eWAT from obese MSEW mice compared to C (16.58±1.5 vs. 8.5±2.1 ug/mg of tissue, p<0.01). Acute stimulation of eWAT with serotonin (10-6 M, 4 sites, 2 ul/site) tend to increase pressor response in MSEW mice (p<0.066, n=2-3). Unlike in female MSEW mice, our study demonstrates that MSEW does not increase circulating and tissue AGT, Ang II and leptin in male mice. Taken together, these data suggest that increased local serotonin could be endogenously sensitizing the sensory neurons in obese MSEW mice contributing to chronic AAR stimulation, directly via TRPV1 channels, or indirectly, via acid-sensing ion channels.