Excitatory Effects of Calcitonin Gene-Related Peptide (CGRP) on Superficial Sp5C Neurons in Mouse Medullary Slices

Calcitonin gene-related peptide (CGRP) exerts membrane, cellular and synaptic actions on serotonergic dorsal raphe neurons ex vivo: Functional implications for a role in dorsal raphe-controlled functions

Serotonin (5-HT) plays a role in limbic-controlled behaviors and is implicated in migraine, which is often co-morbid with cognitive-based affective disorders. The neuropeptide calcitonin gene-related peptide (CGRP) regulates vascular tone. Serotonin-acting drugs and CGRP receptor antagonists have proved therapeutic in management of migraine. Clinical interactions between the two systems have been shown, however, whether CGRP exerts direct actions on serotonergic Dorsal Raphe (DR) neurons is unknown. To fully understand the role of CGRP in control of behavior and to predict how CGRP targeted therapies (i.e. CGRP receptor antagonists) could alter DR neuronal activity, investigation of whether CGRP can directly affect 5-HT DR activity was conducted. Patch clamp electrophysiology and single photon calcium imaging in DR brain slices revealed that CGRP (10-6 M) elicited postsynaptically mediated, potassium-involved outward currents in the majority of 5-HT DR cells. Miniature excitatory synaptic events were reduced in frequency. Further, intracellular calcium was reduced in the majority of neurons, which did not involve actions on the L-type calcium channel. The CGRP agonist SAX replicated effects on the membrane and intracellular calcium. In contrast, the CGRP receptor antagonist MK-3207 blocked the effects on outward current and attenuated the action of CGRP on reducing intracellular calcium. Despite inhibitory membrane and synaptic effects, no change was noted in firing rate. Our findings raise the intriguing possibility that the CGRP system plays a role in mediating limbic-controlled behaviors, at least in part, through direct actions on serotonergic DR neurons, however the effect of CGRP on DR 5-HT output remains to be investigated.

Transcutaneous occipital nerve stimulation alleviated migraine related pain by regulating synaptic plasticity and CGRP expression in the periaqueductal gray of male rats

BACKGROUND

Clinical observations have shown that transcutaneous occipital nerve stimulation (tONS) is effective in treating migraine. However, the underlying mechanisms are poorly understood. This study employs a rodent model to investigate the therapeutic effects of tONS on migraine-related pain and to explore potential mechanisms.

METHODS

The SD rats were used to establish the migraine model by repeated epidural infusions of inflammatory soup (IS). Modified bilateral electrodes were attached noninvasively for tONS treatments. Periorbital mechanical thresholds were assessed using von-Frey filaments, and other pain-related nociceptive behaviors were analyzed through video recordings. The expressions of c-Fos, synaptophysin (Syp) and calcitonin gene-related peptide (CGRP) in the trigeminal nucleus caudalis (TNC) and/or periaqueductal gray (PAG) area were measured by immunofluorescence and western blotting analyses. The excitatory synaptic transmission in the PAG was detected by whole-cell patch-clamp recording among migraine rats.

RESULTS

The reduction in periorbital mechanical thresholds induced by repeated IS infusions was partially reversed by tONS treatments in migraine rats. Other pain-related behaviors, including exploration, rest, and unilateral grooming, consistently improved following tONS treatment. The TNC and PAG area were activated after IS modeling, and the CGRP expressions in the PAG significantly decreased after tONS treatments. tONS could inhibit the enhanced excitatory synaptic transmission in the PAG of migraine rats.

CONCLUSIONS

Our findings suggest that tONS has therapeutic potential in treating migraine, with the PAG excitability and CGRP expression playing a role in its mechanisms of action. tONS may represent a promising non-invasive neuromodulation approach for the management of migraine in the future.

Generation of human region-specific brain organoids with medullary spinal trigeminal nuclei

Brain organoids with nucleus-specific identities provide unique platforms for studying human brain development and diseases at a finer resolution. Despite its essential role in vital body functions, the medulla of the hindbrain has seen a lack of in vitro models, let alone models resembling specific medullary nuclei, including the crucial spinal trigeminal nucleus (SpV) that relays peripheral sensory signals to the thalamus. Here, we report a method to differentiate human pluripotent stem cells into region-specific brain organoids resembling the dorsal domain of the medullary hindbrain. Importantly, organoids specifically recapitulated the development of the SpV derived from the dorsal medulla. We also developed an organoid system to create the trigeminothalamic projections between the SpV and the thalamus by fusing these organoids, namely human medullary SpV-like organoids (hmSpVOs), with organoids representing the thalamus (hThOs). Our study provides a platform for understanding SpV development, nucleus-based circuit organization, and related disorders in the human brain.

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

Serum CGRP in migraine patients using erenumab as preventive treatment

Aim

Serum levels of Calcitonin Gene-Related Peptide (CGRP)-like immunoreactivity (CGRP-LI) in migraine patients before and after starting treatment with erenumab were measured to evaluate the association with clinical treatment response.

Methods

Blood samples were collected from the cubital fossa before (T0) and 2–4 weeks after (T1) starting treatment with erenumab. Clinical response was monitored using a daily headache e-diary. Serum levels of CGRP-LI, assessed using radioimmunoassay, were compared between T0 and T1, correcting for migraine reduction. In addition, for both T0 and T1, linear regression models were constructed using migraine reduction as outcome and serum CGRP-LI as independent variable, corrected for age, gender and monthly migraine days (MMD) at baseline.

Results

Serum CGRP-LI did not differ between T0 and T1 (p = 0.30). However, there was an interaction between time and reduction in MMD (p = 0.01). Absolute reduction in MMD in the third month after treatment with erenumab was associated with serum CGRP-LI at T1, 2–4 weeks after starting treatment with erenumab (p = 0.003), but not with serum CGRP-LI at T0 (p = 0.24).

Conclusion

Lower serum CGRP-LI 2–4 weeks after starting treatment with erenumab was associated with a higher reduction in migraine days after three months of treatment. Although the underlying mechanisms remain to be determined, this suggests that changes in CGRP levels, shortly after starting erenumab, are important for its clinical effect.

• Lower serum levels of calcitonin gene-related peptide (CGRP)-like immunoreactivity (CGRP-LI) in migraine patients at 2–4 weeks after starting treatment with erenumab were associated with better treatment response after three months.

• Early changes in serum CGRP may be important for the clinical effect of erenumab in migraine.

Modulation of Glia Activation by TRPA1 Antagonism in Preclinical Models of Migraine

Preclinical data point to the contribution of transient receptor potential ankyrin 1 (TRPA1) channels to the complex mechanisms underlying migraine pain. TRPA1 channels are expressed in primary sensory neurons, as well as in glial cells, and they can be activated/sensitized by inflammatory mediators. The aim of this study was to investigate the relationship between TRPA1 channels and glial activation in the modulation of trigeminal hyperalgesia in preclinical models of migraine based on acute and chronic nitroglycerin challenges. Rats were treated with ADM_12 (TRPA1 antagonist) and then underwent an orofacial formalin test to assess trigeminal hyperalgesia. mRNA levels of pro- and anti-inflammatory cytokines, calcitonin gene-related peptide (CGRP) and glia cell activation were evaluated in the Medulla oblongata and in the trigeminal ganglia. In the nitroglycerin-treated rats, ADM_12 showed an antihyperalgesic effect in both acute and chronic models, and it counteracted the changes in CGRP and cytokine gene expression. In the acute nitroglycerin model, ADM_12 reduced nitroglycerin-induced increase in microglial and astroglial activation in trigeminal nucleus caudalis area. In the chronic model, we detected a nitroglycerin-induced activation of satellite glial cells in the trigeminal ganglia that was inhibited by ADM_12. These findings show that TRPA1 antagonism reverts experimentally induced hyperalgesia in acute and chronic models of migraine and prevents multiple changes in inflammatory pathways by modulating glial activation.

From spreading depolarization to epilepsy with neuroinflammation: The role of CGRP in cortex

CGRP release plays a major role in migraine pain by activating the trigeminal pain pathways. Here we explored putative additional effects of CGRP on cortical circuits and investigated whether CGRP affects cortical excitability, cortical spreading depolarization (CSD), a phenomenon associated with migraine aura, blood-brain-barrier (BBB) and microglial morphology. We used immunohistochemistry to localize CGRP and the CGRP receptor (CGRP-R) in native cortex and evaluated morphology of microglia and integrity of the BBB after exposure to CGRP. In anesthetized rats we applied CGRP and the CGRP-R antagonist BIBN4096BS locally to the exposed cortex and monitored the spontaneous electrocorticogram and CSDs evoked by remote KCl pressure microinjection. In mouse brain slices CGRP effects on neuronal activity were explored by multielectrode array. CGRP immunoreactivity was detectable in intracortical vessels, and all cortical neurons showed CGRP-R immunoreactivity. In rat cortex in vivo, topical CGRP induced periods of epileptiform discharges, however, also dose-dependently reduced CSD amplitudes and propagation velocity. BIBN4096BS prevented these effects. CGRP evoked synchronized bursting activity in mouse cortical but not in cerebellar slices. Topical application of CGRP to rat cortex induced plasma extravasation and this was associated with reduced ramification of microglial cells. From these findings we conclude that CGRP induces a pathophysiological state in the cortex, consisting in neuronal hyperexcitability and neuroinflammation Thus, CGRP may have a pronounced impact on brain functions during migraine episodes supporting the benefit of CGRP antagonists for clinical use. However, increased cortical CGRP may end the CSD-induced aura phase of migraine.

The Anti-CGRP Antibody Fremanezumab Lowers CGRP Release from Rat Dura Mater and Meningeal Blood Flow

Monoclonal antibodies directed against the neuropeptide calcitonin gene-related peptide (CGRP) belong to a new generation of therapeutics that are effective in the prevention of migraine. CGRP, a potent vasodilator, is strongly implicated in the pathophysiology of migraine, but its role remains to be fully elucidated. The hemisected rat head preparation and laser Doppler flowmetry were used to examine the effects on CGRP release from the dura mater and meningeal blood flow of the subcutaneously injected anti-CGRP monoclonal antibody fremanezumab at 30 mg/kg, when compared to an isotype control antibody. Some rats were administered glycerol trinitrate (GTN) intraperitoneally to produce a migraine-like sensitized state. When compared to the control antibody, the fremanezumab injection was followed by reduced basal and capsaicin-evoked CGRP release from day 3 up to 30 days. The difference was enhanced after 4 h of GTN application. The samples from the female rats showed a higher CGRP release compared to that of the males. The increases in meningeal blood flow induced by acrolein (100 µM) and capsaicin (100 nM) were reduced 13–20 days after the fremanezumab injection, and the direct vasoconstrictor effect of high capsaicin (10 µM) was intensified. In conclusion, fremanezumab lowers the CGRP release and lasts up to four weeks, thereby lowering the CGRP-dependent meningeal blood flow. The antibody may not only prevent the released CGRP from binding but may also influence the CGRP release stimulated by noxious agents relevant for the generation of migraine pain.

Effects of Calcitonin-Gene-Related-Peptide on Auditory Nerve Activity

Calcitonin-gene-related peptide (CGRP) is a lateral olivocochlear (LOC) efferent neurotransmitter. Depression of sound-driven auditory brainstem response amplitude in CGRP-null mice suggests the potential for endogenous CGRP release to upregulate spontaneous and/or sound-driven auditory nerve (AN) activity. We chronically infused CGRP into the guinea pig cochlea and evaluated changes in AN activity as well as outer hair cell (OHC) function. The amplitude of both round window noise (a measure of ensemble spontaneous activity) and the synchronous whole-nerve response to sound (compound action potential, CAP) were enhanced. Lack of change in both onset adaptation and steady state amplitude of sound-evoked distortion product otoacoustic emission (DPOAE) responses indicated CGRP had no effect on OHCs, suggesting the origin of the observed changes was neural. Combined with results from the CGRP-null mice, these results appear to confirm that endogenous CGRP enhances auditory nerve activity when released by the LOC neurons. However, infusion of the CGRP receptor antagonist CGRP (8–37) did not reliably influence spontaneous or sound-driven AN activity, or OHC function, results that contrast with the decreased ABR amplitude measured in CGRP-null mice.