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Cortical spreading depression (CSD) is a wave of transient network hyperexcitability leading to long lasting depolarization and block of firing, which initiates focally and slowly propagates in the cerebral cortex. It causes migraine aura and it has been implicated in the generation of migraine headache. Cortical excitability can be modulated by cholinergic actions, leading in neocortical slices to the generation of rhythmic synchronous activities (UP/DOWN states). We investigated the effect of cholinergic activation with the cholinomimetic agonist carbachol on CSD triggered with 130 mM KCl pulse injections in acute mouse neocortical brain slices, hypothesizing that the cholinergic-induced increase of cortical network excitability during UP states could facilitate CSD. We observed instead an inhibitory effect of cholinergic activation on both initiation and propagation of CSD, through the action of muscarinic receptors. In fact, carbachol-induced CSD inhibition was blocked by atropine or by the preferential M1 muscarinic antagonist telenzepine; the preferential M1 muscarinic agonist McN-A-343 inhibited CSD similarly to carbachol, and its effect was blocked by telenzepine. Recordings of spontaneous excitatory and inhibitory post-synaptic currents in pyramidal neurons showed that McN-A-343 induced overall a decrease of the excitatory/inhibitory ratio. This inhibitory action may be targeted for novel pharmacological approaches in the treatment of migraine with muscarinic agonists.
Learn More >Alleviating chronic pain is challenging, due to lack of drugs that effectively inhibit nociceptors without off target effects on motor or central neurons. Dorsal root ganglia (DRG) contain nociceptive and non-nociceptive neurons. Drug screening on cultured DRG neurons, rather than cell lines, allows the identification of drugs most potent on nociceptors with no effects on non-nociceptors (as a proxy for unwanted side effects on CNS and motor neurons). However, screening using DRG neurons is currently a low-throughput process and there is a need for assays to speed this process for analgesic drug discovery. We previously showed that veratridine elicits distinct response profiles in sensory neurons. Here we show evidence that a veratridine-based calcium assay allows an unbiased and efficient assessment of a drug effect on nociceptors (targeted neurons) and non-nociceptors (non-targeted neurons). We confirmed the link between the oscillatory profile and nociceptors; and the slow-decay profile and non-nociceptors using three transgenic mouse lines of known pain phenotypes. We used the assay to show that blockers for Nav1.7 and Nav1.8 channels, which are validated targets for analgesics, affect non-nociceptors at concentrations needed to effectively inhibit nociceptors. However, a combination of low doses of both blockers had an additive effect on nociceptors without a significant effect on non-nociceptors, indicating that the assay can also be used to screen for combinations of existing or novel drugs for the greatest selective inhibition of nociceptors.
Learn More >The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are voltage-gated ion channels that critically modulate neuronal activity. Four HCN subunits () have been cloned, each having a unique expression profile and distinctive effects on neuronal excitability within the brain. Consistent with this, the expression and function of these subunits are altered in diverse ways in neurological disorders. Here, we review current knowledge on the structure and distribution of the individual HCN channel isoforms, their effects on neuronal activity under physiological conditions, and how their expression and function are altered in neurological disorders, particularly epilepsy, neuropathic pain, and affective disorders. We discuss the suitability of HCN channels as therapeutic targets and how drugs might be strategically designed to specifically act on particular isoforms. We conclude that medicines that target individual HCN isoforms and/or their auxiliary subunit, TRIP8b, may provide valuable means of treating distinct neurological conditions.
Learn More >In the present study, we examined whether LDK1258, which produces strong CB receptor allosteric effects in in vitro assays, would elicit in vivo effects consistent with allosteric activity. In initial studies, LDK1258 reduced food consumption and elicited delayed antinociceptive effects in the chronic constrictive injury of the sciatic nerve (CCI) model of neuropathic pain, which unexpectedly emerged 4 h post-injection. UPLC-MS/MS analysis quantified significant levels of LDK1258 in both blood and brain tissue at 30 min post-administration that remained stable up to 4 h. The observation that LDK1258 also produced respective antinociceptive and anorectic effects in rimonabant-treated wild type mice and CB (-/-) mice suggests an off-target mechanism of action. Likewise, LDK1258 produced a partial array of common cannabimimetic effects in the tetrad assay, which were not CB receptor mediated. Additionally, LDK1258 did not substitute for the CB receptor orthosteric agonists CP55,940 or anandamide in the drug discrimination paradigm. In other in vivo assays sensitive to CB receptor allosteric modulators, LDK1258 failed to shift the dose-response curves of either CP55,940 or anandamide in producing thermal antinociception, catalepsy, or hypothermia, and did not alter the generalization curve of either drug in the drug discrimination assay. Thus, this battery of tests yielded results demonstrating that LDK1258 produces antinociceptive effects in the CCI model of neuropathic pain, anorectic effects, and other in vivo pharmacological effects in a manner inconsistent with CB receptor allosterism. More generally, this study offers a straightforward screening assay to determine whether newly synthesized CB receptor allosteric modulators translate to the whole animal.
Learn More >This study investigated the safety and efficacy of mirogabalin, a novel, potent, selective ligand of the α2δ subunit of voltage-dependent Ca channels, for the treatment of postherpetic neuralgia (PHN). In this multicenter, double-blind, placebo-controlled phase 3 study, Asian patients ≥20 years with PHN were randomized 2:1:1:1 to placebo or mirogabalin 15, 20, or 30 mg/day for up to 14 weeks (NCT02318719). The primary efficacy endpoint was the change from baseline in average daily pain score at week 14, defined as a weekly average of daily pain (0 = "no pain" to 10 = "worst possible pain," for the last 24 hours). Of 765 patients randomized, 763 received ≥ 1 dose of the study drug and were included in the analysis; 303, 152, 153, and 155 received placebo, mirogabalin 15, 20, or 30 mg/day, respectively. A total of 671 (87.7%) patients completed the study. At week 14, the difference in average daily pain score least squares mean vs placebo was -0.41, -0.47, and -0.77, respectively; all mirogabalin groups showed statistical significance. The most common treatment-emergent adverse events were somnolence, nasopharyngitis, dizziness, weight increase, and edema, and all of them were mild or moderate in severity. Mirogabalin was superior to placebo in all groups for relieving PHN and appeared well tolerated.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.
Learn More >Orofacial pain is characterized by its easy spread to adjacent areas, thus presenting with primary hyperalgesia (hypersensitivity at the site of injury) and secondary hyperalgesia (extra-territorial hypersensitivity outside the injured zone). However, the mechanisms behind the secondary hyperalgesia are poorly understood. In the present study, we used a mouse model of partial transection of the infraorbital nerve (pT-ION) to study whether calcium channel subunit α2δ1 (Cavα2δ1) and its downstream signaling contributes to the development of secondary hyperalgesia in the orofacial area. pT-ION caused primary (V2 skin) and secondary (V3 skin) hyperalgesia, which was reversed by the Cavα2δ1 antagonist gabapentin and by the expression of Cavα2δ1-targeting interfering RNA in trigeminal ganglion (TG)-V3 neurons. pT-ION induced increased expression of PKC and TRPA1, which was reversed by Cavα2δ1-targeting interfering RNA, and PKC inhibition reversed the upregulation of TRPA1 and gap junction (GJ) proteins induced by pT-ION. Cavα2δ1 overexpression in TG-V2 neurons induced the upregulation of PKC, TRPA1, and the GJ proteins in the TG and trigeminal subnucleus caudalis and induced hypersensitivity in the V3 skin area, which was reversed by TRPA1, GJ, or PKC blockade. Thus, we conclude that Cavα2δ1 contributes to the development of secondary hyperalgesia through its downstream PKC-TRPA1/GJ signaling pathways. Perspective: This study demonstrates that the activation of Cavα2δ1 and the downstream PKC-TRPA1/GJ signaling pathway contributes greatly to trigeminal nerve injury-induced secondary mechanical and cold hyperalgesia. This suggests that inhibitors of Cavα2δ1, TRPA1, or GJs might be effective treatments for nerve injury-induced spreading of orofacial pain.
Learn More >The aim of this study was to examine the inhibitory effect of teriparatide (TPTD) on pain and on bone loss in ovariectomized (OVX) mice. The mechanism of osteoporotic pain in OVX mice was evaluated through an examination of pain-related behavior as well as immunohistochemical examinations.
Learn More >The anti-seizure racetams may provide novel molecular insights into neuropathic pain due to their unique mechanism involving synaptic vesicle glycoprotein 2A (SV2A). Anti-allodynic effects of levetiracetam (LEV) have been shown in animal models of neuropathic pain. Here, we studied the effect of brivaracetam (BRV), which binds to SV2A with 20-fold greater affinity, and has fewer off-target effects.
Learn More >Many patients use opioids chronically before surgery; it is unclear if surgery alters the likelihood of ongoing opioid consumption in these patients.
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