Suppressive Effects of Cooling Compounds Icilin on Penicillin G-Induced Epileptiform Discharges in Anesthetized Rats

Abstract

More than 30% of patients with epilepsy are refractory and have inadequate seizure control. Focal cortical cooling (FCC) suppresses epileptiform discharges (EDs) in patients with refractory focal cortical epilepsy. However, little is known about the mechanism by which FCC inhibits seizures at 15°C, and FCC treatment is highly invasive. Therefore, new antiepileptic drugs are needed that produce the same effects as FCC but with different mechanisms of action. To address this need, we focused on transient receptor potential melastatin 8 (TRPM8), an ion channel that detects cold, which is activated at 15°C. We examined whether TRPM8 activation suppresses penicillin G (PG)-induced EDs in anesthetized rats. Icilin, a TRPM8 and TRP Ankyrin 1 agonist, was administered after PG injection, and a focal electrocorticogram (ECoG) and cortical temperature were recorded for 4 h. We measured spike amplitude, duration, firing rate, and power density in each band to evaluate the effects of icilin. PG-induced EDs and increased delta, theta, alpha, and beta power spectra were observed in the ECoG. Icilin suppressed EDs while maintaining cortical temperature. In particular, 3.0-mM icilin significantly suppressed PG-induced spike amplitude, duration, and firing rate and improved the increased power density of each band in the EDs to the level of basal activity in the ECoG. These suppressive effects of 3.0-mM icilin on EDs were antagonized by administering N-(3-aminopropyl)-2-[(3-methylphenyl) methoxy]-N-(2-thienylmethyl)-benzamide hydrochloride (AMTB), a selective TRPM8 inhibitor. Our results suggest that TRPM8 activation in epileptic brain regions may be a new therapeutic approach for patients with epilepsy.

Suppressive Effects of Transient Receptor Potential Melastatin 8 Agonist on Epileptiform Discharges and Epileptic Seizures

“…administered a single dose of PTZ (40 mg/kg). A model with focal epilepsy originating in the left cerebral cortex was generated by modifying a previously reported method (Moriyama et al, 2019).…”

“…ECoG was recorded by modifying a previously reported method (Moriyama et al, 2019). EDs developed 10-20 min after PG injection and reached a steady state 1.5 h after PG injection (Moriyama et al, 2019), remaining stable for at least 5 h (data not shown).…”

“…ECoG was recorded by modifying a previously reported method (Moriyama et al, 2019). EDs developed 10-20 min after PG injection and reached a steady state 1.5 h after PG injection (Moriyama et al, 2019), remaining stable for at least 5 h (data not shown). Because icilin, a TRPA1 and TRPM8 agonist, eliminated all EDs for only a few minutes (Moriyama et al, 2019), we regarded the drug efficacy period as 5 min from 5 to 10 min after the start of TRPM8 agonist injection.…”

“…Transient receptor potential melastatin 8 (TRPM8) activation suppresses drug-induced epileptiform discharges (EDs) (Moriyama et al, 2019), and the anti-epileptic-like effects of TRPM8 agonists have received attention. TRPM8 channels are expressed in small numbers in the rodent somatosensory cortex (Ordas et al, 2019) and are activated by TRPM8-selective agonists (Behrendt et al, 2004) or cold temperatures between 10 and 26°C (Bautista et al, 2007).…”

“…Penicillin G potassium (PG), an epilepsy-inducer, inhibits GABA A receptor (Tsuda et al, 1994;Sugimoto et al, 2002), leading to EDs and epileptic seizures (Kida, 2012;Moriyama et al, 2019;Fujii et al, 2012). TRPM8 activation by icilin, a TRPM8 and transient receptor potential ankyrin 1 (TRPA1) agonist, suppresses EDs (Moriyama et al, 2019), indicating that a lack of TRPM8 channels exacerbates epileptic seizures. However, the effects of no TRPM8 channels on EDs and epileptic seizures is unclear.…”