Effects of the calcium channel blocker flunarizine on spinal reflexes in cats

Abstract

We have investigated the effects of the calcium channel blocker flunarizine on spinal monosynaptic reflexes in spinal cats. Flunarizine was administered locally into the spinal cord (10, 50, 100 µM) and intraperitoneally (5, 10, 20 mg/kg). Adult cats (n = 10) weighing 1.5-3 kg were anaesthetized with ketamine (50 mg/kg, IM), artificially ventilated and spinalized at the C1 level. A laminectomy was performed in the lumbosacral region. The ventral and dorsal roots of segment L5 were isolated and a pouch of skin formed at the site of the dissection to allow the exposed tissues to be covered with liquid paraffin. The temperature was kept at 38.5°C with a heating pad. A polyethylene cannula was introduced into the left carotid artery to monitor blood pressure, which was kept above 100 mmHg. The dorsal root of segment L5 was placed on a silver-silver chloride wire electrode for stimulation through an isolation unit. The reflex potentials were recorded from the ipsilateral L5 ventral root, mounted on a silver-silver chloride wire electrode. The systemic (5, l0, 20 mg/kg) and local (50 and 100 µM) dosages of flunarizine significantly decreased the amplitude of the reflex response (P < 0.05). Moreover, the latency of the monosynaptic reflexes increased after administration of the drug (P < 0.05). Voltage-dependent calcium channels in the spinal cord may play an important role in regulating the reflex response.