DEPRESSION OF NOCICEPTIVE SYMPATHETIC REFLEXES BY THE INTRATHECAL ADMINISTRATION OF MIDAZOLAM

The effect of the intrathecal administration of midazolam 0.5–1.0mg in 1–2 ml of physiological saline solution, has beenobserved on responses evoked in renal sympathetic nerves bysupramaximal electrical stimulation of radial and tibial nerves.In artificially ventilated dogs anaesthetized with a-chloralose,the intrathecal administration of midazolam caused a markeddepression of reflexes evoked from the tibial nerve but hadno effect on either spontaneous sympathetic activity or reflexesevoked by radial nerve stimulation. Neither the small amount(1–2 ulitre) of benzyl alcohol, present as a preservative(administered intrathecally), nor midazolam 1 mg kg^–1i.v. caused any significant depression of the evoked somato-sympatheticreflexes. The effects of intrathecal midazolam were reversedby the benzodiazepine antagonists Ro 15–1788 1 mg kg^–1i.v. and Ro 15–3505 1–2 mg kg^–1 i.v. but notby naloxone 2 mg i.v. It is suggested that the antinociceptiveeffect of locally applied midazolam could be the result of anon-opioid GABA-mediated system which may have implicationsin the management of pain. ^*Present address: Tel-Aviv Medical Centre and Tel-Aviv MedicalSchool, Tel-Aviv, Israel.