Suppressant effects of midazolam on responses of spinal dorsal horn neurones in rabbits.
Recordings of noxious intra-arterial bradykinin (BK)-induced chemonociceptive and spontaneous activity from 30 single spinal lamina V neurones of the dorsal horns in non-anaesthetized and decerebrated rabbits, were performed with tungsten microelectrodes. Intravenous injection of midazolam (0.2 mg/kg; 7 neurones) depressed BK-induced neural discharges by 55.0 +/- 6.2% (P less than 0.05) and 57.9 +/- 8.4% (P less than 0.05) 5 and 25 min after administration, respectively. Treatment with flumazenil (0.2 mg/kg, i.v.; 7 neurones), administered 20 min after midazolam, completely reversed the inhibition by midazolam of the BK-induced spinal lamina V neural responses and spontaneous neuronal activity. In contrast, a large dose of naloxone (1.0 mg/kg, i.v.; 6 neurones), administered 20 min after midazolam, failed to alter the midazolam-induced depressant effects on the nociceptive responses, at the spinal dorsal horn. Treatments with flumazenil (5 neurones) and naloxone (5 neurones) did not influence either the spontaneous or the BK-induced neuronal discharges, recorded in spinal lamina V cells. Midazolam depressed the nociceptive responses probably through its agonistic activity on the binding to the GABA-benzodiazepine-barbiturate system in the spinal dorsal horn.
Miyamoto
K
K
Department of Anaesthesiology, Kinki University School of Medicine, Osaka Dental University, Japan.
Wakita
K
K
Okuda
T
T
Fuji
K
K
Suekane
K
K
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D003655:Decerebrate State; D005445:Flunitrazepam / Q000494:pharmacology; D008839:Microelectrodes; D008874:Midazolam / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D010146:Pain / Q000139:chemically induced; D011817:Rabbits; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects*
D009270:Naloxone; D005445:Flunitrazepam; D008874:Midazolam; D001920:Bradykinin