Action of isoflurane on the substantia gelatinosa neurons of the adult rat spinal cord.
BACKGROUND
Although isoflurane, a volatile anesthetic, can block the motor response to noxious stimulation (immobility and analgesia) and suppress autonomic responsiveness, how it exerts these effects at the neuronal level in the spinal cord is not fully understood.


METHODS
The effects of a clinically relevant concentration (1 rat minimum alveolar concentration [MAC]) of isoflurane on electrically evoked and spontaneous excitatory/inhibitory transmission and on the response to exogenous administration of the gamma-aminobutyric acid type A receptor agonist muscimol were examined in lamina II neurons of adult rat spinal cord slices using the whole cell patch clamp technique. The effect of isoflurane on the action potential-generating membrane property was also examined.


RESULTS
Bath-applied isoflurane (1.5%, 1 rat MAC) diminished dorsal root-evoked polysynaptic but not monosynaptic excitatory postsynaptic currents. Glutamatergic miniature excitatory postsynaptic currents were also unaffected by isoflurane. In contrast, isoflurane prolonged the decay phase of evoked and miniature gamma-aminobutyric acid type A receptor-mediated inhibitory postsynaptic currents and increased the amplitude of the muscimol-induced current. Isoflurane had little effect on action potential discharge activity.


CONCLUSIONS
Isoflurane augments gamma-aminobutyric acid-mediated inhibitory transmission, leading to a decrease in the excitability of spinal dorsal horn neurons. This may be a possible mechanism for the antinociceptive effect of isoflurane in the spinal cord.
Wakai
Ayako
A
Division of Anesthesiology, Niigata University Graduate School of Medical and Dental Sciences, Japan.
Kohno
Tatsuro
T
Yamakura
Tomohiro
T
Okamoto
Manabu
M
Ataka
Toyofumi
T
Baba
Hiroshi
H
D000818:Animals; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005971:Glutamates / Q000502:physiology; D066298:In Vitro Techniques; D007530:Isoflurane / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000502:physiology; D013376:Substantia Gelatinosa / Q000187:drug effects* / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D005971:Glutamates; D005680:gamma-Aminobutyric Acid; D007530:Isoflurane