Characterisation of sevoflurane effects on spinal somato-motor nociceptive and non-nociceptive transmission in neonatal rat spinal cord: an electrophysiological study in vitro.

Sevoflurane is the latest halogenated ether introduced in clinical anaesthesia, and its effects at the spinal level are not fully characterised. The rat hemisected spinal cord preparation was used to test the effects of sevoflurane on spinal nociceptive and non-nociceptive synaptic transmission as well as on excitations produced by application of glutamate-receptor agonists. Sevoflurane was dissolved in artificial cerebrospinal fluid (ACSF) with a specific vaporiser, and its final concentration was assessed with gas chromatography. Sevoflurane reduced the mono-synaptic reflex (EC(50) approximately 219 microM) and the slow components of the dorsal root-ventral root potentials (EC(50) approximately 72 microM) elicited by single dorsal root stimulation as well as the cumulative depolarisation (CD) elicited by repetitive stimulation (EC(50) approximately 98 microM). AMPA- and NMDA-induced depolarisations were also reduced by sevoflurane (respective EC(50)s were 206 and 127 microM). Inhibition of NMDA-induced depolarisation was TTX resistant. However, complete blockade of NMDA receptors with d-AP5 did not prevent further reduction of the CD by sevoflurane. All the effects reported were concentration-dependent and reversible. We conclude that sevoflurane applied at clinically relevant concentrations induces a strong depression of nociceptive and non-nociceptive spinal systems, which may be partly mediated by interfering with excitatory amino acid transmission.