Effects of local anesthetics on the neural activity of the dorsal horn investigated optically using a voltage-sensitive dye

Abstract

Although spinal anesthesia using local anesthetics has been often conducted in surgery of the leg and lower abdomen, the mechanism of their pharmacological action in the neuronal network of the dorsal horn has not been fully understood. We intended to analyze the effects of local anesthetics on the local neural circuitry of the dorsal horn. Because an optical recording technique using a voltage-sensitive dye is suitable for the analysis of multi-point neural activities, we investigated the effects of lidocaine and bupivacaine on the dorsal horn neuronal network function. Spinal cord slices of juvenile rats were stained with a voltage-sensitive dye. Neural activity in the dorsal horn elicited by electrical stimulation of the dorsal roots were analyzed using a high-speed optical recording system. Both lidocaine and bupivacaine suppressed neural excitability in a dose-dependent manner with preferential depression of post-synaptic activity. These pharmacological actions were topographically different within the dorsal horn. The depressant effect of bupivacaine was greater and more long-lasting than that of lidocaine. We conclude that synaptic blockade is the major action of local anesthetics in the neuronal network of the dorsal horn in vitro. [Jpn J Physiol 55 Suppl:S170 (2005)]