Effect of propofol on spinal dorsal horn neurons. Comparison with lack of ketamine effects

Background Pentobarbital reduces low-threshold receptive field (RF) size and enhances responses of some spinal dorsal horn neurons to noxious stimulation in cats. To better understand the effects of general anesthetics on spinal sensory processing, this study was designed to determine if intravenous propofol and ketamine have similar effects. Methods Spinal dorsal horn neuronal responses to RF stimulation were observed in physiologically intact, awake, drug-free cats. After baseline observations were made, the effects of propofol (7.5 or 10 mg/kg intravenous) or ketamine (10 mg/kg intravenous) on those neuronal responses were observed. Results Propofol is capable of producing a profound reduction in low-threshold RF size. Propofol also depressed neuronal responses to non-noxious and noxious RF stimulation in many of the neurons tested. Ketamine was not observed to produce any change in either RF size or neuronal response to non-noxious RF stimulation. Conclusions General anesthetics that interact with gamma aminobutyric acid receptors may significantly depress low-threshold sensory information within the spinal dorsal horn. This may contribute to anesthetic-induced loss of sensation. Lack of a ketamine effect suggests an absence of n-methyl-d-aspartate receptor involvement in spinal dorsal horn processing of low threshold sensory information.