Inhibition of spontaneous activity of spinal dorsal horn neurons in the intact cat is naloxone-insensitive

Abstract

Low-threshold neurons in the dorsal horn of the spinal cord of physiologically intact, awake, drug-free cats demonstrate minimal rates of spontaneous activity. Studies in acute animals suggest that the lack of spontaneous activity is due to descending inhibitory control mechanisms. The present study suggests that the inhibition of spontaneous activity is naloxone-insensitive. Intravenously administered naloxone in doses of up to 0.4 mg/kg failed to have any effect on the spontaneous activity of the 34 low-threshold neurons recorded from the dorsal horn of the spinal cord of physiologically intact, awake animals. Stimulus-evoked activity was also not significantly influenced by the doses of naloxone used in this study. These results confirm data previously obtained by others using acute preparations. This confirmation is important is that it demonstrates that, for this system, differences between acute and chronic preparations do not appear to alter neuronal sensitivity to specific drug manipulations. They also verify that, for this system, acute experiments accurately reflect conditions that exist in the intact animal.