A descriptive study of spinal dorsal horn neurons in the physiologically intact, awake, drug-free cat.

The extracellular recording of single neuron activity from the spinal dorsal horn of physiologically intact, awake, drug-free cats (n = 14) revealed two potentially important differences between the intact preparation and data obtained from acute preparations. The first of the differences, as previously reported in intact rat and monkey, is that low-threshold (LT) neurons had very low rates of spontaneous activity. Of 127 LT neurons that were studied in the intact animal, 82% had spontaneous rates less than 1 impulse/s (IPS). The second difference was the low number (n = 13) of wide dynamic range (WDR, multireceptive, convergent) neurons that were encountered in the intact animal. Three chronic intact animals were also recorded from during light barbiturate anesthesia. The presence of barbiturate anesthesia significantly increased both the number of LT neurons with spontaneous rates greater than 1 IPS and the likelihood of encountering dorsal horn neurons with WDR response profiles. In spite of these two differences, many similarities between the chronic preparations and previous acute studies were observed. For example, receptive field size and response properties to natural stimulation for LT, WDR, and proprioceptive neurons were found to be similar to those reported in acute preparations. The results of this study suggest that, although there are many similarities in dorsal horn neurophysiology in acute and chronic cats, important differences that may be attributed to the preparation itself may also exist.