Temporally dependent changes in response properties of dorsal horn neurons after dorsolateral funiculus lesions

Abstract

Previous studies in this laboratory have shown 1) that 19% of L6 and L7 dorsal horn cells in normal cats respond only with excitatory postsynaptic potentials (EPSPs) to sural nerve stimulation, and 2) that the distribution of dorsal horn neurons responding with impulses to sural nerve stimulation is increased in cats with chronic lateral funiculus lesions. The present study was undertaken to determine whether strengthening of subliminal sural nerve projections could account for the changes seen after lateral funiculus lesions and to explore the nature of these changes in greater detail. Ipsilateral L6 and L7 dorsal horn cells of cats with T12 dorsolateral funiculus (DLF) lesions were studied electrophysiologically at less than 1-30 days postoperatively (DPO) and were compared with similar cells recorded in normal cats. The major results were as follows. 1. Responsiveness to peripheral stimulation was depressed for up to 3 DPO following the lesions. 2. The percentage of L6 and L7 dorsal horn cells showing spontaneous activity was elevated at 3 DPO and declined to normal levels by 28 DPO. 3. The percentage of cells that responded to sural nerve stimulation increased over 3-30 DPO and was significantly greater than normal at 28-30 DPO. The increase in the percentage of cells giving impulses to sural nerve stimulation at 28-30 DPO was similar to the percentage of cells with subliminal responses to sural nerve stimulation in normal cats. A subpopulation of identified postsynaptic dorsal column neurons also showed a significant increase in the percentage that responded to sural nerve stimulation after DLF lesions. 4. The percentage of cells that had a cutaneous receptive field (RF) overlapping the region of skin innervated by the sural nerve also increased over time and was significantly greater than normal at 28-30 DPO. 5. Median low-threshold or high-threshold RF areas were not significantly greater than normal ipsilateral to DLF lesions at any survival time. 6. The proportions of low-threshold (LT), high-threshold (HT), and multireceptive (MR) cells were not significantly different from normal at any survival time from less than 1 to 30 DPO.(ABSTRACT TRUNCATED AT 400 WORDS)

c‐Fos expression in the spinal cord after acute sacral segmental nerve stimulation

“…The stimulation amplitude in their study appears to be at a non-nociceptive level; therefore, there was no signi¢cant expression of c-Fos. Previous reports concerned with inhibitory receptive ¢elds of nociceptive dorsal horn neurons described the inhibition produced by non-nociceptive stimuli, also [Gehart et al, 1981: Pubos et al, 1988]. An important common ¢nding in such studies is that inhibition generated by a non-nociceptive stimulus occurs only at the spinal segmental level [Ness and Gebhart, 1991], whereas inhibition generated by a nociceptive stimulus has been demonstrated to be organized at segmental, intraspinal, and supraspinal levels [Pubos et al, 1988].…”

“…Thus, to obtain appreciable clinical results with a lower painful stimulation amplitude, it seems important to stimulate the appropriate spinal segment. The DNIC phenomenon usually involves a supraspinal mechanism [Pubos et al, 1988]. However, in clinical SNS, patients with complete spinal cord injury also demonstrate favorable response to SNS [Ishigooka et al, 1998].…”

Suppression of the descending inhibitory pathway by continuous thoracic intrathecal lidocaine infusion reduces the thermal threshold of the tail-flick response in rats

“…The site of action of analgesics can be determined by suppressing descending inhibitory pathways. Chronic spinal cord injury [1], decerebration [2,3], and anesthetic [4] or cold blockade of the spinal cord [5] have been used to interfere with descending transmission in animals. Lidocaine blockade of the spinal cord has advantages such as reversibility and less damage to the cord when compared with lesioning and cold blockade, although it has disadvantages such as variable onset and a relatively short duration of the peak effect with a single dose [4].…”