Differential Release of Endogenous 5‐Hydroxytryptamine, Substance P., and Neurokinin A from Rat Ventral Spinal Cord in Response to Electrical Stimulation
- 1 August 1993
- journal article
- Published by Wiley in Journal of Neurochemistry
- Vol. 61 (2) , 704-711
- https://doi.org/10.1111/j.1471-4159.1993.tb02176.x
Abstract
The release of endogenous 5‐hydroxytryptamine (5‐HT), substance P (SP), and neurokinin A (NKA) from superfused tissue slices of rat ventral lumbar spinal cord, where SP and NKA coexist with 5‐HT in terminals of descending bulbospinal neurons, was investigated. Electrical field stimulation was performed using square‐wave pulses of 2‐ms duration and 30 mA stimulus intensity. The following four different patterns of stimulation were used: 2 Hz continuous, 20 Hz continuous, 20 Hz intermittent, and 50 Hz intermittent. 5‐HT was measured in the slice superfusates by HPLC with electrochemical detection. SP and NKA were measured by radioimmunoassay. The release of 5‐HT was significantly enhanced using all stimulation paradigms and the evoked release of 5‐HT per pulse was independent of the stimulation frequency. The release was found to be calcium dependent and there was no increase in the efflux of 5‐hydroxyindoleacetic acid in response to stimulation. At 2 Hz (continuous), no significant increase in the release of SP was observed. Stimulation at higher frequencies yielded a significant increase in the release of SP per pulse. At 20 Hz, the release was increased by 73% (continuous) and 74% (intermittent), and at 50 Hz (intermittent) by 175% of basal efflux. The evoked release of NKA was also frequency dependent. At 2 Hz (continuous), no significant increase in the release of NKA was observed. At 20 Hz (intermittent), the evoked release per pulse was increased by 33% and at 50 Hz (intermittent) by 53% compared with the basal efflux of NKA. The results suggest that coexisting neurotransmitters/neuromodulators in the spinal cord may be released in different proportions depending on the stimulation frequency and that only 5‐HT is released when the nerve terminal is activated by low‐frequency stimulation.Keywords
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