Differential release of endogenous 5-hydroxytryptamine, substance P, and neurokinin A from rat ventral spinal cord in response to electrical stimulation.
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.(ABSTRACT TRUNCATED AT 250 WORDS)
Franck
J
J
Department of Physiology, Karolinska Institutet, Stockholm, Sweden.
Brodin
E
E
Fried
G
G
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D015288:Neurokinin A / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism*
D012701:Serotonin; D013373:Substance P; D015288:Neurokinin A; D002118:Calcium