Substance P release in the spinal cord during the exercise pressor reflex in anaesthetized cats.

Abstract

SUMMARY1. The purpose of this study was to determine if static skeletal muscle contraction causes the release of substance P(SP) in the L7-dorsal horn region of the spinal cord. A laminectomy was performed to expose the spinal cord of a-chloralose anaesthetized cats. The L6 spinal root was cut. A microdialysis probe was inserted into the L7 dorsal horn region ipsilateral to the contracting triceps surae muscle. The probe was perfused with a buffer solution at 3 ul/min. Substance P-like immunoreactivity (SP-LI) was measured, from the microdialysis samples, by radioimmunoassay.2. A 5-9 min contraction of the triceps surae muscle was evoked by alternate electrical stimulation of the peripheral ends of the cut L7 and St ventral roots. Basal SP-LI release was 0 20+0 03 fmol/100l ,l and was increased to 0 54 + 0-05 fmol/ 100 ,ul (mean + S.D.) by static muscle contraction. This increase was greatly attenuated after cutting the L7 and St dorsal roots (0 23 + 003 to 039 + 008 fmol/ 100 lO ) or completely abolished by muscle paralysis (027 + 0-03 to 031 + 001 fmol/l00,ul). Muscle contraction also increased mean arterial blood pressure (MAP) 29 + 20 mmHg and heart rate (HR) 11+ 5 beats/min (mean + S.D.). These cardiovascular changes to muscle contraction were abolished by sectioning the dorsal roots or when the ventral roots were electrically stimulated after the cats were paralysed.3. These results demonstrate that static contraction of skeletal muscle increases the release of SP-LI in the dorsal horn of the spinal cord. Furthermore, these data support the hypothesis that SP plays a role in mediating the cardiovascular responses evoked during static exercise.

Role of NO in modulating neuronal activity in superficial dorsal horn of spinal cord during exercise pressor reflex

“…Previous studies (12,13,42,44) have shown the modulatory role of neurotransmitters and neuromodulators in the dorsal horn in the exercise pressor reflex. For example, static muscle contraction increased the extracellular concentration of substance P and glutamate in the dorsal horn (12,42). It was also found that microdialysis of antagonists to substance P and to N-methyl-Daspartic acid (NMDA) and non-NMDA glutamate receptors into the dorsal horn significantly attenuated the reflex cardiovascular responses to static muscle contraction (13,14,44).…”

“…The majority of group III and group IV skeletal muscle afferent fibers make their first synapse in the dorsal horn of the spinal cord (24,29). Previous studies (12,13,42,44) have shown the modulatory role of neurotransmitters and neuromodulators in the dorsal horn in the exercise pressor reflex. For example, static muscle contraction increased the extracellular concentration of substance P and glutamate in the dorsal horn (12,42).…”

“…The majority of group III and group IV skeletal muscle afferent fibers make their first synapse in the superficial dorsal horn of the spinal cord (24,29). Studies (12,13,[42][43][44] have demonstrated the neurotransmitters and neuromodulators that are involved in transmitting the exercise pressor reflex at this site.The purpose of this study was to determine whether muscle contraction activated neurons in the dorsal horn by identifying c-Fos expression. Furthermore, whether c-Fos expression coexisted with nitric oxide (NO) synthase (NOS) in the dorsal horn was examined by double-labeling methods.…”

“…The majority of group III and group IV skeletal muscle afferent fibers make their first synapse in the superficial dorsal horn of the spinal cord (24,29). Studies (12,13,[42][43][44] have demonstrated the neurotransmitters and neuromodulators that are involved in transmitting the exercise pressor reflex at this site.…”

Exercise pressor reflex in health and diseases: Animal studies

“…1). Neural transmitters/modulators which play a role in transmitting afferent signals from exercising skeletal muscle at this site were determined, including ATP 19,20) , glutamate 21,22) , NO 23,24) , and substance P 25,26) . For example, microdialyzing a purinergic 2X receptor blocker into the spinal dorsal horn reduced the EPR response, and microdialyzing α,β-methylene ATP into the dorsal horn augmented the EPR response in anes- …”