Excitatory amino acid concentrations in the spinal dorsal horn of cats during muscle contraction

In anesthetized cats, static hindlimb muscle contraction reflexly increases mean arterial pressure (MAP) and heart rate (HR). Pharmacological and immunohistochemical evidence suggests that excitatory amino acids are involved in the spinal transmission of this reflex. Using microdialysis and highperformance liquid chromatography technology, we tested the hypothesis that static contraction of the triceps surae muscle increases the extracellular concentration of glutamate (Glu) and aspartate (Asp) at the L(7) level of the dorsal horn of the spinal cord. With the exception of the L(7) dorsal root, the L(5)-S-2 dorsal and ventral roots were cut Ipsilateral to the contracting muscle. After the insertion of microdialysis probes and a 3-h recovery period, a a-min static contraction was electrically evoked. MAP and Hn increased by 53 +/- 8 mmHg and 20 +/- 4 beats/min. The concentration of Glu increased from 324 +/- 59 to 857 +/- 80 nM, whereas Asp increased from 199 +/- 57 to 499 +/- 113 nM. These results were repeatable, in that Glu and Asp rose by similar amounts in two subsequent contractions. In both of these latter contractions, MAP and HR were also significantly increased. By contrast, in a subset of cats whose L; dorsal roots were cut after the first contraction, neither MAP, HR, Glu, nor Asp was significantly increased over baseline levels. These data demonstrate that static contraction of the hindlimb increases the extracellular concentration of Glu and Asp in the dorsal horn. In summary, lie results from this study are in agreement with previous findings suggesting that excitatory amino acids are involved in the spinal transmission of sensory information from the hindlimb muscle.