Comparison of two microdialysis approaches in determining peripheral nociceptive input-evoked glutamate release in the spinal cord of rats / 中华麻醉学杂志

ABSTRACT

Objective To validate and compare the two spinal microdialysis techniques a linear tissue probe (LM-3) in the spinal dorsal horn and a loop probe in the cerebral spinal fluid (CSF) in determining peripheral nociceptive stimulation-evoked glutamate (Glu) release in the spinal cord of freely moving rats. Methods Twenty-eight adult male Wistar rats weighing 300-350 g were randomly divided into two groups in group A a LM-3 probe was implanted into the spinal dorsal horn and in group B a loop probe was placed in the CSF. Twenty-four hours after the implantation of the probe, microdialysis was initiated with perfusion of modified Ringer' s solution at a low flow rate of 5 ?l?min-1 . Following an 1 h equilibration phase the baseline Glu concentrations were measured every 10 min for 1 h. Thereafter 50 ?lof 5% formalin was injected into one hindpaw of the rats and samples were collected every 10 min for 90 min. Furthermore 8 rats in group A were further divided into 2 subgroups to investigate the effects of the flow rate of microdialysis and composition of perfusate on the baseline Glu release.Results The baseline levels of Glu were (0.82?0.09) ?mol?L-1 with LM-3 probe and (5.96?0.22) ?mol?L-1 with the loop probe. In group A (LM-3 probe) when the flow rate of the modified Ringer's solution was decreased from 5 to 2 ?l?min-1 the extracellular Glu concentrations were increased to 223%?7% of the baseline (n = 4) , whereas perfusion with artificial CSF reduced Glu concentrations to 62% ?10% of the baseline (n = 4) . Injection of formalin into the hindpaw induced a short-lasting but significant increase in Glu concentration with a similar profile and time course using either of the two microdialysis approaches. Conclusion Microdialysis in the dorsal horn or in the CSF are both effective techniques to assess Glu release in the spinal cord of rats. Peripheral nociceptive input induces a short-lasting increase in Glu release with a similar profile and time course using either of the two microdialysis approaches. The microdialysis of the dorsal horn provides a useful tool to precisely locatewhere the release of the neurotransmitter occurs, whereas the loop probe in CSF is more reproducible for simultaneous investigation of drug effects.