The involvement of metabotropic glutamate receptors in sensory transmission in dorsal horn of the rat spinal cord
Section snippets
Anaesthesia and surgery
Extracellular single-neuron recordings were made in urethane-anaesthetized (1.2 g/kg initial dose, i.p.) male Sprague–Dawley rats (Harlan Sprague–Dawley Inc., Indianopolis, IN) weighing between 350–450 g. A tracheotomy and a cannulation of the external jugular vein were performed after achieving deep anaesthesia. Subsequently, smaller doses of urethane were given intravenously to maintain the level of anaesthesia. The lumbar enlargement (L3–L5 segments) was exposed by a laminectomy and the spinal
Results
Experiments were carried out on a total of 58 spinal dorsal horn neurons in 38 urethane-anaesthetized rats. All cells had excitatory receptive fields located on one of the the hind paws and had little or no spontaneous activity. Neurons were located between 100 and 600 μm from the surface of the dorsal horn, as estimated by microdrive readings. Based on their responses to mechanical stimuli of increasing intensity, including innocuous brush, pressure, noxious pinch and squeeze, 51 of the 58
Discussion
The role of mGluRs in the transmission of somatosensory information by spinal dorsal horn neurons was studied in a selected population of noci-responsive cells. Due to the nature of our search stimulus (brush or pressure) most of the experiments were carried out in wide dynamic range neurons. The present results, confirming previous studies,6, 26, 38but in some discrepancy with others[42]show that activation of mGluRs in dorsal horn neurons of intact spinal cord significantly and unequally
Conclusions
Our data provide further evidence for the involvement of mGluRs in the processing of sensory information in the dorsal horn of the spinal cord. Activation of mGluRs at spinal synapses by local iontophoresis of 1S,3R-ACPD resulted in increased responses of dorsal horn neurons to ionotropic GluR agonists (NMDA and kainic acid) and to innocuous peripheral stimulation. 1S,3R-ACPD also enhanced the frequency-dependent potentiation (wind-up) of dorsal horn neuron activity. The excitatory effects of 1S
Acknowledgements
This work was supported by NIDA Grants RO1-04090 and RO1-00124 to A.A.L. We thank Kelley Kitto for his expert technical assistance.
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2006, NeuropharmacologyCitation Excerpt :The preventative action of AIDA at BIC-induced hyperresponsiveness is in line with previous evidence supporting an enhancing effect for spinal group I mGluRs (mGluR1/5) on synaptic transmission at the dorsal horn level (Neugebauer, 2002; Young et al., 1995, 1998; Karim et al., 2001). It has been shown that group I mGluRs may not only positively modulate spinal ionotropic glutamate receptors (Budai and Larson, 1998) but they may also directly increase glutamate release in substantia gelatinosa (Park et al., 2004). Because central terminals of afferent unmyelinated fibres are devoid of mGluR2/3 or mGluR5 and only 5% of terminals of fine myelinated fibres contain either receptor (Jia et al., 1999), it is questionable that group I–II mGluRs, whose activation is shown here to be required for BIC-induced augmentation of polysynaptic field potentials elicited by A fibre input, actually play a role as autoreceptor in primary afferent fibres.
Kynurenic acid enhances electroacupuncture analgesia in normal and carrageenan-injected rats
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