The Journal of neuroscience : the official journal of the Society for Neuroscience
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Dose-response curves for activation of excitatory amino acid receptors on mouse embryonic hippocampal neurons in culture were recorded for 15 excitatory amino acids, including the L-isomers of glutamate, aspartate, and a family of endogenous sulfur amino acids. In the presence of 3 microM glycine, with no extracellular Mg, micromolar concentrations of 11 of these amino acids produced selective activation of N-methyl-D-aspartate (NMDA) receptors. L-Glutamate was the most potent NMDA agonist (EC50 2.3 microM) and quinolinic acid the least potent (EC50 2.3 mM). ⋯ Small-amplitude nondesensitizing quisqualate receptor responses were activated by much lower concentrations of all quisqualate receptor agonists. Full dose-response curves for the nondesensitizing response were obtained for 9 amino acids; L-glutamate was the most potent endogenous agonist (EC50 19 microM). Domoate (EC50 13 microM) and kainate (EC50 143 microM) activated large-amplitude, nondesensitizing responses.
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Previous experiments have shown that noxious stimulation increases expression of the c-fos proto-oncogene in subpopulations of spinal cord neurons. c-fos expression was assessed by immunostaining for Fos, the nuclear phosphoprotein product of the c-fos gene. In this study, we examined the effect of systemic morphine on Fos-like immunoreactivity (FLI) evoked in the formalin test, a widely used model of persistent pain. Awake rats received a subcutaneous 150 microliters injection of 5% formalin into the plantar aspect of the right hindpaw. ⋯ Staining in the neck of the dorsal horn (laminae V and VI) and in more ventral laminae VII, VIII, and X, was profoundly suppressed by doses of morphine which also suppress formalin-evoked behavior. Although the labeling was also significantly reduced in laminae I and II, at the highest doses of morphine there was substantial residual labeling in the superficial dorsal horn. These data indicate that analgesia from systemic opiates involves differential regulation of nociceptive processing in subpopulations of spinal nociceptive neurons.
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Spinal cord slice preparation and intracellular recording techniques were used to examine the effects of phorbol esters on the sodium- and calcium-dependent action potentials, the excitatory synaptic transmission, the basal (resting) and the dorsal root stimulation-evoked release of 9 endogenous amino acids, including glutamate and aspartate, and the responsiveness of the rat dorsal horn neurons to excitatory amino acids (glutamic, kainic, quisqualic, and N-methyl-D-aspartic). 4-beta-Phorbol-12, 13-dibutyrate and 4-beta-phorbol-12, 13-diacetate produced minor alterations in membrane potential and resistance, but they broadened the sodium-dependent action potential and reduced the duration of the calcium-dependent action potential. In addition, phorbol esters caused a marked and long-lasting increase in the amplitude and the duration of excitatory postsynaptic potentials (EPSPs) evoked in dorsal horn neurons by orthodromic stimulation of a lumbar dorsal root. Phorbol esters produced a brief increase in the basal and electrically evoked release of endogenous excitatory (glutamic, aspartic) and inhibitory amino acids (glycine, GABA). ⋯ Phorbol esters could potentiate excitatory synaptic transmission by acting predominantly at a postsynaptic site (NMDA receptor), since the duration of the increased responsiveness of dorsal horn neurons to glutamate and NMDA correlates better with the enhancement of EPSPs than with the increased release of the stimulation-evoked glutamate and aspartate. The increased release of endogenous amino acids is consistent with a presynaptic (terminal) site of action, but it could also be explained by enhanced interneuronal activity. Although our results suggest that in the rat spinal dorsal horn protein kinase C may have a role in controlling the release of putative excitatory and inhibitory neurotransmitters and may also be involved in the regulation of postsynaptic NMDA receptors, the identity of endogenous substance(s) participating in these effects is presently unknown.
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The effect of a change in neurofilament (NF) and tubulin gene expression on the elongation of axonal sprouts by adult rat sensory neurons was examined. Distal sciatic nerve crush axotomy was used to initiate changes in cytoskeletal gene expression in lumbar dorsal root ganglion (DRG) neurons. In situ hybridization of DRG neurons with 35S-labeled cDNA probes revealed a significant reduction in the level of mRNAs for the low-molecular weight-NF protein and a significant increase in the level of beta tubulin mRNAs by 2 weeks after axotomy. ⋯ In this paradigm, axonal sprouts that formed after the proximal crush axotomy incorporated radiolabeled, slow axonally transported proteins as they elongated. Fluorographs of SDS-PAGE revealed that the regenerating axonal sprouts of primed DRG cells incorporated and conveyed significantly less labeled NF protein than did the regenerating axons of unprimed DRG neurons. Electron microscopy revealed that the regenerating axonal sprouts of primed DRG cells contained numerous microtubules but very few identifiable NFs compared with the regenerating sprouts of unprimed DRG neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
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These experiments further define the organization of peptidergic pathways in the paravertebral sympathetic system of the bullfrog. Populations of axons and synaptic boutons in sympathetic ganglia 9 and 10 were found to express calcitonin gene-related peptide-like immunoreactivity (CGRP-IR) and substance P-like immunoreactivity (SP-IR). CGRP-IR is present in fibers that run through the ganglia and in boutons that make contact with almost half of the principal neurons. ⋯ In the spinal cord, the preganglionic B and C neurons that innervate ganglia 9 and 10 are located in different segments. In segments that contain preganglionic B cells, but not those that contain C cells, there were 243 +/- 37 (mean +/- SD) neurons in the intermediolateral cell column that express CGRP-IR. However, no cell bodies containing SP-IR were found in this region of the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)