Neuroscience
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As excitatory amino acid receptors have been implicated in nociceptive sensory transmission, the principal objective of the present study was to investigate the effects of various excitatory amino acid antagonists on naturally evoked responses in spinal dorsal horn neurons. Extracellular single unit activity was recorded from functionally identified, spinal dorsal horn neurons in unanesthetized, decerebrated cats and in alpha-chloralose-anesthetized cats. The tests included iontophoretic application of the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovaleric acid (APV), the non-N-methyl-D-aspartate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and kynurenate, and also the intravenous administration of the N-methyl-D-aspartate receptor antagonist, ketamine. ⋯ Responses to noxious thermal stimulation were not affected by any of these antagonists, while the response to non-noxious thermal stimulation was blocked by 2-amino-5-phosphonovaleric acid, ketamine and kynurenate in the one neuron studied. The proportion of cells excited by the agonists differed from those observed in decerebrated cats: N-methyl-D-aspartate 9/32 (28%), quisqualate 50/54 (93%), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate 19/23 (83%) and domoate 17/38 (45%). Application of the putative endogenous excitatory amino acid precursor N-acetyl-aspartyl-glutamate (NAAG) did not elicit a response in any of the neurons studied.(ABSTRACT TRUNCATED AT 400 WORDS)
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Comparative Study
Autoradiographic localization of 5-hydroxytryptamine1A, 5-hydroxytryptamine1B and 5-hydroxytryptamine1C/2 binding sites in the rat spinal cord.
Autoradiographic techniques revealed that 5-hydroxytryptamine1A, 5-hydroxytryptamine1B and 5-hydroxytryptamine1C/2 binding sites are differentially distributed in the spinal cords of adult male rats. In the dorsal horn, 5-hydroxytryptamine1A sites were dense in all laminae; 5-hydroxytryptamine1B sites were more dense in laminae I, III and IV than in lamina II; while 5-hydroxytryptamine1C/2 sites were very sparse. The dorsal commissure gray matter also exhibited very dense 5-hydroxytryptamine1A and 5-hydroxytryptamine1B binding. ⋯ In the ventral horn, 5-hydroxytryptamine1A and 5-hydroxytryptamine1B sites were very sparse (except for very dense 5-hydroxytryptamine1A sites located in the dorsolateral nucleus of the pudendal nerve), while 5-hydroxytryptamine1C/2 sites were relatively dense in motor nuclei. Surprisingly, 5-hydroxytryptamine1B sites were moderately dense in the dorsal column corticospinal tract. These studies will provide an anatomical perspective for interpretation of the complex role of 5-hydroxytryptamine in regulating spinal cord function.