Neuroscience
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The rostral ventral medulla has been shown to consist of three distinct subregions: the midline or raphé region, the lateral paragigantocellular-gigantocellular region and the rostro-ventrolateral reticular nucleus. All three regions have been shown to contribute to central vaso-regulation and to project towards sympathetic preganglionic neurons of the thoracic spinal cord. Therefore it is of particular interest to describe the interconnections between the three regions and to see if local afferents reach cells which have been implicated in the regulation of descending inputs. ⋯ The results of the present light microscopic tract-tracing study revealed a different pattern of the intramedullary projection of the lateral paragigantocellular-gigantocellular region and the rostroventrolateral reticular nucleus. These data are in support of the proposed parcellation of the two cytoarchitectonically different areas of the rostral ventrolateral medulla into two functionally distinct subdivisions. Furthermore, the direct anatomical connection revealed in the present study between cells of the rostral ventrolateral and ventromedial medulla oblongata indicates the possibility that vasoregulatory effects of some cells of the rostral ventrolateral medulla oblongata might be executed via direct projections onto serotonin-immunoreactive cells of the medullary raphé nuclei.
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We have used the evoked expression of the immediate early gene-encoded proteins (Krox-24, c-Fos, Fos B, Jun D, Jun B, c-Jun) to monitor visceral processing in both the spinal cord and hindbrain structures of rats undergoing either mechanical colorectal or chemical intraperitoneal stimulation. Experiments were conducted under controlled volatile anaesthesia to suppress affective reactions that visceral stimulations may induce. The results refer to the effects of anaesthesia alone, and of both innocuous and noxious stimulations. ⋯ The Edinger-Westphal nucleus is a structure in which noxious-evoked labelling was superposed onto the anaesthesia-evoked labelling. Nociception-evoked overexpression in this nucleus was maximal for intraperitoneal inflammation. The present work demonstrates that the central effects induced by either anaesthesia or visceroception including pain can be effectively monitored through the induction of an array of immediate early genes.(ABSTRACT TRUNCATED AT 400 WORDS)
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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.
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Dopamine-mediated behaviors and certain biochemical and molecular events associated with these behaviors were examined following continuous infusion of the D1 dopamine agonist SKF38393 or the D2 dopamine agonist quinpirole into mice for six days. SKF38393 produced a transient grooming behavior while quinpirole initially induced stereotypy, which was followed by an increased locomotor behavior. Continuous infusion of quinpirole caused a significant down-regulation of striatal D2 dopamine receptors without significantly changing the density of D1 receptors. ⋯ This treatment also induced a significant decrease in proenkephalin messenger RNA in striatum. Taken together, these results suggest that the down-regulation of D2 dopamine receptor and D2 receptor messenger RNA is the result of the persistent stimulation of D2 receptors and that the up-regulation of mu opioid receptors may be a compensatory response to a decreased biosynthesis of enkephalin. They suggest further that the biochemical and molecular changes that take place in dopaminergic and enkephalinergic systems following continuous treatment with dopamine agonists may underlie the mechanisms by which certain dopamine-mediated behaviors occur.