Maturational changes in analgesia produced by glutamate and morphine stimulation of the periaqueductal gray in infant rats.
Item
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Title
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Maturational changes in analgesia produced by glutamate and morphine stimulation of the periaqueductal gray in infant rats.
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Identifier
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AAI9029984
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identifier
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9029984
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Creator
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Tive, Leslie Anne.
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Contributor
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Adviser: Gordon A. Barr
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Date
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1990
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Language
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English
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Publisher
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City University of New York.
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Subject
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Psychology, Psychobiology
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Abstract
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The periaqueductal grey (PAG) of the midbrain supports opiate-induced (OA) and stimulation-produced analgesia (SPA) in adult animals and humans. The dorsal PAG (dPAG) mediates SPA more effectively, while the ventral PAG (vPAG) mediates OA and SPA. This thesis compared the development of the analgesia produced by glutamate and morphine in the dPAG and vPAG in the rat. The first experiment determined the ontogeny of analgesia produced by glutamate or morphine in the dPAG and the vPAG. Pups were given morphine or glutamate (vehicle, low or high dose) and tested for analgesia against thermal and mechanical noxious stimuli. At 3 and 10 days of age, morphine given to the vPAG produced analgesia against the thermal stimulus whereas glutamate given to the dPAG produced analgesia against the mechanical stimulus. In 14 day old pups, both drugs given to both sites produced analgesia against both types of stimuli. The second experiment assessed the naloxone sensitivity of analgesia supported by dorsal and ventral PAG sites. Naloxone attenuated the analgesia effects of morphine and glutamate given to the vPAG, but not the effects of either compound given to the dPAG. Thus, the PAG has a dorsal and a ventral region. Each region supports either glutamate-produced analgesia (GPA) or OA early in development and both regions support both types of analgesia in mature animals. The vPAG supports an opioid form of analgesia. The third experiment compared the roles of spinal serotonin (5-HT) and norepinephrine (NE) in OA and GPA. Glutamate and morphine were administered to the PAG followed by intrathecal (i.t.) injections of the noradrenergic antagonist phentolamine or the serotonergic antagonist methysergide. When either compound was given to the vPAG, i.t. methysergide more effectively attenuated analgesia against the thermal stimulus and i.t. phentolamine attenuated analgesia against the mechanical stimulus more potently. When glutamate was given to the dPAG, analgesia against both stimulus types was attentuated to the same degree. Therefore, glutamate and morphine activate a common descending system that modulates nociception. Descending serotonin systems exert a stronger modulatory effect on thermal noxious stimuli while NE systems produce stronger effects on mechanical stimuli.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
