Effects of Morphine on Spontaneous and Evoked Activity in the Striatum Corpus

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Title: Effects of Morphine on Spontaneous and Evoked Activity in the Striatum Corpus
Author: Napier, Tavye Celeste
Abstract: This study consisted of three investigations . The first investigation was concerned with unit responses in globus pallidus and caudate nucleus to cumulative doses of morphine . A semichronic , phenobarbital anesthetized rat preparation was used . It was determined that systemically -administered morphine caused a naloxone -antagonized depression of spontaneous neuronal activity in 79 % of recorded pallidal cells (n=24 ) whereas only 27 % of caudate cells (n=26 ) were similarly affected . A Chi Square analysis comparing the number of cells depressed and not depressed in pallidum and caudate was significant (p < 0 .005 ) , clearly verifying area differences in response to morphine . Effects of systemically administered morphine on cortically -evoked unit activity in the caudate nucleus was the concern of the second investigation . A semichronic rat preparation , similar to the previous investigation , was used . Only 4 out of 36 caudate units demonstrated specific (naloxone -antagonized ) morphine -induced alteration of evoked activity . These results indicate that corticostriatal pathways may not be involved in actions that systemic morphine has in the caudate . Effects of microiontophoretically -applied naloxone on striatally -induced suppression of pallidal unit activity was assessed in the third investigation . Twenty -three pallidal cells whose activity was altered by caudate stimulation were recorded in chloral hydrate anesthetized rats . With microiontophoretic application of naloxone an increase in frequency of occurrence of action potentials during ill caudate -induced suppression of pallidal activity was often observed . The ability of naloxone to counteract caudate -induced suppression of pallidal activity indicates an enkephalinergie component in electrophysiological events occurring in the globus pallidus following caudate stimulation . These results demonstrate the ability of an exogenous opiate (morphine ) to alter unit activity in caudate nucleus and globus pallidus . Unit activity alterations produced by morphine , and alteration of stimulation -induced inhibition by naloxone , indicate an involvement of endogenous opiates (e .g . , enkephalins ) in neuronal events of the corpus striatum . Failure of morphine to alter cortically -evoked caudate activity suggests that enkephalin effects within the caudate are not mediated through an alteration of the influence of cortical inputs on striatal neurons .
URI: http : / /hdl .handle .net /2346 /9803
Date: 1982-05

Citation

Napier, Tavye Celeste Effects of Morphine on Spontaneous and Evoked Activity in the Striatum Corpus. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /9803 .

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