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Morphine withdrawal-induced morphological changes in the nucleus accumbens
Saturnino Spiga1, Maria Cristina Puddu, Milena Pisano
1Department of Animal Biology and Ecology, University of Cagliari, Italy.
The European Journal of Neuroscience
|November 3, 2005
Summary
Morphine withdrawal significantly reduces dendritic spine density in nucleus accumbens shell neurons, impacting dopamine transmission. This effect, observed during withdrawal but not chronic morphine use, highlights a key change in opioid dependence.
Area of Science:
- Neuroscience
- Pharmacology
- Addiction Research
Background:
- Opioid dependence is associated with altered mesolimbic dopamine transmission.
- Morphine withdrawal is known to cause hypofunction of mesencephalic dopamine neurons.
- Medium spiny neurons (MSN) in the nucleus accumbens are key targets of dopamine.
Purpose of the Study:
- To investigate the morphological changes in nucleus accumbens MSN during morphine withdrawal.
- To determine if chronic morphine treatment itself, or withdrawal, affects MSN morphology.
- To differentiate the effects on core and shell regions of the nucleus accumbens.
Main Methods:
- Chronic morphine administration to rats at escalating doses.
- Induction of spontaneous and naloxone-precipitated morphine withdrawal.
- Golgi-Cox staining of MSN followed by confocal laser-scanning microscopy (CLSM) analysis.
Main Results:
- Morphine withdrawal, both spontaneous and precipitated, significantly reduced spine density in shell MSN.
- This reduction was selectively localized to second-order dendritic trunks.
- Chronic morphine treatment alone did not alter MSN perikarya size or spine density.
Conclusions:
- Morphine withdrawal, not chronic morphine use per se, alters MSN spine density in the nucleus accumbens.
- The observed reduction in spine density is specific to the shell region of the nucleus accumbens.
- These morphological changes likely contribute to the hypodopaminergic state characteristic of opioid dependence.