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Social defeat stress increases expression of mu-opioid receptor mRNA in rat ventral tegmental area
E M Nikulina1, R P Hammer, K A Miczek
1Department of Psychiatry, Tufts University, New England Medical Center, Boston, MA 02111, USA.
Abstract:
Prompted by previous studies linking social defeat stress to changes in opioid antinociception, we evaluated the expression of mu-opioid receptor (MOR)-encoding mRNA in selected rat brain areas as a function of this type of stress. Because opioids mediate significant regulatory activities of brain dopamine neurons, dopaminergic loci in the ventral tegmental area (VTA) and substantia nigra (SN) were selected for analysis. Within 30 min after social defeat stress, the level of MOR-encoding mRNA, as detected and quantified by in situ hybridization histochemistry, increased in the lateral VTA and this increase was present for at least 6 h. In contrast, defeat stress was without effect on the expression of MOR-encoding mRNA in the SN. These data suggest that stress-induced alteration of MOR-encoding mRNA expression in the VTA may be involved in the consequences of social defeat stress.
Insights
Social defeat stress increases mu-opioid receptor (MOR) mRNA in the rat ventral tegmental area (VTA) but not the substantia nigra (SN). This stress-induced change in MOR mRNA may influence the effects of social stress.
Area of Science:
- Neuroscience
- Neurobiology
- Stress Research
Background:
- Social defeat stress impacts opioid antinociception.
- Opioids regulate dopamine neuron activity in brain regions like the VTA and SN.
Purpose of the Study:
- To investigate the effect of social defeat stress on mu-opioid receptor (MOR)-encoding mRNA expression in specific rat brain areas.
- To determine if stress alters MOR mRNA levels in dopaminergic regions of the VTA and SN.
Main Methods:
- In situ hybridization histochemistry was used to detect and quantify MOR-encoding mRNA levels.
- Analysis focused on the lateral VTA and SN in rats subjected to social defeat stress.
Main Results:
- Social defeat stress significantly increased MOR-encoding mRNA levels in the lateral VTA within 30 minutes.
- This elevated MOR mRNA expression in the VTA persisted for at least 6 hours post-stress.
- No significant changes in MOR-encoding mRNA expression were observed in the SN following defeat stress.
Conclusions:
- Stress-induced alterations in VTA MOR mRNA expression may play a role in the consequences of social defeat.
- The VTA appears to be a key brain region affected by social stress in relation to opioid signaling.
