| Abstract No.: | A-E1160 |
| Country: | Canada |
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| Title: | THE PARAVENTRICULAR NUCLEUS OF THE THALAMUS AS A MODULATOR OF DYNORPHIN NEURONS IN THE NUCLEUS ACCUMBENS |
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| Authors/Affiliations: | 1 Gilbert Kirouac; 1 Sa Li;
1 University of Manitoba, Winnipeg, MB, Canada
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| Content: | Objectives: The paraventricular nucleus of the thalamus (PVT) is part of a group of midline and intralaminar thalamic nuclei implicated in brain arousal mechanisms. The PVT provides an especially impressive projection to both the core and shell of the nucleus accumbens (NAc). However, the types of neurons or neural mechanisms in the NAc influenced by the PVT remain unknown. A large portion of neurons in the NAc (95%) are GABAergic medium spiny neurons (MSN) which contain either the enkephalin or dynorphin opiate peptides as co-transmitters.
Materials and Methods: Experiments were done in the rat to determine if the PVT preferentially innervates a subpopulation of opiate containing MSNs in the NAc. We used a combination of tract-tracing, immunohistochemistry and electrophysiology combined with juxtacellular labeling to examine the connections between the PVT and the NAc in the rat.
Results: Using tract-tracing with the anterograde tracer biotin dextran amine (BDA) and immunohistochemical staining for prodynorphin (peptide precursor for dynorphin), we found that clusters of intense prodynorphin staining in the NAc received an overlapping fiber projection from the PVT. These overlapping clusters of PVT fibers and prodynorphin staining were found in different regions of both the core and shell of the NAc. We found that neurons in the NAc could be activated following electrical stimulation of the PVT (1 ms pulse, 800 ľA). We use juxtacellular labeling with neurobiotin and immunofluoresence to determine if the responsive neurons in the NAc were prodynorphin positive. We found that the majority of neurons in the NAc that were strongly activated by stimulation of the PVT were MSNs which contain prodynorphin. The observation that prodynorphin-positive neurons were excited with short onset latencies (<15 ms) to PVT stimulation is consistent with the PVT providing monosynaptic inputs to these neurons in the NAc.
Conclusion: Dynorphin neurons in the NAc are associated with aversive behavioral states and may play a role in psychiatric conditions such as depression and addiction. Since neurons in the PVT have been shown to be more active during arousal and stress, the results of the present study suggest that the PVT may relay arousal related information to dynorphin neurons. This places the PVT in a key anatomical position to influence adaptive behaviors associated with stress and aversive states.
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