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Mesencephalic substrate of reward: lesion effects
1Centre de Recherche Fernand-Seguin, Hôpital Louis-H. Lafontaine, 7331 Hochelaga, Montreal, Que., Canada H1N 3V2. sboye@crfs.umontreal.ca
Behavioural Brain Research
|October 12, 2004
Summary
Lesions in the posterior mesencephalon (PM) alter brain reward pathways. These findings suggest that reward circuitry is diffusely spread throughout the PM, impacting medial forebrain bundle stimulation effectiveness.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
Background:
- The posterior mesencephalon (PM) is implicated in reward processing.
- A caudal extension of the medial forebrain bundle (MFB) pathway is suggested to involve PM neurons.
Purpose of the Study:
- To investigate the functional link between the PM and reward.
- To characterize how electrolytic lesions of the PM affect the rewarding effectiveness of ventral tegmental area (VTA) stimulation.
Main Methods:
- Electrolytic lesions were made at various sites within the PM of rats.
- The rewarding effectiveness of caudal MFB (VTA) stimulation was assessed before and after PM lesions.
- Changes in reward magnitude were measured based on stimulation parameters.
Main Results:
- PM lesions altered the rewarding effectiveness of VTA stimulation in a site-, current-, and time-dependent manner.
- Rewarding effectiveness was reduced in some rats and potentiated in others, with effects typically appearing two weeks post-lesion.
- Midline PM lesions caused transient reward reductions, while lateral lesions had minimal immediate effects or transient potentiation.
Conclusions:
- The results indicate a distributed reward-relevant circuitry throughout the PM.
- Lesions in the PM significantly modify the brain's response to reward stimulation, highlighting the PM's role in reward pathways.