Escribir un comentario

Review for “A neuropeptide-specific signaling pathway for state-dependent regulation of the mesolimbic dopamine system”

Yue Yu, Theresa Haunold

Preprint doi: https://doi.org/10.1101/2025.07.17.665396

Summary:

In this preprint, the authors use mouse models to investigate the mechanisms and extent to which dopamine (DA) neurons in the ventral tegmental area (VTA) are regulated by interoceptive signals associated with internal states such as hunger and thirst, and how these signals shape consummatory behavior. Using CRISPR/SaCas9-mediated mutagenesis and ex vivo calcium imaging, the authors demonstrate that transient receptor potential canonical type 6 (TRPC6) channels selectively regulate neuropeptide receptor-induced calcium signaling in VTA-DA neurons, while exerting minimal influence on calcium responses driven by neurotransmitter receptors. Whole-cell patch-clamp recordings indicate that Trpc6 mutagenesis does not alter the intrinsic excitability of VTA-DA neurons. Finally, in vivo calcium imaging during a multi-sucrose consumption task in head-restrained mice shows that TRPC6 channels modulate scalable reward evaluation and consummatory behavior in hungry, but not thirsty, mice.

Strengths:

By combining CRISPR/SaCas9-mediated mutagenesis with ex vivo calcium imaging and whole-cell patch-clamp recordings, this preprint provides a robust experimental framework to investigate how hunger- and thirst-related neuropeptides modulate VTA-DA neuron activity and to assess their intrinsic excitability. In vivo calcium imaging during a multi-sucrose consumption task further links neuronal activity to real-time consummatory behavior.

Weakness:

The reliance on bulk fiber photometry limits insight into how individual VTA-DA neurons encode hunger- versus thirst-related behaviors. In addition, the behavioral design using sucrose at varying concentrations may complicate interpretation of internal-state specificity. Finally, the in vivo calcium signals associated with altered reward scaling in sgTrpc6 mice appear modest, raising the question of whether TRPC6 loss produces a sufficiently robust change in DA neuron activity to account for the corresponding behavioral phenotype.

Major comments:

1. In Figure 4 and 5, the conclusions regarding TRPC6-dependent modulation of state-specific reward processing would be substantially strengthened by single-cell calcium imaging during water and food consumption under thirst and hunger. Because the current in vivo data rely on bulk fiber photometry, it remains unclear how individual VTA-DA neurons encode these behaviors and whether TRPC6 loss affects specific neuronal subpopulations that drive the observed phenotype.

2. In Figure 4C-E and Figure 5A-C, both groups exhibited comparable licking behavior and calcium responses across all five solutions, leading the authors to conclude that TRPC channels are dispensable for reward valuation and consummatory behavior in thirsty mice. However, varying sucrose concentrations may confound the evaluation of water’s reward value under thirst. To strengthen this conclusion, the authors could consider assessing licking behavior and performing fiber photometry using water alone in both groups.

3. In Figure 4 and Figure 5, the in vivo calcium signals associated with altered reward scaling in sgTrpc6 mice appear modest, with significant differences emerging only between the 20% and 30% sucrose conditions. This raises questions about whether TRPC6 loss produces a functionally meaningful change in DA neuron activity sufficient to account for the behavioral phenotype. To strengthen the interpretation, it would be helpful to assess neural responses to additional, compositionally distinct food stimuli, such as lab chow, comparing Ensure versus diluted Ensure, or Ensure versus quinine, as shown in prior work (doi.org/10.1016/j.cell.2020.07.031).

4. In Figure 4F-H and Figure 5D-F, the sgTrpc6 group exhibited impaired assessment of reward value and scalable liking behavior for 20% and 30% sucrose in hungry mice. To further verify this deficit, a two-bottle preference assay directly comparing 20% and 30% sucrose could determine whether hungry mice in both groups can properly discriminate between these concentrations.

Minor comments:

1.        In Figure 2A, the authors note no significant difference in the proportion of responsive versus nonresponsive cells. A brief discussion or potential explanation would help contextualize this finding.

2.        In Figure 2D and corresponding text, reporting the percentage of each neuron type observed in control and Trpc6 knockdown conditions would aid interpretability.

3.        On page 7, in the text accompanying Figure 2F, please consider noting that VTA-DA neurons in the sgTrpc6 group showed a significant reduction in the proportion of responsive versus nonresponsive cells at 1uM NTS, and update the text as needed to improve reader understanding.

4.        The authors might consider moving Figure 3A to the first figure, as it provides a helpful schematic of the viral injection strategy used throughout the paper.

5.        To aid interpretation, please consider indicating “NS” for all comparisons that do not reach statistical significance.

6.        On page 6, confirm the reference to Fig. 1A should be corrected to Fig. 2A and update as needed to improve reader understanding.

Competing interests

The authors declare that they have no competing interests.

Use of Artificial Intelligence (AI)

The authors declare that they did not use generative AI to come up with new ideas for their review.