Sexual Dimorphism in the Mouse Kidney-Brain Connectome

In recent years, an increasing number of studies have shown that kidney function is not only influenced by local self-regulation and hormonal systems but is also largely regulated by the nervous system. Although it is known that there are multi-synaptic anatomical connections between central autonomic nuclei and the kidney, it remains unclear whether there are differences in neural connections between the nervous system and the renal cortex and medulla in male and female mice. Against this background, the authors of this paper attempted to map the central nervous system (CNS) neural network of the renal cortex and medulla using the transmission characteristics of pseudorabies virus (PRV).

Research Background and Objectives

The kidney plays a crucial role in maintaining internal homeostasis, including regulating fluid and electrolyte balance, acid-base balance, blood pressure regulation, and erythropoiesis. Recent studies have found that increased renal sympathetic nerve activity often accompanies kidney, cardiovascular, and metabolic diseases under pathological conditions. Research has shown that renal denervation is considered an adjunctive treatment option for refractory hypertension. Although various studies have described the central autonomic network of the kidney, their descriptions of neural connections for different genders and parts of the kidney remain unclear. This study aims to fill this gap by providing a sexually dimorphic kidney-brain connectome for male and female mice.

Paper Overview

This study was conducted by Xulin Li, Yuan Zhou, Feng Wang, and Liping Wang, all affiliated with the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences. The research was published in the 2024 issue of Neuroscience Bulletin.

Methods and Materials

Animal Cultivation

The study used 14- to 18-week-old virgin male and female C57BL/6J mice, with 5 in each group, purchased from Zhejiang Weitong Lihua Experimental Animal Technology Co., Ltd.

Virus Injection

The study used two PRV recombinant viruses, PRV-531 (with EGFP fluorescent marker) and PRV-724 (with mRuby fluorescent marker) for labeling analysis. Mice were weighed and anesthetized with 1% pentobarbital, then a total of 1μl of virus was injected into the left renal cortex and right renal medulla of the mice.

Tissue Preparation and Microscopic Imaging

Five days after virus injection, the mice were perfused and fixed through the heart, then the brain was removed and sectioned. Immunostained sections were photographed using a microscope and automatic section scanner, and neurons marked in specific brain regions were manually counted.

Data Analysis

Data were analyzed using GraphPad Prism 8.3.0 software for two-way analysis of variance (ANOVA). ****P <0.0001, ***P <0.001, **P <0.01, *P <0.05 were considered statistically significant.

Research Results

34 brain regions infected with PRV were labeled and quantified. Most kidney-related neurons were concentrated in the brainstem, midbrain, and hypothalamic regions, indicating that kidney function is fundamental to life and conserved. No significant differences were found in the number of infected neurons in these major subdivisions between male and female mice.

Gender Differences and Left-Right Differences in Renal Neural Connections

By injecting PRV-531 virus into the left kidney and PRV-724 virus into the right kidney, the distribution patterns of neurons connected to the left and right kidneys in the mouse brain were compared. Results showed that some brain regions such as PVN, PSTH, and DMV exhibited obvious lateralization. In terms of gender differences, CEA and PSTH showed stronger renal connections in male mice, while Pno, LDTGV, and NTS were stronger in female mice.

Neural Connections of Renal Cortex and Medulla

To explore the differences in brain connections with the renal cortex and medulla, PRV-531 and PRV-724 viruses were injected into the renal cortex and medulla, respectively. Results showed that neurons connecting the brain to the renal cortex and medulla were mainly distributed in the same brain regions, with no significant differences between male and female mice.

Distribution Patterns of Neurons Simultaneously Connecting Bilateral Kidneys and Renal Cortex/Medulla

Analysis showed that most brain regions had moderate co-labeling rates of virus-labeled neurons connecting the left and right kidneys and renal cortex and medulla, with no significant gender differences found.

Discussion

Unknown Roles of Brain Regions in Renal Function Regulation

The study discovered the importance of previously not extensively discussed brain regions such as RMC, EW, and PSTH in kidney connections. Particularly EW, which corresponds to the midbrain and is associated with various autonomic functions such as energy metabolism and cardiovascular function.

Application and Limitations of Viral Tracing Technology

The PRV virus used in the current study has higher labeling efficiency in the central nervous system, addressing the shortcomings of previous studies that did not distinguish between different substructures of the renal cortex and medulla. However, individual differences and interference from injection techniques may still exist in the experiments.

Impact of Gender Differences on Kidney Function

The results further elucidate potential mechanisms of gender differences in kidney diseases, going beyond traditional understanding of the influence of sex hormones.

Conclusion

This study provides a comprehensive kidney-brain connectome for male and female mice, refining the network structure of brain regions connecting to the renal cortex and medulla, and elucidating gender differences. This will contribute to a better understanding of how the brain coordinates different organs to maintain internal homeostasis and provide support for developing new therapeutic strategies.