Whole-Brain Neural Connectivity to Cholinergic Neurons in the Lower Thoracic Intermediolateral Column

The intermediolateral column (IML) serves as a crucial hub for sympathetic information processing between the brain and peripheral organs, with its defining hallmark being the presence of cholinergic neurons expressing choline acetyltransferase (ChAT). Specifically, the IML of the lower thoracic cord plays a pivotal role in regulating abdominal metabolic and digestive viscera. However, little is known about the whole-brain neural connectivity targeting these lower thoracic IML cholinergic neurons, necessitating further investigation.

Specific retrograde tracing virus was injected into the lower thoracic IML of ChAT-Cre transgenic mice expressing Cre in the cholinergic neurons. After the virus has fully expressed, brain and spinal cord sections were prepared for whole-brain fluorescence imaging and quantitative analysis.

We found that virally labeled neurons were detected in 40 brain regions of ChAT-Cre mice, encompassing the telencephalon, diencephalon, and brainstem. Afferents were predominantly concentrated in 25 brainstem regions, with the pons providing the highest total number of afferents and the medulla offering the highest afferent density across both hemispheres. Although a small subset of regions exhibited strictly unilateral inputs or hemispheric preference, the overall projection pattern remained bilateral. Furthermore, our results revealed extensive projections to the IML from regions classically implicated in sympathetic outflow regulation and homeostatic control, including the paraventricular hypothalamic nucleus (PVN), lateral hypothalamic area (LH), and rostroventrolateral reticular nucleus (RVLM). In addition, inputs were also observed from motor-related regions, such as primary and secondary motor cortices (M1, M2), red nucleus (RN), and gigantocellular reticular nucleus (Gi), suggesting a potential anatomical basis for the central coupling of somatic motor and sympathetic functions.

Our study provides a comprehensive whole-brain anatomical map of inputs to lower thoracic IML cholinergic neurons. This extensive supraspinal network, integrating classical sympathetic and homeostatic centers with motor-related regions, suggests a potential anatomical basis for the central coordination of somatic motor and autonomic functions.