The Mesoscopic Connectome of the Cholinergic Pontomesencephalic Tegmentum

The pontomesencephalic tegmentum, comprising the pedunculopontine nucleus and laterodorsal tegmental nucleus, is involved in various functions via complex connections; however, the organizational structure of these circuits in the whole brain is not entirely clear. Here, combining viral tracing with fluorescent micro-optical sectional tomography, we comprehensively investigated the input and output circuits of two cholinergic subregions in a continuous whole-brain dataset. We found that these nuclei receive abundant input with similar spatial distributions but with different quantitative measures and acquire similar neuromodulatory afferents from the ascending reticular activation system. Meanwhile, these cholinergic nuclei project to similar targeting areas throughout multiple brain regions and have different spatial preferences in 3D. Moreover, some cholinergic connections are unidirectional, including projections from the pedunculopontine nucleus and laterodorsal tegmental nucleus to the ventral posterior complex of the thalamus, and have different impacts on locomotion and anxiety. These results reveal the integrated cholinergic connectome of the midbrain, thus improving the present understanding of the organizational structure of the pontine-tegmental cholinergic system from its anatomical structure to its functional modulation.

Automated summary

In this study, the input and output circuits of two cholinergic subregions in the midbrain were comprehensively investigated using viral tracing and fluorescent micro-optical sectional tomography. The results revealed similar spatial distributions of input and neuromodulatory afferents, as well as different quantitative measures, in these cholinergic nuclei. Additionally, the cholinergic nuclei showed similar targeting areas across multiple brain regions, but had different spatial preferences in 3D. Some cholinergic connections were found to be unidirectional and had different impacts on locomotion and anxiety. Overall, this study provides a better understanding of the organizational structure and functional modulation of the pontine-tegmental cholinergic system.