Rabies Anterograde Monosynaptic Tracing Allows Identification of Postsynaptic Circuits Receiving Distinct Somatosensory Input.

Somatosensory neurons detect vital information about the environment and internal status of the body, such as temperature, touch, itch, and proprioception. The circuit mechanisms controlling the coding of somatosensory information and the generation of appropriate behavioral responses are not clear yet. In order to address this issue, it is important to define the precise connectivity patterns between primary sensory afferents dedicated to the detection of different stimuli and recipient neurons in the central nervous system. In this study we describe and validate a rabies tracing approach for mapping mouse spinal circuits receiving sensory input from distinct, genetically defined, modalities. We analyzed the anatomical organization of spinal circuits involved in coding of thermal and mechanical stimuli and showed that somatosensory information from distinct modalities is relayed to partially overlapping ensembles of interneurons displaying stereotyped laminar organization, thus highlighting the importance of positional features and population coding for the processing and integration of somatosensory information.