CLARITY with neuronal tracing and immunofluorescence to study the somatosensory system in rats.

Abstract Background The CLARITY technique enables researchers to visualize different neuronal connections along the nervous system including the somatosensory system. New method The present work describes the antero-lateral and dorsal column pathways until the thalamic and cortical stations, as well as descending oxytocinergic and vasopressinergic innervations by means of combined CLARITY, neuronal tracing, and immunofluorescence techniques. We used male Sprague-Dawley rats of 13, 30, and 60 days. Results The main results are as follows: A) CLARITY is a reliable technique that can be combined with fluorescent neuronal tracers and immunofluorescence techniques without major procedure modifications; B) at spinal level, some primary afferent fibers were labeled by CGRP, as well as the presence of neuronal populations that simultaneously project to the gracile and ventral posterolateral thalamic nuclei; C) corticothalamic connections were visible when retrograde tracers were injected at thalamic level; D) oxytocin receptors were expressed in the spinal dorsal horn by GABAergic-positive neurons, reinforcing previous outcomes about the possible mechanism for oxytocin blocking the primary afferent sensory input. Comparison with existing methods and Conclusions The CLARITY technique lets us observe in a transparent way the entire processed tissue compared with classical histological methods. CLARITY is a potentially useful tool to describe neuroanatomical structures and their neurochemical stratus.