DISTINCT WIRING OF VENTRAL POSTERIOR AND POSTERIOR THALAMOCORTICAL AXONS IN THE MOUSE THALAMIC RETICULAR NUCLEUS

In addition to innervating somatosensory cortical areas, all axons arising from the ventral posterior nucleus (VP, a “first-order” relay) or the posterior nucleus (Po, a “higher order relay”) target, via collateral axon branches, the thalamic reticular nucleus (TRN). Synaptic interactions with TRN neurons, which project back to VP and Po create a dynamic inhibitory gate on thalamocortical signaling, which shapes what signals reach cortex, when, and in what temporal pattern. Recent studies have revealed differences among the axons arising from the various VP or Po subnuclei in their area / lamina-specific arborization in the cerebral cortex, as well as in axon varicosity/bouton sizes and synapse structure. In contrast, the structure of the VP-TRN and Po-TRN axon branches remains poorly characterized. We combined anterograde micropopulation tract-tracing and Sindbis-Pal-eGFP single-cell transfection of thalamocortical neurons from different VPM, VPL and Po subnuclei of the mouse thalamus. 3D Neurolucida reconstruction and quantitative measurements of the axonal collaterals in the somatosensory sector of TRN reveal significant differences in length, axonal varicosities number and size and distribution. Along with previous evidence regarding different TRN-thalamus axon projection patterns, our observations indicate the presence of parallel and structurally diverse VP and Po thalamo-reticular loops.
Funding: Ministerio de Ciencia e Innovación (MCIN) PID2024-160702NB-I00