Variable varicosity sizes in glutamatergic input axons. Representative axonal varicosities labeled by selective BDA injections in L6a (a), spinal trigeminal nucleus pars oralis (SpVO; b), cortical L5b (c), and ventrolateral part of the principal trigeminal nucleus (PrV-VL; d) in Po. Scale bars: 10 µm. e, Size distribution of axonal varicosities in Po labeled different cortical and subcortical glutamatergic structures. Axonal varicosities were grouped into discrete intervals according to their maximal cross-sectional area. f, Box-plot diagram showing axonal varicosity sizes of all glutamatergic structures innervating Po. SpVC: caudalis spinal trigeminal nuclei; Cu: cuneatus; Gr: gracilis; SC: superior colliculus; SpVI: interpolaris spinal trigeminal nucleus; PrV-DM: dorsomedial part of the principal trigeminal nucleus.