Sensorimotor cortical projections to the marginal zone of the trigeminal subnucleus caudalis

An ultrastructural investigation of the marginal zone (lamina I) of the spinal trigeminal subnucleus caudalis was carried out in 7 adult cats at 30 h through 7 days after ablations of face area of the contralateral sensorimotor cortex. Corticofugal boutons were observed to undergo electron-dense degeneration in the marginal zone beginning 4 days after the cortical lesion. These boutons were small (1--2 micrometers), widely dispersed and made synaptic contacts onto small dendrites or dendritic spines. These new observations indicate that cortical inhibition and facilitation of ascending orofacial sensation may be mediated in part by a direct pathway to the marginal zone.