Anatomical aspects of corticotrigeminal projections to the medullary dorsal horn

Abstract

Corticofugal projections to neurons in the medullary dorsal horn, i.e., the trigeminal spinal subnucleus caudalis (Sp5C), are thought to play a critical role in regulating nociceptive information processing in the trigeminal nervous system. The Sp5C consists of 5 layers, each of which exhibits its own characteristic features of cellular organization. Therefore, the layers receiving corticofugal projections must be identified when discussing the role of the cerebral cortex in nociception arising from the trigeminal nerve. It is also necessary to discriminate between layers of the Sp5C where corticofugal projections terminate, because the Sp5C involves glutamatergic neurons and GABAergic/glycinergic neurons, which correspond to excitatory and inhibitory neurons, respectively. This review summarizes descending projections from the cerebral cortex, including the primary and secondary somatosensory and insular cortices, to the Sp5C.

Descending projections from the insular cortex to the trigeminal spinal subnucleus caudalis facilitate excitatory outputs to the parabrachial nucleus in rats

“…The roles of corticofugal projection neurons in modulating sensory information from the trigeminal nervous system have been explored by electrical stimulation of cerebrocortical regions in combination with recording neural activities in the interpolaris 17 and the Sp5C. 32,52 The suppressive tendency of nociceptive information processing in Sp5C neurons by stimulating the somatosensory cortex is supported by several other studies using c-Fos expression 19 and optogenetics. 7 Corticofugal projections also modulate the frequency and synchronization strength of oscillation activities in the interpolaris and principalis of the trigeminal complex.…”