Trigeminal nerve section induces Fos-like immunoreactivity (FLI) in brainstem and decreases FLI in sensory cortex

Transecting the infraorbital nerve to the rat whiskers induced Fos-like immunoreactivity (FLI) in lamina I and II neuronal nuclei of the spinal trigeminal nucleus pars caudalis (Sp5c). The Fos-like immunostaining persisted for several weeks. The prolonged expression of FLI in Sp5c could be related to persistent activity in the sectioned nerve, or to trophic effects of injured ganglion neurons on brainstem cells. We postulate that Fos and related proteins may be involved in mediating alterations in gene expression associated with relatively long-term CNS adaptations to peripheral nerve injuries. Surprisingly, FLI decreased in contralateral sensory cortex, mainly in layers 2, 3 and 6, up to several days after the lesion. These decreases of cortical FLI may be due to decreased sensory neuronal activity, and/or to reducing the trophic influence of thalamic inputs on cortical neurons.