Distribution of the CXCL12 and CCL2 chemokines in the corneal trigeminal pathways : from the cornea to the brainstem.

Abstract

 

Purpose

 

The sensory innervation of the cornea originated from the ophtalmic division of the trigeminal ganglion whose neurons send fibers centrally to terminate in the trigeminal brainstem complex. Our recents studies showed that the chemokines CXCL12/SDF-1 and CCL2/MCP-1 and their receptors CXCR4 and CCR2 are produced by sensory neurons and glial cells in dorsal root ganglia and the spinal cord (Reaux-Le Goazigo et al., 2012 ; 2013) where both couples (CXCL12/CXCR4 and CCL2/CCR2) play a role in the modulation of spinal pain. To date the precise localization of these chemokines CXCL12 and CCL2 in the trigeminal sensory innervation of the cornea has not been described

 

Methods

 

Tissue preparation: Adult male C57BL/6 mice were deeply anesthetized and perfused with saline followed by 4% paraformaldehyde. Tissues (eye, trigeminal ganglion and brainstem) were kept overnight in 4% paraformaldehyde. Coronal brainstem sections (40 µm) were cut on a vibratome. Eye and trigeminal ganglion were cryoprotected, frozen and cryostat (16 µm) sections were taken. Light and immunofluorescence labeling : tissues sections were incubated with CXCL12 (Torrey Pines) and CCL2 (Torrey Pines) polyclonal antibodies. CXCL12 and CCL2 immunoreactivity (IR) were detected either with 3,3′-Diaminobenzidine (DAB) or fluorescent probes.

 

Results

 

In corneal cryosections, CXCL12-IR and CCL2-IR are detected in epithelial cells and keratocytes. Interestingly, we also observed CXCL12 and CCL2 labelling in corneal nerve fibers. At the trigeminal ganglion level, in the ophtalmic V1 region we noted a basal/ constitutive production of CXCL12 and CCL2 in primary afferent neurons and in glial satellite cells. Microscopic analysis of brainstem sections immunostained with CXCL12 and CCL2 antibodies showed that both chemokines are detected in neurons and nerve fibers at the ventral trigeminal subnucleus interpo-laris- caudalis (Vi/Vc) transition and in the trigeminal subnucleus caudalis-cervical cord (Vc/C1) junction region.

 

Conclusions

 

This anatomical study reported for the first time the distribution of CXCL12 and CCL2 along the corneal trigeminal neuronal pathways. Further investigations are now needed to evaluate whether these chemokines may play a role in the neuromodulation of trigeminal corneal pain.

 

 

CXCL12 immunoreactivity in trigeminal ganglion

 

 

CXCL12-IR in spinal trigeminal nucleus

 

Keywords: 419 anatomy • 480 cornea: basic science • 554 immunohistochemistry