Capsaicin, a transient receptor potential vanilloid type1 (TRPV1) agonist, has been reported to protect against
ischemia-reperfusion injury in various organs, including the brain, heart, and kidney, whereas activation of TRPV1 was also reported to contribute to neurodegeneration, including pressure-induced retinal ganglion cell death in vitro. We histologically investigated the effects of
capsaicin and
SA13353, TRPV1 agonists, on
retinal injury induced by intravitreal
N-methyl-d-aspartic acid (
NMDA; 200 nmol/eye) in rats in vivo. Under
ketamine/
xylazine anesthesia, male Sprague-Dawley rats were subjected to intravitreal
NMDA injection.
Capsaicin (5.0 nmol/eye) was intravitreally admianeously with
NMDA injection.
SA13353 (10mg/kg) was intraperitoneally administered 15 min before
NMDA injection. Morphometric evaluation at 7 days after
NMDA injection showed that intravitreal
NMDA injection resulted in
ganglion cell loss.
Capsaicin and
SA13353 almost completely prevented this damage. Treatment with
capsazepine (TRPV1 antagonist, 0.5 nmol/eye),
CGRP (8-37) (
calcitonin gene-related peptide (
CGRP) receptor antagonist, 0.5 pmol/eye), or RP67580 (
tachykinin NK1 receptor antagonist, 0.5 nmol/eye) almost completely negated the protective effect of
capsaicin in the
NMDA-injected rats. Seven days after intravitreal
NMDA injection, the cell number of retinal ganglion cell was significantly smaller than in the eye that had received
capsaicin in B6.Cg-TgN(Thy1-CFP)23Jrs/J transgenic mice that express the
enhanced cyan fluorescent protein in retinal ganglion cells in the retina. These results suggested that activation of TRPV1 protects retinal neurons from the injury induced by intravitreal
NMDA in rats in vivo. Activation of CGRP and
tachykinin NK1 receptors is possibly involved in underlying protective mechanisms.