Urocortin 2 treatment is protective in excitotoxic retinal degeneration.

Urocortin 2 (Ucn 2) is a corticotrop releasing factor paralog peptide with many physiological functions and it has widespread distribution. There are some data on the cytoprotective effects of Ucn 2, but less is known about its neuro- and retinoprotective actions. We have previously shown that Ucn 2 is protective in ischemia-induced retinal degeneration. The aim of the present study was to examine the protective potential of Ucn 2 in monosodium-glutamate (MSG)-induced retinal degeneration by routine histology and to investigate cell-type specific effects by immunohistochemistry. Rat pups received MSG applied on postnatal days 1, 5 and 9 and Ucn 2 was injected intravitreally into one eye. Retinas were processed for histology and immunocytochemistry after 3 weeks. Immunolabeling was determined for glial fibrillary acidic protein, vesicular glutamate transporter 1, protein kinase Cα, calbindin, parvalbumin and calretinin. Retinal tissue from animals treated with MSG showed severe degeneration compared to normal retinas, but intravitreal Ucn 2 treatment resulted in a retained retinal structure both at histological and neurochemical levels: distinct inner retinal layers and rescued inner retinal cells (different types of amacrine and rod bipolar cells) could be observed. These findings support the neuroprotective function of Ucn 2 in MSG-induced retinal degeneration.

Protective effects of vasoactive intestinal peptide (VIP) in ischemic retinal degeneration.

Vasoactive intestinal peptide (VIP) is a pleiotropic neuropeptide, acting as a neuromodulator and neuroprotective peptide in the CNS after injuries. We have previously described that pituitary adenylate cyclase-activating polypeptide (PACAP), another member of the same peptide family, is retinoprotective in ischemic lesions. The aim of this study was to investigate the protective potential of VIP in bilateral common carotid artery occlusion (BCCAO)-induced ischemic retinal lesion. Two-month-old rats were subjected to BCCAO and treated with intravitreal VIP injection. Their retinas were processed for histology after 2 weeks of survival. We measured the number of the cells/100 µm of the ganglion cell layer and the thickness of each layer such as the outer nuclear, outer plexiform, inner nuclear, and inner plexiform layers as well as that of the whole retina. We found that treatment with 1,000 pmol VIP, but not 100 pmol VIP, had significant protective effects in BCCAO-injured retina, as shown by the morphometric analysis. Comparing the neuroprotective effects of VIP and PACAP in BCCAO-operated retinas, PACAP was more effective, already protective at 100-pmol doses. Similar to other studies, we found that VIP must be given at least in 10 times more concentration than PACAP to achieve a similar degree of neuroprotection in the retina.

Mice deficient in pituitary adenylate cyclase activating polypeptide (PACAP) are more susceptible to retinal ischemic injury in vivo.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuroprotective peptide exerting protective effects in neuronal injuries. We have provided evidence that PACAP is neuroprotective in several models of retinal degeneration in vivo. Our previous studies showed that PACAP treatment ameliorated the damaging effects of chronic hypoperfusion modeled by permanent bilateral carotid artery occlusion. We have also demonstrated in earlier studies that treatment with PACAP antagonists further aggravates retinal lesions. It has been shown that PACAP deficient mice have larger infarct size in cerebral ischemia. The aim of this study was to compare the degree of retinal damage in wild type and PACAP deficient mice in ischemic retinal insult. Mice underwent 10 min of bilateral carotid artery occlusion followed by 2-week reperfusion period. Retinas were then processed for histological analysis. It was found that PACAP deficient mice had significantly greater retinal damage, as shown by the thickness of the whole retina, the morphometric analysis of the individual retinal layers, and the cell numbers in the inner nuclear and ganglion cell layers. Exogenous PACAP administration could partially protect against retinal degeneration in PACAP deficient mice. These results clearly show that endogenous PACAP reacts as a stress-response peptide that is necessary for endogenous protection against different retinal insults.