Effect of somatostatin analogues on chemically induced ischaemia in the rat retina

Abstract

This study investigated the neuroprotective effect of somatostatin, cortistatin and agonists at somatostatin(2) (sst(2)) receptors in retinal explants subjected to chemical ischaemia. Eyecups of female Sprague-Dawley rats (250-300 g) were immersed in PBS buffer or PBS containing iodoacetic acid (IAA; 0.5, 5, 50, 100 mM) and sodium cyanide (NaCN; 2.5, 25, 250, 500 mM) (chemical ischaemia solution) for 15, 30, 45, 60, 120 min (pilot study). Subsequently, eyecups were incubated with (1) PBS, (2) chemical ischaemia solution (5 mM IAA/25 mM NaCN) or (3) somatostatin, cortistatin, BIM23014 or MK678 (0.1, 1, 10 microM) together with the chemical ischaemia solution for 60 min, followed by a second 60-min incubation in PBS (control and ischaemia groups) or ligands in PBS (neuroprotection groups). The eyecups were subsequently fixed and sectioned for immunohistochemistry. Treatment of the eyecups with IAA/NaCN (5/25 mM) for 60 min abolished choline acetyltransferase (ChAT), tyrosine hydroxylase and brain nitric oxide synthase immunoreactivity in the inner nuclear, inner plexiform and ganglion cell layers. It also abolished protein kinase C immunoreactivity in rod bipolar cells and terminals, but did not damage ganglion cells labelled for microtubule-associated protein-1. TUNEL staining provided evidence of cell death in the ischaemic retina. Cortistatin, BIM23014 and MK678 attenuated the retinal damage caused by the chemical ischaemia in a concentration dependent manner. The ligands afforded approximately 58, 76 and 49% neuroprotection, respectively, of the ChAT immunoreactive cells. These results demonstrate that somatostatin analogues can protect the retina from ischaemic damage. The chemical ischaemia model is presently employed for the elucidation of the mechanisms involved in the neuroprotection.

The Neuropeptide Systems and their Potential Role in the Treatment of Mammalian Retinal Ischemia: A Developing Story

“…In studies with an ex vivo model of the rat retina, SRIF analogues have been reported to significantly reduce the ischemic damage suffered by retinal neurons [39]. These observations have been replicated in an ex vivo model of the ischemic mouse retina, where the neuroprotective effects of SRIF have been shown to be mediated by the sst2 receptor.…”

Novel signals mediating the functions of somatostatin: The emerging role of NO/cGMP

“…In this model, somatostatin analogs selective for the sst 2 subtype protected the retina from the ischemic insult and were successful in reversing retinal cell death (Mastrodimou et al, 2005). Recent data have shown that the increased presence of sst 2 receptors, in retinas of mice not expressing the sst 1 receptor subtype, protected the retina from ischemia (hypoxia and iodoacetic acid) (Catalani et al, 2007).…”

“…The study by Mastrodimou et al (2005) suggested that rod bipolar and tyrosinehydroxylase sst 2 containing neurons were protected from the ischemic insult, possibly due to the sst 2 involvement in the attenuation of calcium levels. However, the neuroprotection afforded to cholinergic and nNOS containing neurons, that lack sst 2 receptors, could not be explained.…”

Physiology and pathology of somatostatin in the mammalian retina: A current view

“…protects against ischemia-reperfusion injury (Celiker and Ilhan, 2002) and sst 2 agonists attenuate cell death in rat retinal explants subjected to chemical ischemia (Mastrodimou et al, 2005).…”

“…In particular, in explants of the rat retina subjected in vitro to chemical ischemia, sst 2 agonists prevent, at least in part, the loss of several retinal cell populations, including choline acetyltransferase-, tyrosine hydroxylase-, nitric oxide synthase-positive amacrine cells as well as the rod bipolar cells (Mastrodimou et al, 2005). On the other hand, other studies in a model of in vitro ischemia of the mouse retina have recently demonstrated that the extent of sst 2 -mediated protection may vary among different retinal cell populations , suggesting a high level of complexity within the neuroprotective mechanisms of sst 2 .…”