The neuron-astrocyte-microglia triad in a rat model of chronic cerebral hypoperfusion: protective effect of dipyridamole

Abstract

Chronic cerebral hypoperfusion during aging may cause progressive neurodegeneration as ischemic conditions persist. Proper functioning of the interplay between neurons and glia is fundamental for the functional organization of the brain. The aim of our research was to study the pathophysiological mechanisms, and particularly the derangement of the interplay between neurons and astrocytes-microglia with the formation of “triads,” in a model of chronic cerebral hypoperfusion induced by the two-vessel occlusion (2VO) in adult Wistar rats (n = 15). The protective effect of dipyridamole given during the early phases after 2VO (4 mg/kg/day i.v., the first 7 days after 2VO) was verified (n = 15). Sham-operated rats (n = 15) were used as controls. Immunofluorescent triple staining of neurons (NeuN), astrocytes (GFAP), and microglia (IBA1) was performed 90 days after 2VO. We found significantly higher amount of “ectopic” neurons, neuronal debris and apoptotic neurons in CA1 Str. Radiatum and Str. Pyramidale of 2VO rats. In CA1 Str. Radiatum of 2VO rats the amount of astrocytes (cells/mm2) did not increase. In some instances several astrocytes surrounded ectopic neurons and formed a “micro scar” around them. Astrocyte branches could infiltrate the cell body of ectopic neurons, and, together with activated microglia cells formed the “triads.” In the triad, significantly more numerous in CA1 Str. Radiatum of 2VO than in sham rats, astrocytes and microglia cooperated in the phagocytosis of ectopic neurons. These events might be common mechanisms underlying many neurodegenerative processes. The frequency to which they appear might depend upon, or might be the cause of, the burden and severity of neurodegeneration. Dypiridamole significantly reverted all the above described events. The protective effect of chronic administration of dipyridamole might be a consequence of its vasodilatory, antioxidant and anti-inflammatory role during the early phases after 2VO.

The neuron-astrocyte-microglia triad in CA3 after chronic cerebral hypoperfusion in the rat: Protective effect of dipyridamole

“…We focused on changes in CA3 because it has an important role in memory processing and because it demonstrates milder functional, structural, and morphological alterations during ischemia than CA1. Therefore, a correlation with the modifications previously found in CA1 (Lana et al 2014) will be of particular interest. Furthermore, since few pharmacological therapies able to improve neurodegeneration and memory deficits in patients with chronic cerebrovascular pathologies are so far available, to find targets for new therapeutic strategies it is imperative to understand the pathophysiological mechanisms that link chronic ischemia with neurodegeneration and alterations of brain functions.…”

“…1A, according to the method previously published (Lana et al 2014). Briefly, rats were anesthetised with halothane and the right common carotid artery was occluded, (day -7, Fig.…”

“…The permanent, bilateral occlusion of the common carotid arteries of rats (two-vessel occlusion, 2VO) is a procedure that mimics age-related cerebrovascular stenosis and is widely utilized to investigate the mechanisms of chronic cerebral hypoperfusion and consequent neurodegenerative processes (Farkas et al 2007;Sarti et al 2002aSarti et al , 2002bLana et al 2014). The 2VO model has revealed that, the CA1 region of the hippocampus is particularly vulnerable not only to acute ischemia but also to hypoperfusion given by the 2VO, with consequent failure of neuronal signaling, and to learning and memory disturbances (Farkas et al 2006;Melani et al 2010;Ohtaki et al 2006;Schmidt-Kastner et al 2001;Shibata et al 2004).…”

“…It has been shown that microglia and astrocytes can be neuroprotective to a certain extent (Faulkner et al 2004;Hanisch and Kettenmann 2007;Li et al 2008;Myer et al 2006), but they can be dangerous for neuronal health (Block et al 2007). We have previously demonstrated in rat models of normal brain aging, of brain inflammation and chronic hypoxia, that in CA1 astrocytes and microglia actively collaborate in the clearance of apoptotic neurons and of neuronal debris (Cerbai et al 2012;Lana et al 2014). More specifically, in the rat model of cerebral hypoperfusion we demonstrated (Lana et al 2014) significant alteration in the interplay between neurons and glia in CA1 of 2VO-vehicle rats.…”

“…We have previously demonstrated in rat models of normal brain aging, of brain inflammation and chronic hypoxia, that in CA1 astrocytes and microglia actively collaborate in the clearance of apoptotic neurons and of neuronal debris (Cerbai et al 2012;Lana et al 2014). More specifically, in the rat model of cerebral hypoperfusion we demonstrated (Lana et al 2014) significant alteration in the interplay between neurons and glia in CA1 of 2VO-vehicle rats. The administration of dipyridamole during the acute phase of brain chronic hypoperfusion, reverting many of the effects observed in 2VO-vehicle rats, may be responsible for the prevention of the progression of the pathophysiological mechanisms after 2VO occlusion.…”