Glia–neuron interactions in the mammalian retina

Abstract

The mammalian retina provides an excellent opportunity to study glia-neuron interactions and the interactions of glia with blood vessels. Three main types of glial cells are found in the mammalian retina that serve to maintain retinal homeostasis: astrocytes, Müller cells and resident microglia. Müller cells, astrocytes and microglia not only provide structural support but they are also involved in metabolism, the phagocytosis of neuronal debris, the release of certain transmitters and trophic factors and K(+) uptake. Astrocytes are mostly located in the nerve fibre layer and they accompany the blood vessels in the inner nuclear layer. Indeed, like Müller cells, astrocytic processes cover the blood vessels forming the retinal blood barrier and they fulfil a significant role in ion homeostasis. Among other activities, microglia can be stimulated to fulfil a macrophage function, as well as to interact with other glial cells and neurons by secreting growth factors. This review summarizes the main functional relationships between retinal glial cells and neurons, presenting a general picture of the retina recently modified based on experimental observations. The preferential involvement of the distinct glia cells in terms of the activity in the retina is discussed, for example, while Müller cells may serve as progenitors of retinal neurons, astrocytes and microglia are responsible for synaptic pruning. Since different types of glia participate together in certain activities in the retina, it is imperative to explore the order of redundancy and to explore the heterogeneity among these cells. Recent studies revealed the association of glia cell heterogeneity with specific functions. Finally, the neuroprotective effects of glia on photoreceptors and ganglion cells under normal and adverse conditions will also be explored.

Gap Junction Coupled Cells, Barriers and Systemic Inflammation

“…The Müller cells are specialized radial glial cells and span through the entire thickness of the retina. They regulate the tightness of the BRB and are the link between the neurons and the compartments and represent around 90% of the glia in the retina [8]. Retinal astrocytes are found around blood vessels and the distribution depends on the density of nerve fibers.…”

“…Many human diseases, stroke, infectious and inflammatory processes, Alzheimer's disease, Parkinson's disease, HIV, obesity, type 2 diabetes, atherosclerosis, allergy, age-related macular degeneration (AMD), glaucoma, osteoarthritis (OA), systemic vasculitis, and cardiovascular diseases seem to have features in common, where there is a disruption of homeostasis, and they are nearly universally associated with systemic chronic inflammation [1][2][3][4][5][6][7][8]. Inducers of inflammation trigger the production of inflammatory mediators, which in turn alter the functionality of tissues and organs.…”

“…Cell-cell interactions lead to induction of specialized features of several barriers such as the blood-brain barrier (BBB) [1] and the blood-retinal barrier (BRB) [8]. The BBB controls transport processes between the central nervous system (CNS) and peripheral blood.…”

“…The junctional complexes that create these barriers are composed of distinct proteins; the claudins in forming the barrier, occludin in regulating permeability, and zonula occludens proteins in assembling the barrier by interacting with the transmembrane proteins. The necessity of glia and pericytes to induce the barrier has been demonstrated but it is just in its beginning [8]. The capillaries of the BRB seem to be similar to the capillaries of the BBB [14,17].…”

Ultrastructural Changes in the Retina during the Process of Paclitaxel-Induced Retinotoxicity Correction using Antioxidant Drug

“…Характерним для цьо-го терміну досліду є наявність численних відростків променевих гліоцитів в усіх шарах сітківки. Розга-луження відростків променевих гліоцитів у цей термін підкреслює їхнє значення для підтримки ретинальних нейронів, коли виникає потреба в за-безпеченні їхньої трофіки та антиоксидантної дії на фоторецептори і регуляції гемато-енцефалічногo бар'єру сітківки [8]. Досить часто спостерігаються капіляри як у зовнішньому, так і у внутрішньому капілярному сплетенні сітківки.…”