Brain Synapses: Neurons, Astrocytes and Extracellular Vesicles in Health and Diseases

Synapses, abundant in the brain, are structures needed for life. Our introduction, based on forms of such structures published few decades ago, helped introducing recent concepts of health and diseases. Developing axons govern their growth by cell-to cell communication, axon guidance, synapse orientations. The assembly of synapses requires the organization and function of pre-synaptic and post-synaptic neuron terminals, connected to each other by extracellular thin clefts. Upon synapse stimulation the clefts expand up to several folds while pre- and post-synaptic thickness remain unchanged. In additional responses neurons co-operate with astrocytes and EVs, the latter dependent on extracellular and also on intracellular spaces. Glial cells and/or EV secretions induce neurons by various effects including traveling changes. Pre-synaptic responses are defined canonical if based on neurotransmitter release; non-canonical when dependent without release and also when discharged not of neurotransmitters but of EVs. Healthy and diseases depend on other general properties, such as those defined molecularly. Among neurodegenerative diseases, attention is specified by various properties of Alzheimer’s and other diagnoses. Critical identifications can be due to astrocyte and microglia cells or multiple effects induced by EVs. At present the complexity of the therapies is developing innovative initiatives.