The Dynamics of Neuromodulation

Abstract

We address three aspects of neuroscience, each for long being largely overshadowed by the neuron doctrine's hegemony [1]: neuroglia (including here also the systems of neuronal and glia gap junctions), extracellular fluid in neural tissue (''brain cell microenvironment'' [2]), and neuromodulatory processes. Our leading notion is that the functional state of neurons, individually and in assemblies, is determined by a set of variables (ion conductances and membrane currents, thresholds for neural discharges, synaptic potentials, ion channel kinetics, etc.), whose values at any one time are to varying degrees affected by interactions and interdependencies of these three components, locally as well as globally, and at largely different time scales. In Section 25.2, we review the essential aspects of each of these components separately. This is to provide the basis for our principal objective to analyze in the Section 25.3 the global dynamics of the complex system these components jointly compose, covering a wide range of temporal scales that is characteristic of multifractals. Accordingly, self-similarity and the absence of any specific time scale ensure instant and automatic adaptation to neural impulse traffic over a wide range of frequencies. Background Gap Junctions and NeurogliaIn the normal brain neurons, astrocytes and oligodendrocytes are the most abundant and active cells. They express pannexins and connexins, with protein subunits of two families forming membrane channels. Most available evidence indicates that in mammals endogenously expressed pannexins form only hemichannels, whereas Criticality in Neural Systems, First Edition. Edited by Dietmar Plenz and Ernst Niebur.

Balancing and imbalancing effects of astrocytic receptors in tripartite synapses. Common pathophysiological model of mental disorders and epilepsy

“…However, this elementary synaptic principle has also been shown in tripartite synapses, where astrocytes coordinate synaptic networks leading to a balanced excitation and inhibition [12]. Importantly, every model of synaptic balancing should differentiate between the general principles of ''wiring'' and ''value'' transmission [13][14][15][16]. Hence, we must also refer to extrasynaptic receptors and to the extrasynaptic space in a model of tripartite synapses.…”