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Computations on the Nervous System: Some Results
Published in Theodore B. Achacoso, William S. Yamamoto, AY's Neuroanatomy of C. elegans for Computation, 2022
Theodore B. Achacoso, William S. Yamamoto
Many nervous systems, particularly those like C. elegans, have gap junctions which appear to behave like electrical synapses. These can be shown to be equivalent to a “transform” pair different from the chemical synapse. Further, electrical synapses are evidently more dependent upon the space constant established by the physical location on the soma or dendrite. While this is certainly a consideration also for chemical synapses, the inclusion of these phenomena is omitted from the present discussion.
Introduction to botulinum toxin
Published in Michael Parker, Charlie James, Fundamentals for Cosmetic Practice, 2022
An electrical synapse occurs when the pre- and post-synaptic terminals are in electrical communication with one another. Ions are able to transfer between the synaptic terminals and subsequently these terminals are often bidirectional, allowing for signals to transfer back and forth. In some cases, there are rectifying junctions, which act as a one-way system for ions and subsequently regulate a unidirectional ion flow and synchronise the impulses of nerve cells. The transfer of nerve impulses along electrical synapses occurs almost immediately as the action of ion exchange is incredibly fast.
Synapses
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Electrical synapses, as commonly understood, have a direct connection between the cytoplasms of two cells by means of gap junctions consisting of at least several hundreds of channels (Figure 6.18). In vertebrates, these channels are made up of isoforms of the protein connexin having a molecular mass in the range of 26–57 kD, where a protein isoform is one of the different forms of the same protein. Six connexin molecules, not necessarily identical, form a hexameric hemichannel, or connexon, about 5–7.5 nm long and with an external diameter of about 7 nm. A connexon spans across the cell membrane and extends for 1–1.5 nm into the extracellular space. Each connexon has six protrusions, one from each of the connexin molecules, that fit into the depressions between the protrusions of the other connexon of the channel. A channel having a pore of 1.2–2 nm diameter is thus formed, with tight interlocking in the extracellular gap of 2–3.5 nm separating the membranes of the two cells. The tight interlocking is necessary to prevent leakage of ions between the channel and the extracellular space. The two connexons are held together noncovalently by hydrogen, hydrophobic, and ionic bonds between the extracellular loops of the connexin molecules.
Towards a functional connectome in Drosophila
Published in Journal of Neurogenetics, 2020
Context- and state-dependent neural processing is mediated on the level of neuron to neuron connections. A major limit to connectomes assembled by serial-section electron microscopy is that it lacks details on the nature of synaptic connections. Electrical synapses, which provide excitatory, non-directed and fast connections between neurons, are not reported in any Drosophila EM dataset. Chemical synapses provide directed information flow from pre- to postsynapse. In the Drosophila connectomes, chemical synapses are visually characterized by synaptic densities and vesicles filled with neurotransmitters. The Drosophila nervous system spans the full range of neurotransmitter molecules found in most animals including GABA, glutamate, and acetylcholine, monoamines, and neuropeptides. Without knowing the identity of released neurotransmitters, we cannot infer the sign and strength of synaptic modulation. Analysis of EM datasets allows discriminating small core vesicles containing neurotransmitters and dense core vesicles usually containing monoamines and neuropeptides (Michael, Cai, Xiong, Ouyang, & Chow, 2006), but otherwise provides no information about the neurotransmitter identity. Also, a single neuron can release several types of neurotransmitters or neuropeptides (Croset, Treiber, & Waddell, 2018; Nässel, 2018). Recently, input neurons to the learning and memory center in the fly, the mushroom bodies, have been shown to produce nitric oxide together with dopamine to establish short-term memory (Aso et al., 2019).
Distinctions among electroconvulsion- and proconvulsant-induced seizure discharges and native motor patterns during flight and grooming: quantitative spike pattern analysis in Drosophila flight muscles
Published in Journal of Neurogenetics, 2019
Jisue Lee, Atulya Iyengar, Chun-Fang Wu
We further examined how activity patterns characteristic of each motor programs were affected upon genetic or pharmacological manipulations. We studied well-characterized mutants of major neurotransmission systems known to have clear alterations in physiology and behavioral expression: (1) picrotoxin (PTX), a non-competitive antagonist of the GABAA receptor (Takeuchi & Takeuchi, 1969); (2) a related receptor mutant, Resistant to dieldrin (Rdl) that encodes the GABAA receptor α subunit (Ffrench-Constant, Mortlock, Shaffer, MacIntyre, & Roush, 1991) ; (3) Choline acetyltransferase (Cha) mutants with reduced acetylcholine (ACh) synthesis (Gorczyca & Hall, 1984; Greenspan, Finn, & Hall, 1980); and (4) mutants of ShakB, encoding an innexin gap junction protein required for transmission at electrical synapses (Thomas & Wyman, 1984). These treatments revealed clear quantitative distinctions between the seizure discharge patterns evoked by ECS and that induced by GABA receptor blockade via PTX. Thus, the quantitative approaches undertaken here may be applicable to the study of additional aberrant DLM IDs to explore their potential association with or distinction from the endogenous spike patterns during normal motor activities.
Molecular mechanisms that change synapse number
Published in Journal of Neurogenetics, 2018
Alicia Mansilla, Sheila Jordán-Álvarez, Elena Santana, Patricia Jarabo, Sergio Casas-Tintó, Alberto Ferrús
Electrical synapses are also subject to circadian changes. Rod photoreceptors in the mice kept under circadian conditions show a median junctional conductance of 98 pS during the subjective day and 493 pS during the subjective night. Conductance in dark adapted animals is about 140 pS regardless of the time of the day, while adaptation to bright light reduces it to near 0 pS, at all times during the circadian cycle (Jin & Ribelayga, 2016).