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Synapses
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Neuroactive peptides, also referred to as neuropeptides, can act as neurotransmitters when released by neurons, with some neuropeptides released by glia. Neuropeptides can act as hormones when secreted by glands into the blood stream. More than 100 neuropeptides have been identified and are involved in a wide range of brain functions including sensory perception, feeding behavior, emotions, social behavior, learning, and memory. Examples are oxytocin, vasopressin, substance P, and opioids, which include endorphins, these being endogenous compounds that mimic the action of morphine. However, the site of synthesis of neuropeptides, the type of vesicles in which they are stored, and the mechanism and site of exocytosis are quite different from those of the aforementioned neurotransmitters, which are often referred to as small-molecule neurotransmitters to distinguish them from neuropeptides.
Drugs for Treatment of Neurological and Psychological Conditions
Published in Richard J. Sundberg, The Chemical Century, 2017
The amphetamines and analogs act by releasing noradrenaline and dopamine in the hypothalamus and have a powerful effect of inhibiting appetite (anorexigens). The hypothalamus has receptors for neuropeptides that either enhance (orexigenic) or suppress (anorexigenic) appetite. Norephedrine was available over-the-counter in the United States and Europe as its hydrochloride salt under brand names such as Monydrin, Proin, and Propalin. It was withdrawn in 2000 as a result of studies that indicated an increased risk of hemorrhagic stroke. An amphetamine analog, aminorex, was introduced as an anorexigen in Europe in the 1960s. It was subsequently linked to an increased incidence of primary pulmonary hypertension and was withdrawn from the market in the 1970s. Phentermine was granted FDA approval in the United States in 1959. Fenfluramine was approved in 1973. They were approved only for treatment of obesity and for short-term use. These drugs act by stimulating release of serotonin and activating serotonin receptors. These effects suppress appetite through the effect of serotonin on cerebral centers. During the 1990s, the use of amphetamine weight-loss drugs grew rapidly. The pure active enantiomer of fenfluramine, called dexfenfluramine and sold as Redux, was approved for use in 1995, on a close split vote of the FDA advisory panel. The approved use was for short-term treatment of obesity. Approval was withdrawn in 1997. The combination of fenfluramine and phentermine, known as fen-phen, was introduced in 1992, although the combination was never approved by FDA. It is believed that more than 8 million people, mostly women, received prescriptions. The structures of these drugs are shown in Scheme 17.9.
Aptamers as Therapeutic Tools in Neurological Diseases
Published in Rakesh N. Veedu, Aptamers, 2017
Lukas Aaldering, Shilpa Krishnan, Sue Fletcher, Stephen D. Wilton, Rakesh N. Veedu
Neuropeptides are small protein-like molecules that facilitate communication between neurons. The neuropeptide nociception/orphanin FQ (N/OFQ) is an endogenous ligand of the opioid receptor-like 1 receptor and is associated with the regulation of several biological functions, such as pain and stress. Aptamers have been developed to investigate or antagonize some neuropeptides. Faulhammer et al. [61] developed an L-enantiomeric oligonucleotide ligand that is able to antagonize the binding between N/OFQ and the ORL1 receptor.
Serum substance P level as a marker for subclinical rheumatoid arthritis activity
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Shimaa Borham Mohamed, Mohammed Fouad Elkenawy, Tamer Omar Elsaid, Ghada El-Saeed Mashaly
Substance P (SP) is a neuropeptide containing 11 amino acids in its structure and is encoded by Tachykinin Precursor 1 (TAC1) gene on human chromosome 7 [7]. It is widely present in both central and peripheral nervous systems [8]. Also, SP is released from immune cells such as macrophages, lymphocytes, and dendritic cells [9]. In addition to the role of SP in pain, the non-neuronal effects of SP include vasodilation, smooth muscle contraction, change in cardiovascular tone, blood cell production, pruritus, wound healing, cancer, etc. [8,10].
Intra-carotid body inter-cellular communication
Published in Journal of the Royal Society of New Zealand, 2023
Liam P. Argent, Aabharika Bose, Julian F. R. Paton
In addition to the receptors discussed here, it has also been proposed that there are specialised receptors (e.g. adrenoreceptors) expressed by cells of non-vasculature lineage (e.g. glomus cells) for receiving inputs directly from autonomic neurons (Brognara et al. 2020). Further, neuropeptides such as substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide, endothelin-1 and neuropeptide Y have also been detected in the carotid body (Iturriaga and Alcayaga 2004; Takahashi et al. 2011).
Biological function simulation in neuromorphic devices: from synapse and neuron to behavior
Published in Science and Technology of Advanced Materials, 2023
Hui Chen, Huilin Li, Ting Ma, Shuangshuang Han, Qiuping Zhao
Electrical synapse is the gap junction, a special way of cell-to-cell linkage, which makes the action potential direct transmission between cells (Figure 1(c-i)). For this synapse, the synaptic cleft is very small, only several nanometers. In the presynaptic and postsynaptic membrane, there are some connexons that are made up of connexins. Two connexons form a gap junction channel, a non-gate control channel, which allows some small molecules of water-soluble substances and ions to pass through. When the action potential is generated in a neuron, the local current based on ionic current can be directly stimulated and transmitted to another neuron through the gap junction channel. By this way, the action potential is propagated from neuron to neuron. From this, the electrical synapse has lots of outstanding features, such as low resistive, rapid and bidirectional propagation. Different from electrical synapse, chemical synapse depends on the neurotransmitters to accomplish the information transfer from neuron to neuron (Figure 1(c-ii)). In chemical synapse, there are more mitochondria and a large number of vesicles, in which the latter is also called synaptic vesicle with 20–80 nm diameter and high contains concentrations of neurotransmitters such as acetylcholine or amino acid transmitters, catecholamine transmitters and neuropeptide transmitters. When the action potential is transmitted to the presynaptic terminal of a neuron, the presynaptic membrane depolarizes. After the depolarization exceeds the threshold value, Ca2+ channel is activated and Ca2+ enters into the axoplasm of the terminal from the outside of the cell. The increase of Ca2+ can trigger the efflux of synaptic vesicles and cause the quantized release of neurotransmitters. Meanwhile, excess Ca2+ in the axoplasm is transported outside through Na+-Ca2+ reverse transporter in order to its normal concentration in the presynaptic terminal. Once the neurotransmitters are released, they can enter into the synaptic cleft and reach the postsynaptic membrane by diffusion. Ultimately, these neurotransmitters can act on the ionotropic receptor and control the permeability of certain ions. When certain ions enter the postsynaptic terminal, if the terminal occurs depolarization, the signal is called excitatory postsynaptic potential (EPSP). In this process, the excitatory neurotransmitters act on the ionotropic receptors in the postsynaptic terminal to open the specific ion channels (Na+ and K+). The net inward current is generated because Na+ influx of is greater than K+ outflow, in turn, lead to the depolarization of the postsynaptic terminal. On the contrary, inhibitory neurotransmitters are released from the presynaptic terminal to act on the ionotropic receptors, and then open the Cl- channel to generate the outward current that hyperpolarizes the postsynaptic membrane. In this case, it is called inhibitory postsynaptic potential (IPSP). By this way, the information is transmitted to the next neuron by releasing neurotransmitters. The distinguishing between electrical and chemical synapses is listed in Table 1. However, the chemical synapse is the majority of synapses in the human brain.