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Perspectives for the Study of GUT Neuropeptides
Published in Edwin E. Daniel, Neuropeptide Function in the Gastrointestinal Tract, 2019
The existence of multiple related peptides and receptor subtypes for nearly all neuropeptides is a further technical complication, since in most cases each of the subtypes can recognize several related peptides. For example, among the mammalian tachykinins, substance P, neurokinin A, and neurokinin B are each recognized by each of their receptors (NK-1, NK-2, and NK-3, respectively). Both Met- or Leu-enkephalin are recognized by μ-, δ-, and κ-opioid receptors, although with different affinities. In the case of tachykinin receptors, affinities at each receptor appear to be varying by less than a log unit for each naturally occurring tachykinin. Multiple related peptides and multiple receptor subtypes complicate identification of neurotransmitter and paracrine actions since both the correct peptide and receptor antagonist must be used in comparing putative to real transmitters (e.g., see Reference 7).
Central Stress-Limiting Systems and Cardioprotective Effects of their Mediators and Activators
Published in Felix Z. Meerson, Alexander V. Galkin, Adaptive Protection of The Heart: Protecting Against Stress and Ischemic Damage, 2019
Felix Z. Meerson, Alexander V. Galkin
In stress caused in rats by 18 h hanging by the cervical fold, prior administration of a leu-enkephalin analog (0.1 mg/kg) substantially alleviated the complex of nonspecific stress damage (gastric ulceration, eosinopenia, and atrophy of the thymus) and checked the glucocorticoid elevation in blood.75 Again, in stress caused by acute myocardial ischemia some leu-enkephalin analogs attenuated the stress-induced elevation of blood cortisol and prevented the rise in aldosterone,76,77 as well as attenuated twofold to threefold the stress increase in catecholamine excretion with urine.78 Concurrently, OP administration before such stress prevented the stress decline in insulin secretion and the phenomenon of “stress diabetes”.78 Finally, prior administration of OPs efficiently prevented the rise in blood vasopressin in stress from acute myocardial ischemia or trauma.76
Selective Post-Translational Processing of Opioid Peptides in Cardioregulatory Mechanisms of the Dorsal Medulla
Published in I. Robin A. Barraco, Nucleus of the Solitary Tract, 2019
William R. Millington, Michael D. Hirsch
Prodynorphin processing is relatively uncomplicated compared to POMC and proenkephalin.27,28 The prohormone contains three copies of leu-enkephalin clustered near its C-terminal, each of which forms the N-terminal of a different set of dynorphin peptides; α-neo-endorphin, dynorphin A (dynorphin-1-17), and dynorphin B-29 (leumorphin). These, in turn, serve as precursors to yet smaller forms. Hence, α-neo-endorphin is converted to β-neo-endorphin through removal of its C-terminal arginine residue, and dynorphin-1-17 undergoes endoproteolytic cleavage at a single arginine residue, forming dynorphin-1-8. Dynorphin B-29 is similarly processed at a single arginine, forming a 13-amino-acid peptide, dynorphin B (rimorphin). Leu-enkephalin may also be a product of prodynorphin processing, at least in certain brain regions.60 Like other opioids, the ratio of dynorphin peptides varies regionally, although dynorphin-18, dynorphin B, and α-neo-endorphin predominate in many brain areas.25,26,28,61
Neuropharmacological basis for multimodal analgesia in chronic pain
Published in Postgraduate Medicine, 2022
Ryan Patel, Anthony H Dickenson
The pain-relieving properties of naturally occurring opioids have been utilized for centuries, and today opioids remain the mainstay of treating acute and chronic pain. Morphine has become the gold standard analgesic to which all others are compared. The classical opioid receptors μ, δ and κ are G-protein coupled, and later a fourth opioid-like receptor (ORL1) was described and renamed the nociceptin receptor. Soon after, a series of endogenous peptide ligands were described. Most of these bind to multiple receptors through endomorphin-1/2 and β-endorphin have highest affinity for μ-opioid receptors, met- and leu-enkephalin have highest affinity δ-opioid receptors, dynorphin A/B have highest affinity κ-opioid receptors, and nociceptin/orphanin FQ has highest affinity for the nociceptin receptor [69]. Upon receptor activation neuronal excitability or action potential propagation is inhibited by several mechanisms including opening of G protein–coupled inwardly rectifying potassium channels [70], inhibition of sodium [71] and calcium channels [72], and inhibition of Ih currents [73].
Stimulatory and inhibitory effects of morphine on pentylenetetrazol-induced epileptic activity in rat
Published in International Journal of Neuroscience, 2021
Samrand Rashan, Yousef Panahi, Emad Khalilzadeh
According to Sesack and Pickel, in the ventral tegmental area of rats, approximately 20% of axon terminals immunoreactive for leu-enkephalin are labeled for GABA. In the locus ceruleus, a high proportion (38%) of leu-enkephalin immunoreactive axon terminals is found labeled for GABA. In other studies, single cells received afferents from both encephalin-ergic and GABAergic afferents without the two substances coexisting in the same terminal [11]. The mechanism of this action may be mediated by inhibitory effects on GABAergic activity, not triggering the excitatory glutamate pathways [23]. Some studies report that the number of active GABA receptors on the postsynaptic membrane decreases gradually during prolonged seizures, whereas the number of inactive GABA-A receptors increases. These changes result in a significant reduction in the efficacy of anticonvulsant drugs, such as clonazepam, diazepam, valproic acid, phenobarbital, propofol, and midazolam, which target the GABAergic system [24].
New concepts in opioid analgesia
Published in Expert Opinion on Investigational Drugs, 2018
Endogenous opioid peptides are derived from the precursors proopiomelanocortin (encoding beta-endorphin), proenkephalin (encoding Met-enkephalin and Leu-enkephalin), and prodynorphin (encoding dynorphins). These peptides contain the common Tyr-Gly-Gly-Phe-Met/Leu sequence at their amino terminals, known as the opioid motif. Beta-endorphin and the enkephalins are antinociceptive agents acting at mu- and delta-opioid receptors. Dynorphins can elicit both pro- and antinociceptive effects via N-methyl-D-aspartate receptors and kappa-opioid receptors, respectively. A fourth group of tetrapeptides (endomorphins) with yet unknown precursors do not contain the pan-opioid motif but bind to mureceptors with high selectivity. Opioid peptides are expressed throughout the central and peripheral nervous systems, in neuroendocrine tissues, and in immune cells [10,11,13,15]. Interactions between immune cell-derived opioid peptides and peripheral opioid receptors have been examined extensively, particularly with regard to the generation of analgesia [9–11].