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Neuronal Function
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Several peptides act as neurotransmitters and interact with specific peptide receptors. Morphine receptors bind endogenous opioids (met-enkephalin, leu-enkephalin, dynorphin and β endorphin). Substance P is a neurotransmitter that depolarizes neurons in the spinal cord and the hypothalamus via IP3 activation. Somatostatin is an important neuropeptide that inhibits electrical activity in the hypothalamus, hippocampus, limbic system and neocortex.
Postulated Physiological and Pathophysiological Roles on Motility
Published in Edwin E. Daniel, Neuropeptide Function in the Gastrointestinal Tract, 2019
Hans-Dieter Allescher, Sultan Ahmad
Naloxone caused a concentration-dependent increase of the descending relaxation in the isolated guinea pig or rat colon, whereas the ascending contraction induced by abroad stretching was decreased.500 The opioid agonist Met-enkephalin and, with less potency, dynorphin and morphiceptin decreased descending relaxation and increased the ascending contraction. Additionally, the release of endogenous dynorphin, the putative mediator, was decreased during the descending relaxation and increased during the ascending contraction.500 This experiment suggested that endogenous opioids exert a continuous restraint on intrinsic VIP neurons and that the descending relaxation could be mediated in part by the elimination of this opioid restraint.500 The authors argue that increased opioid activity during the ascending reflex would increase contraction by direct muscle action,500 but alternative explanations for this excitatory effect seem possible, as discussed earlier.
PEPTIDES
Published in Stephen W. Carmichael, Susan L. Stoddard, The Adrenal Medulla 1986 - 1988, 2017
Stephen W. Carmichael, Susan L. Stoddard
To investigate the possibility that the opioid peptide precursor proenkephalin A was glycosylated, Watkinson, Dockray and Young (1988) utilized an antiserum raised against the carboxyl terminus of a [Met]enkephalin octapeptide to identify and characterize enkephalin-containing peptides from extracts of bovine adrenal medulla. This allowed them to isolate and characterize peptides extended from the amino terminus. They presented evidence that precursor polypeptide proenkephalin A can be glycosylated during translation in the rough endoplasmic reticulum.
Orexin one receptors within the basolateral amygdala are involved in the modulation of cognitive deficits associated with a migraine-like state in rats
Published in Neurological Research, 2021
Khadijeh Askari-Zahabi, Mehdi Abbasnejad, Razieh Kooshki, Saeed Esmaeili-Mahani
Some of signaling systems have gained attention in the treatment of migraine headaches. In particular, dysfunction of the orexin system physiology has been associated with the development of migraine attacks [19,20]. The orexins, orexin A and orexin B, act by the activation of two G-protein-coupled receptors, including the orexin one receptor (Orx1R) and orexin two receptor (Orx2R). While orexin-A is equipotent at both receptors, orexin-B shows more competence to Orx2R [21,22]. Previous studies strongly support the important role of orexin receptors in modulating pain-related behaviors and nociceptive processing. Imbalanced orexinergic transmission has been associated with increased sleep-pain processing [23]. In addition, intra-locus coeruleus infusion of Orx1R antagonist SB334,867 inhibited met-enkephalin induced analgesia in rats [24]. Moreover, intra-periaqueductal gray matter orexin-A microinjection decreased formalin-induced nociceptive behaviors in rats [25].
Isolation stress impacts Met-enkephalin in the hypothalamo-pituitary-adrenocortical axis in growing Polish Mountain sheep: a possible role of the opioids in modulation of HPA axis
Published in Stress, 2019
Krystyna Pierzchała-Koziec, Marta Dziedzicka-Wasylewska, Colin G. Scanes
In vitro Met-enkephalin release: In vitro release Met-enkephalin was determined in the presence or absence of naltrexone to examine possible auto-regulatory effects of the opioid peptide. Met-enkephalin release from tissue fragments was determined by the method of Kowalski and Giraud (1993) with some modifications. Briefly, fragments of tissues (20–30 mg) sliced by microtome were placed into 24-well plates each containing 1 ml of Krebs-Ringer bicarbonate buffer and incubated at 37 °C in 500 µl medium. After a 20 min preincubation period, tissues were incubated for 20 min periods with the following sequence: (1) basal medium; (2) in the presence of 100 nM naltrexone; (3) basal medium; (4) basal medium; (5) medium with addition of potassium chloride (56 mM). The ability of the latter treatment to increase Met-enkephalin release was used to demonstrate the viability of the tissues. Based on this provocation test, all tissues responded and were viable.
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].