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Orthostatic Hypotension Induced by Drugs and Toxins
Published in David Robertson, Italo Biaggioni, Disorders of the Autonomic Nervous System, 2019
The mechanism of MAOI-induced orthostatic hypotension is believed to involve the accumulation of “false neurotransmitters”. Tyramine is normally oxidized by monoamine oxidase in the intestinal mucosa and the liver. During MAOI therapy, tyramine reaches the systemic circulation in large quantities, where it is hydroxylated to octopamine, which is then taken up by noradrenergic nerve terminals. Octopamine is a very weak pressor agent and when released instead of noradrenaline results in orthostatic hypotension. The extent of the lowering of supine and upright blood pressure correlated with the percent inhibition of monoamine oxidase in platelets after 6 weeks of phenelzine therapy in one study (Robinson et al., 1982), but no such correlation was found in another study (Georgotas et al., 1987). Treatment considerations for MAOI-induced orthostatic hypotension are similar to those described previously for tricyclic antidepressants.
Sympathetic Neurotransmission
Published in Kenneth J. Broadley, Autonomic Pharmacology, 2017
Since the three amino acid precursors of noradrenaline (L-phenylalanine, L-tyrosine and L-dopa) are all capable of decarboxylation, they can yield alternative intermediates to the major ones shown in Figure 2.4. For example, low levels of tyramine and octopamine (norsynephrine) occur naturally (Figure 2.7). Octopamine does not appear to serve a transmitter role in vertebrates, however, it fulfils many of the functions of adrenaline and noradrenaline in arthropods. It is a circulating hormone in crustaceans and insects. In the locust, octopaminergic nerves have been described which modulate the contractions of the extensor-tibiae muscle of the hind leg. These responses are mimicked by the action of octopamine on specific octopamine receptors. These receptors are said to be different from adrenoceptors, but from agonist and antagonist potencies they resemble α2-adrenoceptors (Evans 1981).
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
Octopamine is a MONOAMINE neurotransmitter but, very unusually, it is present only in INVERTEBRATES. It appears to act in a way homologous with NORADRENALINE in the nervous system of VERTEBRATES; noradrenaline is not functionally active in invertebrate nervous systems. This point of difference between vertebrate and invertebrate nervous systems is most unusual. There are no other differences in either monoamine or amino acid NEUROTRANSMITTERS between vertebrates and invertebrates, and many NEURO PEPTIDES are commonly used by both. Why there should be a difference in this instance is not entirely clear.
Circadian gating of light-induced arousal in Drosophila sleep
Published in Journal of Neurogenetics, 2023
Octopamine is one of the monoamine neurotransmitters in insects and is closely related to norepinephrine in mammals (Roeder, 2005). It is implicated in a broad range of insect physiology including aggression, motor behaviors, alcohol tolerance, metabolism, and arousal (Roeder, 2020; Selcho & Pauls, 2019). Octopamine biosynthesis requires tyrosine decarboxylase 2 (TDC2), which removes the carboxyl group from tyrosine, producing the octopamine precursor tyramine. Genetic deficiency in the octopamine biosynthesis pathway leads to long daytime sleep in Drosophila (Crocker & Sehgal, 2008). On the other hand, transgenic excitation of the TDC2-expressing octopaminergic neurons suppresses nighttime sleep, defining octopamine as a wake-promoting neurotransmitter (Crocker & Sehgal, 2008; Kayser et al., 2015). Intriguingly, most Drosophila octopaminergic neurons are also glutamatergic, and their co-transmission has been shown to play differential roles in aggression and courtship behaviors (Sherer et al., 2020). We thus asked if the dual neurotransmission would contribute to octopamine-relevant sleep regulation.
She’s got nerve: roles of octopamine in insect female reproduction
Published in Journal of Neurogenetics, 2021
Melissa A. White, Dawn S. Chen, Mariana F. Wolfner
Octopamine (OA) is a biogenic monoamine central to invertebrate physiology and behavior. Originally identified in the salivary glands of Octopus vulgaris (Erspamer & Boretti, 1951), OA is abundant in invertebrates but exists only as a trace amine with limited functions in vertebrates (Berry, 2004; Borowsky et al., 2001; Evans, 1985; Orchard, 1982; Roeder, 1999). OA and norepinephrine are structurally and functionally similar, and they are commonly regarded as counterparts in invertebrates and vertebrates, respectively. Across diverse species and organs, OA can function as a neurotransmitter, neuromodulator, and neurohormone (Farooqui, 2012; Orchard, 1982; Roeder, 1999, 2005). Its roles in feeding, sleep, locomotion, flight, learning, memory, and aggression have been reviewed elsewhere (Farooqui, 2012; Roeder, 2005, 2020). In this article, we review OA's role in regulating female reproduction in insects, with a particular focus on the fruit fly, Drosophila melanogaster.
Modulation of neuromuscular synapses and contraction in Drosophila 3rd instar larvae
Published in Journal of Neurogenetics, 2018
Kiel G. Ormerod, JaeHwan Jung, A. Joffre Mercier
Octopamine has long been established as a neurotransmitter, neurohormone and neuromodulator in invertebrates, particularly arthropods, and is thought to function in ‘fight-or-flight’ responses, analogous to epinephrine and norepinephrine in vertebrates (reviewed by Evans & Maqueira, 2005; Evans & Robb, 1993; Farooqui, 2012; Roeder, 1999; Verlinden et al., 2010). In insects, OA plays key roles in desensitizing sensory inputs, initiating and maintaining rhythmic behaviors such as flight, and regulating complex social behaviors such as fighting, courtship and reproduction (e.g. Brembs, Christiansen, Pflüger, & Duch, 2007; Certel, Savella, Schlegel, & Kravitz, 2007; Dierick, 2008; Giurfa, 2006; Hana & Lange, 2017a, 2017b; Hoyer et al., 2008; Rezaval, Nojima, Neville, Lin, & Goodwin, 2014; Suver, Mamiya, & Dickinson, 2012; Wasserman et al., 2015). Most or all of these functions involve effects of OA within the CNS. At the peripheral level, OA’s actions as a neurohormone include mobilization of carbohydrates and lipids to help meet increased energy demands during increased activity and modulation of synaptic and contractile properties of muscles (Farooqui, 2012; Roeder, 1999; Verlinden et al., 2010).