Regulation of melanotropin release from the pars intermedia of the amphibian Xenopus laevis: Evaluation of the involvement of serotonergic, cholinergic, or adrenergic receptor mechanisms

Kemenade, B.M.L. Verburg-van; Jenks, Bruce G.; Overbeeke, A. P. van

doi:10.1016/0016-6480(86)90148-6

Cited by 39 publications

(25 citation statements)

References 24 publications

(17 reference statements)

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“…First it would appear that the receptor involved is not only a dopamine receptor, but dis plays a high sensitivity to all catecholamines. This is con cluded from our earlier finding that both adrenaline and noradrenaline give a full inhibition of MSH release at 10-fold lower concentrations than dopamine [30] and that this effect is fully antagonized by sulpiride, while phentola mine proved to be a poor antagonist (see also table I). Moreover, the effect of adrenaline was easily antagonized by the D-2 antagonists haloperidol and domperidon.…”

Section: Discussionmentioning

confidence: 61%

Characteristics of Receptors for Dopamine in the Pars intermedia of the Amphibian Xenopus laevis

Kemenade¹,

Tonon²,

Jenks³

et al. 1986

Neuroendocrinology

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While mammalian dopamine receptors have been extensively characterized, very little attention has been given to these receptors in lower vertebrates. Dopamine is thought to be a physiologically important melanotropin release-inhibiting factor in amphibians. By administering selective dopamine receptor agonists and antagonists to superfused neurointermediate lobes of Xenopus laevis and monitoring their effect on the release of melanophore-stimulating hormone (MSH), we have examined the characteristics of the receptors involved in the dopamine-induced inhibition of MSH secretion. The results show that the receptor system involved has characteristics of both classical D-2 receptors and α-adrenergic receptors. This is concluded from: (1) the agonistic effect of both the D-2 receptor agonists LY-171555 and apomorphine; (2) the antagonism of this effect, not only by the D-2 receptor antagonists sulpiride, domperidon and haloperidol, but also by the α-adrenergic receptor antagonist phentolamine, and (3) the observation that the effect of adrenaline, which is extremely potent in inhibiting MSH release, could be fully blocked by D-2 receptor antagonists. Both the fact that the dopamine-induced inhibition of MSH secretion could not be blocked by haloperidol, domperidon and phentolamine, and that adrenaline-induced inhibition was hardly blocked by phentolamine, led us to suggest the possible presence of multiple receptors or receptor sites. We find no evidence for the involvement of dopamine D-1 receptors in the regulation of MSH release. The effects of dopamine agonists and antagonists were also studied in vivo by monitoring changes in pigment dispersion of dermal melanophores. The results are consistent with our in vitro findings and indicate, moreover, that in the living animals there must also be a non-catecholaminergic system involved in the inhibition of MSH release from the pars intermedia.

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Section: Discussionmentioning

confidence: 61%

Characteristics of Receptors for Dopamine in the Pars intermedia of the Amphibian Xenopus laevis

Kemenade¹,

Tonon²,

Jenks³

et al. 1986

Neuroendocrinology

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“…This cyclic nucleotide is known to stimulate a-MSH secretion from melano trophs of X. laevis [16]. Moreover, as previsously reported [17], c-AMP production, measured using a c-AMP pro tein binding assay, is stimulated by isoguvacine in stati cally incubated Xenopus neurointermediate lobes.…”

Section: Discussionmentioning

confidence: 69%

Dual Action of GABAA Receptors on the Secretory Process of Melanotrophs of Xenopus laevis

Jenks

Koning²,

Valentijn³

et al. 1993

Neuroendocrinology

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The effects of GABA_a receptor activation on the secretion of α-melanocyte-stimulating hormone (α-MSH) from the superfused pars intermedia of the amphibian Xenopus laevis wereexamined. The GABA_a receptor agonist isoguvacine inhibited secretion of α-MSH from the pars intermedia, an action completely antagonized by the chloride channel blocker picrotoxin. Isoguvacine stimulated secretion from picrotoxin-treated tissue. Both effects were blocked by the GABA_A receptor antagonist bicuculline, indicating that it is a specific action via the GABA_A receptor. We conclude that, besides the inhibitory chloride channel, there is a stimulatory signaling property associated with the GABA_A receptor. Isoguvacine stimulated the production of c-AMP, an action that was not blocked by picrotoxin. This suggests that the stimulatory mechanism of the GABA_A receptor involves, directly or indirectly, the generation of c-AMP.

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“…Ultrastructural immunocytochemistry has shown that Xenopus melanotrope cells are contacted by synaptic structures that contain three transmitters: namely, dopamine (DA), γ‐aminobutyric acid (GABA), and neuropeptide Y (NPY) 25,26. Superfusion studies with isolated neurointermediate lobes (NILs) revealed that all three transmitters inhibit the secretion of αMSH 27‐29. The inhibitions differ in strength and duration, with GABA acting short‐lasting and NPY exerting the most long‐lasting effect 30.…”

Section: Synaptic Inputsmentioning

confidence: 99%

Neuronal, Neurohormonal, and Autocrine Control of Xenopus Melanotrope Cell Activity

Roubos

Scheenen

Jenks

2005

Annals of the New York Academy of Sciences

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Amphibian pituitary melanotropes are used to investigate principles of neuroendocrine translation of neural input into hormonal output. Here, the steps in this translation process are outlined for the melanotrope cell of Xenopus laevis, with attention to external stimuli, neurochemical messengers, receptor dynamics, second-messenger pathways, and control of the melanotrope secretory process. Emphasis is on the pathways that neurochemical messengers follow to reach the melanotrope. The inhibitory messengers, dopamine, gamma-aminobutyric acid, and neuropeptide Y, act on the cells by synaptic input from the suprachiasmatic nucleus, whereas the locus coeruleus and raphe nucleus synaptically stimulate the cells via noradrenaline and serotonin, respectively. Autoexcitatory actions are exerted by acetylcholine, brain-derived neurotrophic factor (BDNF), and the calcium-sensing receptor. At least six messengers released from the pituitary neural lobe stimulate melanotropes in a neurohormonal way: corticotropin-releasing hormone, thyrotropin-releasing hormone, BDNF, urocortin, mesotocin, and vasotocin. They all are produced by the magnocellular nucleus and coexist in various combinations in two types of neurohemal axon terminal. Most of the relevant receptors of the melanotropes have been elucidated. Apparently, the neural lobe has a dominant role in activating melanotrope secretory activity. The intracellular mechanisms translating the various inputs into cellular activities like biosynthesis and secretion constitute the adenylyl cyclase-cAMP pathway and Ca(2+) in the form of periodic changes of the intracellular Ca(2+) concentration, known as Ca(2+) oscillations. It is proposed that the pattern of these oscillations encodes specific regulatory information and that it is set by first messengers that control, for example, via G proteins and cAMP-related events, specific ion channel-mediated events in the membrane of the melanotrope cell.

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Regulation of melanotropin release from the pars intermedia of the amphibian Xenopus laevis: Evaluation of the involvement of serotonergic, cholinergic, or adrenergic receptor mechanisms

Cited by 39 publications

References 24 publications

Characteristics of Receptors for Dopamine in the Pars intermedia of the Amphibian <i>Xenopus laevis</i>

Characteristics of Receptors for Dopamine in the Pars intermedia of the Amphibian <i>Xenopus laevis</i>

Dual Action of GABA<sub>A</sub> Receptors on the Secretory Process of Melanotrophs of <i>Xenopus laevis</i>

Neuronal, Neurohormonal, and Autocrine Control of Xenopus Melanotrope Cell Activity

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