Cloning and sequence analysis of brain cDNA encoding a Xenopus D2 dopamine receptor

AbstractA D2 dopamine receptor pharmacologically different from the mammalian D2 receptor has previously been characterized in the amphibian Xenopus laevis. Here we report the cloning of a Xenopus D2 receptor which revealed about 75% amino acid sequence identity with its mammalian counterpart and the presence of an additional 33 amino acid sequence in the 3rd cytoplasmic loop instead of the additional 29 residues in the large form of the mammalian D2 receptor, All 7 predicted transmembrane domains are highly conserved between the Xenopus and mammalian D2 receptors, as are the 1st and 2nd intracellular loop, the 1st and 3rd extracellular loop and the carboxy-terminal portion of the receptors. The amino-terminal portion, the 2nd extracellular loop and the middle portion of the 3rd intracellular loop of these receptors, however, differ considerably, Knowledge of the locations of these regions of conservation and divergence within the D2 receptors or Xenopus and mammals will help to delineate portions of the receptor molecule that are functionally important. Interestingly, the 5-untranslated region of the Xenopus D2 receptor mRNA contains 4 small open reading frames which may affect translational efficiency

About a Snail, a Toad, and Rodents: Animal Models for Adaptation Research

Neural adaptation mechanisms have many similarities throughout the animal kingdom, enabling to study fundamentals of human adaptation in selected animal models with experimental approaches that are impossible to apply in man. This will be illustrated by reviewing research on three of such animal models, viz. (1) the egg-laying behavior of a snail, Lymnaea stagnalis: how one neuron type controls behavior, (2) adaptation to the ambient light condition by a toad, Xenopus laevis: how a neuroendocrine cell integrates complex external and neural inputs, and (3) stress, feeding, and depression in rodents: how a neuronal network co-ordinates different but related complex behaviors. Special attention is being paid to the actions of neurochemical messengers, such as neuropeptide Y, urocortin 1, and brain-derived neurotrophic factor. While awaiting new technological developments to study the living human brain at the cellular and molecular levels, continuing progress in the insight in the functioning of human adaptation mechanisms may be expected from neuroendocrine research using invertebrate and vertebrate animal models

Chronic Stress Induces Sex-Specific Alterations in Methylation and Expression of Corticotropin-Releasing Factor Gene in the Rat

Contains fulltext : 91627.pdf (publisher's version ) (Open Access

'Identifying the effects of timeliness of DNA crime stain analysis on resultant detections'

SIGLEAvailable from British Library Document Supply Centre- DSC:m03/26232 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Jobs or just promises? The IDB and West Belfast

SIGLEAvailable from British Library Document Supply Centre-DSC:99/21366 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Adaptation Physiology : the Functioning of Pituitary Melanotrope Cells during Background Adaptation of the Amphibian Xenopus laevis

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The secretion of a-MSH from Xenopus melanotropes involves calcium influx through m-conotoxin-sensitive voltage-operated calcium channels

The secretory activity of endocrine cells largely depends on the concentration of free cytosolic calcium. We have studied the mechanisms that are involved in supplying the calcium necessary for the secretion of α-melanophore-stimulating hormone (α-MSH) from melanotrope cells in the pituitary intermediate lobe of the amphibian Xenopus laevis. Using whole-cell voltage clamp, high-voltage activated calcium currents were observed, with a peak current between 0 and +20 mV. Two types of Ca^{2 +}-currents appeared, depending on the experimental setup. An inactivating current, which was observed after a 10 msec depolarizing prepulse, resembled currents through N-type channels as it was clearly inhibited by 1 μM ω-conotoxin. The second type was a non-inactivating current, which was blocked up to 50% by 1 μM nifedipine, indicating its L-type nature. Only a small component of this inactivating current could be blocked by ω-conotoxin. No evidence was found for the presence of transient, low-voltage activated currents. The spontaneous secretion of α-MSH from superfused neurointermediate lobes was dependent on extracellular calcium, as low calcium conditions (10⁻⁴-10⁻⁸ M) rapidly inhibited this process. Under these conditions, secretion was not affected by depolarizing concentrations of potassium chloride. The calcium ionophore A23187 increased secretion under low calcium conditions, but had no effect on spontaneous α-MSH release. Treatment with CoCI₂, a blocker of calcium channels, strongly inhibited the secretory process. These results suggest that spontaneous α-MSH release depends on influx of calcium through voltage-operated calcium channels. Nifedipine did not affect spontaneous secretion from lobes, nor did it affect potassium-induced α-MSH secretion from dispersed melanotropes. Also BAY-K8644, a specific agonist of L-type channels, did not influence α-MSH release, neither under normal nor under low calcium conditions. On the other hand, ω-conotoxin dose-dependently inhibited α-MSH release, to a maximum of 65% at a concentration of 5 μM, and inhibited potassiuminduced secretion by 40%. Thapsigargin, an agent that mobilizes calcium ions from intracellular stores, had no effect on spontaneous α-MSH release under normal or low calcium conditions. From these results it is concluded that the spontaneous release of α-MSH by melanotropes of X. laevis is effectuated by calcium influx through ω-conotoxin-sensitive, voltage-operated N-type calcium channels and that mobilization of calcium from intracellular stores does not play a major role in the regulation of this release

Analysis of autofeedback mechanisms in the secretion of pro-opiomelanocortin-derived peptides by melanotrope cells of <i>Xenopus laevis</i>

The secretion of most pituitary hormones is under the control of feedback mechanisms. The feedback control of α-melanophore-stimulating hormone (α-MSH) from melanotrope cells is controversial. The possible existence of an autofeedback exerted by α-MSH or other POMC-derived peptides on melanotrope cells of the amphibian Xenopus laevis has been investigated. α-MSH or its potent agonist 4-norleucine, 7-d-phenylalanine-α-MSH has no effect on the release of radiolabeled POMC-derived peptides or immunoreactive β-endorphin from superfused neurointermediate pituitary lobes. Melanin concentrating hormone, previously reported to have an α-MSH-like effect on melanophores, did not affect α-MSH secretion. Neurointermediate lobe superfusate, which contains a mixture of POMC-derived peptides, failed to affect the secretory activity of melanotropes. It is concluded that in X. laevis the secretory activity of melanotropes is not under the control of short-term auto-feedback mechanisms involving α-MSH or other POMC-derived peptides