Regulation of neurons in the suprachiasmatic nucleus of Xenopus laevis

Krämer, Bianca; Song, Ji‐Ying; Westphal, Nicole J.; Jenks, Bruce G.; Roubos, Eric W.

doi:10.1016/s1096-4959(01)00539-5

Cited by 50 publications

(12 citation statements)

References 15 publications

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“…In white-adapted animals, synapses were only found at some distance from the SMIN somata. These findings indicate a striking plasticity of the innervation of the SMINs in relation to background adaptation and support the hypothesis that the SMINs are innervated by NPY-containing interneurons that inhibit SMIN activity in black-adapted animals (Kramer et al, 2002b). At the same time, in addition to the SMINs in the ventral SCN, a dorsomedial and a caudal group of SCN neurons were distinguished that differed from the SMINs and from each other as to number, size, and shape (Kramer et al, 2001a, b).…”

Section: The Melanotrope Neuroendocrine Transducer Cells Of the Southsupporting

confidence: 84%

About a snail, a toad, and rodents: animal models for adaptation research

Roubos¹

2010

Front. Endocrin.

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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.

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Section: The Melanotrope Neuroendocrine Transducer Cells Of the Southsupporting

confidence: 84%

About a snail, a toad, and rodents: animal models for adaptation research

Roubos¹

2010

Front. Endocrin.

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“…40 In turn, the SMINs are synaptically regulated by neurons in the dorsal part of the SC. 41,42 Whether these cells, which probably produce NPY, or the SMINs themselves receive direct information about the environmental light condition is not known, but a direct connection between the eyes and (unidentified) neurons in the SC has been demonstrated by retrograde labeling of the optic nerve with horseradish peroxidase. 33 Most likely, the light-driven secretory dynamics of the melanotrope cell are regulated by multiple inhibitory, neuronal, and neurotransmitter actions of the SC.…”

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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“…Moreover, they strongly suggest that dopamine and NPY play a pivotal role during this physiological process. Consistent with this notion, quantitative immunocytochemistry and in situ hybridization studies of the hypothalamus from black background-adapted Xenopus have shown that the levels of NPY mRNA and NPY immunoreactivity are very low in the ventrolateral part of the suprachiasmatic nucleus, where NPYproducing neurons controlling intermediate lobe function are located (25,26,37). In contrast, high mRNA levels and NPY immunoreactivity are found in this hypothalamic region in white-adapted toads (25,26).…”

Section: Discussionmentioning

confidence: 70%

Melanotrope secretory cycle is regulated by physiological inputs via the hypothalamus

Vázquez-Martı́nez

Castaño

Tonon³

et al. 2003

American Journal of Physiology-Endocrinology and Metabolism

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. Melanotrope secretory cycle is regulated by physiological inputs via the hypothalamus. Am J Physiol Endocrinol Metab 285: E1039-E1046, 2003. First published July 22, 2003 10.1152 10. /ajpendo.00238.2003, it has been shown that background color conditions regulate the overall activity of the frog intermediate lobe by varying the proportions of the two subtypes of melanotropes existing in the gland, the highly active or secretory melanotropes and hormone storage melanotropes, depending on melanocyte-stimulating hormone requirements. However, the factors and mechanisms underlying these background-induced changes are still unknown. In the present study, we investigated whether hypothalamic factors known to regulate melanotrope cell function can induce changes in vitro similar to those caused by background adaptation in vivo. We found that the inhibitors apomorphine (a dopamine receptor agonist) and neuropeptide Y decreased the number of active melanotropes and increased simultaneously that of storage melanotropes. On the other hand, the stimulator TRH increased the number of active cells and concomitantly reduced that of storage cells. Inasmuch as none of these treatments modified the apoptotic and proliferation rates in melanotrope cells, it appears that these hypothalamic factors caused actual interconversions of cells from a subpopulation to its counterpart. Taken together, these findings suggest that the hypothalamus would control melanotrope activity not only through short-term regulation of hormone synthesis and release, but also through a long-term regulation of the secretory phenotype of these cells whereby the activity of the intermediate lobe would be adjusted to fulfill the hormonal requirements imposed by background conditions. dopamine; melanotrope cell heterogeneity; neuropeptide Y; secretory cycle; thyrotropin-releasing hormone IN AMPHIBIANS, melanotrope cells of the intermediate lobe regulate a unique physiological process, the adaptation of skin pigmentation to background color conditions (2, 44). Thus high plasma levels of the hormone produced by these cells, melanocyte-stimulating hormone (␣-MSH), induce the dispersion of the pigment melanin in dermal melanophores, causing darkening of the skin, whereas a low level of ␣-MSH prompts aggregation of the pigment and, consequently, skin paling. In a series of studies carried out in our laboratory (21-23), we have demonstrated that, in the frog Rana ridibunda, the overall activity of the intermediate lobe is adjusted by the proportions of two melanotrope cell subtypes, named high-(HD) and low-density (LD) melanotropes on the basis of their sedimentation characteristics in Percoll density gradients. According to their morphofunctional characteristics, HD melanotropes can be defined as a hormone storage cell subset, because they show high ␣-MSH intracellular content but low mRNA levels of the prohormone precursor proopiomelanocortin (POMC) as well as a low basal ␣-MSH secretory rate, whereas LD cells show opposite features, indicative of high biosynthe...

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Regulation of neurons in the suprachiasmatic nucleus of Xenopus laevis

Cited by 50 publications

References 15 publications

About a snail, a toad, and rodents: animal models for adaptation research

About a snail, a toad, and rodents: animal models for adaptation research

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

Melanotrope secretory cycle is regulated by physiological inputs via the hypothalamus

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