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J P Burbach

Publications and source records attributed to J P Burbach.

At least 19 recordsLinked to original sources
PubMed2001

Long-term impairment of social memory in the rat after social defeat is not restored by desglycinamide-vasopressin.

Repeated social defeat followed by individual housing caused a long-term impairment of social memory in male rats. Social memory, as assessed in the social discrimination test using an intertrial interval of 3 min, was impaired for at least 8 weeks after the social defeat experience. Since social memory of male rodents depends on proper functioning of the sexually dimorphic vasopressin system, it was investigated whether a centrally active vasopressin fragment could restore the impaired social memory. Subcutaneous administration of 6 microg/kg of the vasopressin fragment desglycinamide-vasopressin (VP1-8) 40 days after social defeat slightly improved social memory in both control and socially defeated rats. It is concluded that social defeat followed by individual housing caused a long-term impairment of social memory, which was not restored by treatment with VP1-8.

Animals↗
PubMed2001

Common requirements for melanocortin-4 receptor selectivity of structurally unrelated melanocortin agonist and endogenous antagonist, Agouti protein.

The activity of melanocortin receptors (MCR) is regulated by melanocortin peptide agonists and by the endogenous antagonists, Agouti protein and AgRP (Agouti-related protein). To understand how the selectivity for these structurally unrelated agonists and antagonist is achieved, chimeric and mutants MC3R and MC4R were expressed in cell lines and pharmacologically analyzed. A region containing the third extracellular loop, EC3, of MC4R was essential for selective Agouti protein antagonism. In addition, this part of MC4R, when introduced in MC3R, conferred Agouti protein antagonism. Further mutational analysis of this region of MC4R demonstrated that Tyr(268) was required for the selective interaction with Agouti protein, because a profound loss of the ability of Agouti protein to inhibit (125)I-labeled [Nle(4),d-Phe(7)]alpha-melanocyte-stimulating hormone (MSH) binding was observed by the single mutation of Tyr(268) to Ile. This same residue conferred selectivity for the MC4R selective agonist, [d-Tyr(4)]MT-II, whereas it inhibited interaction with the MC3R-selective agonist, [Nle(4)]Lys-gamma(2)-MSH. Conversely, mutation of Ile(265) in MC3 (the corresponding residue of Tyr(268)) to Tyr displayed a gain of affinity for [d-Tyr(4)]MT-II, but not for Agouti protein, and a loss of affinity for [Nle(4)]Lys-gamma(2)-MSH as compared with wild-type MC3R. This single amino acid mutation thus confers the selectivity of MC3R toward a pharmacological profile like that observed for MC4R agonists but not for the antagonist, Agouti protein. Thus, selectivity for structurally unrelated ligands with opposite activities is achieved in a similar manner for MC4R but not for MC3R.

Agouti Signaling Protein↗
PubMed2001

Delayed effect of the vasopressin metabolite VP4-8 on the social memory of sexually naive male rats.

RATIONALE: Endogenous vasopressin is involved in the social memory of the male rat and administration of exogenous vasopressin improves social memory. These findings are mainly based on studies using sexually experienced males that were tested in the social recognition test. OBJECTIVE: The present study was aimed to establish whether the modulation of social memory by vasopressin fragments depends on the sexual experience of the male rat. For this purpose, the social discrimination test was used, since this test is more suitable than the social recognition test for measuring social memory in sexually naive males. METHODS: Male rats were tested in the social discrimination test and treated subcutaneously with the vasopressin metabolite [pGlu4,Cyt6]vasopressin-(4-8) (VP4-8). VP4-8 shares with vasopressin the effects on memory processes but lacks the peripheral effects of vasopressin. RESULTS: VP4-8 (1 microgram/kg) acutely improved the social memory of sexually experienced male rats, confirming previous reports. However, in sexually naive males VP4-8 failed to improve social memory in doses ranging from 0.1 microgram/kg to 1 microgram/kg. Instead, 1 microgram/kg VP4-8 or 6 micrograms/kg desglycinamide-vasopressin were found to exert a delayed effect in sexually naive rats. This delayed effect resulted in an improved social memory 2 days after administration. CONCLUSIONS: Vasopressin sensitisation is discussed as a possible underlying mechanism of the observed delayed effect of vasopressin fragments. It is concluded that in male rats sexual experience can influence the modulation of social memory by vasopressin.

Age Factors↗
PubMed2001

Social memory in the rat: circadian variation and effect of circadian rhythm disruption.

Disruption of circadian rhythm can impair long-term passive avoidance memory of rats and mice. The present study investigated whether disruption of circadian rhythm can also impair social memory of male rats. Social memory was assessed using the social discrimination test, in which a short-term olfactory memory is formed by social interaction with a juvenile rat during a learning trial. After an intertrial interval, a retrieval trial is performed, in which social memory is expressed as a decreased attention paid to the same juvenile as compared to a new juvenile. First, the social memory at four different time points across the light-dark cycle was measured with an intertrial interval of 10 or 25 min. There was no significant circadian variation of social memory across the light-dark cycle. Subsequently, the effect of a -6 or 12-h phase shift on social memory was studied. These phase shifts were previously found to impair long-term passive avoidance memory. However, no effect of either phase shift was observed in the social discrimination test. It is concluded that the disruption of circadian rhythm had no effect on the social memory of rats. Differences between short-term social memory and long-term passive avoidance memory are discussed in relation to their apparent differential susceptibility to the effects of circadian rhythm disruption.

Animals↗
PubMed2001

Total body exposure to ultraviolet radiation does not influence plasma levels of immunoreactive beta-endorphin in man.

BACKGROUND/AIMS: A growing number of reports support evidence of proopiomelanocortin (POMC)-derived peptides in human skin cells, although not consistently. Also the effect of ultraviolet radiation (UVR) on cutaneous and plasma levels of these POMC peptides has not been established unequivocally. We hypothesized that production of beta-endorphin (betaE) may explain the sense of well-being many people experience when sun-bathing. The aim of the present study was to investigate whether exposure of the skin to UVR elevates plasma betaE. METHOD: Healthy volunteers (n=26) received a single, weighted dose of 15 J/cm2 of UVA. Several times during the hour following irradiation, plasma betaE- immunoreactivity (betaE-IR) was determined by radioimmunoassay. The effect of repeated exposure was assessed in 35 patients treated with UVB, UVA, or UVA-1. Plasma ACTH-IR was monitored in parallel. RESULTS: Overall, plasma levels of betaE-IR and ACTH-IR showed no significant changes during the experiment, indicating that these peptides are not influenced by single or repeated exposures to UVR of different wavelengths. CONCLUSION: On the basis of these results, the skin does not appear to contribute significantly to the levels of circulating betaE or ACTH. These data offer no support for the hypothesis that exposure to UVR leads to an increased concentration of circulating betaE, which could contribute to the feeling of well-being that often accompanies sun-bathing.

Adrenocorticotropic Hormone↗
PubMed2001

Gene regulation in the magnocellular hypothalamo-neurohypophysial system.

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Animals↗
PubMed2001

Immunohistochemical localization of the vasopressin V1b receptor in the rat brain and pituitary gland: anatomical support for its involvement in the central effects of vasopressin.

Biological effects of vasopressin (VP) are mediated by four different receptors, two of which (the V1a and the oxytocin receptors) have been well characterized in the rodent brain, suggesting that these are the main receptors responsible for the central effects of VP. However, transcripts of the V1b VP receptor (V1bR) have been detected throughout the rat brain by RT-PCR and in situ hybridization, indicating that the V1bR adds to the population of central VP receptors. Because there are no specific ligands for the V1bR, the receptor protein itself has been difficult to visualize. In the present study, the distribution of the V1bR protein was investigated in the rat forebrain, midbrain, hindbrain, and cerebellum by immunohistochemistry using an antiserum raised against a synthetic fragment of the carboxylterminal of the rat V1bR protein. Immunohistochemistry revealed the presence of the V1bR in pituitary corticotrophs as expected. In naive, untreated rats, fiber networks containing V1bR-immunoreactivity were mainly concentrated in the hypothalamus, amygdala, cerebellum, and particularly in those areas with a leaky blood brain barrier or close to the circumventricular organs (medial habenula, subfornical organ, organum vasculosum laminae terminalis, median eminence, and nuclei lining to the third and fourth ventricles). A strikingly dense network was present in the external zone of the median eminence. Colchicine treatment was required to reveal the localization of V1bR-immunoreactive cell bodies. V1bR-containing cell bodies and associated protrusions were mainly located in the hippocampus, caudate putamen, cortex, thalamus, olfactory bulb, and cerebellum. These results demonstrate the widespread distribution of the V1bR protein in the rat brain over multiple, functionally distinct neuronal systems. These data suggest that the V1bR mediates different physiological functions of VP in the brain.

Animals↗
PubMed2001

Familial neurohypophysial diabetes insipidus in a large Dutch kindred: effect of the onset of diabetes on growth in children and cell biological defects of the mutant vasopressin prohormone.

Familial neurohypophysial diabetes insipidus (FNDI) is an autosomal dominant trait in which expression of a mutant vasopressin prohormone reduces vasopressin production. We investigated the NP85 Cys-->Gly mutant vasopressin prohormone in a large kindred in The Netherlands. We demonstrate that growth retardation is an important early sign in two children from this kindred, which recuperates by substitution therapy with 1-desamino-8-D-arginine vasopressin. To obtain clues about the basis for the dominant inheritance of FNDI, we analyzed the trafficking and processing of the mutant vasopressin prohormone in cell lines by metabolic labeling and immunoprecipitation. The mutant vasopressin prohormone was retained in the endoplasmic reticulum and thus was not processed to vasopressin. This defect was not caused by dimerization of the vasopressin prohormone via its unpaired cysteine residue. High level expression of the mutant vasopressin prohormone in cell lines resulted in strong accumulation in the endoplasmic reticulum and an altered morphology of this organelle. We hypothesize that disturbance of the endoplasmic reticulum results in dysfunction and ultimately cell death of the cells expressing the mutant prohormone. Our data support the hypothesis that FNDI is a progressive neurodegenerative disease with delayed onset of symptoms. Its treatment requires early detection of symptoms for which growth parameters are useful.

Adult↗
PubMed2000

Genetic pathways in the developmental specification of hypothalamic neuropeptide and midbrain catecholamine systems.

The neuropeptide concept concerns the diverse and broad physiological functions of neuropeptides in behavioral adaptation. Neuropeptides like vasopressin and corticotropin-releasing hormone can coordinate multiple brain functions due to the anatomical organization of the neurons producing them. The cell bodies are focally positioned in the hypothalamus and send long-reaching efferents to limbic and brainstem areas. Likewise, midbrain dopamine systems coordinate emotional behaviors and movement control by specific connectivity of neurons in the midbrain to limbic and striatal centers, respectively. The fundament of the functions of these signalling molecules is laid out during development when transmitter identity and connectivity are specified. This is a highly controlled process involving multiple transcription factors and growth factors acting together in genetic pathways. Here, the genetic pathways enrolling in developing vasopressin, corticotropin-releasing hormone, and midbrain dopamine neurons are discussed.

Animals↗
PubMed2000

A diabetes insipidus vasopressin prohormone altered outside the central core of neurophysin accumulates in the endoplasmic reticulum.

Over 20 mutations affecting the neurophysin moiety of the vasopressin prohormone, have been identified in families suffering from familial neurohypophysial diabetes insipidus (FNDI). Only one of these, NP87E-->stop, is located outside the central conserved domain implicated in sorting of the vasopressin prohormone. To obtain clues about the mechanism of induction of FNDI by this atypical mutant we stably expressed wild type and NP87E-->stop vasopressin prohormones in (neuro)endocrine cell lines. Metabolic labeling and immunoprecipitation demonstrated reduced processing of the mutant prohormone to neurophysin. In addition, evoked secretion of neurophysin and vasopressin was diminished, suggesting that part of the mutant is retained in another intracellular compartment than the secretory granules. Indeed, immunofluorescence demonstrated accumulation of the truncated vasopressin prohormone in the endoplasmic reticulum. We conclude that the presence of the vasopressin moiety and the central conserved core of the neurophysin domain suffices for sorting and processing, but not for efficient endoplasmic reticulum exit of the vasopressin-neurophysin molecule.

Animals↗
PubMed2000

Expression of the orphan receptor TR4 during brain development of the rat.

The orphan receptor TR4, member of the nuclear hormone receptor family, is related to the orphan receptors TR2, COUP-TFI and ARP-1, and was originally cloned from the adult rat brain. The latter two orphan receptors have been implicated in central nervous system (CNS) development. To investigate a possible role for TR4 in brain development, expression of TR4 was studied in rat embryos. At embryonic days 14.5 and 19.5, high expression of TR4 was found in the CNS, while low expression was detected throughout the embryo. In postnatal rats, TR4 was mainly expressed in the hippocampus and cerebellum, resembling the expression pattern found in adult brain. These data show that like COUP-TFI and ARP-1, expression of TR4 becomes restricted to distinct areas. In adult brain, TR4 is predominantly expressed in granule cells of both hippocampus and cerebellum. The data suggest a possible role for TR4 during proliferation and maturation of brain structures.

Animals↗
PubMed2000

Condition-dependent presence of beta-lipotropin-like peptide in human keratinocytes.

This study aimed to characterize the beta-endorphin-immunoreactive material (betaE-IR) detectable in normal human keratinocytes (NHK). The effects of different culturing conditions and UV-irradiation on production of betaE-IR by NHK were assessed by radioimmunoassay and HPLC. All culture systems contained low levels of betaE-IR that was increased in conditioned media after UV-irradiation under certain conditions. NHK grown in nutrient-poor medium contained highest levels of betaE-IR that exhibited beta-lipotropin-like properties after HPLC analysis. The other culturing conditions displayed no authentic betaE-related peptides. Our results indicate that under certain culturing conditions NHK can produce POMC peptides like beta-lipotropin, which can be induced by UV-radiation.

Cells, Cultured↗
PubMed2000

Differential responses of phosphorylated mitogen-activated protein kinase and phosphorylated cyclic-AMP response element-binding protein immunoreactivity in the rat brain to sub-convulsive pentylenetetrazol.

The possible advantage of using multiple phospho-specific antibodies to study changes in brain activity was assessed. For this purpose, rats were injected intraperitoneally with either a control treatment or 15 mg/kg pentylenetetrazol. The sub-convulsive dose of pentylenetetrazol did not induce marked behavioural effects. Ten minutes after treatment, the rats were perfused and the brains were dissected. Adjacent brain sections were immunohistochemically stained for phosphorylated cyclic-AMP response element-binding protein and phosphorylated mitogen-activated protein kinase. Opposite effects of pentylenetetrazol treatment were observed on the immunoreactivity of these two antibodies within the hypothalamic paraventricular nucleus, the supraoptic nucleus and the arcuate nucleus. In these regions, pentylenetetrazol treatment increased phosphorylated mitogen-activated protein kinase immunoreactivity, but decreased phosphorylated cyclic-AMP response element-binding protein immunoreactivity. These findings show that changes in the activity of a brain nucleus can be accompanied by differential changes in the activity of two signal transduction pathways, which can be detected immunohistochemically. Therefore, the use of multiple phospho-specific antibodies may enhance our potential to monitor changes in brain activity.

Animals↗
PubMed2000

A second independent pathway for development of mesencephalic dopaminergic neurons requires Lmx1b.

We identified the LIM homeodomain transcription factor Lmx1b in the mesencephalic dopamine (mesDA) systems of embryos and adults. Analysis of spatiotemporal expression in Lmx1b null mutants and wild-type mice implicated a cascade involving Lmx1b in the early development of mesDA neurons. Although disruption of this cascade did not block induction of tyrosine hydroxylase (TH), a key enzyme in DA synthesis, or Nurr1, a nuclear hormone receptor, Lmx1b knockout mice failed to induce the mesDA-specific homeodomain gene Ptx3 in TH-positive neurons. Eventually, this small set of TH-positive neurons was lost during embryonic maturation. The data suggest that at least two molecular cascades operate during the specification of the mesDA system, one specifying neurotransmitter phenotype and another essential for other aspects of mesDA neuron differentiation.

Age Factors↗
PubMed2000

Processing of frameshifted vasopressin precursors.

Biosynthesis of the vasopressin (VP) prohormone in magnocellular neurones of the hypothalamo-neurohypophysial system comprises endoplasmic reticulum (ER) transit, sorting into the regulated secretory pathway and subsequent processing in the individual proteins VP, neurophysin and a glycoprotein. These processes are severely disrupted in the homozygous diabetes insipidus (di/di) Brattleboro rat, which expresses a mutant VP precursor due to a single nucleotide deletion in the neurophysin region of the VP gene resulting in VP deficiency. Previous studies have shown the presence of additional frameshift mutations in VP transcripts, in solitary magnocellular neurones of the di/di rat due to a GA dinucleotide deletion resulting in two different mutant VP precursors with partly restored reading frame. Frameshifted VP precursors are also expressed in several magnocellular neurones in wild-type rats. In this study, we determined if the +1 frameshifted precursors from di/di and wild-type rats can lead to biosynthesis of the hormone VP. Therefore, eukaryotic expression plasmids containing the frameshifted VP cDNAs were transiently expressed in peptidergic tumour cell lines, and cells were analysed by reversed phase high-performance liquid chromatography and specific radioimmunoassays, and by immunofluoresence. Neuro2A neuroblastoma cells expressing the +1 frameshifted precursors of di/di rats retained products in the cell body. Only precursor or insignificant quantities of neurophysin-immunoreactive products were detected. In contrast, in AtT20 cells, frameshifted VP precursors were at least partly processed to yield the VP peptide, indicating that they have access to the regulated secretory pathway. Comparison between the two cell lines showed a very slow ER transit of the wild-type prohormone combined with inefficient processing in Neuro2A cells. The results show that mutant precursors can reach the regulated secretory pathway if ER transport is sufficiently rapid as in the case of AtT20 cells. This suggests that the di/di rat may regain the capacity to biosynthesize authentic VP through these +1 frameshifted precursors in magnocellular neurones.

Animals↗
PubMed2000

Different spatiotemporal expression of DOC2 genes in the developing rat brain argues for an additional, nonsynaptic role of DOC2B in early development.

DOC2A and DOC2B are two homologous genes implicated in synaptic vesicle exocytosis. Their complementary, nonoverlapping expression patterns in adult rat brain suggest that they exert similar functions in different neurons. We have analysed the expression pattern of the two genes in the developing rat brain by in situ hybridization. Unexpectedly, we found no parallel expression of the two genes during development. DOC2B mRNA was highly expressed as early as embryonic day 12 (E12) throughout the neuroepithelium, long before synaptic transmission is functional, and the expression remained abundant from E12 onwards. In contrast, faint expression of DOC2A transcripts was first detected at E17 in ventral brain areas, and it extended gradually to other brain structures in the sequence of their ontology, i.e. structures that had formed first also expressed DOC2A first. At postnatal day 3, both genes were highly expressed throughout the brain. This overlapping expression diverged to the complementary distribution of the adult brain. The temporal and spatial differences in expression point to a functional divergence between these homologous genes during brain development: the pattern of DOC2A is consistent with its proposed synaptic function, whereas that of DOC2B suggests an additional, nonsynaptic role in proliferating cells.

Aging↗
PubMed2000

A response element for the homeodomain transcription factor Ptx3 in the tyrosine hydroxylase gene promoter.

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of catecholamines, which takes place in different types of neuronal systems and nonneuronal tissues. The transcriptional regulation of the TH gene, which is complex and highly variable among different tissues, reflects this heterogeneity. We recently isolated a homeodomain transcription factor, named Ptx3, that is uniquely expressed in the dopaminergic neurons of the substantia nigra pars compacta and ventral tegmental area, which together form the mesencephalic dopaminergic system. This strict localization and its coinciding induction of expression with the TH gene during development suggested a possible role for this transcription factor in the control of the TH gene. We report here the presence of a responsive element for Ptx3 located at position -50 to -45 of the rat TH promoter. Transient transfections using TH promoter constructs and electrophoretic mobility shift assays using Ptx3-containing nuclear extracts demonstrated that this region binds Ptx3 protein and confers a transcriptional effect on the TH gene. Depending on the cell type, the effect of Ptx3 was an eight- to 12-fold enhancement of TH promoter activity in Neuro2A neuroblastoma cells, or a 60-80% repression in nonneuronal human embryonic kidney 293 cells. Despite the close association of the Ptx3-binding site and the major cyclic AMP-response element in the TH gene, no interplay was found between Ptx3 and cyclic AMP-modulating agents. In combination with the orphan nuclear receptor Nurr1, which is required for the induction of the TH gene in mesencephalic dopaminergic neurons, the TH promoter activity to Ptx3 was enhanced in Neuro2A cells. Nurr1 alone displayed only very weak activity on the TH promoter in this cell type. The results demonstrate that the homeodomain protein Ptx3 has the potential to act on the promoter of the TH gene in a markedly cell type-dependent fashion. This suggests that Ptx3 contributes to the regulation of TH expression in mesencephalic dopaminergic neurons.

Animals↗