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Biomedical subjects

D E Wright

Publications and source records attributed to D E Wright.

At least 55 records · Page 3Linked to original sources
PubMed1995

Expression of the neurofibromatosis 2 (NF2) gene isoforms during rat embryonic development.

The neurofibromatosis 2 (NF2) gene product, merlin, encodes a 595 amino acid protein with sequence similarity to a family of proteins linking cell membrane proteins to the cytoskeleton. Two isoforms of merlin have been described which differ by the presence (type 2 merlin) or absence (type 1 merlin) of exon 16 sequences inserted into the extreme carboxyl terminus of the protein. To determine the role of this important negative growth regulator during normal embryonic development, the expression of these two merlin isoforms was examined at representative stages of rat embryogenesis and in adult tissues. Partial sequence analysis of the rat merlin gene demonstrated striking amino acid identity to the published mouse and human merlin gene sequences. In situ hybridization and RT-PCR analyses demonstrated that rat merlin is widely expressed during embryogenesis and early postnatal life in most tissues but becomes restricted to the brainstem, cerebellum, dorsal root ganglia, spinal cord, adrenal gland and testis in adult animals. The elucidation of the pattern of merlin gene expression in adult and embryonic tissues provides the foundations for future studies aimed at determining the function(s) of this protein during cell differentiation and embryonic development.

Adrenal Glands↗
PubMed1995

Expression of the neurofibromatosis 1 (NF1) isoforms in developing and adult rat tissues.

The neurofibromatosis 1 (NF1) gene encodes a large M(r) approximately 250,000 phosphoprotein, the expression of which in adult tissues is limited to neurons, Schwann cells, oligodendrocytes, adrenal medulla, and leukocytes. The presence of two alternatively spliced exons (23a and 48a) in the NF1 gene allow for the generation of four possible neurofibromin isoforms. Type 1 neurofibromin contains neither 23a or 48a exon sequences, while type 2 neurofibromin contains only the 23a exon insertion. Previous studies have demonstrated that types 1 and 2 neurofibromin might have different functional properties relative to microtubule association and GTPase-activating protein activity towards p21-ras. To determine the normal pattern of expression of these NF1 isoforms, the adult and developmental expression of types 1 and 2 NF1 was examined. Herein, we demonstrate that NF1 mRNA is expressed at varying levels in adult tissues and is developmentally regulated during embryogenesis. Neurons in the central nervous system express predominantly type 1 NF1. Using mouse neocortical cultures enriched for neurons or glial cells, type 1 NF1 predominance was demonstrated in neurons, while type 2 NF1 predominated in glial cells. In contrast to central nervous system neurons, neurons expressing the type 2 NF1 isoform were identified in the developing dorsal root ganglia and spinal cord by in situ hybridization using a type 2-specific oligonucleotide probe. The elucidation of the differential expression pattern of these two NF1 isoforms during development and in adult life provides the foundations for future studies aimed at determining the functions of these neurofibromin isoforms.

Animals↗
PubMed1994

Temporal discrimination learning of operant feeding in goldfish (Carassius auratus).

Operant temporal discrimination learning was investigated in goldfish. In the first experiment, there was a fixed daily change in illumination. Eight subjects were trained to operate a lever that reinforced each press with food. The period during which responses were reinforced was then progressively reduced until it was 1 hr in every 24. The final 1-hr feeding schedule was maintained over 4 weeks. The feeding period commenced at the same time each day throughout. The food dispensers were then made inactive, and a period of extinction ensued for 6 days. The pattern of responding suggested that the fish were able to exhibit temporal discrimination in anticipation of feeding time. This pattern of responding persisted for a limited number of days during the extinction procedure. The second experiment produced evidence that operant temporal discrimination could develop under continuous illumination.

Journal Article↗
PubMed1994

Overexpression of nerve growth factor in epidermis of transgenic mice causes hypertrophy of the peripheral nervous system.

Survival of developing neurons is dependent on access to a limited supply of target-derived neurotrophic factors. NGF is the most extensively characterized of these molecules and during development is synthesized by neuronal and nonneuronal target tissues such as the skin. To investigate how target-derived NGF affects neuron survival and development of the PNS, we used an epidermal-specific gene promoter to produce transgenic mice that overexpress the mouse NGF cDNA in skin. Analysis of transgenic skin mRNA synthesis by Northern and in situ hybridizations showed increased levels of transgene-derived mRNA in the epidermis and associated hair follicles. The increase in NGF mRNA correlated with a hypertrophy of peripheral sensory and sympathetic nerves. Immunological analysis of skin using an anti-150 kDa neurofilament antibody showed numerous large nerve bundles and fibers coursing throughout the dermis. Increased numbers of nerve processes in the transgenic skin had immunoreactivity for calcitonin gene-related peptide and tyrosine hydroxylase, indicating that both the sensory and sympathetic systems were hypertrophied. The trigeminal and superior cervical ganglia were greatly enlarged. Cell counts of trigeminal ganglia of control and transgenic mice showed a 26-117% increase in the number of neurons in the transgenics, indicating a reduction or total prevention of the program of naturally occurring cell death. These results demonstrate that NGF production by the epidermal target tissue controls neuronal survival, and in so doing, establishes the level of innervation.

Animals↗
PubMed1993

Lack of expression of serotonin receptor subtype -1a, 1c, and -2 mRNAs in gonadotropin-releasing hormone producing neurons of the rat.

Serotonin is one of the neurotransmitters which participates in the regulation of gonadotropin-releasing hormone (GnRH) release from the hypothalamus. In order to test the hypothesis that serotonin acts directly on the GnRH neurons, dual in situ hybridization with 35S-labeled cRNA probes encoding for the serotonin receptor subtypes-1a, -1c, or -2 together with digoxigenin-labeled GnRH cRNA probes was applied to histological sections of the septum-diagonal band and preoptic area. The results of these studies show that many neurons in these brain regions contain the various serotonin receptor mRNAs, however, no cells were detected that contain both GnRH mRNA and serotonin receptor mRNAs. It is therefore suggested that the effects of serotonin on GnRH release are not mediated by direct actions of the neurotransmitter through serotonin-1a, -1c or -2 receptors on GnRH neurons but instead through other, yet unidentified serotonin receptor subtypes or through non-serotoninergic intermediary neurons.

Animals↗
PubMed1993

Origin of noradrenergic projections to GnRH perikarya-containing areas in the medial septum-diagonal band and preoptic area.

The purpose of the present study was to identify the sites of origin of the noradrenergic fibers that project to areas containing gonadotropin-releasing hormone (GnRH) perikarya since norepinephrine (NE) is known to influence the activity of GnRH neurons. Fluorescent retrograde tracers were used in combination with immunohistochemistry for dopamine-beta-hydroxylase (DBH) and GnRH. Small volumes of either Fluoro-gold (FG) or Fluoro-Ruby (FR) were pressure injected into areas that contain the largest number of GnRH cell bodies, i.e., the medical septum-diagonal band complex or preoptic area. Retrogradely labeled neurons were observed ipsilaterally in the following noradrenergic cell groups: A2 (in the nucleus tractus solitarii), A1 (in the ventrolateral medulla) and locus coeruleus. Approximately 8% of all DBH-positive neurons within the A2-cell group were retrogradely labeled, while 12% of DBH-ir neurons in the A1-group were double-labeled. Only a few retrogradely labeled DBH-ir neurons were observed in the locus coeruleus (< 1%). Double-labeled neurons were not organized into discrete cell groups, but were dispersed among other NE-neurons within the A2- and A1-cell groups. The highest concentrations of double-labeled neurons were located in the central one-third of both the A2 and A1 cell groups. The results suggest that most noradrenergic terminals in the region of the GnRH perikarya in the medial septum-diagonal band/rostral preoptic area originate from ipsilateral neurons in areas A1 and A2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Angiotensin II(3-8) (ANG IV) hippocampal binding: potential role in the facilitation of memory.

The present research characterizes a newly discovered ANG II(3-8) (ANG IV) binding site localized in structures associated with memory function (hippocampus, neocortex, cerebellum), as well as other brain stem structures (thalamus, inferior olivary nucleus). This site is not the AT1 or AT2 site that binds angiotensins II (ANG II) and III (ANG III) nor does it bind the nonpeptide AT1 or AT2 receptor antagonists DuP753 and PD123177, respectively. The intracerebroventricular (ICV) infusion of ANG IV was ineffective at inducing drinking in rats as compared with equivalent doses of ANG II and III. Although not as effective as ANG II or ANG III, ICV infusion of ANG IV did provoke a pressor response at the highest dose (100 pmol/min), which appeared to be mediated by ANG II (AT1)-type receptors and not the specific AIV binding site described here. By contrast, the ICV infusion of ANG IV resulted in greater effects upon retention and retrieval of a passive avoidance task as compared with ANG II. Specifically, ANG II was not different from the ICV infusion of artificial cerebrospinal fluid, while ANG IV improved retention and retrieval of this task.

Angiotensin II↗
PubMed1993

Assessment of atypicality: an adjunct to prenatal screening for Down's syndrome that facilitates detection of other abnormalities.

Current software used for assessment of the risk of Down's syndrome may give misleading risk estimates if applied to other abnormalities. Often the abnormality is reflected in maternal serum alpha-fetoprotein and human chorionic gonadotrophin levels and is then translated into a low risk for Down's syndrome that may not be recognized as significantly atypical of normality. We regard this as a serious deficiency in the current Down's syndrome risk reporting algorithm, and suggest a modification that allows the problem to be overcome.

Algorithms↗
PubMed1991

Gonadotropin hormone-releasing hormone (GnRH) immunoreactivity in the mesencephalon of sharks and rays.

Other than association with the terminal nerve (TN), little is known concerning the distribution of gonadotropin hormone-releasing hormone (GnRH) in elasmobranchs. The purpose of this study was to identify GnRH immunoreactivity in the brains of three elasmobranch species with special regard to the mesencephalon. The round stingray (Urolophus halleri), thornback guitarfish (Platyrhinoidis triseriata), and leopard shark (Triakis semifasciatus) were used and immunocytochemistry was performed with antisera to both salmon and mammalian GnRH. A large GnRH-immunoreactive (ir) nucleus extends rostrocaudally for approximately 1.5 mm along and adjacent to the midline of the midbrain near the area of the oculomotor nerve. GnRH-ir fibers surround the nucleus and are found diffusely throughout the mesencephalon; some of the fibers may contact the ventricle. The medulla and spinal cord contain ir fibers that most likely originate from the midbrain nucleus. Mesencephalic GnRH-ir cell groups have been reported in representatives of all vertebrate classes with the exception of agnathans and mammals. Such a well-developed cell group in elasmobranchs may aid in understanding the evolution of GnRH systems with regard to the mesencephalon as well as providing insight to the functional significance of this cell group. Possible homologies to mesencephalic GnRH systems reported in other vertebrates is discussed as well.

Animals↗
PubMed1987

Decreased potency of glucagon on transformed-induced MDCK cells does not reflect an alteration of adenylate cyclase components.

The selective loss of glucagon sensitivity of transformed MDCK cells can be restored by differentiation inducers, a process which requires RNA and protein synthesis and glycosylation. Although the glucagon dose-response curve of normal MDCK cells resembled that of liver and kidney (Kact = 10 nM), the transformed-induced cells were 10-fold less sensitive to the hormone [activation constant (Kact) = 100 nM]. Additionally, the stimulation of cAMP synthesis by a glucagon fragment (glucagon) in transformed-induced cells was greatly reduced compared to normal cells. The adenylate cyclase regulatory components of transformed-induced MDCK cell membranes seemed unaltered compared to the parental line. Both contained equivalent amounts of cholera and pertussis toxin substrates, and soluble extracts were equally capable of reconstituting isoproterenol responsiveness of S49 cyc- membranes. However, membrane fusion studies demonstrated that the glucagon sensitivity of transformed-induced membranes could not be reconstituted with heterologous membranes. When donor transformed-induced membranes (with inactivated adenylate cyclase) were fused with acceptor HeLa membranes (normally unresponsive to glucagon and prostaglandin E), such hybrids were unresponsive to glucagon, although responsiveness to prostaglandin E was evident. Parallel hybrids with normal MDCK membranes were responsive to both glucagon and prostaglandin E. This difference could not be explained by an inhibitory effect of transformed-induced membranes on receptor-adenylate cyclase coupling under the fusion conditions: the ability of these membranes to serve as an acceptor for the reconstitution of vasoactive intestinal peptide responsiveness was identical to that of normal MDCK cells. The data suggest that the glucagon sensitivity induced in transformed MDCK cells differs significantly from that of the parental line. However, these differences cannot be explained by alterations of transformed-induced membrane components relevant to the coupling of hormone receptors to adenylate cyclase.

Adenylyl Cyclases↗
PubMed1986

Synthesis and quantitative structure-activity relationships of antiallergic 2-hydroxy-N-1H-tetrazol-5-ylbenzamides and N-(2-hydroxyphenyl)-1H-tetrazole-5-carboxamides.

The synthesis and antiallergic activity of a series of 2-hydroxy-N-1H-tetrazol-5-ylbenzamides and isomeric N-(2-hydroxyphenyl)-1H-tetrazole-5-carboxamides is described. A relationship between structure and intravenous antiallergic activity in the rat passive cutaneous anaphylaxis (PCA) test has been established using a Hansch/Free-Wilson model and used to direct studies toward potent derivatives. The contribution of physicochemical properties to activity is discussed. One member of this series, N-(3-acetyl-5-fluoro-2-hydroxyphenyl)-1H-tetrazole-5-carboxamide (3f), which was selected for further evaluation, has an ID50 value of 0.16 mg/kg po and is 130 times more potent than disodium cromoglycate (DSCG) on intravenous administration.

Animals↗
PubMed1985

Detection and localization of the v-myb(AMV) gene products of avian myeloblastosis virus by a synthetic peptide antiserum.

An antiserum made against a synthetic peptide from an internal region of the predicted amino acid sequence of the avian myeloblastosis virus (AMV) transforming v-myb(AMV) gene identified two products, p46v-myb(AMV) and p32v-myb(AMV), which were localized in the nucleus of AMV-transformed myeloblasts. We propose that these proteins are the in vivo products of the v-myb(AMV) gene and thus the transforming protein(s) of AMV.

Animals↗
PubMed1984

Photoaffinity labeling of the glucagon receptor with a new glucagon analog.

The preparation, purification and characterization of N epsilon-4- azidophenylamidinoglucagon are described. This photoreactive peptide was found to be 50% as potent as native glucagon in competing with 125I-labeled glucagon for binding to glucagon receptors on rat liver plasma membranes. Similarly, the analog was 50% as potent as native glucagon in its ability to stimulate adenylate cyclase. The photoreactive glucagon analog was radioiodinated to high specific activity with iodine-125 and was used to label rat liver plasma membrane proteins. Analysis of labeled membrane proteins by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed covalent incorporation predominantly into a protein of relative molecular mass, Mr, of 50 000-60 000. Occasionally a protein of Mr 170 000-180 000 was also labeled. Irradiation of membranes in the presence of unlabeled glucagon or GTP selectively inhibited the labeling of the 50 000-60 000-Mr protein(s). As a result of these studies we suggest that the sodium-dodecyl-sulfate-dissociated glucagon receptor is a 50 000-60 000-Mr protein.

Adenylyl Cyclases↗
PubMed1984

Purification of the photoaffinity-labeled glucagon receptor by gel electrophoretic methods.

Rat liver plasma membrane glucagon receptor has been purified with a yield of 0.01% to an estimated homogeneity of 32-60%, using a 2-stage electrophoretic procedure. SDS-solubilized membrane proteins labeled by the photoaffinity-agent, Ne-4-azidophenylamidinoglucagon (APA-glucagon), were separated by polyacrylamide gel electrophoresis in SDS-containing buffers. Gel slices corresponding to the molecular weight of the receptor were excised, electrophoretically extracted and concentrated. The concentrate was subjected to isoelectric focusing on Sephadex to yield a purified product in which the photoaffinity-labeled receptor, with a molecular weight of 56K and a pI' of 5.9, is the sole major component.

Affinity Labels↗
PubMed1983

Partial purification and characterization of the glucagon receptor.

Specific labeling of liver plasma membrane glucagon receptors has been achieved by the photoincorporation of a 125I-labeled photoderivative of glucagon, NE-4-azidophenylamidinoglucagon. Identification of glucagon receptors was facilitated by irradiating membranes in the presence of excess unlabeled glucagon. Isoelectric focusing of radioiodinated membrane proteins revealed one major band of glucagon displaceable material which had an isoelectric point of 5.85. When this material was isolated and run on SDS-polyacrylamide gels a major labeled band of Mr55000 was obtained which had properties consistent with those of the glucagon receptor. These studies indicate that a purification of the glucagon receptor of greater than 700-fold can be attained through the use of isoelectric focusing and SDS-polyacrylamide electrophoresis.

Animals↗