Search PubMed⌕ Search

Biomedical subjects

H J Cooke

Publications and source records attributed to H J Cooke.

At least 73 records · Page 4Linked to original sources
PubMed1995

Role for 5-HT and ACh in submucosal reflexes mediating colonic secretion.

Neural reflex pathways activated in response to mucosal stroking were investigated in segments of distal colon from guinea pigs. Stroking the mucosal surface of whole thickness or muscle-stripped segments with a brush at 1/s evoked an increase in short-circuit current (Isc) whose duration and amplitude were dependent on the number of strokes. The increase in Isc induced by mucosal stroking was virtually abolished by inhibitors of chloride secretion and by tetrodotoxin. The response was reduced by atropine, renzapride, and N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide but not by mecamylamine, ketanserin, tropisetron, or SDZ-205-557. Mucosal application of 5-hydroxytryptamine and 5-hydroxyindalpine increased Isc, which was attenuated by tetrodotoxin and renzapride. The results suggest that mucosal stroking evokes chloride secretion by activating neural reflex pathways utilizing serotoninergic receptors, of the 5-HT1P class, as well as muscarinic receptors within the submucosal plexus.

Acetylcholine↗
PubMed1994

H3 receptors: modulation of histamine-stimulated neural pathways influencing electrogenic ion transport in the guinea pig colon.

The role of H3 receptors in neurally-evoked recurrent increases in chloride ion secretion evaluated from changes in short-circuit current (Isc) was examined during application of histamine or histamine analogs. Muscle-stripped or whole thickness segments of distal colon were set up in flux chambers. Histamine and dimaprit, an H2 receptor agonist, caused recurrent increases in Isc. Dimaprit-evoked recurrent responses were reduced by the H3 receptor agonists, N alpha-methylhistamine and R alpha-methylhistamine, and the inhibition was reversed by the H3 receptor antagonist, burimamide. Histamine-evoked recurrent increases in Isc were enhanced by the H3 receptor antagonists burimamide and thioperamide. The results indicate that H3 receptors play an inhibitory role in histamine-evoked, neurally-mediated recurrent increases in Isc in guinea pig colon.

Animals↗
PubMed1994

Effect of telomeres on the interphase location of adjacent regions of the human X chromosome.

Chromosomes occupy specific nonrandom domains in the interphase nucleus of eukaryotic cells. We have used a Chinese hamster-human somatic cell hybrid line containing a single human X chromosome to study the interphase distribution of the Xp telomere using fluorescent in situ hybridization and optical sectioning. A derivative cell line in which the X chromosome has been broken at Xq22-24 and healed by the addition of cloned human telomeric sequences was also studied to determine if introduction of these sequences at a previously interstitial site changed its location in interphase. The endogenous Xp telomere occupies a specific, nonrandom, internal domain. Introduction of a telomere at a previously interstitial site did not alter the interphase nuclear location of that site. The results suggest that nonrandom interphase location of telomeres may not be determined solely by the DNA sequence of the telomere.

Cell Nucleus↗
PubMed1994

Analysis of cDNA sequences from mouse testis.

Few mammalian proteins involved in chromosome structure and function during meiosis have been characterized. As an approach to identify such proteins, cDNA clones expressed in mouse testis were analyzed by sequencing and Northern blotting. Various cDNA library screening methods were used to obtain the clones. First, hybridization with cDNA from testis or brain allowed selection of either negative or differentially expressed plaques. Second, positive plaques were identified by screening with polyclonal antisera to prepubertal testis nuclear proteins. Most clones were selected by negative hybridization to correspond to a low abundance class of mRNAs. A PCR-based solid-phase DNA sequencing protocol was used to rapidly obtain 306 single-pass cDNA sequences totaling more than 104 kb. Comparison with nucleic acid and protein databases showed that 56% of the clones have no significant match to any previously identified sequence. Northern blots indicate that many of these novel clones are testis-enriched in their expression. Further evidence that the screening strategies were appropriate is that a high proportion of the clones which do have a match encode testis-enriched or meiosis-specific genes, including the mouse homolog of a rat gene that encodes a synaptonemal complex protein.

Amino Acid Sequence↗
PubMed1994

Mouse centromere mapping using oligonucleotide probes that detect variants of the minor satellite.

Cytologically, the centromere is found at the very end of most Mus musculus chromosomes, co-localizing with an array of minor satellite sequences. It is separated from the euchromatin of the long arm by a large domain of heterochromatin, composed in part of arrays of major satellite sequences. We used oligonucleotide probes that specifically detect regions of sequence variation found in certain cloned minor satellite sequences. They detect a limited subset of the minor satellite arrays in the mouse genome, based on both pulsed-field gel electrophoresis and in situ hybridization data, and provide direct molecular genetic markers for individual centromeres in some inbred mouse strains. Array size polymorphisms detected by these probes map to positions consistent with the centromeres of chromosomes 1 and 14 in the BXD recombinant inbred (RI) strains. The genetic distances between these minor satellite arrays and loci on the long arms of chromosomes 1 and 14 are consistent with repression of meiotic recombination in the heterochromatic domains separating them. The existence of chromosome-specific minor satellite sequences implies that the rate of sequence exchange between non-homologous chromosomes relative to the rate between homologous chromosomes is much lower than has previously been postulated. We suggest that the high degree of sequence homogeneity of mouse satellite sequences may instead reflect recent common ancestry.

Animals↗
PubMed1994

Enhanced tissue responsiveness in colonic ion transport of cow's milk-sensitized guinea pigs.

The effects of leukotriene D4 (LTD4) on ion transport were investigated in submucosa/mucosa colonic segments from guinea pigs sensitized to cow's milk and in age-matched, non-immune animals. Mediators released from mast cells in immune animals challenged with beta-lactoglobulin evoked an increase in short-circuit current that was reduced by SK&F 102922, a peptidoleukotriene antagonist. Serosal addition of LTD4 (0.15-1 microM) evoked a concentration-dependent, bumetanide-sensitive increase in short-circuit current which was greater in immune than non-immune controls. In the absence of ongoing neural activity, 1 microM LTD4 evoked an 8-20 microA/cm2 increase in short-circuit current which was increased 8-13-fold when ongoing neural activity was present. In tissues with ongoing activity, the response to 0.15 microM LTD4 was reduced by SK&F 102922, tetrodotoxin and atropine. LTD4 enhanced the responsiveness of the tissue to carbachol by a factor of two, but did not affect responses of T84 colonic epithelial cell monolayers to this agent. These results show enhanced secretory function for LTD4 in animals with allergy to cow's milk. They suggest that the level of ongoing neural activity in the enteric neural microcircuits is one of the major determinants of colonic secretory capacity.

Animals↗
PubMed1994

Neuroimmune communication in the submucous plexus of guinea pig colon after infection with Trichinella spiralis.

BACKGROUND/AIMS: Enteric neuroimmune communication in gastrointestinal hypersensitivity responses includes antigen detection by mast cells and release of chemical messages to the enteric nervous system. The aim of this study was to analyze the electrical and synaptic behavior of neurons in the colonic submucous plexus during exposure to Trichinella spiralis antigen in animals infected earlier with the parasite. METHODS: Microelectrodes were used to record in submucous neurons of guinea pig distal colon during application of Trichinella antigen. RESULTS: Neurons in sensitized animals were more excitable than in controls. Hyperexcitability was seen as a greater probability of spontaneous action potential discharge and repetitive firing to depolarizing current or exposure to acetylcholine. Application of histaminergic antagonists reversed the augmented excitability, suggesting endogenously released histamine as a responsible factor. Antigenic exposure increased neuronal excitability and suppressed nicotinic transmission at fast cholinergic synapses only in sensitized animals. Effects on excitability, but not presynaptic inhibitory effects, were blocked by cimetidine. CONCLUSIONS: Signaling between mucosal mast cells and the enteric nervous system is involved in colonic anaphylactic responses to sensitizing antigens. Histamine is a paracrine signal in the communication pathway.

Action Potentials↗
PubMed1994

Sandwiching of a gene within 12 kb of a functional telomere and alpha satellite does not result in silencing.

Pericentric heterochromatin and telomeres have been shown to be capable of repressing the expression of genes located in close proximity. The effect of adjacent structural sequences on gene expression will be important in the design of mammalian artificial chromosomes. In the process of using telomere-containing constructs to generate a deletion panel of the long arm of the human X chromosome, several cell lines were produced which appeared by in situ hybridization to be broken in Xq at or near the centromere. After analysis of end clones rescued from these cell lines, only two produced data consistent with breaks in the alpha satellite array without accompanying rearrangements. The mitotic stability of an X chromosome, with at least 750 kb of the alpha satellite array deleted, was compared to controls where the alpha satellite array remained intact. No significant change in the stability of the chromosome was observed, suggesting that the truncated chromosome has a fully functional mitotic centromere. There was no detectable change in the expression of the hygromycin resistance gene, which is located between a functional centromere and telomere, in this cell line. This study indicates that structural elements flanking a mammalian selectable marker do not result in silencing.

Animals↗
PubMed1994

Human male fertility--Y-linked genes and spermatogenesis.

Using a positional cloning approach, we have isolated a new gene family, the Y-located RNA Recognition Motif genes (YRRM), which constitutes a candidate for AZF, the 'azoospermia factor' located principally within band Yq11.23, and thought to be important in the control of human spermatogenesis. The YRRM gene family has at least 15 members, more than one of which are transcribed, some of which are pseudogenes. RNA in situ hybridization to adult human testis tissue indicates that gene expression of the YRRM family is confined to germ cells, notably spermatogonia and/or primary spermatocytes. Similar patterns of hybridization are seen for a second gene family, TSPY, clustered mainly on the short arm of the human Y chromosome. Both YRRM and TSPY show Y chromosome conservation in several mammalian species.

Chromosome Mapping↗
PubMed1994

Neuroimmune signaling in regulation of intestinal ion transport.

Complex interactions between the enteric nervous system, the immune system, and the epithelium govern the transport rates of salt and water across the intestinal lining. Luminal antigens or bacterial products are detected by the immune system, which triggers a cascade of events associated with the release of inflammatory mediators. These mediators, by lowering the response threshold for transmission in some neural circuits, augment ongoing neural reflexes that promote secretion. Associated with these effects is a dampening of responses in other neural circuits innervating the mucosal effectors. Selective excitation and inhibition of the neural reflex circuitry coupled with direct actions of inflammatory mediators on epithelial cells result in stereotypical motility and secretory patterns that are characterized by strong muscular contractions, copious secretion, and diarrhea.

Animals↗
PubMed1994

Neuroimmune communication in the submucous plexus of guinea pig colon after sensitization to milk antigen.

We investigated electrical and synaptic behavior of neurons in the colonic submucous plexus during exposure to beta-lactoglobulin in guinea pigs sensitized by ingestion of milk. Microelectrodes were used to record electrical and synaptic behavior in neurons from milk-sensitized and nonsensitized age-matched animals during exposure to beta-lactoglobulin. Neurons in sensitized animals were hyperexcitable. Application of the histamine H2 antagonist cimetidine reversed the hyperexcitability, suggesting endogenously released histamine as one of the responsible factors. Antigenic exposure suppressed stimulus-evoked nicotinic cholinergic fast excitatory postsynaptic potentials (EPSPs). This was blocked by the selective histamine H3 antagonist burimamide. Suppression of the EPSPs resulted from presynaptic inhibition of acetylcholine release. Increased neuronal excitability and suppression of synaptic transmission was only found in milk-sensitized intestine, not in the intestine from age-matched nonsensitized animals. We concluded that signaling from mucosal mast cells to the enteric nervous system is important in colonic defense against antigenic threats. Histamine is a paracrine messenger in the communication network.

Acetylcholine↗
PubMed1994

Vasoactive intestinal polypeptide: a transmitter in submucous neurons mediating secretion in guinea pig distal colon.

The aim of the study was to investigate the role of vasoactive intestinal polypeptide (VIP) as a transmitter in regulation of epithelial function. Submucosa/mucosa segments from guinea pig distal colon were mounted in flux chambers and increases in short-circuit current were used as an index of secretion. Serosal addition of VIP, peptide histidine isoleucine, helodermin and pituitary adenylate cyclase-activating peptide caused an increase in short-circuit current. Tissues were less responsive to peptide histidine isoleucine, helodermin and pituitary adenylate cyclase-activating peptide than to VIP. In tissues without neurogenic tone, VIP(10-28), but not tetrodotoxin, reduced the response to exogenous VIP. The secretory response to VIP was attenuated by tetrodotoxin and atropine only in tissues with ongoing neural activity influencing basal rates of transport. In the presence of muscarinic blockade, neural stimulation evoked an increase in short-circuit current which was attenuated by VIP(10-28). High extracellular potassium concentrations or carbachol evoked release of endogenous VIP. VIP and VIP (10-28) displaced the binding of [125I]VIP to epithelial receptors. These results provide evidence that VIP is a neurotransmitter within the submucous plexus involved in regulation of epithelial transport in the guinea pig colon.

Animals↗
PubMed1993

Histamine receptors on submucous neurons in guinea pig colon.

Intracellular microelectrodes were used to investigate the actions of histamine in the submucous plexus of the distal colon of the guinea pig. Three effects resulted from application of histamine to submucous neurons. The first was membrane depolarization associated with increased input resistance and augmented excitability. The second was presynaptic suppression of acetylcholine release at nicotinic synapses. The third occurred during long-term application and consisted of recurrent trains of action potentials associated with periodic depolarization of membrane potential. Pharmacological analysis, with selective agonists and antagonists, suggested mediation of the first and third response by postsynaptic histamine H2 receptors. The second response was mediated by presynaptic histamine H3 receptors. These actions of histamine represent a mechanism for neuroimmune signaling between mucosal mast cells and submucous neurons in gastrointestinal type 1 hypersensitivity reactions to allergens.

Animals↗
PubMed1993

Elevation of cAMP facilitates noradrenergic transmission in submucous neurons of guinea pig ileum.

Slow synaptic excitation and inhibition were studied with intracellular microelectrodes in submucous ganglion cells of the guinea pig ileum. Elevation of adenosine 3',5'-cyclic monophosphate (cAMP) after application of forskolin or the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) resulted in slowly activating depolarization of the membrane potential. The depolarization was associated with increased input resistance, enhanced excitability, and suppression of hyperpolarizing afterpotentials. This occurred in AH/type 2 but not S/type 1 neurons. The action of forskolin or IBMX mimicked slow synaptic excitation in the same neurons. Focal electrical stimulation also evoked slow inhibitory postsynaptic potentials (IPSPs). The amplitude and duration of the IPSPs were increased by forskolin or a membrane-permeant analogue of cAMP. Treatment with phentolamine, yohimbine or idazoxan suppressed the IPSPs before and after potentiation by forskolin, suggesting that the IPSPs were mediated by release of norepinephrine acting at alpha 2-adrenoceptors. Application of adenosine or selective adenosinergic A1 agonists suppressed or abolished the IPSPs. The results suggest that elevation of cAMP facilitates the release of norepinephrine at alpha 2-synapses on submucous neurons of guinea pig small bowel.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Coordination of Cl- secretion and contraction by a histamine H2-receptor agonist in guinea pig distal colon.

Short-circuit current (Isc) was measured simultaneously with muscle tension recorded in the longitudinal or circumferential axis from strain-gauge transducers sutured to the serosal surface of whole thickness segments of distal colon from guinea pigs. Isc and the amplitude and frequency of small-amplitude phasic contractions were stable for several hours. The histamine H2-receptor agonist dimaprit (5-10 microM) evoked recurrent increases in Isc at a frequency of 0.32-0.37 cycles/min. Associated with each cyclical Isc response was an increase in muscle tension indicative of large-amplitude phasic contractions. Recurrent cycles of Isc and associated large-amplitude phasic contractions were abolished by 10 microM cimetidine. In the presence of dimaprit, severing the neural connections between the myenteric and submucosal plexuses abolished the large-amplitude phasic contractions but not cyclical Isc. The results suggest that coordination of cyclical secretion and large-amplitude contraction during chronic activation of histamine H2 receptors requires intact neural connections between the submucosal and myenteric plexuses. The findings provide potential mechanisms to explain altered motility and ion transport during inflammatory diseases or allergic responses to food antigens.

Animals↗