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Biomedical subjects

G A Bishop

Publications and source records attributed to G A Bishop.

At least 19 recordsLinked to original sources
PubMed1992

Differential structure-function requirements of the transmembranal domain of the B cell antigen receptor.

By generating phosphorylcholine (PC)-specific, wild-type (mu), and chimeric (mu-I-A alpha) antigen receptor transfectants of mature B cells, we have shown that the COOH terminus of the mu heavy chain is essential for three major functions: immediate signal transduction (measured as changes in intracellular Ca2+), antigen presentation, and induction of immunoglobulin M secretion. A more detailed analysis of structural requirements of the COOH-terminal domains contributing to these functions was achieved by systematically replacing the spacer, cytoplasmic, and transmembranal domains of the mu-I-A alpha chimeric chain with those of mu. Using this rescue approach, we show that the carboxyl two-thirds of the transmembranal domain (proximal to the cytoplasmic domain) is required for induction of intracellular Ca2+, whereas the complete transmembranal domain is required for the function of antigen presentation but is dispensable for induction of antibody secretion.

Amino Acid Sequence↗
PubMed1992

The physiological effects of serotonin are mediated by the 5HT1A receptor in the cat's cerebellar cortex.

Serotonin is present in a fine beaded plexus in the cerebellar cortex of several mammalian species. In the cat, serotoninergic afferents arise from neurons located within the lateral, paramedian and peri-olivary reticular nuclei (Kerr and Bishop, J. Comp. Neurol., 304 (1991) 502-515). In addition to serotoninergic afferents, these same nuclei also contain a separate population of neurons that give rise to mossy fibers to the cerebellar cortex. Physiological studies have shown that mossy fibers are excitatory to their target neurons. The intent of the present study was to determine the physiological effects of serotonin in the cat's cerebellum in an in vivo preparation and to identify the receptor(s) that mediate the observed responses. Iontophoretic application of serotonin (5HT) onto Purkinje cells reduces the spontaneous firing rate of all cells tested (n = 12). Serotonin also blocks the excitatory effects elicited by the application of aspartate in 17 of 19 units tested and of glutamate (n = 62) in all cases. In addition, 5HT potentiated the inhibitory action of GABA (n = 12). Iontophoretic application of the 5HT1A agonists, 8-OH-DPAT and ipsapirone, mimic the suppressive action of serotonin in a dose-dependent manner. This response, as well as the 5HT mediated suppression are blocked by the application of spiperone, a 5HT1A antagonist. Compounds selective for the 5HT1C,2 and 3 receptors are physiologically ineffective. The present data are in partial agreement with previous studies in the rat's cerebellar cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1992

Clinical assessment and incidence of hepatitis C RNA in 50 consecutive RIBA-positive volunteer blood donors.

OBJECTIVES: (i) To assess evidence of liver disease in 50 consecutive volunteer blood donors who were anti-hepatitis C virus (anti-HCV) antibody positive and who were referred to one hepatologist; (ii) to assay for viral RNA in serum in these patients. SETTING: Royal Prince Alfred Hospital, a teaching hospital of the University of Sydney. PATIENTS: Fifty people who were detected by the NSW Red Cross Blood Transfusion Service to be anti-HCV antibody positive and to have a positive result on recombinant immunoblot assay (RIBA) were assessed by one hepatologist for symptoms, signs and biochemical evidence of hepatic dysfunction. These patients were consecutive referrals from this source. Sixteen of these patients also consented to liver biopsy assessment. All patients had serum assayed for viral RNA by polymerase chain reaction with a combination of 3' and 5' primers. RESULTS: The 50 blood donors consisted of 28 men and 22 women, with a mean age of 34.5 years. Forty-six patients were asymptomatic. Only six had a past history of hepatitis while 14 had minor signs of chronic liver disease. In 28, injecting drug use was thought the most likely source of exposure to HCV. The minimal mean time since exposure to HCV in these patients was 8.8 +/- 5.2 years. Eight patients had received a blood transfusion at a mean time of 15.0 +/- 9.8 years from the time of consultation. The mean maximum level of alanine aminotransferase (ALT) in all 50 patients was 102.8 U/L. Five patients had persistently normal ALT levels; another 22 had at least one normal ALT level. Liver biopsies indicated chronic persistent hepatitis in 11 patients, mild chronic active hepatitis in three patients and more severe chronic active hepatitis in one. One patient had cirrhosis on biopsy. Forty-two patients had viral RNA detected in serum. CONCLUSION: Chronic infection with HCV in blood donors was invariably asymptomatic; 78% of patients had no signs of chronic liver disease and 68% had a maximum hepatic transaminase level of less than 100 U/L. Although severe liver disease was seen in two of 16 biopsies, the majority of these patients have mild liver disease despite a mean of about 10 years since exposure to the virus. Eighty-four per cent of patients had evidence of viral RNA in serum.

Adult↗
PubMed1992

Calcitonin gene-related peptide in afferents to the cat's cerebellar cortex: distribution and origin.

In the present study, the distribution and origin of calcitonin gene-related peptide (CGRP) were analyzed in the cat's cerebellum. Following incubation in an antibody generated against rat CGRP and processing with the peroxidase anti-peroxidase (PAP) technique, CGRP immunoreactivity (IR) is found in profiles that have morphological characteristics of both simple and complex mossy fibers. However, all mossy fibers are not CGRP-positive. Further, CGRP-IR mossy fibers have a heterogeneous distribution in the cerebellum. In the vermis, the majority of immunoreactive profiles are in lobules VII, VIII, and the dorsal folia of IX. In anterior vermal lobules, only scattered terminals, located primarily at the apex and along the shoulder of the folia, are present. Laterally, CGRP-IR mossy fibers are located in the paramedian lobule, paraflocculus, and crus II. No CGRP fibers or varicosities are observed in any of the cerebellar nuclei. However, CGRP-positive cell bodies are scattered throughout the nuclear neuropil. A double label technique revealed that CGRP-IR mossy fibers arise from neurons located in the lateral reticular nucleus, external cuneate nucleus, inferior vestibular nucleus, and basilar pons. The present findings, taken together with previous data, indicate that cerebellar afferents are chemically heterogeneous. The findings of the present study suggest that precerebellar nuclei that give rise to the mossy fibers that contain CGRP have the potential for playing a complex role in modulating circuitry in the cerebellar cortex of the cat.

Animals↗
PubMed1992

Signaling to a CD5+ B-cell clone through surface Ig and MHC class II molecules.

Cells of the CD5+ mouse B-cell clone CH12.LX are induced to become antibody-secreting cells by costimulatory signals delivered by binding of their surface Ig and MHC class II molecules. Class II-mediated signals can be delivered by the binding of either T cells or class II-specific monoclonal antibodies. Divalent, but not monovalent antigen-binding fragments of mAbs are effective in signalling, and cross-linking intact anti-class II mAbs with isotype-specific Ab enhance class II-mediated signaling. Class II-mediated signaling is accompanied by a rise in cAMP and is blocked by an adenyl cyclase inhibitor. The cAMP analogue dibutyryl cAMP, can partially but not completely substitute for the class II-mediated signal. The costimulatory Ig-mediated signal can be delivered by binding of either antigen or antiidiotype Ab, but anti-IgM Abs are much less effective. Antibodies specific for Ig constant regions are much more effective, however, if they engage both the mIgM and mIgD molecules; anti-kappa Abs or a combination of anti-IgM and anti-IgD Abs were more effective in signaling.

Adenylyl Cyclases↗
PubMed1992

Ontogenesis of cerebellar afferents identified by cholecystokinin-like immunoreactivity.

The present account provides a developmental timetable for the maturation of cholecystokinin (CCK)-positive fibers in the cerebellar cortex and cerebellar nuclei of the opossum. CCK-positive fibers are in the cerebellar peduncle by postnatal day (PD) 1, however they wait until PD 7 to penetrate the cerebellar anlage. Between PD 7 and PD 20 the fibers wait again in the medullary core of the cerebellum. After PD 20, there are 2 distinct patterns of CCK localization within the overlying cortical layers. The first pattern develops between PD 20-26 when CCK puncta are present in restricted foci within the Purkinje cell layer of the anterior lobe vermis. They distribute in 4 parasagittal bands, 2 on either side of the midline, that extend from the primary fissure rostrally into the anterior lobe of the cerebellum. By PD 33 two additional parasagittal bands are present in the posterior lobe vermis. The vast majority of these CCK puncta are transient in nature as all but a few disappear by PD 84. Those that remain progress through a series of developmental stages characteristic of climbing fiber ontogeny. These climbing fibers persist in lobules V, VII and VIII of the adult cerebellum. Further, there is a transient expression of CCK-immunoreactivity within inferior olivary neurons. These observations support the interpretation that the transient population of CCK-IR puncta are immature climbing fiber axons derived from the inferior olive. The second pattern of CCK localization is evident between PD 30-33, the time when granule cells first can be recognized in a histologically distinct internal granule cell layer (IGL). Between PD 30 and PD 68 there is a differential pattern of distribution of CCK-IR profiles within the lobules of the cerebellum. Initially, CCK-IR axons are only present in the anterior vermis where they are aligned in register with the bands of CCK puncta in the Purkinje cell layer. CCK-IR puncta are not present in the posterior lobe vermis or hemispheres until later stages of development. Further, a sagittal organization is not evident in either of these latter 2 areas. Initially, CCK-IR profiles in the IGL cannot be identified as mossy fibers based on their terminal morphology. When they first enter the IGL they appear as punctate elements. Over time they become increasingly more complex in shape and between PD 68-84 develop morphological characteristics of adult mossy fiber rosettes. The cerebellar nuclei can be distinguished histologically by PD 18, but CCK-IR fibers are not evident among these neurons until PD 36 which corresponds to about the time they can be visualized in the IGL. In addition, CCK-IR cell bodies first appear in the cerebellar nuclei between PD 26-30; these are present in the adult.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1992

Altered zonal expression of the CD26 antigen (dipeptidyl peptidase IV) in human cirrhotic liver.

Dipeptidyl peptidase IV is a cell surface ectopeptidase with widespread tissue distribution. Recently it was shown to display extracellular matrix-binding properties; therefore its role in cirrhosis is of interest. The aim of this study was to use monoclonal antibodies directed against the human CD26 antigen (which has been shown to be dipeptidyl peptidase IV) to study the distribution of this molecule in normal human and cirrhotic liver. Identical staining was obtained with the three monoclonal antibodies (TaI, 1F7 and TS145) and enzyme histochemistry. In normal liver (n = 11) intense staining of hepatic acinar zones 2 and 3 was present, but little staining was seen in zone I. Hepatocyte staining was confined to the bile canalicular domain. In cirrhotic livers (n = 23) obtained at transplantation, staining of regenerating nodules without a zonal pattern was present. In addition, we saw staining of the lymphoid cell infiltrate and proliferating bile ductules. In a minority of cirrhotic biopsy specimens (four) staining of the basolateral hepatocyte domain in regenerating nodules was seen. Biopsy specimens from hepatic allografts (n = 28) were used as disease controls. These samples all showed preferential staining of zones 2 and 3, similar to that in normal biopsy specimens. Eleven of these samples showed staining of the basolateral and bile canalicular domains. In conclusion, the normal acinar distribution of dipeptidyl peptidase IV (zones 2 and 3) is lost in cirrhotic nodules. Furthermore, the altered membrane distribution of this molecule in cirrhosis and allograft rejection may allow increased hepatocyte extracellular matrix interactions during organ remodeling.

Antibodies, Monoclonal↗
PubMed1992

Differential modulation of Purkinje cell activity by enkephalin and corticotropin releasing factor.

Several peptides have been localized within afferents to the opossum's cerebellum, including cholecystokinin (15), enkephalin (16, 17) and corticotropin releasing factor (7, 9). Each of these peptides has a heterogeneous laminar and lobular distribution. Two peptide, enkephalin (ENK) and corticotropin releasing factor (CRF) are present in specific populations of climbing fibers and mossy fibers, which have an overlapping distribution in several areas of the cerebellum, in particular the lateral aspect of vermal lobules VII and VIII. Within this location ENK and CRF are co-localized in individual climbing fibers and mossy fibers (7). In the present study, the physiological effects of these peptides on Purkinje cell activity were analyzed. The data indicate that ENK and CRF have opposite effects on Purkinje cell activity. ENK suppresses spontaneous activity as well as that induced by application of glutamate and aspartate, as described previously (5). In contrast, CRF enhances both spontaneous and amino acid-induced unit activity. Further, when applied simultaneously, CRF blocks the suppressive effect induced by ENK. Previous studies have shown that climbing fibers, as well as the mossy fiber-parallel fiber pathway, are excitatory to Purkinje cells (11). However, immunohistochemical data have shown that these afferents are heterogeneous with respect to their chemical content (7-9, 15-17, 25). As found in the current and previous studies (3, 5) peptides in climbing and mossy fibers modulate the responsiveness of Purkinje cells to primary excitatory neurotransmitters in selected areas of the cerebellar cortex. However, the firing rate of individual Purkinje cells is differentially altered depending on which neurochemical messenger(s) are released.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1992

Use of a cellular ELISA for the detection of cell surface antigens.

A sensitive, convenient and inexpensive enzyme-linked immunosorbent assay (ELISA) is described for the detection and relative quantitation of cell surface antigens. The cells to be tested are rapidly glutaraldehyde-fixed to the wells of microtiter plates, which can be stored for later assay, if desired. Alternatively, adherent cells may be left unfixed. Following incubation with antibodies specific for the antigens of interest, an enzyme-linked second antibody conjugate is added, followed by the substrate for the enzyme, as in a conventional ELISA for soluble proteins. The method is a sensitive and accurate alternative to immunofluorescence flow cytometry for rapid and inexpensive screening of large numbers of cell samples.

Animals↗
PubMed1991

Requirements of class II-mediated B cell differentiation for class II cross-linking and cyclic AMP.

Cells of the mouse B cell clone, CH12.LX, receive Ag-dependent differentiative signals through their surface membrane class II molecules. The present study was performed to determine the role of class II cross-linking and cAMP in the successful delivery of these signals. Delivery of differentiative signals by anti-Ek mAb was increased by further cross-linking with a secondary anti-isotype antibody. Intact or (Fab')2, but not Fab forms of anti-Ek successfully delivered the Ag-dependent differentiative signal. Inability of monovalent Fab fragments to deliver the signal could not be attributed to an inability to adequately bind Ek molecules. The requirement for cAMP for class II-mediated signaling was also examined, because previous studies have implicated elevated cAMP levels as necessary for class II signaling. Both Ag-dependent, Ek-mediated differentiation and the Ek-mediated inhibition of Ag-independent LPS-induced differentiation were inhibited by the adenyl cyclase inhibitor 2'5'ddA, although elevation of cAMP was not in itself sufficient to deliver the differentiative signal. Inhibition of LPS-induced differentiation could be mediated by mAb binding to either Ek, Abk, or Abb on CH12.LX or an Ab-bearing transfectant, CH12.ABB1. This inhibition was abrogated by 2'5'ddA in the case of Ek or Abb, both of which deliver Ag-dependent differentiative signals to CH12.LX cells. In the case of Abk, which does not deliver such signals to CH12.LX, 2'5'ddA did not abrogate anti-Abk-mediated inhibition of the LPS response. The effects of 2'5'ddA were reversed by the cAMP analog, dibutyryl cAMP, and Ag-dependent-induced differentiation of CH12.LX or CH12.ABB1 was accompanied by an increase in cAMP levels.

Adenylyl Cyclase Inhibitors↗
PubMed1991

Topographical organization in the origin of serotoninergic projections to different regions of the cat cerebellar cortex.

The distribution of serotonin immunoreactivity in the cat cerebellum was studied by using the indirect antibody peroxidase-antiperoxidase (PAP) technique. Furthermore, the origin of these chemically defined afferents was determined by combining the retrograde transport of horseradish peroxidase (HRP) with the PAP technique. In the cerebellar cortex, serotonin immunoreactivity is present in a plexus of beaded fibers that is confined almost exclusively to the granule and Purkinje cell layers; a few fibers are present in the molecular layer. Serotoninergic axons and varicosities have a dense and uniform distribution throughout all lobules of the cerebellum with the exception of lobule X where the fiber density is sparse. Serotonin cell bodies were not found within the cerebellar cortex. However, following pretreatment with pargyline and L-tryptophan, serotonin positive cell bodies were found in all deep cerebellar nuclei as well as the raphe and reticular nuclei in the brainstem. The present study demonstrates that the serotoninergic projection to the cat's cerebellum has some degree of topographical organization. Serotoninergic fibers in the anterior vermis (lobules I-V) were shown to arise from neurons located within the paramedian reticular nucleus, the lateral reticular nucleus, and the lateral tegmental field. Injections of HRP into either the posterior vermis (lobule VI-IX) or the paramedian lobule, labeled serotoninergic neurons exclusively in the lateral reticular nucleus. Lobus simplex, crus I and crus II (the hemisphere) receive a serotoninergic input from cells located in the lateral tegmental field, the peri-olivary reticular formation and the paramedian reticular nucleus. In no cases were neurons in the raphe double-labeled, although there were cells positive for HRP or serotonin alone. The data indicate that there is a topographical organization in the serotoninergic projection from the caudal brainstem to specific regions of the cat's cerebellar cortex. In addition to climbing and mossy fibers, this projection represents a third major source of cerebellar afferents based on its dense and widespread distribution as well as its morphological and chemical characteristics.

Animals↗
PubMed1991

Structure function analysis of the H-2 Abp gene.

The gene encoding the H-2 Ap class II beta chain was isolated from a B10.P genomic library and sequenced. This gene was also used to construct transfectants of the CH12 lymphoma clone CH12.LX, which express the Abp gene product in association with the endogenous A alpha k chain. We present here the first report of the complete nucleotide coding sequence of Abp. The predicted amino acid sequence of Abp reveals only five residues different from Abq, four of which are present in the mature peptide. These four amino acid changes could account for the differential susceptibility of H-2q vs H-2p mice to the development of collagen-induced arthritis (CIA). Antibodies specific for the transfected Abp protein induce CH12.LX cells to secrete immunoglobulin in the presence of antigen. Comparison of the amino acid sequence with other A beta chains that have been tested in signal transduction experiments suggests that amino acid 9 may be important to the signaling ability of class II A molecules.

Amino Acid Sequence↗
PubMed1991

Physiological interactions between enkephalin and excitatory amino acids in the cerebellar cortex of the opossum Didelphis marsupialis virginiana.

The opiate peptide enkephalin has been immunohistochemically localized within specific populations of climbing fibers and mossy fibers in the opossum's cerebellum. The intention of the present study was to determine the physiological effects of this peptide on Purkinje cell activity as well as to examine interactions between this peptide and the excitatory amino acids glutamate and aspartate. Iontophoretic application of enkephalin onto Purkinje cells in the posterior lobe vermis and adjacent hemisphere suppressed activity in nine of 16 (56%) spontaneously active units. Enkephalin increased the spontaneous activity of one unit and had no effect on six (38%) of the units. In addition, this peptide blocked the excitatory effects elicited by iontophoretic application of glutamate in 34 of 35 (97%) units tested and of aspartate in all cases. Enkephalin had no effect on one cell activated by glutamate. Simultaneous application of naloxone, a nonspecific opiate receptor antagonist, did not block the suppressive effects of enkephalin. Rather, there was a potentiation of suppressive responses as compared to that seen when each is applied alone. The results suggest that classically defined excitatory afferent projections to the cerebellum may be capable of both exciting and suppressing the activity of their target neurons. The excitatory action is likely mediated by an amino acid, whereas the release of the peptide enkephalin results in a decrease in unit activity. Further, it appears that enkephalin mediates its suppressive effect through mechanisms that are not mediated by opioid receptors.

Animals↗