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J Bormann

Publications and source records attributed to J Bormann.

At least 19 recordsLinked to original sources
PubMed2004

Prediction of daily milk, fat, and protein production by a random regression test-day model.

Test-day genetic evaluation models have many advantages compared with those based on 305-d lactations; however, the possible use of test-day model (TDM) results for herd management purposes has not been emphasized. The aim of this paper was to study the ability of a TDM to predict production for the next test day and for the entire lactation. Predictions of future production and detection of outliers are important factors for herd management (e.g., detection of health and management problems and compliance with quota). Because it is not possible to predict the herd-test-day (HTD) effect per se, the fixed HTD effect was split into 3 new effects: a fixed herd-test month-period effect, a fixed herd-year effect, and a random HTD effect. These new effects allow the prediction of future production for improvement of herd management. Predicted test-day yields were compared with observed yields, and the mean prediction error computed across herds was found to be close to zero. Predictions of performance records at the herd level were even more precise. Discarding herds enrolled in milk recording for <1 yr and animals with very few tests in the evaluation file improved correlations between predicted and observed yields at the next test day (correlation of 0.864 for milk in first-lactation cows as compared with a correlation of 0.821 with no records eliminated). Correlations with the observed 305-d production ranged from 0.575 to 1 for predictions based on 0 to 10 test-day records, respectively. Similar results were found for second and third lactation records for milk and milk components. These findings demonstrate the predictive ability of a TDM.

Animals↗
PubMed2003

Within-herd effects of age at test day and lactation stage on test-day yields.

Variance ratios were estimated for random within-herd effects of age at test day and lactation stage, on test-day yield and somatic cell score to determine whether including these effects would improve the accuracy of estimation. Test-day data starting with 1990 calvings for the entire US Jersey population and Holsteins from California, Pennsylvania, Wisconsin, and Texas were analyzed. Test-day yields were adjusted for across-herd effects using solutions from a regional analysis. Estimates of the relative variance (fraction of total variance) due to within-herd age effects were small, indicating that regional adjustments for age were adequate. The relative variances for within-herd lactation stage were large enough to indicate that accuracy of genetic evaluations could be improved by including herd stage effects in the model for milk, fat, and protein, but not for somatic cell score. Because the within-herd lactation stage effect is assumed to be random, the effect is regressed toward the regional effects for small herds, but in large herds, lactation curves become herd specific. Model comparisons demonstrated the greater explanatory power of the model with a within-herd-stage effect as prediction error standard deviations were greater for the model without this effect. The benefit of the within-herd-stage effects was confirmed in a random regression model by comparing variance components from models with and without random within-herd regressions and through log-likelihood ratio tests.

Age Factors↗
PubMed2002

Cloning and functional characterization of two glycine receptor alpha-subunits from the perch retina.

Glycine receptors are ligand-gated ion channel proteins mediating synaptic inhibition in the spinal cord, retina and brain of vertebrates. We have cloned and functionally characterized two glycine receptor alpha-subunits from the perch (Roccus americana) retina. Based on sequence homology with the mammalian counterparts, we termed these subunits alpha 1 and alpha 3. RT-PCR revealed the presence of both subunits in retina and brain, whereas alpha1 was predominant in spinal cord. A short splice variant of alpha1 was detected in the brain but not in the retina. Functional expression of the perch subunits in HEK-293 cells yielded robust glycine-gated currents sensitive to strychnine. The perch receptors displayed a high efficacy for taurine and GABA and thus differ from the mammalian counterparts. Because the retina is a rich source for taurine, this finding could be of physiological importance. The structural features of the ligand binding domain strongly support the notion of increased glycine/GABA discrimination in higher vertebrates.

Amino Acid Sequence↗
PubMed2000

The 'ABC' of GABA receptors.

In the conventional view, GABA acts at either ionotropic GABAA or metabotropic GABAB receptors. Recently, novel ionotropic GABA receptors that are composed of rho-subunits have been identified in the vertebrate retina. These bicuculline- and baclofen-insensitive GABA receptors are frequently called GABAC, following an early suggestion by Graham Johnston and colleagues. An IUPHAR committee has recommended that the term GABAC be avoided and subclassifies the retinal receptors as GABAA0r. However, new evidence regarding the pharmacology, structure, function, genetics and cellular localization of ionotropic GABA receptors strengthens the case for the existence of two major classes of these receptors, GABAA and GABAC.

Animals↗
PubMed2000

Glutamic acid decarboxylase-positive neuronal cell bodies and terminals in the human cerebellar cortex.

The distribution of gamma-aminobutyric acid (GABA) in the human cerebellar cortex was studied using immunohistochemistry for glutamic acid decarboxylase (GAD), the enzyme that catalyses GABA synthesis. Observations by light microscopy revealed, in all layers of the cerebellar cortex, strong, punctate positivity for GAD, related to putative GABAergic nerve terminals, as well as a diffuse cytoplasmic immunoreactivity within neuronal cell bodies. GAD-positive nerve terminals were found in close relationship with the walls of the cerebellar cortex microvessels. Observations by electron microscopy revealed positive nerve terminals in contact with the astrocyte perivascular sheath of capillaries. GAD immunoreactivity was also detected within astroglial perivascular endfeet and endothelial cells. The findings provide further insights into the GABAergic synapses of the circuitry of the human cerebellar cortex. The detection of 'vascular' GAD immunoreactivities suggests that GABAergic mechanisms may regulate cerebellar microvessel function.

Aged↗
PubMed1999

Dopamine receptor subtypes modulate olfactory bulb gamma-aminobutyric acid type A receptors.

The gamma-aminobutyric acid type A (GABAA) receptor is the predominant Cl- channel protein mediating inhibition in the olfactory bulb and elsewhere in the mammalian brain. The olfactory bulb is rich in neurons containing both GABA and dopamine. Dopamine D1 and D2 receptors are also highly expressed in this brain region with a distinct and complementary distribution pattern. This distribution suggests that dopamine may control the GABAergic inhibitory processing of odor signals, possibly via different signal-transduction mechanisms. We have observed that GABAA receptors in the rat olfactory bulb are differentially modulated by dopamine in a cell-specific manner. Dopamine reduced the currents through GABA-gated Cl- channels in the interneurons, presumably granule cells. This action was mediated via D1 receptors and involved phosphorylation of GABAA receptors by protein kinase A. Enhancement of GABA responses via activation of D2 dopamine receptors and phosphorylation of GABAA receptors by protein kinase C was observed in mitral/tufted cells. Decreasing or increasing the binding affinity for GABA appears to underlie the modulatory effects of dopamine via distinct receptor subtypes. This dual action of dopamine on inhibitory GABAA receptor function in the rat olfactory bulb could be instrumental in odor detection and discrimination, olfactory learning, and ultimately odotopic memory formation.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1998

GABA-gated Cl- channels in the rat retina.

gamma-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian retina, and its physiological action is well established. GABA receptors have been localized immunocytochemically in the retina of different mammalian species, and all major retinal cell types have been found to express GABAA receptor subunits. Recently, a new type of GABA receptor with pharmacological and electrophysiological properties different from the known GABAA and GABAB receptors, has been described. These GABAC receptors are found predominantly in the vertebrate retina. This review concentrates on the electrophysiological characterization of GABA receptors expressed by amacrine and bipolar cells of the rat retina. We recorded GABA-induced currents from cultured neonatal amacrine and bipolar cells as well as from isolated bipolar cells of adult animals. While amacrine cells contain a homogeneous population of GABAA receptors, bipolar cells exhibit both GABAA and GABAC responses. Although both receptors gate chloride-selective ion channels, their biophysical and pharmacological properties differ markedly. These functional differences and the cellular distribution of GABAA and GABAC receptors suggest that they have different inhibitory functions in the rat retina.

Animals↗
PubMed1998

Synaptic clustering of GABA(C) receptor rho-subunits in the rat retina.

Polyclonal antibodies which recognize the rho-subunits of the GABA(C) receptor were applied to sections of the rat retina. Strong punctate immunoreactivity was found in the inner plexiform layer (IPL), which was shown by electron microscopy to represent a clustering of the GABA(C) receptors at synaptic sites. During postnatal development diffuse rho-immunoreactivity was first observed at postnatal day P3. Distinct labelling of bipolar cells appeared at P7 and punctate, synaptic labelling was observed at P10. In order to show that the rho-immunoreactive puncta coincide with the axons of bipolar cells, double immunostainings of retinal sections with an antiserum against syntaxin 3 and with the rho-antiserum were performed. The experiments showed that rho-immunoreactive puncta are preferentially located on the axon terminals of rod and cone bipolar cells. In order to determine whether GABA(C) receptor rho-subunits coassemble with GABA(A) receptor subunits, double-labelling experiments were performed with subunit specific antisera. Punctate, putative synaptic clustering was observed with all antisera applied, however, GABA(C) receptor expressing puncta did not coincide with GABA(A) receptor containing puncta. This suggests that there are no synaptic GABA receptors in the retina in which GABA(A) and GABA(C) receptor subunits are coassembled. Similar double-labelling experiments were also performed to find out whether GABA(C) receptors and glycine receptors are colocalized. They were clustered at different synapses. This suggests that synaptic GABA(C) receptors consist of rho-subunits and are not coassembled with GABA(A)- or glycine-receptor subunits.

Animals↗
PubMed1997

Immunocytochemical localization of the GABA(C) receptor rho subunits in the cat, goldfish, and chicken retina.

Polyclonal antibodies against the N-terminus of the rat rho1 subunit were used to study the distribution of gamma-aminobutyric acid C (GABA(C)) receptors in the cat, goldfish, and chicken retina. Strong punctate immunoreactivity was present in the inner plexiform layer (IPL) of all three species. The punctate labelling suggests a clustering of the GABA(C) receptors at synaptic sites. Weak label was also found in the outer plexiform layer (OPL) and over the cell bodies of bipolar cells. Double immunostaining of vertical sections with an antibody against protein kinase C (PKC) showed the punctate immunofluorescence to colocalize with bipolar cell axon terminals. In the goldfish retina, the axon terminals of Mb1 bipolar cells were enclosed by rho-immunoreactive puncta. In the chicken retina, several distinct strata within the IPL showed a high density of rho-immunoreactive puncta. The results suggest a high degree of sequence homology between the rho subunits of different vertebrate species, and they show that the retinal localization of GABA(C) receptors is similar across different species.

Animals↗
PubMed1996

Immunocytochemical localization of the GABAc receptor rho subunits in the mammalian retina.

Polyclonal antibodies against the N terminus of the rat rho 1 subunit were generated to study the distribution of GABAc receptors in the mammalian retina. The specificity of the antibodies was tested in Western blots and transfected HEK-293 cells. No cross-reactivity with the GABAA receptor subunits alpha 1-3, beta 1-3, gamma 2, delta or with the glycine receptor subunits alpha 1 and beta could be detected. In contrast, the rho 1, rho 2, and rho 3 subunits were all recognized by the antibodies. In vertical sections of rat, rabbit, cat, and macaque monkey retinae, strong punctate immunoreactivity was present in the inner plexiform layer. Weaker immunoreactivity was also present in the outer-plexiform layer, and cell bodies of bipolar cells were faintly labeled. Double immunostaining of vertical sections and immunostaining of dissociated rat retinae showed the punctate immunofluorescence to colocalize with bipolar cell axon terminals. The puncta possibly represent clustering of the rho subunits at postsynaptic sites.

Animals↗
PubMed1995

A single point mutation decreases picrotoxinin sensitivity of the human GABA receptor rho 1 subunit.

The GABA receptor rho subunits are thought to form bicuculline-insensitive and picrotoxinin-sensitive GABAC receptors. We have investigated the role of the amino acid at position 309 in transmembrane segment M2 of the human rho 1 subunit as a determinant for picrotoxinin sensitivity. The mutant rho 1P309S was constructed by exchanging proline 309 for serine, the corresponding amino acid of the human rho 2 subunit. Whole-cell recordings from HEK-293 cells transfected with rho 1P309S cDNA revealed that the sensitivity of the rho 1P309S channels for picrotoxinin was four-fold lower than that of the wild type rho 1 subunit. The affinity of the mutant receptor for GABA was only slightly changed. These results provide direct evidence that the amino acid at position 309 is an important determinant for the picrotoxinin sensitivity of GABA receptors formed by the rho subunits.

Base Sequence↗
PubMed1995

Expression of GABA receptor rho 1 and rho 2 subunits in the retina and brain of the rat.

We have investigated the distribution of GABA receptor rho 1 and rho 2 subunits in the rat central nervous system. Cloning of rat rho 1 and rho 2 cDNA fragments revealed similarities to the corresponding human sequences of 99% (rho 1) and 88% (rho 2) at the protein level. Whereas the human rho 2 subunit has no consensus sequence for phosphorylation by protein kinase C, the cytoplasmic loop of the rat sequence contains two such sites. Use of the polymerase chain reaction with reverse-transcribed total RNA (RT-PCR) from different brain tissues revealed that transcript for the rho 1 subunit was present in the retina only. The rho 2 mRNA was detected in all brain regions, with the highest level of expression in the retina. In situ hybridization of retinal sections revealed that rho 1 and rho 2 transcripts are present in the inner nuclear layer. RT-PCR and in situ hybridization of isolated retinal cells showed that both rho subunits are present in rod bipolar cells. Since these cells express bicuculline-insensitive GABA receptors, our results further support the idea that rho subunits are part of the GABAc receptor.

Animals↗
PubMed1995

Modulation of hippocampal glycine receptor channels by protein kinase C.

The inhibitory glycine receptor (GlyR) is composed of polypeptide subunits that contain intracellular consensus sequences for phosphorylation by protein kinase C (PKC). During whole-cell recording from rat hippocampal neurones, we observed a time-dependent increase of the glycine-induced membrane current. After 22 min the amplitude was 260 + 13% of the initial control response. PKC was involved in the modulation of hippocampal glycine receptors, since the observed effect was more prominent when the phorbol ester PMA, an activator of PKC, was included in the patch pipette. The action of PMA was mimicked by applying the '5-HT2 receptor agonist, alpha-methyl-serotonin, to the cells. The time-dependent increase in glycine responses was reduced by either tamoxifen, an inhibitor of PKC, or by alkaline phosphatase. Protein kinase A and tyrosine kinase were not involved as modulatory drugs of these kinases had no effect. These results provide direct evidence for the regulation of GlyR function by PKC in rat hippocampal neurones.

Animals↗
PubMed1995

GABAC receptors.

gamma-Aminobutyric acid (GABA) is an important neurotransmitter that mediates inhibition in the vertebrate CNS. Until recently, two receptor subtypes were known: bicuculline-sensitive GABAA and baclofen-sensitive GABAB receptors. Several lines of evidence now indicate the existence of a third class of GABA receptor, which is distinct pharmacologically from GABAA and GABAB receptors and is found predominantly in the vertebrate retina. These novel GABAC receptors are Cl- pores. They are insensitive to drugs that modulate GABAA and GABAB receptors and are activated selectively by cis-4-aminoacrotonic acid.

Receptors, GABA↗
PubMed1994

Differential pharmacology of GABAA and GABAC receptors on rat retinal bipolar cells.

GABAA and GABAC receptors were studied on cultured or freshly isolated rat retinal bipolar cells. The cells displayed GABA-induced whole-cell currents, which were only partially blocked by high concentrations (100 microM) of the GABAA receptor antagonist bicuculline. The bicuculline-resistant (GABAC) component was insensitive to the GABAA receptor modulators flunitrazepam (1 microM) and pentobarbital (50 microM). The bicuculline-sensitive portion of the current was strongly augmented by both drugs, indicating that it was mediated by conventional GABAA receptors. The GABAC and GABAA receptor subtypes displayed a 7-fold difference in their binding affinity for GABA, the EC50 values being 4.2 microM and 27.1 microM, respectively. The Hill coefficient was approximately 2 for both receptors. The bicuculline-insensitive GABAC receptors were markedly blocked by 100 microM picrotoxinin, 2-(3-carboxypropyl)-3-amino-6-(4-methoxyphenyl)pyridazinium bromide (SR-95531) and gamma-hexachlorocyclohexane, drugs known to be antagonists of GABAA receptors. Examination of single-channel currents indicated main-state conductances of 7.9 pS and 29.6 pS for GABAC and GABAA receptors, respectively. The pore diameter of open GABAC receptor channels was 5.1 A, i.e. close to the value of 5.6 A reported for the GABAA receptor. These results demonstrate that rod bipolar cells possess two populations of pharmacologically distinct GABA receptors, GABAA and novel-type GABAC receptors, which might subserve different physiological functions in controlling visual transduction in the retina.

Animals↗
PubMed1994

Modulation of GABAC receptors in rat retinal bipolar cells by protein kinase C.

1. The intracellular phosphorylation of bicuculline- and baclofen-insensitive GABAC receptors was investigated in rat retinal bipolar cells. The cells were recorded in organotypic slice cultures by using the whole-cell configuration of the patch-clamp technique. 2. Peak GABA responses recorded in the presence of bicuculline decreased with repetitive GABA applications. Intracellular application of the phorbol ester, phorbol 12-myristate, 13-acetate (PMA) increased this run-down, whilst it was prevented by both tamoxifen and phosphatase. 3. Perfusing the cells extracellularly with L-AP4, trans-(+/-)-1-amino-1,3-cyclopentane dicarboxylate (ACPD) or alpha-methyl serotonin accelerated the run-down of GABAC responses. 4. Modulation of GABAC responses could be induced by intracellular application of GTP gamma S, indicating involvement of G-proteins in the transduction cascade. 5. These results suggest that retinal GABAC receptors in bipolar cells are modulated by protein kinase C. Receptors which stimulate phospholipase C, presumably via Gi or Go, such as some of the metabotropic glutamate receptors or the 5-HT2 receptor, appear to be linked to this regulatory pathway.

Animals↗
PubMed1994

Facilitation of GABAergic signaling in the retina by receptors stimulating adenylate cyclase.

The gamma-aminobutyric acid type A (GABAA) receptor is the predominant Cl(-)-channel protein mediating inhibition in the retina and elsewhere in the mammalian brain. We have observed a time-dependent increase of GABA-induced whole-cell currents when dopamine was applied externally to rat retinal amacrine cells. After 20 min, the peak current was increased to 208% +/- 10% of its initial value. A comparable effect was observed with the dopamine D1 receptor agonist (+)-1-phenyl-2,3,4,5-tetrahydro(1H)-3-benzazepine-7,8-diol hydrochloride (SKF-38393) but not with the D2 agonist bromocryptine. The action of dopamine involved phosphorylation of GABAA receptors by protein kinase A, as evident from intracellular application of protein kinase A, cAMP, and forskolin. Both guanosine 5'-[gamma-thio]triphosphate and cholera toxin augmented the GABA response, indicating a role for the guanosine 5'-triphosphate-binding protein Gs in the transduction cascade. Phosphorylation of GABAA receptors shifted the half-maximally effective GABA concentration from 71 microM to 47 microM without affecting the maximal response amplitude. The elevated binding affinity for GABA was caused by an increase of the open probability of the channels from 0.09 to 0.33 (2 microM GABA); conductance and mean open time did not change. Several other receptor agonists such as adenosine, histamine, somatostatin, enkephalin, and vasoactive intestinal peptide were found to couple to the same intracellular phosphorylation pathway. Since some of these cotransmitters colocalize with GABA in amacrine cells, they may fine-tune GABAergic inhibition in the retina.

Adenylyl Cyclases↗