Biomedical subjects

C Schmauss

Publications and source records attributed to C Schmauss.

At least 19 recordsLinked to original sources

PubMed2001

Amphetamine distorts stimulation-dependent dopamine overflow: effects on D2 autoreceptors, transporters, and synaptic vesicle stores.

Amphetamine (AMPH) is known to raise extracellular dopamine (DA) levels by inducing stimulation-independent DA efflux via reverse transport through the DA transporter and by inhibiting DA re-uptake. In contrast, recent studies indicate that AMPH decreases stimulation-dependent vesicular DA release. One candidate mechanism for this effect is the AMPH-mediated redistribution of DA from vesicles to the cytosol. In addition, the inhibition of stimulation-dependent release may occur because of D2 autoreceptor activation by DA that is released via reverse transport. We used the D2 receptor antagonist sulpiride and mice lacking the D2 receptor to address this issue. To evaluate carefully AMPH effects on release and uptake, we recorded stimulated DA overflow in striatal slices by using continuous amperometry and cyclic voltammetry. Recordings were fit by a random walk simulation of DA diffusion, including uptake with Michaelis-Menten kinetics, that provided estimates of DA concentration and uptake parameters. AMPH (10 microm) promoted the overflow of synaptically released DA by decreasing the apparent affinity for DA uptake (K(m) increase from 0.8 to 32 microm). The amount of DA released per pulse, however, was decreased by 82%. This release inhibition was prevented partly by superfusion with sulpiride (47% inhibition) and was reduced in D2 mutant mice (23% inhibition). When D2 autoreceptor activation was minimal, the combined effects of AMPH on DA release and uptake resulted in an enhanced overflow of exocytically released DA. Such enhancement of stimulation-dependent DA overflow may occur under conditions of low D2 receptor activity or expression, for example as a result of AMPH sensitization.

Amphetamine↗

PubMed2001

Dopamine receptor functions: lessons from knockout mice [corrected].

In the past few years, a number of laboratories have used gene targeting via homologous recombination to generate mice deficient for key molecules involved in dopaminergic (DAergic) transmission. This tremendous effort has resulted in the successful generation and characterization of mice deficient for the neurotransmitter DA, the main terminator of DAergic neurotransmission (the DA transporter), and all five subtypes of DA receptors. This review summarizes the results from studies of the various DA receptor knockout mice and of mice deficient in proteins that mediate DA receptor signaling. It focuses on a comparison of the locomotor phenotypes and responses to drugs of abuse (psychostimulants), and reviews the results of anatomic studies examining the morphological and neurochemical differentiation of the striatum in these mutants. Moreover, an overview of recently published results highlighting the physiological relevance of the interaction between different DA receptors and between DA receptors and other neurotransmitter receptors in the modulation of behavioral and molecular responses to DAergic stimulation is presented. Finally, in view of the recently discovered heteroligomeric assemblies of neurotransmitter receptors that involve DA receptor subtypes, the potential value of knockout mice as a tool for testing the in vivo significance of these heteroligomeric receptors is discussed.

Animals↗

PubMed2000

A single dose of methamphetamine leads to a long term reversal of the blunted dopamine D1 receptor-mediated neocortical c-fos responses in mice deficient for D2 and D3 receptors.

Dopamine D(1) receptors play an essential role in the induction of expression of the immediate-early gene c-fos in response to pharmacological stimuli. In the forebrain of wild-type mice, administration of a D(1) receptor agonist leads to c-fos mRNA expression levels that are substantially higher than corresponding levels expressed after indirect stimulation of dopamine receptors with methamphetamine. In mice deficient for D(2) and D(3) receptors, c-fos mRNA levels expressed in response to D(1) agonist administration are significantly blunted. However, a single dose of methamphetamine (5 mg/kg) leads to a long lasting reversal of the blunted c-fos responses in these mutants. In the forebrain, this reversal is restricted to the neocortex. Moreover, methamphetamine also enhances c-fos expression levels in preadolescent wild-type mice that normally express low c-fos mRNA in response to D(1) agonist stimulation. Thus, a single dose of methamphetamine leads to a long term increase in D(1) receptor-dependent c-fos responses in brains with either low (preadolescent mice) or blunted (adult D(2) and D(3) mutant mice) c-fos expression levels. A similar long term reversal of the blunted c-fos responses is achieved with a single dose of a full D(1) agonist. These results indicate that the constitutive inactivation of D(2) and D(3) receptors leads to a decrease in agonist-promoted D(1) receptor activity that can be reversed by intermittent agonist stimulation.

Animals↗

PubMed2000

Targeted disruption of the dopamine D(2) and D(3) receptor genes leads to different alterations in the expression of striatal calbindin-D(28k).

The present study used mice deficient for dopamine D(2) and D(3) receptors to test whether the expression of these two members of the D(2) class of receptors is essential for the normal expression of three markers that characterize the neurochemical differentiation of the striatum: the calcium-binding protein calbindin, tyrosine hydroxylase and acetylcholinesterase. Results from these experiments revealed that the expression of striatal tyrosine hydroxylase (the rate-limiting enzyme of dopamine synthesis) and acetylcholinesterase is unaffected even by the combined knockout of D(2) and D(3) receptors. However, D(2) and D(3) receptor knockouts differently affect the striatal expression of calbindin-D(28k) immunoreactivity. Prominent changes in the cellular distribution of calbindin are detected in striatal neurons of D(2) mutant mice. Whereas calbindin immunolabeling of wild-type neurons is prominent in the nuclei and the cytoplasm of medium spiny neurons, in D(2) mutant mice, calbindin immunoreactivity is concentrated exclusively in the cytoplasmic rim of these neurons. Such changes in the cellular distribution of calbindin expression are not detected in mice lacking D(3) receptors. In these mutants, however, a lesser density of calbindin-immunoreactive neuropil is detected in the ventral portions of the striatum, i.e. in regions in which D(3) receptors are thought to be expressed at highest levels. Mice lacking both D(2) and D(3) receptors show both phenotypes. The altered cellular distribution of calbindin in D(2) mutants is likely to have functional consequences for some of the Ca(2+)-mediated cellular functions. The topography of the decreased density of striatal calbindin immunorectivity in D(3) mutants suggests a role for D(3) receptors in supporting the expression of striatal calbindin. The observation that mice lacking both D(2) and D(3) receptors show a combination of the D(2) and D(3) mutant phenotypes indicates that each of the different phenotypes detected in the single mutants is indeed related to the lack of the two different D(2)-like receptor subtypes.

Acetylcholinesterase↗

PubMed1999

Decreased c-fos responses to dopamine D(1) receptor agonist stimulation in mice deficient for D(3) receptors.

The acute administration of dopamine D(1) receptor agonists induces the expression of the immediate early gene c-fos. In wild type mice, this induction is completely abolished by pretreatment with the D(1)-selective antagonist SCH23390, and pretreatment with the D(2)-like receptor antagonist eticlopride reduces the levels of c-fos expressed in response to D(1) receptor stimulation. Mice deficient for the dopamine D(3) receptor express levels of D(1) agonist-stimulated c-fos immunoreactivity that are lower than c-fos levels of their wild type littermates. Moreover, the acute blockade of D(2) receptors in D(3) mutant mice further reduces c-fos expression levels. These data indicate that the basal activity of both D(2) and D(3) receptors contributes to D(1) agonist-stimulated c-fos responses. The findings therefore indicate that not only D(2) but also D(3) receptors play a role in dopamine-regulated gene expression.

Animals↗

PubMed1999

Potentiation of the D2 mutant motor phenotype in mice lacking dopamine D2 and D3 receptors.

Within the D2-class of dopamine receptors, the D2 and D3 subtypes share the highest degree of similarity in their primary structure. However, the extent to which these two receptor subtypes have similar or different functional properties is unclear. The present study used gene targeting to generate mice deficient for D2, D3, and D2/D3 receptors. A comparative analysis of D2 and D3 single mutants and D2/D3 double mutants revealed that D2/D3 double mutants develop motor phenotypes that, although qualitatively similar to those seen in D2 single mutants, are significantly more severe. Furthermore, increased levels of the dopamine metabolites dihydroxyphenyl acetic acid and homovanillic acid are found in the dorsal striatum of D2 single mutants. The levels of these metabolites, however, are significantly higher in mice lacking D2 and D3 receptors. In addition, results of immunoprecipitation experiments revealed that D2 single mutants express higher levels of D3 receptor proteins during later stages of their postnatal development. These results suggest that D3 receptors compensate for some of the lacking D2 receptor functions and that these functional properties of D3 receptors, detected in mice with a D2 mutant genetic background, remain masked when the abundant D2 receptor is expressed.

Animals↗

PubMed1997

Expression of dopamine D3 receptor dimers and tetramers in brain and in transfected cells.

The expression and characteristics of the dopamine D3 receptor protein were studied in brain and in stably transfected GH3 cells. Monoclonal antibodies were used for immunoprecipitation and immunoblot experiments. Immunoprecipitates obtained from primate and rodent brain tissues contain a low molecular weight D3 protein and one or two larger protein species whose molecular mass are integral multiples of the low molecular weight protein and thus appear to have resulted from dimerization and tetramerization of a D3 monomer. Whereas D3 receptor multimers were found to be abundantly expressed in brain, the major D3 immunoreactivity expressed in stable D3-expressing rat GH3 cells was found to be a monomer. However, multimeric D3 receptor species with electrophoretic mobilities similar to those expressed in brain were also seen in D3-expressing GH3 cells when a truncated D3-like protein (named D3nf) was co-expressed in these cells. Furthermore, results from immunoprecipitation experiments with D3- and D3nf-specific antibodies show that the higher-order D3 proteins extracted from brain and D3/D3nf double transfectants also contain D3nf immunoreactivity, and immunocytochemical studies show that the expression of D3 and D3nf immunoreactivities overlaps substantially in monkey and rat cortical neurons. Altogether, these data show oligomeric D3 receptor protein expression in vivo and they suggest that at least some of these oligomers are heteroligomeric protein complexes containing D3 and the truncated D3nf protein.

Animals↗

PubMed1997

Enhanced selection for homologous-recombinant embryonic stem cell clones with a neomycin phosphotransferase gene in antisense orientation.

Gene targeting in embryonic stem cells via homologous recombination can occur at a very low frequency. In order to enrich the selection for homologous recombinants, replacement targeting vectors are now commonly used that contain the thymidine kinase gene placed outside of the targeted homology. The additional negative selection requires the presence of antiviral drugs in the culture medium which are known to reduce the ability of embryonic stem cells to colonize the germ line. We have therefore tested alternative negative selection procedures with replacement targeting vectors that allow the expression of either a ribozyme directed against the neomycin-resistance gene (neo(r)) or of an antisense neo(r) RNA at random integration sites. The hammerhead ribozyme was found to be catalytically inactive in embryonic stem cell cultures maintained in the presence of the selecting drug neomycin. Thus, the replacement targeting vector that contains ribozyme sequences did not enhance the frequency of homologous recombination. However, placing a promotor sequence that can enable the transcription of antisense neo(r) RNA outside of the targeted homology led to a significant enrichment of the selection for homologous recombination. This enrichment is similar to previously reported enrichments obtained with the thymidine kinase gene. The advantage, however, is that no antiviral drugs are needed for the selection.

Animals↗

PubMed1996

Enhanced cleavage of an atypical intron of dopamine D3-receptor pre-mRNA in chronic schizophrenia.

The D2-class of dopamine receptors (D2, D3, and D4) is a target for typical and atypical neuroleptic drugs. They have been considered, therefore, as factors that may contribute to the pathophysiology of psychotic disorders. Interestingly, in cortical brain tissues obtained postmortem form patients with chronic schizophrenia D3 mRNA was found to be significantly lower than in the corresponding anatomic regions of controls. Because the expression of a truncated D3-like mRNA (named D3nf) appeared to be unaffected in schizophrenic brains, these findings suggest the possibility that the loss of D3 mRNA results from an abnormal splicing of D3 pre-mRNA in schizophrenia that is accompanied by an increased accumulation of the truncated D3nf mRNA. To test this, three approaches were taken. (1) Substrate D3 pre-mRNA was spliced in vitro in HeLa nuclear extracts. Results from these experiments show that D3nf mRNA results from the alternative removal of a short spliceosomal intron in D3 pre-mRNA that has a noncanonical 3' splice site. (2) Substrate D3 pre-mRNA was spliced in vivo in stably transfected rat GH3 cells. Despite the atypical 3' cleavage that is necessary to generate D3nf mRNA, D3 and D3nf mRNA were found to be processed at similar amounts. (3) The relative D3/D3nf splicing efficiencies were then determined in the anterior cingulate cortex of postmortem brains obtained from controls and from patients with chronic schizophrenia. Significant differences were found between the relative levels of D3 and D3nf mRNA, suggesting that an enhanced D3nf-specific splicing of D3 pre-mRNA in schizophrenia leads to a decreased expression of D3 mRNA.

Aged↗

PubMed1995

The responsiveness of a tetracycline-sensitive expression system differs in different cell lines.

A tetracycline-sensitive inducible expression system was used to regulate the expression of neurotransmitter receptor genes in two mammalian cell lines. The dopamine D3-receptor was stably expressed in GH3 cells, and GluR6 (a glutamate receptor subunit) was stably expressed in human embryonic kidney (HEK 293) cells. Three striking differences were found. 1) In the inactive state, virtually no D3-receptor expression was found in GH3 cells, whereas substantial levels of GluR6 expression were found in HEK 293 cells. 2) The induction of expression obtained upon removal of tetracycline was robust in GH3 cells but only modest in HEK 293 cells. 3) Whereas in each clonal cell line, the expression of a co-transfected hybrid transactivator is clearly regulated in a tetracycline-responsive manner, in the induced state, its mRNA levels were found to be very low in GH3 cells and very high in HEK 293 cells. The results indicate that, in contrast to GH3 cells, HEK 293 cells do not provide a cellular environment in which the expression of a heterologous gene can be tightly controlled in a tetracycline-responsive manner.

Animals↗

PubMed1994

On the origin of mRNA encoding the truncated dopamine D3-type receptor D3nf and detection of D3nf-like immunoreactivity in human brain.

A truncated dopamine D3-receptor-like mRNA, named D3nf, predicts a protein that differs from the D3-receptor only in the carboxyl terminus. However, such a protein has lost the predicted membrane topology typically found for G protein-coupled receptors. Results presented here show that D3nf mRNA arises from the D3-encoded primary transcript via alternative splicing. This splicing, however, appears to involve cleavage of an unusual 3' splice site. Therefore, we tested the possibility that D3nf mRNA results from a splicing error. If this were the case, D3nf mRNA would be expected to be present in the cytoplasm only at very low amounts, and it would not be expected to be translated into protein. However, the relative abundance of cytoplasmic D3/D3nf mRNA in human cortical tissues was found to be similar. Furthermore, we raised polyclonal antisera against the predicted carboxyl-terminal peptide sequence of D3nf that reacts specifically with a protein expressed in stably D3nf mRNA-expressing COS 7 cells. The use of this antiserum also revealed the presence of a approximately 68 kDa D3nf-like immunoreactive protein in human brain, suggesting that the atypically processed D3nf mRNA is translated.

Aged↗

PubMed1994

Functional expression and characterization of human D2 and D3 dopamine receptors.

Functional characteristics of human D2 and D3 receptors (DRs) were examined using a new bioassay suited for the study of Gi-protein-coupled receptors (GiRs). The bioassay utilizes pigment granule aggregation within cultured Xenopus laevis melanophores for the quantitative evaluation of ligands as agonists or antagonists upon particular GiRs. Initial feasibility studies were performed by analyzing a melanocyte receptor endogenous to the melanophores. In dose-dependent manners, melatonin inhibited melatonin-stimulating hormone-induced cAMP accumulation and caused pigment aggregation that could be monitored over time. Next, melanophores were transiently transfected with cDNAs coding for the human D2BR (short form) and D3R. Expression of either receptor conferred upon the cells the ability to aggregate their melanosomes in response to selective dopaminergic agonists. The same ligands also inhibited cAMP accumulation within the transfected melanophores, and the agonist-induced pigment aggregation was shown to be sensitive to pertussis toxin. EC50 and IC50 value determinations revealed that agonists activated the D2R and D3R at similar concentrations, while each of the antagonists displaying an effect was more potent upon the D2R. The results reveal functional similarities and differences between the D2R and D3R.

Animals↗

PubMed1993

Selective loss of dopamine D3-type receptor mRNA expression in parietal and motor cortices of patients with chronic schizophrenia.

The expression of dopamine D3-subtype-receptor mRNA was analyzed in defined anatomic regions of brain obtained postmortem from patients with chronic schizophrenia and from controls. The specific amplification of D3-encoding cDNA by PCR allowed the identification of D3 mRNA expression in a wide variety of anatomic regions in both control brains and brains obtained from schizophrenic patients. However, in the parietal cortex (Brodmann areas 1, 2, 3, and 5) and motor cortex (Brodmann area 4), a selective loss of D3 mRNA expression was found in schizophrenia. A different D3 mRNA species was identified that appears to be widely expressed and that is still found in those regions of schizophrenic brains where D3 mRNA could not be detected. Compared with D3 mRNA this RNA is significantly less abundant, and at present its function (if any) is unclear. Many variables associated with either the course and/or the therapeutic management of the disease may account for the selective loss of D3 mRNA in the motor, somatosensory, and somatosensory association areas of schizophrenic brains.

Aged↗

PubMed1992

The murine gene encoding the highly conserved Sm B protein contains a nonfunctional alternative 3' splice site.

The cDNA and partial genomic nucleotide (nt) sequences were derived for the mouse Sm B polypeptide and compared to the cDNA and genomic sequences encoding human Sm B. The deduced amino acid (aa) sequences from the mouse and human genes are identical with the exception of a single conserved aa substitution, accounting for the ability of anti-Sm antibodies to recognize the Sm polypeptides from a broad range of species. The genomic sequence of mouse B gene is similar to the human B genomic locus that extends from exon 6 to exon 7. These loci include conservation of both 3' alternative splice sites and putative branch points required to process B and B' mRNAs in human cells. However, the nt sequence downstream from the putative distal 3' splice junction and single nt flanking the 3' splice site consensus sequence, differ between mouse and human B. This results in a murine mRNA with a different predicted secondary structure around the distal 3' splice site when compared to humans. Thus, secondary structural constraints in the mRNA or changes in the exon sequence might prevent recognition of this alternative splice site to form B' mRNA in murine tissues.

Animals↗

PubMed1992

The gene encoding the small nuclear ribonucleoprotein-associated protein N is expressed at high levels in neurons.

The highly homologous small nuclear ribonucleoprotein-associated proteins of the Sm group, human N and B/B', are derived from distinct, but similar genes. While the almost identical structural organization of the genes for N and B/B' suggests that they emerged from a common ancestral gene via a duplication event, they now reside on different chromosomes. In contrast to B (which is expressed in all tissues examined) and B' (which is widely expressed with the notable exception of the brain), results from in situ hybridization experiments showed that N is found predominantly in central neurons. Analysis of the transcriptional activity of the 5'-flanking sequences of the human N-encoded gene suggests that the cell-specific expression of N is achieved by selective repression of transcription by distal 5'-flanking sequences.

Animals↗

PubMed1992

[Psychopharmacology and clinical aspects of benzodiazepine dependence].

Recent aspects of mechanism of benzodiazepines (BDZ) via indirect GABA-mimetic inhibitory effects at brain-specific BDZ-GABA receptors may contribute to an understanding of pathophysiological mechanisms of anxiety disorders and drug dependencies. The development of various BDZ receptor ligands with diverse psychopharmacological properties may lead to safer drugs with regard to "drug seeking" and "maintaining" properties. This paper reviews recent research of BDZ receptor pharmacology and clinical aspects of abstinence syndromes including also prospective studies.

Anti-Anxiety Agents↗

PubMed1990

The closely related small nuclear ribonucleoprotein polypeptides N and B/B' are distinguishable by antibodies as well as by differences in their mRNAs and gene structures.

The small nuclear ribonucleoprotein-associated polypeptides N, B and B' comprise a group of highly homologous, Sm epitope bearing proteins. However, N differs from B and B' in several ways. First, despite the extensive homology between their amino acid sequences, the antigenicity of the proteins N and B, as recognized by the monoclonal anti-Sm antibody, Y-12, is different. Second, whereas three distinct mRNA species encode human B, B', and N, only B appears to be ubiquitously expressed. Third, rodents do not contain mRNA that encodes B'. Fourth, in both humans and rats, mRNAs that encode B/B' (humans) or B (rodents) and N are transcribed from different genes. Fifth, N and B/B' specific probes reveal different size DNA fragments after human genomic DNA is amplified by a polymerase chain reaction based on oligonucleotides that simultaneously recognize cDNAs encoding N, B, and B'.

Amino Acid Sequence↗

PubMed1990

Preference for alprazolam as opposed to diazepam in benzodiazepine-dependent psychiatric inpatients.

Fourteen inpatients with long-term benzodiazepine (BDZ)-dependency were gradually withdrawn from their medication. During a four-day study period patients received 5 mg diazepam t.d.s. Under double-blind conditions the 5 mg diazepam was replaced twice, by either 0.5 mg or 0.37 mg alprazolam. When the hypothetically realistic alprazolam to diazepam equivalent ratio of 1:10 with regard to hypnosedative and anxiolytic properties was used, alprazolam was clearly preferred to diazepam in three sensitive tests. When alprazolam and diazepam were tested using the altered equivalent ratio of 1:14, "liking" and "seeking potentials" revealed no significant differences. However, also under these test conditions alprazolam tended to be preferred in a drug choice test. It is concluded that alprazolam appears to implicate somewhat higher reinforcing properties, possibly leading to a higher abuse liability in BDZ-dependent patients as compared to diazepam.

Adult↗