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J F Tallman

Publications and source records attributed to J F Tallman.

At least 19 recordsLinked to original sources
PubMed2000

Development of novel antipsychotic drugs.

The development of the current generation of antipsychotics has depended on animal, biochemical and pharmacological models of the action of drugs discovered serentipidously. They have focused on the dopamine hypothesis of schizophrenia. More recent studies of the structural abnormalities in schizophrenia, coupled with an understanding of the genetics and developmental biology of brain development, point to a new generation of novel medicines and therapies for patients with this disorder.

Animals↗
PubMed2000

Monospecific antibodies as probes for the stoichiometry of recombinant GABA(A) receptors.

GABA(A) receptors composed of alpha1beta3 gamma2 and alpha1beta3 subunits were expressed in insect Sf9 cells and solubilized in 1% Triton X100. In sucrose density gradients, [3H]-Ro15-1788 binding activity, in the case of alpha1beta3 gamma2, and [3H]-muscimol binding activity, in the case of alpha1beta3 containing receptors sedimented as a single sharp peak suggesting the formation of receptors containing a defined number of subunits. When alpha1beta3gamma2 -containing receptors were incubated with an alpha-subunit specific antibody (bd24), a single class of antibody receptor complex was formed irrespective of the receptor-antibody ratio. This is consistent with two alpha subunits cross-linked within the receptor by the antibody. Similar results were obtained using a beta-subunit specific antibody (bd17). Several classes of antibody-receptor complex were formed when receptors were pre-incubated with a gamma specific antibody (anti gamma(2) 1-15 Cys). This profile is consistent with the presence of a single gamma subunit in each complex. Experiments with alpha1beta3 subunit containing receptors and antibody bd24 produced a profile similar to that seen with alpha1beta3 gamma2 receptors, consistent with two alpha subunits per receptor complex. In this case, the anti-beta subunit antibody, bd17, produced a unique and complex profile consistent with three beta subunits per receptor. This method permits the rapid determination of subunit stoichiometries of homogeneous receptor populations

Antibodies, Monoclonal↗
PubMed1999

Neuropsychopharmacology at the new millennium: new industry directions.

Rapid advances in modern gene seeking techniques and the sequence data evolving from related genome research should provide both new targets for drug discovery and new insights into risk factors for many neurological and psychiatric disorders. Coupled with the high speed synthetic capabilities available in many companies, high-throughput screening is identifying potential novel drug candidates at extraordinary rates. This enables the drug discoverer to be more precise in the biological specificity of drugs taken to human trials thereby reducing the potential side-effect profile of clinical candidates. The ability to create large libraries of compounds also allows researchers to focus on metabolism and pharmacokinetics at an earlier stage in the drug development process to minimize drug-drug interactions via common sites of metabolism and optimize duration of action for particular indications. An emerging bottleneck in psychopharmacological drug discovery is the relative paucity of preclinical behavioral models predictive of clinical efficacy and the need to carry out early clinical trials to demonstrate therapeutic utility. However, through the use of recently developed chip technology, coupled with data bases of information about single nucleotide polymorphisms in potential candidate genes or risk factors for psychiatric disorders, it should be possible in the near future to stratify clinical populations genetically for inclusion in specific drug treatment trials. The ultimate goal of this research is to obtain homogeneous populations for trials and to predict risk before the phenotype of the disorder is manifest.

Animals↗
PubMed1997

I. NGD 94-1: identification of a novel, high-affinity antagonist at the human dopamine D4 receptor.

NGD 94-1 was evaluated for selectivity and in vitro functional activity at the recombinant human D4.2 receptor stably expressed in Chinese hamster ovary cells. NGD 94-1 showed high affinity for the cloned human D4.2 receptor (Ki = 3.6 +/- 0.6 nM) and had greater than 600-fold selectivity for the D4.2 receptor subtype compared with a wide variety of monoamine or other neurotransmitter receptor or modulatory sites except for 5-HT1A and 5-HT3 receptors, in which NGD 94-1 was approximately 50- and 200-fold selective, respectively, for the D4.2 receptor. In measures of in vitro functional activity, NGD 94-1 showed an antagonist profile at the cloned human D4.2 receptor subtype. NGD 94-1 completely reversed the decrease in forskolin-stimulated cAMP levels produced by the dopamine receptor full agonist quinpirole. Furthermore, NGD 94-1 produced a complete reversal of GTPgamma35S binding induced by quinpirole, but was unable on its own to affect GTPgamma35S binding. These data suggest that NGD 94-1 functions as an antagonist rather than a full or partial agonist at the human D4.2 receptor. In addition, NGD 94-1 binding affinity at the D4.2 receptor subtype was unaffected by G-protein activation by GTP, consistent with the binding affinity seen for other antagonists at the D4 receptor. The binding of tritiated NGD 94-1 was saturable and of high affinity at cloned human D4.2 receptors. Furthermore, the binding of [3H]NGD 94-1 to cloned human D4.2 receptors expressed in Chinese hamster ovary cells displayed a pharmacological profile similar to that observed with the nonselective dopamine receptor ligand [3H]YM 09151-2. Saturation and pharmacological analyses of [3H]NGD 94-1 binding at cloned human D4.2, D4.4 and D4.7 receptor variants showed no difference between the three variants. NGD 94-1 is a novel, high-affinity, D4 receptor-selective antagonist. The clinical use of this subtype-specific compound should permit direct evaluation of the role of D4 receptors in psychiatric disorders.

Animals↗
PubMed1997

II. Localization and characterization of dopamine D4 binding sites in rat and human brain by use of the novel, D4 receptor-selective ligand [3H]NGD 94-1.

The dopamine D4 selective ligand, [H]NGD 94-1, was used in these studies to characterize binding sites in rat and human brain tissue by membrane binding and autoradiography techniques. Autoradiographic analysis of rat brain showed that specific [3H]NGD 94-1 binding was greatest in entorhinal cortex, lateral septal nucleus, hippocampus and the medial preoptic area of the hypothalamus. This nonstriatal distribution of [3H]NGD 94-1 binding was distinct from the autoradiographic distribution of dopamine D2 and D3 receptor subtypes. In homogenate preparations from rat brain regions, [3H]NGD 94-1 binding sites were low in density (<30.0 fmol/mg protein). The low density of D4 binding sites was corroborated by autoradiographic comparisons in which binding density for D4 receptors as measured by [3H]NGD 94-1 was only 1/7 of D2 and 1/5 of D3 receptor densities, despite corrections for differing radioligand binding characteristics. Pharmacological evaluation showed high affinity at rat [3H]NGD 94-1 binding sites for compounds with known D4 receptor affinity and little displacement by compounds with affinity for dopamine D1/D2/D3 receptor subtypes. Specific, high-affinity [3H]NGD 94-1 binding was also present in several human brain regions, including hippocampus, hypothalamus, dorsal medial thalamus, entorhinal cortex, prefrontal cortex and lateral septal nucleus. High-affinity [3H]NGD 94-1 binding was not present in any human striatal region examined. The pharmacological profile of [3H]NGD 94-1 binding sites in human brain was consistent with that previously demonstrated for cloned human D4 receptors expressed in mammalian cells. These findings suggest that specific, high-affinity [3H]NGD 94-1 binding exists in rat and human brain and that these sites reflect populations of dopamine D4 receptors with a distribution unique among dopamine receptor subtypes.

Animals↗
PubMed1996

Effect of subunit composition on GABAA receptor complex characteristics in a baculovirus expression system.

A baculovirus expression system was used to produce functional human recombinant GABAA receptors in Sf-9 insect cells in order to study the biochemistry, pharmacology and functional characteristics of this receptor complex. We have identified and characterized various factors which influence the level of receptor expression in multiple virus infections. We have shown that the level of expression of the GABAA receptor complex varies with the levels of expression of the individual subunits. We have also shown that the assembly process has a defined timecourse, and it is dependent upon the ratio of the number of infectious virus particles (MOI ratio) of each subunit in multi-virus infections. In multiple infections, the capacity for expression of the infected cell is shared proportionally by entering virus particles and, there is a direct correlation between the amounts of subunit mRNA and levels of subunit protein expression, and the amount of ligand binding to expressed protein. Finally, reinfection of previously infected cells does not result in subsequent protein expression. Knowledge of these various factors allows us to construct recombinant GABAA receptor complexes with reproducibility and flexibility with regard to subunit composition. By co-expression of alpha, beta, and gamma subunits, both the recognition site for GABA and the allosteric (benzodiazepine) modulatory site are formed and appear to reproduce the pharmacology of endogenously expressed receptors as measured in mammalian CNS. Only a single receptor is produced irrespective of the expression levels of the subunits, showing that GABAA receptor assembly is highly regulated.

Animals↗
PubMed1994

Induction of beta 2-adrenergic receptor mRNA and ligand binding in HeLa cells.

HeLa cells express low levels of beta-adrenergic receptor (beta AR) of the beta 2-subtype. When exposed to sodium butyrate, receptor levels increased up to 4-fold in a time dependent manner, reaching a maximum after 12 to 15 h of treatment. Sodium butyrate treatment also caused a 3 to 4 fold increase in levels of beta 2AR mRNA determined by hybridization blot analysis. The induction of beta 2AR mRNA temporally preceded the increase in receptor binding activity, reaching a maximum after 4 to 6 h of treatment, and remaining elevated for up to 24 h. Prior exposure of the cells to the protein synthesis inhibitor cycloheximide prevented the butyrate-induced increase in receptor binding but had no effect on the increase in receptor mRNA. Blocking DNA synthesis and cell growth by excess thymidine did not increase beta 2AR mRNA or binding or prevent the effects of sodium butyrate. Thus, butyrate appears to induce beta 2AR mRNA by a mechanism independent of DNA and protein synthesis.

Butyrates↗
PubMed1992

Differential induction of immediate early genes by excitatory amino acid receptor types in primary cultures of cortical and striatal neurons.

In primary cultures of neurons from cerebral cortex and striatum, 30 s stimulation with the excitatory amino acid glutamate elicited a 5 to 9-fold increase in immediate early gene (IEG) mRNAs. Glutamate increased c-fos, c-jun, jun-B, and NGFI-A (zif/268) mRNAs by binding to both alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor types, and increased c-fos, jun-B, and NGFI-A mRNAs by binding to the metabotropic receptor. NMDA receptor activation elicited IEG expression by a transmembrane calcium influx; AMPA receptor-induced depolarization played a permissive role for the opening of the NMDA receptor channel. The protein kinase C (PKC) inhibitor H-7 (but not inhibitors of cyclic nucleotide-dependent and calcium/calmodulin-dependent protein kinases) partially blocked IEG expression induced by glutamate.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Modulation of protein kinase C translocation by excitatory and inhibitory amino acids in primary cultures of neurons.

In primary cultures of neurons from rat cerebral cortex and neostriatum, excitatory amino acids stimulate the translocation of protein kinase C (PKC) from the cytoplasm to the membrane. In the presence of a physiological concentration of Mg2+ in the extracellular medium, glutamate induces PKC translocation by binding to both N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) excitatory amino acid receptors. Quisqualate translocates the enzyme by stimulating primarily AMPA receptors and possibly metabotropic receptors. NMDA receptor-induced PKC translocation is sodium independent, whereas quisqualate receptor-induced PKC translocation is sodium dependent; none of the agonists is active in the absence of calcium from the extracellular medium. Muscimol does not modify excitatory amino acid stimulation; however, blockade of gamma-aminobutyric acid(A) receptors by bicuculline greatly enhances glutamate-induced PKC translocation. This enhancement is blocked by the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) and by tetrodotoxin.

Amino Acids↗
PubMed1990

Cultured rat neurons and astrocytes express immunologically related epitopes of the GABAA/benzodiazepine receptor.

gamma-Aminobutyric acid (GABA) is the major inhibitory transmitter in the mammalian central nervous system (CNS) and an understanding of the development of receptors for this compound is of considerable interest. In this study, 3 monoclonal antibodies directed against the GABAA/benzodiazepine (GABA/BDZ) receptor were utilized in immunocytochemical experiments to localize receptor sites on neurons in dissociated cultures from fetal rat hypothalamus. Immunoreactivity was restricted to distinct patches on the plasma membrane of neurons. Analogous patches were observed on the surface of type 1 astrocytes, but not on type 2 astrocytes or oligodendrocytes. In membrane extracts from whole brain these antibodies reacted with two proteins (50 and 55 kDa) whereas extracts of cultured astrocytes yielded a single protein of approximately 63 kDa. Thus the identity of the glial protein remains unclear, but this study provides evidence for the presence of shared epitopes of the GABA/BDZ-receptor on both neurons and glia, and suggests that the astrocytic receptors may be important to nervous system function. Moreover it indicates that in vitro GABA/BDZ-receptors may form aggregates which would account for the restricted patterns of GABA sensitivity reported in some electrophysiological studies.

Animals↗
PubMed1990

Relationship of GABAa receptor heterogeneity to regional differences in drug response.

Molecular biological approaches to the GABAa receptor have resulted in new insights into the structure and pharmacology of this complex. It is known that the GABAa complex is a hetero-oligomer composed of multiple subunits which contain binding sites for the GABA, benzodiazepines and barbiturates. These subunits also contain regulatory sites for phosphorylation by intracellular kinases. There appear to be regional differences in the expression of the various subunits for the GABAa receptor complex. The functional significance of molecular heterogeneity is not yet known but it is expected that regional differences may result in pharmacologically diverse responses. Studies on the effects of chronic administration of diazepam have clearly delineated such regional differences. Chronic benzodiazepine administration results in the development of subsensitivity to the electrophysiological actions of GABA in the dorsal raphe, but not in GABA receptive neurons of the substantia nigra pars reticulata. Such data is consistent with regional heterogeneity in response to chronic benzodiazepine exposure. It is hoped that by understanding GABAa receptor heterogeneity, and its molecular basis, we can improve the existing receptor subtype specificity and pharmacology of the benzodiazepines.

Animals↗
PubMed1990

Effects of continuous diazepam administration on GABAA subunit mRNA in rat brain.

Rats treated chronically with diazepam develop tolerance to diazepam effects and show changes in sensitivity of GABAergic systems. In order to investigate possible molecular mechanisms associated with these changes, we have evaluated the effects of acute and chronic diazepam treatment on levels of mRNA for the alpha 1 and beta 1 subunits of the GABAA receptor. Northern blots were hybridized with 32P-labeled GABA alpha 1 and beta 1 cDNA probes, and resulting bands were quantified by autoradiography and densitometry. Levels of alpha 1 mRNA were significantly decreased in cerebral cortex but not in cerebellum or hippocampus of chronic diazepam-treated rats. Acute diazepam treatment did not change levels of alpha 1 mRNA in any of the brain regions. Levels of beta 1 mRNA were examined by Northern blot analysis and also by solution hybridization analysis using a 32P-labeled riboprobe. Both methods showed that beta 1 mRNA was not significantly changed by chronic diazepam treatment. These results demonstrate a specific change in alpha 1 subunit that is associated with a state of altered GABA sensitivity and provide further support for the regional heterogeneity of chronic diazepam effects.

Animals↗
PubMed1990

Chronic antidepressant administration decreases the expression of tyrosine hydroxylase in the rat locus coeruleus.

Regulation of tyrosine hydroxylase expression by antidepressant treatments was investigated in the locus coeruleus (LC), the major noradrenergic nucleus in brain. Rats were treated chronically with various antidepressants, and tyrosine hydroxylase levels were measured in the LC by immunoblot analysis. Representatives of all major classes of antidepressant medication-including imipramine, nortriptyline, tranylcypromine, fluvoxamine, fluoxetine, bupropion, iprindole, and electroconvulsive seizures-were found to decrease levels of tyrosine hydroxylase immunoreactivity by 40-70% in the LC. Decreased levels of enzyme immunoreactivity were shown to be associated with equivalent decreases in enzyme mRNA levels. Antidepressant regulation of LC tyrosine hydroxylase appeared specific to these compounds, inasmuch as chronic treatment of rats with representatives of other classes of psychotropic drugs, including haloperidol, diazepam, clonidine, cocaine, and morphine, failed to decrease levels of this protein. The results demonstrate that chronic antidepressants dramatically downregulate the expression of tyrosine hydroxylase in the LC and raise the possibility that such regulation of the enzyme represents an adaptive response of LC neurons to antidepressants that mediates some of their therapeutic actions in depression and/or other psychiatric disturbances.

Animals↗
PubMed1990

Differential expression of gamma-aminobutyric acidA receptor subunits.

A 1.8-kilobase (kb) cDNA clone for a beta 1 subunit of the human gamma-aminobutyric acidA (GABAA) receptor has been isolated and sequenced. The longest open reading frame of the clone, pCLL610, contains nucleotide sequence encoding a portion of the putative signal sequence followed by 449 amino acids of the entire mature protein. The deduced amino acid sequence of pCLL610 differs from a recently described human beta 1 subunit by a single amino acid. The amino acid sequences of the human GABAA receptor beta 1 subunits share 98% identity with the beta 1 subunits of the bovine and rat GABAA receptor, with the majority of the differences occurring in the intracellular loop between the M3 and M4 transmembrane regions of the protein. A single 11-kb transcript is observed in Northern blots of poly(A)+ RNA isolated from rat brain probed with nick-translated pCLL610. In human brain, the pCLL610 probe recognized the 11-kb message, in addition to two other bands between 8 and 11-kb. Developmental studies of rat brain mRNA show that the message of the GABAA beta 1 subunit is highest at birth, rapidly decreases, and reaches adult levels of 5 to 7 days of age. This is in contrast to the development of the alpha 1 subunit, which is low from days 1 to 5 and increases to adult levels by days 14 to 25. Relative levels of the mRNA for the alpha 1 and beta 1 subunits vary among rat brain regions. The levels of mRNA for the alpha 1 subunit are similar in the cortex, hippocampus, and midbrain, whereas cerebellar levels are twice those in the cortex. The rank order of the relative amount of beta 1 subunit message is hippocampus greater than cortex = midbrain greater than cerebellum. These data, taken with our previous study of the alpha 1 subunits of the GABAA receptor, suggest that the differences in the distribution and regulation of the alpha 1 and beta 1 subunits may reflect a variety of subunit combinations forming the GABAA receptor. Heterogeneity in the GABAA receptor composition may provide a molecular basis for the diverse pharmacological properties associated with this receptor.

Aging↗
PubMed1989

Sodium and potassium regulation of guanine nucleotide-stimulated adenylate cyclase in brain.

The present study examines the influence of potassium and sodium ions on guanine nucleotide regulation of adenylate cyclase in various brain regions, including the locus coeruleus (LC), dorsal raphe (DR), ventral tegmentum (VT), hippocampus (HP), frontal cortex (FC), substantia nigra (SN), neostriatum (NS) and cerebellum (CB). Guanine nucleotide regulation of adenylate cyclase was highest in the LC, DR and VT and lowest in NS and CB. Sodium and potassium ions were found to stimulate basal or GTP-activated adenylate cyclase in NS and SN, whereas the cations were found to specifically inhibit guanine nucleotide-stimulated enzyme activity in all other brain regions with the exception of CB, where there was no effect. With regard to stimulation of adenylate cyclase, lithium was more potent than sodium which was more potent than potassium in SN and NS. With regard to inhibition of the enzyme, potassium was equipotent to lithium which was greater than sodium in the other brain regions examined. Both stimulatory and inhibitory effects of cations in the different regions were significant (P less than 0.05) at 30 mM and were maximal at 90-120 mM. Sodium ion inhibition of GTP-stimulated adenylate cyclase in LC and DR was partially blocked by pertussis toxin treatment, whereas cation stimulation in NS was not affected by the toxin. The results demonstrate marked region-specific effects of sodium and potassium on adenylate cyclase, which could occur at either G-proteins or the catalytic unit of the enzyme. The possibility that ion fluxes alter G-protein function is discussed.

Adenylate Cyclase Toxin↗
PubMed1989

Regulation of G proteins by chronic morphine in the rat locus coeruleus.

A possible role for G proteins in contributing to the chronic actions of opiates was investigated in the rat locus coeruleus (LC). The LC is a relatively homogeneous brain region that appears to play an important role in mediating acute and chronic opiate action in animals, as well as in humans. It was found that chronic, but not acute, treatment of rats with morphine, under conditions known to induce states of opiate tolerance and dependence, produced an increase in the level of pertussis toxin-mediated ADP-ribosylation of G proteins in the LC. The morphine-induced increase in ADP-ribosylation occurred in both Gi and Go, and was observed over a 30-fold range of NAD concentrations used. Concomitant treatment of rats with the opiate receptor antagonist naltrexone blocked the ability of morphine to produce this effect. In contrast, chronic morphine had no effect on pertussis toxin-mediated ADP-ribosylation of Gi and Go in the other brain regions studied, including the neostriatum, frontal cortex, and dorsal raphe. Chronic morphine also had no effect on cholera toxin-mediated ADP-ribosylation of Gs in the LC and these other brain regions. Preliminary immunoblot analysis revealed that increased ADP-ribosylation levels of the alpha subunit of Go in the LC were associated with equivalent increases in the immunoreactivity of this protein in this brain region. It is possible that the observed regulation of G-proteins by morphine in the LC represents part of the changes that underlie opiate addiction in these neurons.

Adenosine Diphosphate Ribose↗