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J R Bunzow

Publications and source records attributed to J R Bunzow.

At least 19 recordsLinked to original sources
PubMed2007

Trace amine-associated receptor 1 displays species-dependent stereoselectivity for isomers of methamphetamine, amphetamine, and para-hydroxyamphetamine.

The synthetic amines methamphetamine (METH), amphetamine (AMPH), and their metabolite para-hydroxyamphetamine (POHA) are chemically and structurally related to the catecholamine neurotransmitters and a small group of endogenous biogenic amines collectively referred to as the trace amines (TAs). Recently, it was reported that METH, AMPH, POHA, and the TAs para-tyramine (TYR) and beta-phenylethylamine (PEA) stimulate cAMP production in human embryonic kidney (HEK)-293 cells expressing rat trace amine-associated receptor 1 (rTAAR1). The discovery that METH and AMPH activate the rTAAR1 motivated us to study the effect of these drugs on the mouse TAAR1 (mTAAR1) and a human-rat chimera (hrChTAAR1). Furthermore, because S-(+)-isomers of METH and AMPH are reported to be more potent and efficacious in vivo than R-(-), we determined the enantiomeric selectivity of all three species of TAAR1. In response to METH, AMPH, or POHA exposure, the accumulation of cAMP by HEK-293 cells stably expressing different species of TAAR1 was concentration- and isomer-dependent. EC50 values for S-(+)-METH were 0.89, 0.92, and 4.44 microM for rTAAR1, mTAAR1, and h-rChTAAR1, respectively. PEA was a potent and full agonist at each species of TAAR1, whereas TYR was a full agonist for the rodent TAAR1s but was a partial agonist at h-rChTAAR1. Interestingly, both isomers of METH were full agonists at mTAAR1 and h-rChTAAR1, whereas both were partial agonists at rTAAR1. Taken together, these in vitro results suggest that, in vivo, TAAR1 could be a novel mediator of the effects of these drugs.

Amphetamine↗
PubMed2001

Dopamine D4 receptor-deficient mice display cortical hyperexcitability.

The dopamine D(4) receptor (D(4)R) is predominantly expressed in the frontal cortex (FC), a brain region that receives dense input from midbrain dopamine (DA) neurons and is associated with cognitive and emotional processes. However, the physiological significance of this dopamine receptor subtype has been difficult to explore because of the slow development of D(4)R agonists and antagonists the selectivity and efficacy of which have been rigorously demonstrated in vivo. We have attempted to overcome this limitation by taking a multidimensional approach to the characterization of mice completely deficient in this receptor subtype. Electrophysiological current and voltage-clamp recordings were performed in cortical pyramidal neurons from wild-type and D(4)R-deficient mice. The frequency of spontaneous synaptic activity and the frequency and duration of paroxysmal discharges induced by epileptogenic agents were increased in mutant mice. Enhanced synaptic activity was also observed in brain slices of wild-type mice incubated in the presence of the selective D(4)R antagonist PNU-101387G. Consistent with greater electrophysiological activity, nerve terminal glutamate density associated with asymmetrical synaptic contacts within layer VI of the motor cortex was reduced in mutant neurons. Taken together, these results suggest that the D(4)R can function as an inhibitory modulator of glutamate activity in the FC.

4-Aminopyridine↗
PubMed2001

Amphetamine, 3,4-methylenedioxymethamphetamine, lysergic acid diethylamide, and metabolites of the catecholamine neurotransmitters are agonists of a rat trace amine receptor.

The trace amine para-tyramine is structurally and functionally related to the amphetamines and the biogenic amine neurotransmitters. It is currently thought that the biological activities elicited by trace amines such as p-tyramine and the psychostimulant amphetamines are manifestations of their ability to inhibit the clearance of extracellular transmitter and/or stimulate the efflux of transmitter from intracellular stores. Here we report the discovery and pharmacological characterization of a rat G protein-coupled receptor that stimulates the production of cAMP when exposed to the trace amines p-tyramine, beta-phenethylamine, tryptamine, and octopamine. An extensive pharmacological survey revealed that psychostimulant and hallucinogenic amphetamines, numerous ergoline derivatives, adrenergic ligands, and 3-methylated metabolites of the catecholamine neurotransmitters are also good agonists at the rat trace amine receptor 1 (rTAR1). These results suggest that the trace amines and catecholamine metabolites may serve as the endogenous ligands of a novel intercellular signaling system found widely throughout the vertebrate brain and periphery. Furthermore, the discovery that amphetamines, including 3,4-methylenedioxymethamphetamine (MDMA; "ecstasy"), are potent rTAR1 agonists suggests that the effects of these widely used drugs may be mediated in part by this receptor as well as their previously characterized targets, the neurotransmitter transporter proteins.

Amino Acid Sequence↗
PubMed1998

Locomotor activity in D2 dopamine receptor-deficient mice is determined by gene dosage, genetic background, and developmental adaptations.

Locomotor activity is a polygenic trait that varies widely among inbred strains of mice (). To characterize the role of D2 dopamine receptors in locomotion, we generated F2 hybrid (129/Sv x C57BL/6) D2 dopamine receptor (D2R)-deficient mice by gene targeting and investigated the contribution of genetic background to open-field activity and rotarod performance. Horizontal activity of D2R-/- mice was approximately half that of drug-naive, strain-matched controls but was significantly greater than haloperidol-treated controls, which were markedly hypokinetic. Wild-type 129/SvEv and C57BL/6 mice with functional D2 receptors had greater interstrain differences in spontaneous activity than those among the F2 hybrid mutants. Incipient congenic strains of D2R-deficient mice demonstrated an orderly gene dosage reduction in locomotion superimposed on both extremes of parental background locomotor activity. In contrast, F2 hybrid D2R-/- mice had impaired motor coordination on the rotarod that was corrected in the congenic C57BL/6 background. Wild-type 129/SvEv mice had the poorest rotarod ability of all groups tested, suggesting that linked substrain 129 alleles, not the absence of D2 receptors per se, were largely responsible for the reduced function of the F2 hybrid D2R-/- and D2R+/- mice. Neurochemical and pharmacological studies revealed unexpectedly normal tissue striatal monoamine levels and no evidence for supersensitive D1, D3, or D4 dopamine receptors in the D2R-/- mice. However, after acute monoamine depletion, akinetic D2R+/- mice had a significantly greater synergistic restoration of locomotion in response to SKF38393 and quinpirole compared with any group of D2R+/+ controls. We conclude that D2R-deficient mice are not a model of Parkinson's disease. Our studies highlight the interaction of multiple genetic factors in the analysis of complex behaviors in gene knock-out mice.

Adaptation, Physiological↗
PubMed1997

Mice lacking dopamine D4 receptors are supersensitive to ethanol, cocaine, and methamphetamine.

The human dopamine D4 receptor (D4R) has received considerable attention because of its high affinity for the atypical antipsychotic clozapine and the unusually polymorphic nature of its gene. To clarify the in vivo role of the D4R, we produced and analyzed mutant mice (D4R-/-) lacking this protein. Although less active in open field tests, D4R-/- mice outperformed wild-type mice on the rotarod and displayed locomotor supersensitivity to ethanol, cocaine, and methamphetamine. Biochemical analyses revealed that dopamine synthesis and its conversion to DOPAC were elevated in the dorsal striatum from D4R-/- mice. Based on these findings, we propose that the D4R modulates normal, coordinated and drug-stimulated motor behaviors as well as the activity of nigrostriatal dopamine neurons.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1997

Mu and delta opioids but not kappa opioid inhibit voltage-activated Ba2+ currents in neuronal F-11 cell.

Whole-cell patch-clamp recordings were used to study Ba2+ currents through voltage-dependent Ca2+ channels in dorsal root ganglion x mouse neuroblastoma hybrid (F-11) cells. Opioid agonists selective for either mu (Tyr-D-Ala-Gly-Mephe-Gly-ol; DAMGO) or delta (Tyr-D-Pen-Gly-Phe-D-Pen-OH; DPDPE) receptors inhibited high-threshold Ba2+ currents. The inhibition was reversible, naloxone-sensitive, and dose-dependent. The inhibitory effects of both DAMGO and DPDPE were blocked by pretreatment of the cells with pertussis toxin (PTX) as well as by brief exposure to the sulfhydryl alkylating agent, N-ethylmaleimide (NEM). The N-type Ca2+ channel antagonist omega-conotoxin GVIA (omega-CTX GVIA) irreversibly inhibited high threshold Ba2+ currents by 66% and blocked the inhibitory effect of DAMGO or DPDPE. In contrast, the L-type Ca2+ channel blocker nifedipine inhibited high threshold Ba2+ currents by 15% and failed to block the inhibitory effect of DAMGO or DPDPE. These results demonstrate that mu and delta opioid receptors are negatively coupled to N-type Ca2+ channels via PTX- and NEM-sensitive GTP-binding proteins in F-11 cells.

Analgesics↗
PubMed1997

Pituitary lactotroph hyperplasia and chronic hyperprolactinemia in dopamine D2 receptor-deficient mice.

Dopamine secreted from hypophysial hypothalamic neurons is a principal inhibitory regulator of pituitary hormone secretion. Mice with a disrupted D2 dopamine receptor gene had chronic hyperprolactinemia and developed anterior lobe lactotroph hyperplasia without evidence of adenomatous transformation. Unexpectedly, the mutant mice had no hyperplasia of the intermediate lobe melanotrophs. Aged female D2 receptor -/- mice developed uterine adenomyosis in response to prolonged prolactin exposure. These data reveal a critical role of hypothalamic dopamine in controlling pituitary growth and support a multistep mechanism for the induction and perpetuation of lactotroph hyperplasia, involving the lack of dopamine signaling, a low androgen/estrogen ratio, and a final autocrine or paracrine "feed-forward" stimulation of mitogenesis, probably by prolactin itself.

Animals↗
PubMed1995

Orphanin FQ: a neuropeptide that activates an opioidlike G protein-coupled receptor.

A heptadecapeptide was identified and purified from porcine brain tissue as a ligand for an orphan heterotrimeric GTP-binding protein (G protein)-coupled receptor (LC132) that is similar in sequence to opioid receptors. This peptide, orphanin FQ, has a primary structure reminiscent of that of opioid peptides. Nanomolar concentrations of orphanin FQ inhibited forskolin-stimulated adenylyl cyclase activity in cells transfected with LC132. This inhibitory activity was not affected by the addition of opioid ligands, nor did the peptide activate opioid receptors. Orphanin FQ bound to its receptor in a saturable manner and with high affinity. When injected intracerebroventricularly into mice, orphanin FQ caused a decrease in locomotor activity but did not induce analgesia in the hot-plate test. However, the peptide produced hyperalgesia in the tail-flick assay. Thus, orphanin FQ may act as a transmitter in the brain by modulating nociceptive and locomotor behavior.

Adenylyl Cyclase Inhibitors↗
PubMed1995

Functional characterization of the human dopamine D4.2 receptor using vaccinia virus as an expression system.

Recombinant vaccinia viruses harboring the human dopamine D4 receptor cDNA containing two 48 base pair-repeats (D4.2) or the rat dopamine D2 short (D2s) receptor cDNA were used to infect rat-1 fibroblasts. Heterologous expression of both dopamine receptors was demonstrated in binding assays. The affinity constants of these receptors were consistent with values previously reported, including D4.2's higher affinity for the antipsychotic clozapine and raclopride's selectivity for D2 receptors. In the presence of 200 microM 5'-guanylyl-imidodiphosphate (Gpp[NH]p) both receptors exhibited reduced affinities for dopamine. Furthermore, when rat-1 cells were infected with the D2s or the D4.2 recombinant vaccinia viruses and exposed to dopamine agonists, the inhibition of adenylyl cyclase activity was prevented in pertussis toxin-treated cells. This study demonstrates the utility of recombinant receptor-vaccinia viruses in studies of expression, pharmacology and functional coupling of inhibitory G protein-coupled receptors.

Adenylyl Cyclase Inhibitors↗
PubMed1995

Characterization and distribution of a cloned rat mu-opioid receptor.

We have cloned and expressed a rat brain cDNA, TS11, that encodes a mu-opioid receptor based on pharmacological, physiological, and anatomical criteria. Membranes were prepared from COS-7 cells transiently expressing TS11 bound [3H]diprenorphine with high affinity (KD = 0.23 +/- 0.04 nM). The rank order potency of drugs competing with [3H]diprenorphine was as follows: levorphanol (Ki = 0.6 +/- 0.2 nM) approximately beta-endorphin (Ki = 0.7 +/- 0.05 nM) approximately morphine (Ki = 0.8 +/- 0.5 nM) approximately [D-Ala2, N-Me-Phe4,Gly-ol5]-enkephalin (DAMGO; Ki = 1.6 +/- 0.5 nM) uch much greater than U50,488 (Ki = 910 +/- 0.78 nM) > [D-Pen2,5]- enkephalin (Ki = 3,170 +/- 98 nM) > dextrorphan (Ki = 4,100 +/- 68 nM). The rank order potencies of these ligands, the stereospecificity of levorphanol, and morphine's subnanomolar Ki are consistent with a mu-opioid binding site. Two additional experiments provided evidence that this opioid-binding site is functionally coupled to G proteins: (a) in COS-7 cells 50 microM 5'-guanylylimidodiphosphate shifted a fraction of receptors with high affinity for DAMGO (IC50 = 3.4 +/- 0.5 nM) to a lower-affinity state (IC50 = 89.0 +/- 19.0 nM), and (b) exposure of Chinese hamster ovary cells stably expressing the cloned mu-opioid receptor to DAMGO resulted in a dose-dependent, naloxone-sensitive inhibition of forskolin-stimulated cyclic AMP production. The distribution of mRNA corresponding to the mu-opioid receptor encoded by TS11 was determined by in situ hybridization to brain sections prepared from adult female rats. The highest levels of mu-receptor mRNA were detected in the thalamus, medial habenula, and the caudate putamen; however, significant hybridization was also observed in many other brain regions, including the hypothalamus.

Amino Acid Sequence↗
PubMed1994

Molecular cloning and tissue distribution of a putative member of the rat opioid receptor gene family that is not a mu, delta or kappa opioid receptor type.

A novel G protein-coupled receptor was cloned by PCR and homology screening. Its deduced amino acid sequence is 47% identical overall to the mu, delta and kappa opioid receptors and 64% identical in the putative transmembrane domains. When transiently expressed in COS-7 cells this receptor did not bind any of the typical mu, delta or kappa opioid receptor ligands with high affinity. In situ hybridization analysis revealed that LC132 mRNA is highly expressed in several rat brain areas, including the cerebral cortex, thalamus, subfornical organ, habenula, hypothalamus, central gray, dorsal raphe, locus coeruleus and the dorsal horn of the spinal cord. Based on this distribution and its high homology with the mu, delta and kappa opioid receptors, it is proposed that LC132 is a new member of the opioid receptor family that is involved in analgesia and the perception of pain.

Amino Acid Sequence↗
PubMed1994

Dopamine D4 receptor repeat: analysis of different native and mutant forms of the human and rat genes.

Recent molecular characterization of the human D4 gene has revealed the existence of various polymorphic forms of this receptor. These variations are found in the putative third cytoplasmic loop region and encode a variable number of repeats of 16 amino acids in length. In the present study we have compared the pharmacological binding profiles of seven different polymorphic variants of the human D4 receptor, the rat D4 receptor, and two different human D4 receptor mutants that were deleted in the repeat sequence. For this purpose we cloned the rat D4 receptor gene and compared its gene structure and its pharmacological binding profile with those of the D4.4 and D4.7 genes. The rat and human D4 genes display a high degree of sequence similarity, especially in the coding regions. An Alu repeat sequence was identified in the first intron of the human D4 gene but is not present in the rat D4 gene. Furthermore, using the polymerase chain reaction we cloned 3-, 5-, 6-, and 9-fold repeat sequences. These cloned repeat sequences were used for the reconstruction of full length cDNAs encoding D4.3, D4.5, D4.6, and D4.9, respectively. These novel forms of the human D4 receptor, as well as the previously cloned D4.2, D4.4, and D4.7 forms, were transiently expressed in COS-7 cells. All of the different forms of the human and rat D4 receptors and repeat deletion mutants displayed similar binding profiles for all ligands tested, although small differences were observed. The affinity for dopamine could be decreased by guanosine-5'-(beta, gamma-imido)triphosphate with the different forms of the D4 receptor, including the two receptor mutants that were deleted in the repeat sequence. These data suggest that the polymorphic repeat sequence has little influence on D4 binding profiles and might not be essential for G protein interaction.

Amino Acid Sequence↗
PubMed1992

Multiple dopamine D4 receptor variants in the human population.

The dopamine D4 receptor structurally and pharmacologically resembles the dopamine D2 and D3 receptors. Clozapine, an atypical antipsychotic that is relatively free of the adverse effects of drug-induced parkinsonism and tardive dyskinesia, binds to the D4 receptor with an affinity 10 times higher than to the D2 and D3 receptors. This may explain clozapine's atypical properties. Here we report the existence of at least three polymorphic variations in the coding sequence of the human D4 receptor. A 48-base-pair sequence in the putative third cytoplasmic loop of this receptor exists either as a direct-repeat sequence (D4.2), as a fourfold repeat (D4.4) or as a sevenfold repeat (D4.7). Two more variant alleles were detected in humans. Expression of the complementary DNA for the three cloned receptor variants showed different properties for the long form (D4.7) and the shorter forms (D4.2, D4.4) with respect to clozapine and spiperone binding. To our knowledge, this is the first report of a receptor in the catecholamine receptor family that displays polymorphic variation in the human population. Such variation among humans may underlie individual differences in susceptibility to neuropsychiatric disease and in responsiveness to antipsychotic medication.

Base Sequence↗
PubMed1991

Multiple human D5 dopamine receptor genes: a functional receptor and two pseudogenes.

Three genes closely related to the D1 dopamine receptor were identified in the human genome. One of the genes lacks introns and encodes a functional human dopamine receptor, D5, whose deduced amino acid sequence is 49% identical to that of the human D1 receptor. Compared with the human D1 dopamine receptor, the D5 receptor displayed a higher affinity for dopamine and was able to stimulate a biphasic rather than a monophasic intracellular accumulation of cAMP. Neither of the other two genes was able to direct the synthesis of a receptor. Nucleotide sequence analysis revealed that these two genes are 98% identical to each other and 95% identical to the D5 sequence. Relative to the D5 sequence, both contain insertions and deletions that result in several in-frame termination codons. Premature termination of translation is the most likely explanation for the failure of these genes to produce receptors in COS-7 and 293 cells even though their messages are transcribed. We conclude that the two are pseudogenes. Blot hybridization experiments performed on rat genomic DNA suggest that there is one D5 gene in this species and that the pseudogenes may be the result of a relatively recent evolutionary event.

Amino Acid Sequence↗
PubMed1991

Molecular biology of the dopamine receptors.

Because of their importance in pathophysiology, the dopamine receptors have been the subjects of intense pharmacological and physiological research. Their structures have remained mostly unknown until recently with the application of molecular biological approaches. The cloning of the first dopamine receptor, the D2 receptor opened a new era in dopamine receptor research. It has led not only to new studies of its own biology but also to the characterization of the other dopamine receptors. The most striking conclusion of this fast moving research is that the dopamine receptors are more diverse than expected from their pharmacological characterizations. We discuss here the history of the cloning of the dopamine receptors and the impact that this research had on our understanding of the dopamine system.

Amino Acid Sequence↗
PubMed1991

Cloning of the gene for a human dopamine D4 receptor with high affinity for the antipsychotic clozapine.

Dopamine receptors belong to the family of G protein-coupled receptors. On the basis of the homology between these receptors, three different dopamine receptors (D1, D2, D3) have been cloned. Dopamine receptors are primary targets for drugs used in the treatment of psychomotor disorders such as Parkinson's disease and schizophrenia. In the management of socially withdrawn and treatment-resistant schizophrenics, clozapine is one of the most favoured antipsychotics because it does not cause tardive dyskinesia. Clozapine, however, has dissociation constants for binding to D2 and D3 that are 4 to 30 times the therapeutic free concentration of clozapine in plasma water. This observation suggests the existence of other types of dopamine receptors which are more sensitive to clozapine. Here we report the cloning of a gene that encodes such a receptor (D4). The D4 receptor gene has high homology to the human dopamine D2 and D3 receptor genes. The pharmacological characteristics of this receptor resembles that of the D2 and D3 receptors, but its affinity for clozapine is one order of magnitude higher. Recognition and characterization of this clozapine neuroleptic site may prove useful in the design of new types of drugs.

Amino Acid Sequence↗