Pokman Chan

Mount Sinai School of Medicine, Manhattan, NY, United States

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Publications (7)86.55 Total impact

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    ABSTRACT: The psychosis associated with schizophrenia is characterized by alterations in sensory processing and perception. Some antipsychotic drugs were identified by their high affinity for serotonin 5-HT2A receptors (2AR). Drugs that interact with metabotropic glutamate receptors (mGluR) also have potential for the treatment of schizophrenia. The effects of hallucinogenic drugs, such as psilocybin and lysergic acid diethylamide, require the 2AR and resemble some of the core symptoms of schizophrenia. Here we show that the mGluR2 interacts through specific transmembrane helix domains with the 2AR, a member of an unrelated G-protein-coupled receptor family, to form functional complexes in brain cortex. The 2AR-mGluR2 complex triggers unique cellular responses when targeted by hallucinogenic drugs, and activation of mGluR2 abolishes hallucinogen-specific signalling and behavioural responses. In post-mortem human brain from untreated schizophrenic subjects, the 2AR is upregulated and the mGluR2 is downregulated, a pattern that could predispose to psychosis. These regulatory changes indicate that the 2AR-mGluR2 complex may be involved in the altered cortical processes of schizophrenia, and this complex is therefore a promising new target for the treatment of psychosis.
    Nature 04/2008; 452(7183):93-7. · 38.60 Impact Factor
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    ABSTRACT: Hallucinogens, including mescaline, psilocybin, and lysergic acid diethylamide (LSD), profoundly affect perception, cognition, and mood. All known drugs of this class are 5-HT(2A) receptor (2AR) agonists, yet closely related 2AR agonists such as lisuride lack comparable psychoactive properties. Why only certain 2AR agonists are hallucinogens and which neural circuits mediate their effects are poorly understood. By genetically expressing 2AR only in cortex, we show that 2AR-regulated pathways on cortical neurons are sufficient to mediate the signaling pattern and behavioral response to hallucinogens. Hallucinogenic and nonhallucinogenic 2AR agonists both regulate signaling in the same 2AR-expressing cortical neurons. However, the signaling and behavioral responses to the hallucinogens are distinct. While lisuride and LSD both act at 2AR expressed by cortex neurons to regulate phospholipase C, LSD responses also involve pertussis toxin-sensitive heterotrimeric G(i/o) proteins and Src. These studies identify the long-elusive neural and signaling mechanisms responsible for the unique effects of hallucinogens.
    Neuron 03/2007; 53(3):439-52. · 15.77 Impact Factor
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    ABSTRACT: We have used a novel conditional transgenic system to study the mechanisms of angioproliferation induced by viral G protein-coupled receptor (vGPCR), the constitutively active chemokine receptor encoded by human herpesvirus 8 (HHV8, also known as Kaposi sarcoma herpesvirus). Using this system, we were able to control temporal expression of vGPCR and to monitor its expression in situ via the use of the surrogate marker LacZ. Upon treatment with doxycycline (DOX), cells expressing vGPCR and LacZ (vGPCR/LacZ(+) cells) progressively accumulated in areas where angioproliferation was observed. Sorted vGPCR/LacZ(+) cells from angiogenic lesions expressed markers characteristic of endothelial progenitor cells, produced angiogenic factors, and proliferated in vitro. Prolonged treatment of transgenic mice with DOX led to development of tumors in the skin of ears, tail, nose, and paws. vGPCR/LacZ(+) cells were frequent in early lesions but scarce within these tumors. Finally, transfer of vGPCR/LacZ(+) cells into Rag1(-/-) mice treated with DOX led to angioproliferation and, with time, to development of tumors containing both vGPCR/LacZ(+) and vGPCR/LacZ(-) cells. Taken together, these results indicate that vGPCR triggers angioproliferation directly and suggest a novel role for this molecule in the pathogenesis of Kaposi sarcoma.
    Journal of Clinical Investigation 06/2006; 116(5):1264-73. · 12.81 Impact Factor
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    ABSTRACT: The number of different subtypes of neurons, which form the basic component of the mammalian brain, has not been determined. Histological study is typically limited to the simultaneous detection of very few markers, in part because of the spectral overlap and quenching properties of organic fluorophores. The photostability and narrow emission spectra of non-organic colloidal quantum-dot fluorophores (QDs) make them desirable candidates for multiplex immunohistochemistry (IHC) and for fluorescent in situ hybridization (FISH). IHC is used to study specific protein epitopes and FISH to study the expression of specific mRNA transcripts. In order to investigate the patterns of coexpression of multiple specific protein and nucleic acid targets within cells in complex tissues, such as brain, we have developed protocols for the multiplex use of different QDs and organic fluorophores for combined IHC and FISH. We developed a method for direct QD labeling of modified oligonucleotide probes through streptavidin and biotin interactions and validated this technique in mouse brainstem sections. The reproducible histological results obtained with this protocol allow the use of high throughput computer image analysis to quantify the cellular and subcellular spatial pattern of expression of all markers studied. This approach is being utilized to generate a multiplex co-expression map of neuronal subtypes in mouse brain regions.
    Proc SPIE 01/2006;
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    ABSTRACT: The maintenance of long-term potentiation (LTP) requires a brief period of accelerated protein synthesis soon after synaptic stimulation, suggesting that an early phase of enhanced translation contributes to stable LTP. The mechanism regulating protein synthesis and the location and identities of mRNAs translated are not well understood. Here, we show in acute brain slices that the induction of protein synthesis-dependent hippocampal LTP increases the expression of elongation factor 1A (eEF1A), the mRNA of which contains a 5' terminal oligopyrimidine tract. This effect is blocked by rapamycin, indicating that the increase in EF1A expression is mediated by the mammalian target of rapamycin (mTOR) pathway. We find that mRNA for eEF1A is present in pyramidal cell dendrites and that the LTP-associated increase in eEF1A expression was intact in dendrites that had been severed from their cell bodies before stimulation. eEF1A levels increased within 5 min after stimulation in a translation-dependent manner, and this effect remained stable for 3 h. These results suggest a mechanism whereby synaptic stimulation, by signaling through the mTOR pathway, produces an increase in dendritic translational capacity that contributes to LTP maintenance.
    Journal of Neuroscience 07/2005; 25(24):5833-43. · 6.91 Impact Factor
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    ABSTRACT: The photostability and narrow emission spectra of non-organic quantum dot fluorophores (QDs) make them desirable candidates for fluorescent in situ hybridization (FISH) to study the expression of specific mRNA transcripts. We developed a novel method for direct QD labeling of modified oligonucleotide probes through streptavidin and biotin interactions, as well as protocols for their use in multiple-label FISH. We validated this technique in mouse brainstem sections. The subcellular localization of the vesicular monoamine transporter (Vmat2) mRNA corresponds when using probes labeled with two different QDs in the same hybridization. We developed protocols for combined direct QD FISH and QD immunohistochemical labeling within the same neurons as well as for simultaneous study of the subcellular distribution of multiple mRNA targets. We demonstrated increased sensitivity of FISH using QDs in comparison with organic fluorophores. These techniques gave excellent histological results both for multiplex FISH and combined FISH and immunohistochemistry. This approach can facilitate the ultrasensitive simultaneous study of multiple mRNA and protein markers in tissue culture and histological section.
    Nucleic Acids Research 02/2005; 33(18):e161. · 8.81 Impact Factor
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    ABSTRACT: Myoclonus dystonia (M-D) is a hereditary movement disorder caused by a maternally imprinted gene that is often associated with psychiatric symptoms. Most cases of M-D are believed to result from mutations of the ϵ-sarcoglycan protein. The neuroanatomical distribution of ϵ-sarcoglycan-like immunoreactivity in mouse was investigated by using an antiserum against the ϵ-sarcoglycan protein. The expression of ϵ-sarcoglycan mRNA was studied by a sensitive fluorescence in situ hybridization (FISH) method. Immunohistochemistry and FISH revealed a wide distribution of ϵ-sarcoglycan protein and mRNA throughout the mouse brain. High expression levels of ϵ-sarcoglycan mRNA and immunoreactivity were found in the mitral cell layer of the olfactory bulb, the Purkinje cell layer in cerebellum, and the monoaminergic neurons in the mouse midbrain. Immunohistochemistry revealed a similar distribution of ϵ-sarcoglycan protein. Double-labeling FISH showed colocalization of tyrosine hydroxylase and ϵ-sarcoglycan mRNAs within all the midbrain dopaminergic (DAergic) cell groups. By combining FISH with fluorescence immunohistochemistry, coexpression of ϵ-sarcoglycan mRNA and tryptophan hydroxylase immunoreactivity was found in the serotonergic (5-HTergic) neurons within the dorsal raphe nucleus. The distribution of ϵ-sarcoglycan in the mouse brain suggests that the symptom complex of M-D may be related to the effects of decreased ϵ-sarcoglycan activity on the development or function of monoaminergic neurons. J. Comp. Neurol. 482:50–73, 2005. © 2004 Wiley-Liss, Inc.
    The Journal of Comparative Neurology 12/2004; 482(1):50 - 73. · 3.66 Impact Factor