Attenuated 5-HT1A receptor signaling in brains of suicide victims: involvement of adenylyl cyclase, phosphatidylinositol 3-kinase, Akt and mitogen-activated protein kinase

Authors

  • Shu-chi Hsiung,

    1. Department of Neuroscience, New York State Psychiatric Institute, New York, USA Departments of
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  • Mella Adlersberg,

    1. Department of Neuroscience, New York State Psychiatric Institute, New York, USA Departments of
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  • Victoria Arango,

    1. Department of Neuroscience, New York State Psychiatric Institute, New York, USA Departments of
    2. Anatomy and Cell Biology and
    3. Psychiatry, Columbia University, College of Physicians and Surgeons, New York, New York, USA
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  • J. John Mann,

    1. Department of Neuroscience, New York State Psychiatric Institute, New York, USA Departments of
    2. Psychiatry, Columbia University, College of Physicians and Surgeons, New York, New York, USA
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  • Hadassah Tamir,

    1. Department of Neuroscience, New York State Psychiatric Institute, New York, USA Departments of
    2. Anatomy and Cell Biology and
    3. Psychiatry, Columbia University, College of Physicians and Surgeons, New York, New York, USA
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  • Kuo-peing Liu

    1. Department of Neuroscience, New York State Psychiatric Institute, New York, USA Departments of
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Address correspondence and reprint requests to Hadassah Tamir, Department of Neuroscience, New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY 10032, USA. E-mail: ht3@columbia.edu

Abstract

Positron emission tomography studies in major depression show reduced serotonin (5-HT)1A receptor antagonist-binding potentials in many brain regions including occipital cortex. The functional meaning of this observation in terms of signal transduction is unknown. We used postmortem brain samples from depressed suicide victims to examine the downstream effectors of 5-HT1A receptor activation. The diagnosis was established by means of psychological autopsy using Diagnostic and Statistical Manual of Mental Disorders (DSM) III-R criteria. Measurements of [35S]GTPγS binding to Gαi/o in the occipital cortex of suicide victims and matched controls revealed a blunted response in suicide subjects and a decrease in the coupling of 5-HT1A receptor to adenylyl cyclase. No significant group differences were detected in the expression levels of Gαi/o, Gαq/11 or Gαs proteins, or in the activity of cAMP-dependent protein kinase A. Studies of a parallel transduction pathway downstream from 5-HT1A receptor activation demonstrated a decrease in the activity of phosphatidylinositol 3-kinase and its downstream effector Akt, as well as an increase in PTEN (phosphatase and tensin homolog deleted on chromosome 10), the phosphatase that hydrolyzes phosphatidylinositol 3,4,5-triphosphate. Finally, the activation of extracellular signal-regulated kinases 1 and 2 was attenuated in suicide victims. These data suggest that the alterations in agonist-stimulated 5-HT1A receptor activation in depressed suicide victims are also manifest downstream from the associated G protein, affecting the activity of second messengers in two 5-HT1A receptor transduction pathways that may have implications for cell survival.

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