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Effects of serotonin on perifornical-lateral hypothalamic area neurons in rat

Authors

  • Sunil Kumar,

    1. Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, 16111 Plummer Street, Sepulveda, California 91343, USA
    2. Department of Medicine and
    3. Department of Zoology, Patna University, Patna, India
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  • Ronald Szymusiak,

    1. Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, 16111 Plummer Street, Sepulveda, California 91343, USA
    2. Department of Medicine and
    3. Department of Neurobiology, School of Medicine, University of California, Los Angeles, California, USA
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  • Tariq Bashir,

    1. Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, 16111 Plummer Street, Sepulveda, California 91343, USA
    2. Department of Medicine and
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  • Seema Rai,

    1. Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, 16111 Plummer Street, Sepulveda, California 91343, USA
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  • Dennis McGinty,

    1. Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, 16111 Plummer Street, Sepulveda, California 91343, USA
    2. Department of Psychology, University of California, Los Angeles, California, USA
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  • Md. Noor Alam

    1. Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, 16111 Plummer Street, Sepulveda, California 91343, USA
    2. Department of Psychology, University of California, Los Angeles, California, USA
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Dr Md. Noor Alam, 1Research Service (151A3), as above.
E-mail: noor@ucla.edu

Abstract

The hypocretin (HCRT) system of the perifornical-lateral hypothalamic area (PF-LHA) has been implicated in the facilitation of behavioral arousal. HCRT neurons receive serotonergic afferents from the dorsal raphe nucleus. Although in-vitro pharmacological studies suggest that serotonin (5-HT) inhibits HCRT neurons, the in-vivo effects of 5-HT on HCRT neurons in the PF-LHA and associated behavioral changes have not been described. We examined the effects of 5-HT delivered locally into the PF-LHA using reverse microdialysis on its neuronal activity and the consequent sleep–wake changes in rats. First, we quantified Fos expression (Fos-IR) in HCRT and other PF-LHA neurons following unilateral 5-HT perfusion in awake rats. Second, we determined the transient effects of 5-HT perfusion on the extracellular activity of the PF-LHA neurons recorded via microwires placed adjacent to the microdialysis probe. Third, we examined the effects of 5-HT perfusion into the PF-LHA on the sleep–wake profiles of the rats during the lights-off period. Unilateral perfusion of 5-HT into the PF-LHA in awake rats dose-dependently decreased the number of HCRT neurons exhibiting Fos-IR. 5-HT also inhibited the discharge activity of four of five responsive wake-related, putative HCRT neurons. However, unilateral perfusion of 5-HT into the PF-LHA did not produce significant behavioral changes during the 2-h recording period. These results confirm the in-vitro findings that 5-HT exerts inhibitory influences on HCRT neurons but further suggest that the inactivation of a limited number of HCRT neurons by unilateral 5-HT microdialysis may not be sufficient to induce behavioral changes.

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