Opioids interact with receptors on neurons, leading to a variety of effects, e.g., analgesia, euphoria, and diuresis. It is not known, however, whether the primary target for these effects are at somata and/or synapses in the central nervous system. The electrical and secretory activities of the hypothalamo-neurohypophysial system are affected by both exogenous and endogenous opioids. The specific effects of opioids on membrane ionic conductances in these neurons and their nerve terminals, however, are unknown. Vasopressin and oxytocin have crucial roles in fluid homeostatic mechanisms and in various reproductive functions. These peptide neurohormones are synthesized by magnocellular neurons of the hypothalamus and secreted from neurohypophysial terminals. Furthermore, the hypothalamo-neurohypophysial system develops tolerance and dependence to morphine during chronic administration suggesting that this central nervous system is a good model for studying the physiological mechanisms underlying these phenomena. The hypothalamo-neurohypophysial system affords the unique opportunity of unraveling the complicated effects of opioids in the central nervous system by comparing such effects on the different components of central nervous system neurons. The goal of the research proposed here is to determine membrane mechanisms that mediate opioid-induced modifications of neurohormone secretion and the responses of nerve terminals vs. neuronal cell bodies. To achieve these objectives, perforated patch recordings of action potentials and of Ca2+ and K+ currents will be made from identified, isolated neuroendocrine cells and nerve terminals obtained from the hypothalamo-neurohypophysial system of adult rats. Effects on release will be compared between magnocellular neurons and NH terminals by the use of radioimmununoassays and capacitance measurements. These studies will provide a unique opportunity to determine how acute opioid effects occur at the somata and or terminals of central nervous system neurons.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA010487-03
Application #
6150475
Study Section
Human Development Research Subcommittee (NIDA)
Program Officer
Lin, Yu
Project Start
1998-03-15
Project End
2003-01-31
Budget Start
2000-02-01
Budget End
2001-01-31
Support Year
3
Fiscal Year
2000
Total Cost
$212,767
Indirect Cost
Name
University of Massachusetts Medical School Worcester
Department
Physiology
Type
Schools of Medicine
DUNS #
660735098
City
Worcester
State
MA
Country
United States
Zip Code
01655
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Ortiz-Miranda, Sonia I; Dayanithi, Govindan; Velázquez-Marrero, Cristina et al. (2010) Differential modulation of N-type calcium channels by micro-opioid receptors in oxytocinergic versus vasopressinergic neurohypophysial terminals. J Cell Physiol 225:276-88
Ortiz-Miranda, S; Dayanithi, G; Custer, E et al. (2005) Micro-opioid receptor preferentially inhibits oxytocin release from neurohypophysial terminals by blocking R-type Ca2+ channels. J Neuroendocrinol 17:583-90
De Crescenzo, Valerie; ZhuGe, Ronghua; Velazquez-Marrero, Cristina et al. (2004) Ca2+ syntillas, miniature Ca2+ release events in terminals of hypothalamic neurons, are increased in frequency by depolarization in the absence of Ca2+ influx. J Neurosci 24:1226-35
Ortiz-Miranda, S I; Dayanithi, G; Coccia, V et al. (2003) mu-Opioid receptor modulates peptide release from rat neurohypophysial terminals by inhibiting Ca(2+) influx. J Neuroendocrinol 15:888-94
Wang, Gang; Dayanithi, Govindan; Custer, Edward E et al. (2002) Adenosine inhibition via A(1) receptor of N-type Ca(2+) current and peptide release from isolated neurohypophysial terminals of the rat. J Physiol 540:791-802