[125i]IPH, an epibatidine analog, binds with high affinity to neuronal nicotinic cholinergic receptors

Martha I. Dávila-García, John L. Musachio, David C. Perry, Yingxian Xiao, Andrew Horti, Edythe D. London, Robert F. Dannals, Kenneth J. Kellar

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An analog of epibatidine (EB) was synthesized with an iodine atom in the 2 position of the pyridyl ring. This analog, (±)-exo-2-(2-iodo-5-pyridyl)- 7-azabicyclo[2.2.1]heptane (IPH), as well as its two stereoisomers, displayed high affinity for neuronal nicotinic receptors; therefore, radioiodinated IPH, [125I]IPH, was synthesized with specific radioactivities consistently > 1000 Ci/mmol, and its properties as a radioligand for neuronal nicotinic receptors were evaluated. The characteristics of [125I]IPH binding in tissue homogenates appeared to be virtually identical to those reported for [3H]epibatidine binding; but the high specific radioactivity of [125I]IPH greatly facilitated measurements of nicotinic receptors in tissues with relatively low receptor densities and/or where tissues are in limited supply. Autoradiography with [125I]IPH provided clear localization of nicotinic receptors in brain and adrenal gland after film exposure times of ≤2 days. We conclude that [125I]IPH will be a very useful radioligand for the study of neuronal nicotinic receptors in brain and in peripheral ganglia.

Original languageEnglish (US)
Pages (from-to)445-451
Number of pages7
JournalJournal of Pharmacology and Experimental Therapeutics
Issue number1
StatePublished - Jul 1997

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology


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