ISSN:
1619-7089
Keywords:
Radioiodination
;
Brain imaging
;
Receptor autoradiography
;
Nicotinic acetylcholine receptors
;
Neurotransmission
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract A novel radiochemical method is presented to synthesize 5-[123I/125I/131I]-dl-nicotine by radioiodination of 5-bromonicotine. Radioiodination of the precursur 5-dl-bromonicotine was achieved using a copper (I)-assisted nucleophilic exchange reaction in the presence of reducing agent. The reaction conditions were optimized by varying pH, concentration of Sn(II) salt, ascorbic acid, Cu(I)chloride and reaction temperature. After purification by high-performance liquid chromatography the radiochemical purity of the product exceeded 98%, with a radiochemical yield of 55% and a specific activity ≥5 GBq/µmol. Specific binding of the iodinated nicotine was demonstrated in rat brain by autoradiography. The radioactivity from the specific structures was displaced by an excess of non-radioactive nicotine (10−3 M) withK D andB max of 13.1±7.8 nM and 22±2.7 fmol/mg protein and unspecific binding of about 40%. The in vivo distribution of 5-[131I]iodonicotine was determined in 20 female Wistar rats at various time intervals of 15 s to 90 min post injection (p.i.) by well counting and autoradiography. Brain activity peaked within 0.5 min p.i., and then showed a biexponential washout. Initially, activity within the cerebral cortex exceeded that of the cerebellum by a factor of 1.5–2.0. It was also increased in the striatum and thalamus. However, as soon as 15 min p.i. activity was almost homogeneously distributed. In conclusion, synthesis of 5-iodo-dl-nicotine (labelled with131I,125I or123I, respectively) with appropriately high specific activity for receptor studies was achieved and specific binding to nicotine receptors in rat brain was demonstrated; following intravenous injection, however, there is considerable unspecific binding, obviously due to highly flow-dependent tissue retention.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01731839
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