[125I]RTI‐55 Binding to Cocaine‐Sensitive Dopaminergic and Serotonergic Uptake Sites in the Human Brain

Karley Y. Little, Jacob A. Kirkman, F. Ivy Carroll, George R. Breese, Gary E. Duncan

Research output: Contribution to journalArticle

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Abstract

[125I]RTI‐55 is a newly synthesized cocaine congener that may offer advantages over other ligands previously used to examine cocaine binding sites. However, the in vitro pharmacological and anatomical characterization of [125I]RTI‐55 binding sites has not been previously performed in human brain. To determine the specificity, stability, and feasibility of [125I]RTI‐55 for use in radioligand binding assays in postmortem human tissue, a series of experiments were performed characterizing [125I]RTI‐55 binding sites in human brain using homogenized membrane preparations and quantitative autoradtography. Analysis of the association, dissociation, and saturation data favored two‐phase processes. A curve‐fitting analysis of the data derived in saturation experiments found a high‐affinity site with KD= 66 ± 35 pM and Smax= 13.2 ± 10.1 pmol/g of tissue and a low‐affinity site with KD= 1.52 ± 0.55 nM and Bmax of 47.5 ± 11‐2 pmol/g of tissue. Competition by ligands known to bind to the dopamine transporter showed a rank order of RTI‐55 > GBR‐12909 > mazindol > WIN 35428 > = methylphenidate > (−)‐cocaine > buproprion > (±)‐amphetamine. Binding to serotonergic sites was evaluated in the midbrain. Results of the saturation experiment performed autoradiographically in the midbrain showed a single site with KD= 370 ± 84 pM. It appears that [125I]RTI‐55 should be useful in further studies of the regulation of cocaine binding sites using postmortem human specimens.

LanguageEnglish (US)
Pages1996-2006
Number of pages11
JournalJournal of Neurochemistry
Volume61
Issue number6
DOIs
StatePublished - Jan 1 1993

Fingerprint

Cocaine
Brain
Binding Sites
Tissue
Mesencephalon
Mazindol
Ligands
Radioligand Assay
Dopamine Plasma Membrane Transport Proteins
Methylphenidate
Experiments
Curve fitting
Amphetamine
RTI 55
Assays
Association reactions
Pharmacology
Membranes

Keywords

  • Cocaine congener
  • Dopamine transporter
  • Human brain.
  • Serotonin transporter
  • [I]‐RTI‐55

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

Cite this

[125I]RTI‐55 Binding to Cocaine‐Sensitive Dopaminergic and Serotonergic Uptake Sites in the Human Brain. / Little, Karley Y.; Kirkman, Jacob A.; Carroll, F. Ivy; Breese, George R.; Duncan, Gary E.

In: Journal of Neurochemistry, Vol. 61, No. 6, 01.01.1993, p. 1996-2006.

Research output: Contribution to journalArticle

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abstract = "[125I]RTI‐55 is a newly synthesized cocaine congener that may offer advantages over other ligands previously used to examine cocaine binding sites. However, the in vitro pharmacological and anatomical characterization of [125I]RTI‐55 binding sites has not been previously performed in human brain. To determine the specificity, stability, and feasibility of [125I]RTI‐55 for use in radioligand binding assays in postmortem human tissue, a series of experiments were performed characterizing [125I]RTI‐55 binding sites in human brain using homogenized membrane preparations and quantitative autoradtography. Analysis of the association, dissociation, and saturation data favored two‐phase processes. A curve‐fitting analysis of the data derived in saturation experiments found a high‐affinity site with KD= 66 ± 35 pM and Smax= 13.2 ± 10.1 pmol/g of tissue and a low‐affinity site with KD= 1.52 ± 0.55 nM and Bmax of 47.5 ± 11‐2 pmol/g of tissue. Competition by ligands known to bind to the dopamine transporter showed a rank order of RTI‐55 > GBR‐12909 > mazindol > WIN 35428 > = methylphenidate > (−)‐cocaine > buproprion > (±)‐amphetamine. Binding to serotonergic sites was evaluated in the midbrain. Results of the saturation experiment performed autoradiographically in the midbrain showed a single site with KD= 370 ± 84 pM. It appears that [125I]RTI‐55 should be useful in further studies of the regulation of cocaine binding sites using postmortem human specimens.",
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