High‐affinity binding of [¹²⁵I]RTI‐55 to dopamine and serotonin transporters in rat brain

Abstract

RTI-55 (3 beta-(4-iodophenyl)tropan-2 beta-carboxylic acid methyl ester), one of the most potent inhibitors of dopamine uptake reported to date, was radioiodinated and tested as a probe for the cocaine receptor in Sprague-Dawley rat brain. Saturation and kinetic studies in the striatum revealed that [125I]RTI-55 bound to both a high- and low-affinity site. The Kd for the high-affinity site was 0.2 nM, while the Kd for the low-affinity site was 5.8 nM. The corresponding number of binding sites in the striatum was 37 and 415 pmol/g protein. The pharmacological profile of specific [125I]RTI-55 binding in the striatum was consistent with that of the dopamine transporter. Additionally, [125I]RTI-55 was found to bind with high affinity to the cerebral cortex. Scatchard analysis revealed a single high-affinity component of 0.2 nM with a density of 2.5 pmol/g protein. The pharmacological profile demonstrated by [125I]RTI-55 in the cerebral cortex matched that of the serotonin transporter. Autoradiographic analysis of sagittal brain sections with [125I]RTI-55 binding was consistent with these findings. Specific binding of [125I]RTI-55 was blocked by dopamine uptake inhibitors in areas rich in dopaminergic nerve terminals. Conversely, serotonin uptake inhibitors blocked the binding of [125I]RTI-55 in brain areas rich in serotonergic neurons. These results demonstrate that [125I]RTI-55 may be a very useful ligand for the dopamine and serotonin transporters.

Impaired Object Recognition Memory Following Methamphetamine, but not p-Chloroamphetamine- or d-Amphetamine-Induced Neurotoxicity

“…In all, 25-mm-thick coronal sections were cut in a cryostat at the level of the striatum and dorsal hippocampus (HC), and sections were incubated with 21 pM [ 125 I]RTI-55 for autoradiographic localization of DA transporters (DAT) in the striatum and 5-HT transporter (SERT) in the HC and perirhinal (pRh) cortex, using the procedures of Boja et al (1992). DAT binding in these limbic areas (HC and pRH cortex) is quite low, and constitutes a small percentage of the total binding (Tohyama and Takatsuji, 1998;Ritchand et al, 1995;Donnan et al, 1989).…”

1-(m-Chlorophenyl)piperazine (mCPP) Dissociates In Vivo Serotonin Release from Long-Term Serotonin Depletion in Rat Brain

“…The binding of dFEN and mCPP to SERT and DAT was determined in rat caudate using the high affinity cocaine analog [ 125 I]RTI-55 as the radioligand (Boja et al 1992). Membranes were prepared from rat caudate as described .…”

[123I]-β-CIT SPECT Imaging Shows Reduced Thalamus–Hypothalamus Serotonin Transporter Availability in 24 Drug-Free Obsessive-Compulsive Checkers

“…[ 123 I]-2b-carbomethoxy-3b-(4-iodophenyl)tropane ([ 123 I]-b-CIT), a radiotracer with high affinity to monoamine transporters (Innis et al, 1991;Boja et al, 1992), can be used to mark the central dopamine (DAT) and serotonin transporters (SERT) of the human brain in vivo with the aide of single photon emission computed tomography (SPECT) (Brücke et al, 1993;Kuikka et al, 1993;Pirker et al, 2000). b-CIT accumulates in specific areas of the brain, these being primarily striatal, diencephalic, midbrain, and brainstem regions (Innis et al, 1991;Laruelle et al, 1993).…”