Simultaneous [99mTc]TRODAT-1 and [123I]ADAM brain SPECT in nonhuman primates

Effects of dextromethorphan on MDMA-induced serotonergic aberration in the brains of non-human primates using [123I]-ADAM/SPECT

3,4-Methylenedioxymethamphetamine (MDMA), a common recreational drug, is known to cause serotonergic neurotoxicity in the brain. Dextromethorphan (DM) is a widely used antitussive reported to exert anti-inflammatory effect in vivo. In this study, we examined the long-term effect of MDMA on the primate serotonergic system and the protective property of DM against MDMA-induced serotonergic abnormality using single photon emission computed tomography (SPECT). Nine monkeys (Macaca cyclopis) were divided into three groups, namely control, MDMA and co-treatment (MDMA/DM). [¹²³I]-ADAM was used as the radioligand for serotonin transporters (SERT) in SPECT scans. SERT levels of the brain were evaluated and presented as the uptake ratios (URs) of [¹²³I]-ADAM in several regions of interest of the brain including midbrain, thalamus and striatum. We found that the URs of [¹²³I]-ADAM were significantly lower in the brains of MDMA than control group, indicating lower brain SERT levels in the MDMA-treated monkeys. This MDMA-induced decrease in brain SERT levels could persist for over four years. However, the loss of brain SERT levels was not observed in co-treatment group. These results suggest that DM may exert a protective effect against MDMA-induced serotonergic toxicity in the brains of the non-human primate.

Comparison of simultaneous and sequential SPECT imaging for discrimination tasks in assessment of cardiac defects

Simultaneous rest perfusion/fatty-acid metabolism studies have the potential to replace sequential rest/stress perfusion studies for the assessment of cardiac function. Simultaneous acquisition has the benefits of increased signal and lack of need for patient stress, but is complicated by cross-talk between the two radionuclide signals. We consider a simultaneous rest (99m)Tc-sestamibi/(123)I-BMIPP imaging protocol in place of the commonly used sequential rest/stress (99m)Tc-sestamibi protocol. The theoretical precision with which the severity of a cardiac defect and the transmural extent of infarct can be measured is computed for simultaneous and sequential SPECT imaging, and their performance is compared for discriminating (1) degrees of defect severity and (2) sub-endocardial from transmural defects. We consider cardiac infarcts for which reduced perfusion and metabolism are observed. From an information perspective, simultaneous imaging is found to yield comparable or improved performance compared with sequential imaging for discriminating both severity of defect and transmural extent of infarct, for three defects of differing location and size.

The SPECT tracer [123I]ADAM binds selectively to serotonin transporters: a double-blind, placebo-controlled study in healthy young men

Purpose

The tracer ¹²³I-2-([2-({dimethylamino}methyl)phenyl]thio)-5-iodophenylamine ([¹²³I]ADAM) has been developed to image serotonin transporters (SERTs) with SPECT. Preclinical studies have shown that [¹²³I]ADAM binds selectively to SERTs. Moreover, initial human studies have shown that [¹²³I]ADAM binding could be blocked by selective serotonin reuptake inhibitors (SSRIs). However, in humans it has not been proven that [¹²³I]ADAM binds selectively to SERTs.

Methods

We examined the in vivo availability of SERTs in 12 healthy young volunteers 5 h after bolus injection of [¹²³I]ADAM. To evaluate the selectivity of binding, four participants were pretreated (double-blinded design) with placebo, four with paroxetine (20 mg) and four with the dopamine/norepinephrine blocker methylphenidate (20 mg). SPECT studies were performed on a brain-dedicated system (Neurofocus), and the SPECT images were coregistered with individual MR scans of the brain. ADAM binding in SERT-rich brain areas and cerebellar cortex (representing non-specific binding) was assessed by drawing regions of interest (ROIs) on the individual MR images. Specific to non-specific ratios were used as the outcome measure.

Results

We found that specific to non-specific ratios were statistically significantly lower in paroxetine-pretreated participants than in placebo- or methylphenidate-pretreated participants. No such difference was found between groups pretreated with placebo or methylphenidate.

Conclusion

Our preliminary findings suggest that [¹²³I]ADAM binds selectively to SERTs in human brain.