In vivo imaging of muscarinic cholinergic receptors in temporal lobe epilepsy with a new PET tracer: [76Br]4-bromodexetimide.
Muscarinic acetyl cholinergic receptors (mAChRs) may be involved in the pathophysiology of partial epilepsy. Previous experimental and imaging studies have reported medial temporal abnormalities of mAChR in patients with medial temporal lobe epilepsy (MTLE). Suitable radiotracers for mAChR are required to evaluate these disturbances in vivo using PET. Dexetimide is a specific mAChR antagonist that has been labeled recently with 76Br. This first study in humans focused on regional distribution and binding kinetics of [76Br]4-bromodexetimide (BDEX) in patients with MTLE.


METHODS
Ten patients with well-lateralized MTLE had combined MRI, 18F-fluorodeoxyglucose (FDG) PET and 76Br-BDEX PET studies. Time-activity curves were generated in PET-defined regions of interest, including the medial, polar and lateral regions of the temporal lobe; the basal ganglia; the external and medial occipital cortex; and the white matter.


RESULTS
The highest radioactivity concentration was observed in the basal ganglia and in the cortical regions, whereas radioactivity was lower in the white matter. On late images of PET studies, 76Br-BDEX uptake was statistically significantly decreased only in the medial temporal region ipsilateral to the seizure focus (1.37 +/-0.28, P < 0.01) as determined by FDG PET imaging, anatomic MRI and electroencephalogram correlation, compared with the contralateral medial temporal region (1.46 +/- 0.31).


CONCLUSIONS
76Br-BDEX concentration is reduced in the temporal lobe ipsilateral to the seizure focus in patients with MTLE. This preliminary study suggests that 76Br-BDEX is a suitable radiotracer for studies of mAChR in humans. Further studies are required to investigate the potential value of 76Br-BDEX PET in other neurological disorders with muscarinic disturbances.
Dupont
S
S
CEA, SHFJ, Orsay, France.
Semah
F
F
Loc'h
C
C
Strijckmans
V
V
Baulac
M
M
Samson
Y
Y
Mazière
B
B
D000328:Adult; D000818:Animals; D001967:Bromine Radioisotopes; D002540:Cerebral Cortex / Q000000981:diagnostic imaging / Q000378:metabolism; D003909:Dexetimide / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D004833:Epilepsy, Temporal Lobe / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018727:Muscarinic Antagonists / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D011976:Receptors, Muscarinic / Q000378:metabolism / Q000502:physiology; D013702:Temporal Lobe / Q000000981:diagnostic imaging / Q000378:metabolism; D013997:Time Factors; D014055:Tomography, Emission-Computed
D001967:Bromine Radioisotopes; D018727:Muscarinic Antagonists; D019275:Radiopharmaceuticals; D011976:Receptors, Muscarinic; C099688:4-bromodexetimide; D003909:Dexetimide