[Mechanisms of opioid tolerance and opioid dependence]

Placebo Response in a Patient with Chronic Migraine and Ergotic Overuse

Facilitation of nociceptive systems has been implicated in Chronic-Migraine pathogenesis. Daily consumption of medication may be a contributing factor. The patient was male, aged 76 years, with history of migraine without aura. Six years ago, he presented with a mild-moderate daily pulsating headache. He was overusing analgesics and ergotamine. After withdrawing, the patient started a non-pulsating headache, diffuse and constant. During follow up, he was refractive to several symptomatic and prophylactic treatments. When we treated him with placebo capsules, the headache responded very well. At first, pain-relief occurred for 6 h and progressively, extended. Two years later, when our patient started to use transdermal patches of fentanyl for treatment of a complex regional pain syndrome type 1, his headache did not improve. Patient has maintained prolonged response to placebo. Actually, he is pain-free for 2-3 days with 1 placebo capsule. We discuss mechanisms of chronic-migraine, drug-overuse, drug-induced headache and placebo addiction. Powerful psychological mechanisms could determine response to placebo in this patient.

Synthesis, radiolabeling and in vivo evaluation of [11C]RAL-01, a potential phosphodiesterase 5 radioligand

Very few tracers are available for imaging studies of second messenger systems. We developed a radiosynthesis for the phosphodiesterase (PDE) 5 inhibitor [(11)C]RAL-01. Whole body distribution studies using positron emission tomography (PET) revealed a time-dependant passage through the liver and accumulation of radioactivity in the bile of the Landrace pig. Displaceable binding was readily discerned in the myocardium, and traces of binding were seen in pulmonary tissue, consistent with the use of this class of drug in the treatment of pulmonary hypertension and heart failure. [(11)C]RAL-01 readily entered the brain and obtained an equilibrium distribution volume of 4-5 ml g(-1). Mean parametric images suggested the presence of a small displaceable binding component, but this binding was not significant in the present group of three pigs. Thus, [(11)C]RAL-01 shows considerable promise for PET studies of biliary elimination and of PDE5 binding in the cardiovascular system. However, analogues of higher affinity may be required for investigations of central nervous system binding sites.