Accumulation of α-synuclein (α-syn) is a neuropathological hallmark of synucleinopathies. To date, no selective α-syn positron emission tomography (PET) radiotracer has been identified. Our objective was to develop the first original, selective, and specific α-syn PET radiotracer. Chemical design inspired from three structural families that demonstrated interesting α-syn binding characteristics was used as a starting point. Bioinformatics modeling of α-syn fibrils was then employed to select the best molecular candidates before their syntheses. An in vitro binding assay was performed to evaluate the affinity of the compounds. Radiotracer specificity and selectivity were assessed by in vitro autoradiography and in vivo PET studies in animal (rodents) models. Finally, gold standard in vitro autoradiography with patients' postmortem tissues was performed to confirm/infirm the α-syn binding characteristics. Two compounds exhibited a good brain availability and bound to α-syn and Aβ fibrils in a rat model. In contrast, no signal was observed in a mouse model of synucleinopathy. Experiments in human tissues confirmed these negative results.

[(18)F]F15599 is a radiofluorinated agonist presenting interesting characteristics for probing in vitro and in vivo the high-affinity states of the 5-HT(1A) receptors. Its differential labelling of 5-HT(1A) receptors in vitro and in vivo may result from its reported preferential interaction with receptors coupled to specific G-protein subtypes.

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Despite the important role of cannabinoid CB1 receptors (CB1R) in brain development, little is known about their status during adolescence, a critical period for both the development of psychosis and for initiation to substance abuse. In the present study, we assessed the ontogeny of CB1R in adolescent and adult rats in vivo using positron emission tomography with [18F]MK-9470. Analysis of covariance (ANCOVA) to control for body weight that would potentially influence [18F]MK-9470 values between the two groups revealed a main effect of age (F(1,109)=5.0, P = 0.02) on [18F]MK-9470 absolute binding (calculated as percentage of injected dose) with adult estimated marginal means being higher compared to adolescents amongst 11 brain regions. This finding was confirmed using in vitro autoradiography with [3H]CP55,940 (F(10,99)=140.1, P < 0.0001). This ontogenetic pattern, suggesting increase of CB1R during the transition from adolescence to adulthood, is the opposite of most other neuroreceptor systems undergoing pruning during this period.

PET imaging studies using 5-HT 1A receptor radiotracers show a decreased density of this receptor in hippocampi of patients with Alzheimer's disease (AD) at advanced stages. However, current 5-HT 1A receptor radiopharmaceuticals used in neuroimaging are antagonists, thought to bind to 5-HT 1A receptors in different functional states (i.e., both the one which displays high affinity for agonists and is thought to mediate receptor activation, as well as the state which has low affinity for agonists).Comparing the PET imaging obtained using an agonist radiotracer, which binds selectively to functional receptors, with the PET imaging obtained using an antagonist radiotracer would therefore provide original information on 5-HT 1A receptor impairment during AD. Quantitative autoradiography using [

Infections during pregnancy and adolescent cannabis use have both been identified as environmental risk factors for schizophrenia. We combined these factors in an animal model and looked at their effects, alone and in combination, on serotonin 5HT1A receptor binding (5HT1AR) binding longitudinally from late adolescence to adulthood. Pregnant rats were exposed to the viral mimic poly I:C on embryonic day 15. Adolescent offspring received daily injections of the cannabinoid HU210 for 14 days starting on postnatal day (PND) 35. Hippocampal and cortical 5HT1AR binding was quantified autoradiographically using [3H]8-OH-DPAT, in late adolescent (PND 55), young adult (PND 65) and adult (PND 90) rats. Descendants of poly I:C treated rats showed significant increases of 15–18% in 5HT1AR in the hippocampus (CA1) compared to controls at all developmental ages. Offspring of poly I:C treated rats exposed to HU210 during adolescence exhibited even greater elevations in 5HT1AR (with increases of 44, 29, and 39% at PNDs 55, 65, and 90). No effect of HU210 alone was observed. Our results suggest a synergistic effect of prenatal infection and adolescent cannabinoid exposure on the integrity of the serotoninergic system in the hippocampus that may provide the neurochemical substrate for abnormal hippocampal-related functions relevant to schizophrenia.

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