Changes in sleep electroencephalogram and nocturnal hormone secretion after administration of the antidyskinetic agent sarizotan in healthy young male volunteers

PET tracers for 5-HT(1A) receptors and uses thereof

The serotonin 5-HT(1A) receptor is implicated in the pathophysiology of major neuropsychiatric disorders, including depression, suicidal behavior, panic disorder, epilepsy, bulimia, schizophrenia, Parkinson's disease, and Alzheimer's disease and is, therefore, an important target for drug therapy. 5-HT(1A) receptors are expressed as somatodendritic autoreceptors in serotonin neurons of the raphé nuclei (presynaptic) and as postsynaptic receptors in cortical and subcortical serotonin terminal fields in the brain. Due to the higher concentration and heterogeneous distribution of this receptor, it is an attractive target for quantification in vivo using positron emission tomography (PET) and single photon emission tomography (SPECT). Here, we review the PET radioligands employed for imaging 5-HT(1A) receptors in living brain.

Synthesis and in vivo evaluation of a novel 5-HT1A receptor agonist radioligand [O-methyl-11C]2-(4-(4-(2-methoxyphenyl)piperazin-1-yl)butyl)-4-methyl-1,2,4-triazine-3,5(2H,4H)dione in nonhuman primates

PURPOSE

Serotonin1A (5-HT1A) receptors exist in high- and low-affinity states, and agonist ligands bind preferentially to the high-affinity state of the receptor and provide a measure of functional 5-HT1A receptors. Although the antagonist tracers are established PET ligands in clinical studies, a successful 5-HT1A receptor agonist radiotracer in living brain has not been reported. [11C]MPT, our first-generation agonist radiotracer, shows in vivo specificity in baboons; however, its utility is limited owing to slow washout and immeasurable plasma free fraction. Hence we performed structure-activity relationship studies of MPT to optimize a radiotracer that will permit valid quantification of 5-HT1A receptor binding. We now report the synthesis and evaluation of [11C]MMP as an agonist PET tracer for 5-HT1A receptors in baboons.

METHODS

In vitro binding assays were performed in bovine hippocampal membranes and membranes of CHO cells expressing 5-HT1A receptors. [11C] labeling of MMP was performed by reacting desmethyl-MMP with [11C]CH(3)OTf. In vivo studies were performed in baboons, and blocking studies were conducted by pretreatment with 5-HT1A receptor ligands WAY-100635 and (+/-)-8-OH-DPAT.

RESULTS

MMP is a selective 5-HT1A receptor agonist (Ki 0.15 nM). Radiosynthesis of [11C]MMP was achieved in 30 +/- 5% (n = 15) yield at EOS with a specific activity of 2,600 +/- 500 Ci/mmol (n = 12). PET studies in baboons demonstrated specific binding of [11C]MMP to 5-HT1A receptor-enriched brain regions, as confirmed by blockade with WAY-100635 and (+/-)-8-OH-DPAT.

CONCLUSION

We identified [11C]MMP as an optimal agonist PET tracer that shows quantifiable, specific binding in vivo to 5-HT1A receptors in baboons.

Changes of sleep architecture, spectral composition of sleep EEG, the nocturnal secretion of cortisol, ACTH, GH, prolactin, melatonin, ghrelin, and leptin, and the DEX-CRH test in depressed patients during treatment with mirtazapine

The noradrenergic and specific serotoninergic antidepressant mirtazapine improves sleep, modulates hormone secretion including blunting of hypothalamic-pituitary-adrenocortical (HPA) activity, and may prompt increased appetite and weight gain. The simultaneous investigation of sleep electroencephalogram (EEG) and hormone secretion during antidepressive treatment helps to further elucidate these effects. We examined sleep EEG (for later conventional and quantitative analyses) and the nocturnal concentrations of cortisol, adrenocorticotropin (ACTH), growth hormone (GH), prolactin, melatonin and the key factors of energy balance, ghrelin, and leptin before and after 28 days of treatment of depressed patients (seven women, three men, mean age 39.9+/-4.2 years) with mirtazapine. In addition, a sleep EEG was recorded at day 2 and the dexamethasone-corticotropin-releasing hormone (DEX-CRH) test was performed to assess HPA activity at days -3 and 26. Psychometry and mirtazapine plasma concentrations were measured weekly. Already at day 2, sleep continuity was improved. This effect persisted at day 28, when slow-wave sleep, low-delta, theta and alpha activity, leptin and (0300-0700) melatonin increased, and cortisol and ghrelin decreased. ACTH and prolactin remained unchanged. The first two specimens of GH collected after the start of quantitative EEG analysis were reduced at day 28. The DEX-CRH test showed, at day 26, a blunting of the overshoot of ACTH and cortisol found at day -3. The Hamilton Depression score decreased from 32.1+/-7.3 to 15.5+/-6.7 between days -1 and 28. A weight gain of approximately 3 kg was observed. This unique profile of changes is compatible with the action of mirtazapine at 5-HT-2 receptors, at presynaptic adrenergic alpha 2 receptors, at the HPA system, and on ghrelin and leptin.