Constitutive activity of histamine h(3) receptors stably expressed in SK-N-MC cells: display of agonism and inverse agonism by H(3) antagonists

Agonist-independent activity of G-protein-coupled receptor, also referred to as constitutive activity, is a well-documented phenomenon and has been reported recently for both the his-tamine H1 and H2 receptors. Using SK-N-MC cell lines stably expressing the human and rat H3 receptors at physiological receptor densities (500–600 fmol/mg of protein), we show that both the rat and human H3 receptors show a high degree of constitutive activity. The forskolin-mediated cAMP production in SK-N-MC cells is inhibited strongly upon expression of the Gi-coupled H3 receptor. The cAMP production can be further inhibited upon agonist stimulation of the H3 receptor and can be enhanced by a variety of H3 antagonists acting as inverse agonists at the H3 receptor. Thioperamide, clobenpropit, and iodophenpropit raise the cAMP levels in SK-N-MC cells wit

Measurement of hypocretin/orexin content in the mouse brain using an enzyme immunoassay: the effect of circadian time, age and genetic background

International audienceThe hypocretins (1 and 2) have emerged as key regulators of sleep and wakefulness. We developed a high-throughput enzyme immunoassay (EIA) to measure total brain hypocretin levels from large numbers of mice. Hypocretin levels were not altered by circadian time or age. However, significant differences in one or both hypocretin peptides were observed between different mouse strains. We studied hypocretin levels in knockout and transgenic mouse models with obesity, circadian gene mutations or monoaminergic defects. Compared to controls, only histamine receptor knockouts had lower hypocretin levels. This was most pronounced in H1 receptor knockouts suggesting the existence of a positive feedback loop between hypocretin and histaminergic neurons