Circadian-related heteromerization of adrenergic and dopamine D₄ receptors modulates melatonin synthesis and release in the pineal gland.

The role of the pineal gland is to translate the rhythmic cycles of night and day encoded by the retina into hormonal signals that are transmitted to the rest of the neuronal system in the form of serotonin and melatonin synthesis and release. Here we describe that the production of both melatonin and serotonin by the pineal gland is regulated by a circadian-related heteromerization of adrenergic and dopamine D₄ receptors. Through α(₁B)-D₄ and β₁-D₄ receptor heteromers dopamine inhibits adrenergic receptor signaling and blocks the synthesis of melatonin induced by adrenergic receptor ligands.

A2A adenosine receptor ligand binding and signalling is allosterically modulated by adenosine deaminase.

A2ARs (adenosine A2A receptors) are highly enriched in the striatum, which is the main motor control CNS (central nervous system) area. BRET (bioluminescence resonance energy transfer) assays showed that A2AR homomers may act as cell-surface ADA (adenosine deaminase; EC 3.5.

Biotin ergopeptide probes for dopamine receptors.

The incorporation of chemical modifications into the structure of bioactive compounds is often difficult because the biological properties of the new molecules must be retained with respect to the native ligand. Ergopeptides, with their high affinities at D(1) and D(2) dopamine receptors, are particularly complex examples. Here, we report the systematic derivatization of two ergopeptides with different peptide-based spacers and their evaluation by radioligand binding assays.

GPCR homomers and heteromers: a better choice as targets for drug development than GPCR monomers?

G protein-coupled receptors (GPCR) are targeted by many therapeutic drugs marketed to fight against a variety of diseases. Selection of novel lead compounds are based on pharmacological parameters obtained assuming that GPCR are monomers. However, many GPCR are expressed as dimers/oligomers.

Novel pharmacological targets based on receptor heteromers.

Studies performed in the last 10 years have provided solid evidence indicating that G-protein-coupled receptors are expressed on the plasma membrane as homo and heterodimers. The first consequence of this fact is that homo and heterodimers are the true targets of natural (hormones, neurotransmitters) and synthetic drugs. Furthermore a given receptor in a heteromer may display a different functional and/or pharmacological profile than the same receptor characterized as monomer or as homodimer.

Expression of C/EBPalpha and C/EBPbeta in glial cells in vitro after inducing glial activation by different stimuli.

We studied the involvement of two members of the CCAAT/enhancer binding proteins (C/EBPs) family of transcription factors, C/EBPalpha and C/EBPbeta, in glial activation induced by different stimuli in rat cerebellar neuronal-glial cultures. Glial activation was induced by two types of neuronal death--excitotoxic and apoptotic. We had previously reported that these two induction mechanisms resulted in different patterns of glial activation (K.

Excitotoxic and apoptotic neuronal death induce different patterns of glial activation in vitro.

We have studied glial activation in rat cerebellar neuronal-glial cultures after inducing neuronal death using various stimuli. Cultures were exposed to 100 microm glutamate for 20 min, which induces excitotoxic neuronal death, or to potassium/serum deprivation, which induces apoptosis of granule neurons. We evaluated alterations in several parameters related to glial activation: nuclear factor-kappaB activation, nitric oxide and tumour necrosis factor-alpha production, which are associated with a pro-inflammatory response, glial proliferation and phagocytic activity.

Glial activation modulates glutamate neurotoxicity in cerebellar granule cell cultures.

We studied the influence of glial cells on the neuronal response to glutamate toxicity in cerebellar granule cell cultures. We compared the effect of glutamate on neuronal viability in neuronal vs. neuronal-glial cultures and determined this effect after pretreating the cultures with the lipopolysaccharide (LPS) of Escherichia coli, agent widely used to induce glial activation.