Lourdes Carbonell

Adenosine receptors interacting proteins (ARIPs): Behind the biology of adenosine signaling

Adenosine is a well known neuromodulator in the central nervous system. As a consequence, adenosine can be beneficial in certain disorders and adenosine receptors will be potential targets for therapy in a variety of diseases. Adenosine receptors are G protein-coupled receptors, and are also expressed in a large variety of cells and tissues. Using these receptors as a paradigm of G protein-coupled receptors, the present review focus on how protein-protein interactions might contribute to neurotransmitter/neuromodulator regulation, based on the fact that accessory proteins impinge on the receptor/G protein interaction and therefore modulate receptor functioning. Besides affecting receptor signaling, these accessory components also play a key role in receptor trafficking, internalization and desensitization, as it will be reviewed here. In conclusion, the finding of an increasing number of adenosine receptors interacting proteins, and specially the molecular and functional integration of these accessory proteins into receptorsomes, will open new perspectives in the understanding of particular disorders where these receptors have been proved to be involved.

G protein-coupled receptor oligomerization and brain integration: focus on adenosinergic transmission.

The control of glutamatergic corticostriatal transmission is essential for the induction and expression of plasticity mechanisms in the striatum, a phenomenon thickly regulated by G protein-coupled receptors (GPCRs). Interestingly, in addition to dopamine receptors, adenosine and metabotropic glutamate receptors also play a key role in striatal functioning. The existence of a supramolecular organization (i.e. oligomer) containing dopamine, adenosine and metabotropic glutamate receptors in the striatal neurons is now being widely accepted by the scientific community. Indeed, these oligomers may enhance the diversity and performance by which extracellular striatal signals are transferred to the G-proteins in the process of receptor transduction, and also may allow unpredictable receptor-receptor allosteric regulations. Overall, here we want to review how formations of adenosine, dopamine and metabotropic glutamate receptors-containing oligomers impinge into striatal functioning in both normal and pathological conditions. This article is part of a Special Issue entitled: Brain Integration.

Demonstration of inhibition of cyclic AMP accumulation in brain by very low concentrations of lithium in the presence of α-adrenoceptor blockade

In the present paper, we have studied the effect of lithium on cAMP levels induced by isoprenaline and norepinephrine in the presence of alpha- or beta-adrenoceptor antagonists. Our results show that low lithium concentrations, starting at 0.3 x 10(-3) M, have a significant inhibitory effect on cAMP content induced by isoprenaline in brain tissue pretreated with the alpha-adrenoceptor blocker phenoxybenzamine. On the other hand, the inhibitory effect of lithium on cAMP levels induced by norepinephrine when beta-adrenoceptors are blocked with propranolol, is observed at concentrations starting at 2.5 x 10(-3) M. These results show that in the presence of alpha blockade, low lithium concentrations which are within the therapeutic plasma range for treatment of manic patients, are able to act on an adenylate cyclase-cAMP system coupled to beta-adrenoceptors.

Effect of chronic lithium treatment on the turnover of α2-adrenoceptors after chemical inactivation in rats

One of the most effective psychotherapeutic agents in the treatment of bipolar disease is lithium. Chronic lithium treatment affects some signal transduction mechanisms such as cAMP, cGMP, inositol 1,4,5 P(3), Gi protein, protein kinase C and can also modify gene expression in rat brain. In a previous study, we observed a greater inhibitory effect of lithium on cAMP production after blockade of alpha(2)-adrenoceptors in rat cerebral cortex. Here we examine the influence of chronic lithium treatment on turnover of alpha(2)-adrenoceptors after their inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) in rat cerebral cortex. After treatment with lithium for 10 days (120 mg/kg/day, i.p.), there was a significant increase in the appearance and disappearance rate constants of these adrenoceptors and a significant reduction of their half-life. These results suggest that chronic lithium administration alters the alpha(2)-adrenoceptor turnover in rat brain.

Caffeine improves attention deficit in neonatal 6-OHDA lesioned rats, an animal model of attention deficit hyperactivity disorder (ADHD)

Nowadays the pharmacological treatment of the attention deficit hyperactivity disorder (ADHD) is based on amphetamine derivatives (i.e. methylphenidate). However, these drugs induce a large array of adverse side effects, thus less aggressive psychostimulant drugs (i.e. caffeine) are being proposed in the management of ADHD. Following this tendency, we decided to study the possible therapeutic use of caffeine in an animal model of ADHD, namely the neonatal 6-hydroxy-dopamine (6-OHDA)-lesioned rat. Therefore, at postnatal day 7 rats were lesioned at the left striatum with 6-OHDA or with saline. Thereafter, at postnatal day 25 their activity and attention were measured with the Olton maze before caffeine was administered ad libitum in the drinking water. Next, after 14 days of caffeine treatment, we repeated these measurements to assess the effect of caffeine on motor activity and attention deficit. Interestingly, while no changes in the motor activity measurements were observed before and after caffeine administration, a significant improvement in the attention deficit of the 6-OHDA lesioned rats was achieved after caffeine treatment. Thus, our results led us to hypothesize that caffeine might be useful to manage the attention deficit during the prepubertal period of ADHD.

Targeting striatal metabotropic glutamate receptor type 5 in Parkinson's disease: bridging molecular studies and clinical trials.

Metabotropic glutamate (mGlu) receptors are G protein-coupled receptors expressed primarily on neurons and glial cells modulating the effects of glutamatergic neurotransmission. The pharmacological manipulation of these receptors has been postulated to be valuable in the management of some neurological disorders. Accordingly, the targeting of mGlu5 receptors as a therapeutic approach for Parkinsons disease (PD) has been proposed, especially to manage the adverse symptoms associated to chronic treatment with classical PD drugs. Thus, the specific pharmacological blocking of mGlu5 receptors constitutes one of the most attractive non-dopaminergic-based strategies for PD management in general and for the L-DOPA-induced dyskinesia (LID) in particular. Overall, we provide here an update of the current state of the art of these mGlu5 receptor-based approaches that are under clinical study as agents devoted to alleviate PD symptoms.

Effect of α2-adrenoceptor blockade on lithium action in the rat brain

The inhibitory effect of different concentrations of lithium (0.15-10 x 10(-3) M) on cAMP production induced by isoprenaline (1 x 10(-4) M) after the blockade of alpha(2)-adrenoceptors in the rat cerebral cortex was investigated. Low lithium concentrations (0.3-0.6 x 10(-3) M) exerted a significant inhibitory effect after yohimbine (1 x 10(-5) M) addition, but had no effect when isoprenaline alone or prazosin (1 x 10(-7) M) was added. The recovery of [3H]yohimbine binding after irreversible inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) was evaluated in cortical membranes to study how alpha(2)-adrenoceptor repopulation affects the action of lithium on the adenylyl cyclase-cAMP system. When the density of alpha(2)-adrenoceptors was lower than 21%, lithium showed a significant inhibitory effect at all concentrations tested. However, at higher densities, increased concentrations of lithium were required to inhibit cAMP production. Our results suggest that the inhibitory effect of lithium on cAMP levels in the rat brain is conditioned by alpha(2D)-adrenoceptors.

Deciphering G Protein-Coupled Receptor Biology with Fluorescence-based Methods

G-protein-coupled receptors (GPCRs) represent the main family of cell surface receptors and are virtually expressed in all eukaryotic cells. Interestingly, a large number of clinically used drugs exert their pharmacological effect via a GPCR, thus it seems crucial to deeply understand the biology of these receptors. The study of GPCR activation and signaling has been classically performed by physiological, biochemical and pharmacological approaches using radioactivity-based tools. However, apart from the potential hazards of radioisotope handling and environmental burden, these approaches have some technical limitations. Therefore, the development of fluorescence-based techniques in general and fluorescence and bioluminescence resonance energy transfer (FRET and BRET) in particular have revolutionized the way to study GPCR functioning both in vitro and in vivo. Indeed, these techniques allow the characterization and visualization of all the individual GPCR signaling steps (i.e. ligand binding, receptor activation, G-protein coupling, G-protein activation, GPCR desensitization) with high temporal and spatial resolution. Here, we review the use and impact of fluorescent-based methodologies on the deciphering of GPCR biology.