Brain iron deficiency changes the stoichiometry of adenosine receptor subtypes in cortico-striatal terminals. Implications for restless legs syndrome

Brain iron deficiency (BID) constitutes a primary pathophysiological mechanism in restless legs syndrome (RLS). BID in rodents has been widely used as an animal model of RLS, since it recapitulates key neurochemical changes reported in RLS patients and shows an RLS-like behavioral phenotype. Previous studies with the BID-rodent model of RLS demonstrated increased sensitivity of cortical pyramidal cells to release glutamate from their striatal nerve terminals driving striatal circuits, a correlative finding of the cortical motor hyperexcitability of RLS patients. It was also found that BID in rodents leads to changes in the adenosinergic system, a downregulation of the inhibitory adenosine A1 receptors (A1Rs) and upregulation of the excitatory adenosine A2A receptors (A2ARs). It was then hypothesized, but not proven, that the BID-induced increased sensitivity of cortico-striatal glutamatergic terminals could be induced by a change in A1R/A2AR stoichiometry in favor of A2ARs. Here, we used a newly developed FACS-based synaptometric analysis to compare the relative abundance on A1Rs and A2ARs in cortico-striatal and thalamo-striatal glutamatergic terminals (labeled with vesicular glutamate transporters VGLUT1 and VGLUT2, respectively) of control and BID rats. It could be demonstrated that BID (determined by measuring transferrin receptor density in the brain) is associated with a selective decrease in the A1R/A2AR ratio in VGLUT1 positive-striatal terminals

Control of glutamate release by complexes of adenosine and cannabinoid receptors

Background It has been hypothesized that heteromers of adenosine A2A receptors (A2AR) and cannabinoid CB1 receptors (CB1R) localized in glutamatergic nerve terminals mediate the integration of adenosine and endocannabinoid signaling involved in the modulation of striatal excitatory neurotransmission. Previous studies have demonstrated the existence of A2AR-CB1R heteromers in artificial cell systems. A dependence of A2AR signaling for the Gi protein-mediated CB1R signaling was described as one of its main biochemical characteristics. However, recent studies have questioned the localization of functionally significant A2AR-CB1R heteromers in striatal glutamatergic terminals. Results Using a peptide-interfering approach combined with biophysical and biochemical techniques in mammalian transfected cells and computational modeling, we could establish a tetrameric quaternary structure of the A2AR-CB1R heterotetramer. This quaternary structure was different to the also tetrameric structure of heteromers of A2AR with adenosine A1 receptors or dopamine D2 receptors, with different heteromeric or homomeric interfaces. The specific quaternary structure of the A2A-CB1R, which depended on intermolecular interactions involving the long C-terminus of the A2AR, determined a significant A2AR and Gs protein-mediated constitutive activation of adenylyl cyclase. Using heteromer-interfering peptides in experiments with striatal glutamatergic terminals, we could then demonstrate the presence of functionally significant A2AR-CB1R heteromers with the same biochemical characteristics of those studied in mammalian transfected cells. First, either an A2AR agonist or an A2AR antagonist allosterically counteracted Gi-mediated CB1R agonist-induced inhibition of depolarization-induced glutamate release. Second, co-application of both an A2AR agonist and an antagonist cancelled each other effects. Finally, a CB1R agonist inhibited glutamate release dependent on a constitutive activation of A2AR by a canonical Gs-Gi antagonistic interaction at the adenylyl cyclase level. Conclusions We demonstrate that the well-established cannabinoid-induced inhibition of striatal glutamate release can mostly be explained by a CB1R-mediated counteraction of the A2AR-mediated constitutive activation of adenylyl cyclase in the A2AR-CB1R heteromer

Adenosine A2A Receptors in the Rat Prelimbic Medial Prefrontal Cortex Control Delay-Based Cost-Benefit Decision Making

Adenosine A2A receptors (A2ARs) were recently described to control synaptic plasticity and network activity in the prefrontal cortex (PFC). We now probed the role of these PFC A2AR by evaluating the behavioral performance (locomotor activity, anxiety-related behavior, cost-benefit decision making and working memory) of rats upon downregulation of A2AR selectively in the prelimbic medial PFC (PLmPFC) via viral small hairpin RNA targeting the A2AR (shA2AR). The most evident alteration observed in shA2AR-treated rats, when compared to sh-control (shCTRL)-treated rats, was a decrease in the choice of the large reward upon an imposed delay of 15 s assessed in a T-maze-based cost-benefit decision-making paradigm, suggestive of impulsive decision making. Spontaneous locomotion in the open field was not altered, suggesting no changes in exploratory behavior. Furthermore, rats treated with shA2AR in the PLmPFC also displayed a tendency for higher anxiety levels in the elevated plus maze (less entries in the open arms), but not in the open field test (time spent in the center was not affected). Finally, working memory performance was not significantly altered, as revealed by the spontaneous alternation in the Y-maze test and the latency to reach the platform in the repeated trial Morris water maze. These findings constitute the first direct demonstration of a role of PFC A2AR in the control of behavior in physiological conditions, showing their major contribution for the control of delay-based cost-benefit decisions

Boosting brain glucose metabolism to fight neurodegeneration?

© The Author(s).Alzheimer’s disease (AD) is the main cause of dementia in the elderly population with increasing prevalence. Despite the huge efforts invested in AD research, no therapeutic breakthrough has been witnessed yet. Likely, novel approaches and sweeping ideas will be necessary to effectively treat AD. Nevertheless, the earlier the disease is detected the more efficacious the therapy is

N-acyldopamines control striatal input terminals via novel ligand-gated cation channels

http://www.sciencedirect.com/science/article/B6T0C-4V3HHM3-1/2/22d594101b6927eca47e1b39b53ffce

Differential glutamate-dependent and glutamate-independent adenosine A1 receptor-mediated modulation of dopamine release in different striatal compartments

Adenosine and dopamine are two important modulators of glutamatergic neurotransmission in the striatum. However, conflicting reports exist about the role of adenosine and adenosine receptors in the modulation of striatal dopamine release. It has been previously suggested that adenosine A1 receptors localized in glutamatergic nerve terminals indirectly modulate dopamine release, by their ability to modulate glutamate release. In the present study, using in vivo microdialysis, we provide evidence for the existence of a significant glutamate-independent tonic modulation of dopamine release in most of the analyzed striatal compartments. In the dorsal, but not in the ventral, part of the shell of the nucleus accumbens (NAc), blockade of A1 receptors by local perfusion with the selective A1 receptor antagonist 8-cyclopentyl-1,3-dimethyl-xanthine or by systemic administration of the non-selective adenosine antagonist caffeine induced a glutamate-dependent release of dopamine. On the contrary, A1 receptor blockade induced a glutamate-independent dopamine release in the core of the NAc and the nucleus caudate2013putamen. Furthermore, using immunocytochemical and functional studies in rat striatal synaptosomes, we demonstrate that a fraction of striatal dopaminergic terminals contains adenosine A1 receptors, which directly inhibit dopamine release independently of glutamatergic transmission

Increase of cannabinoid CB1 receptor density in the hippocampus of streptozotocin-induced diabetic rats

In the hippocampus, impaired neurophysiology, compromised neurogenesis, and eventually apoptosis accompany cognitive deficits in insulinopenic (type-1) diabetes (T1D). The underlying pathological mechanisms remain to be defined. The hippocampus has a high density of the cannabinoid type 1 receptor (CB1R), which has been shown to control several brain functions affected by diabetes, such as synaptic plasticity, glucose utilisation, memory consolidation and cognition, and maturation and survival of hippocampal neurons. However, the role of this receptor has not been investigated yet in diabetic encephalopathy. We report now that in the streptozotocin animal model of T1D, the hippocampal densities of CB1R protein and of specific CB1R binding sites are significantly increased both in the nerve terminals and in total membranes (changes between 13% and 38%), whereas CB1R mRNA expression is decreased by 25%, suggesting that CB1Rs might play a role in diabetic encephalopathy.http://www.sciencedirect.com/science/article/B6WFG-4MSY8KB-1/1/f6aea3c2bf8969bbc4a66f55cda209a

Modification upon aging of the density of presynaptic modulation systems in the hippocampus

Different presynaptic neuromodulation systems have been explored as possible targets to manage neurodegenerative diseases. However, most studies used young adult animals whereas neurodegenerative diseases are prevalent in the elderly. Thus, we now explored by Western blot analysis how the density of different presynaptic markers and receptors changes with aging in rat hippocampal synaptosomes (purified nerve terminals). Compared to synaptosomal membranes from 2-month-old rats, the density of presynaptic proteins (synaptophysin or SNAP-25) decreased at 18-24 months. In parallel, markers of glutamatergic terminals (vGluT1 or vGluT2) and cholinergic terminal markers (vAChT) constantly decreased with aging from 12 to 18 months onwards, whereas the densities of GABAergic (vGAT) only decreased after 24 months. Inhibitory A1 and CB1 receptor density tended to decrease with aging, whereas facilitatory mGluR5 and P2Y1 receptor density was roughly constant and facilitatory A2A receptor density increased at 18-24 months. Thus aging causes an imbalance of excitatory versus inhibitory nerve terminal markers and causes a predominant decrease of inhibitory rather than facilitatory presynaptic modulation systems.http://www.sciencedirect.com/science/article/B6T09-4S02T4M-1/1/e64b5e4577dafc00487393f333c02a4