Immunostaining of adenosine receptors in the hippocampus and cerebral cortex from necropsies of Alzheimer's disease (AD) patients shows that there is a change in the pattern of expression and a redistribution of receptors in these brain areas when compared with samples from controls. Adenosine A1 receptor (A1R) immunoreactivity was found in degenerating neurons with neurofibrillary tangles and in dystrophic neurites of senile plaques. A high degree of colocalization for A1R and pA4 amyloid in senile plaques and for A1R and tau in neurons with tau deposition, but without tangles, was seen. Additionally, adenosine A2A receptors, located mainly in striatal neurons in controls, appeared in glial cells in the hippocampus and cerebral cortex of patients. On comparing similar samples from controls and patients, no significant change was evident for metabotropic glutamate receptors. In the human neuroblastoma SH‐SY5Y cell line, agonists for A1R led to a dose‐dependent increase in the production of soluble forms of amyloid precursor protein in a process mediated by PKC. A1R agonist induced p21 Ras activation and ERK1/2 phosphorylation. Furthermore, activation of A1R led to and ERK‐dependent increase of tau phosphorylation and translocation towards the cytoskeleton. These results indicate that adenosine receptors are potential targets for AD.

Recently, evidence has emerged that seven transmembrane G protein-coupled receptors may be present as homo-and heteromers in the plasma membrane. Here we describe a new molecular and functional interaction between two functionally unrelated types of G proteincoupled receptors, namely the metabotropic glutamate type 1␣ (mGlu 1␣ receptor) and the adenosine A1 receptors in cerebellum, primary cortical neurons, and heterologous transfected cells. Co-immunoprecipitation experiments showed a close and subtype-specific interaction between mGlu 1␣ and A1 receptors in both rat cerebellar synaptosomes and co-transfected HEK-293 cells. By using transiently transfected HEK-293 cells a synergy between mGlu 1␣ and A1 receptors in receptorevoked [Ca 2؉ ] i signaling has been shown. In primary cultures of cortical neurons we observed a high degree of co-localization of the two receptors, and excitotoxicity experiments in these cultures also indicate that mGlu 1␣ and A1 receptors are functionally related. Our results provide a molecular basis for adenosine/glutamate receptors cross-talk and open new perspectives for the development of novel agents to treat neuropsychiatric disorders in which abnormal glutamatergic neurotransmission is involved.Glutamate is the major excitatory neurotransmitter in the central nervous system (1), and its function through ionotropic and metabotropic (mGlu) 1 glutamate receptors can be modulated by other neurotransmitters/neuromodulators (2). Eight members of the mGlu receptor family have been identified and categorized into three subgroups on the basis of their sequence homology, agonist selectivity, and signal transduction pathway. Group I contains mGlu 1 and mGlu 5 subtypes, which are coupled to phospholipase C in transfected cells, and have quisqualic acid as their most potent agonist. Five splice variants of mGlu1 receptor have been described, mGlu 1␣ , mGlu 1␤ , mGlu 1c , mGlu 1d , and mGlu 1e receptors (3, 4), all of them differing in the length of their C-terminal tail. The functional significance of the different splice variants has not yet been fully explored. It has been suggested that the C-terminal tail, which is intracellular, might play a role in the subcellular targeting of the receptor (5). Recently, we have reported that the C terminus of mGlu 1␣ receptor interacts with tubulin (6) and that it can regulate the cell surface expression of the receptor (7) and its plasma membrane anchoring (8, 9).Adenosine is an important neuromodulator implicated in a variety of brain activities, particularly those related to sleep and ischemic-hypoxic episodes (10). This ubiquitous nucleoside exerts its actions via specific receptors, four of which (A1, A2A, A2B, and A3) have been cloned (11). The A1R is functionally coupled to members of the pertussis toxin-sensitive family of G proteins (G i1 , G i2 , G i3 , and G o ), and its activation regulates several membrane and intracellular proteins such as adenylate cyclase, Ca 2ϩ channels, K ϩ channels, and phospholipase C (11). Of the multiple neurophys...

The absence of adenosine A 2A receptors, or its pharmacological inhibition, has neuroprotective effects. Experimental data suggest that glial A 2A receptors participate in neurodegeneration induced by A 2A receptor stimulation. In this study we have investigated the effects of A 2A receptor stimulation on control and activated glial cells. Mouse cortical mixed glial cultures (75% astrocytes, 25% microglia) were treated with the A 2A receptor agonist CGS21680 alone or in combination with lipopolysaccharide (LPS). CGS21680 potentiated lipopolysaccharide-induced NO release and NO synthase-II expression in a time-and concentration-dependent manner. CGS21680 potentiation of lipopolysaccharide-induced NO release was suppressed by the A 2A receptor antagonist ZM-241385 and did not occur on mixed glial cultures from A 2A receptor-deficient mice. In mixed glial cultures treated with LPS + CGS21680, the NO synthase-II inhibitor 1400W abolished NO production, and NO synthase-II immunoreactivity was observed only in microglia. Binding experiments demonstrated the presence of A 2A receptors on microglial but not on astroglial cultures. However, the presence of astrocytes was necessary for CGS21680 potentiating effect. In light of the reported neurotoxicity of microglial NO synthase-II and the neuroprotection of A 2A receptor inhibition, these data suggest that attenuation of microglial NO production could contribute to the neuroprotection afforded by A 2A receptor antagonists.

Gene expression throughout the different stages of Alzheimer's disease was analysed in samples from cerebral cortex. The gene encoding the voltage-gated potassium channel Kv3.4 was already overexpressed in early stages of the disease, and in advanced stages Kv3.4 was present at high levels in neurodegenerative structures. This subunit regulates delayed-rectifier currents, which are primary determinants of spike repolarization in neurones. In unique samples from a patient with Alzheimer's disease whose amount of amyloid plaques was decreased by b amyloid immunization, Kv3.4 was overexpressed. The channel subunit was expressed in the neuropil, in the remaining conventional plaques in the frontal cortex and in collapsed plaques in the orbitary cortex.Therefore, amyloid deposition in plaques does not seem to be responsible for the increase in Kv3.4 levels. Nevertheless, Kv3.4 up-regulation is related to amyloid pathology, given that transgenic mice with the Swedish mutation of amyloid precursor protein showed increased expression of Kv3.4. Upregulation of voltage-gated potassium channel subunits alters potassium currents in neurones and leads to altered synaptic activity that may underlie the neurodegeneration observed in Alzheimer's disease. Thus, Kv3.4 likely represents a novel therapeutic target for the disease. Keywords: amyloid plaques, degenerative disease, genomics, neurofibrillary tangles, spike currents. Alzheimer's disease (AD) is the most prevalent age-related neurodegenerative disorder leading to dementia. It affects approximately 10% of the population older than 65 years of age and its prevalence steeply increases after 80. AD is characterized by progressive dementia, declining cognitive function and loss of memory. The aetiology and pathogenesis of AD seem complex, involving both genetic and epigenetic factors. Brains of AD patients are characterized by cortical atrophy, prominent cortical neurone loss, the presence of senile plaques resulting from extracellular accumulation of amyloid b peptide (Ab) derived from the amyloid precursor protein (APP), and the presence of intracellular neurofibrillary tangles (NFT), which are aggregates of abnormally hyperphosphorylated tau proteins in paired helical filaments Address correspondence and reprint requests to Rafael Franco, Department of Biochemistry and Molecular Biology, University of Barcelona, Marti Franques 1, 08028 Barcelona, Spain. E-mail: rfranco@ub.edu 1 These authors contributed equally to this study.Abbreviations used: Ab, amyloid b peptide; AD, Alzheimer's disease; APP, amyloid precursor protein; CKId, casein kinase I d; eNOS, endothelial nitric oxide synthase; HKG, housekeeping gene; NFT, neurofibrillary tangles; PP2B, serine/threonine protein phosphatase 2B; RT-PCR, reverse transcription-polymerase chain reaction.