n(6)-cyclohexyladenosine and Alzheimer-Disease

Adenylyl cyclase (AC) activity was studied in post mortem hippocampus and cerebellum from eight patients with Alzheimer's disease/senile dementia of the Alzheimer type (AD/SDAT) and seven non-demented control patients. AC was stimulated via stimulatory guanine nucleotide binding proteins (Gs) using guanosine triphosphate (GTP) and GppNHp (both 10(-4) M) or directly with either forskolin (10(-4) M) or Mn2+ (10(-2) M). Inhibition of AC via A1-receptors was performed with N6-cyclohexyladenosine (CHA) under basal conditions and in the presence of forskolin (10(-5) M). In both brain regions AC activity was significantly reduced in AD/SDAT when compared to controls. Under basal conditions and after stimulation via Gs mean reduction in hippocampus and cerebellum was 47.7% and 58.2%, respectively. The reduction was less pronounced after direct activation of the AC, amounting to 21.8% in hippocampus and 28.1% in cerebellum. CHA inhibited basal and forskolin-stimulated AC concentration-dependently by about 20% (basal) and 30% (forskolin). Inhibition by CHA was similar in hippocampus and cerebellum and tended to be more pronounced in AD/SDAT than in controls. Since the reduction of AC activity in AD/SDAT is greater after stimulation via Gs than after direct activation of the catalytic subunit, we suggest that both Gs and the catalytic subunit seem to be impaired. The fact that CHA-mediated inhibition of AC is not significantly different in AD/SDAT and controls, indicates that in contrast to Gs-, inhibitory G-proteins (Gi) coupling to AC remains intact in Alzheimer's disease.

Topics: Adenosine; Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Aged; Aged, 80 and over; Alzheimer Disease; Brain; Cerebellum; Colforsin; Enzyme Activation; Female; GTP-Binding Proteins; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Hippocampus; Humans; Male; Manganese; Middle Aged; Neurotransmitter Agents; Purinergic P1 Receptor Antagonists; Signal Transduction

The alterations in Alzheimer's disease (AD) of two binding sites in the striatum suggested to have a presynaptic localisation have been investigated by quantitative ligand binding autoradiography. Adenosine A1 binding sites labelled with [3H]cyclohexyladenosine (CHA) and kappa 1 opioid binding sites labelled with [3H]U-69593 were studied in adjacent sections of the striatum obtained postmortem from 10 patients with AD and 9 matched controls. In AD, there was a significant reduction of [3H]CHA binding sites in the caudate nucleus (control = 88 +/- 4; AD = 56 +/- 6 pmol/g tissue; mean +/- S.E.M.) and putamen (control = 83 +/- 4; AD = 58 +/- 7 pmol/g). In control subjects, highest levels of [3H]U-69593 binding were localised to patches within the caudate nucleus (9.66 +/- 0.58 pmol/g) with lower levels in the matrix (5.54 +/- 0.48 pmol/g). There was no alteration in [3H]U-69593 binding sites in either the caudate nucleus (patches and matrix) or putamen of AD patients. The activity of choline acetyltransferase (ChAT), determined in the same tissue samples used for autoradiographic analysis, was significantly reduced in AD (control = 124 +/- 11; AD = 64 +/- 14 nmol/h/mg protein). There was a positive correlation between ChAT activity and [3H]CHA binding (r = 0.769), but not [3H]U-69593 binding (r = 0.197). The results indicate that a marked loss of adenosine A1 receptors occurs in the striatum of AD with no loss of kappa 1 opioid receptors, and that the loss of A1 receptors parallels the loss of choline acetyltransferase activity.

Topics: Adenosine; Aged; Aged, 80 and over; Alzheimer Disease; Analgesics; Autopsy; Autoradiography; Benzeneacetamides; Caudate Nucleus; Choline O-Acetyltransferase; Corpus Striatum; Female; Humans; Male; Middle Aged; Putamen; Pyrrolidines; Receptors, Opioid, kappa; Receptors, Purinergic; Reference Values; Tritium

Binding to adenosine A1 receptors and the status of their coupling to G proteins were studied in the hippocampus and parahippocampal gyrus of Alzheimer individuals and age-matched controls. The binding to A1 receptors was compared with binding to the N-methyl-D-aspartate receptor complex channel-associated sites (labeled with (+)-[3H]5-methyl-10,11-dihydro-5H- dibenzo[a,d]cyclohepten-5,10-imine maleate). In vitro quantitative autoradiography demonstrated a similar anatomical distribution of A1 receptors labeled either with an agonist ((-)-[3H]phenylisopropyladenosine) or antagonist ([3H]8-cyclopentyl-1,3-dipropylxanthine) in the brains of elderly controls. In Alzheimer patients, significant decreases in the density of both agonist and antagonist binding sites were found in the molecular layer of the dentate gyrus. Decreased A1 agonist binding was also observed in the CA1 stratum oriens and outer layers of the parahippocampal gyrus, while reduced antagonist binding was found in the subiculum and CA3 region. Reduced density of the N-methyl-D-aspartate receptor channel sites was found in the CA1 region and parahippocampal gyrus. The reductions in binding to adenosine A1 and N-methyl-D-aspartate receptors were due to a decrease in the density of binding sites (Bmax), and not changes in receptor affinity (KD). In both elderly control and Alzheimer subjects, GTP substantially reduced the density of A1 agonist binding sites with a concomitant increase in the KD values, whereas antagonist binding was unaffected by GTP. The results suggest that adenosine A1 receptor agonists and antagonists recognize overlapping populations of binding sites. Reduced density of A1 receptors in the molecular layer of the dentate gyrus most probably reflects damage of the perforant path input in Alzheimer's disease, while altered binding in the CA1 and CA3 regions is probably due to loss of intrinsic neurons. Similar effects of GTP on binding to A1 receptors in control and Alzheimer individuals suggest lack of alterations in coupling of A1 receptors to G proteins in Alzheimer's disease, thus supporting the notion of normal receptor coupling to their effector systems in Alzheimer's disease.

Topics: Adenosine; Aged; Aged, 80 and over; Alzheimer Disease; Autoradiography; Dizocilpine Maleate; Female; GTP-Binding Proteins; Hippocampus; Humans; Kinetics; Male; Organ Specificity; Pyramidal Tracts; Receptors, N-Methyl-D-Aspartate; Receptors, Purinergic; Tritium; Xanthines

The cells of origin of the perforant pathway are destroyed in Alzheimer's disease (AD). In rat the adenosine A1-receptors are specifically localized on the perforant path terminals in the molecular layer of the dentate gyrus. In the present study the density of A1-receptors in the hippocampus of Alzheimer's disease (AD) patients (n = 9) and non-dement controls (n = 3) has been investigated autoradiographically with [3H]8-cyclopentyl-1,3-dipropylxanthine ([3H]CPDPX) as the ligand probe. In AD hippocampi binding of [3H]CPDPX was greatly reduced in the outer two thirds of the dentate gyrus molecular layer, likely due to the degeneration of the perforant path. Binding of [3H]CPDPX was not significantly altered in other parts of the AD hippocampus, e.g. the CA1 and the CA3, in spite of a pronounced cellular pathology and reduced N-methyl-D-aspartate (NMDA) receptor densities, assessed as strychnine insensitive [3H]glycine autoradiography. This contrasts with the presumed localization on dendrites of pyramidal neurons of A1 receptors within the CA1 and the CA3.

Topics: Adenosine; Aged; Aged, 80 and over; Alzheimer Disease; Autoradiography; Female; Hippocampus; Humans; Male; Middle Aged; Neural Pathways; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Receptors, Purinergic; Xanthines

Previous studies showed that adenosine receptors of the temporal and frontal cortices were not affected in Alzheimer's disease (AD). Here, we assessed the specific binding of [3H]cyclohexyladenosine to adenosine1 (A1) receptors in hippocampus from AD subjects and age-matched controls. By both particulate membrane and in vitro autoradiographic receptor binding methods we demonstrate that A1 receptors are significantly reduced by 40-60% in AD subjects. Scatchard analysis showed that maximum binding capacity (Bmax) was affected and there was no evidence for a change in the affinity of the receptor for the ligand (Kd). Receptor autoradiography revealed that although several regions including CA1, CA3 and deep layer of the subiculum were affected, the loss in A1 receptors was most prominent in the molecular layer of the dentate gyrus. In view of previous evidence indicating that these receptors are associated with the perforant pathway and dendritic fields of the CA1 and CA3 regions, our findings suggest loss of the presynaptic A1 receptors on axon terminals of extrinsic pathways including the perforant path and intrinsic pyramidal neurons which release glutamate.

Topics: Adenosine; Aged; Aged, 80 and over; Alzheimer Disease; Hippocampus; Humans; Middle Aged; Receptors, Purinergic; Tritium