Impaired phosphorylation of cyclic AMP response element binding protein in the hippocampus of dementia of the Alzheimer type

Cyclic AMP (cAMP) is disrupted in the brain in dementia of the Alzheimer type (DAT). We investigated whether the cAMP reduction is accompanied by an alteration in the cAMP response element binding protein (CREB) downstream in DAT and control hippocampi. Immunoreactivity of pCREB was significantly decreased in DAT, while total CREB level was unchanged. These findings indicate that impaired cAMP signaling may contribute to the pathophysiology of the disease.     

Systemic amyloid deposition in old age and dementia of Alzheimer type: the relationship of brain amyloid to other amyloid

Summary We investigated amyloid deposition in the brain and other organs in 105 consecutive autopsy cases, aged 59 to 101 years. They consisted of two groups; 15 patients with dementia of Alzheimer type (DAT) and 90 patients without DAT. Amyloid deposition was found in 93% of all cases. The incidence of amyloid deposition increased with age. The number of organs affected with amyloid deposition in each case also increased with age. The incidence of amyloid deposition in each organ was as follows; 88% in pituitary gland, 66% in brain [amyloid of senile plaque (SP) (61%) and/or cerebral amyloid angiopathy (CAA) (56%)], 33% in pancreas, 3% in heart, and less in others. In immunohistochemical studies using the antisera to the various kinds of amyloid or related proteins, amyloid protein was demonstrated in brain amyloids including SP and CAA, but not in others. Cardiac amyloid was positive for prealbumin. Pituitary amyloid and CAA were positive for amyloid P-component. The incidence of brain amyloids in DAT were significantly higher than that in non-DAT. There was no significant difference in the incidence of pituitary and pancreatic amyloid between DAT and non-DAT. In the non-DAT patients, there were significant positive correlations in amyloid deposition between the brain and pituitary gland and between the brain and pancreas. Acceleration of amyloid deposition would be a process confined to the brain in the patients with DAT. The pathogenesis of the accelerated deposition of brain amyloids is discussed from the point of view of amyloidosis.Supported in part by the Research Committee on Primary Amyloidosis, Ministry of Health and Welfare, Japan     

Influence of vitamin B12 on brain methionine adenosyltransferase activity in senile dementia of the Alzheimer's type

Summary The influence of vitamin B₁₂ on the activity of methionine adenosyltransferase (MAT) in postmortem brains of patients with senile dementia of the Alzheimer's type (SDAT) was investigated. In samples of cortex gyrus frontalis from SDAT patients with normal and low levels of serum B₁₂, MAT V_max was significantly increased by 25% and 19%, respectively. MAT V_max from a SDAT group chronically treated with B₁₂ was similar to controls. In contrast to cortex gyrus frontalis, no significant alterations were seen in MAT activity in nucleus caudatus. This study provides evidence that SDAT is associated with significant alterations in transmethylation mechanisms in specific regions of the brain. The relationship between blood levels of B₁₂ and the actual status of this vitamin in the brain influencing the rates of synthesis of both methionine and SAM may, however, be far more complex and cannot be directly clarified on the basis of the present human brain results.     

Senile dementia of the neurofibrillary tangle type (tangle‐only dementia): Neuropathological criteria and clinical guidelines for diagnosis*

Senile dementia of the NFT type (SD‐NFT) is a subset of dementia in the elderly, characterized by numerous NFT in the hippocampal region and absence or scarcity of senile plaques throughout the brain. Senile dementia‐NFT has also been referred to as tangle‐only dementia, NFT‐predominant form of SD, SD with tangles, or limbic NFT dementia. Herein are proposed the criteria for neuropathological diagnosis of SD‐NFT: (i) late‐onset dementia with abundant NFT in the hippocampal region and absence or scarcity of senile plaques (amyloid β protein deposits) throughout the brain; and (ii) exclusion of other dementias with NFT. Some elderly individuals suffering from memory disorder without obvious dementia have neuropathological findings similar to SD‐NFT, and they would represent a condition in the process of formation of the SD‐NFT pathology. Guidelines for the clinical diagnosis of SD‐NFT are also proposed; development of reliable diagnostic tests is necessary to differentiate AD and other neurodegenerative dementias from SD‐NFT.     

Changes in pyruvate dehydrogenase complex (PDHc) activity and [3H]QNB-receptor binding in rat brain subsequent to intracerebroventricular injection of bromopyruvate

Summary Pyruvate dehydrogenase complex (PDHc), a link between carbohydrate and acetylcholine metabolism, is a regulatory enzyme for glucose and neurotransmitter metabolism in the brain and is reduced in Alzheimer-diseased brain. To study functional consequences of an inhibition of PDHc on muscarinic receptor binding, bromopyruvate, a suicide inhibitor of PDHc, was injected intracerebroventricularly (icv) in rats. Bromopyruvate caused a reduction of PDHc activity in the 3 brain regions examined, however, reaching significance only in the cerebral cortex and the hippocampus and not in the striatum, 24h after injection. 3, 6, and 12 weeks later, there was a normalization or transiently increased activity, respectively, of PDHc in these brain regions. No changes in concentrations of energy-rich phosphates could be demonstrated in the cerebral cortex 12 weeks after brompyruvate injection. The number of muscarinic receptors was significantly reduced in the cerebral cortex 12 weeks after injection. the data indicate that a transient reduction of brain PDHc activity in vivo is associated with a long-lasting reduction in muscarinic cholinergic receptors. Because comparable changes of PDHc and muscarinic receptors are found in dementia of Alzheimer type, the model of bromopyruvate inhibition of PDHc in rats is suggested to be useful for experimental dementia research.     

Low affinity binding of the classical D1 antagonist SCH23390 in rodent brain: potential interaction with A2A and D2-like receptors

Whereas structurally dissimilar D(1) antagonists competing for [(3)H]-SCH23390 binding recognize primarily one site in striatum, two distinct affinity states are observed in both amygdala and hippocampus. The binding profile of SCH23390 is similar in both of these regions, with the high affinity site (K(D) approximately 0.4 nM) consistent with D(1)/D(5) receptors. The appearance of the low affinity site (K(D) approximately 300 nM) is dependent upon the absence of MgCl(2), but independent of D(1) expression (i.e., still present in D(1) knockout mice). Although the density of high affinity state receptor is lower in hippocampus or amygdala of D(1) knockout mice, some residual binding remains, consistent with the known expression of D(5) receptors in these regions. Remarkably, in hippocampus, the affinity of the low affinity site is shifted rightward in the presence of the D(2) antagonist domperidone and is largely absent in the hippocampus of D(2) knockout animals. Additionally, this site is also shifted rightward in the presence of the A(2A) ligands SCH58261, CSC, or NECA, or in the absence of A(2A) receptors. The affinity of SCH23390 for this low affinity site is greater than seen for SCH23390 binding to D(2) receptors in heterologous expression systems, consistent with the hypothesis that both D(2) and A(2A) receptors are involved in the low affinity binding site. Therefore, we suggest that the heteromerization of D(2) and A(2A) receptors reported previously in vitro also may occur in the brain of both rats and mice.