Altered phosphorylation but no neurodegeneration in a mouse model of tau hyperphosphorylation.

The role of hyperphosphorylation of tau in Alzheimer's disease is still unsolved. Here we describe a novel transgenic mouse model, expressing a pseudohyperphosphorylated (PHP) variant of the longest human CNS tau isoform in forebrain neurons. We report that pseudohyperphosphorylation decreases phosphorylation at T205 while other sites (T212, S262) are less or not affected compared to mice expressing wildtype tau. Despite the differences in phosphorylation, the subcellular distribution of tau is not affected and mice do not develop highly aggregated states of tau. PHP tau expressing mice do not show any evidence for neurodegeneration as determined from morphometric measurements of neocortical regions, caspase activation, analysis of mitochondrial dysfunction, or determination of spine densities. In agreement, no differences in learning and memory are observed. The data indicates that moderate levels of modified tau alone are not sufficient to induce tau aggregation or neurodegeneration in transgenic mice. With our model it becomes possible to study the effects of hyperphosphorylation at conditions which may prevail in an early preaggregation state of the disease.

Ontogeny of calmodulin gene expression in rat brain.

Calmodulin (CaM), a multifunctional intracellular calcium receptor, is a key element in signaling mechanisms. It is encoded in vertebrates by multiple apparently redundant genes (CaM I, II, III). To investigate whether differential expression takes place in the developing rat brain, a quantitative in situ hybridization analysis was carried out involving 15 brain areas at six ages between embryonic day 19 and postnatal day 20 (PD20) with gene-specific [(35)S]cRNA probes. A widespread, developmental stage-specific and differential expression of the three CaM genes was observed. The characteristic changes in the CaM mRNA levels in the examined time frame allowed the brain regions to be classified into three categories. For the majority of the areas (e.g. the piriform cortex for CaM III), the signal intensities peaked at around PD10 and the expression profile was symmetric (type 1). Other regions (e.g. the cerebral cortex, layer 1 for CaM II) displayed their highest signal intensities at the earliest age measured, followed by a gradual decrease (type 2). The signal intensities in the regions in the third group (e.g. the hypothalamus for CaM III) fluctuated from age to age (type 3). Marked CaM mRNA levels were measured for each transcript corresponding to the three CaM genes in the molecular layers of the cerebral and cerebellar cortici and hippocampus, suggesting their dendritic translocation. The highest signal intensity was measured for CaM II mRNA, followed by those for CaM III and CaM I mRNAs on PD1. However, the CaM II and CaM III mRNAs subsequently decreased steeply, while the CaM I mRNAs were readily detected even on PD20. Our results suggest that during development (1) the transcription of the CaM genes is under differential, area-specific control, and (2) a large population of CaM mRNAs is targeted to the dendritic compartment in a gene-specific manner.

Slide-binding characterization and autoradiographic localization of delta opioid receptors in rat and mouse brains with the tetrapeptide antagonist [3H]TIPP.

Slide-binding and autoradiographic studies were performed on cryostat sections from brains of adult Sprague-Dawley rats and BALB C mice to describe the binding characteristics of the tetrapeptide [3H]TIPP, an antagonist with high specificity and affinity for the delta opioid receptors. Steady-state binding of [3H]TIPP to cryostat sections of brain paste was reached in 120-180 min of incubation. Specific [3H]TIPP binding resulted in maximal numbers of binding sites (Bmax) of 15.59 and 23.91 fmol/mg protein, and dissociation constants (Kd) of 0.46 and 0.85 nM for rat and mouse brain paste sections, respectively. TIPP displayed the highest affinity for delta opioid receptors in inhibiting specific [3H]TIPP binding, with IC50 values of 0.82 nM and 0.14 nM in rat and mouse brain sections, respectively. While DPDPE was also effective in displacing the specific binding of [3H]TIPP (IC50 = 3.18 +/- 0.53 nM and 0.63 +/- 0.42 nM in rat and mouse brain paste sections, respectively), other subclass-selective or nonopioid ligands were much less effective, or ineffective. Autoradiographic localization of [3H]TIPP binding revealed the characteristic distribution of delta opioid receptors in both species. In consequence of its antagonistic nature, and of its unnatural amino acid residue, which makes this ligand more resistant to biodegradation, [3H]TIPP is a superior ligand for evaluation of the binding characteristics and autoradiogaphic distribution of the delta opioid receptors.