Acetylcholinesterase stain intensity variation in the rat dentate gyrus: a quantitative description based on digital image analysis

Focal expression of mutated tau in entorhinal cortex neurons of rats impairs spatial working memory

Entorhinal cortex neuropathology begins very early in Alzheimer's disease (AD), a disorder characterized by severe memory disruption. Indeed, loss of entorhinal volume is predictive of AD and two of the hallmark neuroanatomical markers of AD, amyloid plaques and neurofibrillary tangles (NFTs), are particularly prevalent in the entorhinal area of AD-afflicted brains. Gene transfer techniques were used to create a model neurofibrillary tauopathy by injecting a recombinant adeno-associated viral vector with a mutated human tau gene (P301L) into the entorhinal cortex of adult rats. The objective of the present investigation was to determine whether adult onset, spatially restricted tauopathy could be sufficient to reproduce progressive deficits in mnemonic function. Spatial memory on a Y-maze was tested for approximately 3 months post-surgery. Upon completion of behavioral testing the brains were assessed for expression of human tau and evidence of tauopathy. Rats injected with the tau vector became persistently impaired on the task after about 6 weeks of postoperative testing, whereas the control rats injected with a green fluorescent protein vector performed at criterion levels during that period. Histological analysis confirmed the presence of hyperphosphorylated tau and NFTs in the entorhinal cortex and neighboring retrohippocampal areas as well as limited synaptic degeneration of the perforant path. Thus, highly restricted vector-induced tauopathy in retrohippocampal areas is sufficient for producing progressive impairment in mnemonic ability in rats, successfully mimicking a key aspect of tauopathies such as AD.

Alterations in septohippocampal cholinergic neurons resulting from interleukin-2 gene knockout

Interleukin-2 (IL-2) has potent effects on acetylcholine (ACh) release from septohippocampal cholinergic neurons and trophic effects on fetal septal and hippocampal neuronal cultures. Previous work from our lab showed that the absence of endogenous IL-2 leads to impaired hippocampal neurodevelopment and related behaviors. We sought to extend this work by testing the hypotheses that the loss of IL-2 would result in reductions in cholinergic septohippocampal neuron cell number and the density of cholinergic axons found in the hippocampus of IL-2 knockout mice. Stereological cell counting and imaging techniques were used to compare C57BL/6-IL-2(-/-) knockout and C57BL/6-IL-2(+/+) wild-type mice for differences in choline acetyltransferase (ChAT)-positive somata in the medial septum and vertical limb of the diagonal band of Broca (MS/vDB) and acetylcholine esterase (AChE)-labeled cholinergic axons in hippocampal projection fields. IL-2 knockout mice had significantly lower numbers (26%) of MS/vDB ChAT-positive cell bodies than wild-type mice; however, there were no differences in striatal ChAT-positive neurons. Although AChE-positive axon density in CA1, CA3b, the internal, and external blades of the dentate gyrus did not differ between the knockout and wild-type mice, the distance across the granular cell layer of the external blade of the dentate gyrus was reduced significantly in IL-2 knockout mice. Further research is needed to determine whether these outcomes in IL-2 knockout mice may be due to the absence of central and/or peripheral IL-2 during brain development or neurodegeneration secondary to autoimmunity.

Acetylcholinesterase activity and post-lesional plasticity in the hippocampus of young and aged rats

Applying quantitative microscopic histochemistry, the activity of acetylcholinesterase was determined in the various layers of the rat hippocampus at three different levels along the rostrocaudal extent. Two age groups of animals were examined: young adults (two to three months old) and aged subjects (26 months old). Young adults were divided into controls, and animals killed eight and 35 days following bilateral ibotenate lesioning of the medial septum-diagonal band complex. Aged rats were divided into controls and animals 35 days post-lesion. Analysis of variance revealed that the mean acetylcholinesterase activities of the entire hippocampus of individuals were not significantly different between young and aged rats when averaged across controls and 35 days post-lesion. There was a significant decrease of acetylcholinesterase activity (-52%) in young adults eight days post-lesion as compared to controls, but a significant increase (+63%) took place until 35 days post-lesion as compared to eight days post-lesion. Significantly lower activities existed, however, in young (-22%) and aged rats (-18%) 35 days post-lesion as compared to controls. This decrease in mean activity was not age dependent. As acetylcholinesterase is considered to be a good cholinergic indicator in the hippocampus, the results suggest a homotypic collateral sprouting from spared cholinergic afferents following ibotenate lesion of the medial septum-diagonal band complex in young and aged rats. Based on the data obtained, it is reasonable to assume that there was no difference in the post-lesional plasticity of neuronal acetylcholinesterase between young adult and aged rats.

Distribution of acetylcholinesterase in the hippocampal region of the mouse. III. The area dentata

The distribution of acetylcholinesterase (AChE) was examined in the area dentata of the adult mouse (Mus musculus domesticus). A distinctly stratified distribution of the enzyme was observed and was compared in detail with cytoarchitectural fields and layers. In the stratum moleculare, bands of relatively high AChE activity were seen immediately beneath the pia, at the borders between the outer, middle, and deep portions of the stratum moleculare, and superficial to the granule cell layer. AChE activity was low in the intervening parts of the stratum moleculare. In contrast to the rat, three sublaminae could be discerned in the hilus of the mouse at most septotemporal levels: a limiting subzone, a hilar plexiform layer, and a deep hilar cell mass. Deep to the granule cell layer, AChE activity was high in the limiting subzone and, septally, in the hilar plexiform layer. The deep hilar cell mass stained lightly towards the septal pole of the region but darker at more temporal levels. Numerous AChE-stained cells were seen in the hilus, with the exception of the most temporal levels. A comparative analysis of the AChE pattern of the area dentata reveals that 1) AChE-intense supra- and infragranular bands are found in all mammals, whereas 2) considerable difference between various strains of mice and between species are seen in the stratum moleculare. The functional significance of the AChE pattern is discussed in relation to species differences and connectivity and also with respect to possible activities of the enzyme other than hydrolysis of ACh, which may be involved in growth-related functions and in the plastic and degenerative processes observed in Alzheimer's disease.

In situ measurements of enzyme activities in the brain

The present review focuses on enzymes involved in the metabolism of amino acid neurotransmitters and the microphotometric determinations of their activities in various layers of the rat hippocampus. The enzymes are NAD-linked isocitrate dehydrogenase (NAD-ICDH), glutamate dehydrogenase (GDH), and GABA transaminase (GABAT), all of which are localized in mitochondria. GDH seems to be restricted to astrocytes, whereas NAD-ICDH and GABAT are localized in neurons as well as in astrocytes. NAD-ICDH is an important enzyme of the tricarboxylic acid cycle and may deliver alpha-ketoglutarate for the formation of glutamate and GABA, which serve as neurotransmitters in the hippocampus. GDH catalyses the interconversion of alpha-ketoglutarate and glutamate, whereas GABAT is the important GABA-degrading enzyme and requires alpha-ketoglutarate for its activity. While differing in their cellular distribution and activity levels, NAD-ICDH, GDH and GABAT are significantly correlated in their hippocampal distribution. Furthermore, developmental and pharmacohistochemical studies suggest that the distribution and activity of astrocytic GDH is correlated with amino-acidergic neurotransmission in the hippocampus. The data reported give further evidence for a metabolic relationship between neurons and astrocytes in the turnover and metabolism of glutamate and GABA.

Distribution of [3H]QNB and [125I]alpha-bungarotoxin binding and acetylcholinesterase activity in visual system and hippocampal structures of eleven mammalian species

This study assessed interspecies differences in regional brain distribution of [3H]QNB binding, [125I]alpha-bungarotoxin binding and acetylcholinesterase activity, by autoradiographic and histochemical methods. Eleven mammalian species were examined, including carnivores (cat, dog), a lagomorph (rabbit), and rodents (squirrel, guinea pig, gerbil, hamster, vole, lemming, rat, mouse). Comparisons were based on primary visual system structures (superior colliculus, lateral geniculate nucleus, primary visual cortex) and the hippocampal formation. The two radioligands differed greatly in the degree of interspecies variation: while the pattern of [3H]QNB binding was quite similar across species, [125I]alpha-bungarotoxin showed striking interspecies diversity. This contrast was most obvious in laminar patterns of the visual cortex and hippocampal formation. Regional distributions of acetylcholinesterase staining were fairly diverse, and were unlike the patterns of either [3H]QNB or [125I]alpha-bungarotoxin. The two ligands showed more consistency in overall levels across species than did acetylcholinesterase. Possible correlates of the differences in interspecies diversity are discussed.