Correlation of choline acetyltransferase activity between the nucleus basalis of Meynert and the cerebral cortex

Cognitive Correlates of Basal Forebrain Atrophy and Associated Cortical Hypometabolism in Mild Cognitive Impairment

Degeneration of basal forebrain (BF) cholinergic nuclei is associated with cognitive decline, and this effect is believed to be mediated by neuronal dysfunction in the denervated cortical areas. MRI-based measurements of BF atrophy are increasingly being used as in vivo surrogate markers for cholinergic degeneration, but the functional implications of reductions in BF volume are not well understood. We used high-resolution MRI, fluorodeoxyglucose-positron emission tomography (PET), and neuropsychological test data of 132 subjects with mild cognitive impairment (MCI) and 177 cognitively normal controls to determine associations between BF atrophy, cortical hypometabolism, and cognitive deficits. BF atrophy in MCI correlated with both impaired memory function and attentional control deficits, whereas hippocampus volume was more specifically associated with memory deficits. BF atrophy was also associated with widespread cortical hypometabolism, and path analytic models indicated that hypometabolism in domain-specific cortical networks mediated the association between BF volume and cognitive dysfunction. The presence of cortical amyloid pathology, as assessed using AV45-PET, did not significantly interact with the observed associations. These data underline the potential of multimodal imaging markers to study structure-function-cognition relationships in the living human brain and provide important in vivo evidence for an involvement of the human BF in cortical activity and cognitive function.

The cholinergic system in Alzheimer's disease

The past decade has witnessed an enormous increase in our knowledge of the variety and complexity of neuropathological and neurochemical changes in Alzheimer's disease. Although the disease is characterized by multiple deficits of neurotransmitters in the brain, this overview emphasizes the structural and neurochemical localization of the elements of the acetylcholine system (choline acetyltransferase, acetylcholinesterase, and muscarinic and nicotinic acetylcholine receptors) in the non-demented brain and in Alzheimer's disease brain samples. The results demonstrate a great variation in the distribution of acetylcholinesterase, choline acetyltransferase, and the nicotinic and muscarinic acetylcholine receptors in the different brain areas, nuclei and subnuclei. When stratification is present in certain brain regions (olfactory bulb, cortex, hippocampus, etc.), differences can be detected as regards the laminar distribution of the elements of the acetylcholine system. Alzheimer's disease involves a substantial loss of the elements of the cholinergic system. There is evidence that the most affected areas include the cortex, the entorhinal area, the hippocampus, the ventral striatum and the basal part of the forebrain. Other brain areas are less affected. The fact that the acetylcholine system, which plays a significant role in the memory function, is seriously impaired in Alzheimer's disease has accelerated work on the development of new drugs for treatment of the disease of the 20th century.

Neuropharmacological correction of cognitive processes disrupted by extirpation of the AI-AII and Ep fields in cats

An original neuropsychophysiological battery of tests was used to study the possibility of neuropharmacological correction of compensatory-restorative processes in cats after extirpation of a defined zone of the temporal cortex; studies were carried out in conditions of free behavior. In a variety of activation and inhibition regimes, systemic administration of cholinergic, dopaminergic, GABAergic, and serotoninergic agents could have favorable effects on restorative mechanisms, depending on cortical psycho-organic symptoms. Each cognitive activity studied (perception, gnosis, thought) had its own specific positive neuromediator "profile" in terms of compensatory outcomes.

The neurotrophic effects of ebiratide, an analog of ACTH4-9, on cultured septal cells and aged rats

The neurotrophic effects of ebiratide, an ACTH4-9 analog, have been examined using both fetal rat septal cultures and aged rats. The 5-day treatment with ebiratide (10-100 pmol/ml) partially prevented neuronal degeneration that occurred in the cultures in which cells were sparsely plated. Ebiratide (10 pmol/ ml) increased choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities up to 1.5 and 1.2 times the respective control values in the sub-confluent cultures. AChE cytochemistry of the cultures has shown that ebiratide increased the stained area per cell. Ebiratide subcutaneously administered by constant infusion (10 nmol/body/hr) for 4 weeks elevated ChAT activities in the septum (35% over control), neocortex (79%) and hippocampus (89%) of aged rats. Thus, the present study indicates that ebiratide shares neurotrophic properties which may prove beneficial in the therapy for CNS degenerative disorders, especially Alzheimer's disease.

Effects of choline administration on in vivo release and biosynthesis of acetylcholine in the rat striatum as studied by in vivo brain microdialysis

The purpose of the present study is to clarify the effects of the administration of choline on the in vivo release and biosynthesis of acetylcholine (ACh) in the brain. For this purpose, the changes in the extracellular concentration of choline and ACh in the rat striatum following intracerebroventricular administration of choline were determined using brain microdialysis. We also determined changes in the tissue content of choline and ACh. When the striatum was dialyzed with Ringer solution containing 10 microM physostigmine, ACh levels in dialysates rapidly and dose dependently increased following administration of various doses of choline and reached a maximum within 20 min. In contrast, choline levels in dialysates increased after a lag period of 20 min following the administration. When the striatum was dialyzed with physostigmine-free Ringer solution, ACh could not be detected in dialysates both before and even after choline administration. After addition of hemicholinium-3 to the perfusion fluid, the choline-induced increase in ACh levels in dialysates was abolished. Following administration of choline, the tissue content of choline and ACh increased within 20 min. These results suggest that administered choline is rapidly taken up into the intracellular compartment of the cholinergic neurons, where it enhances both the release and the biosynthesis of ACh.

Quantitative assessment of cortical synaptic density in Alzheimer's disease

Significant progress has been made over the last decade in delineating the neuropathological and neurochemical changes in the brains of patients with Alzheimer's disease (AD). Less well studied are the actual synaptic connections of affected areas of the brain, such as the cerebral cortex. Because the final common pathway for neurotransmission involves synaptic integrity, we quantitatively assessed synaptic number and synapse size in lamina III and V of human frontal cortex (Brodmann area 9) in patients with AD and age-matched controls. Samples were also matched for postmortem interval, and artifacts associated with postmortem change were eliminated. We found a significant decrease in synaptic number per unit volume in both lamina, more marked in lamina III (-42%) than V (-29%). In both normal controls and AD brains, there was a negative correlation between synapse number and synapse size as indexed by the length of the postsynaptic density (PSD); cortical samples with fewer synapses had larger synapse size. This appeared to be a compensatory response, rather than a selective loss of small synapses, since the total amount of synaptic contact area per unit volume did not decline in lamina V (despite a 29% loss of synapses); in lamina III it was reduced 11% despite a 42% loss of synapses. The loss of synapses in AD is widespread and significant in frontal cortex; there is observable compensation by enlargement of synaptic size. This compensatory effort is overcome by the continuing loss of synapses in areas most affected by the degeneration.

Regional difference in the kinetics of choline acetyltransferase in brains of neurologically normal elderly people and those with Alzheimer-type dementia

In order to clarify the biochemical changes which occur in the brains of patients suffering from Alzheimer-type dementia (ATD), the kinetics of choline acetyltransferase (ChAT) were measured in 8 or 11 regions of post-mortem brains of 6 patients with non-neurological diseases (control subjects) and 8 patients with ATD. In the control subjects, Michaelis constants (Km) of ChAT for choline were lower in the caudate nucleus and putamen than in other regions examined, whereas Km values for acetyl-CoA in these two regions were higher. Maximal velocities (Vmax) for the control subjects were higher in the caudate nucleus and putamen than in the other regions studied. Km values for choline of ATD patients were higher than those of control subjects in all regions except the amygdala and substantia innominata (innominate); however, Km values for acetyl-CoA of ATD patients were higher than those of control subjects only in the caudate nucleus, putamen and thalamus. Vmax values of ATD patients were lower than those of control subjects in all the regions of brains with ATD. These results suggest that the binding site of ChAT for choline is sensitive to the pathological process of ATD, whereas the binding site for acetyl-CoA is resistant. Based on the presence or absence of variations of Km values, we have classified brain regions into 3 types: highly sensitive, somewhat sensitive or resistant to the pathological process of ATD.

Qualitative and quantitative changes in normal aging and Alzheimer's disease

Qualitative changes in normal aging and Alzheimer's disease (AD) are as important as quantitative changes. Although qualitative changes do not c-vary with quantitative differences in every respect, quantitative changes, nevertheless, often accurately reflect qualitative changes. Moreover, the complementary use of each provides a more detailed characterization of brain changes with aging and AD. The quantitative and qualitative changes of choline acetyltransferase, as well as somatostatin-containing neurons and dendrites, in human cortex are described as examples of this.