Acetylcholine synthesis and glucose oxidation are preserved in human brain obtained shortly after death

Characterization of synaptosomal dopamine release in rat and human brain after post-mortem storage and cryopreservation

In preparing pathobiochemical studies on [(3)H]dopamine (DA) release in post-mortem human brain, freezing methods were tested regarding their applicability for cryopreservation of brain tissue. An optimal method was to incubate pieces of the nucleus accumbens of rats or humans in 0.32 M sucrose containing 5% dimethylsulfoxide before freezing the brain material. After cryopreservation of these pieces in liquid nitrogen the synaptosomal K(+)-stimulated [(3)H]DA release was found to be unchanged in comparison with the values obtained before freezing. Moreover, the inhibition of K(+)-stimulated [(3)H]DA release by extracellular DA, which is mediated by DA autoreceptors, was also detectable after using this freezing method. During post-mortem storage of rat brains in situ for up to 48 h it was found that [(3)H]DA release changes occurred in dependence on storage temperature: at 2 degrees C no alteration was noted, however, at 22 degrees C a relatively rapid, biphasic exponential decrease was found. Furthermore, subchronic haloperidol pretreatment of rats did not have any influence on post-mortem changes of [(3)H]DA release and its modulation by DA autoreceptors. In conclusion, it seems that post-mortem human brain is suitable for investigating synaptosomal K(+)-stimulated [(3)H]DA release and its autoreceptor-mediated inhibition. For this end a suitable cryopreservation method is presented and a correction for post-mortem delay is proposed which is based on changes of [(3)H]DA release at 22 degrees C in rats.

Tacrine, a drug with therapeutic potential for dementia: post-mortem biochemical evidence

A review of biochemical findings is presented which support the idea that Alzheimer's disease represents a condition for which tetrahydroaminoacridine (tacrine) may have a beneficial effect. There is evidence that clinical and histopathologic hallmarks of the disease relate to cholinergic and serotonergic dysfunction, with less obvious abnormalities in other neurotransmitters (aspartate, dopamine, gamma-aminobutyrate, glutamate, noradrenaline and somatostatin). Clinically relevant concentrations of tacrine may ameliorate the above presynaptic deficits without producing harmful (neurotoxic) effects of aspartate and glutamate. The disease seems to be associated with an early and clinically relevant degeneration of some neurons with cortical perikarya that release these amino acid transmitters. Studies are now required on the effect of tacrine on postulated harmful peptide-bond hydrolase activity within and around such cells.

A comparison of methodologies for the study of functional transmitter neurochemistry in human brain

A number of different approaches to the study of functional neurochemistry in human brain are discussed. The advantages and disadvantages of three main techniques are contrasted: (i) using animal tissue preparations as models of the human brain; (ii) using human peripheral tissue preparations as models of dynamic CNS processes; and (iii) studying human tissue, obtained postmortem, directly. Animal models are often readily obtained and reliable, and the high degree of inbreeding of common laboratory animals ensures that they usually yield consistent results. However, there are a number of human disorders for which animal models are either poor or unavailable, and species differences make extrapolation from the animal to the human case difficult. Human peripheral tissue models rely on a degree of homology between peripheral and CNS processes; in most cases, the evidence for such homologies derives from animal, rather than human, studies. Moreover, several examples are known where a peripheral process mimics the equivalent glial cell activity more closely than the neuronal, which can be a serious drawback for studies of neurotransmission. The use of postmortem human brain tissue presents a number of obvious difficulties, resulting from variations in the patient's age, agonal state, sex, preterminal medication, postmortem delay, etc. Human beings are genetically and nutritionally heterogeneous, so that data variability is usually greater here than when using tissue from laboratory animals. However, it is possible to control for a number of these factors, for example, by matching samples for basal metabolic rate and tissue integrity, and recently developed tissue freezing and storage techniques permit the use of within-subject experimental designs to help reduce experimental variation. A range of neurotransmitter functions are well retained in such tissue samples, so that regional variations, differential transmitter activities, drug effects, etc., can be studied in normal tissue samples, as well as in samples taken from cases of neurological and psychiatric disease. This allows, for example, changes in neuroanatomical indices to be correlated with localised alterations in a specific neurotransmitter function. A systematic approach to the analysis and matching of tissue samples is advocated. The three approaches should be considered to be complementary, especially for the study of human brain diseases.

Evidence of glutamatergic denervation and possible abnormal metabolism in Alzheimer's disease

Excitatory dicarboxylic amino acids previously have been ascribed several functions in the brain. Here their total concentration and proposed neurochemical markers of neurotransmitter function have been measured in brain from patients with Alzheimer's disease (AD) and controls. Specimens were obtained antemortem (biopsy) approximately 3 years after emergence of symptoms and promptly (less than 3 h) postmortem some 10 years after onset. Early in the disease a slight elevation in aspartic acid concentration of cerebral cortex was observed in the patients with AD. A reduction in glutamic acid concentration of a similar magnitude was found. It is argued that this, together with a decrease in CSF glutamine content and lack of change in the phosphate-activated brain glutaminase activity of tissue, reflects an early metabolic abnormality. Later in the disease evidence of glutamatergic neurone loss is provided by the finding that in many regions of the cerebral cortex the Na+-dependent uptake of D-[3H]aspartic acid was almost always lowest in AD subjects compared with control when assessed by a method designed to minimise artifacts and epiphenomena. Release of endogenous neurotransmitters from human brain tissue postmortem did not appear to have the characteristics of that from human tissue antemortem and rat brain.

Human retinas synthesize and release acetylcholine

Human retinas have the capacity to synthesize and release [3H]acetylcholine ([3H]ACh) after an incubation in [3H]choline ([3H]Ch). Synthesis of [3H]Ch by retinal homogenates was determined using either high-voltage paper electrophoresis (HVPE) or a two-step enzymatic/extraction assay for separating [3H]ACh from [3H]Ch. The enzymatic/extraction assay is shown to be accurate over a wide range of concentrations (10(-6)-10(-12) M). Homogenates of human retina synthesize [3H]ACh from [3H]Ch. We find an approximate Km of 50 microM and a Vmax of about 20 nmol/mg protein/h (at 37 degrees C) for the synthesis of labeled ACh by retinal homogenates. Human retinas also release [3H]ACh after a pulse of [3H]Ch. Release of labeled transmitter is stimulated by potassium depolarization. The potassium-stimulated release is partially blocked by magnesium or cobalt ions. Release data were analyzed by both the enzymatic/extraction assay and HVPE; the results are qualitatively identical in both cases. The data reported here provide additional evidence for cholinergic neurotransmission in the human retina.

Excitatory amino acid-releasing and cholinergic neurones in Alzheimer's disease

Brains of normal controls and patients with primary degenerative dementia were investigated for choline acetyltransferase (ChAT) activity in the frontal, temporal and parietal cortex, hippocampus, amygdala and thalamus. A few patients with Alzheimer's disease were unusual as the cholinergic marker was unaffected, except in the amygdala. Other patients with dementia and undiagnosed neurodegenerative disorder had elevated cortical ChAT activity. The interpretations offered are: (a) the syndrome of dementia and Alzheimer pathologic change precedes significant loss of cortical cholinergic innervation; (b) denervation in dementia can occur early in olfactory areas, exemplified here by the amygdala; (c) dementia is associated with the loss of non-cholinergic structure. An indication of structures involved was given by loss of a marker of excitatory amino acid-releasing neurones.

Changes in the human visual evoked potential caused by the anticholinergic agent hyoscine hydrobromide: comparison with results in Alzheimer's disease

The anticholinergic drug hyoscine hydrobromide produced a slowing of the P2 and N3 components of the flash visual evoked potential (VEP) in young normals but did not affect the pattern reversal VEP. These results, which are similar to those found in Alzheimer's disease, could be explained by an underlying defect of the cholinergic system.

Agonal status affects the metabolic activity of nerve endings isolated from postmortem human brain

Isolated nerve endings (synaptosomes) that show high rates of metabolic activity have been prepared up to 24 h postmortem from the brains of patients who have died suddenly. In contrast, similar preparations from brains of patients dying after a prolonged terminal illness showed little or no respiration. These data suggest that the agonal state of the patient is of major importance when investigating specific defects in neurotransmitter function in cerebral disorders and effects of neuroactive drugs on human tissue.

The evoked release of endogenous amino acids from tissue prisms of human neocortex

The K+-evoked release of 13 amino acids has been determined from tissue prisms of neocortex from patients of various ages, and from rats. Prisms were prepared from various regions of human neocortex obtained at neurosurgery. Upon depolarization aspartate, glutamate and gamma-aminobutyrate (GABA) were shown to be preferentially released. The efflux of glutamate was calcium-dependent. Prisms prepared from human neocortex obtained shortly after death also exhibited preferential K+-induced release of putative amino acid transmitters. Absolute concentrations released into the media were similar to those found for neurosurgical samples. Comparison of the release data for rat and human samples revealed that the efflux of aspartate, glutamate and GABA occurred to a greater extent from rat brain preparations. The K+-evoked release of glutamate from human samples showed a significant linear increase from 12 to 68 years of age.