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Biomedical subjects

P R Dodd

Publications and source records attributed to P R Dodd.

At least 73 records · Page 4Linked to original sources
PubMed1986

Uptake of gamma-aminobutyric acid and glycine by synaptosomes from postmortem human brain.

Synaptosomes prepared from frozen postmortem human brain accumulated the neurotransmitter gamma-aminobutyric acid (GABA) and the conformationally restricted GABA analogue cis-3-aminocyclohexanecarboxylic acid (ACHC) by a sodium-dependent, temperature-sensitive, high-affinity transport process into an osmotically sensitive compartment. This transport process could be inhibited by GABA analogues (ACHC, 2,4-diaminobutyric acid, nipecotic acid, arecaidine, guvacine) that have been shown in studies on other species to be relatively selective for neuronal rather than glial uptake systems, whereas the glial uptake inhibitor beta-alanine was ineffective. Synaptosomes prepared from frozen post-mortem human medulla and spinal cord, but not cerebral cortex, took up the neurotransmitter glycine by a sodium-dependent high-affinity transport process. The kinetic parameters for the high-affinity uptake of GABA, ACHC, and glycine were Km = 10 +/- 3, 49 +/- 19, and 35 +/- 19 microM; and Vmax = 98 +/- 15, 84 +/- 25, and 5.5 +/- 2.5 nmol/min/100 mg protein, respectively. These results demonstrate the feasibility of using human CNS preparations for studying GABA and glycine uptake, and suggest that such studies may be useful neurochemical markers for transmitter-specific presynaptic terminals in health and disease.

Aged↗
PubMed1985

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.

Adult↗
PubMed1984

Amino acid transport by synaptosomes isolated from post mortem human brain.

Synaptosomes isolated from post mortem human brain release the transmitter amino acids upon depolarisation. Active preparations can be isolated for up to 24 hours post mortem. The amount of depolarisation-induced release of the transmitter amino acids is correlated with the rate of oxygen uptake. Only when this correlation is taken into consideration would it be possible to detect disease-related changes in presynaptic amino-acid transport systems.

Alanine↗
PubMed1984

Release of aspartate and glutamate caused by chloride reduction in synaptosomal incubation media.

Release of the amino acid neurotransmitter candidates aspartate and glutamate from synaptosomes can be stimulated by reduction of [Cl-] in the incubation medium by replacement with the impermeant anions propionate and isethionate. Replacement by the permeant anion Br- is without effect on amino acid release. This release offers a biochemical method of studying the Cl-ion channel in CNS membrane.

Animals↗
PubMed1984

Intralaminar neurochemical distributions in human midtemporal cortex: comparison between Alzheimer's disease and the normal.

The intralaminar distributions of transmitter and nontransmitter enzyme activities and amino acid levels were determined in the midtemporal cortices from normal individuals and established cases of Alzheimer's disease. In the normal, choline acetyltransferase (CAT) and acetylcholinesterase (AChE) activities were relatively high in the outer cortical layers, particularly, for CAT, in the two granular layers (II and IV). Both activities were reduced in Alzheimer's disease at all, although generally most extensively in the outer and middle layers of the grey matter whereas activities were near normal in the white matter. Further, the enzyme distribution patterns of these cholinergic activities were also disrupted in Alzheimer's disease and the activity of CAT throughout the cortex was generally reduced to that found in the white matter. No such differences in distribution were found for two other enzymes, pseudocholinesterase and lactate dehydrogenase. Assessment of the gamma-aminobutyric acid (GABA) system in the normal revealed a much more extensive intralaminar variation in the enzyme, glutamate decarboxylase, compared with the level of GABA itself. In contrast with the cholinergic enzymes, neither the levels nor intralaminar patterns of GABA were altered in Alzheimer's disease. From an analysis of free amino acids at the different cortical levels, the cortical pattern of glutamic acid in the normal was different from that for GABA, aspartic acid, or nontransmitter amino acids such as alanine. Neither of the putative amino acids, glutamate or aspartate, was altered in Alzheimer's disease. These findings demonstrate the relatively selective nature of microchemical changes occurring in the cortex in Alzheimer's disease and suggest that a functional abnormality in cholinergic input to the outer neocortical layers (I-IV) with predominantly receptive and associative functions may be an important feature of the disease.

Acetylcholinesterase↗
PubMed1983

Metabolically active synaptosomes can be prepared from frozen rat and human brain.

Nerve ending particles (synaptosomes) were prepared from pieces of rat and human brain and from brain homogenate that had been frozen and thawed under a variety of conditions. Their purity, as judged by electron microscopy, and performance in terms of a number of metabolic and functional parameters [accumulation of tissue potassium, respiration, release of transmitter amino acids, and the responses on these indices to depolarisation by veratrine (VX)] were compared with those of fresh tissue-derived synaptosomes. It was found that rapid freezing and/or slow thawing severely impaired the subsequent performance of incubated synaptosomes. In contrast, synaptosomes from tissue frozen slowly and thawed rapidly showed relatively good retention of morphology and metabolic performance. It was better to use whole (1-5 g) pieces of tissue than tissue homogenate: the synaptosome fraction from frozen tissue pieces contained 80% of the proportion of identified synaptosomes found in the fresh tissue synaptosome fraction, its respiratory rate was 65%, and its tissue potassium content 70% of that of fresh controls. Moreover, it responded to VX or potassium stimulation by showing increased respiratory rate, decreased tissue potassium, and increased release of neurotransmitter amino acids, to an extent that was comparable to that of fresh tissue fractions. Thus, preparations from frozen rat and human brain were shown to be metabolically and functionally active, and can be used for a variety of neurotransmitter-related studies.

Animals↗
PubMed1982

Use of post-mortem human synaptosomes for studies of metabolism and transmitter amino acid release.

Synaptosomes have been prepared from human brain obtained at autopsies carried out up to 24 h postmortem (p.m.). They showed generally good retention of morphology, as well as accumulation of tissue potassium and linear rates of oxygen uptake. In response to veratrine depolarization they showed increased respiration rate, decreased tissue potassium content and the specific release of transmitter amino acids. Regression analysis indicated that metabolically and functionally active preparations may be obtained up to ca. 25 h p.m. Preparations obtained from patients dying with brain injury were inactive.

Adult↗
PubMed1981

A rapid method for preparing synaptosomes: comparison, with alternative procedures.

A method for the rapid (1-1.5 h) preparation of nerve ending particles (synaptosomes) from rat cerebral cortex is described. The synaptosome fraction has been characterized by quantitative electron microscopy and enzyme distribution studies. By these criteria, the fraction showed a degree of enrichment in synaptic structures which was comparable to that of the standard (4-5 h) preparation, and substantially better than an alternative fast (2-2.5 h) method. On incubation, synaptosomes obtained by the new procedure accumulated a high tissue concentration of potassium and showed a high, linear rate of oxygen uptake. Depolarization by veratrine caused a significant increase in the rate of respiration and in the release of the physiologically active amino acids; glutamate, aspartate and GABA, as well as a significant reduction in tissue potassium. Thus, the new procedure compared favourably with alternative methods as judged by these indices of metabolic and functional performance. The new preparation method has been found to be of value in metabolic studies of synaptosomes prepared from human post-mortem brain.

Amino Acids↗
PubMed1981

Degradation of luteinizing hormone-releasing hormone by serum and plasma in vitro.

Luteinizing hormone-releasing hormone (LH-RH) is degraded in vitro by serum and plasma from several species (human, rat, guinea-pig and cattle). Separation of the degradation products by high-performance liquid chromatography (HPLC) followed by amino acid analysis and radioimmunoassay showed that the main sites of cleavage are the Trp3-Ser4 and Tyr5-Gly6 bonds. Two peptidases are responsible since the cleavage at Trp3-Ser4 can be selectively inhibited by EDTA. In human plasma, the peptidase responsible for Trp3-Ser4 hydrolysis has a Km of 2.9 . 10(-4) M and V of 30 nmol/h per ml plasma. The half-life in vitro of LH-RH in serum and plasma from various species ranges from 3 h (guinea-pig) to 9.8 h (human). The peptidase cleaving LH-RH at Tyr5-Gly6 is present as an impurity in some commercial bovine serum and plasma albumins. Such contamination may have important practical implications for work involving peptide assays where albumins are used as carrier proteins.

Amino Acids↗
PubMed1980

Release of amino acids from chronic epileptic and subepileptic foci in vivo.

Perforated discs of cobalt or nickel were implanted onto the sensorimotor strip of the cerebral cortex of rats. Co discs gave rise to myoclonic contralateral limb-jerks in a manner similar to Co powder lesions. In contrast, Ni-implanted animals were never observed to show overt limb-jerks. On superfusion with an in vivo cannula system, both types of lesion released increased amounts of glutamate, valine and glycine as compared with unlesioned tissue. However, the enhancement of release from epileptogenic Co lesions was approximately 3-fold greater than that from non-epileptogenic lesions. In addition, epileptogenic lesions showed a marked reduction in glutamine release compared to controls, while non-epileptogenic lesions did not. The possible involvement of local disorders of the glutamate/glutamine system in the generation of cobalt focus hyperactivity is discussed.

Amino Acids↗
PubMed1979

Peripheral sensory stimulation and the release of transmitter amino acids in vivo from specific regions of cerebral cortex.

The effects of sensory stimulation on the release of amino acids from sensorimotor and visual cortex have been studied using a superfusion technique. Electrical stimulation of the brachial plexus contralateral to the superfusion cannula increased significantly the release of glutamate and glutamine from the sensorimotor cortex of anaesthetized rats. No clear effect was observed with the other amino acids. Stimulation of the ipsilateral plexus had no effect on glutamate and glutamine release. In unanaesthetized animals stimulation of the contralateral brachial plexus raised the levels of all the amino acids in sensorimotor cortex superfusate. Weak photic stimulation of the eyes of dark-adapted rats increased glutamate release from the visual cortex but caused no significant change in the release of other amino acids. All evoked increases in amino acids release were reversible at the cessation of the stimuli.

Amino Acids↗
PubMed1979

Metabolic and secretory processes in nerve-endings isolated from post-mortem brain.

Isolated nerve ending particles (synaptosomes) prepared from rat and human cerebral cortex, after varying conditions of post-mortem storage were shown to possess good structural and morphological integrity and metabolic activity. Respiration, potassium retention, lactate dehydrogenase content, and stimulus-induced release of transmitter candidate amino acids, as well as the neuropeptide somatostatin, were measured. These preparations from post-mortem material showed properties which were closely comparable with similar preparations from fresh material. The relevance of these findings to studies on human post-mortem material is discussed.

Aged↗
PubMed1976

Release of amino acids from the maturing cobalt-induced epileptic focus.

A study was made of the release of excitatory, inhibitory and other amino acids from epileptic foci induced in the sensorimotor cortex of rats by cobalt implantation. A new in vivo superfusion method was employed which gives free movement to the animals and allows study over periods of days and weeks. Most amino acids showed maximum release rates during the first 2 or 3 days after surgery. Glutamate showed maximum release rates during days 3-6 when epileptic limb jerks were at a maximum. This pattern was not seen for other physiologically active amino acids.

Amino Acids↗