Subcellular fractions of normal human substantia nigra and caudate nucleus; a study of their morphology and some enzymes including glutamate decarboxylase and choline acetyltransferase

Subcellular fractionation and distribution of cholinergic binding sites in fetal human brain

Conventional subcellular fractionation techniques have been applied to human fetal brain (13-15 weeks gestation) and the fractions have been characterized by assaying for marker enzymes, cholinergic binding sites and electron microscopy. Fractionation of the homogenate resulted in a nuclear pellet (P1), a crude mitochondrial pellet (P2) and a supernatant (S2). Further resolution of the P2 fraction by density gradient centrifugation resulted in two bands at the gradient interfaces and a pellet. The P2 and subsequently the P2B fraction contained intact plasma membrane profiles as judged by the predominance of adenylate cyclase activity and the presence of occluded lactate dehydrogenase which constituted over 70% of the total activity in these fractions. Morphological examination of the gradient fractions revealed that the P2B fraction contains membrane bound structures which resemble synaptosomes prepared from neonatal rat brain. These structures have a granular matrix in which mitochondria and frequently, neurofilaments were observed. Very few synaptic vesicles were present and there was no evidence for post synaptic attachments. The cholinergic markers choline acetyltransferase, acetylcholinesterase and receptor sites defined by quinuclidinyl benzilate and alpha-bungarotoxin binding were enriched in fractions P2 and P2B which contained the bulk of nerve ending particles. This enriched preparation of fetal synaptosomes may be valuable for functional studies on pre-synaptic terminals in developing brain.

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.

Comparative studies of fresh and postmortem isolated rat cortical synaptosomes: morphology, K+ transport, and respiration

Synaptosomal fractions were isolated from rat cerebral cortex immediately and at 1, 2, 3, and 4 h postmortem. The capability to undergo function-dependent configurational changes in relation to ouabain- and protoveratrine-sensitive K+ uptake, and the rate of O2 consumption were compared between fresh and postmortem synaptosomal fractions. Our results suggest that a 2 h postmortem storage at room temperature does not decrease substantially the functional performance of synaptosomes, while longer storage periods interfere with their capacity to maintain intracellular cation levels. The findings appear to be relevant to the use of human autopsy material for the preparation of synaptosomes.

The subcellular fractionation of the bovine caudate nucleus

Two synaptosomal fractions could be obtained from bovine caudate nucleus on sucrose density gradients one of which had a much greater capacity for 'high affinity' choline uptake than the other but comparable amounts of CAT and choline kinase activity. Specific binding of QNB was widely distributed among all the subcellular fractions except the mitochondrial fraction and in quantitative terms by far the greatest amount was in the microsomal fraction. Only the microsomal fraction contained measurable amounts of glycerophosphocholine phosphodiesterase.

Synaptosomes prepared from fresh human cerebral cortex; morphology, respiration and release of transmitter amino acids

Synaptosomes prepared from fresh human cerebral cortex were shown to be morphologically similar to those from other species. On incubation, they took up oxygen at a high and linear rate and accumulated potassium against a concentration gradient. In response to depolarization by raised extracellular K+ or addition of veratrine, they showed increased respiration, lowered tissue potassium, and enhanced release of glutamate, aspartate and GABA. The preparation may be of value for studies of neurological disorders.

The fragility of cerebral lysosomes in multiple sclerosis

The possibility that cerebral lysosomes in the white matter from patients with multiple sclerosis (MS) are more fragile than in normal controls was investigated in tissue obtained at necropsy. In the MS cases no differences were found in results from samples obtained from histologically distinct areas of white matter, i.e. plaque, periplaque and macroscopically normal white matter. However, in comparison to white matter from a group of controls, certain differences were found. Firstly, the cerebral lysosomes in MS white matter appeared to be more fragile than those in the control cases. Secondly, the remaining intact lysosomes in MS cases showed different characteristics from those obtained in control cases. These results, in the light of earlier experiments in rat brain, were interpreted as further evidence of a greater fragility in the cerebral lysosomes from MS cases. The implications of these results in relation to current thinking on the aetiology of MS are discussed.

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.