Separation of catecholamine storing synaptosomes in colloidal silica density gradients

The Study of Postmortem Human Synaptosomes for Understanding Alzheimer's Disease and Other Neurological Disorders: A Review

Synaptic dysfunction is thought to play important roles in the pathophysiology of many neurological diseases, including Alzheimer’s disease, Parkinson’s disease, and schizophrenia. Over the past few decades, there have been systematic efforts to collect postmortem brain tissues via autopsies, leading to the establishment of dozens of human brain banks around the world. From cryopreserved human brain tissues, it is possible to isolate detached-and-resealed synaptic terminals termed synaptosomes, which remain metabolically and enzymatically active. Synaptosomes have become important model systems for studying human synaptic functions, being much more accessible than ex vivo brain slices or primary neuronal cultures. Here we review recent advances in the establishment of human brain banks, the isolation of synaptosomes, their biological activities, and various analytical techniques for investigating their biochemical and ultrastructural properties. There are unique insights to be gained by directly examining human synaptosomes, which cannot be substituted by animal models. We will also discuss how human synaptosome research has contributed to better understanding of neurological disorders, especially Alzheimer’s disease.

Thirty years of synaptosome research

Detached synapses (synaptosomes), first isolated by the author in 1958 and identified as such in 1960, are sealed presynaptic nerve terminals often with a portion of the target cell--sometimes amounting to a complete dendritic spine--adhering to their external surface. They can be prepared in high yield from brain tissue and also in decreasing yield from spinal cord, retina, sympathetic ganglia, myenteric plexus and electric organs. They are sealed structures which, under metabolizing conditions, respire, take up oxygen and glucose, extrude Na+, accumulate K+, maintain a normal membrane potential and, on depolarization, release transmitter in a Ca(2+)-dependent manner. They thus provide an excellent preparation with which to investigate synaptic function without the complications encountered with synapses in situ. They also serve as the parent fraction for preparations of synaptic vesicles and other synaptic components.

Rapid preparation of synaptosomes from mammalian brain using nontoxic isoosmotic gradient material (Percoll)

A new procedure is described for the isolation of synaptosomes from various parts of mammalian brain. This method utilizes an isoosmotic Percoll/sucrose discontinuous gradient and has some advantages over the traditionally used synaptosomal isolation techniques: (1) it is possible to prepare suitable gradients while retaining isoosmolarity; (2) the time of the preparation is remarkably short (approximately 1 h); (3) if necessary, the gradient material can be easily removed from the samples. Intact synaptosomes were recovered from the 10%/16% (vol/vol) Percoll interphase. The fractions were identified and characterized by electron microscopy and by several biochemical markers for synaptosomes and other subcellular organelles. The homogeneity of the preparations is comparable to or better than that of synaptosomes prepared by the conventional methods. This procedure has been successfully used for the isolation of synaptosomes from very small tissue samples of various experimental animals and human brain.

Role of brain lysosomes in the development of manganese toxicity in mice

To study the mechanism of development of manganese toxicity, the manganese content in blood, brain, liver, and subcellular fractions of brain was measured at several intervals following ip injection of a single dose of manganese (245 mg Mn(CH3COO)2 X 4H2O/kg body wt) in mice. The ultrastructural alterations in neurons were correlated with the data for manganese content. Peak concentrations of manganese in blood and liver occurred and disappeared in less than 24 hr. In brain, however, manganese concentration was maintained for 4 days and decreased very little during the 10-day postdose interval studied. Most of the absorbed manganese in brain was recovered in mitochondria and lysosome-rich fractions separated by density gradient centrifugation. Lysosomes took up manganese to a greater extent than mitochondria when compared to controls. Electron microscopy revealed that by 24-hr postdose the number of lysosomes in neurons increased in corpus striatum and midbrain in mice given manganese by ip injection. These results suggested that brain lysosomes play an important role in the cellular metabolism of manganese and in the development of manganese toxicity.

Isolation of synaptic junction-enriched fraction from the forebrain of day-old chickens. Preparation and characterization of chick forebrain subcellular fractions

Synaptosomal plasma membrane (SPM) and other subcellular fractions were isolated from the forebrain of 1-day-old chickens by a procedure based on that of Davis and Bloom (16) and Cotman and Taylor (13). The procedure involves the centrifugation through a discontinuous sucrose gradient of a crude synaptosomal-mitochondrial fraction which has been lysed and weighed with iodonitrotetrazolium. SPM isolated by this method contains only small amounts of lysosomal or mitochondrial membranes and is practically devoid of contaminating microsomal membranes, as estimated by enzyme marker assays. The purity of chick-brain SPM prepared by this method is compared to the purity of chick-brain fractions obtained by two other laboratories, using different methods (4, 59). The SPM were extracted with Triton X-100 and all fractions solubilized in sodium dodecyl sulfate (sds). The delipidated proteins of all fractions were subjected to SDS-polyacrylamide electrophoresis on slab gels and stained for protein. A distinct difference was observed between the patterns given by the Triton-soluble and -insoluble fractions. Electron microscopy of the synaptic junction fraction showed numerous junctional complexes.

Some physical properties of adrenal medulla chromaffin granules isolated by a new continuous iso-osmotic density gradient method

Centrifugation of crude preparations of chromaffin granules on iso-osmotic continuous gradients of sucrose and metrizamide produce granule fractions of high purity without pelleting. These granules have a buoyant density of 1.123 at 300 mosM, which increases to 1.222 at 1800 mosM. Exchange of water for 2H2O greatly increases the density of the granules. An apparent water space for the granules can be calculated from the difference in density in 2H2O and water. The water space of 0.63 at 300 mosM diminishes as the osmolality of the suspension medium is increased, suggesting that the granule membrane is a good osmometer and that the core contains a large osmotically active water space. Other separation methods for chromaffin granules are discussed in terms of these results.