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Biomedical subjects

P Buma

Publications and source records attributed to P Buma.

100 records · Page 6Linked to original sources
PubMed1986

Ultrastructural demonstration of nonsynaptic release sites in the central nervous system of the snail Lymnaea stagnalis, the insect Periplaneta americana, and the rat.

Release of neuronal secretory products by exocytosis was studied ultrastructurally in the central nervous systems of three different species (the snail Lymnaea stagnalis, the cockroach Periplaneta americana and the rat). Tissues were fixed with: (1) a mixture of glutaraldehyde and osmium tetroxide, (2) the tannic acid-glutaraldehyde-osmium tetroxide (TAGO) method, and (3) the tannic acid-Ringer incubation (TARI) method. Especially after TARI-treatment, release of the contents of the secretory vesicles by exocytosis could be clearly demonstrated in: (1) synapses, (2) neurohaemal axon terminals (L. stagnalis), and (3) neuronal processes without morphological synaptic specializations (nonsynaptic release sites). Release from nonsynaptic release sites occurs in most cases over a large area of the plasma membrane of a neuronal process facing several neural elements. On the basis of the differences in morphology of the secretory vesicles at nonsynaptic release sites, it is proposed that various types of (peptidic) messenger are released from such sites. In some neurones of L. stagnalis nonsynaptic release sites have been found together with synapses, or with neurohaemal axon terminals (caudodorsal cells, light green cells and light yellow cells). The possibility that nonsynaptic release sites represent the morphological correlates of nonsynaptic communication in the central nervous system has been discussed.

Animals↗
PubMed1984

Ultrastructural demonstration of exocytosis of neural, neuroendocrine and endocrine secretions with an in vitro tannic acid (TARI-) method.

The release of neural, neuroendocrine, and endocrine secretory products by exocytosis was ultrastructurally studied by means of tissue incubation in Ringer containing tannic acid (Tannic Acid Ringer Incubation-method; TARI -method), followed by conventional fixation. Tannic acid strongly enhances the electron density of extracellular (secretory) substances. During TARI -treatment of tissues exocytosis proceeds, but the exteriorized contents of the secretory granules are immediately fixed by tannic acid and do not diffuse away into the extracellular space. In this way detection of exocytosis is markedly facilitated since the number of exocytosis phenomena visible at the ultrastructural level considerably increases with progressing incubation time. Studies of the central nervous system of the mollusc Lymnaea stagnalis show that the occurrence of exocytosis during TARI -treatment is calcium-dependent. With the TARI -method exocytosis has been clearly demonstrated in a variety of structures (endocrine cells, neurohaemal axon terminals, synapses) of L. stagnalis, the insect Locusta migratoria, and the rat, including cell types where exocytotic release had not been shown before.

Animals↗
PubMed1984

Isolation of neurosecretory granules from the neurohaemal areas of peptidergic systems of Lymnaea stagnalis, with special reference to the ovulation hormone-producing caudodorsal cells.

Neurosecretory granules (NSG) were isolated by density-gradient centrifugation from homogenates of the intercerebral commissure (COM) and the median lip nerves (LN) of the freshwater snail Lymnaea stagnalis. COM and LN are rich in axon terminals of the ovulation hormone-producing caudodorsal cells (CDC) and of the growth hormone-producing light green cells (LGC), respectively. Electron microscopy of COM isolates showed that a single fraction contained large numbers of NSG, which were identical to NSG of CDC axon terminals of the intact COM. High ovulation hormone activity was associated with this fraction. LN NSG were also isolated in large numbers in a single fraction. The isolated LN NSG were identical to NSG of intact LGC axon terminals. They appeared to have a higher specific gravity than CDC NSG.

Animals↗
PubMed1983

Calcium dynamics, exocytosis, and membrane turnover in the ovulation hormone-releasing caudo-dorsal cells of Lymnaea stagnalis.

The axon terminals of the neuroendocrine caudo-dorsal cells (CDC) of the freshwater snail Lymnaea stagnalis release an ovulation-stimulating hormone by exocytosis in a calcium-dependent way. Ultrastructural studies of the terminals, involving the K-pyroantimonate method for the demonstration of calcium and control tests with EGTA, show that calcium occurs in mitochondria and in various types of vesicular structure. Quantitative investigations indicate that mitochondria accumulate calcium during a short period of high neurohormone-release activity ("active state"; ca. 45 min) and release it again into the axoplasm some hours later, during a period of low secretory activity ("resting state"). Probably, in this way mitochondria play an important role in the buffering of the axoplasmic calcium concentration during high hormone-release activity. HRP-incorporation studies strongly suggest that the calcium-containing vesicular structures constitute a mechanism of membrane sequestration by which the CDC axon terminals resorb, transform, and release parts of the axolemma after exocytotic hormone release. The results furthermore indicate that this mechanism also may be involved in the control of the calcium concentration of the axoplasm, by taking up calcium from the axoplasm and releasing it into the extracellular space.

Animals↗
PubMed1983

Integration of biphasic synaptic input by electrotonically coupled neuroendocrine caudodorsal cells in the pond snail.

The ovulation hormone-producing caudodorsal cells (CDCs) of the pond snail Lymnaea stagnalis form two clusters of electrotonically coupled cells, each containing a few specialized (ventral) cells that connect the clusters. The hormone is secreted during a pacemaker-driven discharge. The CDCs receive a biphasic cholinergic postsynaptic potential (PSP), consisting of a rapid excitatory postsynaptic potential (EPSP) and a slow inhibitory postsynaptic potential (IPSP) that is elicited by stimulation of nerves. The effect of the synaptic input on the discharge of the CDCs is described and the location of the synapse investigated by a combination of electrophysiological recordings and morphological techniques. The PSP interrupts the discharge and hastens its termination. In addition, it causes a reversal of the temporal order of the spikes of ventral cells (that normally lead) and dorsal cells (that lead only after the PSP). Ion-substitution experiments indicate that the ionic mechanism underlying the biphasic PSP is conventional, involving a conductance increase for Na+ (EPSP) and K+ (IPSP). Receptors mediating the inhibitory component occur only on the proximal axons of the ventral cells, both components are larger and reverse more readily in ventral cells. These findings suggest that the PSP is generated in the ventral cells. The biphasic PSP has no effect on electrical coupling, suggesting that it is not generated along the electrical pathways among the cells. Horseradish peroxidase (HRP) staining reveals that the lateral branches emerge from the proximal axons of the ventral cells only. In HRP-filled preparations processed for electron microscopy (EM) acetylcholinesterase is demonstrated at these branches where it occurs associated with synapses. The location on fine branches of the ventral cells explains the absence of an effect on electrotonic transmission, whereas the reluctance of components of the PSP to reverse at the expected potentials is due to the distribution of the synapses over more than one cell. It is concluded that the biphasic PSP is received only by the ventral cells and that it is conveyed electrotonically to the other cells.

Acetylcholinesterase↗
PubMed1981

Adenylate cyclase activity in axon terminals of ovulation-hormone producing neuroendocrine cells of Lymnaea stagnalis (L.).

Adenylate cyclase activity was demonstrated ultracytochemically in the neurohaemal area of the ovulation-neurohormone producing Caudo-Dorsal Cells (CDC) of the freshwater snail L. stagnalis. During electrical activity the axon terminals of the CDC release the hormone by exocytosis and show high adenylate cyclase activity on their plasma membranes. Electrically inactive terminals hardly show exocytosis and exhibit only little reaction product of adenylate cyclase. This result indicates that cAMP plays a role in the control of release of the CDC hormone.

Adenylyl Cyclases↗
PubMedDate not supplied

Electron microscopical study in multiple epiphyseal dysplasia type II.

An electron microscopic examination of articular cartilage of two cases with multiple epiphyseal dysplasia type II was performed. The cartilage had a normal cell distribution and no signs of gross degeneration were found. Chondrocytes showed normal ultrastructural characteristics without dilation of the rough endoplasmic reticulum. The matrix contained normal banded collagen fibrils, proteoglycans, and aggregated fibrils.

Adolescent↗
PubMedDate not supplied

Synaptic and nonsynaptic release of neuromediators in the central nervous system.

Different types of release site were studied ultrastructurally with tannic acid and immunohistochemical techniques in the central nervous system (CNS) of the invertebrate pond snail Lymnaea stagnalis and in two neuromediator rich core regions in the CNS of the rat, viz., the median eminence (ME) and the mesencephalic central grey substance (MCG). In the CNS of the snail, release of the contents of the secretory granules could be clearly demonstrated in (1) neurohaemal axonterminals, (2) synapses and (3) in nonsynaptic release sites: neuronal processes without morphological synaptic specializations. In the ME, release of secretory products by exocytosis was found in neurohaemal axonterminals in the external part of the palisade layer and in nonsynaptic release sites in all other layers of the median eminence. It was found that oxytocine and vasopressin were released by exocytosis into the extracellular space from such (preterminal) nonsynaptic release sites. Serial section analysis revealed three types of fibre in the MCG, viz. (1) varicose fibres that made synaptic contacts with MCG dendrites on every varicosity, (2) fibres with two types of varicosity, viz. synapse-bearing varicosities and varicosities without synaptic specializations, and (3) varicose fibres without any synaptic specializations. It has been discussed that the nonsynaptic release sites in the CNS of the snail Lymnaea stagnalis, and the nonsynaptic varicosities in the rat brain are the morphological correlates of nonsynaptic communication in the CNS. The results further indicate that particular peptidergic neuromediators are released from such nonsynaptic varicosities, and may reach via the extracellular space receptors located at some distance.

Animals↗