Changes in osmotic resistance of erythrocytes of human blood caused by Vipera berus venom

The effect of Berus viper's venom on the osmotic globular resistance of human blood, incubated for a period of 2 hours at 20 degrees C with amounts of venom in the range of 200 to 400 gamma/ml of blood, has been studied. The hemolytic effect occurs to a greater extent at NaCl concentrations higher than 0,60%.     

Fine structure of the neuromuscular junctions in the alimentary tract of phylogenetically different animal species

Authors studied the fine structural characteristics of the neuromuscular junctions in the alimentary tract of phylogenetically different animal species. Nearly in each studied species the so-called close contacts were observable, where the sarcolemma and axolemma establish a junction; the gap of this contact is 10-100 nm wide, and the neurotransmitters can affect the muscles through non-synaptic release (exocytosis). The junctional gap is widest in the gut wall of earthworm: 100-200 nm. Only close contacts are to be found in the alimentary canal of snail, and here, the junctional gap is as narrow as 10-15 nm. Beside close contacts synaptic neuromuscular junctions also occur in the locust gut. Their fine structural organization refer to that of chemical synapses. As in the tench intestine both striated and smooth muscular elements can be found, motor endplates as well as close contacts take part in their innervation. Only close contacts are in the smooth muscular layer of domestic fowl. Authors emphasize the role of close contacts in the regulation of gut peristalsis and only secondary importance is attached to other different junctions.     

Trace postsynaptic reactions in neuromuscular junctions

Factors which control the duration of postsynaptic responses in neuromuscular junctions are discussed together with a possibility of origin of trace postsynaptic reactions (potentiation and desensitization). In experiments on nerve-muscle preparations of various vertebrates (lamprey, frog, chicken, rat), the key role of functional activity of acetylcholinesterase was revealed in regulation of the duration of both short- and long-living postsynaptic responses. The significance of sufficient activity of acetylcholinesterase for normal realization of neuromuscular transmission presumably increases in the course of evolution of vertebrates. An analysis of possible molecular nature of trace reactions on the postsynaptic membrane was carried out.     

Development of neuromuscular junctions in rat embryos

Physiological properties of nerve-muscle junctions were studied in intercostal muscles of rat embryos of 13 to 21 days gestation and in neonates. Nerve bundles grew into the muscle region by Day 13 of gestation. Myotubes began to appear on Days 13–14. Myotubes were electrically coupled before birth, allowing the spread of depolarization laterally between fibers. The strength of coupling declined with embryonic age and disappeared after birth. At early times, some fibers of adjacent segments were also coupled, end to end. Resting potentials of myotubes were high (70–90mV) from the time of their appearance. Miniature end-plate potentials were recorded in some myotubes on Day 14 of gestation. At that time also, nerve stimulation could evoke an end-plate potential which was capable of triggering muscle contraction. The mean quantal content of transmitter released from individual terminals was small compared to that in adult muscle; it remained small through the first postnatal week. Individual myofibers had a single end-plate site near their center, which could receive as many as six distinct synaptic inputs. The number of inputs per fiber reached a peak at Day 17 of gestation, and then began to decline before birth, reaching its adult value of one input per fiber within the second postnatal week. The internal intercostal muscles contained about 30 motor units, each confined to a small zone in the muscle. The region occupied by a single motor unit was not obviously reduced in size as the number of synaptic inputs per fiber declined. At Day 17 of gestation 40% of the muscles contained one or more aberrant motor units, the parent axons of which projected out through the ventral roots of adjacent segments. Elimination of these units commenced at the same time as did the reduction in number of synaptic inputs to single myofibers, and 70% of the aberrant units were eliminated before birth.     

Fine structure of tight junctions between rat choroidal cells after osmotic opening induced by urea and sucrose

After ventriculo-cisternal perfusion of hypertonic urea or sucrose, both the choroid plexus permeability to horseradish peroxidase and the structure of tight junctions between choroidal cells are modified. Intercellular spaces are swollen, continuous ridges are fragmented and intrajunctional spaces are invested by many membranous particles. These morphological alterations appear to be reversible. These ultrastructural data are related to an osmotic maladjustment induced by the introduction of hypertonic solutions into the cerebro-spinal fluid.     

Adrenergic neuromuscular junctions in the cerebral arteries of birds

By means of the histochemical and electron microscopical methods, adrenergic innervation of the middle cerebral artery and its branches have been investigated in three sparrows (Passer montanus), blue rock pigeons (Columba livia), hens (Gallus domestica), hazel-grouses (Tetrastes bonasia), large billed crows (Corvus levaillantii), ducks (Anas domestica) and slaty backed gulls (Larus schistisagus). Neuromuscular connections in all the birds investigated have similar organizational features. Some adrenergic effectors are situated 700 nm from the external layer of myocytes in the vascular middle tunic, and they perform the distant transmission. Other effectors are at the distance of 40-80 nm from myocytes, and they are built according to the synaptic type. They produce certain action upon single muscle cells, thus performing local transmission. For the neuromuscular connections of the cerebral vessels in the birds, presence of multiaxonal complexes is specific. Axons of the complex innervate groups of muscle cells and they are at the distance of 50-270 nm from their plasmic membranes. Perhaps, they combine the local and distant means of transmission.     

Development of rat neuromuscular junctions in organ culture

Pieces of thoracic body wall, including intercostal muscles, ribs, and the spinal cord were explanted from 15 to 18-day embryonic rats and maintained in organ culture for up to 6 days. During the time in culture muscle fibers continued to increase in size, and nerve sprouts extended along the center of the muscle. When muscle-spinal cord explants were cultured at 15 days gestation, the number of synaptic inputs per fiber increased with time in culture. Subsequently synapse elimination began with a time course similar to that recorded in vivo. In 15-day explants acetylcholine receptors were uniformly distributed along the fibers and focal cholinesterase (ChE) was not detected. The cholinergic receptors started to cluster at the midregion of the fibers after 1 day explantation, and ChE was detected in the fibers after 2 days in culture. The central receptor clusters were associated with ChE and their formation was dependent on the presence of nerve terminals. We conclude that neuromuscular contacts develop in organ culture with a pattern and time course similar to that of synapes developing in utero.     

Changes in the ratio of quantum-vesicular parameters in the presence of disrupted synaptic transmitter secretion in the neuromuscular junctions of mammals

To test the vesicular hypothesis of quantum release, some parameters of synaptic vesicles (SV) and miniature end plate potentials (MEPPs) were compared in phrenic neuromuscular junctions of rats poisoned with tetanus toxin (TT). The poisoning with TT that suppresses the transmitter release led to marked changes in the distribution of MEPPs amplitudes and SV diameters as compared to normal, namely to the transformation of unimodal histograms for both parameters to polymodal ones. The transformation was accompanied by a significant increase in variation coefficients of both distributions, thus indicating the disturbances of vesicle-quantum formation. The total number of SV in the poisoned terminal increased by 59% which might reflect both the lifetime situation characteristic for normal and/or real accumulation of the transmitter quanta as a result of the TT-hampered exocytosis through the presynaptic membrane, since during the reactivating action of ouabain, the transmitter release level from the poisoned terminal exceeded that for normal to about the same measure. The results obtained may be regarded as providing evidence in favour of the vesicular hypothesis.     

Changes in haemolymph osmotic pressure in Locusta migratoria larvae in relation to feeding

An account is given of the effect of feeding on haemolymph osmotic pressure in larvae of Locusta migratoria. Changes in concentration of solutes and haemolymph volume are investigated and discussed.