Nifedipine, a calcium-blocking agent, inhibits smooth muscle contractions in various organs including gastric muscle in vitro. Despite this, nifedipine has been found to have no effect on gastric emptying in man. We have investigated the effect of nifedipine on gastric emptying of liquids and solids and on gastrointestinal motility in six healthy subjects. For this, isotopic techniques and manometric methods were used. We confirm that nifedipine 30 mg per os does not modify gastric emptying of liquids or solids. By contrast, antral motility was significantly inhibited (P less than 0.05) and duodenal motility increased. These results could be interpreted as (1) gastroduodenal motility changes are not severe enough to alter emptying or (2) isotopic techniques are not sensitive enough to detect subtle changes in gastric emptying.
We have studied the neuroectoderm of the chicken embryo, from the beginning of somitic segmentation up to the stage at which it has seven somites, i. e. the period covering the passage from the ‘neural canal’ into the ‘neural tube’. This paper was devoted mainly to the study of the ultrastructural cytodifferentiation which takes place during the stages in which the neural canal closes up, and at the level of the first area of contact between the ‘neural crests’ – roughly at the level of the third somite. We used eggs from a hen of the White Leghorn breed, incubated at 38 °C, from which we extracted chicken embryos after 24–30 h of incubation, corresponding to Hamburger-Hamilton’s stages 7, 8 and 9. Thus we were able to obtain several series of embryos with three, six and seven somites. The neural canal, or tube, at the level of the third somite, was fixed in glutaraldehyde at 6.25% for 30 min and postfixed in 1% osmium tetroxide for 2 h embedded in Araldite, and the sections were then stained with lead citrate. We observed that the vacuoles in the free edge of the neural canal gradually disappear as the canal closes up, while we gradually witness the appearance of the ‘closure apparatus’ (or the safety or occlusion apparatus) of what is beginning to form the ependymal epithelium, and the first rudimentary outlines of the cilia. All these changes begin to be observed at the seven-somite stage, i.e. when the neural canal is beginning to close up. The ‘closure apparatus’ consists of a number of intercellular joint complexes, of the ‘close-joint’ type, between which we observe a number of fine filaments, like a terminal velum’, or veil, which we call ‘interconnecting filaments’. In the ‘raphe’, whereby contact is established between the neural crests, we observe the initial stages of fusion between the vacuolated edges, with the plasmatic membrane of these cells forming very fine cytoplasmic ‘tongues’ which interdigitate with cells from the opposite neural crest and finally constitute the so-called close joints.
The neurons of the dorsal periaqueductal nucleus of the mesencephalon and their synaptic contacts were observed under a transmission electron microscope. We found various types of synapses which constituted an exception to Cajal’s neuron theory (law of neuron independence). Some of these synapses had an open communicating or continuity ‘passage’ between the presynaptic bouton of a neuron (first neuron) and the postsynaptic portion of another neuron (second neuron). The ‘communicating’ passage (located in the synaptosome) is formed by the continuity of the presynaptic and postsynaptic membrane, and its limits or rims are the reflexion points of the membranes. When only two neurons intervene they could be termed ‘simple communicating synapses’. We found three types: I = communicating axosomatic synapses; 11 = communicating axodendritic synapses, and 111 = communicating axoaxonic synapses’. When three neurons intervene in the synaptic contact, they could be termed ‘complex communicating synapses’. In these the first and second neurons form a normal synapse but the lateral portion of the presynaptic bouton of the first neuron also enters into contact with a third neuron, with which it establishes an open communicating or continuity passage . The points of these passages are collateral to the synapse and may be in the presynaptic or pre-postsynaptic portions simultaneously, communicating collaterally with the third neuron. We found a further three types: IV = complex communicating axosomatic and dendritic synapses; V = complex communicating axoaxonic and somatic synapses, and VI = complex communicating axodendritic and double-somatic synapses. It is suggested that communicating synapses may constitute an exception to CajaΓs neuron theory, representing functional states for the acceleration, retardation or modulation of the synaptic function. The neurotransmitters would pass en masse through the communicating passage and the depolarization wave would pass through the rims without being retarded. In the simple communicating synapses, their action would be intensifying. In the complex communicating synapses, their action would be modulating or retarding, since the collateral communicating passage would function as an ‘escape valve’ through which part of the impulse reaching the presynaptic bouton would escape.
Ultrastructural images of some neurons and their synaptic connections, belonging to the nucleus of the periaqueductal grey substance in the domestic cat mesencephalon, are shown. The finding that some axosomatic synapses showed an open communication between the pre- and postsynaptic portion attracted our attention. In this way a continuity is made between the presynaptic bouton of one neuron (axon) and the postsynaptic portion of the other (neuronal soma). Synapses having these interneuronal communications could be denominated communicating synapses. Accepting Cajal’s neuron theory and his law of neuronal independence, it is very difficult to interpret these images. We wonder if this type of communicating synapses could be the exception that proves the rule of the neuron independence.
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