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Biomedical subjects

J Vajda

Publications and source records attributed to J Vajda.

At least 73 records · Page 4Linked to original sources
PubMed1979

Frequency resonance investigation of the H reflex.

Results of a previous study demostrated transformation of the sustained activity of a muscle into rhythmic, tremor-like activity by stimulation of different motor centres. The optimum for this transformation was in the 4-7 Hz frequency band (resonance band). Sustained rhythmic stimulation with stimuli at 0.1-20 per second caused a normal frequency curve of the H reflex in subjects with intact motor systems. The resonance phenomenon of the frequency curve of the H reflex was in agreement with that found in previous studies stimulating the different motor centres. As this requires connections between spinal and higher motor centres, it is suggested that this investigation is appropriate for a detailed functional study of spinal cord lesions.

Electric Stimulation↗
PubMed1979

Interneuronal synapses in the local ganglia of the cat urinary bladder.

The interneuronal synapses of the urinary bladder in the cat were studied by electron microscopy. The great majority of the fibres containing vesicles are found within the ganglia occurring in the trigonum area. Morphologically differentiated synaptic contacts could be observed on the surface of the local neurons and between the different nerve processes. The presynaptic terminals can be divided into three types based on a combination of synaptic vesicles. Type I terminals, presumably cholinergic synaptic terminals, contain only small clear vesicles of 40-50 nm in diameter. Type II terminals, presumably adrenergic terminals, are characterized by small granulated vesicles of 40-60 nm in diameter. Type III terminals, probably of local origin, contain a variable number of large granulated vesicles of 80-140 nm in diameter. Occasionally, a single nerve fibre contacted several (two or four) other nerve processes forming a typical synapse. In other cases, on one nerve cell soma or on other nerve processes there are two or three different-type nerve terminals establishing synapses. It might be inferred from these observations that convergence and divergence can occur in the local ganglia and that cholinergic and adrenergic synaptic terminals can modulate the ganglionic activity. However, a local circuit also can play an important role in coordinating the function of the bladder.

Animals↗
PubMed1979

Ultrastructure of the nerve cells and fibres in the urinary bladder wall of the cat.

The nerve elements in the urinary bladder of the cat were studied by electron microscopy. According to their ultrastructure, nerve cell somata can be classified into three types: the large cells with a cytoplasm rich in organelles, several processes and numerous synaptic contacts on their surface; the cytoplasm contained 80- 120-nm granulated vesicles. The second type is poor in cytoplasmic organelles and has very few processes and virtually no synaptic contacts on the soma. The third type contains numerous large 160- to 220-nm 'neurosecretory' vesicles in the cytoplasm. According to the morphology of the vesicle population, four types of nerve processes could be distinguished: Type a, with a dominant population of small (40-60 nm) agranular vesicles. These are thought to be sacral parasympathetic fibres. Type b, with small (40-60 nm) granular vesicles, which may be the noradrenergic sympathetic fibres. Type c, with 80- to 120-nm granulated vesicles, probably of local origin. Typed d, with large 160- to 220-nm 'neurosecretory' vesicles also of local origin. Different types of nerve fibres are converging on the local nerve cells. This suggests that the local circuits can play an important role in coordinating the function of the bladder. Therefore, ganglia may be considered as an elementary functional unit.

Animals↗
PubMed1978

Morphological changes in the small intestine of the cat following transection of the vagal nerve.

An attempt was made to identify the vagal fibres of the small intestine and to investigate their course by secondary degeneration after transection of both vagus nerves just below the ganglion nodosum. Under the electron microscope, degenerated fibres could be observed in the myenteric and submucous plexuses, in the longitudinal and circular muscular coats of the duodenum and jejunum. No signs of degeneration were encountered in the wall of the ileum. Direct synaptic relationship between these degenerated fibres and the nerve cells and intact nerve processes could scarcely be found. The degenerated axons do not differ basically from other, intrinsic nerve processes containing round clear vesicles (30--60 nm in diameter) and granular vesicles (80--120 nm in diameter). The sporadic occurrence of the degenerated axons on the surface of cell somata and processes might indicate that the vagal nerve innervates only a few neurons in the small intestine and that the intrinsic neurons contact a large number of other neurons via processes in the intestinal wall. The vagal nerve fibres thus seem to have a modulatory effect on the activity of the intestinal wall.

Animals↗
PubMed1977

The study of recovery and modification of the evoked potentials and motor answers in the motor system.

After an electrical stimulus within the motor system there will follow a compulsion, a reflexlike process in functional dependency, naturally in illness (function disturbance) dependency as well. We can detect this process with the evoked potentials at the non-stimulated sites of the motor system and with the motor answers at the periphery. Because the motor system acts as a whole, it is certain that every process at a site has its correlates at the other sites, but the different part of the same process will be in a different grade pronounced (many times in opposite direction) at the different sites. If we want to know something from the basic process and to find the real correlates, we have to compare different evoked potentials within the motor system and motor responses at the periphery, or we have to enhance or depress the whole process or its parts. For the latter the double stimulation technique is suitable, but we have to take into consideration that during this investigation two alternating processes affect each other and therefore the result will not be direct.

Brain↗
PubMed1976

The motor mechanism of some types of epilepsy.

In the types of epilepsy studied if the irritative epileptic activity evokes a motor response this response will be a special type. The epileptic activity is working on a normal motor system and will affect it in space and time at a special point. From this point of view it is possible to compare-during stimulation of the motor system--the evoked potential and the evoked epileptic potential, i.e. the evoked motor activity and the epileptic motor activity. It appears that--in the types of epilepsy studied--the motor resting state promotes the spontaneous and the evoked epileptic activity or the epileptic evoked motor activity. It is very probable that the epileptic activity does not employ the short, phasic motor responses, but the tonic, automatic, reflex motor ones.

Electroencephalography↗
PubMed1976

Selective sympathetic denervation induced by 6-hydroxy-dopamine in the small intestine.

The structure of the nerve fibres in the intact and neurally isolated intestine of the cat was studied after 6-OHDA treatment by fluorescence and electron microscopy. A gradual disappearance of green fluorescence in the monoaminergic fibers was observed. Degeneration of nerve fibres containing 30--60 nm agranular and 30--60 nm densecore (granular) vesicles could be seen in all layers of the small intestine. Sporadically, degeneration of the presynaptic elements occurred also in the synapses of myenteric ganglia. A large number of degenerating fibres could be observed in close relation to blood vessels. These were thought to be monoaminergic because 6-OHDA selectively affected their terminals. In the chronically isolated small intestine degenerated nerve processes could not be observed following 6-OHDA treatment. It is concluded that the intrinsic nerve elements do not contain monoamines. Accordingly, the previously observed yellow fluorescence of the nerve elements of the isolated small intestine might be due to some other kind of neurotransmitter, possibly tryptamine.

Animals↗
PubMed1975

Arterial and respiratory influences on intracranial pressure in infancy.

Ventricular and subdural pressures have been monitored in 23 infants. Pressure waves which were influenced by respiratory and cardiac activity were noted. These were rather long lasting and were influenced more by respiration than by cardiac activity, when the intracranial pressure is low. Respiration and arterial pressure have similar effects when the intracranial pressure is normal, but when the intracanial pressure is increased the effects of respiratory activity are diminished.

Brain Diseases↗