Circulating met-enkephalin in trained athletes during rest, exhaustive treadmill exercise and marathon running.

Twelve trained male athletes were subjected to a progressive intensity treadmill exercise test to total exhaustion and at a later date took part in the Comrades Marathon. Blood was taken in order to determine whether plasma met-enkephalin levels increase in an exercise-intensity dependent manner. The mean concentrations in f mol/ml were as follows: post-exercise levels (266) were significantly higher than basal levels (172), and the post-marathon levels (378) rose significantly above the post-exercise levels. The magnitude of the responses is thus correlated with the amount of work performed and would suggest that this opioid peptide is involved in physiological actions that perhaps extend beyond the pharmacological actions of opiate drugs.

Effect of exercise on met-enkephalin in unfit and superfit individuals.

Twenty-four unfit volunteers and twenty-three superfit athletes were subjected to a progressive intensity treadmill exercise to total exhaustion in order to study the plasma met-enkephalin response to exercise. Blood samples were collected before and 5 min post-exercise. The basal met-enkephalin levels were significantly higher in the superfit individuals (180 fmol.ml-1) than in the unfit individuals (126 fmol.ml-1). Post-exercise the increase from basal levels of plasma met-enkephalin was significantly higher in the superfit athletes (180-278 fmol.ml-1) than in the unfit individuals (126-157 fmol.ml-1). The magnitude of the met-enkephalin responses to exercise therefore appears to be dependent on the amount of work performed and the degree of previous physical training. Peripherally circulating opioid peptides may, therefore, possibly play a role in the body's adaptation to exercise training.

[The influence of certain contextual factors on voice onset time, vowel duration and utterance duration in verbal apraxia]. / Die involved van sekere kontekstuele faktore op stemaavangstyd, vokaalduur en uitingduur by verbale apraksie.

The concept of context sensitivity as borrowed from the coalition model has important implications for the interpretation of the symptoms of apraxia of speech and for a better understanding of the nature of the disorder. In this study which was part of the wider investigation into the effect of variation in contextual factors on apraxia of speech (van der Merwe, Uys, Loots and Grimbeek, 1987; 1988), the effect of two contextual factors namely sound structure and articulatory features on voice onset time, vowel duration and utterance duration was acoustically analysed. Four subjects with acquired apraxia of speech and one with developmental apraxia of speech were tested. Findings indicated that voice onset time is not context sensitive. Errors in voice onset time were not true substitutions with voiceless sounds but were inconsistent distortions due to an inability to keep interarticulator synchronization within the critical temporal boundaries of motor equivalence. Vowel and utterance duration were found to be context sensitive. The deviation in duration increased with increased complexity of the utterance. As was the case with the auditorily perceived symptoms, the temporal characteristics of apraxia of speech can also be classified into core symptoms and associated symptoms based on their context sensitivity.

Synaptic and non-synaptic components of the dorsal horn potential in isolated hamster spinal cord.

Slow negative potentials, evoked by stimulation of the lumbar dorsal roots, have been demonstrated in the dorsal horn of an isolated, hemisected spinal cord preparation from golden hamsters. Paired stimuli revealed a period of partial suppression of this slow potential persisting for up to 2 s following the conditioning stimulus, but with high stimulation frequencies this effect was masked and above 20 Hz a tetanic train of stimuli produced a smoothly rising potential. The response evoked by tetanic stimulation was shown to consist of two components, a manganese-sensitive, synaptically generated component, and a manganese-resistant, frequency-dependent element. Treatment with 10(-4) M 4-aminopyridine blocked the manganese-resistant tetanic response but did not reduce the manganese-sensitive component. Bicuculline, picrotoxin and tubocurare had little effect upon the tetanic response, but 10(-3) M procaine blocked it completely. The possibility that the manganese-resistant response was due to the release of potassium ions is considered.

The effect of folates on the reflex activity in the isolated hemisected frog spinal cord.

Folates may play a role in epileptic phenomena and may also be involved in synaptic events. Recently methyltetrahydrofolate was found to be a potent competitor for 3H-kainic acid binding sites in the cerebellum. The effects of 1 mM methyltetrahydrofolate (MTHF), 1 mM formyl-tetra-hydrofolate (FTHP) and 1 mM Na-folate (Na-F) were tested on the reflex activity of the isolated hemisected frog spinal cord. MTHF and FTHP were found to have an initial excitatory effect on the evoked ventral root responses. This was followed by a gradual decrease in the amplitudes of the ventral root responses. Sodium folate had only an inhibitory effect on these responses. When the evoked ventral root responses were totally inhibited by the folates the preparations did not respond to any of the following substances: (a) Kainic acid (KA), (b) L-glutamic acid (LG), (c) picrotoxin or (d) strychnine. All the folates had an inhibitory effect on the dorsal root responses. In most preparations neuronal activity was only partially restored by perfusion with normal Ringer solution. When the isolated spinal cords were bathed in either 0,5 mM KA or 1 mM LG similar results were obtained to that found with MTHF and FTHF. Glutamic acid diethyl ester (GDEE, 1 mM), however, yielded similar results to that seen with Na-F. It seems that the glutamates and related substances differ in their ability as neuroexcitants, but all share the common ability to inhibit synaptic activity when nervous tissue is exposed to the substances for long periods. Some of the folates share with KA some degree of neurotoxicity. These experiments could also not point out a separate kainic receptor in the frog spinal cord.

The flow volume curve as a diagnostic tool.

The flow volume curve is useful for differentiating the various types of airway abnormalities. The conventional spirometric data have not been very useful in this regard, and therefore flow volume curves are now used as an adjunct measure in most laboratories in which pulmonary function is measured clinically. This article reviews the basic physiological concepts underlying the usefulness of the flow volume curve and describes the abnormalities which can be detected by this technique, with special reference to its role in clinical medicine.

A rapid silver impregnation method for nervous tissue: a modified protargol-peroxide technic.

A rapid, reliable silver impregnation method is described for nervous tissue fixed in formol-saline, Bouin or Susa. Sections are impregnated for 10-15 minutes at room temperature or 37 C in a solution containing 0.5 g Protargol-S, 0.005-0.01 g allantoin, 1 ml of 1% Cu[NO3]2, 1 ml of 1% AgNO3, and 1-2 drops of 30% H2O2 in 100 ml distilled water. Thereafter the sections are reduced in a hydroquinone-formalin solution. This is followed by gold toning and subsequent reduction and mounting. Alternatively, following the first reduction, the silver image can be intensified by placing sections in a silver-allantoin bath which is followed by reduction and mounting. This method is very reliable and selective, making it suitable for general routine and research use.

The effect of allantoin on cellular multiplication in degenerating and regenerating nerves.

Injury to a peripheral nerve is, among other things, followed by degeneration of axons and myelin, as well as by a sharp increase in the number of cells (especially Schwann cells) in the part distal to the injury. The effect of allantoin--a cell proliferant--was tested on the above-mentioned reactions in the sciatic nerve of rats. The nerves were crushed and re-exposed 7, 14, 21, 35 and 90 days after the injury, and removed for histological examination. The results obtained in a group of rats treated with allantoin were compared with those obtained in a control group of rats. The results showed that allantoin had a statistically significant effect on the cellular multiplication seen in the nerve 7 and 14 days after the injury. Myelin degeneration was also found to be more advanced in the allantoin-treated nerve preparations examined 14 and 21 days postoperatively than in the control nerve preparations.

A silver impregnation method for nervous tissue suitable for routine use with mounted sections.

A simple, reliable silver impregnation method for nervous tissue is described for tissues fixed in various fixatives including formalin, Bouin, and Susa. Sections are impregnated in a solution containing 1 g Protargol, 2 ml of a 1% Cu(NO3)2 solution, 2 ml of a 1% AgNO3 solution, and 2-4 drops 30% H2O2 in 100 ml distilled water. Sections are impregnated 2-5 days at 37 C and thereafter reduced in a hydroquinone-formalin solution. This is followed by gold toning and subsequent reduction, dehydration and mounting. This method has been found to be very reliable and selective.

Experimental microsurgery in peripheral nerves.

A surgical technique for the reconstruction of severed peripheral nerves is described. This technique reduces the mechanical manipulation and trauma to the nerve during suturing. Histological studies revealed that scar formation at the suture site was reduced to a minimum. The suture material did not prevent the downgrowth of regenerating axons. Nerves in which suturing was either inaccurately or accurately done, were compared. Histological examination of these nerves revealed that axonal regeneration in nerves with 8 or more sutures was superior to that in nerves with only 2 sutures.

Ultrastructural localisation of calcium in peripheral nerves of the rat.

An ultrastructural method which is specific for calcium was applied in a study of calcium distribution in the axoplasm of myelinated nerve fibres of rat sciatic nerves. Electron-dense deposits of calcium oxalate were seen in smooth-membraned vesicles within the axoplasm, and between the two external membranes of axoplasmic mitochondria. The significance of calcium localisation at these sites is discussed, with special reference to the role of calcium in fast axoplasmic transport.

The effect of porphyrin precursors on monosynaptic reflex activity in the isolated hemisected frog spinal cord.

The porphyrin precursors beta-aminolevulinic acid (beta-ALA) and porphobilinogen (PBG) which accumulate, and are excreted in the urine in increased amounts during acute attacks of porphyria, were tested for their effects on reflex activity in the isolated hemisected spinal cords of Xenopus laevis. The two compounds were found to exert an inhibitory effect on monosynaptic ventral root responses, as well as on dorsal root responses (DRR) and dorsal root potentials (DRP). The latent period for inhibition of the monosynaptic response was longer than that for the DRR and DRP. The sensitivity of the preparations to the effect of the porphyrin precursors was subject to some seasonal variation. BETA-ALA and PBG did not effect conduction in isolated sciatic nerves at a concentration of 1 mg/ml.

Effects of Naja nivea venom on nerve, cardiac and skeletal muscle activity of the frog.

1. The effects of 1 mg/ml whole Naja nivea (Cape cobra) venom, and of three different toxins isolated from it, on spinal reflex excitability and cardiac and skeletal muscle activity of the frog (Xenopus laevis), were studied. Isolated spinal cords, sciatic nerve-gastrocnemius muscle units and isolated heart preparations were used.2. Synaptic efficiency and/or motoneurone excitability ceased totally and irreversibly after the application of whole venom within 18.5 minutes. The application of alpha toxin caused polysynaptic reactivation of the motoneurones after the monosynaptic response elicited by electrical stimulation, i.e. it had an excitatory effect, which was retained after washing off the toxin. The effect of beta toxin resembled that of alpha toxin, except that the effect was lost after the toxin was washed off. The delta toxin abolished all nervous reactivity irreversibly and was found to be 2.64 times more effective in this respect than whole venom.3. Responses of the gastrocnemius muscle to electrical stimulation of its motor nerve ceased 10 to 20 min after application of the venom. The muscle usually still responded slightly to direct stimulation for a few minutes. The effect was irreversible. The venom did not only block neuromuscular transmission, but also affected the muscle fibre itself. Nerve conductivity was relatively resistant to the venom; alpha and beta toxins produced similar results but were less effective.4. The application of whole venom (1 mg/ml) to the isolated heart resulted in complete spasm of the ventricle within 3 to 8 minutes. The atria continued contracting long after the ventricle ceased. When the venom was washed off, contractions of the atria were restored, while the ventricle remained irreversibly in a state of spasm. The alpha, beta and delta toxins weakened the contractions of the ventricle, but did not produce spasm. The effect on the ventricle was reversible. Contractions of the atria remained apparently unaltered.