Changes in the properties of mechanomyographic signals and in the tension during the fatigue test of rat medial gastrocnemius muscle motor units.

The influence of activity-related changes in tension on properties of the mechanomyogram (MMG) was investigated in fast fatigue-able, fast resistant and slow motor units (MUs). A standard fatigue test was used in which rhythmically repeated unfused tetani were evoked. The amplitudes of the rise in tension of the first and the last contraction within the unfused tetanus and the amplitudes of accompanying signals in MMG were calculated. For fast fatigue-able MUs a parallel decrease in the amplitudes of both analysed contractions and in the amplitudes of accompanying MMG signals during the fatigue test was observed. For majority of fast resistant MUs at the beginning of the fatigue test a potentiation occurred and this phenomenon increased the tension of the first contraction and of the peak tetanic tension. However, the potentiation coincided also with a decrease of the amplitude of the last contraction in the tension recording of an unfused tetanus. The MMG reflected both, the increase of amplitude of the first contraction and the decrease of the amplitude of the further contractions within the tetanus. The single twitch contraction evoked immediately before and after the fatigue test was additionally recorded. A decrease (fatigue) or an increase (potentiation) of the twitch tension after the fatigue test was reflected by a decrease or an increase in the amplitude of MMG, respectively. However, the fatigue failed to change significantly the time parameters of MMG. To conclude, fatigue and potentiation can occur during activity of fast MUs and both these phenomena involve changes in the amplitude of oscillations in tension of unfused tetani which are reflected in MMG.

Mechanomyographic signals generated during unfused tetani of single motor units in the rat medial gastrocnemius muscle.

The aim of this study was to investigate mechanomyograms (MMGs) accompanying unfused tetani of fast fatigable (FF), fast fatigue-resistant (FR) and slow (S) motor units. Signals in the MMG were analyzed during tetanus, which was fused to a variable degree, evoked by electrical stimulation at three frequencies: 20, 40 and 80 Hz. Unfused tetani were characterized by an oscillating tension. Each oscillation in the tension of an unfused contraction was reflected by a parallel pressure wave signal in the MMG. The mean peak-to-peak amplitude of signals in the MMG, the amplitude of oscillation in the tension, the velocity of the tension increase and the fusion index were calculated for the unfused tetanic contraction. The increase in stimulation frequency resulted in an increase in the peak tension, an increase in the fusion of the tetanus, a decrease in the amplitude of force oscillation in the unfused contraction and a decrease in the peak-to-peak amplitude of signals in the MMG. Moreover, it was found that the MMG amplitude was correlated with the amplitude of the three analyzed properties of the unfused contraction. It is concluded that the amplitude of signals in MMGs depends mainly on the dynamic properties of the tetanic contraction, whereas the static component of the contraction (i.e., the level around which the tension oscillates) is not reflected in the MMG.

Areas of operation of interneurons mediating presynaptic inhibition in sacral spinal segments.

Sources of primary afferent depolarization (PAD) of skin afferents in the sural (Sur) nerve and of group-II muscle afferents in the posterior biceps and semitendinosus (PBST) nerve were compared at several sites, about 2 mm apart, within the L7-S2 segments in order to define areas of projection of sacral interneurons mediating PAD of these afferents. Just rostral to the pudendal nucleus, strong PAD of Sur afferents was evoked by stimulation of skin nerves, while stimulation of muscle nerves had only marginal effects. This indicates that sacral PAD interneurons co-excited by skin and muscle afferents operate primarily within the regions overlying the pudendal nucleus. Furthermore, PAD evoked by muscle afferents was weaker over the rostral part of the pudendal nucleus than over the caudal part of this nucleus, where hamstring afferents became its main source, both in Sur and in PBST group-II afferents. By correlating the relative strength of PAD at the levels of the rostral and caudal parts of the pudendal nucleus with the previously established input from muscle and cutaneous afferents to interneurons at these levels, it is therefore proposed that sacral PAD interneurons operate over shorter distances than indicated by previous experiments: over either rostral or caudal parts of the pudendal nucleus, i.e., about 2 mm, rather than over the whole length of this nucleus, i.e., 4-5 mm. Sacral PAD interneurons may, thus, modulate synaptic transmission to even more spatially restricted neuronal populations than previously proposed.

Relationship between the tension-time area and the frequency of stimulation in motor units of the rat medial gastrocnemius muscle.

The tension-time area is an estimation of the work performed by contracting motor units. The relationship between tension and frequency of stimulation and between tension-time area and frequency have been studied on 148 single motor units of the rat medial gastrocnemius muscle, under isometric conditions. Motor units were classified as fast fatigable (FF), fast resistant to fatigue (FR) or slow (S). Trains of stimuli of increasing frequency and constant duration were used. For all motor units a half of the maximum tetanic tension corresponded to lower frequencies compared to frequencies at a half of the maximum tension-time area. Moreover, the slopes of tension-frequency and area-frequency curves (change of tension or area per 1 Hz rise in frequency) were higher for slow than for fast motor units. The tension-time area per one pulse was calculated for different frequencies of stimulation. For slow units the maximum area per pulse corresponded to significantly lower frequencies than for fast ones, especially of FF type. However, for all three types of motor units this optimal frequency corresponded to sub-fused tetani with a tension of about 75% of the maximum tension, and with the fusion index slightly over 0.90. The absolute values of the maximum tension-time area per pulse revealed that in one contraction within the tetanus, slow units are generating greater work than FR units. The work performed by FF units is nearly two times larger than for S units, although the tension of slow units is over eight times lower. The presented results reveal that the contraction of slow motor units is much more effective than was suggested based on their low tension.

Mechanomyograms recorded during evoked contractions of single motor units in the rat medial gastrocnemius muscle.

Acoustic phenomena accompanying contractions of single motor units (MUs) have previously received little attention. Therefore, in the present study, the mechanomyographic (MMG) signals during evoked contractions of single MUs have been recorded from the medial gastrocnemius muscle of the rat. A piezoelectric transducer immersed in a paraffin-oil pool was used for the measurement of these signals. Muscle fibre action potentials, tension and MMG were recorded in parallel during twitch (the weakest) and fused tetanic (the strongest) MU contractions. It was observed that the onset of the MMG signals was coincident with the beginning of the increase in tension for both the twitch and tetanus. Weaker MMG signals than those accompanying the beginning of the first phase of the fused tetanus were seen during the beginning of the relaxation after tetanic contraction. During contraction and relaxation, MMG signals were characterised by the reverse-direction of the first extreme phase, positive and negative, respectively. No MMG signals were observed when the tension was constant during the fused tetanus. The amplitude of MMG signals was correlated with both the tension increase and the velocity of tension increase during both the twitch and the fused tetanus. The strongest MUs (fast fatiguable) generated MMG signals of the highest amplitude. MMG signals were not detected for some of the weakest slow MUs (with tension increases of < or = 2 mN). These results indicate a strong correlation between the MMG and the change of tension. Therefore, we believe that MMG signals are generated by muscle deformation that occurs during the contraction of MU muscle fibres. We conclude that the number of active muscle fibres, their topography, and their localisation in relation to the muscle surface (which is variable for different types of MUs) influence these MMG phenomena.

The influence of increasing and decreasing frequency of stimulation on the contraction of motor units in rat medial gastrocnemius muscle.

Motoneurons during their activity can generate firings at changing rate. Therefore, the present paper aimed at studying the evoked contractions of different types of motor units to stimulation at progressively decreasing or increasing interpulse intervals. The influence of both patterns of stimulation on the tension, the duration and the tension-time area of motor units in rat medial gastrocnemius muscle was studied. The decreasing stimulation frequency resulted in generation of a bigger tension-time area although a slightly lower tension and a shorter duration of a contraction were observed in majority of studied units. For fast units a bigger tension-time area observed during the stimulation at decreasing frequency is probably due to the potentiation resulting from the initial high-frequency stimulation. On the other hand, at increasing frequency of stimulation the influence of the initial low-frequency stimulation can depress the tension-time area. The decreasing rate of stimulation during relaxation appeared to support the tension more effectively in slow-twitch motor units than in fast ones. Therefore, slow motor units are well suited to support the tension of tonic contractions.

Fatigability of motor units estimated by changes in work performed during their repetitive stimulation during the fatigue test.

In numerous studies resistance to fatigue is evaluated by measuring the peak tension of motor units in muscle. In the present study, the work performed within successive tetani during the fatigue test of rat medial gastrocnemius motor units was estimated by assessing of the area under the tension record. Resistance to fatigue was evaluated by a modified fatigue index which is expressed as the ratio of the area under a tetanus recorded two minutes after maximal potentiation of tension has been reached to the area under this maximally potentiated tetanus. The values of this modified fatigue index were compared to the standard fatigue index which was taken as the ratio of peak tensions for corresponding tetani. For fast fatigable units, values of the modified fatigue index were significantly lower than those of the standard index. This observation resulted from changes in the shape of unfused tetani accompanying developing fatigue. These changes strongly influenced the area under the tension record whereas the peak tension of these tetani diminished less significantly. For slow and a part of fast resistant to fatigue units (with the standard fatigue index above 0.85) the modified fatigue index was slightly higher than the standard one although the difference was not significant. This phenomenon was due to the prolongation of relaxation which was visible in the last part of the fatigue test. It is being concluded that the modified fatigue index describes more precisely the fatigue-induced changes in tetani during the fatigue test than the standard fatigue index, especially in fast fatigable units.

Differences in the profile of unfused tetani of fast motor units with respect to their resistance to fatigue in the rat medial gastrocnemius muscle.

In most studies performed on motor units in mammalian muscles the division of these units into fast and slow types has been based on the 'sag' visible in the profile of unfused tetanus. The time course of the sag in unfused tetani of fast motor units was analysed in the present study. Fast units of rat medial gastrocnemius muscle were classified as fast fatigable (FF) or fast resistant to fatigue (FR) on the basis of a fatigue index calculated during the standard fatigue test. In middle-fused tetani (fusion index 0.25-0.75), it was observed that for FF motor units the sag was shorter and occurred earlier than for FR units. Moreover, in FF units, the sag was followed by potentiating tension, whereas for FR units this potentiation was weaker or even absent. A tetanus shape index, which expressed the ratio of the area of the first part of the tetanus record (between the tension record and the baseline, from the beginning of tetanus up to the lowest point during the sag in the tension record) to the area under the second part of tetanus (from this lowest point up to the end of the record) was introduced. For FF units, this index ranged from 0.13 to 0.47, whereas for FR units it ranged from 0.54 to 17.8 (with one exception). These results showed that the difference in unfused tetanus expressed in this tetanus shape index could be used as an accurate alternative method of dividing fast units into FF and FR groups. Moreover, the difference in sag time course in FF and FR groups. Moreover, the difference in sag time course in FF and FR units suggests that the metabolism responsible for this contractile phenomenon is significantly different time courses in IIa and IIb muscle fibres, constituting FF and FR units, respectively.

Relationship between mechanomyogram signals and changes in force of human forefinger flexor muscles during voluntary contraction.

In previous studies on mechanomyogram (MMG) signals no analysis of these signals accompanying force generation has been performed. Therefore, we have recorded MMG signals (previously referred to as muscle sound or acoustomyographic signals) during voluntary contractions of forefinger flexor muscles in 31 young subjects. These subjects made contractions to produce force records of triangular or trapeziform shape. The peak target force amounted to 10, 20 or 40 N which represented less than 40% of maximal voluntary contraction. The MMG signals during the transient phases of force generation at three different rates were analysed. The MMG intensity level calculated for MMG records and the peak-to-peak amplitude of MMG signals correlated with both the velocity of force increase and the contraction force. The occurrence of the strongest MMG signals corresponded to changes in contractile force. Therefore, it is suggested that measurements of these parameters could be a useful tool in studies of changes in contractile force.

The rate of changes in tension within fused tetani of single motor units in rat medial gastrocnemius muscle.

The time course of fused tetani of three main types of motor units: slow (S), fast resistant (FR) and fast fatigable (FF) was studied in the rat medial gastrocnemius. The rate of tension generation and of the relaxation within a tetanus was measured under isometric conditions. These measurements were performed at three points during both the contraction and relaxation: the beginning, the middle and the end of the phase of changes in tension. Significant differences were found in the rate of tension changes between fast and slow units. Comparison of FF and FR units showed less pronounced differences in their rates of the contraction and the relaxation. Moreover, slow units showed significantly greater slowing of both the contraction and relaxation within a tetanus in relation to the speed of their twitch when compared to fast motor units. The rate of changes in tetanic tension correlated to twitch time parameters and to tension generated during twitch or tetanus. The results point out that the well known difference in the speed of twitch contraction between fast and slow units is also visible in their fused tetani.

Axonal conduction velocity of motor units of rat's medial gastrocnemius muscle.

Axonal conduction velocity and its relations to different contractile properties of motor units of medial gastrocnemius muscle were investigated in nine Wistar rats anaesthetized with pentobarbitone. Functionally isolated motor units were identified as slow (S), fast resistant (FR) and fast fatigable (FF). Axons of S motor units conducted significantly more slowly than of fast units, while there was considerable overlap between conduction velocities measured for FR and FF types. The mean values of conduction velocity were 50.9 m/s for S, 68.9 m/s for FR and 71.3 m/s for FF type motor units. Strong and significant negative correlation between conduction velocity and contraction time as well as half-relaxation time was demonstrated. However, only a weak correlation between conduction velocity and twitch tension, tetanic tension or fatigue index was found. The multiple regression analysis revealed that the major factor to determine conduction velocity was contraction time.

Changes in fusion index during the fatigue test of fast motor units in the medical gastrocnemius muscle of the rat.

Changes in the fusion of tetani were investigated in fatigue tests of 50 fast motor units of the rat medical gastrocnemius muscle. Fusion of the tetani was measured using the fusion index, being the ratio of the tension to which motor unit relaxed before the last component of tetanus to the peak tension of the last component. In both types of fast units (fast fatigable and fast resistant) the changes in the fusion index were similar to those in tetanic tension: first they increased and then decreased. However, the increase of the fusion index was longer than that of tension and the subsequent decrease in the fusion index smaller than that of tetanic tension. Furthermore, the initial increase in the fusion index of fast fatigable motor units was greater than in the tension. The dependence of the fusion index on twitch time enables the analysis of the influence of changes in the twitch time on changes in tension of unfused tetani observed during activity of fast motor units.

Experimental chlorphentermine lipidosis of the retina in albino rats.

Chronic administration of chlorphentermine leads to an accumulation of lysosomal inclusions in the retina of young rats. The cells of the pigment epithelium, the perikeratic part of the ganglial cells and their axones are filled with inclusions, whereas other parts of the retina remain free. As soon as the treatment is discontinued, the alterations recede completely. The experiment can be considered to be a model for the lysosomal capacity of those parts of the retina concerned; in addition, it supplies information on the metabolism of phospholipids in these structures.

[Surgical treatment of traumatic amaurosis]. / Ein Beitrag zur operativen Behandlung der traumatischen Amaurose.

Exploration of the optic canal was performed in 5 patients with traumatic amaurosis. Fractures of the optical canal were found in 4 cases. One case in which the canal was intact was interpreted as evulsion of the optic nerve. Vision improved in one of the cases with a fractured optical canal. Exploration of the optic nerve is recommended in cases of traumatic amaurosis, always provided that the indication is correct.

Nutritional and immunological investigations in head and neck cancer patients before and after therapy.

We studied the nutritional and immunological states of 20 patients with advanced head and neck carcinomas. Treatment included chemotherapy with methotrexate, cis-platinum and bleomycin prior to operation and radiotherapy. Nutritional and immunological parameters were examined before and after each therapy given. Most of these parameters decreased during chemotherapy. However, while we found that nutrition improved or normalized by the end of the primary tumor treatment, immunologic parameters failed to change significantly.

A comment on laryngeal cytology.

Cytology of the laryngeal mucosa proved to be a suitable method for diagnosing low-grade and intermediate dysplasia, but it did not allow any distinction between high-grade dysplasia and invasive cancer. In our experience, the use of this method should be restricted to a few conditions, such as the persistance of recurrent dysplasias and certain extended lesions from which biopsies give a high risk for scarring and permanent hoarseness.

Cisplatin-induced ototoxicity: audiometric findings and experimental cochlear pathology.

Twenty-four (48%) out of a group of 50 patients treated with one to three single doses of cisplatin compound (cis-DDP), at a dosage of 60 mg/m2 body surface, were found to have deterioration of post-treatment pure tone audiometric threshold levels. Statistical analysis of pre- and post-treatment hearing losses by means of the paired t-test, however, did not show any significant hearing loss associated with cis-DDP-toxicity, nor could hearing loss following treatment be correlated to ages of the patients, pre-treatment hearing impairments, specific frequencies, or the number of treatment courses given. In contrast, cochlear damage was studied in the guinea pig model by daily administration of high cumulative doses of cis-DDP, and was found to be dose-dependent and selectively restricted to the outer hair cells of the inner ear and corresponding nerve fibers. Hair cell degeneration was most severe in the basal turn of the cochlea, and progressed in an apical direction so that the cells in the first row were the most affected.

[Clinical aspects and therapy of parotid tumors]. / Zur Klinik und Therapie der Parotistumoren.

The authors report on their cases of parotid tumours between 1972-1982. Not only benign and malignant neoplasms but also inflammatory "tumours" were included, since they often exhibit signs of real neoplasms. The patient material and the results obtained agree well with the literature. The great value of computed tomography is underlined especially in cases with hidden parapharyngeal tumours. Hopefully, recently performed measurements of serum isoamylase will be a valuable diagnostic test for parotid diseases, particularly in differentiating between real neoplasms and chronic inflammatory diseases.

[Vitamin A level and dark adaptation in patients with tumors]. / Untersuchung des Vitamin-A-Spiegels und der Dunkeladaptation bei Tumorpatienten.

Twenty patients with tumors of the head and neck region were found to have delayed dark adaptation. The serum vitamin A levels in these patients were significantly diminished in comparison with normal controls. Since disturbance of dark adaptation does not occur without prolonged vitamin A deficiency, it was reasonable to assume that the deficiency had been in existence for a long time. The antineoplastic effect of vitamin A is considered an important factor in tumor development and growth. Long-term malnutrition may be the reason for the disturbed vitamin A metabolism. Patients who do not attain mesopic vision should be advised against driving at night.

Some morphological features of neurons in the rat spinal ganglion.

By means of serial sections in different planes, the perikarya in the rat spinal ganglion were found to be of an irregular spherical shape, with the largest maximal diameter and perimeter in tangential sections. Type-I and type-II neurons have a mean size of about 18 micrometers and 13 micrometers, respectively. Since some type-I perikarya are in the range of type-II cells, it is not possible to distinguish them from type-II cells in unstained thick sections. Some type-I cell perikarya exhibit areas with a reduced number of organelles. These cells are considered as being in a generating state, a fact finally leading to an age-dependent loss of neurons.