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Biomedical subjects

P Hník

Publications and source records attributed to P Hník.

At least 19 recordsLinked to original sources
PubMed2004

Activation and modulation of ligand-gated ion channels.

Ligand-gated ionic channels are integral membrane proteins that enable rapid and selective ion fluxes across biological membranes. In excitable cells, their role is crucial for generation and propagation of electrical signals. This survey describes recent results from studies performed in the Department of Cellular Neurophysiology, Institute of Physiology ASCR, aimed at exploring the conformational dynamics of the acetylcholine, glutamate and vanilloid receptors during their activation, inactivation and desensitization. Distinct families of ion channels were selected to illustrate a rich complexity of the functional states and conformational transitions these proteins undergo. Particular attention is focused on structure-function studies and allosteric modulation of their activity. Comprehension of the fundamental principles of mechanisms involved in the operation of ligand-gated ion channels at the cellular and molecular level is an essential prerequisite for gaining an insight into the pathogenesis of many psychiatric and neurological disorders and for efficient development of novel specifically targeted drugs.

Allosteric Regulation↗
PubMed1999

Permanent alterations of spinal cord reflexes following nerve lesion in newborn rats.

Sciatic nerve lesion in newborn rats is known to cause degeneration of a large number of axotomized motoneurones and spinal ganglion cells. Some of the surviving motoneurones exhibit abnormal firing properties and the projection pattern of central terminals of sensory neurones is altered. We report here on long-term changes in spinal cord reflexes in adult rats following neonatal nerve crush. In acutely spinalized and anaesthetized adult rats 4-6 months old in which the sciatic nerve had been crushed on one side at birth, the tibial nerve, common peroneal nerve or sural nerve were stimulated on the reinnervated and control side and reflex responses were recorded from the L5 ventral spinal roots. Ventral root responses (VRRs) to tibial and peroneal nerve stimulation on the side of the nerve lesion were significantly smaller in amplitude representing only about 15% of the mean amplitude of VRRs on the control side. The calculated central delay of the first, presumably monosynaptic component of the VRR potential was 1.6 ms on the control side while the earliest VRR wave on the side of the nerve lesion appeared after a mean central latency of 4.0 ms that seems too long to be of monosynaptic origin. These results suggest that neonatal sciatic nerve injury markedly alters the physiological properties and synaptic connectivity in spinal cord neurones and causes a marked depression of spinal cord responses to peripheral nerve stimulation.

Animals↗
PubMed1997

Nociceptive atrophy of the rat soleus muscle induced by bone fracture: a morphometric study.

Reflex atrophy of the soleus muscle induced by ipsilateral metatarsal bone fracture in Sagatal-anesthetized adult male rats was studied by using two-dimensional stereological methods 7 days after the operation. When compared with contralateral solei, the wet weight of the experimental soleus muscles was decreased by approximately 24% and the area of the entire muscle section by approximately 29%. In atrophied solei, the number of type 1 fibers was lower by approximately 8%, resulting in lower total number of fibers (by approximately 6%). This indicates that slow motor units might be more sensitive to nociceptive stimulation. However, with respect to the fiber area, the reflex atrophy induced by metatarsal bone fracture in the rat soleus muscle resembles simple atrophy after 7 days, as the mean muscle fiber area was decreased by approximately 26% with no significant difference between atrophy in type 1 and type 2a fibers (by 27.3 and 23.0%, respectively).

Animals↗
PubMed1996

[History of physiology journals].

Two physiological journals were founded in Czechoslovakia in 1952, namely Ceskoslovenská fyziologie and an international version which was then named Cechoslovackaja fiziologija, later renamed Physiologia Bohemoslovaca. The first three volumes of the latter journal were published exclusively in Russian with German summaries. It was not until 1956 that most reports began to be published in English, with Russian summaries. In 1958, the content of both journals at last became separated. Cs. fyziol. started to publish review articles in Czech or Slovak, abstracts of communications reported at various scientific meetings, news from international symposia, etc. Physiol. Bohemoslov. continued to print the results of original experimental work. The major personality standing at the cradle of the two journals was Ernest Gutmann. Both journals were published by the Institute of Physiology of the Czechoslovak Academy of Sciences in Prague. In an attempt to make the latter journal more attractive to perspective authors from abroad, the international journal was renamed Physiological Research (formerly Physiologia Bohemoslovaca) in 1991 and still is being published by the same institution. It is indexed and abstracted by Current Contents, Excerpta Medica/Medline, Biological Abstracts, Chemical Abstracts, Current Awareness in Biological Sciences and Science Citation Index. A major change also occurred with the journal Ceskoslovenská fyziologie. This is now (since 1992) being published by the Czech Medical Society J.E. Purkynĕ. Besides publishing reviews intended as pregraduate and postdoctoral training for physiologists, physicians, pharmacologists and others working in allied fields of science, the journal informs members of the Czech and Slovak Physiological Societies about domestic and world news in physiology.

Czech Republic↗
PubMed1993

Bone fracture induces reflex muscle atrophy which is sex-dependent.

Longlasting nociceptive stimulation is known to cause atrophy of adjacent muscles. The aim of this study was to determine further the possible mechanisms of this pathological phenomenon. Unilateral fracture of the paw was performed under pentobarbital anaesthesia in several experimental groups (n = 8-11) of female and male rats. Dry muscle weights of the soleus (SOL), extensor digitorum longus (EDL), gastrocnemius (GA) and tibialis anterior (TA) were determined 7 days following the bone fracture and compared to the weight of contralateral control muscles. To demonstrate the reflex origin of this atrophy, deafferentation of the paw by dorsal root section (L4-6) was performed before or after unilateral fracture of hindlimb metatarsal bones. In female rats, the fracture resulted in a significant loss of muscle weight in all the four muscles examined. When the hindlimb was deafferented prior to the fracture, no muscle atrophy developed, and neither did deafferentation itself cause any appreciable change in muscle weight except in male rats. This supports the concept that this type of atrophy is reflex in origin. Deafferentation, when performed after the fracture, did not prevent the weight loss in extensor muscles (SOL, GA), while the flexors (EDL, TA) did not in general lose any weight. The results in male rats had a similar trend as in female rats, although the weight loss was significantly smaller. Our results showed that the mechanism of reflex muscle atrophy following metatarsal bone fracture involves a component which is dependent on afferent information from the injured paw.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1992

Reaching behavior in the rat: absence of forelimb peripheral input.

In order to test whether peripheral input from a moving forelimb is essential for reaching in rats, the effects of dorsal rhizotomy C5-Th2 were examined. Rats were trained to reach for a food pellet in the horizontal tube or on a tray. Reaching attempts before and after bilateral forelimb deafferentation were monitored by continual recording using magnetic induction. Deafferented animals were able to initiate and generate the motor program of reaching, but modulation of its ongoing execution was lost. Peripheral input from moving forelimb was necessary for the effective performance of grasping; the duration of the manipulative part of reaching was significantly prolonged and the success of grasping was markedly decreased. Also, the aiming of forelimb was impaired, probably by disturbing of body forelimb postural coordination. No significant changes were found in the execution of forelimb protraction. It is concluded that somesthetic feedback is not required for execution of forelimb protraction, but it is necessary for grasping.

Animals↗
PubMed1991

Motor functions in rat hindlimb muscles following neonatal sciatic nerve crush.

The sciatic nerve was crushed in the right hindlimb in newborn (3-8 h old) rats. Two to four months later, electromyographic activity was recorded from both the control and reinnervated ankle extensor muscles soleus or lateral gastrocnemius and from the ankle flexor muscle tibialis anterior. Tonic postural activity was present in the extensor muscles on both sides during quiet stance. The control flexor muscles were usually silent in this situation, but the reinnervated flexors exhibited abnormal sustained activity. During locomotion, the control extensors were activated during the stance phase and their mean burst made up 61.5% of the step cycle. The control tibialis anterior muscle fired only during the swing phase, with the burst lasting 18.1% of the step cycle. In the reinnervated extensor muscles, the mean burst duration was decreased (46% of the cycle) but the basic locomotor pattern was not impaired. The reinnervated tibialis muscle, however, was activated abnormally, with one appropriate flexor burst during the swing phase and an "extensor-like" burst during the stance phase of the step. Reflex responses to stretch were weak or absent on the operated side. Histological examination showed that the reinnervated soleus and tibialis muscles were almost devoid of muscle spindles. The motor unit mean firing rates in the reinnervated soleus (22 imp/s) and lateral gastrocnemius (45 imp/s) matched those of the control muscles (25 and 42 imp/s, respectively). In contrast to the phasic, high-frequency firing (52-80 imp/s) in the control tibialis, the reinnervated tibialis motor units fired at significantly lower rates (22-56 imp/s).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

[Characterization of vertebrogenic pain using the short form of the McGill Pain Questionnaire].

A Czech translation of the short form McGill Pain Questionnaire was tested in a group of patients suffering from pain of vertebrogenic origin. The results support the hypothesis that the questionnaire will be an asset in various disciplines of medical practice. While taking up little time it provides a comprehensive and valid picture of the quality and intensity of pain experienced by the patient. The results indicated that the questionnaire can differentiate between different syndromes of pain and is sensitive to the effect of placebo.

Adult↗
PubMed1990

Immobilization atrophy and membrane properties in rat skeletal muscle fibres.

Wet mass, resting membrane potential, frequency of miniature end-plate potentials and the concentration of [3H]ouabain-binding sites were studied after 7 days' immobilization of the rat soleus and extensor digitorum longus (EDL) muscles in the shortened or stretched position and after 3 and 7 days of remobilization. We observed that the loss of muscle mass by 37% in the rat soleus immobilized for 7 days in the shortened position is accompanied by a membrane depolarization of about 5 mV, a decrease in frequency of miniature end-plate potentials by 60% and a decrease of [3H]ouabain binding by 25%. Only minor changes were found in stretched soleus and in shortened and stretched EDL. After 3 days of remobilization of stretched soleus the muscle mass, [3H]ouabain binding and miniature end-plate potential frequency recovered to control values but the resting membrane potential continued to decrease. All changes induced by immobilization disappeared on day 7 of remobilization.

Animals↗
PubMed1989

Function and structure of atypical muscle spindles after neonatal nerve crush in rats.

During the early postnatal period, the differentiation and maturation of muscle spindles in the rat is still dependent on their sensory innervation. When a nerve is crushed during this period, most spindles in the denervated muscles degenerate and after reinnervation only occasional spindles of atypical structure are to be found in these muscles. We determined the basic functional properties of these atypical spindles in adult rats and attempted to correlate them with their structural characteristics. The discharge rates of 13 afferent units from the soleus or lateral gastrocnemius muscles were evaluated in response to stretch. These units were capable of a slowly adapting response to 2-4 mm stretches. Their mean discharge frequencies at any point of the ramp-and-hold stretch were, however, on an average 50% lower than normal values. The conduction velocities of afferents from the atypical spindles were in the range of 10-40 m/s. Histological examinations revealed that 90% of the atypical muscle spindles found in the soleus or lateral gastrocnemius muscles had only 1 or 2 intrafusal fibres without any nuclear accumulations as compared to four intrafusal fibres in normal muscle spindles in the rat. The proportional decrease of the discharge rate in both the dynamic and static part of the response of these atypical spindles could be due to the decreased synaptic area between the sensory terminals and the intrafusal fibres and/or to altered structural properties of the intrafusal fibres.

Action Potentials↗
PubMed1986

EMG activity in "compensatory" muscle hypertrophy.

The functional elimination of synergistic muscles leads to dramatic muscle hypertrophy. However, neither resting EMG activity recorded by an implanted electrode array, nor activity during locomotion have substantiated the assumption that the hypertrophy in the rat soleus muscle is caused by hyperactivity.

Adaptation, Physiological↗
PubMed1986

Controversial aspects of skeletal muscle tone.

It is being proposed that "muscle tone" comprises at least two mechanisms: a) reflex, neurogenic ("extrinsic") tone which is graded by reflex pathways and mediated by action potentials, and b) resting, myogenic ("intrinsic") tone which is not mediated by conducted action potentials, but is dependent upon local conditions in the muscle and is given by the number of sarcomeres and their mean length.

Action Potentials↗
PubMed1985

Quantitative evaluation of electromyogram activity in rat extensor and flexor muscles immobilized at different lengths.

Because immobilization of muscles in the "long" position mitigates the effects of inactivity and rapid wasting occurs when muscles are immobilized in the "short" position, a study was made of the EMG activity in the soleus (SOL)--an extensor muscle--and the tibialis anterior (TA)--a flexor muscle--in order to clarify the possible role of muscle function in modifying the course of disuse atrophy. EMG activity was recorded in the SOL and TA muscles in adult rats in which the ankle had been immobilized in a plaster cast either in plantar flexion or dorsiflexion. The number of action potentials per minute in samples of the EMG activity from control and immobilized muscles was assessed before, for 10 days during immobilization, and up to 9 days after removal of the cast. Immobilization in the short position (plantar flexion) led to a dramatic reduction in the EMG activity of the SOL (to 10% of the control). On the other hand, fixation of the SOL in the long position was without effect upon resting EMG activity. In the TA, EMG activity was exclusively phasic in character and corresponded to about 3% of that of the SOL. Neither the fixation of the ankle in plantar flexion nor dorsiflexion had any appreciable effect upon EMG activity in the TA. We conclude that, because immobilization in the lengthened position does not increase EMG activity in either extensor or flexor muscles, passive stretch appears to be the factor mainly responsible for mitigating the effects of disuse in this situation. On the other hand, when a typical extensor muscle (SOL) is immobilized in the shortened position and undergoes rapid wasting, an accessory role of decreased activity cannot be excluded.

Animals↗
PubMed1985

The postnatal functional development of muscle stretch receptors in the rat.

The response to a 5-sec stretch of the triceps muscle was studied in dorsal root filaments L5 of 72 infant rats (1-19 days old) under urethane anesthesia. More than 50% of all units in 1-day-old rats responded by repetitive firing until the end of the 5-sec stretch (slowly adapting or SA receptors), while the rest ceased to fire earlier (relatively rapidly adapting or 1/2 SA receptors), or gave an "on" response only. The number of units exhibiting an SA response increased with age and attained 80% in 5-day-old rats. By the 10th day of life, almost 90% of endings behaved as SA receptors. During development, the maximal discharge frequencies at the peak of stretch increased markedly, and their values in 18-day-old rats were comparable to those in adult rats. The phasic component of the response to stretch, although less well defined in the younger animals, was already present even in 1-day-old rats. Adaptation of the static response during maintained stretch was relatively steep in all the age groups studied. The results indicate that, in the rat, large numbers of muscle stretch receptors are capable of responding to sustained stretch as SA receptors, even at an age when their morphological and ultrastructural maturation is not yet fully accomplished.

Adaptation, Physiological↗
PubMed1985

Postural EMG activity in the soleus muscle of adult rats following thyroidectomy.

An electrode array was implanted for chronic recording of EMG activity in both soleus muscles (SOL) in adult albino rats (Wistar strain) of 250 g mean body weight. After 12-13 days, surgical thyroidectomy was performed and the postural EMG activity in both SOL muscles up to 16 weeks after the operation was quantitatively compared (spikes per minute) with the EMG activity before the operation. The results showed that the EMG activity in the SOL is significantly decreased after thyroidectomy.

Action Potentials↗
PubMed1985

The use of chronic polyelectromyography in neurophysiological and behavioural experiments.

A method of electromyography (EMG) recording is described which makes it possible to follow simultaneously the activity of 4 muscles in awake, unrestrained rats and cats for 3-5 months. The implantable recording array consists of a percutaneous connector, steel wire spiral leads contained in silicone tubing and bipolar platinum electrodes embedded in silicone platelets. These electrode probes can be fixed onto the surface of various muscles without direct injury to the muscle and, at the same time, without electrical interference from neighbouring muscles. In most rats, EMG activity was recorded bilaterally from the soleus and tibialis anterior muscles. This method has so far been employed for assessing the muscle activity in experiments on reflex muscle atrophy, unilateral hindlimb deafferentation, disuse muscle atrophy induced by limb immobilization and compensatory muscle hypertrophy. A simple computer program has been used to evaluate the resting, postural activity. Objective information about muscle coordination, patterns of locomotor and reflex activity, muscle use and disuse under specific experimental conditions can only be obtained in awake, unrestrained laboratory animals by recording electromyographic (EMG) activity in chronic experiments. For this purpose we developed a method of chronic polyelectromyography allowing recording from 4 muscles in rats and cats (Hník et al. 1978) for several months. The method is briefly reviewed here, together with some applications to animal experiments.

Animals↗