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.

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.

A multicenter comparison study of the Humphrey Field Analyzer I and the Humphrey Field Analyzer II.

PURPOSE: The purpose of the study is to determine the comparability of the 30-2 full-threshold program in the original Humphrey Field Analyzer (HFA) I to the same test procedure in the new Humphrey Field Analyzer II. METHODS: At each of five clinical centers, one eye of patients with ocular hypertension and normal visual fields, patients with early glaucomatous visual field loss, and patients with more advanced visual field loss were tested with the two instruments plus a retest on a separate HFA I. All participants had undergone at least one prior visual field examination. To minimize the influence of any residual learning or fatigue effects, the order of testing for the three visual field examinations was counterbalanced across subjects. A total of 250 patients were tested (81 patients with ocular hypertension, 81 patients with early glaucomatous visual field loss, and 88 patients with more advanced glaucomatous visual field loss). RESULTS: No statistically significant differences were observed between thresholds, visual field indices, or reliability indices obtained with the HFA I and the HFA II. The small differences between the two instruments were equivalent to the variation observed for test-retest measures using only the HFA I. These results were consistent across the range of visual field characteristics shown by the ocular hypertensive, early glaucoma, and moderate glaucoma patient groups. CONCLUSIONS: The authors' results indicate that there are no differences in the visual field results obtained with the HFA I and the HFA II. These findings suggest that with careful attention to test protocols, the HFA I and HFA II may be used interchangeably to observe patients, even within the context of multicenter clinical trials.

Reproducibility of retinal and optic nerve head blood flow measurements with scanning laser Doppler flowmetry.

PURPOSE: To evaluate the interobserver variability and the reproducibility of retinal and optic nerve head capillary blood flow measurements performed with a new noninvasive equipment, the scanning laser Doppler flowmeter (Heidelberg Engineering, Heidelberg, Germany). METHODS: Blood flow measurements were performed during three independent sessions in six patients with glaucoma and five normal subjects using the scanning laser Doppler flowmeter (SLDF), which allows the visualization of perfused capillaries and vessels of the retina and optic nerve head and enables the quantification of capillary blood volume, flow, and velocity in any selected area of the perfusion map. To evaluate the interobserver variability in selecting the areas in the perfusion map to be measured, three observers tried to locate the same areas in the perfusion map of images obtained during the first session. To evaluate the reproducibility of the measurements, the observers measured correspondent areas in the peripapillary retina and in the optic nerve head of images from the three sessions. Areas of different sizes (10 x 10 pixels and 4 x 4 pixels) were measured. RESULTS: The agreement between readings performed by the three observers was very good, with the reliability coefficient for the various parameters varying from 0.90 to 0.98. The reproducibility of retinal and lamina cribrosa measurements with the 10 x 10 pixel square target was good (reliability coefficient for the different parameters ranging from 0.70 to 0.85) and much better than the reproducibility of the 4 x 4 pixel target. The measurements performed in the neuroretinal rim area also had poor reproducibility. The measurements from the patients with glaucoma tended to be more reproducible than those from normal subjects. CONCLUSIONS: The SLDF allows reproducible blood perfusion measurements of retinal and lamina cribrosa areas when a target square of 10 x 10 pixels is used.

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).

Comparison of psychophysical and electrophysiological testing in early glaucoma.

PURPOSE: To compare the sensitivity and specificity of a wide range of psychophysical and electrophysiological tests in the detection of early glaucomatous damage. METHODS: Forty-three normals and 43 patients with early glaucoma, some still without field defects, were tested with differential light threshold perimetry, short-wavelength automated perimetry, high-pass resolution perimetry, motion detection, flicker contrast sensitivity, flickering and isoluminantly matched letter tests, and pattern and flash electroretinography, including photopic, scotopic, oscillatory potentials, and 30 Hz flicker. Receiver operating characteristic analysis was applied to continuous variables derived from each of the tests. RESULTS: Most parameters reflected glaucomatous loss to some degree, even though only single variables were analyzed separately in the receiver operating characteristic analysis. The pattern electroretinogram and some of the letter acuity tests had the best sensitivity and specificity, followed by short-wavelength automated perimetry and high-pass resolution-perimetry. Motion detection, flicker contrast, and flash electroretinogram parameters scored poorly. Six patients with normal results on the Humphrey field test had abnormal results on many of the other tests. CONCLUSIONS: Applying different psychophysical and electrophysiological tests may add to our ability to detect early glaucomatous damage.

Scanning laser Doppler flowmeter study of retinal and optic disk blood flow in glaucomatous patients.

PURPOSE: To examine blood flow in the retina and optic nerve head of patients with primary open-angle glaucoma. METHODS: Retinal and optic nerve head blood flow of glaucoma patients and control subjects of similar age and gender were measured in arbitrary units with the Heidelberg Retina Flowmeter, a scanning laser Doppler flowmeter (Heidelberg Engineering, Heidelberg, Germany). A total of 33 glaucoma patients and 29 control subjects were included in this study. Microvascular blood volume, flow, and velocity were analyzed in four areas of the retina approximately 100 microns from the edge of the optic disk (two temporal, one superior, and one inferior), in one area of the neuroretinal rim, and in the lamina cribrosa. RESULTS: The glaucoma patients had significantly decreased blood volume, flow, and velocity in one temporal retinal area (P < .006) and in blood volume in the inferior retinal area (P = .04). They also had significantly decreased blood volume, flow, and velocity in the lamina cribrosa (P < .0004), which also had more areas the investigators judged to be avascular compared to control subjects (P < .0001). No differences between glaucoma and control subjects in the blood flow measurements of the neuroretinal rim were found. CONCLUSION: These findings suggest that glaucoma patients tend to have less blood volume, flow, and velocity in the lamina cribrosa and upper temporal peripapillary retina. The temporal area below the horizontal, corresponding to the papillomacular bundle, did not show this difference. The findings may be significant in the pathogenesis of primary open-angle glaucoma.

Contrast sensitivity for flickering and static letters and visual acuity at isoluminance in glaucoma.

PURPOSE: Psychophysical testing was used to assess the effects of early glaucomatous damage on visual functions mediated by the magnocellular and parvocellular pathways. METHODS: We studied 57 eyes with early glaucoma, 92 eyes suspect for glaucoma, and 88 normal eyes. Tests were designed to target the functions of the magnocellular (M) or the parvocellular (P) pathways, and included measurements of contrast sensitivity for letter recognition, using both static presentation, and counterphase modulation at 25 Hz. We assumed that ability to perform the latter task would depend on the integrity of the M-cell pathway. To evaluate P-cell function we measured spatial acuity for a green letter presented against an isoluminant white background. Tests were carried out in the fovea, and at 3 degrees nasal, superior, temporal and inferior to the fovea. RESULTS: Glaucomatous eyes showed, on average, defects in almost all of the functions tested. Threshold elevations for static and isoluminant presentations were generally as large as those for flickering stimuli. The inferior paracentral part of the retina was generally more severely affected than the other locations tested. The defects observed in the suspect population were similar to, although smaller in magnitude than, those found in eyes with glaucoma. A discriminant analysis identified a subset of five tests, including P as well as M pathway tests, which was able to correctly classify 89% of normal and 79% of glaucomatous eyes. CONCLUSIONS: Putative M- and P-cell functions are both impaired at a relatively early stage of glaucoma. Deficits for both types of test are most severe in the inferior paracentral area of the retina (superior visual fields). Psychophysically based detection of the condition can benefit if results from different tests, done at different retinal locations, are combined.

[History of physiology journals]. / K dejinám fyziologických casopisu.

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. Purkyne. 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.

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)

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.

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)

[Characterization of vertebrogenic pain using the short form of the McGill Pain Questionnaire]. / Charakterizace vertebrogenní bolesti zkrácenou formou dotazníku 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.

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.

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.

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.

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.

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.