Search PubMed⌕ Search

Biomedical subjects

U Proske

Publications and source records attributed to U Proske.

At least 73 records · Page 4Linked to original sources
PubMed1994

Blockade of intrafusal neuromuscular junctions of cat muscle spindles with gallamine.

This is a report on the resistance to block of the motor terminals on intrafusal fibres of cat soleus muscle spindles using the drug gallamine triethiodide (Flaxedil). To minimize diffusion barriers and to permit accurate measurements of time courses, rather slow rates of gallamine infusion were used (0.15 mg min-1). The main finding made was that after gallamine infusion, when extrafusal tension had dropped to half, all dynamic fusimotor effects and eight of twenty static effects had fallen to 40% or less of their control value. The remaining static effects persisted at 60-80% of their control value. Where fusimotor fibres were stimulated together with one or two skeletomotor fibres, the influence of the skeletomotor axons was significant only after spindle biasing had fallen to low levels. When gallamine infusion was stopped extrafusal tension returned to control levels within 20-75 min, depending on the length of the block, while fusimotor responses did not fully recover within the recording period of up to 150 min. The combination for some fusimotor responses of an early fall and a late recovery when compared with extrafusal tension, suggested a greater sensitivity of these endings to the drug. A comparison of spindle responses to the drug succinyl choline (SCh) and to fusimotor stimulation in the presence of gallamine showed that SCh responses were rapidly reduced by gallamine and had a long recovery time course, as were some fusimotor responses. From this it is argued that fusimotor effects with a high sensitivity to gallamine blockade were associated with nuclear bag fibre contractions and the more resistant effects with nuclear chain fibre contraction. It is generally believed that intrafusal neuromuscular junctions are more resistant to neuromuscular blockers than extrafusal junctions. The present experiments provide evidence to the contrary for some intrafusal junctions. Since muscle relaxants are often used in general anaesthesia it is interesting to speculate about the recovery of function of proprioceptive reflexes and of kinaesthesia during the immediate post-anaesthetic period, in view of the large difference in recovery time for transmission at intrafusal and extrafusal junctions.

Animals↗
PubMed1994

Correlating resting discharge with small signal sensitivity and discharge variability in primary endings of cat soleus muscle spindles.

1. In a previous report we proposed that primary endings of cat soleus muscle spindles can be separated into two kinds. One kind, called by us silent endings, at muscle lengths shorter than Lm -10 (maximum body length -10 mm), fell silent after a 5 mm shortening step. Spontaneous endings, on the other hand, were able to resume a resting discharge after a brief pause at all muscle lengths down to Lm -20. This report examines further differences between the two kinds of endings. 2. There were consistent differences in the muscle length dependence of the maintained level of resting discharge of the two kinds of endings, measured after a conditioning contraction or a contraction followed by a shortening step. The resting discharge of spindles with spontaneous endings, after both forms of conditioning increased progressively with length. For silent endings, after a conditioning contraction, resting discharge fell slightly at longer lengths. 3. Discharge variability, measured at a number of muscle lengths, showed a dependence both on mean interimpulse interval and on spindle type, being higher in silent than spontaneous spindles. 4. Small signal sensitivity was measured with the use of 1 Hz sinusoidal stretches applied longitudinally to the tendon. Sine wave amplitude was adjusted to give a 30% depth of modulation of the resting discharge. Spontaneous endings were consistently less sensitive to the stretches than silent endings at all muscle lengths. Average sensitivities, measured over a range of lengths between Lm -4 and Lm -20 mm were 0.30 imp.s-1.microns -1 for spontaneous endings and 0.66 imp.s-1.microns -1 for silent endings.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of repeated eccentric contractions on structure and mechanical properties of toad sartorius muscle.

It has been proposed that lengthening of active muscle at long lengths is nonuniformly distributed between sarcomeres, with a few being stretched beyond overlap and most hardly being stretched at all. A small fraction of the overstretched sarcomeres may fail to reinterdigitate on subsequent relaxation, leading to progressive changes in the muscle's mechanical properties. Sartorius muscles of the toad Bufo marinus were subjected to repeated lengthening (eccentric) contractions at long lengths, while controls were passively stretched and then contracted isometrically or stretched at short lengths. The muscles undergoing eccentric contractions showed a progressive shift to the right of the length-tension curve, a fall in the yield point during stretch, an increase in slope of the tension response during stretch, and a fall in isometric tension. In control muscles, changes, if any, were significantly less. In electron micrographs, muscle fibers that had been subjected to a series of eccentric contractions showed sarcomeres with A bands displaced toward one half-sarcomere, leaving no overlap in the other half. Adjacent regions often looked normal. These results are all in agreement with the predictions of the nonuniform stretch of sarcomeres hypothesis.

Animals↗
PubMed1992

Sprouting of fusimotor neurones after partial denervation of the cat soleus muscle.

Normally, gamma motoneurones innervate only the intrafusal fibres of muscle spindles. This is a report of sprouting of gamma motoneurones to innervate extrafusal muscle fibres following partial denervation of the soleus muscle of kittens. In eight newborn animals, the L7 ventral root was cut on one side under anaesthesia and the animals were then allowed to recover. At approximately 100 days of age animals were reanaesthetised and a study made of mechanical properties of motor units whose axons ran in the S1 ventral root and supplied the partially denervated soleus muscle. Evidence was obtained for sprouting of all surviving alpha motoneurones. In addition, in four experiments axons conducting within the gamma range, on stimulation, produced measurable tension. In one experiment, stimulation of one such gamma axon also produced specific fusimotor effects on four afferents identified as coming from primary endings of muscle spindles. The gamma axon was therefore a fusimotor axon. The effect observed on stimulation of the gamma axon suggested a largely dynamic action. Other examples of gamma axons were encountered that on stimulation produced tension, but which could not be specifically associated with spindles. In addition, a number of gamma axons that did not develop tension were shown, on stimulation, to have fusimotor effects that were static in action. It is concluded that in extensively denervated muscles gamma motoneurones may sometimes sprout to innervate extrafusal fibres. The mechanical properties of the extrafusal fibres innervated by such gamma axons were similar to those of ordinary alpha motor units.

Animals↗
PubMed1992

Development of the sensory innervation of muscle spindles in the kitten.

This is a report of the changes observed in the pattern of sensory innervation of muscle spindles in hindlimb muscles of kittens during the first four weeks of life. The structural analysis, made on teased, silver-stained preparations, was complemented by a series of recordings of afferent responses of kitten spindles during ramp-and-hold stretches of the muscle. The primary endings of spindles from newborn animals showed a large degree of variability in their branching pattern and branches formed a network across the intrafusal fibres. In older animals there was less variability and lateral branches of stem axons began to encircle the intrafusal fibres. The process of maturation was characterized by a more uniform shape of the endings and more complete, evenly spaced, annulospiral terminals. Recordings of the responses of primary endings of spindles during muscle stretch showed that several features of the adult response were already present in the newborn, although the overall rate of discharge was very much lower. It was concluded that the changes observed in the structure of the sensory endings of kitten spindles did not have clearly identifiable physiological correlates. It appears that an annulospiral shape of the sensory terminals is not a necessary prerequisite for the generation of stretch responses. The predominant factor which appears to determine the responses of spindles to stretch is the maturity of the intrafusal fibres, in particular, the bag2 fibre.

Aging↗
PubMed1992

Muscle history dependence of responses to stretch of primary and secondary endings of cat soleus muscle spindles.

1. Responses were recorded from both primary and secondary endings of soleus muscle spindles in the anaesthetized cat during slow stretches of the muscle after conditioning contractions at different lengths. 2. After a 5 mm length step and a fusimotor-strength contraction given at the longer length, on return to the initial length the response to a slow test stretch (0.5 mm s-1) showed a change in slope midway through the stretch which was attributed to taking up of slack in intrafusal fibres. 3. The onset of the change in slope during the test stretch depended on the size of the conditioning step. With no conditioning length change, just a fusimotor-strength contraction, there was no slope change and the response consisted of an initial burst followed by a maintained high rate of discharge. 4. Following a conditioning length step, the point of onset of the slope change during the test stretch could be altered by stimulating single identified fusimotor fibres to the spindle. Stimulating some static axons produced large changes in the stretch response while other static axons and dynamic axons had only small effects. 5. Many secondary endings showed a delay in onset of their response to a test stretch, dependent on the size of the preceding conditioning step, signalling the presence of slack in much the same way as the primary endings. Other secondary endings, however, appeared to have stretch responses that were largely independent of muscle conditioning. 6. Muscle history-independent responses of secondary endings were associated with low axonal conduction velocities. It is proposed that secondary endings which remain unaffected by muscle conditioning lie on more distal regions of nuclear chain fibres in the S2-S5 position. Here they are stimulated during both the take-up of slack and the subsequent direct stretch of the intrafusal fibres.

Animals↗
PubMed1992

The central projection of electrosensory information in the platypus.

1. This is the first detailed description of the projection to the cerebral cortex of afferent information coming from electroreceptors in the bill of the platypus, Ornithorhynchus anatinus. 2. In animals anaesthetized with chloralose, with the bill immersed in tap water, applying a potential difference between plate electrodes on either side of the bill produced large amplitude potentials from the surface of a postero-lateral region of cerebral cortex. Response threshold was 300 microV cm-1, somewhat lower than threshold measured for single identified electroreceptors. Electroreceptor threshold was at least three orders of magnitude lower than threshold of mechanoreceptors to electrical stimuli (Gregory, Iggo, McIntyre & Proske, 1989a). 3. Monopolar stimulation of the bill revealed a crossed projection. The map on the cortical surface had the bill oriented dorso-laterally, its base towards the mid-line, the tip on the lateral edge, pointing slightly forwards. The edge of the bill faced backwards. Electrosensory information coming from the edge of the bill appeared to be much more strongly represented than input from the dorsal surface. 4. Weak electrical and mechanical stimuli applied to the bill both evoked large amplitude potentials from the same region of cortex indicating that there was complete overlap between the regions receiving tactile and electrosensory inputs. 5. Inserting microelectrodes into the deeper layers of cortex revealed burst discharges in single cells and groups of cells in response to weak electrical stimulation of the bill. Activity could be recorded over a range of depths from 0.3 to 4 mm, with the majority of responses coming from cells 1-3 mm deep. Histological examination of lesion sites made at 1.1 mm and at 3 mm suggested that cells in the pyramidal and ganglion layers were involved in generating the activity. 6. Some evidence was obtained for interactions at the level of the cerebral cortex between activity generated by tactile and electrosensory inputs. When electrical and mechanical stimuli were both applied to the bill with an interstimulus interval of less than 25 ms, cortical neuronal responses generated by one stimulus were completely suppressed by the other. However no evidence was obtained of a direct convergence at the level of the cortex between the two modalities. 7. Cortical activity could be evoked in response to rapidly changing voltage fields. This observation, together with our earlier finding of a high rate sensitivity of the receptors, emphasizes the high dynamic sensitivity of the system. 8. It is concluded that the electrosensory system of the platypus is closely associated with the sense of touch.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Responses of primary endings of cat muscle spindles to locally applied vibration.

Responses of muscle spindles in the cat soleus muscle have been studied during vibration applied locally to the belly of the muscle. Bursts of vibration at 170 Hz and with a peak amplitude of 200 microns were applied to a site at which local pressure initiated impulses from the spindle. The response to vibration depended on the conditioning of the muscle immediately beforehand and the placement of the vibrator. The length at which the vibration was applied was called the test length; this was typically 10 mm less than the muscle's maximum length in the body. After a fusimotor strength contraction at a length 2-5 mm longer than the test length, vibration sensitivity, measured on return to the test length, was low. If the muscle was contracted at a length 2-5 mm shorter than the test length, vibration sensitivity was high. The low vibration sensitivity following conditioning at the longer length was attributed to the development of slack in intrafusal fibres. In the presence of slack, stimulation of some static fusimotor fibres was able to restore vibration sensitivity fully. It is suggested that the vibration sensitivity of passive spindles arises largely in bag2 intrafusal fibres.

Animals↗
PubMed1991

The anatomy and fine structure of the echidna Tachyglossus aculeatus snout with respect to its different trigeminal sensory receptors including the electroreceptors.

The gross anatomy and nerve supply of the bill of echidna (Tachyglossus aculeatus) is described in relation to its function as an outstanding sensory organ. The sensory innervation of the skin of the echidna snout was investigated by means of frontal serial sections, after decalcification of the specimens. A comprehensive light and electron microscopic description of the location and fine structure of cutaneous sensory receptors of the trigeminal system was made by this means. The encapsulated and non-encapsulated Ruffini receptors, the types of other free receptors in the connective tissue and the Merkel cell receptor do not differ morphologically from those of higher mammals, whereas the pacinian-like corpuscle shows a unique organization of its outer core. This is composed of large perineural cells containing a unique reticulum of parallel-orientated endoplasmic membranes. Lamellated corpuscles, seen in isolation or in association with push rods, are numerous in the snout and in the tip of the tongue of echidna. Push rod receptor organs occur in the hairless skin of the bill with a very dense array at its rostral end and in the pseudopalatal ridges. Gland duct receptors are restricted to the skin adjacent to the nostrils and the mouth opening, including the pseudopalatal plates. Only about one quarter of the total number of 400 seromucous glands receive a sensory innervation of their intraepidermal duct segment. Within each innervated gland two types of receptor terminals are identified. The distributions of the different receptor types are mapped for different regions of the skin, the mucous membrane of the nasal and oral vestibule and the tip of the tongue. The fine structure of nerve terminals is discussed from a comparative anatomical point of view, and some speculations are made about possible transduction processes that underlie the known electrophysiological properties. The sensory organs such as the "push rod" and "gland duct receptor", and most of their sensory terminals, are less differentiated in echidna snout than in the platypus (Ornithorhynchus anatinus) bill.

Animals↗
PubMed1991

Extrafusal and intrafusal motor units in the kitten.

In the lateral flexor digitorum longus muscle (FDL) of anaesthetized kittens aged 3-21 days, alpha (alpha) and gamma (gamma) motoneurone conduction velocities were measured together with motor unit tensions. Conduction velocity lay in the range 8-27 msec-1 for alpha motoneurones and 2-10 msec-1 for gamma motoneurones. Motor unit tetanic tensions were 3-47 mN with the largest units being 2-2.2% of whole muscle tension. The hypothesis was tested that motor axons conducting within the gamma range and presumed to be innervating the intrafusal fibres of muscle spindles, on stimulation, produced measurable tension. Stimulating gamma motoneurones in the adult produces no tension. The hypothesis was based on histological observations that while in the adult, intrafusal fibres were about one third of the size of extrafusal fibres, in kittens the two were nearly equal, both in length and diameter. It was shown by means of signal averaging during stimulation of ventral root filaments that whenever tension was recorded in the muscle an impulse could be detected in the muscle nerve conducting at alpha motoneurone tempo. It is concluded that in the kitten, despite the fact that intrafusal and extrafusal fibres are of similar size, stimulating single gamma motoneurones does not develop measurable tension.

Animals↗
PubMed1991

Where in the muscle spindle is the resting discharge generated?

This is a report of experiments on muscle spindles of the soleus muscle of the anaesthetized cat. Following a step shortening of the muscle, muscle spindles fall silent. At suitable muscle lengths their discharge may restart several seconds later to gradually recover a maintained rate of discharge. These experiments examine the question of where within the spindle the resumption of a resting discharge may originate. It was found that stimulation of some static fusimotor fibres immediately after the shortening led to early recovery of the resting discharge. Stimulation of dynamic and other static gamma motoneurones had much less effect. Since the dynamic gamma axons innervate almost exclusively the bag1 intrafusal fibre, contraction of this fibre appears to have little influence on the mechanisms responsible for restarting the resting discharge. Bag2 and chain fibres do seem to be involved. For primary endings, the bag2 fibre contraction was especially effective since static axons, which did not evoke 'driving' of the afferent response, and which are thought to predominantly innervate bag2 fibres, did restart the resting discharge. For secondary endings, stimulation of nearly all gamma axons led to an early restart of the resting discharge suggesting that here the nuclear chain fibres were responsible.

Animals↗
PubMed1991

Responses of cat muscle spindles which lack a dynamic fusimotor supply.

1. The experiments reported here support the view that some spindles in the peroneus tertius muscle of the anaesthetized cat lack a nuclear bag1 intrafusal fibre. 2. The bag1 fibre is characterized by the fact that it is innervated exclusively by dynamic fusimotor axons. A method was devised to test each spindle in peroneus tertius for a dynamic fusimotor innervation. The ventral roots containing the muscle's motor supply were subdivided into five portions, approximately equal in terms of the tension they generated, and each piece was stimulated in turn, repetitively, at fusimotor strength, during ramp stretch of the muscle, to look for a large increase in dynamic response. 3. The method allowed confirmation that the majority of spindles in peroneus tertius had a dynamic fusimotor innervation. However, where the dynamic effect was weak and accompanied by a strong static fusimotor action and extrafusal unloading, it risked being overlooked. 4. The confirmatory test for the presence of a bag1 fibre was whether or not the spindle showed a large increase in dynamic response in the presence of the drug succinyl choline (SCh) injected arterially close to the muscle in which the spindle is located. SCh is known to induce a contracture in the bag1 fibre and therefore mimics tonic dynamic fusimotor stimulation. 5. In five experiments, of a total of forty-two spindles with afferents conducting within the group I range, five examples were encountered where there was no increase in dynamic response, either with ventral root stimulation or perfusion with SCh. It was concluded that these were spindles which lacked a bag1 fibre. 6. Passive stretch of such spindles revealed no feature in the response which allowed them to be distinguished from spindles in which the bag1 fibre was present. This conclusion posed the question, what contribution, if any, does the bag1 fibre make to the stretch response? 7. It was possible to show that under some conditions the bag1 fibre did contribute to the response to stretch. If the spindle was conditioned by repetitive nerve stimulation, at fusimotor strength, at a length longer than that at which a test stretch was applied, the response to the stretch was delayed, and it began at a lower rate than after conditioning stimulation at the test length. The delayed response was attributed to the presence of slack in intrafusal fibres.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Two kinds of resting discharge in cat muscle spindles.

1. The behavior of primary endings of cat soleus muscle spindles was studied during shortening steps carried out at different muscle lengths. 2. Spindles were of two kinds: one, silent spindles, whose afferents fell silent after the shortening, at least over part of the range of lengths tested. The second, spontaneous spindles, resumed firing at all lengths. 3. For silent spindles, the duration of the silent period, measured at lengths where they did recover a resting rate, depended directly on muscle length and became shorter at longer lengths. This is what would be expected if the slack introduced in the spindle by the shortening step was removed more rapidly at longer lengths by the higher passive tension. For spontaneous spindles, on the other hand, the duration of the silent period after the shortening was largely independent of muscle length and depended on the spindle's rate of firing immediately before the shortening. 4. At intermediate lengths the discharge of slack spontaneous spindles remained unaffected by an isometric muscle contraction. It was therefore not possible to produce a pause in the discharge, behavior normally taken as typical of spindles. The discharge could be interrupted by the contraction if this was combined with a large shortening movement. 5. It is proposed that when intrafusal fibers are slackened by a shortening step, the resting discharge in spontaneous spindles is generated by a maintained depolarization of the annulospiral ending resulting from extension of the terminal coils by forces from within the receptor. A shortening contraction compresses the spirals to interrupt the discharge. The sensory endings of silent spindles remain below threshold until the spirals have been opened out sufficiently by external stretch.

Afferent Pathways↗
PubMed1991

Effect of muscle length on phasic stretch reflexes in humans and cats.

1. This is a report of the effects at different muscle lengths of the muscle's immediate history on the tendon jerk and Hoffman (H)-reflex in triceps surae of human subjects and cats. 2. In adult human subjects the size of the tendon jerk was measured as electromyogram (EMG) and torque in response to a tendon tap. Before each test tap the muscle was conditioned by a maximum voluntary contraction carried out with the foot either plantarflexed or dorsiflexed by 30 degrees from the test position. After a contraction with the foot dorsiflexed, the subsequent reflex response was smaller than after a contraction with the foot plantarflexed. 3. The same conditioning procedure was carried out with the H-reflex. The reflex was elicited by transcutaneous electrical stimulation of the tibial nerve in the popliteal fossa. Here the reflex after a contraction with the foot dorsiflexed was larger than after plantarflexion. In other words, the effects of conditioning were the opposite for the tendon jerk and H-reflex. 4. The effects of muscle conditioning were tested over a range of muscle lengths. As the test length was made progressively longer, that is, the foot more dorsiflexed, the difference in size of the tendon jerk following the two forms of conditioning became less, whereas for the H-reflex it remained the same. 5. These findings were confirmed in cats anesthetized with alpha-chloralose. The tendon jerk was elicited by a quick stretch applied to the triceps surae muscle group, and the H-reflex represented by the monosynaptic reflex recorded from the central, cut end of the ventral root in response to electrical stimulation of the triceps nerve. Muscle conditioning consisted of a 1-s period of stimulation at 20 pulses/s, at fusimotor strength, of the peripheral end of the cut ventral root at a muscle length 5 mm longer or shorter than the test length. In the cat, as in human subjects, the effect of conditioning on the tendon jerk reversed at long muscle lengths, whereas the monosynaptic reflex showed no reversal. 6. It had been proposed previously that the effects of conditioning on stretch reflexes could be explained by development of slack in the intrafusal fibers of muscle spindles after a contraction at a longer-than-test length. The presence of slack lowers the resting discharge of spindles and reduces the afferent response to a tendon tap.(ABSTRACT TRUNCATED AT 400 WORDS)

Achilles Tendon↗
PubMed1990

Summation of tension in motor units of the soleus muscle of the cat.

In the cat soleus muscle which is exclusively composed of slow motor units the discrepancy between the sum of individual tensions and the tension on combined stimulation of several motor units was found to be much less than previously reported for slow motor units of peroneus longus. In peroneus the tension on combined stimulation was systematically larger than the value predicted from the sum of individual tensions. For both muscles it was possible to reduce the difference between observed and expected values by comparing the tension on combined stimulation with the sum of tensions, not of single motor units, but of groups of units. It is concluded that whenever tension is measured for single motor units, especially slow units in mixed muscles, the values obtained may be modified by frictional forces. The size of the effect appears to vary from one preparation to the next.

Action Potentials↗
PubMed1990

Intermittent stimulation of fusimotor fibres during slow stretch of muscle spindles in the cat.

Responses of muscle spindles of the peroneus tertius muscle of the cat were recorded during intermittent fusimotor stimulation, applied during slow stretch, after muscle conditioning by stimulation of the nerve at the test length or at a length 2.5 mm longer. Some static and all dynamic axons evoked afferent bursts whose amplitude was relatively independent of the level of stretch response. Other static axons produced bursts that grew in size with the stretch.

Action Potentials↗
PubMed1990

Slowing of the discharge of secondary endings of cat muscle spindles during fusimotor stimulation.

Responses of secondary endings of muscle spindles of the peroneus tertius muscle of the anaesthetized cat have been recorded during repetitive stimulation of functionally single fusimotor fibres that produced slowing of the discharge. In a sample of 125 pairs of single fusimotor fibres and secondary spindle afferents 5 examples of slowing were seen. The amount of slowing became less at longer muscle lengths. Conditioning the spindle by stimulating the muscle nerve at fusimotor strength, at a length 2.5 mm longer than the test length, and then returning to the test length 3 seconds later led to a greater degree of slowing of the discharge than after conditioning stimulation at the test length. With one exception, responses to muscle stretch were reduced during stimulation of a fusimotor fibre that produced slowing. On two occasions stimulating a fusimotor fibre that produced slowing of the response of one secondary ending, led to excitation of two other endings. Two possible explanations for the generation of slowing responses have been considered. The first is that the slowing is the result of contraction of the region of intrafusal fibre directly underlying the secondary sensory ending. The second, which we favour since it accounts for the facts more adequately, is that slowing is the result of shortening of the region of nuclear chain fibres on which the sensory ending lies, produced by movement in an adjacent nuclear bag fibre.

Animals↗