A comparison of tactile, visual, and auditory warnings for rear-end collision prevention in simulated driving

OBJECTIVE

This study examined the effectiveness of rear-end collision warnings presented in different sensory modalities as a function of warning timing in a driving simulator.

BACKGROUND

The proliferation of in-vehicle information and entertainment systems threatens driver attention and may increase the risk of rear-end collisions. Collision warning systems have been shown to improve inattentive and/or distracted driver response time (RT) in rear-end collision situations. However, most previous rear-end collision warning research has not directly compared auditory, visual, and tactile warnings.

METHOD

Sixteen participants in a fixed-base driving simulator experienced four warning conditions: no warning, visual, auditory, and tactile. The warnings activated when the time-to-collision (TTC) reached a critical threshold of 3.0 or 5.0 s. Driver RT was captured from a warning below critical threshold to brake initiation.

RESULTS

Drivers with a tactile warning had the shortest mean RT. Drivers with a tactile warning had significantly shorter RT than drivers without a warning and had a significant advantage over drivers with visual warnings.

CONCLUSION

Tactile warnings show promise as effective rear-end collision warnings.

APPLICATION

The results of this study can be applied to the future design and evaluation of automotive warnings designed to reduce rear-end collisions.

Use of an infusion-baited gravid trap to collect adult Ochlerotatus japonicus

Ochlerotatus japonicus adults have proven difficult to collect in significant numbers in the USA. Standard trapping and collection methods have been ineffective. Infusion-baited gravid traps, typically intended to attract Culex spp., have provided the greatest number and most consistent supply of Oc. japonicus adults collected in New Jersey.

Ochlerotatus japonicus collected from natural rockpools in New Jersey

Ochlerotatus japonicus larvae were collected from natural rockpools in New Jersey within the Delaware Water Gap National Recreational Area. Previously reported collections of Oc. japonicus in the United States have been limited to artificial containers and an occasional treehole.

Use of an AC induction motor system for producing finger movements in human subjects

This report describes the set-up and evaluation of a novel system for producing precise finger movements, for tests of movement perception. The specifications were to construct a system using commercially available components that were easy to use but which offered both flexibility and also high precision control. The system was constructed around an industrial AC induction motor with an optical encoder, controlled by an AC servo digital control module that could be programmed using a simple, high-level language. This set-up fulfilled the requirements regarding position and velocity control for a range of movements and also the facility for the subject to move the joint voluntarily while still attached to the motor. However a number of problems were encountered, the most serious being the level of vibration and the inability to vary the torque during movements. The vibration was reduced to the point where it did not affect the subject, by the introduction of mechanical dampening using an anti-vibration coupling and a pneumatic splint. The torque control could not be modified during rotation and so the system could only be operated using constant torque for any given movement.

Tendon organ sensitivity to steady-state isotonic contraction of in-series motor units in feline peroneus tertius muscle

1. Measurements have been made of the sensitivity of tendon organs to steady-state, isotonic contractions of single and groups of in-series motor units in the peroneus tertius muscle of the cat hindlimb. 2. Linear relationships were found between the Ib afferent discharge and the contractile tension generated by tetanic stimulation of single motor units. These relationships held for the fast, fatiguable (FF) units and for all but the lowest tensions generated by the slow (S) and some fast, fatigue resistant (FR) units. The sensitivity of the organs was independent of the contractile properties of the units. 3. Groups of three motor units were stimulated isotonically at low rates (around 30 Hz), but asynchronously to produce a smooth tension profile. Again, linear relationships pertained between the discharge rate and the tension, and the sensitivity was the same for different motor unit types. 4. Under isotonic conditions, therefore, the tendon organs showed linear responses to the tension with similar sensitivities, indicating that tendon organs may have the capacity to signal faithfully steady-state contractile tensions.

The dynamic response of feline Golgi tendon organs during recovery from nerve injury

The dynamic response of tendon organs to isometric contractions of activating motor units has been examined during recovery from nerve crush or nerve transection followed by suture repair. After nerve crush the characteristic response was rapidly restored, although the early and late phases of the dynamic response were altered differentially. Following nerve transection, recovery was much poorer and many responses were abnormal. Normal responses were only observed in a minority of tendon organ-motor unit interactions but every tendon organ studied did respond normally to at least one motor unit, with a range of dynamic sensitivities similar to normal. This suggests that the abnormalities observed reflect changes in the mechanical input to the organ, due to motor unit reorganisation, rather than abnormalities of the transduction process.

The static sensitivity of tendon organs during recovery from nerve injury

An investigation has been carried out into the physiological properties of tendon organs and their interactions with motor units following two types of nerve injury: nerve crush and nerve transection followed by suture repair. Recovery from nerve crush was very successful: 6 weeks after the injury 60% of the tendon organ-motor unit interactions (n = 62) evoked normal or near-normal patterns of afferent discharge but with reduced firing rates. After 10 weeks of recovery 81% of the interactions (n = 43) were normal. The main abnormality observed was a phasic-only pattern of discharge. The overall reductions in firing rate during early recovery may be attributable to the lower contractile forces generated by the reinnervated muscle units, while the phasic-only responses may also represent immaturity of the transduction mechanism of the regenerated afferent axons. Following nerve transection the quality of recovery was much lower and a range of abnormal, as well as normal patterns of response were observed. For all the afferents studied, both types of response were recorded, suggesting that although there may be changes in the sensitivity of the afferents to muscle contraction, the abnormal responses more probably reflect changes in the form of the mechanical input rather than abnormalities of the transduction process.

The dynamic response of Golgi tendon organs to tetanic contraction of in-series motor units

Golgi tendon organs (TOs) display a dynamic response related to the rate of tension development by the motor units (MUs) which activate each TO. When several MUs are activated together the response increases non-linearly with respect to tension. The dynamic response has been re-examined by recording the responses of TOs, in the adult cat, to tetanic, isometric contractions of one or more MUs and has been found to comprise two components: for each MU-TO pair the instantaneous frequency between the first two impulses of the response was linearly related to the rate of rise of the tension, the slope of the relationship being greatest for the slow units. Similarly, when activating MUs were stimulated together, the relationships between frequency and the initial rate of tension rise were linear. When the relationships were expressed in terms of relative tension rate the organs were found to be most strongly activated by the IIb muscle fibres, the responsiveness at the level of the whole muscle being reduced by unloading effects. The later component of the response showed an exponential relationship between discharge frequency and rate of tension development, the slope of the relationship between frequency and the logarithm of tension rate being independent of MU size. Although absolute tension increases during a contraction, this did not appear to impinge on the response which was dominated by the dynamic parameters of the contraction.

Skeletofusimotor (beta) innervation of proximal and distal forelimb muscles of the cat

The innervation of muscle spindles by skeletofusimotor (beta) axons has been compared in two long digit extensor muscles with three elbow extensor muscles of the cat forelimb. The proportion of muscle spindle poles with p1-endplates was analysed in silver impregnated teased material. The proximal and distal muscles displayed a significant difference in their proportion of muscle spindle poles with p1-endplates. The distal muscles had an estimated proportion of more than 70% beta innervation of their muscle spindles, the proximal muscles of 41-47%. This difference is discussed with respect to the different circuitry of the motoneurones. We suggest that the high proportion of beta-innervated spindles in distal muscles obtained with the absence of a recurrent inhibitory system in the innervating motoneurones [18] serves the execution of manipulative movements.

Small-signal sensitivity of muscle spindles reinnervated after long-term denervation

After long periods of denervation regenerated muscle spindle afferents show functional recovery despite gross histological abnormalities in their ending structure. This study prevents results examining the responses of such afferents to small amplitude stimuli, within the linear range of the spindle. The majority of regenerated afferents responded to the stimuli with a sensitivity similar to that of normal afferents.

Evaluation of a fluorescence feedback system for guidance of laser angioplasty

BACKGROUND AND OBJECTIVE

Laser-induced fluorescence spectroscopy (LIFS) may be capable of guiding laser angioplasty by discriminating normal and atherosclerotic artery and by determining catheter-tissue environment. Previous optical multichannel analyzer based LIFS systems have been expensive and cumbersome. To simplify LIFS, a system based on photomultiplier tubes was developed and evaluated.

STUDY DESIGN/MATERIALS AND METHODS

Tissue fluorescence was induced by a helium cadmium laser (wavelength = 325 nm, power = 0.2-0.5 mW), collected by clinical multifiber laser angioplasty catheters and directed through one of two filters (10 nm bandpass, 380 nm or 440 nm peak transmission) to a photomultiplier tube. An LIFS ratio was defined as the relative intensity at 380:440 nm after calibration with an elastin fluorescence spectrum; 157 coronary artery cadaveric specimens were evaluated spectroscopically and histologically. To evaluate the utility of LIFS to optimize catheter position by determining catheter-tissue contact, by determining saline dilution of blood, and by orienting eccentric multifiber catheters a new variable, the total fluorescence intensity (TFI) was defined as the sum of arterial fluorescence intensities at 380 nm and 440 nm. TFI was recorded in vitro through multifiber catheters from 20 arterial specimens in vitro in blood and evaluated as a function of the catheter-to-tissue distance (d) over a range from 0 to 400 mu.

RESULTS

Defining normal specimens as those with an intimal thickness < or = 200 mu, and atherosclerotic as those with an intimal thickness > 200 mu, 47/50 (94%) normal and 85/107 (79%) atherosclerotic specimens were correctly classified using a threshold LIFS ratio of 2.0. Mean (+/- SE) normal ratio was 1.76 +/- 0.02 and mean atherosclerotic ratio was 2.78 +/- 0.08 (P < or = 0.01). The classification accuracy of atherosclerotic specimens increased with intimal thickness so that 95% of atherosclerotic specimens (69/73) with intimal thickness > or = 400 mu were correctly classified. TFI was capable of determining catheter-tissue contact as maximal TFI was recorded with the catheter in contact with the tissue (d = 0 mu) and decreased markedly with distance (to 52 +/- 6% at d = 100 mu, 19 +/- 4% at d = 200 mu, and 3 +/- 1% at d = 300 mu). TFI was recorded from ten arterial specimens in blood/saline mixtures ranging in hematocrit from 0% (saline) to 50% (whole blood). TFI was capable of detecting saline hemodilution of blood as TFI decreased markedly at higher hematocrits such that TFI could only by recorded at hematocrits < 10% for catheter-to-tissue distances > or = 300 mu. TFI was recorded through ecentric multifiber catheters from 25 arterial specimens and eval-uated as a function of the degree of catheter-tissue overlap. TFI was capable of detecting maximal catheter-tissue overlap as TFI correlated linearly with the area (A) of overlap (TFI = 1.12 A + .07, r = 0.92).

CONCLUSIONS

By discriminating atherosclerotic from normal tissue and by confirming catheter-tissue contact and saline hemodilution, fluorescence feedback should minimize irradiation of normal tissue and/or blood and enhance the safety and efficacy of laser angioplasty.

Specificity of hydrolysis of phytic acid by alkaline phytase from lily pollen

Phytases are the primary enzymes responsible for the hydrolysis of phytic acid, myo-inositol-1,2,3,4,5,6-hexakisphosphate (I-1,2,3,4,5,6-P6). A number of phytases with varying specificities, properties, and localizations hydrolyze phytic acid present in cells. The specificity of hydrolysis of phytic acid by alkaline phytase from lily (Lilium longiflorum L.) pollen is described. Structures of the intermediate inositol phosphates and the final product were established by a variety of nuclear magnetic resonance techniques (1H-, 31P-, and 31P-1H-detected multiple quantum coherence spectroscopy, and total correlation spectroscopy). On the basis of the structures identified we have proposed a scheme of hydrolysis of phytic acid. Initial hydrolysis of the phosphate ester occurs at the D-5 position of phytic acid to yield the symmetrical I-1,2,3,4,6-P5. The two subsequent dephosphorylations occur adjacent to the D-5 hydroxyl group to yield I-1,2,3-P3 as the final product. Alkaline phytase differs from other phytases in the specificity of hydrolysis of phosphate esters on the inositol ring, its high substrate specificity for phytic acid, and biochemical properties such as susceptibility to activation by calcium and inhibition by fluoride. The physiological significance of alkaline phytase and the biological role of I-1,2,3-P3 remain to be identified.

Static sensitivity of tendon organs to tetanic contraction of in-series motor units in feline peroneus tertius muscle

1. The results of several studies have indicated an absence of any consistent relationship between the discharge of Ib Golgi tendon organ afferents and the steady-state tetanic tension generated by activating motor units. This question has been re-examined by recording the responses of individual tendon organs to tetanic, isometric contractions of one or more motor units from the peroneus tertius muscle of anaesthetized cats. 2. In three experiments, seventy-three individual tendon organ-motor unit interactions were recorded. The motor units were stimulated at 30-150 s-1 and for each tendon organ-motor unit pair a linear relationship was found between steady-state tetanic tension and Ib afferent discharge. The slopes of these relationships (the static sensitivities) were steepest for the weakest units. 3. When motor units were stimulated in combination, the relationship between discharge frequency and plateau tension was again linear but the static sensitivities were generally much lower than for single units and approached 1 impulse s-1 g-1. 4. Expression of these relationships in terms of the relative tensions generated revealed that the tendon organs were activated most strongly by the IIb muscle fibres, the static sensitivities being reduced by unloading effects. 5. The linear relationships observed during stimulation of single, and groups of, motor units suggest that the patterns of discharge from the tendon organs can mirror the steady-state contractile tensions within the muscle.

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)

Photoinhibition of smooth muscle cell migration: potential therapy for restenosis

Evidence from animal, autopsy, and atherectomy studies demonstrates that migration and proliferation of smooth muscle cells of medial origin result in neointima formation and decreased luminal cross-sectional area. The purpose of this study was to evaluate whether low energy light irradiation can inhibit smooth muscle cell migration and therefore potentially reduce the degree of neointima formation and the incidence of restenosis. The migration kinetics of bovine aortic smooth muscle cell monolayers were examined using a fence assay. The effect on smooth muscle cell migration of irradiation with monochromatic light at wave-lengths ranging from 400 to 700 nm was compared to the migration of cells irradiated with broadband white light or maintained in the dark. Wavelength specific photoinhibition of smooth muscle cell migration was observed; 594-600 nm light reproducibly inhibited migration by 12-29% (P < 0.05). Migration rate was significantly reduced following daily radiant exposures of 1.0 J/cm2 as well as following a single radiant exposure of 0.09 or 0.9 J/cm2. The decrease in migration was not associated with any change in cell proliferation or [3H] thymidine incorporation. We conclude that 594-600 nm light inhibits smooth muscle cell migration in vitro and may potentially be used in vivo to decrease fibrointimal thickening following arterial injury. This application of photoinhibition may be useful in retarding restenosis following angioplasty.

The 'initial burst' of muscle spindle afferents with or without terminals on the bag1 intrafusal muscle fibre

The initial burst has been re-examined following conditioning of the muscle to investigate its intrafusal origins. The burst was present in the response to stretch of spindle afferents that innervated the bag1 fibre and those that did not. There was, however, a difference in amplitude of the burst. These findings are discussed in terms of intrafusal mechanisms.

A study of glycogen depletion and the fibre-type composition of cat skeleto-fusimotor units

1. We have used the glycogen-depletion technique, combined with myofibrillar ATPase (mATPase) staining for muscle fibre type, to study the fibre-type composition of four skeleto-fusimotor (beta) units in cat peroneus tertius, namely, one beta dynamic (beta d) unit and three beta static (beta s) units. 2. Depletion of glycogen was observed in serial cross-sections of thirty-four beta-unit extrafusal muscle fibres of various types traced from origin to insertion. No fibre was depleted of glycogen throughout its length; depletion was restricted to a number of zones, usually about five. Oxidative (type I) and oxidative-glycolytic (type IIA) fibres were depleted for a significantly greater proportion of their total length than glycolytic IIB fibres. 3. The fibre-type composition of the beta d unit was determined by tracing its fibres from end to end. The muscle unit consisted of one intrafusal bag1 fibre and ninety-three extrafusal muscle fibres comprising seventy-six type I fibres, eleven IIC fibres, and six fibres that changed from IIC to I during the course of their length (IIC/I fibres). The extrafusal fibre-type composition was thus 81.7% I plus 18.3% IIC and IIC/I. 4. The three beta s units (beta s1, beta s2, beta s3) were all fast-contracting and fatigued rapidly. Identification of their extrafusal fibre types, made in 1 mm2 areas sampled from different parts of each unit, gave mixed compositions as follows: beta s1, IIB + 6.7% IIA; beta s2, IIB + 5.8% IIA; beta s3, IIB + 29.9% IIA. The intrafusal component of each unit included either one or two long chain fibres. 5. In a discussion of the results, the fact that the continuous stimulation of extrafusal muscle fibres does not deplete them of glycogen throughout their length is examined in relation to the work of others who have assumed that it did. With regard to the finding of mixed extrafusal fibre types in the beta units, a distinction is drawn between minimal (around 5%) and moderate mixing. It is suggested that minimal mixing may occur in any motor unit as the outcome of endplate degeneration with foreign replacement, but that moderate mixing indicates an on-going process of conversion from one fibre type to another which in the adult may prove to occur only among beta units.

Detection of calcified atherosclerotic plaque by laser-induced plasma emission

The use of fluorescence spectroscopy to discriminate atherosclerotic from normal tissue is limited by a lower sensitivity for calcified than noncalcified atherosclerotic plaque (65% vs. 93%, respectively). To evaluate plasma emission as a means to detect calcified plaque, 325 normal and atherosclerotic cadaveric aortic sites were irradiated through a 100-micron silica fiber in blood by a pulsed holmium laser (lambda = 2.1 microns, fluence = 4 J/mm2). A photodiode positioned near the proximal end of the fiber detected plasma emission during a laser pulse. Plasma emission was detected at 0% (0/110) of normal, 0% (0/107) of noncalcified atherosclerotic tissue, and 91% (98/108) of calcified atherosclerotic sites. Spectroscopic analysis confirmed the presence of calcium lines in the plasma emission from calcified atherosclerotic plaque. Although ablative fluences (greater than 3 J/mm2) were required for plasma generation, a single laser pulse ablated only to a depth of 67 +/- 16 microns in normal tissue. In an additional 10 calcified atherosclerotic sites, laser ablation was continued as long as plasma emission was detected. In all cases, plaque ablation was terminated before arterial perforation. Furthermore, the adjunctive use of plasma detection improved the accuracy of fluorescence spectroscopic classification of normal and atherosclerotic tissue. In conclusion, plasma detection has a high sensitivity (91%) and specificity (100%) for calcified atherosclerotic plaque and may be a useful adjunct for laser angioplasty guidance. Furthermore, plasma detection can be implemented both simply and inexpensively.

Functional recovery following direct or graft repair of nerve gaps in the rat

The tibial functional index has been employed to assess functional recovery in rats following nerve repair by direct coaptation under tension or by grafting. Recovery after direct repair of small to moderate gap sizes was better than that after grafting.

Recovery of denervated muscle receptors following treatments to accelerate nerve regeneration

Nerve regeneration promoters offer the possibility of enhancing recovery following nerve injury by increasing the numbers of regenerating axons and decreasing the period of tissue denervation. To date, recent studies have concentrated on evaluating the action of such promoters on the nerve itself and on the restoration of motor function. This study examines afferent regeneration by evaluating the recovery of muscle spindles and tendon organs after nerve injury and treatment with alpha-melanocyte stimulating hormone or nerve stimulation. Treatment was found to be effective in enhancing short-term recovery after nerve-crush injury in terms of increasing the rate of functional and morphological recovery. Following nerve section, there was an increase in the number of reinnervating axons compared with control values.

Alkaline phytase activity in nonionic detergent extracts of legume seeds

Alkaline phytase activity, with a pH optimum of 8, was recovered from detergent extracts of dormant seeds of nine varieties of Phaseolus vulgaris L., Pisum sativum L. var. Early Alaska, and Medicago sativa L. This alkaline phytase of legume seeds was activated by calcium and differed from most seed phytases in its relative insensitivity to inhibition by fluoride.

Responses of Ia afferent axons from muscle spindles lacking a bag1 intrafusal muscle fibre

The Ia afferent axon innervating the muscle spindle is characterised by the dynamic nature of its response to stretch. Traditionally this response has been attributed to the properties of the bag1 intrafusal muscle fibre, a view supported recently by reports of stretch-activation of the bag1 fibre. Some spindle capsules lack a bag1 fibre and the Ia afferent axon terminates on the bag2 and chain fibres only. Such axons may be identified by their lack of an enhanced dynamic response to infusions of succinylcholine. In these experiments the responses to passive stretch of these axons have been investigated and found to be indistinguishable from those of the main Ia population. This implies that the bag1 fibre is not essential to the generation of the dynamic response of primary endings.

Regeneration and recovery of cat muscle spindles after devascularization

1. We have assessed the sensory reinnervation and recovery of regenerated muscle spindles in extensor digitorum longus (EDL) 6, 8 and 13 weeks after the muscle, with its nerve left intact, had been devascularized. Recordings were made from the dorsal roots of the responses of single afferent fibres to ramp-and-hold stretch of the regenerated spindles whose sensory reinnervation was subsequently examined in teased, silver preparations. 2. The spindle population in four normal EDL muscles ranged from 53 to 83 (mean 69); analysis of the afferent innervation of 166 normal b1b2c spindles showed that 23% had primary endings supplied by two Ia afferents. Regenerated spindles were identified as belonging to one of four groups in which afferents establish sensory endings on intrafusal muscle fibres in groups 1-3, but not in group 4. Sensory reinnervation was complete after 6 weeks recovery and similar proportions of group 1-3 spindles occurred after each recovery period, i.e. 58% after 6 weeks, 65% after 8 weeks and 62% after 13 weeks. We estimate that about half the original spindle population was lost owing to persistent ischaemic necrosis; that 30% regenerated and acquired functional afferent connections (group 1-3 spindles); and that the total loss of spindle afferents was over 60%. 3. The conduction velocities of the regenerated spindle afferents were very similar to those of normal EDL spindle afferents. The proportions that responded normally to ramp-and-hold stretch at the end of each recovery period increased from 58% after 6 weeks to 61% after 8 and 88% after 13. Other responsive spindle afferents were either predominantly phasic or only responded to supramaximal stretch. The proportions of these decreased as recovery progressed reducing from 19% after 6 weeks to 9% after 13 weeks in the case of those giving predominantly phasic responses and from 23% after 6 weeks to 3% after 13 weeks in the case of those unresponsive to physiological stretch. 4. The mean peak and held firing rates of regenerated spindle afferents responsive to 10 mms-1 ramp-and-hold stretches were all significantly lower than normal. There was no marked trend towards higher firing rates after longer periods of recovery through, considered separately, the mean peak firing rates of the normally responding afferents did show a distinct improvement. The mean dynamic and velocity indexes were not significantly different from normal. 5. The ratio of Ia:spindle II afferents, as identified by their responses to stretch, was 1:1.22 in the control animals and 1:1.26 in the experimental series.(ABSTRACT TRUNCATED AT 400 WORDS)

Classification of muscle spindle afferents in the peroneus brevis muscle of the cat

Muscle-spindle afferents are commonly classified according to their conduction velocity. Under certain conditions such classifications may not be feasible and another form of identification is required. In this study 5 tests, comprising either quantitative or qualitative criteria, have been evaluated as a means of classifying spindle afferents. The choice of these tests was made on the basis of predicted physiological differences arising from the structural variations in the endings. Prior conditioning of the spindles was found to enhance the distinction between the two types of afferent. All the tests generated similar identifications with a maximum of 10% of afferents being classified differently by any two tests.

The sensory reinnervation of muscles following immediate and delayed nerve repair in the cat

An experiment has been performed on adult cats to investigate the sensory reinnervation of muscle spindles and tendon organs in peroneus brevis following immediate and delayed repair of the divided muscle nerve. The results demonstrate that delaying nerve repair for up to 6 weeks does not give rise to any significant detrimental effect on such reinnervation.

Responses of cat muscle spindle afferents after short periods of denervation and reinnervation

The functional recovery of cat muscle spindles has been examined following short periods of denervation and reinnervation. The restoration of function was more rapid than after longer periods of denervation though the firing rates showed a similar reduction except after the shortest recovery periods when a number of highly dynamic afferents were recorded.

Activation of cat motor units by paired stimuli at short intervals

1. In adult cats, paired stimulations at short intervals were applied in ventral root filaments to single motor axons innervating the peroneus tertius muscle. Paired impulses were recorded from the muscle nerve simultaneously with the electrical and mechanical responses of the muscle portion of the motor unit (muscle unit). The interstimulus interval was gradually reduced in order to determine the minimum compatible with a full activation of the muscle unit by the second impulse. 2. For motor units of all physiological types, this minimum stimulus interval was the shortest interval allowing initiation and conduction of two impulses in the axon, that is, the absolute refractory period for conduction. Its duration ranged between 0.58 and 0.88 ms, displaying no correlation with the axonal conduction velocity. 3. The amount of tension enhancement produced by paired stimulations at the shortest interval varied with the type of the motor unit: it was largest for fast-fatigable units, intermediate for fast-resistant units and smallest for slow units. 4. Paired impulses elicited by paired stimulations at the shortest possible interval arrived near the muscle at a longer interval because the second impulse was conducted at a slower velocity. The minimum interval between arrival of impulses at the muscle depended on conduction velocity and on conduction distance. 5. In motor axons to peroneus tertius, paired impulses leaving the spinal cord at a mean interval of 0.78 ms arrived near the muscle separated by a mean interval of 1.90 ms. Since such an interval always allowed full activation of the muscle unit by the second impulse, this interval is longer than the refractory period of motor units in this muscle.

The number and distribution of muscle spindles and tendon organs in the peroneal muscles of the cat

An analysis has been made of the numbers and distributions of muscle spindles and tendon organs in the three peroneal muscles of the lower hindlimb of the adult cat. Both peronei brevis and tertius were richly supplied with spindle capsules and tendon organs in comparison with peroneus longus and other muscles of the cat's lower hindlimb. A large number of the capsules in each muscle was involved in tandem linkages, some of these capsules comprising only a bag and some chain fibres. Such capsules were especially prevalent in peroneus tertius. The numbers of extrafusal muscle fibres inserting into each tendon organ indicated that the activity of each motor unit should be monitored by at least one tendon organ. The distributions of the receptors are discussed in relation to the proportion and density of oxidative muscle fibres.

The reinnervation of cat muscle spindles by skeletofusimotor axons

Tests were made to ascertain the numbers of skeletofusimotor axons reinnervating muscle spindles following crush or section of the nerve to peroneus tertius in adult cats. After short periods of recovery there was no change in the proportion of skeletofusimotor axons compared with normal animals.

Reinnervation and recovery of cat muscle receptors after long-term denervation

After nerve injury muscles remain denervated until axons return to begin reinnervation and recovery. The delay between injury and recovery in human limb nerves averages 13 weeks after crush, and 16 weeks after transection and suture. In order to assess the effects of such long denervation periods on the recovery of cat muscle receptors, we crushed the common peroneal nerve and denervated peroneus brevis for 10 to 134 days; 39 days were allowed for reinnervation in each experiment. After 50 days denervation, the mean number of terminal bands in the regenerated spindle primary endings was 10.3 compared with a normal mean of 29.0. After 134 days, the mean was 0.6 and spindles were severely atrophied. Despite this most spindle afferent fibers continued to respond normally to ramp-and-hold stretch, abnormal responses being recognized as those that failed to maintain firing during the held phase of the ramp. After 50 days, 21% of spindle afferent fibers responded abnormally and about this proportion did so after all the longer denervation periods. Maximum afferent firing rates were all significantly lower than normal, and many afferent fibers fatigued more rapidly. Tendon organs were atrophied after 113 and 134 days and received fewer terminals, but their afferents fired apparently normally during muscle twitch. These results imply that the consequences of long-term denervation on human muscle spindles would be unlikely to affect the overall pattern of response to stretch of any Ia or II afferent fibers reinnervating them, though the quality of their response might be impaired.

A Calcium-Activated Phytase from Pollen of Lilium longiflorum

A phytase was isolated and partially purified from the pollen of Lilium longiflorum Thumb. Optimum activity was at pH 8.0. The phytase was activated by Ca(2+) and Sr(2+) but not by the other divalent cations tested. Activity was inhibited by ethylenediaminetetraacetate. The phytase had a temperature optimum of 55 to 60 degrees C and an activation energy of about 12,700 calories/mole. Extraction of L. longiflorum pollen with 0.1% Triton X-100 increased recovery of the phytase by nearly 4-fold. The phytase had a molecular weight of about 88,000 as determined by gel filtration chromatography and a K(m) value of 7.2 micromolar for phytic acid in the presence of Ca(2+).

Activation of cat muscle spindles by static skeletofusimotor axons

The discharges from primary and secondary spindle endings of the cat peroneus tertius muscle were recorded during stimulation of static skeletofusimotor (static beta) axons at frequencies comparable with the presumed range of motoneuronal firing rates. When stimulated at 20-40/s, static beta-axons exerted typical static actions on the spindles they innervated, including activation of primary endings with reduction of their dynamic sensitivity and activation of secondary endings. For these frequencies, the extrafusal portions of static beta-motor units developed unfused contractions producing oscillations of tension within the muscle. After suppression of extrafusal contractions, the effects of the stimulation of static beta-axons on spindle discharge could persist unaltered, showing that extrafusal events need not interfere with the specific intrafusal actions of static beta-axons. Stimulation of a static beta-axon at 20-40/s often elicited a response of primary endings in which the discharge exactly followed the stimulation frequency, i.e. it was driven 1:1. Purely mechanical excitation of a spindle by unfused extrafusal contractions could also drive its discharge at the stimulation frequency. The persistence of static beta-driving after suppression of extrafusal contraction provided evidence for its intrafusal origin. Driving elicited by static beta-axons could persist during changes in muscle length, but small fluctuations in the delay between each impulse and the preceding stimulus were observed. These fluctuations were clearly related to the changes in muscle length, indicating that although the primary ending discharge remained driven 1:1 at the stimulation frequency, the receptor was not totally insensitive to length changes.

Regeneration of gamma-fusimotor axons after nerve-freeze injury in the cat

Nerve injury was produced by application of dry ice to the common peroneal nerve. After 20 weeks, muscle-spindle primary endings responded normally to stretch and the spindles were found to have a fully functional fusimotor innervation.

Sensory reinnervation of cat peroneus brevis muscle spindles after nerve crush

Results are presented of examining the postcrush sensory reinnervation of cat peroneus brevis muscle spindles previously investigated physiologically by Hyde and Scott. It is shown that primary and secondary endings were successfully restored in their final form in the early stages of recovery. The primary endings were shorter than normal and had fewer transverse bands; 12% were judged to be hyperinnervated. Some secondary endings showed signs of growth through the primary region apparently designed to establish secondary terminals in the opposite pole. This is compared with the collateral regeneration of intact motor axons in partially denervated muscle. It is concluded that the defects observed in the regenerated sensory endings had no effect on their functional recovery.

Lead exposure and changes in the renin-angiotensin-aldosterone system in man

We have studied the effects of chronic slight to moderate lead exposure on the renin-angiotensin-aldosterone system in normotensive man. Plasma renin activity (PRA), blood angiotensin I (AI) concentration, angiotensin converting enzyme (ACE) activity and aldosterone concentration were measured in 33 normotensive men, 25 of whom were occupationally exposed to lead. Positive exponential relationships were found between blood lead and PRA, AI, ACE and aldosterone. Linear relationships were observed between PRA and AI, and between AI and ACE. PRA, AI, and ACE did not significantly correlate with aldosterone. Chronic lead exposure enhanced PRA with a resulting increase in AI levels, which in turn may have produced a substrate-induced increase in ACE. The effects of lead on aldosterone may be mediated in part by an independent pathway. These changes may contribute to the development of hypertension in chronically lead-exposed man.

Some effects of sympathetic stimulation and isoprenaline on fatigued tetanic contractions of skeletal muscle in the cat

In anaesthetized cats, stimulation of the lumbar sympathetic trunk inconsistently elicited small increases in the contraction of fatigued Peroneus Longus muscles (Orbeli phenomenon). Facilitation of this anti-fatigue effect was regularly observed following close intra-arterial injection of isoprenaline, a beta-adrenergic agonist. Injection of the drug by itself exerted a marked anti-fatigue effect on muscle contraction.

Responses of cat peroneus brevis muscle spindle afferents during recovery from nerve-crush injury

The responses of regenerated muscle spindle afferents to ramp-and-hold stretch of the peroneus brevis muscle in the cat were recorded at periods from 26 to 140 days after crushing the common peroneal nerve. During the early stages of recovery a number of abnormally responding afferents were observed. The most marked abnormality was the absence or rapid failure of firing during the held phase of the stretch. The proportion of abnormal afferents became less as recovery progressed. Electrical stimulation of isolated static and dynamic gamma-axons increased the firing rates of the afferents during the ramp-and-hold stretch such that a gamma static axon would restore the response of an abnormal afferent to the held phase of the stretch. The regenerated afferents have been classified according to the degree of abnormality displayed. These abnormalities can be accounted for by assuming a subtractive reduction in the firing frequency of the regenerated afferents. This is attributed to an increase in the pacemaker threshold.