Phosphodiesterase 11 (PDE11) regulation of spermatozoa physiology.

Fertilization is well correlated with sperm concentration, rate of forward motility, and percentage of live, uncapacitated ejaculated spermatozoa, which is regulated in part by cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterases (PDEs) hydrolyze cyclic nucleotides to their corresponding monophosphates, thereby counterbalancing the activities of cAMP and cGMP, and PDE11 is highly expressed in the testis, prostate, and developing spermatozoa. However, a physiological role of PDE11 is not known. We generated PDE11 knockout (PDE11-/-) mice to investigate the role of PDE11 in spermatozoa physiology. Ejaculated sperm from PDE11-/- mice displayed reduced sperm concentration, rate of forward progression, and percentage of live spermatozoa. Pre-ejaculated sperm from PDE11-/- mice displayed increased premature/spontaneous capacitance. These data are consistent with human data and suggest a role for PDE11 in spermatogenesis and fertilization potential. This is the first phenotype described for the PDE11-/- mouse and the first report of a physiological role for PDE11.

Cloning and characterization of two splice variants of human phosphodiesterase 11A.

Phosphodiesterase 11A (PDE11A) is a recently identified family of cAMP and cGMP hydrolyzing enzymes. Thus far, a single splice variant designated as PDE11A1 has been reported. In this study, we identify and characterize two additional splice variants of PDE11A, PDE11A2 and PDE11A3. The full-length cDNAs are 2,141 bp for PDE11A2 and 2205 bp for PDE11A3. The ORF of PDE11A2 predicts a protein of 576 aa with a molecular mass of 65.8 kDa. The ORF of PDE11A3 predicts a protein of 684 aa with a molecular mass of 78.1 kDa. Comparison of the PDE11A2 sequence with that of PDE11A1 indicates an additional 86 aa at the N terminus of PDE11A2. Part of this sequence extends the potential cGMP binding region (GAF domain) present in PDE11A1. Compared with PDE11A2, PDE11A3 has an additional 108 N-terminal amino acids. Sequence analysis of PDE11A3 indicates the presence of another GAF domain in this region. This diversification of regulatory sequences in the N-terminal region of PDE11A splice variants suggests the interesting possibility of differential regulation of these enzymes. Recombinant PDE11A2 and -A3 proteins expressed in the Baculovirus expression system have the ability to hydrolyze both cAMP and cGMP. The K(m) values for cAMP hydrolysis are 3.3 microM and 5.7 microM for PDE11A2 and PDE11A3, respectively. The K(m) values for cGMP hydrolysis are 3.7 microM and 4.2 microM for PDE11A2 and PDE11A3, respectively. Both PDEs showed a V(max) ratio for cAMP/cGMP of approximately 1.0. PDE11A2 is sensitive to dipyridamole, with an IC(50) of 1.8 microM, and to zaprinast, with an IC(50) of 28 microM. PDE11A3 demonstrated similar pattern of inhibitor sensitivity with IC(50) values of 0.82 and 5 microM for dipyridamole and zaprinast, respectively.

Molecular cloning and characterization of a distinct human phosphodiesterase gene family: PDE11A.

We report here the cloning, expression, and characterization of human PDE11A1, a member of a distinct cyclic nucleotide phosphodiesterase (PDE) family. PDE11A exhibits

Bite force, endurance and masseter muscle fatigue in healthy edentulous subjects and those with TMD.

It is well known that bite force and EMG activity are considerably reduced in edentulous patients, but the susceptibility of their jaw-closing muscles to localized fatigue is less certain. This information is even less clear for edentulous subjects who have TMD. Eleven healthy edentulous subjects and 10 edentulous subjects with TMD participated in this study. Maximum bite force was measured first, with the transducer placed on the canine-first premolar region bilaterally, and then two rapid relaxations were made from a brief voluntary clench to 50% of maximum. A sustained voluntary clench of 50% of maximum was then maintained and endurance time was noted. EMG was recorded from both masseter muscles and the median frequency of the power spectrum of the EMG from 2 s at the beginning of the sustained clench and 2 s at the end was subsequently calculated. Two more rapid relaxations from brief clenches were performed immediately after the sustained clench. The mean maximum bite force in the healthy group was 115 N (SD +/-41) and in the TMD group was 75 N (SD +/-22), this difference being significant (P = 0.0013). The mean endurance time in the healthy group was 86 s (SD +/-51) and in the TMD group was 63 s (SD +/-20). The percentage change in the median frequency in the healthy group as a result of the sustained contraction was 6% (left) and 8.6% (right) and in the TMD group was 13.9% (left) and 12.8% (right). The percentage change in the mean relaxation half time for the healthy group was 28.5% and for the TMD group was 72%, a significant difference (P = 0.0046). It was apparent that the maximum bite force was low in edentulous subjects and was further reduced in edentulous TMD subjects; endurance time was reduced in TMD subjects; fatigue resistance of the masseter muscles was reduced in TMD subjects.

The variability of bite force measurement between sessions, in different positions within the dental arch.

The effect of measuring bite force with different patterns of transducer on different occasions was studied. Maximum voluntary bite force was measured in eight volunteers. Three transducer positions, each with a different pattern of transducer, were used; between the anterior teeth, between the second premolar and the first molar on one side and between the second premolars and first molars on both sides. Visual feedback of force was provided. Two sets of five maximum clenches were recorded with a rest period in between. This sequence was repeated for each transducer and the experiment was repeated on three different days. The highest forces were measured with the bilateral posterior transducer (mean 580 N, s.d. 235) and the lowest on the anterior transducer (mean 286 N, s.d. 164). The standard deviations of the bite force mean values were used as an indication of the variability and were subjected to a non-parametric anova (Kruskal-Wallis). The forces recorded with each transducer position were significantly different between the transducers (P < 0.01) and the maximum bite force showed least variability when measured between the posterior teeth on one side only. There was little difference in bite force between the three different sessions (P > or = 0.05) when measured in the same position within the dental arch, whichever of the three positions that may be.

Variability of the dishabituation of flexion reflexes for FES assisted gait in spinal injured man.

Flexion reflexes, elicited by surface stimulation, can be used to produce a simple form of stepping in spinal cord injured (SCI) humans. A drawback of this approach is a decreasing magnitude of flexion reflex to repeated presentations of the stimuli (habituation). Pilot data indicated that high intensity stimulation could produce dishabituation of the reflex. The aim of this study was to examine and quantify the inter- and intra-subject variability of the short and long term conditioning effect of high intensity stimulation on the magnitude of flexion reflexes in a larger number of SCI subjects. Dishabituation was observed in all subjects, however the amount of dishabituation observed was small and highly variable. However the use of high intensity conditioning stimulation may offer a means of coping with habituation in a small number of subjects.

Acoustic myography, electromyography and bite force in the masseter muscle.

Acoustic myography (AMG) offers some advantages over electromyography (EMG) in certain circumstances, but the use of AMG on the jaw-closing muscles has not been fully tested. The purpose of this study was to examine the relationship between AMG, EMG and force in the masseter muscles of nine healthy male subjects. The AMG was recorded using a piezoelectric crystal microphone and the EMG was recorded simultaneously with surface electrodes. Force was recorded between the anterior teeth with a strain-gauge transducer. Analysis showed that Pearson's correlation coefficient was 0.913 for force/AMG and 0.973 for force/EMG in all subjects, indicating a linear relationship between force, AMG and EMG at the four different force levels tested (25-75% of maximum). It is apparent that AMG may be used as an accurate monitor of masseter muscle force production, although some care is required in the technique.

Twitch interpolation in the assessment of the maximum force-generating capacity of the jaw-closing muscles in man.

The method of twitch interpolation was employed to study the maximum potential bite forces of humans. Transcutaneous electrical stimuli were applied to parts of one or both masseter muscles in eight volunteers while they bit with a variable but controlled isometric force on a unidirectional force transducer held between the anterior teeth. In all participants the twitch force produced by a single 1-ms pulse, of 25 50 mA intensity, was inversely and linearly related to the voluntary bite force. For each participant the slope of the regression between twitch force and bite force depended on the stimulus intensity and not on whether the stimulus was applied to one or both masseters. Extrapolation of the regression lines to zero twitch force showed that they converged towards a bite-force value that, for any given participant varied only a small amount between different stimulus intensities. For most participants this bite force lay above the maximum that they produced voluntarily: voluntary maximum bites ranged from 153 to 593 N, while the extrapolations predicted a narrower and higher potential range of 282-629 N. It was concluded that, for the masseters at least, there is often spare force-generating capacity which individuals are either unable or not prepared to utilize. This method is non-invasive and may help to define better the maximum bite-force potential of humans.

The action of knee joint afferents and the concomitant influence of cutaneous (sural) afferents on the discharge of triceps surae gamma-motoneurones in the cat.

Electrical stimulation of group II joint afferents of the posterior articular nerve (PAN) to the knee evoked short-latency facilitation and/or inhibition of the background discharge of gastrocnemius-soleus (GS) gamma-motoneurones in decerebrated spinal cats. The latencies of these responses were consistent with mediation via segmental oligosynaptic spinal pathways. In addition, a longer-latency facilitation was frequently observed. Mechanical non-noxious stimulation of the skin within the field of innervation of the sural nerve, on the lateral aspect of the heel, suppressed the short-latency facilitation, but not the inhibition or long-latency facilitation. Brief mechanical indentation of the posterior aspect of the knee joint capsule could elicit facilitation or inhibition of gamma-motoneurones. Facilitation, but not inhibition, was blocked by anaesthesia or section of the PAN. Both actions could be suppressed by mechanical stimulation of the heel. We conclude that GS gamma-motoneurones receive both facilitatory and inhibitory segmental inputs from group II articular afferents arising in the knee joint. Cutaneous afferents from the sural field exert a selective inhibitory influence over the facilitation of fusimotor discharge by articular afferents.

Evidence for a human spinal stepping generator.

Flexion reflexes elicited by surface stimulation in spinal cord-injured man have been used to provide limb flexion in gait restoration. In this study, the pattern of the flexion reflexes observed in one subject supports the theory that a spinal stepping generator exists in man.

Masseter muscle relaxation rate in volunteers with a myogenous craniomandibular disorder.

Twelve volunteers were investigated to determine their masseter muscle relaxation rate following voluntary contractions. Four of these volunteers were patients diagnosed as having a myogenous craniomandibular disorder. Electromyograms were recorded from the left and right masseter muscles and maximum bite force was recorded in the midline between the incisor teeth. A sustained contraction was maintained at 50% maximum voluntary bite force for 90 s, during which there was a brief relaxation every 10 s. Recordings were continued for a 3 min recovery period. This sequence was then repeated at 25% of maximum bite force. Median power frequencies were calculated from the power spectra for the first and last 3 s of the sustained contractions. Relaxation rates were measured for each brief relaxation during the sustained contraction and for the relaxation from each brief clench during the recovery period. It was found that maximum bite force values were very similar for volunteers in both the patient and control groups. Relaxation rates slowed more and percentage changes in median frequency were greater in the controls than in the patients during the sustained contractions. However, relaxation rates returned to initial levels more quickly in the controls than in the patients.

The effect of the hypermobility syndrome on knee joint proprioception.

Proprioceptive sensory feedback is utilized by the central nervous system for conscious appreciation of the position and movement of the body and limbs. In patients with the hypermobility syndrome (HMS), it has been suggested that there is alteration of proprioceptive acuity. Proprioceptive performance of the knee joint was investigated in 10 female subjects who suffered from HMS using a threshold detection paradigm (accurate determination of the onset and direction of knee joint displacement at constant angular velocity). Compared to age- and sex-matched controls, HMS subjects showed significantly higher detection levels at starting knee flexion angles of 30 degrees P < 0.001) and 5 degrees (P < 0.001). Control subjects showed no significant difference in threshold acuity between the sexes (at 5 degrees P = 0.63, at 30 degrees P = 0.48). The increased acuity in proprioception observed towards full extension in the control population (P < 0.001) was absent in the HMS subjects (P = 0.596). Findings reported here suggest that HMS subjects have poorer proprioceptive feedback than controls. Reduced sensory feedback may lead to biomechanically unsound limb positions being adopted. Such a mechanism may allow acceleration of degenerative joint conditions, and may account for the increased prevalence of such conditions seen with HMS subjects.

Excitation of soleus/gastrocnemius gamma-motoneurones by group II knee joint afferents is suppressed by group IV joint afferents in the decerebrate, spinalized cat.

Electrical stimulation sufficient to excite group II/III afferent fibres in the posterior articular nerve (PAN) of the cat knee joint facilitated gamma-motoneurone firing in filaments of the lateral gastrocnemius/soleus (LGS) nerve. Repetitive (0.5-2.0 Hz) electrical stimulation of the PAN, produced a short latency increase of gamma-motoneurone firing with a latency ranging from 8 to 35 ms. The shortest of these delays suggests a segmental link between group II knee joint afferents and lateral gastrocnemius/soleus gamma-motoneurones. This facilitation was diminished or abolished if the first stimulus was preceded by a conditioning stimulus which excited the group IV afferents in the PAN. This depression of facilitation was dependent on the interval between the test and conditioning stimuli and the interval which produced the greatest depression was consistent with the effect being due to group IV afferents. Inhibition of the facilitation did not significantly alter the on-going discharge rate of the gamma-motoneurones. This suggests that it was not due to direct inhibition of the motoneurones.

Fatigue and EMG changes in the masseter and temporalis muscles during sustained contractions.

Local muscle fatigue was investigated in the anterior temporal and masseter muscles during sustained isometric contractions. The volunteers' subjective perception of fatigue or pain was recorded at intervals during the sustained contractions, and this level was then compared to objective measures of fatigue. These objective measures included shift in median frequency of the power spectrum of the surface-detected EMG signal, and change in signal amplitude. The relationship was investigated while closing on a bite force meter placed between the second premolars and first molars unilaterally, and while simply clenching with the teeth together without the bite force meter. It was found that the subjective perception of fatigue, as measured on a visual analogue scale (VAS), had a nearly linear relationship with time, and that the relationship between the VAS score and median frequency shift was rather closer than the relationship with amplitude change.

Improving limb flexion in FES gait using the flexion withdrawal response for the spinal cord injured person.

In the restoration of gait for paraplegics using functional electrical stimulation, the method most commonly used to produce hip flexion for the swing phase of gait has been the elicitation of the flexion withdrawal response. Several problems have been noted with the response: there is a decrease in the magnitude of the hip flexion to repeated stimuli (habituation); long latency; and inhibition of the response when stimulated bilaterally. These have been characterized and methods for overcoming the problems tested. Results show that increasing stimulation frequency reduces latency. Habituation can be reduced in some subjects by multiplexing two sites of stimulation. Habituation can further be reduced by applying single high-intensity pulses and this has been used in a one-step-ahead controller for regulating hip flexion angle. Inhibition due to bilateral stimulation had been significantly reduced by altering the timing of the stimulation to the two legs.

Dishabituation of the flexion reflex in spinal cord-injured man and its application in the restoration of gait.

The flexion withdrawal reflex, evoked by surface electrical stimulation, has been used to provide hip flexion for the restoration of gait in paraplegics. A major limitation to its use has been the decrease in the magnitude of the response to repeated stimulation (habituation). In this study it was found that by using high intensity stimulation the response could be dishabituated. It was demonstrated that sufficient hip flexion for functional electrical stimulation-assisted gait was maintained using high intensity pulses in a one-step-ahead controller.

Fourier analysis of the relation between the discharge of quadriceps motor units and periodic mechanical stimulation of cat knee joint receptors.

It has been widely assumed that joint receptors contribute to the reflex regulation of movement and posture, although there have been few clear demonstrations of joint-mediated reflex actions on alpha-motoneurones other than those attributable to flexor reflex afferents. The present study extends our recent work on joint-mediated reflexes by using Fourier analysis of spike train interactions to demonstrate that restricted mechanical activation of a small number (one to five) of knee joint receptors by localized indentation of the joint capsule can modify the firing pattern of quadriceps motoneurones in decerebrated cats. The modulation of this discharge pattern can be reversibly abolished by application of droplets of lignocaine directly to the joint nerve and consequently can be attributed unambiguously to articular afferents. Activation of single joint afferents could on occasion produce changes in motor unit firing patterns, but usually activation of two or more was required before secure effects were observed. Increasing the intensity of indentation (resulting in activation of greater numbers of joint receptors) increases the strength of coupling between joint afferent input and motor unit responses, although the relationship is not linear. The relation between the discharge patterns of pairs of motor units was also examined, and it was found that significant coupling occurred at the stimulus frequency, superimposed on a 'background' coupling from unidentified sources. The phase relationship between pairs of motor units was not affected by the periodic stimulus. However, it was observed that if two motor units were firing independently of one another in the absence of capsule probing, maintained capsular indentation produced a striking synchronization between the discharges of the two motor units. These experiments show strong joint-mediated reflex effects on motor unit firing indicating that joint receptors may have an important role to play in motor control.

A preliminary electromyographic study of bite force and jaw-closing muscle fatigue in human subjects with advanced tooth wear.

The maximum bite force was recorded in five experimental volunteers with advanced tooth wear and five control volunteers who showed no abnormal wear. All subjects were then asked to maintain a force of 50% of the maximum for as long as possible while surface electromyograms from the masseter and temporalis muscles were recorded. The bite force and endurance time were found to be slightly increased in the experimental group, but no conclusions could be drawn regarding the state of fatigue. Two significant problems with regard to fatigue studies of the jaw-closing muscles emerged from the study, namely the use of the canine position for recording of the force, and the thickness of the force meter.

Responses of quadriceps motor units to mechanical stimulation of knee joint receptors in the decerebrate cat.

Recordings were obtained from single quadriceps motor units in decerebrate cats. Tonic discharges were induced in these units by stretch applied to the patellar tendon. The activity of these motor units was examined during repetitive mechanical indentation of the posterior aspect of the knee joint capsule. The amplitude of indentation could be graded to regularly elicit a volley of one or more action potentials from afferents travelling in the posterior articular nerve (PAN). Either repetitive indentation at a fixed frequency or random indentation resulted in entrainment of motor unit discharge with a latency of 6.5-17 ms from the onset of the first PAN spike. This effect was achieved in one case by a single joint afferent. Usually two or more afferents were required to produce entrainment. This effect was mediated by joint receptors as its reversibly abolished by application of lignocaine to the joint nerve. The modal reflex latency suggests that group II joint afferents were responsible for this effect. Stimulation of some areas of the joint capsule readily produced motor unit entrainment whereas other areas did not although PAN afferents were also activated at the latter sites, suggesting inhomogeneity in the synaptic actions of joint afferents.