A novel estimate of biological aging by multiple fitness tests is associated with risk scores for age-related diseases

Introduction: Recent research highlights the need for a correct instrument for monitoring the individual health status, especially in the elderly. Different definitions of biological aging have been proposed, with a consistent positive association of physical activity and physical fitness with decelerated aging trajectories. The six-minute walking test is considered the current gold standard for estimating the individual fitness status in the elderly. Methods: In this study, we investigated the possibility of overcoming the main limitations of assessing fitness status based on a single measure. As a result, we developed a novel measure of fitness status based on multiple fitness tests. In 176 Sardinian individuals aged 51-80 years we collected the results of eight fitness tests to measure participants' functional mobility, gait, aerobic condition, endurance, upper and lower limb strength, and static and dynamic balance. In addition, the participants' state of health was estimated through validated risk scores for cardiovascular diseases, diabetes, mortality, and a comorbidity index. Results: Six measures contributing to fitness age were extracted, with TUG showing the largest contribution (beta = 2.23 SDs), followed by handgrip strength (beta = -1.98 SDs) and 6MWT distance (beta = -1.11 SDs). Based on fitness age estimates, we developed a biological aging measure using an elastic net model regression as a linear combination of the results of the fitness tests described above. Our newly developed biomarker was significantly associated with risk scores for cardiovascular events (ACC-AHA: r = 0.61; p = 0.0006; MESA: r = 0.21; p = 0.002) and mortality (Levine mortality score: r = 0.90; p = 0.0002) and outperformed the previous definition of fitness status based on the six-minute walking test in predicting an individual health status. Discussion: Our results indicate that a composite measure of biological age based on multiple fitness tests may be helpful for screening and monitoring strategies in clinical practice. However, additional studies are needed to test standardisation and to calibrate and validate the present results.

Clinical evaluation of efficacy and tolerance of a skin reconditioning compound for anti-aging

Facial aging involves all facial structures located at different levels: bones soft tissues and skin with a reduction of the extracellular matrix. The aim of the study was to evaluate the efficacy of the injectable solution antiaging complex composed by non-reticulated hyaluronic acid (HA) and amino acids vitamins and antioxidants conveyed with mesotherapy technique in subjects with different expressions of aging. 114 patients with different expressions of aging were enrolled in this study with mean age (49±6). HA and amino acids vitamins and antioxidants complex solution Neofound (Love Cosmedical, Castagneto, Italy) was injected on the dermal plane or superficial subdermal plane. Among the various imperfections, fine roughness surface irregularities skin firmness brightness/discoloration cutaneous hydration were those with the greatest response to therapy. The clinical data showed that the medical device Neofound is effective and safe to treat various skin signs of chrono and photoaging thanks to its ability to protect tissues from oxidative stress and hydrate the skin.

Contralateral Effects of Unilateral Strength and Skill Training: Modified Delphi Consensus to Establish Key Aspects of Cross-Education

Background

Cross-education refers to increased motor output (i.e., force generation, skill) of the opposite, untrained limb following a period of unilateral exercise training. Despite extensive research, several aspects of the transfer phenomenon remain controversial.

Methods

A modified two-round Delphi online survey was conducted among international experts to reach consensus on terminology, methodology, mechanisms of action, and translational potential of cross-education, and to provide a framework for future research.

Results

Through purposive sampling of the literature, we identified 56 noted experts in the field, of whom 32 completed the survey, and reached consensus (75% threshold) on 17 out of 27 items.

Conclusion

Our consensus-based recommendations for future studies are that (1) the term ‘cross-education’ should be adopted to refer to the transfer phenomenon, also specifying if transfer of strength or skill is meant; (2) functional magnetic resonance imaging, short-interval intracortical inhibition and interhemispheric inhibition appear to be promising tools to study the mechanisms of transfer; (3) strategies which maximize cross-education, such as high-intensity training, eccentric contractions, and mirror illusion, seem worth being included in the intervention plan; (4) study protocols should be designed to include at least 13–18 sessions or 4–6 weeks to produce functionally meaningful transfer of strength, and (5) cross-education could be considered as an adjuvant treatment particularly for unilateral orthopedic conditions and sports injuries. Additionally, a clear gap in views emerged between the research field and the purely clinical field.

The present consensus statement clarifies relevant aspects of cross-education including neurophysiological, neuroanatomical, and methodological characteristics of the transfer phenomenon, and provides guidance on how to improve the quality and usability of future cross-education studies.

Electronic supplementary material

The online version of this article (10.1007/s40279-020-01377-7) contains supplementary material, which is available to authorized users.

Gait changes following direct versus contralateral strength training: A randomized controlled pilot study in individuals with multiple sclerosis

BACKGROUND

Contralateral strength training (CST) is increasingly investigated and employed as a non-conventional way to induce an indirect gain in strength in the weakened untrained limb. However, its effects on gait performance are more controversial.

RESEARCH QUESTION

To assess and compare the effects of contralateral (CST) and direct (DST) strength training on spatio-temporal parameters, kinematic and kinetic descriptors of gait in persons with relapsing-remitting multiple sclerosis (PwMS).

METHODS

Twenty-eight PwMS (EDSS 2.0-5.5) with inter-side difference in ankle dorsiflexors' strength ≥ 20 % and moderate gait impairment (walking speed 0.70-0.94 m/s), were randomly assigned to a CST (undergoing training of the less-affected dorsiflexors) or DST group (where the most-affected dorsiflexors were trained). Before and after a 6-week high-intensity resistance training (three 25-minute sessions/week), PwMS underwent bilateral measurements of dorsiflexors' maximal strength and assessment of gait spatio-temporal parameters, lower limb joint kinematics and kinetics.

RESULTS AND SIGNIFICANCE

Following the training period, muscle strength increased significantly in both groups (on average, CST + 29.5 %, p < 0.0005; DST + 15.7 %, p = 0.001) with no difference between the two interventions. Significant changes in gait speed (+16.5 %; p < 0.0001) and stride length (+6.0 %; p = 0.04) were detected only after DST, while no difference was detected in the CST group. Ankle moment and ROM were unaffected by the training. In PwMS with mild to moderate disability and lower limb dorsiflexors' strength asymmetry, CST was not inferior to DST in inducing significant strength gains in the untrained most-affected limb. However, only DST significantly improved gait performance and, specifically, walking speed. Even though CST did not worsen asymmetry, data suggest that contralateral approaches should not be recommended straightaway if the training goal is to improve outcomes other than strength and, specifically, walking speed.

Intracortical circuits, sensorimotor integration and plasticity in human motor cortical projections to muscles of the lower face

Previous studies of the cortical control of human facial muscles documented the distribution of corticobulbar projections and the presence of intracortical inhibitory and facilitatory mechanisms. Yet surprisingly, given the importance and precision in control of facial expression, there have been no studies of the afferent modulation of corticobulbar excitability or of the plasticity of synaptic connections in the facial primary motor cortex (face M1). In 25 healthy volunteers, we used standard single- and paired-pulse transcranial magnetic stimulation (TMS) methods to probe motor-evoked potentials (MEPs), short-intracortical inhibition, intracortical facilitation, short-afferent and long-afferent inhibition and paired associative stimulation in relaxed and active depressor anguli oris muscles. Single-pulse TMS evoked bilateral MEPs at rest and during activity that were larger in contralateral muscles, confirming that corticobulbar projection to lower facial muscles is bilateral and asymmetric, with contralateral predominance. Both short-intracortical inhibition and intracortical facilitation were present bilaterally in resting and active conditions. Electrical stimulation of the facial nerve paired with a TMS pulse 5-200 ms later showed no short-afferent inhibition, but long-afferent inhibition was present. Paired associative stimulation tested with an electrical stimulation-TMS interval of 20 ms significantly facilitated MEPs for up to 30 min. The long-term potentiation, evoked for the first time in face M1, demonstrates that excitability of the facial motor cortex is prone to plastic changes after paired associative stimulation. Evaluation of intracortical circuits in both relaxed and active lower facial muscles as well as of plasticity in the facial motor cortex may provide further physiological insight into pathologies affecting the facial motor system.

Theta burst stimulation induces after-effects on contralateral primary motor cortex excitability in humans

Interhemispheric interactions between the primary motor cortices (M1) have been described with a variety of TMS methods. Here we give a detailed description of the interhemispheric interactions of a period of theta burst simulation (TBS), a rapid method of producing long lasting after-effects on the excitability of the stimulated M1. A total of 18 right handed healthy subjects participated. In most experiments, continuous and intermittent TBS (cTBS and iTBS) were delivered over the right M1 using a coil orientated to induce antero-posterior followed by postero-anterior (AP-PA) currents in the brain. The intensity of stimulation was 80% of active motor threshold (AMT), and a total of 600 pulses were applied. The effects on the amplitude of motor evoked potentials (MEPs), short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated in the left and right M1 before and at three different times after TBS. We also tested long-interval intracortical inhibition (LICI) in right M1 and interhemispheric inhibition (IHI) from right to left M1. Finally, to explore the effect of different polarities of cTBS over dominant and non-dominant hemisphere we delivered AP-PA and postero-anterior followed by antero-posterior (PA-AP) cTBS over either right or left M1 and tested MEPs in both hemispheres. In the stimulated hemisphere, cTBS reduced MEPs and SICI whereas iTBS increased MEPs and SICI. In the non-stimulated hemisphere cTBS increased MEPs and reduced SICI, while iTBS reduced MEPs and increased SICI. There were no effects on ICF, LICI or IHI. Although both AP-PA cTBS and PA-AP cTBS reduced MEPs in the stimulated M1, the former increased MEPs from non-stimulated M1 whereas the latter did not. There was no difference in the effect of cTBS on the dominant or non-dominant hemisphere.

A monosynaptic pathway links the vestibular nuclei and masseter muscle motoneurons in rats

Physiological evidence indicates that vestibular signals modulate the activity of motoneurons innervating the masseter muscle. Recently, experiments using transynaptic retrograde transport of pseudorabies virus provided anatomical evidence that many neurons concentrated in the dorsomedial part of the parvicellular division of the medial vestibular nucleus (MVePC) and the caudal prepositus hypoglossi (PH) provide inputs to motoneurons innervating the lower third of the superficial layer of the masseter muscle. However, it was not clear whether this vestibulo-trigeminal projection was monosynaptic or polysynaptic. The present study sought to determine whether neurons in the MVePC or PH project directly to motoneurons controlling the masseter muscle in rats. For this purpose, an anterograde tracer (biotinylated dextran amine, BDA) was injected into vestibular nuclei (mainly MVePC) or PH and a retrograde tracer (the beta-subunit of cholera toxin, b-CT) was injected into the masseter muscle ipsilateral or contralateral to the BDA injection site. Following injections of BDA into the vestibular nuclei or PH, anterogradely labeled axon terminals were observed bilaterally in the motor trigeminal nucleus (Mo5), particularly in the ventral, medial, and lateral portions of the nucleus; projections to dorsal Mo5 were sparse. In addition, retrogradely labeled motoneurons were located in the ventral and lateral portions of the ipsilateral Mo5. Moreover, anterogradely labeled terminals were observed to be in close proximity to motoneurons in the Mo5 that were retrogradely labeled from b-CT injections into the masseter muscle. This study provides direct evidence that a monosynaptic pathway exists between the MVePC and PH and masseter motoneurons.

Transneuronal tracing of vestibulo-trigeminal pathways innervating the masseter muscle in the rat

Previous studies reported that the activity of trigeminal motoneurons innervating masseter muscles is modulated by vestibular inputs. We performed the present study to provide an anatomical substrate for these physiological observations. The transynaptic retrograde tracer pseudorabies virus-Bartha was injected into multiple sites of the lower third of the superficial layer of the masseter muscle in rats, a subset of which underwent a sympathectomy prior to virus injections, and the animals were euthanized 24-120 h later. Labeled masseteric motoneurons were first found in the ipsilateral trigeminal motor nucleus following a 24-h postinoculation period; subsequent to 72-h survival times, the number of infected motoneurons increased, and at > or =96 h many of these cells showed signs of cytopathic changes. Following 72-h survival times, a few transynaptically labeled neurons appeared bilaterally in the medial vestibular nucleus (MVe) and the caudal prepositus hypoglossi (PH) and in the ipsilateral spinal vestibular nucleus (SpVe). At survival times of 96-120 h, labeled neurons were consistently observed bilaterally in all vestibular nuclei (VN), although the highest concentration of infected cells was located in the caudal part of the MVe, the SpVe, and the caudal portion of PH. The distribution and density of labeling in the VN and PH were similar in sympathectomized and nonsympathectomized rats. These anatomical data provide the first direct evidence that neurons in the VN and PH project bilaterally to populations of motoneurons innervating the lower third of the superficial layer of the masseter muscle. The MVe, PH, and SpVe appear to play a predominant integrative role in producing vestibulo-trigeminal responses.

[The influence of occlusion on sporting performance]

AIM

The purpose of the present study is to investigate the relationship between dental occlusion and physical performance using the Ergo-jump platform, and to highlight connections, if any.

METHODS

For the purpose of this research, 30 patients suffering from cervico-facial pathology and 10 without temporomandibular joint dysfunction were selected from within the Dental Clinic of the University of Sassari. For the first group a resin plate was prepared to correct the malocclusion, while for the control group a bite was prepared that created it. Subjects carried out exercises with the Ergo-jump platform, a device that assesses physical capabilities and athletic performance. Patients were asked to do 2 exercises, a counter movement jump and a mechanical power test, with plate and without plate.

RESULTS

The tests of the first group were as follows: flying times with the bite were 0.01 s longer; the average elevation in the counter movement jump test did not give statistically significant results; execution of the mechanical power test suggests an increase in average mechanical power with the plate. Execution of the same exercises in the other group showed greater flight times without the place; average elevation was not statistically significant; the execution of the mechanical power test showed a decrease in average mechanical power with the occlusion plate.

CONCLUSION

Statistical analysis of individual results showed that patients do not always obtain a benefit during physical exercise using the bite. Research shows that the same pathology can cause different physical performance in different individuals; in fact, not all craniomandibular disturbances have repercussions on posture.

Jaw muscle response to stimulation of type II somatosensory afferents of limbs in the rat

Convergence of various afferent inputs onto brainstem neurones may play an important role in the regulation of trigeminal motor activity. In particular, previous studies suggest that, besides sensory inputs arising from the orofacial region, extratrigeminal information may modulate jaw muscle function. In the present study the actions exerted on masseter and digastric muscles by the activation of somatosensory afferents coming from fore- and hind limbs were examined. The electromyographic activity (EMG) of masseter and digastric muscles was recorded in 20 anaesthetised rats, and EMG responses to single and paired electrical stimulation of common radial and sciatic nerves, at a threshold intensity for the activation of group II afferent fibres, were studied. The stimulation induced an excitatory response in both masseter and digastric muscles bilaterally. Ipsiand contralateral radial nerve stimulation evoked masseter responses at latencies of 13.8 +/- 2.4 ms and of 18.0 +/- 2.6 ms, respectively, and digastric responses 1.6 +/- 0.4 ms later. Ipsi- and contralateral sciatic nerve stimulation elicited masseter responses at latencies of 21.4 +/- 2.6 ms and of 23.3 +/- 2.0 ms, respectively, and digastric responses 2.0 +/- 0.2 ms later. The same masseter and digastric motor units were excited by both radial and sciatic nerve stimulation; this suggests a convergence of somatosensory inputs arising from fore- and hind limbs on the same pool of masseter and digastric motoneurones. Paired stimulation of the two nerves did not induce any summation of the responses; this finding suggests that the two inputs, reaching a common relay station, could give rise either to occlusion or to inhibitory interactions. Spinotrigeminal relationship evidenced in this study may be involved in the coordination of jaw and limb movements.

Masseter muscle activity during vestibular stimulation in man

Experimental data report that vestibular afferents affect trigeminal system activity. The aim of this work was to evaluate whether static vestibular stimulation affects the excitability of trigeminal motoneurons in man. In order to assess this, voluntary EMG activity of masseter muscles as well as duration and latency of the early and late components of EMG exteroceptive silent period were evaluated while keeping the subject in vertical position and during 20 degrees static tilt. The experiments were performed on ten adult subjects with no orofacial, neurologic and otologic disorders. Each subject sat on a chair, which kept the complex head-jaw-neck-trunk and the limbs securely fixed, in order to minimize any interference due to the activation of somatosensory and proprioceptive afferents from these districts. The subjects were instructed to contract masseter muscles at 25% of their maximum bite force and the isometric force monitoring was used as visual feedback. Exteroceptive silent period (ESP) of masseter EMG was elicited by electrically stimulating the inferior inter-incisal gum. Results showed that static vestibular stimulation induced asymmetrical responses on voluntary masseter muscle activity, which was reduced to 70.3 +/- 16.1% (mean +/- S.D.) of the control value during ipsilateral tilt and increased to 128.8 +/- 13.0% during contralateral tilt. The duration of the early (ESP1) and late (ESP2) silent periods was also affected: during ipsilateral tilt ESP1 and ESP2 duration increased to 130.0 +/- 3.5% and to 122.1 +/- 2.1% of control, respectively; during contralateral tilt it was reduced to 76.8 +/- 1.2% and to 83.0 +/- 1.7% of control, respectively. On the contrary, changes in latencies were not significant. These data evidenced an asymmetrical effect exerted on trigeminal motor activity by static tilt. Since the influence of all receptors which could be activated by static tilt, except that arising from the macular ones, was minimized in this study, it is likely that the observed effects, induced by static tilt on masseter muscle activity, were of macular origin.

Trigeminal integration of vestibular and forelimb nerve inputs

Experiments were carried out on anaesthetized guinea pigs to evaluate whether vestibular and somatosensory informations converge upon the same trigeminal motoneurones and, if so, how they interact in the modulation of their activity. It was found that excitatory responses occurred in these motoneurones when an appropriate electrical stimulation was applied to the common radial nerve. The same was true if the electrical stimulus was applied to the vestibular ampullae. In another set of experiments the stimulation was applied both to the vestibular ampullae and to the common radial nerve at various time-intervals. The amplitude of the motoneuronal responses to common radial nerve stimulation was reduced when preceded by a vestibular stimulation. The same was true when the sequence of stimulations was reversed: in this case there was a decrease in amplitude of the testing response to vestibular stimulation. The degree of these reductions depended upon the time-interval elapsed between the afferent stimulations. The maximal degree of depression was observed at 4-6 ms time-interval for conditioning vestibular stimulation and at 10-12 ms time-interval for conditioning radial nerve stimulation. It appears, therefore, that somatosensory and vestibular signals may modulate the activity of trigeminal motor units innervating masticatory muscles, suggesting that extratrigeminal afferents may control the contraction of these muscles.

Inner ear pressure changes modify ADH secretion in freely moving guinea pig

The present study was designed to elucidate the relationship between endolymphatic pressure and plasma ADH levels in conscious guinea pigs. Plasma ADH (pADH) was measured in basal conditions and after having applied positive or negative pressure of 20 cmH2O to the inner ear. The experimental protocol was designed to avoid any interference on ADH release caused by anesthesia and surgical stress. There was no change in blood pressure, heart rate, plasma Na (pNa) and osmolality (pOsm) after inner ear pressure (IEP) modifications. However, pADH was inversely related with IEP: pADH averaged 31.4 +/- 7.0 pg/ml (mean +/- S.D.) in basal conditions, rising to 48.8 +/- 19.3 when IEP was lowered and falling to 16.6 +/- 10.3 when IEP was raised. These results confirm that structures in the inner ear help control of ADH release.

Responses of vestibular neurons to arginine vasopressin microinjection

The aim of the present research was to evaluate the effects induced by arginine vasopressin (VP) microinjection on the electrical activity of single vestibular neurons. Experiments were performed on anaesthetized guinea-pigs in which the spontaneous and the evoked electrical activity of vestibular neurons were recorded before and after intranuclear VP microinjection (0.25.10(-5) pg VP in 0.25 microliter NaCl 0.9% solution). Results showed that VP microinjection affects the spontaneous as well as the evoked vestibular neuron activity. More precisely, 60% of 30 tested neurons were inhibited, 30% were excited and the remaining 10% were unaffected by VP microinjection. The changes in neuronal activity reported above were attributed to a direct action exerted by the polypeptide on vestibular complex neurons. The possible role played by VP in the mechanisms of postural control exerted by the vestibular system was considered as well.

Effect of atrazine administration on spontaneous and evoked cerebellar activity in the rat

The effect of atrazine oral administration on cerebellar forelimb projection area was studied in rats in vivo. Rats acutely treated with atrazine (100 mg kg-1, BW) showed a significant decrease in spontaneous Purkinje cell firing rate. Atrazine also decreased the cerebellar potentials evoked by electrical stimulation of the ipsilateral radial nerve, affecting mostly the response to climbing fiber input. These results demonstrate that atrazine exerts a toxic action on central nervous system. The effects on the cerebellar somatosensory cortex could be responsible for motor disorders frequently observed in animals intoxicated with atrazine.

Co-variation of free amino acids in brain interstitial fluid during pentylenetetrazole-induced convulsive status epilepticus

Effects of pentylenetetrazole (PTZ)-induced convulsive status epilepticus on free amino acids changes in venous blood, CSF and interstitial fluid (IF) of the brain were examined in dogs. A volume of brain IF sufficient for analysis was obtained by chronically implanted tissue cages. The onset of PTZ-induced convulsive seizures seemed mainly related to a marked increase of glutamate, aspartate, taurine, glycine and phosphoserine while, the maintenance and frequency of seizures seemed related to a marked increase of serine and glycine, in combination with a moderate rise of glutamate. L-alpha-Aminoadipate was recovered in moderate amount in epileptic brain IF, while, in controls, this compound was present in minimal amount. The observed complex temporal variation of the amino acidic pattern may play a role in PTZ-induced seizures and, possibly, in pharmacological kindling and brain structural alterations induced by PTZ.

Does long-term potentiation occur in guinea-pig Deiters' nucleus?

Long-term potentiation (LTP) was studied in the lateral vestibular nucleus (LVN-Deiters' nucleus) in guinea-pigs in vivo. Field potentials and extracellular single unit discharges were recorded in the LVN following electrical stimulation of the ipsilateral VIIIth nerve. High-frequency stimulation (HFS) of the VIIIth nerve fibres produced LTP of the monosynaptic component of the vestibular field potential. The LTP of the field potentials was paralleled by an increase of the evoked spike activity. Intranuclear administration of the NMDA antagonist MK-801 prevented LTP of the monosynaptic component of the vestibular field potentials and significantly suppressed the spontaneous firing of lateral vestibular neurones in a dose-dependent fashion. These results demonstrate that synapses between primary afferent fibres and second order LVN neurones undergo long lasting changes following HFS of the ipsilateral vestibular nerve.

Sympathetic control of skeletal muscle function: possible co-operation between noradrenaline and neuropeptide Y in rabbit jaw muscles

Stimulation of the cervical sympathetic nerve at 10/s increases by 12.9 +/- 0.7% peak tension of maximal twitches in the directly stimulated jaw muscles and markedly depresses (41.6 +/- 1.3%) the tonic vibration reflex (TVR) elicited in the same muscles by vibration of the mandible. Both effects are not significantly influenced by administration of beta-adrenoceptor antagonists. When both alpha- and beta-adrenergic receptors are blocked, sympathetic stimulation induces a very small increase in twitch tension (3.8 +/- 0.7%), while no detectable change in the TVR is observed. Close arterial injection of alpha 1-adrenoceptor agonist phenylephrine mimics the effects induced by sympathetic stimulation on twitch tension and TVR, dose-dependently. The noradrenaline co-transmitter neuropeptide Y also produces a long-lasting, dose-dependent increase in the twitch tension which is unaffected by blockade of adrenergic receptors as well as of the neuromuscular junctions. Contribution of neuropeptide Y to the sympathetically-induced reduction of the stretch reflex is not clearly demonstrated. These data suggest that co-operation between noradrenaline and neuropeptide Y may be effective in determining sympathetic modulation of skeletal muscle function.

The early development of muscle spindle in human foetus

The normal development of muscle spindles has been carefully described in a variety of species but only a few attempts were made to study the embryological development of the muscle spindle in humans. Most of the studies aimed to define the early development of muscle spindle in human foetuses, stated the begin of this process at the 11th week of intrauterine life, when the formation of a network of very fine nerve fibres with enlargements and ringle around developing muscle cells occur. In the present study we tried to document the probably earliest time of appearance of muscle spindles in the skeletal muscle of human foetuses. To this aim we examined fragments of deltoid and gastrocnemius muscles removed from human foetuses at the 9th and 10th week of gestation by using the light microscope technique. Data collected in muscle specimens at the 9th and 10th week of gestation showed the presence, at this time, of a structure with features clearly different from that of the adjacent muscular areas. This structure consists in a number of flat mesenchymal cells surrounding and forming several layers around a bundle of myoblasts smaller and lesser differentiated than the muscle cells located around and it is in close relationship with nervous fibres. These morphological findings might allow to identify the earliest stage of muscle spindle formation in human species.

Sympathetically-induced changes in microvascular cerebral blood flow and in the morphology of its low-frequency waves

The effect of bilateral cervical sympathetic nerve stimulation on microvascular cerebral blood flow, recorded at various depths in the parietal lobe and in ponto-mesencephalic areas, was investigated by laser-Doppler flowmetry in normotensive rabbits. These areas were chosen as representative of the vascular beds supplied by the carotid and vertebro-basilar systems, which exhibit different degrees of sympathetic innervation, the former being richer than the latter. Sympathetic stimulation at 30 imp/s affects cerebral blood flow in 77% of the parietal lobe and in 43% of the ponto-mesencephalic tested areas. In both cases the predominant effect was a reduction in blood flow (14.7 +/- 5.1% and 4.1 +/- 2.4%, respectively). The extent of the reduction in both areas was less if the stimulation frequency was decreased. Sometimes mean cerebral blood flow showed a small and transient increase, mainly in response to low-frequency stimulation. The morphology was analysed of low-frequency spontaneous oscillations in cerebral blood flow, attributed to vasomotion. Present in 41% of the tested areas (frequency 4-12 cycles/min, peak-to-peak amplitude 10-40% of mean value), these waves decreased in amplitude and increased in frequency during sympathetic stimulation, irrespective of changes in mean flow. The possibility has been proposed that the sympathetic action on low-frequency spontaneous oscillations may contribute to the protective influence that this system is known to exert on the blood-brain barrier in hypertension.

A comparative study of changes operated by sympathetic nervous system activation on spindle afferent discharge and on tonic vibration reflex in rabbit jaw muscles

The effect of sympathetic activation on the spindle afferent response to vibratory stimuli eliciting the tonic vibration reflex in jaw closing muscles was studied in precollicularly decerebrate rabbits. Stimulation of the cervical sympathetic trunk, at frequencies within the physiologic range, consistently induced a decrease in spindle response to muscle vibration, which was often preceded by a transient enhancement. Spindle discharge was usually correlated with the EMG activity in the masseter muscle and the tension reflexly developed by jaw muscles. The changes in spindle response to vibration were superimposed on variations of the basal discharge which exhibited different patterns in the studied units, increases in the firing rate being more frequently observed. These effects were mimicked by close arterial injection of the selective alpha 1-adrenoceptor agonist phenylephrine. Data presented here suggest that sympathetically-induced modifications of the tonic vibration reflex are due to changes exerted on muscle spindle afferent information.

Trigeminal motoneuron responses to vestibular stimulation in the guinea pig

Experiments performed in the guinea pig were aimed at evaluating the effect of electric or caloric stimulations of the vestibular afferents on the electrical activity of the jaw-closing and jaw-opening trigeminal motoneurons. Results showed that masseter and digastric motoneurons mainly responded to vestibular ampullar activation with excitatory responses, with latencies being shorter for contralateral than ipsilateral ampullar stimulation. Differences in latencies between the jaw-closing and jaw-opening trigeminal motoneurons were observed: the masseter motoneurons constantly responded about 2 msec earlier than the digastric motoneurons. These results suggest that the vestibular-trigeminal relationship is quite complex and uses multiple systems to connect the vestibular apparatus with the trigeminal motor nuclei. From the functional point of view, the vestibular-trigeminal relationship may play a role in the dynamic control of the jaw muscle tone during head movements.

Effects of cervical sympathetic nerve stimulation on the cerebral microcirculation: possible clinical implications

The action of bilateral cervical sympathetic nerve (CSN) stimulation on mean cerebral blood flow (CBF) and on its rhythmical fluctuations was studied in normotensive rabbits by using laser-Doppler flowmetry (LDF). A reduction in mean CBF, mediated by alpha-adrenoceptors, was the predominant effect; it was more often present and larger in size in the vascular beds supplied by the carotid than in those supplied by the vertebro-basilar system. This suggests that the sympathetic action facilitates a redistribution of blood flow to the brain stem. The effect induced by CSN stimulation on CBF spontaneous oscillations was a consistent decrease in amplitude and an increase in frequency, irrespective of the changes produced on the mean level of CBF. The possible implications of the sympathetic action on the state of the blood-brain barrier (BBB) are discussed. Experimental and clinical data dealing with the influence of sympathetic activation on the cerebrovascular system have been compared. As a result the possibility of analysing the spontaneous oscillations of CBF for clinical purposes is suggested.

A simple, non-invasive and inexpensive method for evaluating the displacement of local tissue surfaces: from vascular changes to muscle contraction

This paper describes a non-invasive, very inexpensive method of estimating tissue displacements of various origin that is easy and fast to set up. This technique utilizes an inductive proximity sensor (IPS), which is a non-contact length transducer measuring the distance between its probe and a metal target. Its working principle is based on the electromagnetic coupling originating between the sensor probe, a source of high-frequency magnetic field, and the metal target where parasitic currents take place. The linear working range of the IPS model used here is 0.1 to 6 mm probe-target distance, its resolution is about 2 microns. The IPS has been employed on rabbits and humans to measure the displacement of a target glued to the skin of various body areas with respect to the fixed probe of the sensor. Its high resolution, together with an extensive working range, allows the evaluation of numerous physiological events which produce displacements ranging from 2 microns -- to 9 mm, reflecting either tissue volume changes or movements. In particular, an interesting application is to monitor, through volume variations, the extent and the time course of local vascular modifications induced by manoeuvres which elicit changes in vasomotor tone; vascular filling, tissue swelling etc. Therefore, this measure may be considered a 'surface plethysmography' record. In addition, the contractions of skeletal muscles, under either isotonic or isometric conditions, can be estimated through this sensor. This system may therefore find applications for research purposes and practical demonstrations to students.

Antiepileptic treatment and oculomotor neurons

This report describes the changes of the spontaneous firing rate due to an acute non-toxic dose of phenytoin (PHT), a drug commonly used in antiepileptic therapy, in the pre-motor neurons involved in saccadic movement. The drug (500 mg/kg of a 10% PHT suspension in arabic gum) was orally administered, and plasma and brain levels were regularly evaluated (EMIT assay). Results show that PHT significantly modifies the spontaneous electrical activity of the pre-motor neurons localized in the paramedian pontine reticular formation by inducing excitation, inhibition, or a biphasic effect. PHT action was observed 10-15 min after drug administration, when plasma and brain concentrations were still very low. The oculomotor system neurons appear to be a more specific target to this drug in comparison to the cerebellum and the vestibular system. Since the PHT action was observed 1 hour after drug administration in the vestibular nuclei and the cerebellum, which are extensively connected with the oculomotor neurons, it is possible to hypothesize that PHT can affect the oculomotor neurons directly and, with longer latency, indirectly through the vestibular nuclei and the cerebellum.