Muscular torque generation during imposed joint rotation: torque-angle relationships when subjects' only goal is to make a constant effort

It is a reasonable expectation that voluntarily activated spinal motoneurons will be further excited by increases in spindle afferent activity produced by muscle stretch. Human motor behavior attributed to tonic stretch reflexes and to reflexes recruited by relatively slow joint rotation has been reported from several laboratories. We reinvestigated this issue by rotating the elbow joint over the central portion of its range while subjects focused on keeping their elbow flexion effort constant at one of three different levels and made no attempt to control the position, speed or direction of movement of their forearm. There is evidence that subjects' voluntary motor status is constant under these conditions so that any change in torque would be of involuntary origin. On average, torques rose somewhat and then fell as the elbow was flexed through a range of 80° at 10, 20 and 60°/s and a similar pattern occurred during elbow extension; i.e., both concentric and eccentric torque-angle profiles had roughly similar shapes and neither produced consistent stabilizing cross-range stiffness. The negative stiffness (rising torque) during the early part of a concentric movement and the negative stiffness (falling torque) during the later part of an eccentric movement would not have occurred if a stabilizing stretch reflex had been present. Positive stiffness rarely gave rise to torque changes greater than 20% in either individual or cross-subject averaged data. When angular regions of negative stiffness are combined with regions of low positive stiffness (torque change 10% or less), much of the range of motion was not well stabilized, especially during eccentric movements. The sum of the EMGs from biceps brachii, brachioradialis and brachialis showed a pattern opposite to that expected for a stretch reflex; there was an upward trend in the EMG as the elbow was flexed and a downward trend as the elbow was extended. There was little change in the shape of this EMG-angle relationship with either direction or velocity. The individual EMG-angle relationships were distinctive for each of these three elbow flexor muscles in four of the six subjects; in the remaining two, biceps was distinctive, but brachioradialis and brachialis appeared to be coupled. Although the EMGs of individual muscles were modulated over the angular range, no consistent stretch reflexes could be seen in the individual records. Thus, we could find no clear evidence for stretch reflex stabilization of human subjects maintaining a constant effort. Rather, muscle torque appears to be reflexly modulated across a much used portion of the elbow's angular range so that any appreciable stabilizing stiffness that is sustained for more than fractions of a second is associated with a change in effort.     

Humoral factors released during trauma ofAplysia body wall

1. Preliminary, general chemical characteristics of substances in artificial sea water (ASW) washed through stimulated body wall (SBW) and in hemolymph taken from noxiously stimulated animals (SHL) were consistent with those of classical neurotransmitters, amino acids, and small- to medium-sized peptides. 2. 5-Hydroxytryptamine (5HT) and acetylcholine (ACh), unlike SBW and SHL, caused relaxation when perfused into isolated body wall. FMRFamide produced a biphasic response--brief contraction followed by prolonged relaxation. 3. Small cardioactive peptide (SCPB) caused body wall contractions similar to those produced by SBW and SHL, except that SCPB contractions displayed more desensitization and were completely blocked by 30 mM CoCl2. SCPB and SBW contractions were synergistic. 4. Dopamine caused persistent body wall contractions similar to those of SBW and SHL. Dopamine contractions were reduced but not blocked by 30 mM CoCl2. Unlike SBW activity, dopamine activity was reduced by alkalinization. 5. Glutamate and taurine produced strong but usually short-lasting body wall contractions. Adenosine, octopamine, arginine vasotocin, and cholecystokinin (CCK-8) caused weak or variable contractions. Met-enkephalin and somatostatin caused no obvious body wall responses. 6. When superfused over the fully sheathed abdominal ganglion, FMRFamide, met-enkephalin, glutamate, aspartate, and taurine reduced the magnitude of the gill-withdrawal reflex elicited by siphon nerve stimulation. 7. Taken together with earlier results, these data suggest a preliminary framework for trauma signal pathways. It is proposed that stress hormones (perhaps including FMRFamide, SCPs, 5HT, and dopamine) are released into hemolymph from neuroendocrine cells. Effective amounts of active intracellular solutes such as amino acids may also be released by extensive cellular rupture. Various humoral signals produce slow effects that contribute to hemostasis, balling up, increased cardiac output, and reflex suppression.     

Synaptic interactions between nonspiking local interneurones in the terminal abdominal ganglion of the crayfish

Nonspiking local interneurones are the important premotor elements in arthropod motor control systems. We have analyzed the synaptic interactions between nonspiking interneurones in the crayfish terminal (6th) abdominal ganglion using simultaneous intracellular recordings. Only 15% of nonspiking interneurones formed bi-directional excitatory connections. In 77% of connections, however, the nonspiking interneurones showed a one-way inhibitory interaction. In these cases, the presynaptic nonspiking interneurones received excitatory synaptic inputs from the sensory afferents innervating hairs on the surface of the uropods and the postsynaptic nonspiking interneurones received inhibitory synaptic inputs that were partly mediated by the inputs to the presynaptic nonspiking interneurones. The membrane hyperpolarization of the postsynaptic nonspiking interneurones mediated by the presynaptic nonspiking interneurones was reduced in amplitude when the hyperpolarizing current was injected into the postsynaptic interneurones, or when the external bathing solution was replaced with one containing low calcium and high magnesium concentrations. The role of these interactions in the circuits controlling the movements of the terminal appendages is discussed.Abbreviations AL antero-lateral - epsp excitatory postsynaptic potential - ipsp inhibitory postsynaptic potential - PL postero-lateral     

A reliability study on the cumulative averaging method for estimating effective stimulus time in vibration studies

Finding the reflex circuitry responsible for high-frequency vibration-induced muscle contraction takes work. The main challenge is to determine the effective stimulus time (EST) point at which continuous (sinusoidal) stimulation (i.e., vibration) triggers the reflex response. A novel “cumulated averaging method” has been previously proposed for estimating the EST point. In the current study, we aimed to test the reliability of the cumulated average method. We used five different whole-body vibration (WBV) frequencies in two experiments. The consistency between the EST points estimated from the first and second experiments was analysed with the intraclass correlation (ICC) and technical error of measurement (TEM). The ICC coefficient with 95% CI for the EST point estimation was 0.988 (0.950–0.997). The relative TEM was 1.3%. We concluded that the cumulated average method is highly reliable in estimating the effective stimulus time point for high-frequency continuous sinusoidal signals.     

Do “glanduliferous” larvae of Galerucinae (Coleoptera: Chrysomelidae) possess defensive glands? A scanning electron microscopic study

Larvae of the chrysomelid taxon Galerucinae, Sermylini, are known to release a fluid from dorsolateral segmental openings when disturbed. The release of this fluid resembles the discharge of secretion from well-studied exocrine defensive glands in larvae of Chrysomelinae, the putative sister group of Galerucinae. Thus, Sermylini larvae have been named “glanduliferous” ones. However, no comparative analyses of the internal structures of the segmental openings in Sermylini larvae have been available prior to this study. Therefore, segmental larval openings in 10 Sermylini species were investigated by scanning and light microscopy. Two types of segmental openings were detected: (1) the opening is visible as an integumental slit which can be opened and closed by muscles. No specific glandular structures are associated with this slit. (2) The opening is covered internally by a cuticular sac which can be everted to the outside. A cuticular duct of a gland is leading into this sac. Haemolymph is discharged from both types of openings. These structures are discussed with respect to reflex bleeding in other taxa. Furthermore, a common origin of the segmental openings in larvae of Sermylini and the segmental exocrine glands in chrysomeline larvae is critically questioned.     

Cutaneous silent period evoked in human first dorsal interosseous muscle motor units by laser stimulation

Painful stimulation of the hand results in an inhibitory response in the hand muscles known as the cutaneous silent period (CSP). In this study, we employed probability- and frequency-based analysis methods to examine the CSP induced by laser stimuli. Subjects were asked to contract their first dorsal interosseous muscle so that selected motor units discharged at a rate of about 8 Hz. Laser pulses were delivered to the palm of the hand, and reflex responses were recorded. The stimuli generated CSP in all test subjects. We found that the latency of the CSP evoked using laser stimulation was longer than that the previously published latency values of the CSP evoked using electrical stimulation.Using only the presently generated laser induced CSP data, the CSP duration was longer when analyzed via peristimulus frequencygram method compared to the probability-based methods such as peristimulus time histogram and surface electromyogram.In the light of the current results, we suggest that laser stimulation could be used when studying pain pathways in human subjects and the frequency-based analysis methods can be preferred because they are previously shown to be more reliable for obtaining the synaptic activity profile. These results can be used to standardize the CSP methods in basic and clinical research.     

The integration of antagonistic reflexes revealed by laser ablation of identified neurons determines habituation kinetics of the Caenorhabditis elegans tap withdrawal response

Previously, we described the circuitry that underlies the tap withdrawal response of the nematode Caenorhabditis elegans. In response to a light mechanosensory stimulus a worm will withdraw, usually by initiating backward locomotion, but occasionally with increased forward locomotion. The form of an animal's response is a product of the balance between two antagonistic reflexes: backward locomotion (reversals) triggered by anterior mechanosensory input and forward locomotion (accelerations) triggered by posterior mechanosensory input. During habituation of this reflex, the frequency of forward and backward locomotion in response to tap is modulated by both experience and interstimulus interval; reversals are more frequent early in a habituation series and at longer Inter stimulus intervals. Single-cell laser microsurgery was used to study each of the subcomponents of the intact behavior during habituation training. Groups of intact or laserablated worms were habituated at either a 10-s or a 60-s inter stimulus interval and the kinetics of habituation in each group was analyzed. We demonstrate that each component of the behavior habituates and does so with kinetics that are consistent with the decrement observed in the intact animal.Abbreviations ALM anterior lateral microtubule - AVM anterior ventral microtubule - ISI interstimuls interval - NGM nematode growth medium - PLM posterior lateral microtubule - PVC posterior ventral interneuron C     

Neuronal mechanisms underlying behavioral switching in a pteropod mollusc

Summary In the pteropod mollusc Clione limacina, wing retraction takes precedence over spontaneous and continuous swimming, a phenomenon here defined as behavioral switching. The wing retraction system is organized as a simple reflex in which wing mechanoreceptors activate a pair of retraction interneurons which in turn excite at least two pairs of retraction motoneurons.Activation of individual mechanoreceptors does not inhibit swimming or trigger wing retraction. A pair of retraction interneurons can fully suppress swimming when induced to fire at physiological frequencies, and may be both sufficient and necessary for swim inhibition.Retraction interneurons monosynaptically inhibit both swim interneurons and swim motoneurons. Retraction motoneurons inhibit swim motoneurons through a polysynaptic pathway.A model summarizing the neural circuitry underlying behavioral switching in Clione is presented. A comparison of this model with the behavioral choice model in Pleurobranchaea reveals that the overall neural mechanisms for behavioral choice and behavioral switching are similar as both involve dual function interneurons that not only activate their own motor pathway, but also inhibit the competing motor system. While inhibition is biased toward the afferent side of the competing circuit in behavioral choice, it is biased to the efferent side in behavioral switching.     

Antidiuretic responses to osmotic cutaneous stimulation in the toad,Bufo arenarum

Summary Osmotic stimulation of the skin of the toadBufo arenarum with isotonic (115 mM) or hypertonic (400 mM) NaCl solutions produced a marked and reversible antidiuresis within 5 min. No changes in plasma osmolarity were detected in the course of this response.Hypophysectomized animals exhibited a lower and delayed antidiuresis when exposed to a hypertonic environment (400 mM NaCl). This antidiuretic response was drastically reduced in normal toads after ten consecutive days of administration of the sympatoplexic guanethidine.The existence of a feed-forward control of urine production initiated by cutaneous osmotic sensors and involving an adrenergic component is proposed.