The response of Golgi tendon organs to single motor unit contractions

1. Cross-correlation analysis has been used to quantify the responses of cat soleus tendon organs to repetitive twitch contractions of: (a) different motor units within the muscle, (b) single motor units at different muscle lengths, and (c) single motor units when the pulse-train pattern of stimulation delivered to the motor unit axon was altered. 2. Ib afferents were observed which responded to each of several hundred successive motor unit twitches with identical numbers of spikes and with relatively invariant latencies. 3. The present results show that tendon organs are sensitive to subtle alterations in motor unit twitch wave form and amplitude, and that this sensitivity is reflected in the precise timings of their afferent discharge. 4. Examination of these tendon organ responses indicates that the forces produced by single motor units couples to the receptor capsule are well above threshold. Calculations based on these results, and earlier soleus motor unit and muscle fibre data, suggest that the absolute force threshold for tendon organs may be as little as 4 mg, which is less than the estimated minimum twitch force generated by individual soleus muscle fibres. 5. Considering the number of tendon organs in a muscle, and the likelihood that every motor unit is connected with at least one receptor, the sensitivity of tendon organs ensures that every twitch of every motor unit will be reflected in the population of afferent signals projecting to the spinal cord.     

Gliding function following flexor-tendon injury. A biomechanical study of rat tendon function

Gliding function of flexor tendons one hour to eight weeks after a standard injury was studied in rat digits by determining terminal force of flexion, tendon excursion, and work of flexion using a tensile testing machine. A rapid decrease in gliding occurred within hours of injury, indicating that the postoperative hematoma and edema restrict gliding long before collagenous adhesions are synthesized. The improvement in gliding function with time implies that fibrous adhesions can be remodeled. Surgical methods and therapeutic agents, therefore, should be directed toward limiting early tissue injury and seeking ways to enhance the late remodeling of fibrous peritendinous adhesions along functional lines.     

A quantitative immunohistochemical study of the cellular response to crush injury in optic nerve

BACKGROUND: Excitotoxicity may contribute to neuronal degeneration in Huntington's disease (HD). N-methyl-D-aspartate (NMDA) receptor antagonists can prevent neuronal degeneration caused by excitotoxicity, but their effects in HD patients are not known. METHODS: We investigated the acute cognitive, behavioral, and motor effects of the NMDA-receptor antagonist ketamine in HD patients. Double-blind infusions of 0.10, 0.40, and 0.60 mg/kg/hr ketamine were given to 10 HD patients on one test day and compared with placebo infusions on a second, identical testing day. Linear mixed-effects models and randomization tests were used to identify whether, and at which dose, a significant change from baseline occurred in outcome variables. RESULTS: We demonstrated that ketamine is well tolerated at low and intermediate subanesthetic doses. Intermediate ketamine doses produced specific decline in memory and verbal fluency. Higher subanesthetic doses caused a significant increase in psychiatric symptoms and impairment of eye movements. CONCLUSIONS: These results describe the spectrum of clinical effects produced by increasing NMDA receptor blockade in HD patients. The clinical effects appearing with higher levels of NMDA receptor blockade can identify the range of doses used in clinical trials of NMDA receptor antagonists.     

Enhanced human T-cell lymphotropic virus type I expression following induction of the cellular stress response

Human T-cell lymphotropic virus type I (HTLV-I) infection is typically associated with long incubation periods between virus exposure and disease manifestation. Although viral protein expression is considered to play an important role in the pathogenesis of HTLV-I-associated diseases, limited information is known regarding host cell mechanisms that control viral gene expression. This study was designed to evaluate modulation of HTLV-I gene expression following induction of the cellular stress response in HTLV-I-infected lymphocytes. The cellular stress response was elicited by treatment with either Na arsenite or thermal stress and was monitored by demonstrating increased expression of the 72-kDa heat shock protein. Induction of the cellular stress response in HTLV-I-infected lymphocytes resulted in significantly increased HTLV-I-mediated syncytia formation due to enhanced HTLV-I envelope (gp46) expression. Intracellular viral proteins and released p24 capsid protein were increased in stressed infected lymphocytes as compared to nonstressed infected lymphocytes. Furthermore, HTLV-I-LTR reporter gene constructs had increased activity (three- to sixfold) in a transiently transfected, uninfected lymphocyte cell line following induction of the cellular stress response. Quantitation of HTLV-I RNA expression by slot blot analysis of infected lymphocytes suggested variable increases in RNA accumulation. Northern blot analysis demonstrated no qualitative changes in expression of RNA species. These data suggest a relationship between modulation of viral replication and a basic cellular response to stress and have important implications for understanding host cell control mechanisms of HTLV-I expression.     

Failure of heparin to inhibit the expression of the thrombin receptor following endothelial injury of the rabbit carotid artery

Rhythms of daily activity are found in all vertebrate species, some of them being diurnal (like humans, dogs, pigeons), others--nocturnal (like mice, rats and bats). Some species undergo very pronounced seasonal changes, as they hibernate in the winter or mate only at the specific seasons. The main regulator (a clock and a calendar) for daily and seasonal rhythms is the periodicity of the external light-darkness, reflected by the periodicity of melatonin secretion from the pineal gland, which is inhibited by light and induced during the darkness. In contrast to melatonin which peaks during the night both in diurnal and noctural species, the cyclicity of other hormones and several immune parameters correlates with the pattern of the animal locomotor activity-resting. The immune parameter that peaks at one time of day for a diurnal species peaks about 12 h later for a nocturnal one. Various immune parameters peak at various time points, anticipating an encounter with pathogens during the period of activity while energetically expensive resolution of the immune response during the resting. Daily and seasonal cyclicity of the immune functions are temporally integrated with other physiologic and behavioral processes and all of them are regulated and coordinated with daily and seasonal changes of an external environment by the neuroendocrine homeostatic system.     

Differential Opa specificities for CD66 receptors influence tissue interactions and cellular response to Neisseria gonorrhoeae

The ability of all 11 variable opacity (Opa) proteins encoded by Neisseria gonorrhoeae MS11 to interact directly with the five CD66 antigens was determined. Transfected HeLa cell lines expressing individual CD66 antigens were infected with recombinant N. gonorrhoeae and Escherichia coli strains expressing defined Opas. Based upon the ability of these bacteria to bind and invade and to isolate specifically CD66 antigens from detergent-soluble extracts of the corresponding cell lines, distinct specificity groups of Opa interaction with CD66 were seen. Defining these specificity groups allowed us to assign a specific function for CD66a in the Opa-mediated interaction of gonococci with two different target cell types, which are both known to co-express multiple CD66 antigens. The competence of individual Opas to interact with CD66a was strictly correlated with their ability to induce an oxidative response by polymorphonuclear neutrophils. The same Opa specificity was observed for the level of gonococcal binding to primary endothelial cells after stimulation with TNFalpha, which was shown to increase the expression of CD66a rather than CD66e. As CD66e alone is expressed on other target tissues of gonococcal pathogenicity, Opa variation probably contributes to the cell tropism displayed by gonococci.     

Differential effects of hippocampectomy on classically conditioned rabbit nictitating membrane response related to interstimulus interval.

The effects of hippocampal ablation on acquisition rates and temporal characteristics of classically conditioned nictitating membrane responses were examined in 54 New Zealand albino rabbits trained with a 150-, 300-, or 600-msec interstimulus interval. Acquisition rates were accelerated in the 150- and 600-msec groups. No effect was present in the 300-msec group. Response onset latencies were also affected in the 150-msec group. Results indicate that damage to the hippocampus influences the acquisition of classically conditioned responses only when temporal parameters are relatively complex. Findings also support the notion that the hippocampus modulates learned motor behavior by a neural model of the response to be executed. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bowstring injury of the flexor tendon pulley system: MR imaging

OBJECTIVE. The flexor tendon pulley system is often ruptured when a flexed finger is forcibly extended. In the acute phase, soft-tissue swelling and pain often make clinical evaluation difficult. These pulleys are not constantly visualized on MR imaging. Rupture of the pulley system can be inferred by observing bow stringing of the underlying flexor tendons when MR imaging is obtained with the finger in flexion. Our objective is to describe the flexor tendon pulley system and present our MR technique.     

Deformity of the foot following anterior transfer of the posterior tibial tendon and lengthening of the Achilles tendon for spastic equinovarus

Twenty-four children with spastic equinovarus deformity due to cerebral palsy were treated by anterior transfer of the posterior tibial tendon and Achilles tendon lengthening. In five patients, the operation was performed on both sides, making a total of 29 feet available for evaluation after an average follow-up of five years. Only 38 per cent of the results were graded "good" or "satisfactory." Sixty-two per cent were rated as "poor" because of valgus, calcaneus or equinus deformity severe enough to require re-operation. The post-operative deformity was generally evident one or more years after surgery, often progressive, and more disabling as well as more difficult to correct than the original condition. Although the percentage of acceptable results was considerably higher for hemiplegic patients than for others in the study, we conclude that in this group and in all other categories of spastic patients anterior transfer of the posterior tibial tendon should not be performed.     

Neuronal unit activity in the abducens nucleus during classical conditioning of the nictitating membrane response in the rabbit (Oryctolagus cuniculus).

Recorded neuronal unit activity from the abducens (6th nerve) nucleus during conditioning of the nictitating membrane (NM) response in 16 male New Zealand white rabbits, using a tone CS, an air puff UCS, 250-msec interstimulus interval, and 60-sec intertrial interval. Ss were given 2 days of training (104 trials in 8 blocks/day) and 1 day of extinction. Control Ss were given comparable periods of stimulus presentations, explicitly unpaired. Activity of small clusters of units—multiple unit recording—was compared with the amplitude/time course of NM response. Between-blocks comparisons of neural and behavioral responses indicated almost perfect correlation during acquisition of the CR and a slightly lower correlation during extinction for the conditioning Ss. Within-blocks comparisons indicated close correspondence between histograms of unit activity and the amplitude/time course of the NM response for the conditioning Ss in all phases of training and for controls in the UCS trial blocks. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Callus response to micromovement after elongation in the rabbit

The purpose of this investigation was to determine whether induced micromovement could improve the consolidation of diaphyseal elongation by callus distraction. Two series of paired rabbit hindlimbs were studied. The surgical procedure, waiting period, and elongation period were identical. One hindlimb was then left under neutralization conditions, but the other limb was stimulated by axial micromovements. Reproducible tibial osteotomy and lengthening of the two tibiae were confirmed radiographically. The mineralized callus was quantified by dual-beam x-ray absorptiometry. The anteroposterior and lateral diameters of the callus were measured. A semiquantitative histologic study allowed the ratio between fibrous or cartilaginous callus or both and mineralized callus to be determined. Bones were axially compressed to failure. Callus volume, callus mineral content, callus mineral density, and mechanical forces required to failure were significantly superior on the stimulated side compared with the neutralized side, so micromovements applied after the end of elongation were beneficial for bone healing. Mechanical forces required to failure were significantly correlated to callus volume and callus mineral density.     

Differential cognitive response to a mood challenge following successful cognitive therapy or pharmacotherapy for unipolar depression.

This study examined the nature of cognitive reactivity to mood changes in formerly depressed patients. Patients who recovered either through cognitive–behavior therapy (CBT; N?=?25) or through pharmacotherapy (PT; N?=?29) completed self-reported ratings of dysfunctional attitudes before and after a a negative mood induction procedure. In response to similar levels of induced sad mood, PT patients showed a significant increase in dysfunctional cognitions compared with patients in the CBT group. To evaluate the effects of such cognitive reactivity on the subsequent course of depression, follow-up analyses reassessed 30 patients several years after initial testing. Results indicated that patients' reactions to the mood induction procedure were predictive of depressive relapse. These findings argue for differential effects of treatment on cognitive reactivity to mood induction and for the link between such reactivity and risk for later depressive relapse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Progression towards a 'no manual lifting' policy within the intensive care unit

Nurses within the critical care environment are at increased risk of back injury, due to the high dependence of the patients. A move towards a 'no manual lifting' policy is desirable to reduce the costs of staff sickness, compensation claims and to comply with new legislation. Implementation of a 'no manual lifting policy' within intensive care poses a unique challenge due to the special needs of the critically ill patient. The call has gone out to avoid all manual lifting in all but exceptional and life-threatening situations.     

Cerebrovascular response in infants and young children following severe traumatic brain injury: a preliminary report

PURPOSE: Endotoxin (lipopolysaccharide [LPS])-induced systemic organ injury leads to disruption of normal systemic organ metabolic processes, which are manifest clinically by signs of accelerated anaerobic metabolism (e.g., tissue acidosis and hyperlactatemia) and altered VO2-DO2 relationships. The association of increased anaerobic metabolism with VO2-DO2 alterations has led to the notion that ischemia/ reperfusion (I/R) injury may be a prerequisite for the development of VO2-DO2 alterations during endotoxemia. However, in contrast to sepsis, in which oxygen consumption is often increased, oxygen consumption is severely decreased after I/R injury. Based on these observations, we hypothesized that I/R injury would result in systemic organ VO2-DO2 alterations, which are distinct from those that occur in sepsis. MATERIALS AND METHODS: We used the in situ autoperfused feline ileal preparation to simultaneously examine microvascular permeability, reflected as the ileal lymph to plasma protein concentration ratio (CL/CP), and ileal VO2-DO2 relationships after either intravenous LPS (2.0 mg/kg; n = 5) or I/R injury (n = 5), and in matching controls (n = 5). RESULTS: As expected, all LPS-treated and I/R-injured animals were found to have extensive ileal histological damage and marked increases in the CL/CP compared with controls (0.315 +/- 0.009 and 0.329 +/- 0.034, respectively, v 0.097 +/- 0.009; P < .001, both comparisons). In addition, the critical DO2 (DO2c) was elevated, and the critical oxygen extraction was decreased in both the I/R and LPS groups relative to controls. However, as initially hypothesized, the VO2 at the critical DO2 was markedly decreased in the I/R group compared with that of the LPS group. CONCLUSIONS: These data indicate that I/R injury is insufficient to account for the systemic organ VO2-DO2 alterations that occur with LPS injury.