Persistent electrical coupling and locomotory dysfunction in the zebrafish mutant shocked

On initial formation of neuromuscular junctions, slow synaptic signals interact through an electrically coupled network of muscle cells. After the developmental onset of muscle excitability and the transition to fast synaptic responses, electrical coupling diminishes. No studies have revealed the functional importance of the electrical coupling or its precisely timed loss during development. In the mutant zebrafish shocked (sho) electrical coupling between fast muscle cells persists beyond the time that it would normally disappear in wild-type fish. Recordings from sho indicate that muscle depolarization in response to motor neuron stimulation remains slow due to the low-pass filter characteristics of the coupled network of muscle cells. Our findings suggest that the resultant prolonged muscle depolarizations contribute to the premature termination of swimming in sho and the delayed acquisition of the normally rapid touch-triggered movements. Thus the benefits of gap junctions during early synapse development likely become a liability if not inactivated by the time that muscle would normally achieve fast autonomous function.     

Monitoring CD4+ T cell responses against viral and tumor antigens using T cells as novel target APC

CD4+ T cells play an important role in the induction and maintenance of an effective antiviral and antitumor immune response. However, standardized monitoring of antigen-specific CD4+ T cells has not been established at the single-cell level. We now present a sensitive, specific, and simple methodology in which purified memory CD4+ T cells are expanded from PBMC in a single cycle of antigen-driven stimulation and quantitatively assayed by interferon-gamma ELISPOT. Issues of nonspecific background in assays were resolved with the use of innovative target cells, autologous PHA-expanded CD4+ T cells (T-APC). Remarkably, T-APC could not only present peptide epitopes from model antigens NY-ESO-1 and influenza nucleoprotein, but could also process full-length antigen endogenously expressed from recombinant fowlpox vector. This approach makes it possible to monitor CD4+ T cells in large series of patients, regardless of HLA haplotype, against the full peptide repertoire of a given antigen.     

Extinction responding by septal and normal rats following acquisition under four schedules of reinforcement

Extinction responding of animals with septal lesions was compared to that of normal animals following acquisition training under either DRL, FI, VI or FR reinforcement schedules (Part 1). During both acquisition and extinction, septals bar pressed more than normals. However, regardless of response levels, a given schedule changed behavior in the same direction for both septals and normals. Thus, if a given schedule led to a decrease in bar pressing by normals, it also led to a decrease by septals, although the absolute level of responding at which this occurred might be different for the two groups. Similarly, if a schedule led to an increase in responding by normals, it also led to an increase by septals. In Part 2 of the experiment operant levels of septals were not found to be different from those of normals, and noncontingent food delivery generated no more nor less bar pressing in septals than in normals. It was proposed that the septal area may be of importance in the initiation of behavior which competes with the required or reinforced response.     

Augmented sympathetic vasoconstriction in exercising forearms of postmenopausal women is reversed by oestrogen therapy

Sympathetic vasoconstriction is normally attenuated in exercising muscles of young men and women. Recent evidence indicates that such modulation, termed functional sympatholysis, may be impaired in older men. Whether a similar impairment occurs in older women, and what role oestrogen deficiency might play in this impairment, are not known. Based on the strong positive correlation between circulating oestrogen levels and functional sympatholysis previously reported in female rats, we hypothesized that sympatholysis would be impaired in oestrogen-deficient postmenopausal women, and that this impairment would be reversed by oestrogen replacement. To test these hypotheses, we measured vasoconstrictor responses in the forearms of pre- and postmenopausal women using near infrared spectroscopy to detect decreases in muscle oxygenation in response to reflex activation of sympathetic nerves evoked by lower body negative pressure (LBNP). In eight premenopausal women, LBNP decreased muscle oxygenation by 20 ± 1% in resting forearm, but only by 3 ± 2% in exercising forearm  ( P < 0.05)  . In contrast, in eight postmenopausal women, LBNP decreased muscle oxygenation by 15 ± 3% in resting forearm, and by 12 ± 4% in exercising forearm  ( P > 0.05)  . After 1 month of transdermal oestradiol replacement in these women, the normal effect of exercise to blunt sympathetic vasoconstriction was restored (rest, −19 ± 3%; exercise, −2 ± 3%;   P < 0.05  ). These data indicate that functional sympatholysis is impaired in oestrogen-deficient postmenopausal women. The effect of short-term unopposed oestrogen replacement to correct this impairment implicates a role for oestrogen in the sympathetic neural control of muscle haemodynamics during exercise.     

Wear-particle-induced osteoclast osteolysis: the role of particulates and mechanical strain

Periprosthetic osteolysis involves osteoclast activation by wear particulates and their exposure to mechanical perturbation through exposure to shear forces generated by periprosthetic fluid as well as interface micromotion. This study aimed to determine the interactions between wear particulates, mechanical stimulation, and osteoclasts. In static cultures, wear particulates increased osteoclast differentiation. Addition of neutralizing antibodies to RANKL (receptor activator of nuclear factor kappa ligand) inhibited the particle-induced increase in osteoclast numbers. Cyclic 5000 microstrains were applied with the use of a custom-built device to marrow-derived cultures to assess the effect on osteoclast differentiation. Mechanical strain application alone decreased osteoclast differentiation, which was further decreased by the addition of particles despite increases in the soluble RANKL to osteoprotegerin (OPG) ratio. Mechanical strain alone induced mature osteoclast apoptosis in a dose-dependent manner. In contrast, in the mature osteoclast model, the addition of nonmetal particulates protected the osteoclasts from becoming apoptopic. Titanium (Ti) and cobalt chromium (CoCr) particles, however, induced osteoclast apoptosis, whereas polyethylene (PE) and polymethylmethacrylate (PMMA) did not. Wear particulates and mechanical stimulation interact via an eicosanoid-dependent pathway to alter osteoclast function and survival. The addition of mechanical perturbation to a particle-laden system thus appears to enhance the potential for osteolytic activity by enhancing osteoclast survival.     

COMP mutation screening as an aid for the clinical diagnosis and counselling of patients with a suspected diagnosis of pseudoachondroplasia or multiple epiphyseal dysplasia

The skeletal dysplasias are a clinically and genetically heterogeneous group of conditions affecting the development of the osseous skeleton and fall into the category of rare genetic diseases in which the diagnosis can be difficult for the nonexpert. Two such diseases are pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED), which result in varying degrees of short stature, joint pain and stiffness and often resulting in early onset osteoarthritis. PSACH and some forms of MED result from mutations in the cartilage oligomeric matrix protein (COMP) gene and to aid the clinical diagnosis and counselling of patients with a suspected diagnosis of PSACH or MED, we developed an efficient and accurate molecular diagnostic service for the COMP gene. In a 36-month period, 100 families were screened for a mutation in COMP and we identified disease-causing mutations in 78% of PSACH families and 36% of MED families. Furthermore, in several of these families, the identification of a disease-causing mutation provided information that was immediately used to direct reproductive decision-making.     

Novel and recurrent mutations in the C-terminal domain of COMP cluster in two distinct regions and result in a spectrum of phenotypes within the pseudoachondroplasia -- multiple epiphyseal dysplasia disease group

Pseudoachondroplasia (PSACH) and some forms of multiple epiphyseal dysplasia (MED) result from mutations in the gene encoding cartilage oligomeric matrix protein (COMP). COMP is a large pentameric glycoprotein found predominantly in the extracellular matrix of cartilage, tendon, and ligament. As a modular protein, it is composed of a coiled-coil domain, four type II (T2) repeats, eight type III (T3) repeats, and a large globular C-terminal domain (CTD). The majority (>85%) of COMP mutations causing PSACH or MED are found in the exons encoding the T3 repeats, and the disease mechanism has been characterised in detail. Much less is known about disease-causing mutations in the CTD; in 10 years only seven mutations have been identified. In this study, we describe eight novel and two recurrent mutations that we have recently identified in patients with PSACH or MED. Interestingly, these mutations result in a spectrum of disease, ranging from mild MED to severe PSACH. Mapping of all known COMP CTD mutations on a three-dimensional model of the C-terminal domain shows that the CTD mutations cluster in two distinct regions. These regions are probably important in stabilising the T3-CTD structure and mediating intra- or intermolecular interactions.     

Shoulder muscle activity in Parkinson’s disease during multijoint arm movements across a range of speeds

Bradykinesia is one of the primary symptoms of Parkinson disease and leads to significant functional limitations for patients. Single joint movement studies, that have investigated the mechanism of bradykinesia, suggest that several features of muscle activity are disrupted, including modulation of burst amplitude and duration, and the number of bursts. It has been proposed that it is the blending of these different burst deficits that collectively defines bradykinesia. This study adds two new approaches to the study of bradykinesia. First, we examined the features of shoulder muscle activities during multijoint arm movement in bradykinetic and control subjects, such that previously reported single joint hypotheses could be tested for generalized arm movement. Second, we directly manipulated speed while keeping distance constant for a large range of speeds. In this manner, we could compare individual trials of muscle activity between controls and subjects with Parkinsons disease (PD) for movements matched for both speed and movement duration. Our results showed that while a multiple burst pattern of shoulder muscles was a common strategy for all subjects (young, elderly controls and PD), subjects with PD showed several burst abnormalities, including deficits in initial agonist burst amplitude and duration at both fast and slow speeds. Subjects with PD also (1) failed to produce a one-burst pattern at fast speeds and, instead, produced a predominance of multiple burst patterns and (2) showed a relationship between the number of burst deficits and the severity of disease. These results extend the findings of single joint studies to multi-joint and similarly indicate that a combination of burst modulation abnormalities correlate with bradykinesia and disease severity.     

Psychosocial factors related to long-term survival with HIV/AIDS

Only a few studies of long-term survivors of AIDS (those who survive more than twice the median expected time) have been done but these reveal a constellation of psychological characteristics including, but not limited to, those with active coping, social support, life involvement, ability to communicate, and active collaboration with one's doctor. Another related literature consists of longitudinal studies following people infected with the HIV virus to determine whether psychological characteristics are related to disease progression. These studies have focused on coping, depression, negative expectancies and social support as predictors. This article reviews and integrates the two bodies of literature combining the variables identified into four psychosocial strategies related to longer survival with HIV/AIDS: following healthy self care; maintaining connectedness; having a sense of meaning or purpose in life; and maintaining perspective. Affect, beliefs, and behaviour are all seen as important. Biological variables, SES and psychological resources that the person brings to the situation and external stresses are seen as important variables to consider in prediction studies. The pathways through which these four strategies may operate (both psychological and biological) to impact on health are discussed. Psychological pathways include distress and behavioural disengagement, while biological pathways involve the sympathetic nervous system, neuroendocrine and immune mediation. Finally suggestions for future research are given.