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Biomedical subjects

A Roberts

Publications and source records attributed to A Roberts.

At least 181 records · Page 10Linked to original sources
PubMed1994

A longitudinal gradient of synaptic drive in the spinal cord of Xenopus embryos and its role in co-ordination of swimming.

1. Intersegmental co-ordination in Xenopus embryos could be influenced by longitudinal gradients in neuronal properties or synaptic drive. To determine if such gradients exist intracellular recordings were made from putative motoneurones at different spinal levels. 2. No evidence was found of a longitudinal gradient in neuronal resting potentials. In a rostrocaudal direction the duration of current-evoked spikes increased and the amplitude of the spike after-hyperpolarization (AHP) decreased. 3. During fictive swimming the amplitude of the tonic excitatory synaptic input and the mid-cycle IPSPs declined in a rostrocaudal direction. The rise-time and fall-time of mid-cycle IPSPs increased in a rostrocaudal direction. 4. Rostral to the eighth post-otic segment mid-cycle IPSPs occurred on all cycles of fictive swimming episodes. More caudally IPSPs became irregular in occurrence and caudal to the twelfth post-otic segment no mid-cycle IPSPs could be detected, even during the injection of depolarizing current or when recording with KCl-filled electrodes. 5. The duration of spikes occurring during fictive swimming increased and the amplitude of spike AHP decreased in a rostrocaudal direction. A spike AHP was absent during fictive swimming activity in neurones caudal to the ninth post-otic segment even though it was present in current-evoked spikes in the same neurones. 6. On-cycle IPSPs (occurring shortly after the spike at phase values less than 0.4) were observed predominantly at the beginning of swimming episodes in neurones recorded rostral to the eighth segment, but were not detected at all in more caudal neurones. 7. If the rostrocaudal gradients in synaptic excitatory and inhibitory drive to putative motoneurones during fictive swimming are also present in premotor spinal interneurones they would be expected to have a strong influence on rostrocaudal delays. Such gradients could therefore be important components of the mechanism underlying intersegmental co-ordination.

Action Potentials↗
PubMed1994

Lack of efficacy of fluoxetine in recurrent brief depression and suicidal attempts.

Recurrent brief depression (RBD) fulfills DSM-III-R symptom criteria for major depression but the episodes are of shorter duration than the 2 weeks required by DSM-III-R. The clinical importance of the disorder has been observed in prophylactic studies of suicidal behavior. The possibility that antidepressants with selective action on the reuptake of serotonin might be effective in preventing recurrences of brief depression has been investigated. Fluoxetine in a dose of 120 mg a week, administered biweekly, had no effect on the recurrence rate, which was maintained at approximately the same rate on fluoxetine (1 every 18.7 days) as with placebo (1 every 17.6 days). In a group of patients with two or more prior episodes of suicidal behavior, there were 18 attempted suicides in the 54 patients treated with fluoxetine and the same number in the 53 patients treated with placebo. Fluoxetine neither raised nor lowered the suicide attempt rate as compared with placebo, providing no evidence to support the drug's role in either suicide provocation or prevention. Since fluoxetine is clearly effective with recurrent major depression, it would appear that recurrent brief depression has a different pharmacology.

Bipolar Disorder↗
PubMed1994

Immunoglobulin deficiency and recurrent postmenopausal endometritis.

Secretory immunoglobulin A is the principal immunoglobulin of mucosal surfaces and may be reduced in postmenopausal women because of estrogen deficiency. This can manifest as recurrent infections and may be a cause of undiagnosed postmenopausal bleeding. Regular serum immunoglobulin therapy is appropriate for these patients.

Agammaglobulinemia↗
PubMed1994

Guiding the selection of human antibodies from phage display repertoires to a single epitope of an antigen.

We have developed a strategy for guiding the selection of human antibody fragments from phage display repertoires to a single epitope of an antigen, using rodent monoclonal antibodies as a template. Thus the heavy chain of a rodent antibody (MAb32) directed against human tumor necrosis factor alpha (TNF alpha) was cloned and paired as a template chain with a repertoire of human light chains for display as Fab fragments on filamentous phage. The phage were selected by binding to the antigen. The selected human light chains were in turn paired with a repertoire of human heavy chains displayed on phage, and the phage selected again. The isolated phage displaying human antibody fragments binding to TNF alpha also bound to a peptide comprising the N-terminal region of TNF alpha as with MAb32. One of the human Fab fragments was recloned for expression as a glycosylated human antibody in mammalian cells: Binding to TNF alpha could be competed with MAb32 or with anti-serum to the peptide, indicating the same epitope. The human antibody was found to have a binding affinity (Kd = 15 nM) similar to MAb32 (Kd = 26 nM). The process contrasts with existing means of "humanizing" rodent monoclonal antibodies in that the antibodies derived are completely human.

Amino Acid Sequence↗
PubMed1994

Placebo-controlled efficacy of antidepressants in continuation treatment.

All episodes of depression require treatment after symptomatic response of the acute episode in order to consolidate response. If treatment is discontinued early, 30% to 50% of patients will suffer a relapse of the inadequately treated episode. Placebo-controlled studies with a variety of antidepressants, old and new, have provided compelling evidence of the efficacy of anti-depressants on relapse prevention. A recent study of citalopram has also shown the need for long-term treatment with anti-depressants in patients whose acute episode of depression appeared to respond to placebo since their response was not maintained.

Antidepressive Agents↗
PubMed1994

Note on assessing a mentor program.

To clarify the literature on mentor programs, self-esteem and grade point average after such a program were assessed for 30 boys and 46 girls in Grade 11 from 2 high schools. Mixed findings were discussed in terms of possible influences.

Adolescent↗
PubMed1994

Longitudinal gradients in the spinal cord of Xenopus embryos and their possible role in coordination of swimming.

We consider the hypothesis that the normal rostrocaudal spread of motor activity during swimming in Xenopus embryos depends on a longitudinal, rostrocaudal gradient in synaptic drive received by the pattern generating neurons in the spinal cord. Anatomical evidence shows that there is a rostrocaudal gradient in excitatory and inhibitory premotor interneuron numbers. Intracellular recordings were therefore made from neurons at different longitudinal positions to seek direct evidence for a gradient in synaptic drive. The main finding was that during fictive swimming the amplitude of the tonic excitatory synaptic input and the mid-cycle inhibition declined in a rostrocaudal direction and caudal to the twelfth postotic segment inhibition was absent altogether. Experimental manipulation of the gradients by the caudal application of pharmacological agents lead to changes or even reversal of the normal direction of spread of motor activity. To test whether a gradient in synaptic drive could organize a rostrocaudal spread of activity we have used a 48 neuron, 12 segment model of the spinal pattern generating network. This has shown that the gradient hypothesis can provide a sufficient explanation for much of the embryo's motor coordination. A gradient in synaptic drive provides a flexible mechanism to control sequences of motor activity.

Animals↗
PubMed1993

Spinal cord neuron classes in embryos of the smooth newt Triturus vulgaris: a horseradish peroxidase and immunocytochemical study.

Spinal cord neurons were investigated in embryos of Triturus vulgaris, the smooth newt, just prior to hatching. These embryos can swim if freed from their egg membranes. Horseradish peroxidase (HRP) labelling, together with GABA and glycine immunocytochemistry (ICC), revealed nine distinct anatomical classes of neuron. 1. Ventrolateral motoneurons with mainly dorsal dendrites, sometimes a descending central axon and peripheral axon innervating the trunk muscles. 2. Dorsal primary sensory Rohon-Beard neurons innervating skin and with dorsal ascending and descending axons in spinal cord. 3. Commissural interneurons with mid-cord unipolar soma, glycine-like immunoreactivity, dendrites on initial segment of ventral axon which crosses cord to ascend or branch. 4. Dorsolateral commissural interneurons with multipolar soma in dorsolateral position with dorsal dendrites and ventral axon which crosses and ascends or branches. 5. Giant dorsolateral commissural interneurons with large dorsolateral somata widely spaced (130-250 microns spacing) with process projecting dorsally to other side, dorsolateral dendrites and ventral axon which crosses to ascend and branch. 6. Dorsolateral ascending interneurons in dorsolateral position with multipolar soma and ascending axon on same side. 7. Ascending interneurons with unipolar soma, GABA-like immunoreactivity and ascending axon on same side. 8. Descending interneurons with bi- or multi-polar soma, extensive dorsal and ventral dendrites, and descending axon on same side. They may also have ascending axons. 9. Kolmer-Agduhr cerebrospinal fluid contacting neurons with cilia and microvilli in lateral corners of neural canal. GABA-like immunoreactivity, no dendrites and ascending axon. Eight of the nine cells classes were found to bear a marked resemblance to neurons previously described in zebrafish and Xenopus embryos in terms of their anatomy, distribution and immunoreactivity to GABA and glycine. Homologies and possible functions are discussed. Giant dorsolateral commissural neurons, were not found in Xenopus or teleosts but were present in Ambystoma mexicanum and Neoceratodus. The regular, possibly segmental longitudinal distribution pattern of these cells within the cord is unusual among amphibian spinal neurons.

Animals↗
PubMed1993

Neuronal control of swimming locomotion: analysis of the pteropod mollusc Clione and embryos of the amphibian Xenopus.

It is rare to be able to explain the behaviour of a whole animal at the level of the properties and connections of characterized CNS neurones. In a marine mollusc, Clione, and a lower vertebrate embryo, Xenopus, it is possible to make intracellular recordings during fictive swimming behaviour. This has allowed us to analyse the operation of two central pattern generators (CPGs) at the cellular level. Although the timeframes over which the two CPGs operate are different, there are significant similarities in their patterns of neural output. A detailed analysis of the neural networks involved reveals that the swimming CPGs of Clione and Xenopus have several common operating principles, which suggests that common mechanisms have evolved to perform similar tasks, despite differences in neuronal 'hardware'.

Animals↗
PubMed1993

Feeding status affects glucose metabolism in exercising horses.

Four standardbred horses were used in a Latin square design experiment to evaluate the effects of feeding status on metabolic response to exercise. Horses were deprived of food overnight and then fed 0 (control condition), 1, 2 or 3 kg of corn grain approximately 2.5-3 h before exercise. The exercise test consisted of a warm-up phase (heart rate mean = 144 beats/min) followed by 800 m of walking and then a high intensity work bout for 1600 m (heart rate mean = 206 beats/min). All tests were conducted on a high speed equine treadmill on which the horses had been previously conditioned. During exercise, the control treatment resulted in steady plasma glucose concentrations, whereas all other treatments (1, 2 or 3 kg corn) caused a decline in plasma glucose. Liver glycogen concentration was decreased by exercise in the horses only when they received the control treatment. Plasma lactate concentration was increased by exercise but was not affected by feeding state. Plasma free fatty acid concentrations were highest when the horses received the control treatment. In addition, when horses received the control treatment, plasma free fatty acid concentrations decreased during the warm-up and high intensity phases of the test and increased during the walk phase. Free fatty acid concentrations changed in the horses receiving 1, 2 or 3 kg of corn grain only during the high intensity phase of the exercise test. Feeding status affects the metabolic response of horses to exercise thus further studies are necessary to evaluate the effect of feeding status on exercise performance.

Analysis of Variance↗
PubMed1993

An approach to training and retaining primary care physicians in rural Appalachia.

The West Virginia School of Osteopathic Medicine (WVSOM) educated and retained more primary care physicians for practice in rural Appalachia than did any other U.S. medical school from 1978 through 1990. This article describes the most important methods used at WVSOM to place physicians in rural areas: (1) The school has a focused, achievable mission (to provide primary care physicians who are trained to meet the medical needs of rural Appalachia and to improve the health care of the rural Appalachian population) that is agreed upon by the administration, faculty, and students; (2) it participates in a multistate educational exchange program with a similar mission; (3) it emphasizes personalized and interactive recruiting, admission, and placement processes aimed to attract nontraditional, rural students; (4) it provides early and long-term clinical training in rural sites (both hospitals and physicians' offices); (5) it is dedicated primarily to the education of medical students rather than to research or other goals; and (6) it is a freestanding school in a rural environment. The authors state that although WVSOM is unusual in some respects, at least some of its methods may be useful to other medical schools as they seek to produce more primary care physicians for rural and other underserved areas.

Appalachian Region↗
PubMed1993

Orthopedic aspects of neuromuscular disorders in children.

Studies using movement analysis confirm that multiple soft tissue releases improve function in the ambulant child with cerebral palsy, and highlight the fine adjustments of ankle-foot orthosis, which benefit children with myelomeningocele. For both of these disorders, there is information with regard to hip subluxation and dislocation. The normal increase of hamstring tightness during childhood is documented, as well as a new approach for surgical release in the nonambulant spastic child. Dramatic survival curves are presented to show the benefit of spinal instrumentation in Duchenne muscular dystrophy. Finally, there is a useful review and guide for the management of obstetric brachial plexus lesions.

Bone Diseases↗