Effects of hypercapnia and hypoxemia on fetal breathing after decortication

The effects of hypercapnia and hypoxemia on breathing movements were studied in 12 chronically decorticated fetal sheep, 127-140 days gestation. The fetal state of consciousness was defined in terms of activity of the lateral rectus and nuchal muscles. Arterial blood pressure was monitored. Fetal breathing was determined by integrated diaphragmatic electromyogram (EMG) and analyzed in terms of inspiratory time (TI), expiratory time (TE), electrical equivalent of tidal volume (EVT), breath interval (TT), duty cycle (TI/TT), mean inspiratory flow equivalent (EVT/TI), and instantaneous ventilation equivalent (EVT/TT). Fetal breathing occurred only during episodes of rapid-eye movements, and the response to hypercapnia consisted of an increase in EVT, TI, EVE, and EVT/TI and a decrease in the coefficient of variation of all measured parameters. Induction of hypoxia during episodes of spontaneous fetal breathing produced a decrease in the rate of breathing and an increase in EVT and TI with no change in the variability of all parameters studied. Since similar responses to hypercapnia and hypoxemia are seen in the intact fetus, we conclude that the cerebral cortex has no obvious effect on the chemical control of fetal breathing.     

Characteristic Features of Disorders of the Upright Posture in Patients with Poststroke Hemipareses

Characteristic features of upright posture maintenance and mechanisms of postural disorders in poststroke hemiparetic patients were studied using a bilateral force platform. The following features of postural disorders were revealed in the patients tested: an increase in the velocity and amplitude of the center-of-pressure (CP) sway as compared to in healthy subjects, an absolute decrease in the half-cycles of the CP sway, asymmetry of weight bearing by both feet, and a shift of the center of pressure of an affected foot towards the toe. The disturbance of stability of the vertical posture in such patients is to a greater extent associated with weight-bearing asymmetry. It was shown that the character of the CP sway is mainly determined by a disorder of the sensory motor control, whereas damage to the efferent pathways is responsible for the postural asymmetry. Increase in the muscle tone restricts the sway amplitude. Thus, several forms of postural instability are characteristic of hemiparetic patients. Predominantly sensory, motor, or tonic disorders are responsible for these disturbances of stability.     

Nature of functional motor asymmetry in animals: state of the problem

Handedness in skilled movements of animals is a result of interaction of innate motor preference and learning. The nature of the innate preference is not clear. Breeding of right-handed and left-handed mice revealed that the degree rather than direction of motor preference is an inherited feature. There is, however, a correlation between the direction of preference and a number of morphological, functional, and neurochemical characters. Shifts of a preference direction were found in some strains of mice. Differences between right-handed and left-handed rats were revealed in social behavior, learning, and resistance to forced retraining. Strains of rats with different forms of genetic epilepsy were characterized by the predominance of animals with a certain direction of the motor preference. This evidence suggests some genetic influence on a direction of the motor preference. Perhaps, genetic and environmental factors closely interact in determining motor preference in animals.     

Features of learning voluntary control of posture after pyramidal and nigrostriatal lesions

The study was aimed at investigation of a deficit of learning the center-of-pressure voluntary control in patients with lesions of corticospinal and nigrostriatal systems. Thirty three patients with Parkinson's disease and 20 patients with hemiparesis after cerebrovascular accidents in the MCA participated in the investigation. The subjects stood on a force platform and in the form of a computer game were trained to match the projection of the center of pressure (a cursor) with a target on the screen under the visual feedback control. Two different postural tasks were presented. In the first task the direction of the center-of-pressure shift was not known before, so the subject learned the general strategy of the center-pressure control. In the other task a precise postural coordination should be formed. The voluntary control of the center-of-pressure position was found to be impaired in both groups of patients. In the task of moving the center of pressure in various directions (general strategy), no differences in the initial deficit of the task performance were found between the groups, but the learning was more efficient in the group of hemiparetic patients. However, in the task with precise postural coordination, despite the greater initial deficit in the parkinsonian patients, the learning in this group of patients was substantially more efficient than in hemiparetic patients. The results suggest both common and different features of the involvement of the corticospinal and nigrostriatal systems in learning voluntary control of posture.     

Angiopoietin-1 protects the adult vasculature against plasma leakage

Pathological increases in vascular leakage lead to edema and swelling, causing serious problems in brain tumors, in diabetic retinopathy, after strokes, during sepsis and also in inflammatory conditions such as rheumatoid arthritis and asthma. Although many agents and disease processes increase vascular leakage, no known agent specifically makes vessels resistant to leaking. Vascular endothelial growth factor (VEGF) and the angiopoietins function together during vascular development, with VEGF acting early during vessel formation, and angiopoietin-1 acting later during vessel remodeling, maturation and stabilization. Although VEGF was initially called vascular permeability factor, there has been less focus on its permeability actions and more effort devoted to its involvement in vessel growth and applications in ischemia and cancer. Recent transgenic approaches have confirmed the profound permeability effects of VEGF (refs. 12-14), and have shown that transgenic angiopoietin-1 acts reciprocally as an anti-permeability factor when provided chronically during vessel formation, although it also profoundly affects vascular morphology when thus delivered. To be useful clinically, angiopoietin-1 would have to inhibit leakage when acutely administered to adult vessels, and this action would have to be uncoupled from its profound angiogenic capabilities. Here we show that acute administration of angiopoietin-1 does indeed protect adult vasculature from leaking, countering the potentially lethal actions of VEGF and inflammatory agents.     

Control of different electromyogram levels of M. abductor pollicis brevis by means of visual feedback in healthy subjects

We studied voluntary control of integrated electromyogram (IEMG) in the range of 20 +/- 5% and 40 +/- 5% of the IEMG of m. abductor pollicis brevis during its maximum voluntary contraction with and without visual feedback. Healthy subjects performed IEMG control with visual feedback in 5 trials; IEMG control with visual feedback in 5 trials for 5 days, and the reproduction of memorized IEMG value without visual feedback after 5 trials of IEMG under the visual control. The accuracy of IEMG control was estimated by the following parameters: time of IEMG being out of the required 10% range (ERROR); IEMG variability (VARIABILITY), and the bias of IEMG mean level (BIAS) during 30-sec trials. The IEMG control in the range of 20 +/- 5% with visual feedback improved in all subjects over the course of 5 trials. Within 5-day training, ERROR and VARIABILITY reduced on the first day only; during the last 4 days there was no accuracy increase. ERROR increased more than twice when the 20% IEMG level was reproduced without vision. The IEMG control in the range of 40 +/- 5% improved neither during 5 trials, nor during 5 days of training with visual feedback. ERROR increased for about 1.5 times when the 40% IEMG level was reproduced without vision. It was concluded that the motor system, particularly the motor cortex, could control the given level of muscle activity using the visual feedback.     

Paradoxical antagonism of PACAP receptor signaling by VIP in Xenopus oocytes via the type-C natriuretic peptide receptor

Atrial natriuretic peptide (ANP) and the closely-related peptides BNP and CNP are highly conserved cardiovascular hormones. They bind to single transmembrane-spanning receptors, triggering receptor-intrinsic guanylyl cyclase activity. The "truncated" type-C natriuretic peptide receptor (NPR-C) has long been called a clearance receptor because it lacks the intracellular guanylyl cyclase domain, though data suggest it might negatively couple to adenylyl cyclase via G(i). Here we report the molecular cloning and characterization of the Xenopus laevis type-C natriuretic peptide receptor (XNPR-C). Analysis confirms the presence of a short intracellular C-terminus, as well as a high similarity to fish and mammalian NPR-C. Injection of XNPR-C mRNA into Xenopus oocytes resulted in expression of high affinity [(125)I]ANP binding sites that were competitively and completely displaced by natriuretic analogs and the unrelated neuropeptide vasoactive intestinal peptide (VIP). Measurement of cAMP levels in mRNA-injected oocytes revealed that XNPR-C is negatively coupled to adenylyl cyclase in a pertussis toxin-sensitive manner. When XNPR-C was co-expressed with PAC(1) receptors for pituitary adenylyl cyclase-activating polypeptide (PACAP), VIP and natriuretic peptides counteracted the cAMP induction by PACAP. These results suggest that VIP and natriuretic peptides can potentially modulate the action of PACAP in cells where these receptors are co-expressed.