Mechanical energy in toddler gait - A trade-off between economy and stability?

Mechanical energy expenditure was investigated in children who are just learning to walk and compared with adult mechanical energy expenditure during walking. First, we determined whether the inverted pendulum (IP) mechanism of energy exchange was present in toddlers. It seems that new walkers partially make use of this energy saving mechanism, but it is less efficient than in adults. The reduced recovery values (R=40% at optimal speeds in toddlers compared to 70% in adults) can be explained by their low self-selected walking speed in combination with their tossing gait (large vertical oscillations of the body) and by the observation that during as much as 25–50% of the gait cycle kinetic and potential energy are oscillating in-phase. The second step was to calculate positive external mechanical work (Wext). Since the IP mechanism is less efficient in toddlers, more mass-specific positive work has to be performed to lift and accelerate the centre of mass than in adults walking at the same speed, even when differences in body size are taken into account. The amount of positive internal work (Wint,k) necessary to move the body segments relative to the centre of mass was the third parameter we calculated. In toddlers Wint,k is largely determined by the kinetic energy of the lower limb. Compared to adults, toddlers have to perform less mass-specific work per unit distance to accelerate the body segments since the upper body is kept relatively stiff during walking and there is no arm swing. Apart from work performed on the centre of mass and work performed to move the body segments relative to the centre of mass, when walking some work is also performed during double contact as both legs are pushing against each other. Two methods were used to calculate this amount of work, both leading to the same conclusions. Mass-specific work during double contact is small in toddlers compared to adults because of their low walking speed. Finally the total amount of mechanical work performed in toddlers was compared to the work production observed in adults. Wext seems to be the major determinant for total mechanical energy expenditure. At intermediate froude numbers work production is comparable between adults and toddlers, but at low and high froude numbers Wtot increases due to the steep increases in Wext. Despite the fact that mechanical work requirements in toddler gait are underestimated if work during double contact is not taken into account, it is not a major determinant of the energy cost of walking

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Transgenic APP23 mice were generated to model Alzheimer's disease. The APP23 model develops pathological features, learning deficits, and memory deficits analogous to dementing patients. In this report, transgenic mice exhibited several behavioral disturbances indicating the presence of neuropsychiatric symptoms of dementia. Aiming to verify whether the model also develops other behavioral problems, the authors investigated ingestive behavior in APP23 males of 3, 6 and 12 months. In addition, body weights of a naive male group were longitudinally monitored starting at weaning. Olfactory acuity was evaluated in mice of different age groups. Although olfactory functioning of APP23 mice appeared intact, they drank more and took more food pellets compared with wild-type littermates during a 1-week registration period. From the age of 4.5 weeks onward, APP23 males weighed significantly less than their control littermates, whereas this difference became more prominent with increasing age. Our results suggest the presence of a hypermetabolic state in this model. This is the first report, evidencing the presence of changes in eating and drinking behavior in a single transgenic Alzheimer mouse model.status: publishe

Modest phenotypic improvements in ASA-deficient mice with only one UDP-galactose:ceramide-galactosyltransferase gene

BACKGROUND: Arylsulfatase A (ASA)-deficient mice are a model for the lysosomal storage disorder metachromatic leukodystrophy. This lipidosis is characterised by the lysosomal accumulation of the sphingolipid sulfatide. Storage of this lipid is associated with progressive demyelination. We have mated ASA-deficient mice with mice heterozygous for a non-functional allele of UDP-galactose:ceramide-galactosyltransferase (CGT). This deficiency is known to lead to a decreased synthesis of galactosylceramide and sulfatide, which should reduce sulfatide storage and improve pathology in ASA-deficient mice. RESULTS: ASA-/- CGT+/- mice, however, showed no detectable decrease in sulfatide storage. Neuronal degeneration of cells in the spiral ganglion of the inner ear, however, was decreased. Behavioural tests showed small but clear improvements of the phenotype in ASA-/- CGT+/- mice. CONCLUSION: Thus the reduction of galactosylceramide and sulfatide biosynthesis by genetic means overall causes modest improvements of pathology

Behavioural and psychological symptoms of dementia in Down syndrome: Early indicators of clinical Alzheimer's disease?

Behavioural and Psychological Symptoms of Dementia (BPSD) are a core symptom of dementia and are associated with suffering, earlier institutionalization and accelerated cognitive decline for patients and increased caregiver burden. Despite the extremely high risk for Down syndrome (DS) individuals to develop dementia due to Alzheimer's disease (AD), BPSD have not been comprehensively assessed in the DS population. Due to the great variety of DS cohorts, diagnostic methodologies, sub-optimal scales, covariates and outcome measures, it is questionable whether BPSD have always been accurately assessed. However, accurate recognition of BPSD may increase awareness and understanding of these behavioural aberrations, thus enabling adaptive caregiving and, importantly, allowing for therapeutic interventions. Particular BPSD can be observed (long) before the clinical dementia diagnosis and could therefore serve as early indicators of those at risk, and provide a new, non-invasive way to monitor, or at least give an indication of, the complex progression to dementia in DS. Therefore, this review summarizes and evaluates the rather limited knowledge on BPSD in DS and highlights its importance and potential for daily clinical practice

Liver Transplantation Prevents Progressive Neurological Impairment in Argininemia

Argininemia is a rare hereditary disease due to a deficiency of hepatic arginase, which is the last enzyme of the urea cycle and hydrolyzes arginine to ornithine and urea. The onset of the disease is usually in childhood, and clinical manifestations include progressive spastic paraparesis and mental retardation. Liver involvement is less frequent and usually not as severe as observed in other UCDs. For this reason, and because usually there is a major neurological disease at diagnosis, patients with argininemia are rarely considered as candidates for OLT despite its capacity to replace the deficient enzyme by an active one. We report on long-term follow-up of two patients with argininemia. Patient 1 was diagnosed by the age of 20 months and despite appropriate conventional treatment progressed to spastic paraparesis with marked limp. OLT was performed at 10 years of age with normalization of plasmatic arginine levels and guanidino compounds. Ten years post-OLT, under free diet, there is no progression of neurological lesions. The second patient (previously reported by our group) was diagnosed at 2 months of age, during a neonatal cholestasis workup study. OLT was performed at the age of 7 years, due to liver cirrhosis with portal hypertension, in the absence of neurological lesions and an almost-normal brain MRI. After OLT, under free diet, there was normalization of plasmatic arginine levels and guanidino compounds. Twelve years post-OLT, she presents a normal neurological examination. We conclude that OLT prevents progressive neurological impairment in argininemia and should be considered when appropriate conventional treatment fails

Transport characteristics of guanidino compounds at the blood-brain barrier and blood-cerebrospinal fluid barrier: relevance to neural disorders

Guanidino compounds (GCs), such as creatine, phosphocreatine, guanidinoacetic acid, creatinine, methylguanidine, guanidinosuccinic acid, γ-guanidinobutyric acid, β-guanidinopropionic acid, guanidinoethane sulfonic acid and α-guanidinoglutaric acid, are present in the mammalian brain. Although creatine and phosphocreatine play important roles in energy homeostasis in the brain, accumulation of GCs may induce epileptic discharges and convulsions. This review focuses on how physiologically important and/or neurotoxic GCs are distributed in the brain under physiological and pathological conditions. Transporters for GCs at the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCSFB) have emerged as substantial contributors to GCs distribution in the brain. Creatine transporter (CRT/solute carrier (SLC) 6A8) expressed at the BBB regulates creatine concentration in the brain, and represents a major pathway for supply of creatine from the circulating blood to the brain. CRT may be a key factor facilitating blood-to-brain guanidinoacetate transport in patients deficient in S-adenosylmethionine:guanidinoacetate N-methyltransferase, the creatine biosynthetic enzyme, resulting in cerebral accumulation of guanidinoacetate. CRT, taurine transporter (TauT/SLC6A6) and organic cation transporter (OCT3/SLC22A3) expressed at the BCSFB are involved in guanidinoacetic acid or creatinine efflux transport from CSF. Interestingly, BBB efflux transport of GCs, including guanidinoacetate and creatinine, is negligible, though the BBB has a variety of efflux transport systems for synthetic precursors of GCs, such as amino acids and neurotransmitters. Instead, the BCSFB functions as a major cerebral clearance system for GCs. In conclusion, transport of GCs at the BBB and BCSFB appears to be the key determinant of the cerebral levels of GCs, and changes in the transport characteristics may cause the abnormal distribution of GCs in the brain seen in patients with certain neurological disorders

Moral enhancement: do means matter morally?

One of the reasons why moral enhancement may be controversial, is because the advantages of moral enhancement may fall upon society rather than on those who are enhanced. If directed at individuals with certain counter-moral traits it may have direct societal benefits by lowering immoral behavior and increasing public safety, but it is not directly clear if this also benefits the individual in question. In this paper, we will discuss what we consider to be moral enhancement, how different means may be used to achieve it and whether the means we employ to reach moral enhancement matter morally. Are certain means to achieve moral enhancement wrong in themselves? Are certain means to achieve moral enhancement better than others, and if so, why? More specifically, we will investigate whether the difference between direct and indirect moral enhancement matters morally. Is it the case that indirect means are morally preferable to direct means of moral enhancement and can we indeed pinpoint relevant intrinsic, moral differences between both? We argue that the distinction between direct and indirect means is indeed morally relevant, but only insofar as it tracks an underlying distinction between active and passive interventions. Although passive interventions can be ethical provided specific safeguards are put in place, these interventions exhibit a greater potential to compromise autonomy and disrupt identity

Internet-based search of randomised trials relevant to mental health originating in the Arab world

BACKGROUND: The internet is becoming a widely used source of accessing medical research through various on-line databases. This instant access to information is of benefit to busy clinicians and service users around the world. The population of the Arab World is comparable to that of the United States, yet it is widely believed to have a greatly contrasting output of randomised controlled trials related to mental health. This study was designed to investigate the existence of such research in the Arab World and also to investigate the availability of this research on-line. METHODS: Survey of findings from three internet-based potential sources of randomised trials originating from the Arab world and relevant to mental health care. RESULTS: A manual search of an Arabic online current contents service identified 3 studies, MEDLINE, EMBASE, and PsycINFO searches identified only 1 study, and a manual search of a specifically indexed, study-based mental health database, PsiTri, revealed 27 trials. CONCLUSION: There genuinely seem to be few trials from the Arab world and accessing these on-line was problematic. Replication of some studies that guide psychiatric/psychological practice in the Arab world would seem prudent