Neuronal nitric oxide synthase: its role and regulation in macula densa cells

Macula densa (MD) cells detect changes in distal tubular sodium chloride concentration ([NaCl](L)), at least in part, through an apical Na:2Cl:K co-transporter. This co-transporter may be a site for regulation of tubuloglomerular feedback (TGF), and recently angiotensin II (Ang II) was shown to regulate the MD Na:2Cl:K co-transporter. In addition, nitric oxide (NO) produced via neuronal NO synthase (nNOS) in MD cells attenuates MD-TGF signaling. This study investigated [NaCl](L)-dependent MD-NO production, the regulation of co-transporter activity by NO, and the possible interaction of NO with Ang II. MD cell Na(+) concentration ([Na(+)](i)) and NO production were measured using sodium-binding benzofuran isophthalate and 4-amino-5-methylamino-2',7'-difluorescein diacetate, respectively, using fluorescence microscopy. Na:2Cl:K co-transport activity was assessed as the initial rate of increase in [Na(+)](i) when [NaCl](L) was elevated from 25 to 150 mM. 10(-4) M 7-nitroindazole, a specific nNOS blocker, significantly increased by twofold the initial rate of rise in [Na(+)](i) when [NaCl](L) was increased from 25 to 150 mM, indicating co-transporter stimulation. There was no evidence for an interaction between the stimulatory effect of Ang II and the inhibitory effect of NO on co-transport activity, and, furthermore, Ang II failed to alter MD-NO production. NO production was sensitive to [NaCl](L) but increased only when [NaCl](L) was elevated from 60 to 150 mM. These studies indicate that MD-NO directly inhibits Na:2Cl:K co-transport and that NO and Ang II independently alter co-transporter activity. In addition, generation of MD-NO seems to occur only at markedly elevated [NaCl](L), suggesting that NO may serve as a buffer against high rates of MD cell transport and excessive TGF-mediated vasoconstriction.     

Thromboprophylaxis practice patterns in hip fracture surgery patients: experience in Perth, Western Australia

Background: International guidelines recommend that all patients undergoing hip fracture surgery receive specific thromboprophylaxis. The purpose of the present study was to examine current thromboprophylaxis practice patterns in patients undergoing hip fracture surgery at Royal Perth Hospital. Methods: A total of 129 consecutive patients admitted to Royal Perth Hospital between 4 February and 21 July 2002 for surgical repair of a fractured neck of femur, was studied. The primary outcome was the frequency, type, and duration of thromboprophylaxis use during hospitalization. Results: Mean patient age was 79.4 ± 13.4 years and 69.8% (90/129) were female. Seventy‐four patients (57.8%; 95% confidence interval (CI): 48.8?66.8%) received specific thromboprophylaxis during hospitalization, including 50 patients (39.1%; 95%CI: 30.6?48.1%) who received pharmacological prophylaxis only, three (2.3%; 95%CI: 0.5?6.7%) who received mechanical prophylaxis only, and 21 (16.4%; 95%CI: 10.5?24.0%) who received both mechanical and pharmacological prophylaxis. Of those receiving pharmacological prophylaxis, 35 (49.3%; 95%CI: 37.2?61.4%) received low‐molecular‐weight heparin, 26 (36.6%; 95%CI: 25.5?48.9%) received low‐dose unfractionated heparin, eight (11.3%; 95%CI: 5.0?21.0%) received warfarin, 35 (49.3%; 95%CI: 37.2?61.8%) received aspirin or clopidogrel, and 27 (38.0%; 95% CI: 26.8?50.3%) received combined anticoagulant and antiplatelet prophylaxis. The median duration of mechanical prophylaxis was 8 days (range: 6?12 days) and that of pharmacological prophylaxis was 12 days (range: 6?26 days). When the 32 patients already taking aspirin or warfarin at the time of admission were excluded, only 45 (46.9%; 95%CI: 36.6?57.3%) of the remaining 96 patients received specific thromboprophylaxis. Conclusion: Specific thromboprophylaxis remains under‐utilized in patients undergoing surgery for hip fracture at Royal Perth Hospital. These data should prompt the implementation of effective strategies to improve thromboprophylaxis practice patterns in high‐risk orthopaedic patients.     

Steroidogenic acute regulatory protein in the rat brain: cellular distribution, developmental regulation and overexpression after injury

The central nervous system synthesizes steroids which regulate the development and function of neurons and glia and have neuroprotective properties. The first step in this process involves the delivery of free cholesterol to the inner mitochondrial membrane where it can be converted into pregnenolone. This delivery is mediated by steroidogenic acute regulatory protein (StAR). Here, we present a detailed analysis of the distribution of StAR expression in neurons and glia, in the developing, adult and aged male rat brain. Immunohistochemical analysis revealed that StAR is widely distributed throughout the brain, although in each brain area it is restricted to very specific neuronal and astroglial populations. In most regions expressing StAR, immunoreactivity appeared at P10 and the levels of expression then either increased or remained constant until adulthood. In 2-year-old rat brains, StAR immunoreactivity was increased compared to young adults. StAR was expressed in the subventricular zone of the adult brain, in proliferating cells which incorporate BrdU as well as in germinal layers in the developing brain. These findings indicate that StAR expression is developmentally regulated and that StAR may play some function in regulating cell proliferation in the brain. Furthermore, StAR mRNA and protein levels were acutely and transiently increased in the hippocampus following excitotoxic brain injury induced by the administration of kainic acid. This raises the possibility that the up-regulation of StAR expression and the subsequent modifications in steroidogenesis may be part of the mechanisms used by the brain to cope with neurodegeneration.     

An antagonist of estrogen receptors blocks the induction of adult neurogenesis by insulin-like growth factor-I in the dentate gyrus of adult female rat

Interdependence between estradiol and insulin-like growth factor-I has been documented for different neural events, including neuronal differentiation, synaptic plasticity, neuroendocrine regulation and neuroprotection. In the present study we have assessed whether both factors interact in the regulation of neurogenesis in the adult rat dentate gyrus. Wistar albino female rats were bilaterally ovariectomized and treated with estradiol, insulin-like growth factor-I and/or the estrogen receptor antagonist ICI 182,780. Estradiol was administered in a subcutaneous silastic capsule. Insulin-like growth factor-I and ICI 182,780 were delivered in the lateral cerebral ventricle. Animals received six daily injections of 5-bromo-2-deoxyuridine and were killed 24 h after the last injection. The total number of 5-bromo-2-deoxyuridine-positive neurons was significantly increased in animals treated with insulin-like growth factor-I, compared with rats treated with vehicles, while rats treated with both insulin-like growth factor-I and estradiol showed a higher number of 5-bromo-2-deoxyuridine-positive neurons than rats treated with insulin-like growth factor-I or estradiol alone. The antiestrogen ICI 182,780 blocked the effect of insulin-like growth factor-I on the number of 5-bromo-2-deoxyuridine neurons with independence of whether the animals were treated or not with estradiol. These findings suggest that estrogen receptors are involved in the induction of adult neurogenesis by insulin-like growth factor-I in the dentate gyrus, and that estradiol and insulin-like growth factor-I have a cooperative interaction to promote neurogenesis. The interaction between insulin-like growth factor-I and estradiol may participate in changes in the rate of neurogenesis during different endocrine and physiological conditions, and may be related to the decline in neurogenesis with ageing.     

Effect of 6-hydroxydopamine on striatal GDNF and nigral GFRalpha1 and RET mRNAs in the adult rat

Exogenous GDNF as well as vectors containing the gene for this trophic factor has been shown to be neuroprotective in animal models of Parkinson's disease. We therefore investigated whether changes in striatal GDNF protein and nigral mRNA levels of its co-receptors GFRalpha1 and RET occur in response to lesions of dopamine (DA) neurons and examined the temporal profile of these changes as they relate to the loss of dopaminergic markers. Rats were lesioned with 6-hydroxydopamine and sacrificed 3 h to 60 days post-infusion. DA tissue levels in the striatum and tyrosine hydroxylase immunoreactivity in the substantia nigra (SN) and ventral tegmental area (VTA) were used to determine the size of the lesions. GDNF protein was measured in the striatum using radioimmunocytochemistry. In situ hybridization was used to determine alterations in the mRNAs of RET and GFRalpha1 in the SN and VTA. We observed no persistent changes in GDNF protein in the striatum in response to 6-hydroxydopamine over the 60-day observation period, suggesting that compensatory changes in this trophic factor do not occur in response to injury. Dramatic decreases in RET and GFRalpha1 were observed in both SN and VTA that were generally correlated with the loss of TH protein and striatal DA content, strongly suggesting that these receptors are located on DA neurons and that the protective effect of GDNF reflects a direct action of the trophic factor on these neurons.     

Parkinson's disease and CYP2D6 polymorphism in Asian populations: A meta-analysis

Polymorphism of CYP2D6 and its relationship with the development of Parkinson's disease (PD) has been controversial. The distribution of the B-mutation of CYP2D6, a mutation that results in the absence of a functional protein, differs by ethnicity and accounts for less than 1% of the 'poor metabolizer' phenotype in Asians. Thus, a meta-analysis was conducted to determine if polymorphism, other than the B-mutation, within the CYP2D6 gene confers a greater susceptibility to PD outcome among Asian populations. Eleven studies were identified, two of which were excluded due to unavailability in the English language or availability of the same original data in more detail in another publication. None of the studies showed a statistically significant association between CYP2D6 polymorphism and PD (p<0.05). The overall odds ratio was 0.84 (95% confidence interval 0.66-1.08). We conclude that among Asian populations, there is no convincing evidence of an association between CYP2D6 polymorphism and the risk of developing PD.     

Polymicrogyria and absence of pineal gland due to PAX6 mutation

Identification of genes involved in human cerebral development is important for our understanding of disorders with potential neurodevelopmental causes such as epilepsy and learning disability. Murine models suggest that PAX6 plays a key role in human brain development. With magnetic resonance imaging in 24 humans heterozygous for defined PAX6 mutations, we demonstrated widespread structural abnormalities including absence of the pineal gland and unilateral polymicrogyria.     

Lifetime antecedents of cognitive reserve

We used path analysis on data from the British 1946 birth cohort to model lifetime antecedents of cognitive reserve, represented by the NART at 53 years, and compared this model for verbal memory and psychomotor function at this age, cognitive outcomes that are sensitive to age-associated decline. We showed independent paths from childhood cognition, educational attainment and adult occupation to cognitive reserve, with that from childhood cognition the strongest, and that from adult occupation the weakest. A similar pattern was found for the verbal memory and psychomotor outcomes, although the pathways were weaker than those to the NART. The pattern was also mirrored by the paths from paternal occupation to childhood cognition, educational attainment and adult occupation, with that to childhood cognition the strongest, and that to adult occupation the weakest. The direct influence of paternal occupation on cognitive reserve was negligible, and almost entirely mediated by childhood cognitive ability and educational attainment.