Computational models of the basal ganglia: from robots to membranes

With the rapid accumulation of neuroscientific data comes a pressing need to develop models that can explain the computational processes performed by the basal ganglia. Relevant biological information spans a range of structural levels, from the activity of neuronal membranes to the role of the basal ganglia in overt behavioural control. This viewpoint presents a framework for understanding the aims, limitations and methods for testing of computational models across all structural levels. We identify distinct modelling strategies that can deliver important and complementary insights into the nature of problems the basal ganglia have evolved to solve, and describe methods that are used to solve them.     

Tacrolimus toxicity associated with concomitant metoclopramide therapy

Subtherapeutic tacrolimus trough concentrations were noted in a 52-year-old woman who had undergone liver transplantation. Her tacrolimus dosage was increased from 7 to 28 mg twice/day, and ketoconazole therapy was added; however, her tacrolimus concentration remained undetectable. Metoclopramide 10 mg 4 times/day was begun to control the patient's new-onset nausea and vomiting. Within 48 hours of increasing the dosage to 20 mg 4 times/day, her tacrolimus trough concentration exceeded 30 ng/ml. Signs and symptoms were suggestive of tacrolimus nephrotoxicity and neurotoxicity. According to the Naranjo scale, this adverse drug event was probably the result of improved absorption of tacrolimus secondary to metoclopramide therapy. The patient's subtherapeutic tacrolimus concentration at baseline was probably secondary to poor absorption due to impaired gastric emptying. Coadministration of metoclopramide significantly improved gastric motility and delivery of tacrolimus to the small intestine, increasing tacrolimus bioavailability, thus resulting in acute-onset tacrolimus toxicity. When tacrolimus is administered with metoclopramide in patients with gastric dysmotility, tacrolimus concentrations should be monitored closely to minimize the risk of toxicity.     

COX-2 and colorectal cancer

Metabolites of arachidonic acid participate in normal growth responses and in aberrant cellular growth and proliferation, including carcinogenesis. The key step in the conversion of free arachidonic acid to prostaglandins is catalyzed by the cyclooxygenase enzyme (COX). There are two COX enzymes, COX-1 and COX-2. COX-1 is expressed constitutively and is part of normal cell metabolic functions. COX-2, on the other hand, is induced and expressed in neoplastic growths. The connection between COX expression and carcinogenesis was first implicated in studies that demonstrated the efficacy of aspirin and non-steroidal anti-inflammatory drugs to reduce the relative risk of colon cancer and also promote tumor regression in both humans and animal models of colon cancer. Investigation of the molecular basis of these observations showed that high levels of COX-2 protein were present in both human and animal colorectal tumors. A variety of evidence gathered from epidemiological, whole animal, and cellular studies indicate that unregulated COX-2 expression is a rate-limiting step in tumorigenesis and also that the loss of regulation occurs early in carcinogenesis. The interest in the COX-2 enzyme is that specific inhibition of COX-2 could theoretically avoid the gastrointestinal and other complications observed with the use of nonspecific COX inhibitors (most NSAIDs) or COX-1 inhibitors. The mechanisms by which COX-2 inhibitors lead to decreased colon carcinogenesis are not fully understood but they involve an increase not only in COX-2 dependent but also in COX-2 independent mechanisms.     

Vital exhaustion as a risk factor for ischaemic heart disease and all-cause mortality in a community sample. A prospective study of 4084 men and 5479 women in the Copenhagen City Heart Study

BACKGROUND: Vital exhaustion, a psychological measure characterized by fatigue and depressive symptoms, has been suggested to be an independent risk factor for ischaemic heart disease (IHD) but the generality of the phenomenon remains in question. The aim of this study is to describe prevalence of these symptoms in a community sample and determine whether they prospectively predict increased risk of IHD and all-cause mortality in men and women. METHODS: The study base was 4084 men and 5479 women aged 20-98 free of IHD examined in 1991-1993 in the Copenhagen City Heart Study. Events were ascertained through record linkage until 1998 for IHD and September 2000 for all-cause mortality. There were 483 first hospital admissions and deaths caused by IHD and 1559 deaths from all causes during follow-up. RESULTS: The 17 items on the vital exhaustion questionnaire were frequently endorsed with prevalence ranging from 6 to 47 per cent, higher in women. All but 4 of the 17 items were significantly associated with IHD with significant relative risks (RR) ranging between 1.36 (95% CI: 1.08, 1.72) and 2.10 (95% CI: 1.63, 2.71). Associations with all-cause mortality were also observed, but were weaker. RR of both IHD and all-cause mortality increased with increasing item sum score and were similar in men and women. For IHD, RR reached a maximum of 2.57 (95% CI: 1.65, 4.00) for subjects endorsing >9 items. The similar RR for all-cause mortality was 2.50 (95% CI: 2.09, 2.99). Multivariate adjustment for biological, behavioural, and socioeconomic risk factors did not substantially affect the association for IHD but attenuated the association with all-cause mortality. CONCLUSIONS: Measures of fatigue and depression were common symptoms in this population sample and convey increased risk of IHD and of all-cause mortality. We propose this knowledge begin to be implemented in risk assessment in clinical practice.     

Multiple metastatic deposits of a left breast cancer into a right fibroadenoma

We present a case which we believe to be the first report of carcinoma of the breast metastasising into a long-standing fibroadenoma in the contralateral breast.     

alpha 2u-Globulin nephropathy, renal cell proliferation, and dosimetry of inhaled tert-butyl alcohol in male and female F-344 rats.

tert-Butyl alcohol (TBA) has been shown to cause kidney tumors in male rats following chronic administration in drinking water. The objective of the present study was to determine whether TBA induces alpha 2u-globulin (alpha 2u) nephropathy (alpha 2u-N) and enhanced renal cell proliferation in male, but not female, F-344 rats, and whether the dosimetry of TBA to the kidney is gender specific. Male and female F-344 rats were exposed to 0, 250, 450, or 1750 ppm TBA vapors 6 h/day for 10 consecutive days to assess alpha 2u-nephropathy and renal cell proliferation and for 1 and 8 days to evaluate the dosimetry of TBA following a single and repeated exposure scenario. Protein droplet accumulation was observed in kidneys of male rats exposed to 1750 ppm TBA, with alpha 2u-globulin immunoreactivity present in these protein droplets. A statistically significant increase in alpha 2u concentration in the kidney, as measured by an enzyme-linked immunosorbent assay, was observed in male rats exposed to 1750 ppm TBA with a exposure-related increase in renal cell proliferation. Renal alpha 2u concentration was positively correlated with cell proliferation in male rat kidney. No histological lesions or increased renal cell proliferation was observed in female rats exposed to TBA compared to controls. The TBA kidney:blood ratio was higher at all concentrations and time points in male rats compared with female rats, which suggests that TBA is retained longer in male rat kidney compared with female rat kidney. Together these data suggest that TBA causes alpha 2u-N in male rats, which is responsible for the male rat-specific increase in renal cell proliferation.     

Influence of ascertainment strategy on finding sex differences in genetic estimates from twin studies of alcoholism

Twin studies have yielded contradictory findings about sex differences in genetic influences on the etiology of alcoholism. Studies based on population registers or epidemiological samples have yielded similar estimates of heritability (50-60% of the total variance) for males and females. In contrast, studies of twins identified through treatment settings have found sizeable genetic contributions to alcoholism in males but usually negligible heritabilities for females. We investigated this discrepancy by applying a "simulated" treatment ascertainment strategy to data on alcohol-related disorders collected by structured interviews with a population-based sample of adult twins aged 18-56 years from the Mid-Atlantic Twin Registry. Structural models were used to estimate heritabilities for two definitions of treatment, and these estimates were compared with those obtained from the population-based sample. In males, heritability estimates were similar across sampling methods, but the treatment ascertainment methods yielded higher estimates of common environmental influences. For females, heritability estimates based on a broad definition of treatment were similar to those obtained by using the random ascertainment design. However, estimates based on sampling women who had been in alcohol-treatment programs were (nonsignificantly) lower than those obtained with the other methods. These results provide partial support for the hypothesis that differences in sampling method may account for differences in heritability estimates for alcoholism among studies of female twins. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:754-761, 2000.     

MICs of oxazolidinones for Rhodococcus equi strains isolated from humans and animals

Eperezolid and linezolid are representatives of a new class of orally active, synthetic antimicrobial agents. The in vitro activity values (MICs) of linezolid, eperezolid, and comparator antibiotics against 102 strains of Rhodococcus equi isolated from humans and animals were determined. Linezolid was more active than eperezolid against the strains tested; premafloxacin was the most active comparator antibiotic.     

Therapeutic misadventure with paracetamol: fact or fiction?

As a consequence of its consistent safety profile and the low incidence of side effects, paracetamol is one of the most widely used analgesics, both in adults and children. However, paracetamol has the potential for hepatotoxicity, usually as a result of deliberate self-poisoning or, to a much lesser extent, accidental overdose. A variety of factors is thought to influence hepatotoxicity, including dose, concomitant use of microsome-inducing agents and other drugs, underlying disease, malnutrition, fasting, acute and chronic alcohol intake, ethnicity, and age. Unfortunately, none of these factors has been properly studied in humans. From a physiological standpoint, acute paracetamol hepatotoxicity at therapeutic doses is extremely unlikely despite reports of so-called therapeutic misadventure. It is clear that, in many of these cases, grossly excessive doses of paracetamol have been taken. Analyzing the various reports is difficult as the data are often incomplete. In summary, although hepatic toxicity is recognized in patients taking a major paracetamol overdose, the incidence of adverse events with its proper use is very low, particularly when considering with the enormous volume of drug use. Therapeutic misadventure is extremely uncommon and the facts are often misrepresented.