The concept of compensation in cognitive aging: the case of prose processing in adulthood.

Although the rule of cognitive aging appears to be one of generalized decline with advancing age, much recent theoretical and empirical work has addressed a variety of potential exceptions to this rule. One mechanism through which decline might not be experienced is known as compensation. We describe a conceptualization of compensation that applies to lifespan cognitive development, in general, and the aging of prose processing skills, in particular. Our model of the forms and processes of compensation directs attention to the developing dynamics of cognitive skills and compensatory mechanisms. We outline three main approaches to research on compensation in cognitive aging: a) the logical experimental, b) on-line observation and manipulation, and c) several verbal report procedures. In summarizing our own research program, we emphasize that a) each of these approaches can render valuable information, b) each have some limitations, and c) there are potential theoretical benefits from employing more than one of them in a given study.     

Tissue homogenization with sterile reinforced polyethylene bags for quantitative culture of Candida albicans.

A simple method of tissue homogenization with sterile reinforced polyethylene bags for quantitative fungal cultures was evaluated with mice infected with Candida albicans. This new method correlated well with standard methods (P less than or equal to 0.01) for quantifying viable fungus in homogenates of brain, kidney, spleen, liver, and lungs and may be applicable in clinical and experimental mycology laboratories.     

Computed tomography of the post-operative lumbar spine: the need for, and optimal dose of, intravenous contrast medium

Forty-five patients who had undergone previous lumbar spine surgery with symptoms and signs warranting further investigation were examined by computed tomography (CT). The findings in three separate subgroups of 15 patients were compared. The first randomly selected group underwent CT without the use of intravenous contrast medium; the second and third groups were examined both before and after the administration of contrast medium, using 16.25 g and 32.5 g iodine, respectively. In the latter two groups the CT studies were reported both before and after enhancement. In the 15 patients in the first group (no contrast medium), uncertainty as to whether disc material or fibrosis was responsible for the radiological abnormalities was expressed in the final report at six of the 20 post-surgical sites. Among the 30 patients who received contrast medium, 40 post-surgical sites were examined; at six of these sites there was no radiological cause for concern; at 16 sites there were unequivocal radiological appearances of either disc material or fibrosis. Enhancement resolved the radiological uncertainty at 13 of the remaining 18 sites, almost always by reinforcing the initial radiological opinion; this left five sites where uncertainty persisted in the final report. The larger dose of contrast medium caused the more marked enhancement of those abnormalities considered to be due to fibrosis, although enhancement was readily recognised using the lower dose. While intravenous enhancement assists radiological interpretation at those sites where diagnostic uncertainty persists after routine CT, it would seem that it is not essential in patients in whom routine CT studies show no serious abnormality or the characteristic appearances of disc material or fibrosis.     

Prognostic significance of oestrogen and progestogen receptor activities in breast cancer

The prognostic significance of the tumour activities of 2 steroid receptors, those for oestrogen (ER) and for progestogen (PgR), has been studied in 372 patients with breast cancer, in whom follow-up was available for 2-6 years (median 41 months). Of 252 patients with operable disease, 75.8 per cent had ER-positive tumours and 46.4 per cent had PgR-positive tumours, though a small additional fraction (6.3 per cent) had an equivocal PgR assay result. For the 236 patients with unequivocal receptor status, the relationships between disease-free interval or overall survival and receptor activity and other factors were evaluated by univariate and multivariate analyses. The latter revealed that only tumour size, node status, menstrual status and ER status related significantly to both disease-free interval and survival, though adjuvant therapy also related to disease-free interval, and tumour grade related to survival. It is concluded that measurements of PgR activity do not add to the prognostic significance of ER status.     

Remodeling of B-50 (GAP-43)- and NSE-immunoreactive mucosal nerves in the intestines of rats infected with Nippostrongylus brasiliensis.

Intestinal mucosal mast cells (IMMCs) are closely apposed to nerves, which is consistent with other evidence suggesting that mast cells are innervated. Recent studies have indicated that coordinated changes in mast cell and nerve densities occur in the gut mucosa, during progressive fibrosis, but there is a lack of experimental evidence to support remodeling of intestinal nerve fibers as part of a disease process. Infection of rats with the nematode Nippostrongylus brasiliensis (Nb) results in an initial loss of stainable IMMCs, during an acute inflammatory phase, with subsequent mast cell hyperplasia. Accordingly, we employed the Nb model to look for structural neuroplasticity of intestinal mucosal nerves during inflammation. Immunocytochemical labeling of neurofilament subunits was very low in the jejunal mucosa of all animals, whereas neuron-specific enolase (NSE)-immunoreactive nerves were relatively abundant in control animals. The number of NSE-immunoreactive profiles increased approximately 2.5-fold by day 10 (d10) postinfection (p less than 0.01) and returned to near control values by d14. Immunoreactivity for B-50/GAP-43 was more extensive, labeling more than four times the number of nerves per villus, compared with NSE (p less than 0.0001). B-50 immunoreactivity decreased minimally (ca. 20%) by d7 postinfection, and then increased through control values between d10 and d21, to 30% greater than controls at d49 (p less than 0.05). Subclassification of the B-50-immunoreactive nerves according to cross-sectional area revealed a greater than twofold increase in the proportions of large fibers at d7 and d10. Subsequently, the proportions of small nerves were increased compared with controls. The fiber size changes were found to correlate with mast cell densities (r = -0.72 for large and r = 0.76 for small nerves). At d10, dilated B-50- and NSE-immunoreactive nerves predominated, and extraneuronal NSE was noted. Electron microscopy revealed that this was due to axonal dilation and degeneration. These data provide evidence for plasticity of intestinal mucosal nerve fibers during inflammation. This includes early degenerative and later regenerative phases that appear to correlate with mast cell densities. The phenotype of mucosal nerves in control animals suggests ongoing modeling of these fibers.     

Staircase bioassay: the up-and-down method

Experiments are conducted to estimate the threshold for an all-or-none response. Threshold is defined to be a point above which 50% of the subjects will respond and below which 50% of the subjects will not respond. Examples are death, death in a fixed time period, shock, fibrillation, emesis. Staircase designs, in particular up-and-down trials, produce median (ED50) estimates of given standard error with as few as one-fifth the number of subjects as the traditional designs with preset numbers of tests at each of several levels of stimulus. We discuss these estimates and their efficiency as well as procedures to estimate standard deviation and its use in designing up-and-down trails. The advantages in using several short series in factorial experiments are presented. Suggestions are given for minimizing the complications of sequential designs. Case studies indicate the efficiency of the design for various applications.     

The use of acyclovir in suspected encephalitis.

The early use of intravenous acyclovir in herpes simplex encephalitis (HSE) is essential. However, rapid diagnostic tests are not freely available. Hence, all patients with suspected encephalitis may need to be commenced on acyclovir. In our study, of 34 patients with suspected encephalitis, only two eventually had HSE confirmed, 19 had encephalitis not due to herpes simplex and in 13 a non-encephalitis illness was finally diagnosed. Guidelines for the use of acyclovir in suspected encephalitis are given aimed at minimizing the drug cost whilst still protecting all cases of presumed HSE.