Age-related changes in the visual cortex

The ability to accurately perceive the speed of moving objects is one of many visual functions that decline with age. One factor that may contribute to this is a deterioration in temporal processing speed. At present, there is a dearth of information concerning how this may occur in the central nervous system, particularly in the visual cortex. Thus, in the present study, we investigated the neural basis of speed and temporal processing in areas 17 and 18 of visual cortex in young and aged rats using either a moving bar of light or a series of flashing lights. Our results showed that the mean preferred speed of a moving bar of light was significantly reduced in aged as compared to young animals. We also found that cells recorded from young animals were able to entrain to a higher frequency of flashing light stimuli than those recorded from aged animals. In addition, we found no age-related differences between cortical fields. These results suggest an age-related difference in temporal processing speed at the level of visual cortex.     

Computed tomography colonography (virtual colonoscopy): review

Computed tomography examination of the colon performed after bowel cleansing and distension of the lumen with gas goes by several different names--CT colonography (CTC) and CT colography perhaps being the most common. Strictly, the term 'virtual colonoscopy' (VC), should be reserved for the process of examining 3-D, simulated endoluminal images with a capability to navigate through the bowel using appropriate software. Computed tomography colonography appears to be the name that has gained favour among radiologists, although it is suspected that 'virtual colonoscopy' will persist as a generic term due to its attractive 'high-tech' connotations for non-radiological medical and lay persons. Whatever the name, the technique has been made possible through the advent of fast helical CT scanners which allow acquisition of a volume of data, and of proprietary software which enables multiplanar reformatting and 3-D endoluminal reconstructions. It is evident that if CTC/VC can be shown to be acceptable to patients, safe, affordable and accurate, it has enormous potential as a diagnostic and screening tool for colorectal neoplasia.     

The sleep-inducing effect of ethanol microinjection into the medial preoptic area is blocked by flumazenil

Previous studies have shown that a wide range of sedative/hypnotic agents, including ethanol, induce sleep when microinjected into the medial preoptic area (MPA) of the anterior hypothalamus. The mechanism by which ethanol acts at this site to induce sleep has not been clear, though possibilities include alterations of chloride channel function in the GABA(A)-benzodiazepine receptor complex, or increases in neuronal membrane fluidity. In order to explore the former possibility, we have microinjected into the MPA ethanol 0.24 and 0.47 microM, alone and in combination with the benzodiazepine receptor antagonist flumazenil, which has no effects on membrane fluidity or voltage-dependent calcium channel function. Ethanol microinjections significantly reduced sleep latency, and tended (P<0.06) to increase total sleep time. Flumazenil given by itself had no significant effects on sleep, but when given in combination with both doses of ethanol, blocked its hypnotic effects. These data suggest that the sleep-inducing action of ethanol microinjections into the MPA is mediated by ethanol-induced alteration of GABA(A)-benzodiazepine receptor function.     

The international collaborative study of maternal phenylketonuria: status report 1994

Neonatal screening for phenylketonuria (PKU) has created a problem as females with PKU are reaching child-bearing age. Surveys have revealed that maternal phenylalanine blood concentrations greater than 1200 μmol/l are associated with fetal microcephaly, congenital heart defects and intrauterine growth retardation. It is estimated that as many as 3000 hyperphenylalaninemic females may be at risk of producing these fetal abnormalities. To examine this problem, the international maternal PKU collaborative study was developed to evaluate the efficacy of a phenylalanine-restricted diet in reducing fetal morbidity. Preliminary findings have indicated that phenylalanine restriction should begin before conception for females with PKU planning a pregnancy. Dietary control should maintain maternal blood phenylalanine levels between 120 and 360 μmol/l and should provide adequate energy, protein, vitamin and mineral intake. Pregnant hyperphenylalaninemic females who achieved metabolic control after conception or by the 10th week of pregnancy had a better offspring outcome than anticipated. The results of 402 pregnancies are reviewed.     

Alcohol self-administration by female macaque monkeys: a model for study of alcohol dependence, hyperprolactinemia and amenorrhea

Chronic alcohol dependence produces persistent amenorrhea in alcoholic women and female Macaque monkeys but the mechanism is unknown. In one amenorrheic alcohol-dependent monkey, prolactin levels increased from 16.5 to 63 ng/ml during chronic, high-dose alcohol self-administration (3.4 g/kg/day) and immunocytochemical examination of the anterior pituitary showed apparent hyperplasia of the lactotrophs. These data suggested that hyperprolactinemia might contribute to alcohol-induced amenorrhea. Four amenorrheic cycles (85-194 days) from two other alcoholic female monkeys that self-administered an average of 2.97 to 4.4 g/kg/day of alcohol were also studied. Each monkey became amenorrheic during the first menstrual cycle that alcohol was available. One monkey developed galactorrhea during a 97-day amenorrheic cycle when alcohol self-administration averaged 3.35 g/kg/day. Although prolactin levels were intermittently elevated above 20 ng/ml, average levels during these amenorrheic cycles (14.7 +/- 1.8 to 19.6 +/- 1.5 ng/ml) did not differ significantly from prolactin levels during normal ovulatory menstrual cycles when no alcohol was available (19.7 +/- 0.36 ng/ml). There was a negative correlation between daily alcohol dose and prolactin levels (p less than .01). High-dose alcohol self-administration was often associated with low normal prolactin levels, but a relative fall in alcohol dose was usually associated with elevated prolactin levels. These data suggest that both alcohol intoxication and relative alcohol withdrawal may alter basal prolactin levels. LH levels were significantly lower during amenorrheic cycles (16.9 +/- 1.2 to 24 +/- 1.4 ng/ml) than during nonalcohol control cycles (28 +/- 1.2 to 30 +/- 2.2 ng/ml) (p less than .001). These data are consistent with clinical data that suggest that hypothalamic amenorrhea is associated with suppression of gonadotropin secretory activity.