Disruption of imprinting by memory inhibitors

Several amnestic drugs were administered intracranially to day-old chicks at selected times around a 10-min exposure to an imprinting stimulus. The drugs used were monosodium glutamate, ouabain, cycloheximide and amino-iso-butyrate. The chicks were tested for 10 min in the same apparatus two days later, and the time spent following the stimulu was recorded., The index of memory retention was the difference between the time spent following on test and the time spent following on the initial exposure. When compared with saline-injected control, glutamate administered 5 min before the beginning of the initial exposure was effective in producing a reduction in following times and hence amnesia. Ouabian was effective when injeced before the beginning and immediately after the end of the initial exposure; while cycloheximide was effective when administered as late as 5 min after the initial exposure. The effective times of administration for the drugs to produce a reduction in following times were similar to that observed for amnesia in passive avoidance memory tasks. The increase in following shown by the control chicks was not a developmental effect due to the increae in age on test. Experiments involving a choice of stimuli on test support the invovement of a memoryrelated phenomenon in these experiments.     

Discontinuation syndrome after continuous infusion of clonidine in the spontaneously hypertensive rat

In conscious spontaneously hypertensive rats prepared with permanent indwelling aortic catheters the continuous infusion of clonidine (500 μg/kg/day) via an ALZET miniosmopump induced significant reductions in blood pressure and heart rate. These effects were well sustained during 12 days of treatment. A marked overshoot in heart rate was observed following withdrawal of clonidine administration. The tachycardia persisted for more than 36 hours. Mean arterial pressure exceeded control level slightly in the immediate withdrawal period only, whereas significant blood pressure lability was observed for more than 36 hours. These withdrawal symptoms were accompanied by an elevation of plasma noradrenaline concentration. The present study shows the consistent antihypertensive and bradycardic activities of clonidine during 12 days of infusion in spontaneously hypertensive rats. Furthermore, this model may provide a useful tool in the study of withdrawal phenomena of antihypertensive drugs.     

A pellet method to demonstrate nitrogen fixation by free-living rhizobia

Summary A method is described to demonstrate nitrogen fixation by free-living Rhizobium cells. After aerobic growth in a nutrient solution, the bacteria are centrifuged. Acetylene reduction by the rhizobial cells in the pellet can be measured within a few days. Hydrogen gas frequently stimulates acetylene reduction.     

Chronic granulomatous otitis media in bottle-fed Inuit children.

Otitis media in Inuit children is a problem of relatively recent origin and unknown cause. The prevalence of otitis media in 238 Inuit and 47 Caucasian children in Nain, a small community in Labrador, was determined by examination, and the history of breast-feeding or bottle-feeding was obtained. The prevalence of otitis media was found to be inversely related to the age at which bottle-feeding was started. Clinical observations suggest that otitis media in Inuit children is part of a process leading to chronic foreign body granuloma of the middle ear, and that the granuloma is formed from milk introduced into the relatively short and straight eustachian tubes of Inuit infants by the high negative intraoral pressure necessary for bottle-feeding.     

Effect of lectins on the interactions between human peripheral blood lymphocytes and monocytes

Interactions between normal human peripheral blood T lymphocytes and monocytes were investigated by measuring the in vitro cellular adherence of these cells in the presence and in the absence of mitogens. Concanavalin A (Con A), lentil lectin (Lc), and phytohemagglutinin (PHA) in mitogenic doses increased 15 to 20 times the binding of T lymphocytes to monocytes. The lectin-induced binding was similar to that produced by neuraminidase-gal-actose-oxidase treatment. A good correlation was found between the early cellular adherence induced by these lectins and by neuraminidase-galactose-oxidase and the blastogenesis of the T lymphocytes measured after 3 days of culture by [³H]thymidine uptake. However, wheat germ agglutinin (WGA), a nonmitogenic lectin, also increased the binding of T lymphocytes to monocytes. Addition of specific carbohydrates completely inhibited the cellular interactions induced by lectins. Peanut agglutinin (PNA) induced adherence of lymphocytes only after treatment of these cells with neuraminidase. Striking differences were not found between the lectin-induced adherence observed with autologous and heterologous cells. Killing of monocytes abolished entirely the lectin-induced adherence of lymphocytes, however killed T lymphocytes were still able to interact weakly with live monocytes. Dexamethasone was found to be a potent inhibitor of mitogen-induced cellular interactions.