Effects of unilateral parietal lesions on spatial localization in the rat.

In the first of two experiments, rats with left or right parietal lesions and controls were tested in place and landmark navigation in the water maize. Right parietal lesions resulted in deficits in both tasks, but especially landmark navigation. Lateralized effects appeared mainly in latency to find the platform. Experiment 2 investigated the role of the corpus callosum. Split-brain rats with unilateral parietal lesions were tested on the same two tasks. Place and landmark deficits were particularly severe, but lateralization was weaker. Callosum section had its own effect, impairing the learning of both tasks. There appear to be additive effects of unilateral cortical lesions and bisection of the hemispheres. The impairment from left lesions equaled the right-lesion deficit because of the interruption of compensatory information from the intact right hemisphere and the effect of callosum section itself.

Constitutive and induced trehalose transport mechanisms in spores of the fungus Myrothecium verrucaria.

Trehalose is absorbed by two distinct systems-one constitutive, the other induced by turanose and to a lesser extent by nigerose but not by trehalose. The constitutive system is apparently mediated by a surface trehalase; the induced system has the characteristics of a permease. The specificity of the induced system is apparently limited to the alpha glucosyl-glucose or glucosyl-fructose linkage, because absorption of kojibiose, nigerose, maltose, isomaltose, turanose, sucrose, and melezitose, in addition to that of trehalose, was increased. Absorption of beta-linked or of galactose-containing disaccharides was not increased. The constitutive and induced trehalose-absorbing systems differ in their activity, specificity, lability to acid treatment, effects of substrate concentration, and pH optima. Both systems require oxygen, and no marked differential effects of inhibitors were observed. The activity of the induced system is proportional to log turanose concentration (from about 1 to 300 mug/ml), and is an approximate linear function of time of exposure (from about 1 to 50 min). Accumulation of trehalose occurred against a concentration gradient in both systems but particularly in the induced. No leakage was observed. The activity of the induced system declined slowly upon removal of the inducer. Accumulated trehalose is metabolized after activation by azide as are the endogenous trehalose reserves. The accumulated trehalose appears to enter the endogenous trehalose pool found in these spores, although some data suggest it may be more accessible. Respiratory data indicate that absorbed trehalose is available for metabolism while in transit from the external membrane to the internal pool.