Inhibition of nitric oxide (NO) production selectively impairs learning and memory in the rat.

Animals administered the nitric oxide (NO) synthase inhibitor N-w-nitro-L-arginine methyl ester (NAME) for five days exhibited severe deficits in acquisition of a place-navigation learning task. The effect of NAME was selective to place-navigation learning. NAME had no effect on sensorimotor or motivational processes in a related task. These results are consistent with the view that NO participates in learning and execution of memory tasks.

Spontaneous categorizers retain more than spontaneous alphabetizers.

Immediate and delayed free recall of unstructured verbal materials were assessed for alphabetizers and categorizers after varying study times. Alphabetizers and categorizers did not differ in immediate recall, but retention following a 6-day interval was consistently higher for categorizers than for alphabetizers. Both immediate and delayed recall increased with study time, which did not interact with learning strategy. In the next experiment alphabetizers and categorizers learned two lists, the second of which was categorically structured or unstructured. No retroactive interference on first-list recall was produced by the learning of the structured list, but the learning of the unstructured list produced retroactive interference for the alphabetizers only. It was suggested that, although both alphabetizers and categorizers probably use their respective strategies for other verbal tasks, the categoric strategy should create less interference because specific 'categories are rarely encountered in successive tasks.

Interaction of the estradiol receptor from calf uterus with its nuclear acceptor sites.

The specific interaction between 17 beta-estradiol-receptor complex and nuclear acceptors was analyzed by immobilizing various nuclear proteins to CNBr-activated agarose. The specific, high affinity sites identified in a fraction of basic proteins that can be solubilized from purified nuclei of calf uterus (Puca, G.A., Sica, V., and Nola. E (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 979-983) were chromatographed on Sephadex G-100 columns. Elution of the acceptor activity depends on the pH and ionic strength of the buffer used. With 5 mM HCl, however, a peak of acceptor activity with a molecular weight of about 70,000 was partially dissociated from the other basic nuclear proteins. The high affinity binding of the receptor to the acceptor proteins was estradiol-, but not progesterone-, cortisone-, or testosterone-dependent; it was very sensitive to ionic strength and showed a physiological pH optimum. Low affinity binding, such as that seen between receptor and histone, showed no estradiol dependence and little ionic strength and pH sensitivity. Native or heat-denatured DNA strongly modified the receptor-acceptor interaction, reducing the number of binding sites of acceptor for the receptor without changing the high affinity of the interaction. Heating of the acceptor protein before its covalent linkage to agarose considerably increased the affinity of the resulting agarose derivative. Free sulfhydryl groups of the receptor but not of the acceptor molecule play an important role in the acceptor-receptor interaction. When receptor and acceptor preparations were incubated in solution, the resulting complex was included on a Sephadex G-100 column and it eluted from DEAE-cellulose columns at lower ionic strength than the receptor alone. Even though not absolutely specific, these two properties allowed determination of the molecular weight (85,000) of the acceptor protein at neutral pH and more nearly physiological ionic strength. The apparent KD of the acceptor-receptor interaction was determined to be 2 x 10(-10) M at O degrees. Apparently similar, high affinity binding sites for estradiol receptors are also present in nuclei of other tissues.