Task difficulty determines the differential memory-impairing effects of EAA antagonists in gerbils

Excitatory amino acid antagonists (EAAAs) have been shown to disrupt learning and memory in a variety of cognitive tasks. EAAAs have been reported to produce differential effects on working memory (WM) and reference memory (RM) or to have no effect at all. Apparent selective effects of EAAAs on WM and/or RM may have been due to differences between the effects of competitive and noncompetitive EAAAs, dose selection, or to different task requirements for the WM and RM components. In the present experiments, we assessed the effects of a noncompetitive EAAA (MK-801), a competitive EAAA (CPP), and the muscarinic antagonist scopolamine in two cognitive tasks, the split-stem T-maze and the eight-arm radial maze. In these two tasks, the WM and the RM components differed in their relative degree of difficulty. Gerbils were trained on either the T-maze, where WM was more difficult than RM, or on the radial arm maze, where RM was more difficult than WM. In the T-maze, MK-801 (0.1 mg/kg, IP, 30 min prior), CPP (30.0 mg/kg, IP, 2 h prior) and scopolamine (0.3 mg/kg, IP, 30 min prior) impaired both WM and RM, but the magnitude of the impairing effect was statistically greater for the WM component, the more difficult of the two components. Lower doses of these three compounds produced either selective effects on WM or no effect at all. In the radial arm maze all three drugs impaired both components, but the magnitude of the impairing effect was statistically greater for the RM component, the more difficult of the two components.(ABSTRACT TRUNCATED AT 250 WORDS)

Gonadotropin dynamics in women receiving immediate or delayed transdermal estradiol after oophorectomy

A prospective study was performed in 24 premenopausal women to evaluate the gonadotropin dynamics of pharmacologic doses of transdermal estradiol-17 beta (E2) administered after bilateral oophorectomy. Patients were given 0.2-mg transdermal E2 patches for 2 weeks, followed by 0.1-mg patches for 4 weeks either immediately postoperatively (immediate estrogen replacement therapy [ERT]) or beginning 12-14 days after surgery (delayed ERT). Serum gonadotropins and E2 levels were measured serially, and postmenopausal symptoms were prospectively recorded. Administration of 0.2 mg transdermal E2 immediately after surgery suppressed the post-castration rise in gonadotropins for at least 4 days, but LH and FSH levels did increase to the menopausal range after 2 weeks despite continued therapy. Sustained circulating levels of E2 with transdermal E2 therapy were comparable to follicular phase values. Vasomotor symptoms were well controlled by 0.2 mg of transdermal E2 in the majority of patients during the clinical trial. There was no significant estrogen-related morbidity despite the large doses used. Two patients had skin irritation at the patch site causing discontinuation of therapy. These data suggest that large doses of transdermal E2 can suppress gonadotropin levels only for a brief interval. We were unable to demonstrate any long-term alteration in the hypothalamic-pituitary set point for sensitivity to exogenous E2.

Assessment of lipoprotein activators of skim milk lipoprotein lipase and the relationship between lipoprotein lipase activity and milk fat synthesis

Bovine plasma and lipoproteins isolated by gel filtration chromatography were examined for their ability to activate skim milk lipoprotein lipase. Addition of equal amounts of protein from either triglyceride-rich lipoprotein, low density lipoprotein, high density lipoprotein or plasma to a lipoprotein lipase assay resulted in 6.0, 2.2, 2.5, or 1.1% hydrolysis of radiolabelled triglyceride emulsion. Lipoprotein lipase activity in skim milk was evaluated as an indicator of mammary lipid secretory capacity. Skim milk lipoprotein lipase activity was significantly lower immediately prepartum as compared with activity immediately postpartum (.2 vs. 5.4% of substrate hydrolyzed). Skim milk lipoprotein lipase was significantly higher during the final 12 d of lactation than in samples obtained 12 d after machine milking was terminated (5.6 vs. less than 1% of substrate hydrolyzed). Although skim milk lipoprotein lipase activity appeared positively related to mammary lipid secretory capacity during the time immediately surrounding initiation and cessation of copious milk production, activity between those periods was not correlated to milk fat percentage, milk fat yield, or stage of lactation.