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While characterizing the effects of estrogen on an ovariectomized (OVX) rat model of bone loss, we examined several weight-matching regimens [e.g., ad libitum (feed bins continually full), weight matched (rate of weight gain for OVX and Sham-OVX groups was equalized), and weight restricted (weight gain rates for all groups were equalized to that of estrogen-treated OVX rats)] for possible effects. Bone loss following ovariectomy is primarily the result of an increase in bone resorption and is extremely sensitive to the effects of estrogens. Thus, in all of our analyses, treatment with 17 beta-estradiol served as a positive control for the prevention of bone loss. Each weight-matching study had three groups: control (Sham-OVX), OVX, and OVX + 17 beta-estradiol (0.1 mg/kg/day), and lasted for either 2, 4, or 6 weeks. Throughout the study, each Sprague Dawley rat was weighed every other day, and following sacrifice, a femur was removed for bone mineral density (BMD) analysis at the distal metaphysis by single photon absorptiometry. Following 2 weeks of dietary modifications, no significant differences were detected in BMD among the ad lib or weight matched groups. However, an estradiol-preventable reduction in BMD in restricted OVX rats was detected at 2 weeks postovariectomy. Additionally, OVX rats in all three dietary regimens displayed an estrogen-preventable reduction in proximal femur BMD at 4 and 6 weeks postovariectomy. These results indicate that a 4-week rat ovariectomized model of bone loss, under conditions of ad libitum feeding, shows great potential for pharmacologic manipulation.

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Behavioral interactions were examined in two species of salamanders, Desmognathus quadramaculatus and D. monticola, in artificial stream tanks. Substrate choice for D. monticola was altered in the presence of D. quadramaculatus, but the converse was not observed. The substrate choice of small D. monticola was altered in the presence of larg~ D. mon_ticola. Interspecific competition for substrate was not detected, and the species-spe~tfic avmdance of D. quadramaculatus by D. monticola may thus represent predator a_v~ndance. Intraspecific competition for substrate was detected in D. monticola. Compe-titiOn and predatiOn both appear to structure desmognathine salamander communities.