A small tablet of 5-bromodeoxyuridine (BrdU), implanted subcutaneously in a mouse, provides sustained release of base analog sufficient to effect substitution of DNA throughout an entire replication period. As illustrated by studies of mouse bone-marrow and spleen cells in the presence or absence of cyclophosphamide, this depot method of BrdU administration greatly simplifies in vivo analysis of sister-chromatid-exchange formation.

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The combination of dextroamphetamine and morphine has been shown to be synergistic for analgesia and antagonistic for most other effects. However, the claim that dextroamphetamine antagonizes the respiratory depression caused by morphine has not been well substantiated. In this double-blind study, we investigated respiratory effects, including resting respiration, isohypercapnic ventilation, CO2 response, dose response, and duration of these effects with dextroamphetamine alone and in combination with morphine. Dextroamphetamine alone (0.215 mg/kg) caused increases in minute ventilation and a leftward shift of the CO2 response curve that lasted for less than 2 hours. Dextroamphetamine combined with low-dose morphine (0.15 mg/kg) antagonized respiratory depression throughout the 5-hour observation period. Dextroamphetamine combined with high-dose morphine (0.30 mg/kg) was unable to completely antagonize depressed ventilation, and some residual effects of morphine persisted at 23 hours.

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