Differential Effects of Acute Progesterone Administration on Spatial and Object Memory in Middle-Aged and Aged Female C57BL/6 Mice

摘要

The present study examined the effects of acute progesterone administration on hippocampal-dependent memory consolidation in ovariectomized middle-aged (16 month) and aged (22 month old) female mice. Spatial memory was tested in a 2-day Morris water maze task and object memory was tested using an object recognition task with 24- and 48-hour delays. Immediately after water maze training, mice received i.p. injections of vehicle, or 5.0, 10.0, or 20.0 mg/kg of water-soluble progesterone. Twenty-four hours later, retention of the platform location was tested. No overnight forgetting of the platform location was observed in middle-aged vehicle-treated mice. Acute progesterone administration had no effect on spatial memory in middle-aged mice. However, aged vehicle-treated mice demonstrated impaired memory for the platform location on Day 2 relative to Day 1. Twenty mg/kg, but not 5 or 10 mg/kg, progesterone reversed these deficits, suggesting that 20 mg/kg progesterone can improve spatial memory in aged females. In the object recognition task, mice explored two identical objects and then immediately received vehicle or progesterone injections. In middle-aged mice, 10 and 20 mg/kg progesterone enhanced object memory consolidation, relative to chance, after 24-hours, but all doses were ineffective after 48-hours. In aged mice, 10 mg/kg progesterone enhanced object memory consolidation, relative to chance, after 24 hours, whereas both 5 and 10 mg/kg progesterone enhanced memory after 48 hours. Together, these results indicate that acute progesterone differentially enhances hippocampal-dependent memory in middle-aged and aged females.