[Abstract Title]. - Society for Neuroscience

hippocampus are major targets of steroid hormones, yet few studies have examined the effects of
steroid hormones on neuronal activity in vivo. Therefore, we tested whether a type of behaviorrelated
synchronized CA3 activity, SPWs, would change across the estrous cycle. Twisted
bipolar electrodes were implanted in area CA3 of adult female Sprague-Dawley rats using
stereotaxic methods. Cycle stage was monitored by vaginal cytology each morning, and only
those animals with 4-day estrous cycles were included. Starting 1 week after surgery, continuous
recordings were made for 30 minutes during sleep, immobility and exploration in the home cage.
After 4-5 estrous cycles, animals were euthanized to confirm electrode locations. SPWs were
defined as 70-200 msec spikes in the baseline recordings that were greater than two standard
deviations of the noise, and 2 minutes of continuous, artifact-free record were used to count
SPWs for each behavioral state. SPW frequency was low during exploratory periods, and the
frequency did not vary significantly with cycle stage (p>0.05; n=5). Mean SPW frequency
during sleep and immobility varied significantly across the estrous cycle (one way ANOVA;
p=0.017, n=5) increased at proestrus (123.8 and 130.7% respectively, normalized to diestrus 2),
and remained elevated at estrus (136.1, 135.8%). The results suggest that the preovulatory
estrogen surge initiates an increase in CA3 SPWs, which lasts for at least 48 hours. The increase
in SPWs appears to follow the rise in brain-derived neurotrophic factor (BDNF) that potentiates
mossy fiber transmission, suggesting an underlying mechanism. The changes in SPW during
sleep and immobility may preferentially increase memory consolidation for events occurring
during wakefulness, and ultimately facilitate reproductive success.
Disclosures: P. Pearce, None; D. Friedman, None; H. Scharfman, None.
Poster
279. Steroids and Plasticity I
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 279.14/MM28
Topic: E.01.c. Steroids and plasticity
Support: NIH grant NIDA R01 DA019921
NIH Grant 2 P20 RR016479
NIH COBRE P20 RR15567
Title: Estrogen regulation of proteins in the rat ventromedial nucleus of the hypothalamus