Abstract
We have hypothesized that estradiol enhances basal forebrain cholinergic function and cognitive performance, at least in part, via activation of the novel estrogen receptor GPR30. Here we evaluated the effects of estradiol, G-1 (a selective GPR30 agonist), and tamoxifen (TAM; an ERα/ERβ antagonist that also acts as a GPR30 agonist), on acetylcholine (ACh) release in the hippocampus, as well as the ability to block the effects of 17β-estradiol (E) or TAM with the GPR30 antagonist G-15. Note that G-1 was included to evaluate the effects of selectively activating GPR30, whereas TAM was included to differentiate effects of E associated with activation of GPR30 vs. ERα or ERβ. The study was designed to test effects on potassium-stimulated release, as well as on ACh release stimulated by feeding. Effects of feeding were included because the tasks we used previously to demonstrate beneficial effects of E on cognitive performance were motivated by food reward, and we hypothesized that E may enhance performance by increasing ACh release in association with that reward. Ovariectomized rats were treated for 1week, and ACh release was evaluated using in vivo microdialysis. In addition, rats were fed at the same time daily for several days and were fasted overnight prior to microdialysis. For each rat, ACh release was evaluated under basal conditions, in response to feeding, and in response to elevated potassium. Both feeding and elevated potassium increased ACh release in the hippocampus. In response to feeding, E, G-1, and TAM all significantly increased the percent change in release. The effects of E and TAM were blocked by G-15, and the effects of combining E+TAM did not differ significantly from the effects of E or TAM alone. In response to elevated potassium, E, and TAM significantly increased the percent change in ACh release. G-1 produced a slightly lesser effect. The effect of TAM was reduced by G-15, but the effect of E was not. These findings suggest that activation of GPR30 is both necessary and sufficient to account for the effects of E on ACh release associated with feeding. In contrast, activation of GPR30 appears to be sufficient, but may not be necessary for increased release associated with elevated potassium. The changes associated with feeding are consistent with the effects of E, G-1 and G-15 on acquisition of a spatial learning task previously described. These data confirm and extend previous reports, and support a hypothesis wherein E treatment can improve learning on specific tasks by activating GPR30 and enhancing ACh release in association with food reward.