Disruption of estrogen receptor β gene impairs spatial learning in female mice

Abstract

Here we provide the first evidence, to our knowledge, that estradiol (E 2) affects learning and memory via the newly discovered estrogen receptor ␤ (ER␤). In this study, ER␤ knockout (ER␤KO) and wild-type littermates were tested for spatial learning in the Morris water maze after ovariectomy, appropriate control treatment, or one of two physiological doses of E 2. Regardless of treatment, all wild-type females displayed significant learning. However, ER␤KOs given the low dose of E 2 were delayed in learning acquisition, and ER␤KOs administered the higher dose of E2 failed to learn the task. These data show that ER␤ is required for optimal spatial learning and may have implications for hormone replacement therapy in women.T he steroid hormone estradiol (E 2 ) either is required for or significantly modulates many behaviors, including cognitive behaviors (1-9). Learning tasks that involve reference memory tend to be impaired by E 2 (1,7,8). In contrast, low levels of E 2 may facilitate working memory (5, 9). In women, changes in ability on visuospatial tasks and memory recall over the menstrual cycle have been documented (10, 11). Also, beneficial effects of estrogen replacement on cognition have been noted in normally aging women (12, 13) and in women suffering from dementia associated with Alzheimer's disease (14,15).How estrogen acts on learning and memory is not clear. Estrogen binding has been reported throughout the rodent brain, including the hippocampus and cortex (16). Both characterized nuclear estrogen receptors (ER␣ and -␤) are present in extrahypothalamic regions (17,18). In addition, in vitro work suggests that estrogen acts in a nongenomic fashion in hippocampal tissues (19,20). Mice lacking functional ER␣ have severe deficits in several aspects of reproduction, including behavior (21-24). On the other hand, ER␤ knockout mice (ER␤KO) are subfertile, and sexual behavior is normal (25, 26). Thus, there has been speculation that ER␤ regulates estrogen's nonreproductive functions in the central nervous system (21, 27, 28).Here we describe our work on spatial learning in female ER␤KO mice. When treated with doses of E 2 that do not affect learning in wild-type (WT) littermates, ER␤KO mice had impaired ability to escape from the Morris water maze. Interactions between ER␣ and -␤ may contribute to the learning response; to test the hypothesis that lack of ER␤ influences the level of ER␣ protein, mouse brains were examined for ER␣ immunoreactivity (ER␣-ir), with emphasis on the hippocampus (HIPP). MethodsAnimals. Female mice (ages 5-7 mos) were of mixed 129͞J and C57BL͞6J background. Subjects were generated by crossing heterozygotic mating pairs carrying a single copy of the disrupted ER␤ gene (25). The resulting offspring were genotyped by PCR amplification of tail DNA. WT and ER␤ disrupted (ER␤KO) littermates were used in these studies. The ER␤ gene disruption was created by Neo insertion into exon 3 (25), thus the following three primers were used: one from intron 2 (5Ј-GGAGTAGAAACAAGCAATCCAGACATC-3Ј), a...

Estrogen Receptor β, but not α, Mediates Estrogen's Effect on Cocaine-Induced Reinstatement of Extinguished Cocaine-Seeking Behavior in Ovariectomized Female Rats

“…However, it may be that activation of ERb with DPN resulted in a more consistent retention of this previously learned association than was produced by activation of ERa by PPT. Studies that have examined the role of ERs in estrogen's effects on learning and memory have suggested that the ERb subtype is important for learning and memory, including spatial learning (Rissman et al, 2002) and retention of spatial and inhibitory avoidance memory tasks (Rhodes and Frye, 2006). Conversely, activation of the ERa subtype may inhibit learning (Fugger et al, 2000).…”

“…Use of these techniques have helped to identify the involvement of ERa and/or ERb in several biological functions, including mating and reproduction (Ogawa et al, 1998(Ogawa et al, , 1999Hewitt and Korach, 2003), anxiety (Krezel et al, 2001;Walf and Frye, 2005;Imwalle et al, 2005;Lund et al, 2005), learning and memory (Fugger et al, 2000;Rissman et al, 2002), wheel running (Ogawa et al, 2003), and food intake (Geary et al, 2001;Roesch, 2006). For example, ERKO studies in mice have shown that ERa is required for normal sexual receptivity and fertility in mice and rats, whereas ERb does not appear to be critical for reproductive function (Hewitt and Korach, 2003).…”

“…Studies in rats using SERMs have demonstrated that activation of ERb increases, whereas activation of ERa decreases or has no effect on, the number of entries or time spent in the open arms of an elevated plus maze, indicating that ERb mediates the anxiolytic effects of estrogen (Lund et al, 2005;Walf and Frye, 2005). Furthermore, studies using both techniques have suggested that ERa and ERb may both be important for hippocampaldependent learning and memory, although results can vary depending on the task (eg, inhibitory avoidance and spatial learning, and so on) being measured (Fugger et al, 2000;Rissman et al, 2002).…”

Estradiol to aged female or male mice improves learning in inhibitory avoidance and water maze tasks

“…E 2 may have actions in the hippocampus to improve learning via traditional ligand-dependent actions at intracellular ERs [19,20,42]. In support, E 2 administered to ERβ knockout mice does not enhance spatial learning compared to vehicle [73]. Further, there may be ER specific effects of E 2 to enhance learning.…”

Differential Expression of Estrogen Receptors in Two Hippocampal Regions During the Estrous Cycle of the Rat

“…In the same line, ERb knockout mice are unable to learn a spatial task (Rissman et al, 2002;Liu et al, 2008), while the administration of an agonist of these receptors, but not an ERa agonist, improves the performance of mice in hippocampus-dependent memory tasks (Liu et al, 2008).…”