Young, Lauriann E.; Palmer, K.O.; Young, Ronald E.
Author Affiliation, Ana.
Deapartment of Basic Medical Sciences
Effects of estrogen and testosterone on the rate of learning and extinction time in negative patterning discrimination in aged male rats
Society for Neuroscience Abstracts Viewer
Date of Publication
In humans, aging is accompanied by a convergence of reduced gonadal steroid production and an increased incidence of senile dementia. Sex differences are observed in the incidence of senile dementia and gonadal steroid production. This study was designed therefore, to evaluate whether the difference seen in estrogen (E2) production in aged male and female rats could, in part, explain differences in the incidence of senile dementia. Three groups of Sprague-Dawley male rats (each with n = 6), aged 24 months, were assigned to different treatment groups, viz: E2, anastrozole (an E2-inhibitor) and oil, and later compared with non-treated aged male (n = 12) and female (n = 12) controls. Rats were trained in a computerized Lafayette operant system, utilizing a negative patterning discrimination learning task. Rats had to learn (and were rewarded) to press a lever when a single stimulus, light or tone, was presented, but were not rewarded if they pressed the lever when both stimuli (light/tone) were simulatneously presented. Plasma estradiol and testosterone levels were verified using chemiluminescence enzyme immunoassay and enzyme immunoassay, respectively. Aged male Sprague-Dawley rats chronically treated with E2 (silastic implants) showed a significant enhancement of learning (p<0.007); while, those with low E2 levels showed a significantly reduced rate of learning (p<0.001). In assessment of memory, estradiol-treated aged male rats showed a significant (p = 0.0001) increase in time-to-extinction of negative patterning discriminarion as compared to anastrozole-treated (low estrogen, high testosterone), oil and control groups. Additionally, aged male rats performed better at the negative patterning discrimination learning task than their aged female counterparts. These findings suggest that 17b-estradiol provides neuroprotection against cognitive decline in aged male rats.....