Microinjection of Dihydrotestosterone as a 5α-Reduced Metabolite of Testosterone into CA1 Region of Hippocampus Could Improve Spatial Learning in the Adult Male Rats

Abstract

CA1 region of hippocampus has an important role in learning and memory. Previous reports have shown that androgens like testosterone and its metabolites are present in high concentration in CA1 region of hippocampus. Androgen receptors have also high density in this region. Therefore, it is suggested that neurohormones in CA1 have an important role in learning and memory. It is likely that testosterone exerts its effect via its metabolites, especially dihydrotestosterone (DHT), a 5α-reduced androgen. In this research, we conducted an experiment to assess the path of testosterone›s effectiveness on spatial learning and memory. Adult male rats were randomly divided into 4 groups and, bilaterally, cannulated into CA1 region of hippocampus. One week after the surgery, animals received DMSO 0.5 μL as a control group and different doses of dihydrotestosterone (DHT) (0.25, 0.5 and 1 µg/0.5 μL/side) 25-30 min before the training in spatial version of Morris Water Maze task. Training session contained two blocks which animals had to learn the position of hidden platform in 4 trials. On the test session (next day), rats performed a one-trial probe test and then a visible platform one. The results showed that escape latency and traveled distance were decreased significantly in DHT-treated (0.5 µg/0.5 μL/side) rats. This finding suggested that DHT may have improved the effect on acquisition of spatial learning and memory.

Keywords: Androgen; CA1; DHT; Rat; Spatial learning and memory.

Figure 1

Nissl-stained coronal brain section from cannulated and injected rats. Cannula (C) and injection position (I) are shown.

Figure 2

Comparison of (A) escape latency, (B) traveled distance and (C) swimming speed across training day within different groups.

Figure 3

Comparison of (A) escape latency and (B) traveled distance during visible platform test. There were no significant differences between groups.

Figure 4

Comparison of (A) escape latency and (B) traveled distance during visible platform test. There were no significant differences between groups.