Related Experiment Video
Updated: Jul 13, 2026

Protocol for Studying Extinction of Conditioned Fear in Naturally Cycling Female Rats
Published on: February 23, 2015
Effects of gonadectomy and hormone replacement on brain monoamine synthesis in male rats
Abstract:
The synthesis of catecholamines and serotonin in the brains of castrated male rats was analyzed at either various times after castration or at various ages. It was found that (a) castration of rats at 50 days or later causes an increase in brain monoamine synthesis, and (b) this phenomenon was not observed until 20 days after castration. The increase in brain monoamine synthesis following castration was counteracted by treatment with testosterone, thus relating the biochemical consequences of castration with changed hormonal conditions of the animal. It is suggested that testosterone exerts an inhibitory influence on monoamine synthesis.
Related Concept Videos
Gonadal and Placental Hormones
In males, testosterone is the primary gonadal androgen. It plays a central role in the maturation of male reproductive organs — the penis and testes. Additionally, testosterone is instrumental in the development of secondary sexual characteristics — a deep voice as well as facial and pubic hair growth — and...
Drugs Affecting Neurotransmitter Synthesis
Menopause

