Expression, distribution, and function of sex hormone receptors in the rabbit brain

Sex hormones such as estradiol, progesterone, and testosterone are crucial for vertebrate brain functions by interacting with their specific receptors. In rabbits, these hormones regulate sexual behavior, scent marking, nest building, and nipple searching across different brain regions. However, information on sex hormone receptors in the rabbit brain is limited. We examined intracellular progesterone (PR), estrogen (ER), and androgen receptors (AR) in the rabbit brain. PR activation by progesterone is associated with pregnancy and maternal behaviors like nest building and nipple searching. PR is expressed in female and male rabbits' cerebral cortex, hypothalamus, preoptic area, and hippocampus. In males, it is also found in the olfactory bulb, mesencephalon, and cerebellum. Rabbits express two ER subtypes, ERα and ERβ, with different expression patterns and functions. The former is in the amygdala, bed nucleus of the stria terminalis, hippocampus, hypothalamus, preoptic area, septum, and thalamus of females. In males, ERα is expressed in the hypothalamus, olfactory bulb, prefrontal cortex, preoptic area, mesencephalon, and cerebellum. Both ERs are located in male rabbits' amygdala, claustrum, and hippocampus. ERs influence estrous behavior and chinning. ERα has a role in rabbit hippocampus development and plasticity. AR is expressed in male rabbit hypothalamus, olfactory bulb, prefrontal cortex, hippocampus, preoptic area, mesencephalon, and cerebellum, related to sexual behavior and chinning. Interestingly, sex hormones regulate their own receptor expression and those of other sex hormones. Thus, estradiol regulates PR expression. This review summarizes the expression and distribution of sex hormone receptors in the rabbit brain and their behavioral role.