Dr. Yoram Ben-Shaul
Neuronal Processing underlying Reproductive Function
How are socially relevant chemical cues detected and processed to control reproductive function?
Sexual behavior and sexually related physiological changes are controlled by neurons in the hypothalamus, a brain region with numerous sub-divisions containing intermixed and interrelated neuronal populations. To a large extent, these hypothalamic populations are conserved among species, and thus studies in mammalian animal models are highly relevant to humans. Yet, there are major differences among species in the sensory modalities that modulate these hypothalamic populations. While in humans, vision, olfaction, audition, and touch all play important roles, in rodents (which account for most mammalian species), chemosensation is the dominant modality.
In mice, chemical cues are detected by multiple chemosensory systems. Our research primarily involves the vomeronasal system because it is strongly implicated it in controlling reproductive function. Indeed, vomeronasal sensory neurons are a major source of input to hypothalamic neurons. Yet, they do not target hypothalamic neurons directly. Rather, the immediate target of vomeronasal sensory neurons is the accessory olfactory bulb (AOB), which is thus the first brain region with access to vomeronasal chemosensory information. Accessory olfactory bulb neurons then send axons to more centrally located regions, primarily to the vomeronasal amygdala which contains neurons that directly reach the hypothalamus. This completes a pathway that starts with stimulus detection at the vomeronasal organ and ends with hypothalamic activation.
The brain regions that link vomeronasal sensory neurons to the hypothalamus are not merely passive relays. Instead, each has distinct roles in the process of combining sensory information with external states to control reproductive function. On a phenomenological level, we study the neuronal activity in each of these brain regions upon exposure to various sensory cues and under various internal states. Such experiments have already provided important insights on the distinct features of each of these brain regions. However, a mechanistic understanding of information processing involves understanding the functional links between neurons in different brain regions and between internal sensors of the physiological state and these neurons. We believe that both lines of research are required to provide a complete explanation of the neuronal control of reproductive function.