The researchers also sought to determine whether pheromones could trigger olfactory pathways to activate GnRH neurons. To investigate this, they exposed male and female mice, respectively, to female or male sex-related pheromones and measured how neurons that are connected to GnRH neurons reacted. They also exposed the males to clean bedding, which was thought to be a neutral stimulus.
They found that pheromones triggered responses in neurons upstream of GnRH neurons in both odor and pheromone relay areas. "This suggests that there is a redundancy in pheromone detection, with at least some pheromone information being conveyed by both the main and accessory systems," said Buck. "This redundancy is not too surprising, if you consider how important it is to the animal to be able to sense pheromones. The redundancy might guard against the loss of a pheromone receptor from either the VNO or the olfactory epithelium causing a devastating loss of pheromone detection."
The studies showed that the odor of clean bedding also activated some neurons upstream of GnRH neurons. "This suggests that the animal's environment could also influence GnRH neurons, perhaps signaling whether the animal is in the optimal environment for mating." Buck said.
In tracing the connections between GnRH neurons and neurons throughout the brain, Boehm and his colleagues soon found that they had undertaken an enormous task to figure out these connections. "We were really shocked with what we found," Buck said. "We found that, although the GnRH neurons number only about eight hundred in mice, they connect directly with about fifty thousand other neurons. And these neurons are in brain areas involved in a wide array of functions -- for example, ap
Source:Howard Hughes Medical Institute