( xt. As a result the researchers could ...)Olfactory system detects pheromones that control reproduction

"Our conditional tracing studies showed a major projection to LHRH neurons from the main olfactory epithelium and the structures that comprise the primary olfactory complex," said Dulac. "This major route was never suspected. In addition, we were quite surprised when we realized we could not identify any connections with the vomeronasal system, which led us to attempt to confirm the experiment on a wide range of mice," she said.

As a control, the researchers performed a separate set of experiments using a non-conditional strain of the pseudorabies virus. These studies confirmed that the virus was capable of infecting all nuclei comprising the vomeronasal system.

Next, the researchers postulated that one should be able to identify functional correlates of the anatomical circuit linking olfactory neurons and LHRH-producing neurons. They studied the sexual behavior of mutant mouse strains that lacked either a functional olfactory epithelium or vomeronasal organ. They also studied the behavior of normal mice in which the olfactory epithelium had been selectively destroyed by a drug.

They found that the male mice that lacked a functioning olfactory epithelium showed little interest in females, with greatly reduced investigatory or mounting behavior. By contrast, male mice lacking a vomeronasal organ were able to mate. The researchers also discovered that LHRH neurons in the olfactory-deficient male mice were no more activated by exposure to female urine -- which normally elicits sexual behavior -- than exposure to water.Future studies will aim at further characterizing the network of connections from the olfactory system to LHRH neurons in many brain structures, said Dulac. Also, the researchers plan to explore how olfactory and vomeronasal neurons work together in mice to control reproductive
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Source:Howard Hughes Medical Institute