Pheromone 3kPZS evokes context-dependent serotonin sexual dimorphism in the brain of the sea lamprey (Petromyzon marinus).

Mature male sea lampreys (Petromyzon marinus) release a sex pheromone, 3-keto-petromyzonol sulfate (3kPZS), that induces sexually dimorphic behavioral responses in conspecifics. However, the neural mechanism of such responses is mostly unknown. We examined the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) and the expression of 5-HT1A receptors in the forebrain and brainstem of sea lamprey exposed to the vehicle (0.91 ppm methanol) or 10(-10) M 3kPZS for 2 h using high performance liquid chromatography-electrospray ionization tandem mass spectrometry, immunohistochemistry and real-time quantitative polymerase chain reaction. Exposure to 3kPZS for 2 h increased 5-HT concentration in the forebrain of adult females, whereas 5-HT was not detected in the forebrain of adult males. On the contrary, 3kPZS exposure decreased 5-HT concentration in the brainstem of adult females and had no effect in adult males. Pheromone exposure evoked context-dependent sexual dimorphism in brain 5-HT1A receptor immunoreactivity, but had no effect on 5-HT1A mRNA concentrations in the brain with 2 h exposure time. It appears that in sea lamprey pheromone 3kPZS affects the 5-HT system in the brain in a context-dependent, sexually dimorphic manner.