Serotonin-immunoreactive structures in the central nervous system of the garfish Lepisosteus productus...

Serotonin-immunoreactive (5HT-IR) neurons were investigated in the brain and rostral (cervical) spinal cord of the garfish, a non-teleost actinopterygian. The diencephalon contained a prominent 5HT-IR cell group consisting mainly of liquor-contacting neurons in the hypothalamic periventricular wall. Their ependymofugal processes formed thick bundles or patches within the hypothalamus and then arborized profusely. Other groups of 5HT-IR cells were found in the dorsal thalamus and in the caudal cortex of the hypothalamic inferior lobe. In the caudal brainstem, 5HT-IR cells were predominant in the raphe region. The spinal 5HT-IR cells were scattered rostrocaudally in the ventromedial zone. The structure corresponding to the submeningeal serotonergic system in the ventral spinal cord of the lamprey and stingray was demonstrated also in the garfish.