[The neurosecretory structures in the spinal cord of sturgeons]

Fluorescent histochemistry, electron microscopy and immunocytochemistry revealed many different monoaminergic structures in the caudal spinal cord of Acipenseridae in the contrast to the rest one. Morphological analysis revealed two functional types of the monoaminergic structures: neuronal and neurosecretory those. The former structures were found at the middle and caudal levels of the spinal cord where they innervate peptidergic components of the caudal neurosecretory system and other structures. The neurosecretory structures were found only in the caudal portion. The monoamines produced by them are released into the meningeal blood vessels in the neurohemal area of the caudal neurosecretory system. A system of serotonin-positive neurosecretory elements was immunocytochemically revealed in the caudal portion. The significance of the spinal cord's neurosecretory structures in lower vertebrates is discussed.