Birth and migration of neurons in the central posterior/prepacemaker nucleus during adulthood in weakly electric knifefish (Eigenmannia sp.).

In contrast to mammals, fish maintain their capacity to generate neurons in the central nervous system even during adulthood for prolonged periods of life. By employing immunohistochemical, autoradiographic, and electron microscopic techniques, we studied such a postnatal neurogenesis within the complex of the central posterior/prepacemaker nucleus (CP/PPn) in knifefish (Eigenmannia sp.), a weakly electric teleost. The CP/PPn is a bilateral cluster of neurons in the thalamus. It controls frequency modulations of the electric organ discharge as they are used during social interactions. In the CP/PPn region adjacent to the wall of the third ventricle ("ventricular zone"), cells are born continuously and at high rates. They undergo multiple cell divisions before differentiating into neurons. Concomitant with this development, the newborn neurons migrate toward lateral regions of the CP/PPn. In the course of this lateral migration, they appear to acquire immunological and morphological characteristics that are typical for mature CP/PPn neurons. We hypothesize that at least some of the newly generated cells develop finally into functional CP/PPn neurons.