A DISTINCT POPULATION OF NEURONS IN THE CENTRAL POSTERIOR PREPACEMAKER NUCLEUS PROJECT TO THE NUCLEUS PREOPTICUS PERIVENTRICULARIS IN THE WEAKLY ELECTRIC GYMNOTIFORM FISH, APTERONOTUS-LEPTORHYNCHUS/

The central posterior/prepacemaker nucleus of weakly electric gymnotif orm fish is a cell cluster in the dorsal thalamus involved in neural c ontrol of electric behaviors. By employing anterograde and retrograde tract-tracing techniques, we examined the neural connection between th is complex and the preoptic area in Apteronotus leptorhynchus. Unilate ral application of biocytin restricted to the region defined by the so mata of the central posterior/prepacemaker nucleus revealed a network of fibers and terminals bilaterally in the anterior and posterior subd ivisions of the nucleus preopticus periventricularis. Application of b iocytin to the nucleus preopticus periventricularis demonstrated that these fibers arise from a small population of cell bodies located pred ominantly in the central and medial portions of the central posterior/ prepacemaker nucleus. These somata were distinguished from the remaini ng cells in this complex not only by their pattern of connectivity, bu t also by their position within the cluster and by the relatively larg e size. The projection from the central posterior/prepacemaker nucleus to the nucleus preopticus periventricularis may provide a feedback lo op complementing a recently described connection projecting from the p reoptic area to the central posterior/prepacemaker nucleus with one sy naptic link in the preglomerular nucleus. (C) 1997 Elsevier Science B. V.