Development of the habenulointerpeduncular tract of rats

Development of the habenulointerpeduncular tract has been carried out on fixed brains obtained from 21 day rat embryos and from neonatal animals on the 0 and 9 days of postnatal development by DiI tracing method (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) along neuronal membranes. The marker was inserted into the nuclei of the habenula, the interpeduncular nucleus, and into the area of raphe nuclei. Neurons and fibers that contained DiI were identified on vibratome sections by fluorescent and confocal microscopy. We have found that reciprocal connections between the lateral habenular nucleus and raphe nuclei are formed in the prenatal period by stage E21. Raphe nuclei innervating neurons were located in dorso- and ventrocaudal parts of the lateral habenular nucleus. Projections of the medial habenular nucleus onto interpeduncular nucleus were found only in the postnatal period from P2. Neurons that provide a source of these projections form characteristic groups inside the medial habenular nucleus. Therefore, the present study for the first time describes heterogenic formation of different projection systems that are included in the habenulointerpeduncular tract of rats at perinatal ontogenesis.