[Changes of the structural organization of the nucleus raphe pallidus after the decrease of endogenous serotonin...

The role of serotonin in the nucleus raphe pallidus (NRP) development and the dynamics of its serotonin-producing neurons were studied during various time points of the postnatal period in normal Wistar rats and in animals developing prenatally under the conditions of serotonin deficiency. It was shown that NRP contained 2 populations of serotoninergic neurons with different morphological characteristics. At the initial stages of postnatal development (Day 5) serotonin-producing neurons included only large neurons, while the synthetic activity of small neurons appeared later (by Day 10). With age, under normal conditions,the size of large neurons and their number were increased which is indicative of continuing process of differentiation and/or functional load augmentation. The size and number of small neurons were practically unchanged with age. Serotonin deficiency during prenatal development lead to the disturbance of NRP structural organization. In comparison with the control animals, the size and the number of serotonin-producing neurons of both populations was decreased, their size remained unchanged with the age. Part of the neurons underwent degeneration, resulting in the reduction of their numbers. The damage observed may change the serotoninergic innervation of the medullary nuclei, responsible for the cardiorespiratory the control, thus causing the disturbances of cardio-vascular and respiratory systems.