Structural Changes in the Subnuclei of the Parabrachial Complex in Rats with Serotoninergic System Deficiency during Prenatal Development

Abstract

Experiments were performed on the offspring of female Wistar rats (n = 8) given parachlorophenylalanine on day 16 of pregnancy to decrease endogenous serotonin levels in the offspring. Histological, immunocytochemical, and morphometric methods were used in rat pups on days 10 and 14 of postnatal development (5–6 individuals at each time point) for studies of the dorsal and ventral subnuclei of the lateral part of the parabrachial complex. The results showed that serotonin deficiency led to changes in the structure of these subnuclei. The population of large, multipolar neurons in the ventral subnucleus was found to be more sensitive to decreased serotonin levels. Experimental animals showed decreases in the body sizes of these neurons by a factor of 1.6 compared with controls, with virtually no change in the number of cells in this population. The morphological characteristics of small neurons corresponded to those in controls, though there was a reduction in the number of cells, which may explain the rarefaction of neurons in this nucleus. In the dorsal subnucleus of experimental animals, neurons of both of the populations in this structure underwent more marked changes. The sizes of both large and smaller neuron cell bodies decreased significantly, by factors of 2.0 and 1.8 respectively; the cytoplasmic volumes of these cells decreased compared with controls; the numbers of cells in both populations remained largely unaltered. Reactions detecting glial fibrillary acidic protein showed increases in the numbers of the astrocyte glial population in the early postnatal period in the experimental animals.