Effects of serotonin on neurite outgrowth from thalamic neurons in vitro

Altering levels of serotonin in the primary somatosensory cortex during ear ly postnatal life influences thalamocortical development. Recent in vivo ex periments suggest that serotonin may have direct effects on the growth of t halamocortical axons, and the present study was undertaken to determine whe ther this amine influences process outgrowth from thalamic cells maintained in culture. Ventrobasal thalamic neurons were harvested from newborn rats and maintained in culture for eight days. At the end of this period, 0, 10, 25, 50 or 100 mu M serotonin was added to the culture medium. After an add itional six days, cultures were fixed and stained with neuron-specific enol ase. Quantitative analysis of >500 cells from each condition indicated that 25 mu M serotonin, but not the other concentrations of this amine, signifi cantly increased the length of the primary (longest) process growing out fr om the cell body (P < 0.001), the total (summed) length of all processes (P < 0.0001), total neurites per cell (P < 0.05), number of branch points per cell (P < 0.01) and branch points on the primary neurite (P < 0.0005). These results demonstrate that exposing thalamic cells to serotonin increas es process outgrowth from them in the absence of their cortical targets. (C ) 1999 IBRO. Published by Elsevier Science Ltd.