3,5,3'-L-TRIIODOTHYRONINE PROMOTES SURVIVAL AND AXON ELONGATION OF EMBRYONIC RAT SEPTAL NEURONS

The effect of 3,5,3'-L-triiodothyronine (T-3) on survival and morpholo gy of primary cultured neurons of the fetal rat brain was studied. In defined conditions of serum-free culture media we found the death prev enting effect of T-3 in all tested neuronal populations cultivated at high initial densities of plating (10(5) cells/cm(2)). While the survi val of cerebrocortical neurons was improved very slightly, the number of surviving hippocampal and septal neurons reached 127.2 +/- 2.0% or 134.8 +/- 12.3% of their respective controls. The septal neurons respo nded at normal physiological concentration of T-3 (1 nM) in high densi ty as well as in low density cultures (5 X 10(3) cells/cm(2)). Moreove r the treatment with 10 nM of T-3 caused significant extension of the axon elongation of septal neurons (194.5 +/- 15.7%). These findings su ggest the direct positive effect of T-3 on pure cell population of sep tal neurons derived from embryonic rat brain and support the evidence for the role of this peripheral hormone during neuritogenesis.