Effects of extracellular acidic-alkaline stresses on trigeminal ganglion neurons in the mouse embryo in vivo

Acidic-alkaline stresses caused by ischemia and hypoglycemia induce neuronal cell death resulting from intracellular pH disturbance. The effects of acidic-alkaline disturbance on the trigeminal ganglion (TG) neurons of the embryonic mouse were investigated by caspase-3-immunohistochemistry and Nissl staining. TG neurons exhibited apoptosis in 3.08 ± 0.55% of neurons in intact embryos at day 16. Intraperitoneal injection of alkaline solution (pH 8.97; 0.005-0.1 M K₂HPO₄ or 0.01-0.04 M KOH) into the embryo at embryonic day 15 significantly increased the number of apoptotic neurons in the TG at embryonic day 16 with dependence on concentration (3.40-6.05 and 2.93-5.55%, respectively). On the other hand, acidic solutions (pH 4.4; 0.01-0.2 M KH₂PO₄) slightly, but not significantly, increased the number of apoptotic cells (3.64-5.15%, without dependence on concentration). Neutral solutions (pH 7.4; 0.01-0.2 M potassium phosphate buffer) had no effect on neuronal survival in the TG (2.89-3.48%). The results indicated that alkaline stress significantly increased apoptosis in the developing nervous system, but acidic stress did not.