Re-evaluation of acute neurotoxic effects of Cd 2+ on mesencephalic trigeminal neurons of the adult rat

Abstract

The mechanism of Cd 2+ neurotoxicity, which is considered to be secondary to changes in blood vessels, was re-evaluated in dissociated mesencephalic trigeminal (Me5) neurons of the adult rat. Cd 2+ induced morphological changes in Me5 neurons at 0.1 and 1 mM but not at 0.01 mM. The changes appeared predominantly in the cytoplasm: destruction of the cytoplasmic organelles, swelling and vacuolization of the cell body, and finally resulted in cell lysis. These observations indicate necrosis rather than apoptosis, and no sign of degraded nuclear DNA, characteristic to apoptosis, was detected by the TUNEL technique. Using a Ca 2+-sensitive dye Indo-1, Cd 2+ was found to elevate the intracellular Ca 2+ concentration [Ca 2+] i (both in the cytoplasm and the nucleus). Both the elevation in [Ca 2+] i and the morphological alteration were inhibited either by removing Ca 2+ from the bathing medium or by the application of BAPTA/AM (10 μM), a membrane-permeable intracellular Ca 2+ chelator. Furthermore, neither morphological changes nor elevation in [Ca 2+] i by Cd 2+ occurred in the presence of Zn 2+. It is concluded that (1) Cd 2+ can directly affect nerve cells, (2) toxicity of Cd 2+ on Me5 neurons is mediated by continuous elevation in [Ca 2+] i, (3) Cd 2+ induces necrotic cell death, and (4) Cd 2+ neurotoxicity can be antagonized by Zn 2+.