Selective neurotoxicity induced by lasalocid in dissociated cerebral cultures

Dispersed cerebral cells prepared from 15–16-day mouse foetuses were cultured for 7 days and exposed to lasalocid for periods of 4, 18 or 48 hr. Cultures were examined by phase contrast microscopy and processed for scanning electron microscopy. Lasalocid (1 and 2 μ m) induced neurotoxic effects that were evident already at 4 hr, including swelling of perikarya, followed by cytolysis of most neurons present in the cultures. During the following 18 hr virtually the entire neuronal population degenerated completely. Cultures exposed to a lower concentration of lasalocid (0.5 μ m) for 48 hr showed only mild damage to some neurons, and at 0.2 μ m no damage could be observed, even after several days of continuous exposure. Notably, glial and other non-neuronal cells were not damaged by exposure to 2 μ m-lasalocid, and cell division resumed on returning the cultures to regular growth media. Similarly, lasalocid (2 μ m) was not toxic to cultured rat astrocytes. These morphological observations were followed by measurements of 45Ca 2+ influx in the dissociated cerebral cultures. Lasalocid (1 μ m) induced 45Ca 2+ influx of 40% above dimethyl sulphoxide control values. The voltage-sensitive calcium channel antagonists nimodipine (10 μ m) and D-600 (50 μ m) did not inhibit lasalocid-mediated 45Ca 2+ influx, whereas MK-801 [10 μ m; a non-competitive N-methyl- d-aspartate (NMDA) receptor/channel antagonist] exclusively blocked this influx and prevented cytotoxic damage. Conversely, NMDA and glutamate, which by themselves mediated 45Ca 2+ influx in these cultures, both potentiated lasalocid-induced 45Ca 2+ influx and cellular damage. These observations clearly demonstrate the selective neurotoxicity of lasalocid to cultured cerebral neurons, and may imply involvement of the NMDA receptor/channel in lasalocid-mediated neurotoxicity.