Early events in the development of neuronal polarity in vitro are altered by ethanol.

Among the neuropathological effects of prenatal exposure to ethanol is the disruption of neuromorphogenesis. The effects of ethanol on early events in the development of axons and dendrites were studied using cultured embryonic rat hippocampal neurons, which develop in vitro in a stereotypical sequence of events that mimics their development in vivo. During the first 24 hr in culture, hippocampal neurons attach to the substrate and develop into one of three stages identified by phase-contrast microscopy: (i) neurons having lamellipodia and no processes (stage 1); (ii) neurons developing minor processes (<40 microm) that subsequently become the cell's axon or dendrites (stage 2); or (iii) polarized neurons with at least one axon (process with length > or =40 microm) (stage 3). Exposure to ethanol (300 mg/dl or 800 mg/dl) in the culture medium resulted in an increase in both the number of minor processes per neuron and the number of stage 3 neurons having more than the typical single axon. In addition, ethanol exposure significantly altered the proportion of neurons in the three early stages of development at 18 to 24 hr in vitro, without affecting overall neuron survival. With ethanol, there was a smaller proportion of neurons in the first stage of development, and a greater proportion of polarized stage 3 neurons. These findings suggest that ethanol alters the normal establishment of neuronal polarity, disrupting mechanisms that ensure the formation of the appropriate number of processes and that regulate the timing of process outgrowth.