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In developing neurons the frequency of long duration, spontaneous, transient calcium (Ca2+) elevations localized to the growth cone, is inversely related to the rate of axon elongation and increases several fold when axons pause. Here we report that these spontaneous Ca2+ transients with slow kinetics, called Ca2+ waves, are modulated by conditions of ethanol exposure that alter axonal growth dynamics. Using time-series fluorescence calcium imaging we found that acute treatment of fetal rat hippocampal neurons with 43 or 87 mM ethanol at an early stage of development in culture decreased the percent of axon growth cones showing at least one Ca2+ wave during 10 min of recording, from 18% in controls to 5% in cultures exposed to ethanol. Chronic exposure to 43 mM ethanol also reduced the incidence of Ca2+ waves to 8%, but exposure to 87 mM ethanol increased their incidence to 31%. Neither chronic nor acute ethanol affected the peak amplitude, time to peak or total duration of Ca2+ waves. In some experiments, we determined the temporal correlation between Ca2+ waves and growth and non-growth phases of axonal growth dynamics. As expected, waves were most prevalent in stationary or retracting growth cones in all treatment groups, except in cultures exposed chronically to 87 mM ethanol. Thus, the relationship between growth cone Ca2+ waves and axon growth dynamics is disrupted by ethanol.

SUMMARY: BACKGROUND Previous studies in this laboratory have shown that, like their counterparts in vivo, fetal rat hippocampal pyramidal neurons in culture develop abnormally small dendritic arbors when exposed to ethanol. This study asked whether ethanol''s inhibitory effects on dendritic development differ when the duration of ethanol exposure and timing of withdrawal are varied to correspond with early versus later stages of development and whether ethanol withdrawal influences survival of these neurons.METHODS We compared neurons exposed continuously for 6 or 14 days to ethanol (70 mM) with neurons transferred from ethanol-containing medium to control medium either 1 day after adding ethanol (before dendrites elongated) or 6 days after adding ethanol (after dendrites began elongating). We then performed morphometric and cell density analyses at 6 and 14 days using digital images of neurons immunostained with microtubule-associated protein 2 (MAP2) to visualize dendrites.RESULTS Continuous exposure to ethanol decreased the length and number of dendrites formed but had no effect on neuron survival compared with controls without ethanol. Dendritic length was less inhibited when ethanol was withdrawn after 1 day, but the number of dendrites per cell was unchanged compared with neurons continuously exposed to ethanol. Withdrawal from ethanol at 1 day slightly enhanced the survival of neurons assessed at 14 days compared with neurons in control medium and with neurons exposed continuously to ethanol. In contrast, withdrawal from ethanol at 6 days severely decreased the number of neurons at 14 days.CONCLUSIONS These results suggest that dendrites can achieve normal length when ethanol exposure is limited to only 1 day and withdrawal occurs before dendrites begin elongating. However, a persistent reduction in dendrite number results in smaller overall dendritic arbor size. Although continuous exposure to ethanol has little effect on neuron survival in these cultures, and exposure limited to 1 day followed by withdrawal can be neuroprotective against cell death associated with increased time in culture, longer exposure before withdrawal can trigger cell death. [ABSTRACT FROM AUTHOR]