Chronic, but not acute, ethanol exposure impairs central hypercapnic ventilatory drive in bullfrog tadpoles

Abstract

Chronic ethanol exposure early in development is deleterious to neural development and may impair responses to ventilatory stimuli (ventilatory drive) that maintain homeostasis. Central hypercapnic ventilatory drive (CHVD) increases ventilation to ensure pH homeostasis and accommodate the metabolic production of CO2. We tested the hypothesis that chronic ethanol exposure impairs CHVD in bullfrog tadpoles. Early and late metamorphic tadpoles were exposed in vivo to 0.12–0.06g/dL ethanol for either 3- or 10-wk durations. Brainstems from these animals were isolated and the neural correlates of ventilation were recorded in vitro during superfusion with normocapnic (1.5% CO2:98.5% O2) and hypercapnic (5.0% CO2:95.0% O2) artificial cerebral spinal fluid. Normocapnic neuroventilation was unaffected by chronic ethanol exposure. The typical response to hypercapnia, an increase in lung burst frequency, was lost following 10 but not 3wk of ethanol exposure in both early and late metamorphic tadpoles. The neuroventilatory effects of chronic ethanol exposure were distinguishable from those of acute central ethanol (0.08g/dL) exposure, which attenuated early metamorphic tadpole normocapnic neuroventilation, but had no effect on tadpole CHVD. Thus, 10wk of ethanol exposure both early and late in metamorphosis impairs CHVD in bullfrog tadpoles.