Involvement of cholinergic mechanisms in the central control of respiration in the cane toad, Bufo marinus

Timing and duration of developmental nicotine exposure contribute to attenuation of the tadpole hypercapnic neuroventilatory response

The ability for air-breathing vertebrates to adjust ventilation in response to increased CO(2) (hypercapnia) is fundamental to maintaining pH homeostasis. Developmental nicotine exposure has been shown to impair tadpole neuroventilatory responses to hypercapnia following 8-12 weeks of exposure. It is not clear, however, to what extent the timing of exposure during development and/or the duration over which the exposure takes place contribute to this impairment. Here, tadpoles were exposed to 30 microg/L of nicotine for 3- or 10-week durations, either early or late in tadpole development. Correlates of tadpole lung neuroventilation were monitored during normocapnic (1.5% CO(2)) and hypercapnic (5% CO(2)) conditions of isolated brainstems. Preparations derived from early metamorphic tadpoles failed to increase lung neuroventilation in response to hypercapnia whether they had been exposed to nicotine for 3 or 10 weeks. Preparations derived from late metamorphic tadpoles failed to respond to hypercapnia after being exposed to nicotine for 10 weeks. These results suggest that both the developmental timing and duration of exposure are important when considering nicotine's effect on the hypercapnic neuroventilatory response.