We evaluated genioglossus (GG) gross motoneuron morphology, electromyographic (EMG) activities and respiratory patterning in rat pups allowed to develop without interference (unexposed) and pups born to dams subjected to osmotic mini-pump implantation in utero (saline exposed). In experiment one, forty eight Sprague-Dawley rat pups (Charles-River Laboratories) ages post-natal day 7 (P7) through post-natal day 10 (P10) were drawn from two experimental groups: saline-exposed (N=24) and unexposed (N=24) and studied on post-natal day P7, P8, P9, or P10. Pups in both groups were sedated (Inactin hydrate, 70 mg kg-1) and fine-wire electrodes inserted into the genioglossus (GG) muscle of the tongue and intercostal muscles to record EMG activities during breathing in air and at three levels of normoxic hypercapnia (FICO2: 0.03, 0.06, 0.09). Using this approach, we assessed breathing frequency, heart rate, apnea type, respiratory event types and respiratory stability. In experiment two, sixteen rat pups were drawn from the same experimental groups: saline exposed (N=9) and unexposed (N=7) and used in motoneuron labelling studies. In these pups a retrograde dye was injected into the GG muscle, and the brainstems subsequently harvested and sliced. Labeled GG motoneurons were identified with microscopy, and impaled and filled with Lucifer yellow. Double-labeled motoneurons were reconstructed and the number of primary projections and soma volumes calculated. Whereas pups in each group exhibited the same number (p=0.226) and duration (p=0.093) of respiratory event types and comparable motoneuron morphologies, pups in the implant group exhibited more central apneas and respiratory instability relative to pups allowed to develop without interference.
- Copyright © 2016, Journal of Applied Physiology