Fig. 8.
Lack of respiratory drive in the 12th cranial nerve. A, Electrophysiological recordings of descending respiratory discharge from hypoglossal nerve. Control (con, Dnmt12lox/2lox) and conditional mutant mice were dissected from the uterus at E18.5 and E19.5 and immediately prepared for 12th nerve recording as described in the Materials and Methods. Only occasional spontaneous gasping was observed in mutant mice. The gasping discharge also could be induced occasionally by tail pinching of mutant mice when an initial recording did not show any spontaneous signals. Similar results were obtained with six control and five mutant mice. Insets for each trace are EKG recordings obtained with subcutaneous electrodes (the EKG in the second control trace was derived from the diaphragmatic EMG recording). B, Normal morphology of hypoglossal motor neurons in the brainstem. E18.5 control (CON) and mutant embryos were fixed with 10% formalin and processed for paraffin histology. Brain sections were stained with cresyl violet. No obvious morphological difference was observed between control and mutant hypoglossal motor nuclei. Scale bar, 37.5 μm.