| The preBotzinger Complex (preBotC) is composed of a group of neurons located in the ventrolateral medulla that is necessary for the generation of mammalian respiratory rhythm. The main focus of this thesis was toward understanding preBotC and medullary development in normal and pathological conditions using rodent models. Four major studies were undertaken. I determined the birth date, the settlement, and the inception of preBotC formation in the developing embryonic rat. That fundamental study provides a key foundation for work examining the ontogeny of respiratory neural control. I then performed a comprehensive anatomical study of the developing brainstem in a necdin deficient mouse model of Prader-Willi Syndrome (PWS). These mice, and newborn children with PWS, have abnormal breathing patterns. The data revealed wide-spread anatomical defects, including nuclei and axonal tracts that provide modulatory synaptic input to the preBotC. A second mutant mouse model, lacking the gene for the homeodomain transcription factor Lbx1, was examined. This study initially focused on understanding the basis for the severe respiratory dysfunction at birth in the mice and subsequently expanded into a detailed study of Lbx1 expression and its role in the developing medulla. I determined that Lbx1 is a key regulator for determining neuronal cell fate and neurotransmitter phenotype in the medulla. Those data, in conjunction with previous studies of Lbx1 in the spinal cord, provide a comprehensive understanding of Lbx1 function in the developing neuraxis. Finally, I developed a novel experimental method that will allow for the precise targeting of preBotC neurons expressing neurokinin-1 receptors (NK1R), to which the neuropeptide Substance P binds. These neurons have been hypothesized to be essential for respiratory rhythmogenesis. Specifically, I determined that the internalization of tetramethylrhodamine conjugated Substance P in rhythmically active medullary slice preparations provided clear visualization of NK1R-expressing neurons for subsequent whole-cell patch clamp recordings. This approach should greatly expedite studies necessary for elucidating the cellular mechanisms within the preBotC. |
