Respiratory neurons located in the Nucleus Tractus Solitarius (NTS) and the ventrolateral respiratory group (VG) will be recored with microelectrodes. While recording from the neurons, the vagus nerve, the inspiratory-inhibitory region of the Nucleus Parabrachialis Medialis (NPBM), and the cervical spinal cord will be stimulated to determine possible efferent and afferent connections to the recorded cells. The neuronal firing will be analyzed using post-stimulus histograms (PSH) to determine whether the neurons receive inputs from stimulated regions and the latencies between stimuli and elicited action potentials. Possible antidromic action potentials indicating efferent projections from recorded cells to stimulus sites will be tested using collision techniques. We will also analyse the firing patterns of late-inspiratory beta neurons (cells receiving a direct volume input) to determine the relationship between the firing pattern of these neurons and inspiratory inhibition during the graded reversible phase of inhibition. A temporal correlation has been previously shown between the firing onset of these neurons and the onset of the period of graded reversible inhibition. Because of suggestive anatomical and electrophysiological evidence, we will investigate respiratory neurons located in the most rostral part of the VL in the region of the retrofacial nucleus (RFN) for possible connection with the inhibitory NPBM and contralateral NTS. PSH will again be used to analyze the latency between stimulus and response. Since it is known that temperature greatly alters the respiratory rhythm, we will also examine the effects of heating the temperature regulating areas of the hypothalamus. We will record from neurons in the NTS and RFN before, during, and after heating. Cycle-triggered neuron firing histograms will determine the effect of heating on the response of these neurons.