A novel functional neuron group for respiratory rhythm generation in the ventral medulla.

Onimaru H, Homma I. J Neurosci. 2003 Feb 15;23(4):1478-86. This paper looked at respiratory-related neurons in the RVLM. What they wanted to know was how the neuronal activity was related to the different phases of respiratory activity. To examine this, they used a voltage sensitive dye in order to visually observe increases in activity, and compared it to the phases of respiration. By using the increase in activity in the motor inspiratory nerve as a trigger, they found that they were able to "see" action potentials occurring approximately 500ms before inspiration occurred. The voltage-induced signal increased until just before inspiration (rat brainstem spinal cord preparation), and decreased after that. It seems that the signal was initiated in the region of the RVLM just ventrolateral to the facial nucleus and near the ventral surface. After that, the increase in dye signal spread caudal and medial to the point of initiation. The other paper I blogged this week studied cells that were modulated by respiratory activity, but this one looks at cells that seem to generate respiratory activity. I can't guarantee it right now, but I'm pretty sure that if I were to look at my recordings, I've seen some cells that have their bursts cut short by the ventilator, and others that burst at other phases. I don't know how physiologically relevant those are, since being on a ventilator is not exactly natural, but it does reinforce that the RVLM is pretty heterogeneous and we should keep that in mind when we plan experiments and look at our data. -DH