Dendritic Calcium Activity Precedes Inspiratory Bursts in pre-Bötzinger Complex Neurons

Each and every physiological process inside the human body is a complex process that requires precise coordination of signals and substances to be carried out. Naturally, this is no different for breathing, one of the essential life processes. Up until this point, researchers have been able to conclude breathing is in part controlled by inspiratory neural rhythms that originate in the pre-Bötzinger complex (preBötC) of the ventral medulla. The rythmogenic core of the ventral medulla is known to be made up of glutamatergic interneurons, but one of the key puzzles facing this line of research is the spatiotemporal distribution of active conductances in the somatodendritic membrane and their role in rhythmogenesis. Understanding this mechanism was the key reason for this study conducted by Del Negro et al. from the College of William and Mary. One explanation offered to date is that recurrent synaptic interactions evoke postsynaptic conductances to generate inspiratory bursts. More specifically, these recurrent synaptic interactions may elevate Ca²⁺ and activate nonspecific catatonic current (I_CAN)_. Previous studies have shown that I_CAN is an important charge carrier in respiratory rhythm.

For this reason, Del Negro and his colleagues wanted to look at the role of glutamatergic pre-BötC neurons in exciting their postsynaptic targets and causing Ca²⁺ to accumulate in the dendrites before inspiratory bursts. To do this, they needed to carefully measure the flows of Ca²⁺ using the fluorescent calcium indicator, Fluo-8 AM. This particular indicator is exceptionally effective because of its increased signal intensity and its robust results. Since it fluoresces between 2 and 4 times brighter than previous indicators, researchers can carefully measure Ca²⁺ flows, allowing them to make accurate and valid conclusions during their investigation.

By measuring Ca²⁺ dynamics in soma-close and soma-distal dendritic locations in acute slices that retain respiratory function in vitro, Del Negro and his team were able to determine that the endogenous synaptic drive evokes dendritic Ca²⁺ transients before somatic inspiratory burst. This is significant as it indicates that synaptically activated dendritic conductances may influence respiratory rhythm generation, which helps to gain a deeper and more complete understanding of respiratory activity. As is evident, a study like this is very much dependent on the visual representation of Ca²⁺; whether studying flows or accumulation, understanding how this substance is affected helps to gain this understanding and has profound implications. However, results like this would not be possible were it not for reliable and robust indicators such as the Fluo-8 AM fluorescent calcium indicator. This indicator is easy and reliable to load at room temperature, which helps to maintain the integrity of the results and allows images like these to factor in to key studies like this. When dealing with processes that involve such miniscule properties and such sensitive samples, it is important that the tools being used are accurate but non-invasive. This allows researchers to stay focused on the investigation and on delivering useful insights into the inner workings of the human body.

References

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1. Del Negro, Christopher A., John A. Hayes, and Jens C. Rekling. "Dendritic calcium activity precedes inspiratory bursts in preBötzinger complex neurons." Journal of Neuroscience 31.3 (2011): 1017-1022.