Specific respiratory neuron types have increased excitability that drive presympathetic neurones in neurogenic hypertension.

Moraes DJ, Machado BH, Paton JF.

Hypertension. 2014 Jun;63(6):1309-18.

In this paper they were trying to find out what differences between spontaneously hypertensive (SH) rats and WKY control rats are responsible for the increases in nerve activity and blood pressure seen in the SH group. To investigate this they looked at a lot of nerves, a lot of neurons, and a lot of factors that our lab often don’t consider. Their primary focus was on seeing if the increased respiratory modulation RVLM neurons seen in hypertensive rats was due to changes in the RVLM neurons themselves, or if it was due to changes in synaptic input. To make a long paper short, they found differences in nerve activity and neuronal behavior between groups (SH rats showed increases in both categories) that pretty much disappeared when they blocked synaptic input to the RVLM. This suggested that the changes in neuron and nerve activity actually came from upstream sources, altering synaptic communication in the RVLM.

They then started looking at the pre-BotC to see if the differences might be there, because respiratory modulation of RVLM neurons seems to be sourced from a place full of respiratory neurons.  What they found was that pre-inspiratory neurons in the pre-BotC were more excitable in SH rats, and it seemed to be due to reductions in the leak-K current compared to WKY rats (which should make Dr. Holt happy to learn). They also looked at post-inspiratory neurons and found these to be more excitable in SH rats as well. However, in their case, it appeared that it was due to reductions in the big calcium-activated potassium current. In fact, when they blocked the BKca channels in WKY rats, the recordings from WKY rats started to look like those from SH rats. There was no effect of the drug on SH rats, indicating that this current was pretty much non-functional, so they couldn’t drug it out.

This was a difficult paper to read and it had a lot of detail, but it really does take a good look at some of the inputs to the RVLM, and makes me remember that the RVLM isn’t an island, and it’s not the only thing that changes in hypertensive rats. -DH