#SfN13: Day 2

Another poster from North Carolina caught my eye today. Zhenglin Gu and Jerrel Yakel, neuroscientists at Research Triangle Park in Raleigh, North Carolina kindly presented some compelling research about the medial septum to me. I know, I know, I posted research about the medial septum yesterday. But that little brain structure has a lot of secrets people are interested in!

Their study used a medial septum (MS)-hippocampus co-cultured preparation where both structures are removed from the brain and placed side by side for many days so that the MS can regrow connections to the hippocampus. They then looked at the cooperation between the MS and Schaffer collaterals (SC) in producing theta rhythms in the CA1 region of the hippocampus. Here's how it goes:

  • By just stimulating the SC with a stimulating electrode, no theta is evoked in CA1.
  • However, if you first stimulate the MS (they used channelrhodopsin with 10 ms pulses of light at 10 Hz for one second), and then stimulate the SC, they detected theta in CA1, measured with an extracellular recording electrode. They called this phenomenon theta "induction".
  • Then, after 3-5 times of this pairing between MS and SC inputs to CA1, something changes and simply stimulating the SC is sufficient to evoke theta. They called this theta "expression".

Induction of theta was blocked by the drugs atropine, MLA, and APV. Expression, on the other hand, was not blocked by atropine, MLA, or DHβE, but was blocked by APV. Clearly NMDA is important in this process.

Next, they looked at which type of receptors in CA1 neurons are necessary for this type of theta generation. They found that NMDA receptors on glutamatergic neurons weren't necessary, but that nicotinic acetylcholine receptors on GABAergic neurons were. Narrowing it down further, they discovered that somatostatin GABAergic neurons were necessary for theta induction, but parvalbumin GABAergic neurons were necessary for theta expression. They have yet to test the role of muscarinic acetylcholine receptors, but I think that's somewhere in the pipeline.

The next step they're going to work on is whole-cell recordings from single neurons in CA1 in order to understand their contributions to theta individually. One of the challenges in dealing with the medial septum and theta is that we have a growing body of observations that have yet to be linked together. I am hopeful that their research will combine with research from other labs to help bring the many pieces of the puzzle together and we will understand this important rhythm soon. See you tomorrow!

2013-11-10 22.19.12-1

Posted November 11th, 2013 in Career, Neuroscience, Science.