This week, the list of journal articles that I simply must manage to finish reading includes a technical tour de force from the lab of J Julius Zhu (UVA), entitled “The organization of two new cortical interneuronal circuits”. The co-first authors are Xiaolong Jiang (now a Research Assistant Professor at Baylor College of Medicine) and Guangfu Wang (currently a Research Associate at UVA). Now, I’ve not yet finished reading the paper, so I’m not going to be able to provide the kind of in-depth description of its findings/protocols/implication. (It’s only Wednesday, proper article-reading protocol requires at least 2 days of sitting half-read on my desk.) That being said, folks interested in cortical microcircuits, inhibitory networks, and astonishing efforts in patch-clamp electrophysiology would do well to pick up this article.
The general gist of the study: it is a painstaking examination of the connection patterns of two distinct subtypes of cortical layer 1 inhibitory interneurons. The authors provide convincing evidence for two never-before-described circuits, involving these layer 1 interneurons: one circuit serves to enhance a particular form of activation, known as complex spikes, in downstream layer 5 pyramidal neurons; the other circuit suppresses this same form of activation. The two subtypes of layer 1 interneuron generate their opposing effects on layer 5 pyramidal neuron activity via distinct connections with additional interneurons located in layer 2/3.
As I said, I won’t go in depth into the findings of the paper. Instead, I’d like to focus on the methods, which as I mentioned, could be described as a technical tour de force. But really, tour de force doesn’t quite capture the ludicrous amount of work that must have gone into this study. One the surface, the techniques used are fairly straightforward, patch clamp electrophysiology, a technique first developed by Burt Sakmann and Erwin Neher, and used daily by scientists in research labs across the world (including myself). However, it is in the application of the technique, that this study sets itself apart.
Some background for the non-patch-clamp physiologists in the room. Most of the time, patch-clamp electrophysiologists record from individual neurons within a brain slice; if the experimental question requires, sometimes two neurons will be patched simultaneously. Simultaneous recordings can be technically tricky, requiring a stable recording setup and a skilled patch-clamper; so although dual recordings are pretty common these days, they still represent a technical achievement. Simultaneously recording more than 2 neurons (say 3-4)? A rare event.
To demonstrate the patterns of connectivity between the various subtypes of neurons (those located in layer 1, 2/3 and 5), Jiang, Wang and company patch clamped up to 8 neurons simultaneously. In total, they report testing “14,832 connections between 1,703 L1 neurons, 3,310 L2/3 interneurons and/or 3,394 L5 pyramidal neurons in the cortical slices.”
To best illustrate my reaction to reading this particular sentence, I present my marginalia:
As a patch-clamp electrophysiology, I am absolutely staggered by the prospect of patching that many neurons. And to collect those numbers while attempting (and succeeding) in simultaneously patching up to 8 neurons… These folks are crazy.
Take a look at Figure 3, in which the authors characterize the connectivity between 7 simultaneously recorded neurons. Oh, and did I mention that the authors recovered the anatomy of the vast majority of their interneurons and pyramidal cells – 85% and 99%, respectively. (I’ve got a hit rate of 50-60%, on good day. Damn people.)
Technically, this paper is ridiculously impressive, in a “damn-how-long-did-that-take-you-no-wait-how-did-you-do-that-um-can-I-buy-you-a-patch-clamp-machine-please” way. And the science is pretty cool too (although again, I’ve not yet finished the paper, so “pretty cool too” should be seen as an initial impression only. And an understatement.).
But seriously, Xiaolong Jiang, Guangfu Wang, Alice J Lee, Ruth L Stornetta, and lab head J Julius Zhang have produced a paper of breathtaking technical mastery of patch clamp physiology. We all should read it and appreciate their hard, hard work. And then get them one of these: http://autopatcher.org/
Jiang, Wang, Lee, Stornetta and Zhu (2013). The organization of two new cortical interneuronal circuits. Nature Neuroscience, 16(2): 210-218. doi:10.1038/nn.3305. Available online here.