Cortical interneurons show layer-specific activities

Researchers examine the firing patterns of interneurons throughout all layers of the somatosensory cortices of alert mice.  

To find their particular cells of interest—somatostatin(Sst)-expressing interneurons—in live murine cortices, the researchers used mice in which these cells, and only these cells, contained channelrhodopsin—a light-sensitive cell activator. The recording pipette contains a light source, Rudy explained. “So you touch a cell, you shine the light, if that cell has channelrhodopsin, it starts firing action potentials, and you know you’ve got the right cell.” Importantly, the pipette can be plunged beyond the viewing depths of a microscope.

Using this approach, the team identified and recorded from more than 90 Sst interneurons within the cortices of mice that were whisking—moving their whiskers back and forth in an alert and exploratory fashion. That’s “an impressive number of recordings,” neuroscientist Matthew Larkum of Humboldt University in Berlin wrote in an email to The Scientist. (Moore agreed, calling the effort “heroic.”)

“It is important because it is the first work—that I know of—that thoroughly checks the properties of cells through all the cortical layers,” Larkum wrote. “This uncovered properties that were layer-specific.”

The team went on to investigate how the Sst interneurons were being regulated in each layer. Another type of interneuron, called vasoactive intestinal peptide-expressing (Vip) cells, has been shown to suppress Sst cells. Sure enough, synaptic inputs from Vip cells to Sst cells were stronger in L2 and L3 than in L4 and L6, the researchers showed. By contrast, activation of the Sst cells in L4 and L6 was found to depend on signaling through these cells’ acetylcholine receptors. This result in itself is interesting, said Moore, because “a variety of studies have shown that cholinergic tone can be very closely related to arousal and attentional focus”—like that seen during whisking.
Although the paper does not examine how the activities of these cells impact perception—which is “the big open question,” said Scanziani—the findings “help to constrain your hypotheses,” he said, and thus offer a better shot at the answer.

Illustration of interneurons spanning cortical layers
NYU LANGONE

Source:TheScientist