he McCloskey Laboratory’s research at the College of Staten Island,City University of New York (CUNY) is focused on understanding the ways that neurons in the naked mole-rat brain participate in networks to produce complex behaviors such as learning and memory, as well as to examine the effect of hypoxia in brain cells. The Lab uses electrophysiological tools to monitor neuron function, from the level of the isolated single cell to the whole brain. Its methods range from patch clamp measures on cultured neurons through single- and multi-ion channel recording of acutely isolated brain regions, to electroencephalograms (EEGs) in awake and moving animals.

Using low-powered USB/computer-connected microscopy for targeting and patch clamping, and higher powered confocal microscopy for imaging, the McCloskey Laboratory has relied upon air tables for vibration isolation, a critical component for micron-level neuronal electrophysiological microscopy. But the Labs air table vibration isolation has had limitations, particularly isolating vibrations at lower frequencies below 5 Hz, caused by the buildings HVAC system, closing of doors, and researchers bumping into tables and equipment. This has introduced excessive noise into data, and at times interrupted research to replace fragile micron-scale glass electrodes which were damaged by vibration.

Air systems provide limited isolation vertically and very little isolation horizontally. Yet, electrophysiology microscopy demands vibration isolation requirements that are able to isolate very low-frequency vibrations in both the vertical and horizontal axes.

Targeting Neurons
Electrophysiology is very sensitive, said Michael Zions, a researcher and doctoral candidate with the McCloskey Laboratory. Our research involves making thin brain slices, about 300 microns in thickness, from the hippocampus of naked mole-rats, which we then keep alive in a bath of artificial cerebral spinal fluid. Once the sample is in the fluid, we now have a complete neuronal network that can pass signals along intact neurons. But these slices are also extremely delicate. We then insert a glass micropipette into a singular neuronal cell, or line up alongside one, and electrical stimulation is applied to mimic normal signaling or isolate a particular feature of the cell. A multichannel electrode array can also be applied to the slice, to provide an overview of the organization and to track signal propagation through the network.

We are working with real-time electrical measurements on a very small scale with delicate cells and fragile glass instruments, so vibrations are a big problem for us, continued Zions. If the pipette shifts just a little bit, it will at best miss the target. Often the electrode just shatters instead, spoiling that area and compromising the sample. We can replace an electrode, but it takes time and the samples are only viable for a short while. Limiting vibration reduces our vulnerability to disruption.

Crashing Micropipette Electrodes
The micropipette electrode is inserted into the neuron to a depth of 75 to 100 microns from the top surface, leaving approximately 200 microns of space to the bottom of the dish, which is holding the brain specimen in the cerebral spinal fluid. Once embedded, sideways shear can crack the electrode, and vertical shock will crash it into the floor of the chamber.

A crashed single electrode takes fifteen minutes to replace. If the electrode was silylated or specially drawn, the project might be done for the day, and the hippocampal slices will need to be replaced for the next experiment. This adds hours and cost. And if the crashed electrode was a multichannel array, the delay stretches to weeks and several thousand dollars. Unfortunately, this became such a common event that a more effective answer needed to be found.

We needed a vibration isolation solution that was compact, not electrically noisy, and could contend with challenges along any axis and across broad frequencies in the damaging ranges we had encountered explained Zions. Ideally, we could just swap it in for our existing air table.