What if you could dissect the synaptic dynamics with millisecond precision? To resolve controversial questions in neurobiology employing new techniques for visualizing cellular activity is essential. The recycling of synaptic vesicles in nerve terminals involves multiple steps, underlies all aspects of synaptic transmission. It is a key to understanding the basis of synaptic plasticity. To follow membrane dynamics at synaptic terminals, neurons must be immobilized at defined time points after stimulation with millisecond precision.
In this webinar, we will introduce the features and applications of the Leica EM ICE high pressure freezer with light stimulation, emphasizing the physics and technical solutions behind the user interface. We will discuss parameters such as dwell time, pressure and temperature correlation, how they are measured and what the displayed data means. We will also explain how light stimulation is synchronized with the freezing process to give you millisecond precision in your experiments.
Application Note for Leica EM ICE, Leica EM AFS2 - Electrical stimulation of neurons combined with high-pressure freezing allows physiological activation of synaptic activity and precise control over the time frame of the induced synaptic activity.
Application Note for Leica EM ICE - Rat Hippocampal neurons, cultured on 50 μm thick Aclar (Aclar embedding film, EMS) for 19 days, were frozen in the 100 μm deep side of lecithin coated (detailed protocol Appendix I) type A 3 mm Cu/Au carriers (Leica) and sandwiched with the flat side of lecithin coated type B 3 mm Cu/Au carriers (Leica). No additional filler was used, only cell culture medium with the addition of Hepes buffer pH 7.2 to a final concentration of 25 mM. Samples were frozen in a high-pressure freezer (Leica EM ICE).
Application Note for Leica EM ICE - WT hippocampal neurons were plated at a density of 80,000 cells/cm2 on 6 mm sapphire disks for 14 days. Sample were frozen using a high-pressure freezer (Leica EM ICE) under a pressure of 2100bar by mounting it into a sandwich support with extracellular solution containing 15% of Ficoll 400, to assess ice crystal damage. The Cryo-fixation was achieved within milliseconds allowing simultaneous immobilization of all macromolecular components. After freezing, sample was transferred into cryovials containing 1% glutaraldehyde, 1% osmium tetroxide, 1% milliQwater in anhydrous acetone and processed in an automated freeze-substitution device (Leica EM AFS2).
Sun screen lotion was carefully filled in the 100 μm incision of a 3 mm copper/gold plated flat carrier and covered with 3 mm sapphire disk. The sun screen lotion sample was then high pressure frozen with a Leica EM ICE with and subsequently without light stimulation. The light stimulated samples were exposed to a UV light for 500 milliseconds.
Water is the most abundant cellular constituent and therefore important for preserving cellular ultra-structure. Currently the only way to fix cellular constituents without introducing significant structural alterations is by cryo-fixation. There are currently two common methods employed; plunge freezing and high pressure freezing.
We have used cultured UMR106-01 osteoblastic cells to investigate the process of bone mineralization. UMR106-01 cells as well as primary calvarial bone cells assembly spherical extracellular supramolecular protein-lipid complexes, termed biomineralization foci (BMF), in which the first crystals of hydroxyapatite mineral are deposited (Midura et al., 2004; Wang et al., 2004). A major difference between these culture models is the speed with which mineralization occurs, ranging from 12–16 days after plating for primary osteoblastic cells to 88 h for UMR106-01 cells.
Especially in core EM-facilities one is confronted with material (microorganisms and cells) which are infectious. It is a must to follow the safety rules according to the National regulations. However even when safe laboratories are available it is very convenient to know that the applied high pressure freezing system is in itself safe.