Action Potentials for February
1: Last summer, I covered a company that is reportedly starting work in the area of reversible cryopreservation. This past month, a new study from an unrelated academic group led by Alexander German makes a significant step in this space, by writing up a complete manuscript demonstrating functional recovery of adult mouse brain slices after vitrification.
The goal of vitrification is to cryopreserve the tissue while transforming into a glass-like state, to avoid damaging ice crystals. The authors developed a protocol for vitrification using a mixture of cryoprotectants (which they call V3) including dimethyl sulfoxide, formamide, and ethylene glycol.
The protocol is pretty involved. The tissue is first exposed to gradually increasing concentrations of cryoprotectant at 10°C, and then to higher concentrations at -10°C, before being cooled to -196°C. After storage (ranging from 10 minutes to 7 days), the tissue is carefully rewarmed and the cryoprotectant is removed through another series of concentration steps:
The structure of the tissue remained intact after going through this cryopreservation protocol and subsequently being immersion fixed with aldehydes, as seen by both light and electron microscopy. The cellular structure looks like what most would consider well-preserved:
They also found that individual neurons maintained most of the electrophysiological properties they tested. After rewarming, both pyramidal cells in the CA1 region and granule cells in the dentate gyrus had normal resting membrane potentials, continued to show spontaneous synaptic activity, and had intact long-term potentiation. However, while dentate gyrus granule cells maintained their normal action potential firing patterns, CA1 pyramidal cells were found to be less excitable after vitrification, with unclear implications:
I consider this to be a careful and impressive achievement from a relatively small research group. Kudos to them. It adds another important data point showing that neural functions can be recapitulated even from brain tissue that has been “paused” into a static state via preservation.
2: A connectomics study examines the cellular and synaptic organization of the octopus vertical lobe, which is a key brain structure in the octopus for learning and memory.
One finding is that there were cells with morphologies similar to neural progenitor cells and immature neurons. This is significant because it means that there could be a niche for adult neurogenesis in the vertical lobe, which would suggest the ongoing integration of new neurons throughout an octopus’s life, similar to what is seen in the mammalian hippocampus.
3: An electron microscopy method uses energy-dispersive X-ray imaging to map the distribution of heavy elements like phosphorus and osmium. This allows researchers to identify subcellular structures like insulin or glucagon granules, lysosomes, heterochromatin, and cell membranes, all based on their elemental composition:
4: An image restoration technique for X-ray holographic nanotomography data, which requires a synchrotron particle accelerator, doubles the spatial resolution and increases contrast by 5x. This allows them to achieve resolutions of 37-96 nm. This still does not quite match the few nanometer resolution of electron microscopy, but this technique could allow larger volumes to be more easily imaged. In mouse olfactory bulb tissue, small structures like mitochondria, endoplasmic reticulum, and synapses are clearly visible:
5: A new method for 3d tissue imaging allows antibodies and molecular probes to penetrate deep into biological samples up to centimeter scales. The researchers used this method to image neurofilament staining patterns in the human cerebellum:
Of note, they report that they did “perfusion fixation with 4% paraformaldehyde via the femoral artery” and that the “post-mortem delay to fixation and tissue harvesting was 4 weeks at −18 °C refrigeration.” I am surprised that (a) they could get adequate whole body perfusion after the freeze-thaw and that (b) the freezing did not affect the tissue structures. However, perhaps the conventional wisdom on this topic is wrong. It would be interesting to see this aspect of the paper replicated.
6: New study of white matter tissue from the anterior cingulate cortex that was preserved via immersion fixation after a postmortem interval of 16-99 hours (average 32 hours). They claim that the ultrastructural preservation quality is generally good, allowing them to study how thin axons differ between brain donors with and without autism spectrum disorder:
7: New study examines changes in blood perfusion of the brain during aging and how this varies between men and women:
8: United Therapeutics has received FDA clearance to begin the first-ever xenotransplantation clinical trial designed to support a Biologics License Application. They plan to transplant kidneys from pigs with 10 genetic edits into up to 50 patients with end-stage renal disease, starting around mid 2025. While other xenotransplants have been performed before, this trial is unique in being a potential pathway for FDA approval as a standard medical treatment.
I think United Therapeutics has to be considered one of the most uniquely innovative companies in the world. I’m not sure why they don’t get more attention. Probably because they don’t seek it. Here is their pipeline:
Their CEO Martine Rothblatt is extremely impressive. Here is her 2012 talk at Alcor, “Detecting Heartbeat Cessation Outside of Hospitals As Soon As Possible.”
9: An argument by Scott Small against the claim that extracellular amyloid aggregates are “the” cause Alzheimer’s disease. While he acknowledges that these aggregates are cognitively detrimental (as shown by clinical trials of amyloid-clearing drugs), he argues that intracellular amyloid-related pathology (specifically endosomal enlargement) better explains neurodegeneration due to its localization in brain regions first affected by Alzheimer’s and its mechanistic link to synaptic function.
10: Study of 202 people finds that ketamine treatment alone produced equivalent short-term improvements in depression and PTSD symptoms compared to ketamine combined with psychotherapy during six treatment sessions over 30 days:
11: I mostly agree with this post by David Pinsof, which argues that: (a) The feeling of happiness serves as a prediction error signal rather than a goal; (b) We habituate to sources of happiness quickly; (c) Happiness declines with age, which is an extremely well-replicated effect; (d) Although the “pursuit of happiness” is a bit of a sacred value in Western culture, what humans tend to actually be pursuing are evolutionary fitness proxies (food, status, safety, etc) rather than the feeling of happiness itself; and (e) It might be better to be more cognizant of this.
One of my disagreements is that the analysis needs more Fun Theory. Just because something no longer reliably makes you more happy when you do it, that doesn’t mean it’s no longer fun. There’s a difference. I think that people don’t distinguish as much between “happy” and “fun” and sometimes they are referring to the latter when they say they want to be “happy,” and ignoring this means that it turns into a semantic discussion over what “happy” means, which is tedious.
Another note: The perception that emotions never fully return to their pre-medication intensity after discontinuing long-term SSRIs is confounded by the natural age-related decline in emotional intensity that likely would have happened anyway. To be clear, I’m not claiming that this phenomenon is not real, I’m claiming that the effect is confounded.
12: The first randomized controlled trial of semaglutide (a GLP-1 agonist, aka Ozempic) for alcohol use disorder showed no significant reduction in real-world drinking. The trial was nine weeks and small (n = 48).
13: An article on misophonia, which is defined as a “disorder of decreased tolerance to specific sounds or stimuli associated with such sounds.” The field is getting increased funding due to the philanthropy of Steve and Diane Miller, whose daughter was diagnosed with the condition. In 2019 they created the Misophonia Research Fund and donated $12 million for scientific study.
14: Jim Phelps argues that lamotrigine should be used more in depression relative to SSRIs because the long-term side effects are less bad. A compelling argument IMO.
15: Trial of the antipsychotic lumateperone for depressive episodes with mixed features finds that it significantly decreases both symptoms of depression and mania. The most common side effects were somnolence (placebo, 1.6%; lumateperone, 12.5%), dizziness, and nausea. There were minimal metabolic or movement disorder side effects (at least over the 6 weeks of the trial), which is thought to be a benefit of lumateperone compared to many other antipsychotics.
16: I saw a study linked on r/ScienceBasedParenting (🤔): “Low to Moderate Prenatal Alcohol Exposure and Facial Shape of Children at Age 6 to 8 Years”.
In the study, they use machine learning on 3D facial scans to claim that low to moderate alcohol exposure during pregnancy is “associated with characteristic changes” in children’s facial features. However, the facial variations that they found were different from classic fetal alcohol syndrome features, which makes me skeptical.
And the study has what to me is a key limitation: they did not control for potential genetic differences in facial features between the mothers who did and did not report drinking. If there were genetic differences in their sample associated with both the propensity to drink (or report drinking) during pregnancy and any kind of facial morphology, it seems to me that this study could exclusively be measuring that, and there would be no way to distinguish it.
One day, it will be standard to adjust for genetics in observational studies. But that day has not yet come.
(To be clear, my critique is purely about this study’s methods. More broadly, I fully defer to the CDC: “There is no known safe amount of alcohol use during pregnancy.”)
17: New survey data from Tokyo on the motivations of people who register to donate their brains to science. 86.5% want to contribute to disease research and 82.7% desire to be “useful even after death.”
18: New substack by Ariel Zeleznikow-Johnston, which will also serve as the newsletter of the Brain Preservation Foundation. Highly recommended.
19: An essay on how moral psychology creates barriers to rational discussion of structural brain preservation technologies, including cryonics. They note that disgust reactions and cultural assumptions sometimes cause unthinking opposition instead of people actually attempting to think logically about the topic.
The authors introduce a “Schrödinger’s chrono-cat” thought experiment, wherein a cat must choose between certain death outside a time machine or the uncertain possibility of future survival inside it. The idea is that this metaphor might help people bypass emotional triggers in thinking about the topic practically. They also explore variations of the metaphor to represent different scenarios: opt-out cryonics (cat starts inside), compulsory cryonics (locked inside; I certainly think this is a very bad idea!), illegal cryonics (locked outside), and expensive cryonics (door requires payment). Sadly, cryonics really is illegal in many circumstances.
I'm always happy to see a new post from you. The amount of detail and useful info in these is spectacular.