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Michael’s SFN 2010 List

Culling through the SFN abstract browser is an imperfect process.  Keyword searches can be helpful, particularly if you’re interested in a fairly specific topic, like, say, “1-bromopropane” (1 hit).  But if you’re interested in “postnatal neurogenesis” (292 hits) or “hippocampus memory” (1118 hits), make sure your scrolling finger is rested and well-fed.  Because there will be scrolling. Or you might try searching by name.  You’ll avoid delayed-onset finger soreness, but you’ll inevitably forget about so-and-so and that other guy, and -worse- you’re certain not to discover anyone new.

So you end up supplementing your name searches with some combinatorial keyword strategy.  You find some cool posters.  And then you discover that your blogging partner already found the same posters and posted about them two days ago.  So you ice your scrolling finger and post about a few cool abstracts he didn’t already mention. Continue reading Michael’s SFN 2010 List

#SFN10 Itinerary Pt. 2

Continuing on…

1) 31.20/C37 – Dentate network activity modulates integration of newborn granule cells
1Inst. of Cell Biology, Swiss Federal Inst. of Technol. (ETH), Zürich, Switzerland; 2Brain Res. Inst., Univ. of Zürich, Zürich, Switzerland; 3Univ. of Lausanne, Lausanne, Switzerland; 4Brain Res. Inst., Univ. of Zurich, Zürich, Switzerland; 5Swiss Federal Inst. of Technol. (ETH), Zürich, Switzerland

This looks interesting because there is so little known about how neuronal activity regulates neurogenesis. In 2007 Toni et al. suggested that dendritic filopodia on new neurons form synapses with presynaptic boutons that have already formed a synapse onto a different (presumably mature) neuron. The question addressed here is whether altering excitability/plasticity at those pre-existing synapses affects the subsequent formation of new neuron synapses. In other words, if you make old neurons more plastic, will they outcompete new neurons for synaptic space? Seems maybe they do.

2) 203.9/KKK52 – Coding of temporal context in the hippocampus: Do rate codes offer insight into a time-of-day signature?
1Dept of Neurosci., Univ. of Lethbridge, Lethbridge, AB, Canada; 2Ctr. for Neural Circuits and Behavior, Neurobiol Section, Div. of Biol Sci., UCSD, LA JOLLA, CA

We all know the hippocampus is important for episodic (-like) memory yet activity in hippocampal neurons is usually only measured in relation to spatial information. Memories also often contain temporal information and Rob Sutherland (one of the authors) has shown that rats indeed integrate time-of-day information into their memories. Here, measuring electrophysiological activity in hippocampal neurons, it is reported that 1) hippocampal neurons fire when a rat is in a specific spatial location, as expected; 2) when nearby contextual features are altered (square vs circular exploration chamber) the same population of neurons are active in the same places but they fire at different rates (rate coding); 3) what is unique here: hippocampal neurons also used a rate code to differentiate between a given context explored in the morning vs the afternoon. Thus, time-of-day is a contextual feature that is encoded in the hippocampus. Interestingly, it is reported that the rate codes for spatial and temporal information are carried by different populations of neurons.

3) 330.6/A6 – Experience specific information encoding by newborn neurons of the adult dentate gyrus
Salk Inst., La Jolla, CA

This presentation builds on Kee 2007, who showed that 10-week-old neurons are only activated in the water maze if they were functional at the time of the original water maze training, and Tashiro 2006 who claimed that, when a mouse re-experiences something, it is new neurons that were in their critical period during the original experience that are activated. We still have a ways to go before we understand how faithful new neurons are in their responding to different experiences – their enhanced plasticity and unique physiology has caused some speculation that they could be promiscuous, participating in many different experiences. This study seems like it may have the best evidence that young neurons are in fact quite selective in what they encode.

SFN2010 Itinerary Pt. 1

I have 62 items in my itinerary and I expect to add to it in the following weeks. There are always great presentations I find out about last minute and undoubtedly others that never see the light of (my) day. So fill me in if you have any tips. It’s not always the data that’s the most interesting part but often the presenter themselves, their ideas, methods, or the fact that you’ve known them since undergrad and you want to see baby pictures. My plan here is to share some of the potentially (you never know til you’re there) interesting presentations in my itinerary, bit by bit, over the next couple weeks.

1) 99.8/JJJ44 – The hippocampus is required for social recognition but not object recognition in Octodon degus
1Doshisha Univ., Kyotanabe City, Japan; 2RIKEN BSI, Lab. for Biolinguistics, Wako City, Japan

Huh? Octogon what? They’re rodents unlike any other rodent. They perform communal digging, nurse each other’s young, are born with their eyes open, and are intolerant of sugar and get diabetes. Even more interesting is the fact that they can switch their circadian rhythms between nocturnal or diurnal patterns and they’re apparently able to use tools (at least according to Wikipedia). So, basically I want to chat about Degus with these guys.

2) 100.19/KKK35 – Hippocampal granular neuron recruitment during the evocation of a recent or remote object recognition memory
1Neurobiologia Conductual y Cognitiva, Inst. de Neurobiologia, Univ. Nacional Autonoma de Mexico, Queretaro, Mexico; 2Neurobiologia Conductual y Cognitiva, Inst. de Neurobiologia UNAM, Queretaro, Mexico

Victor Ramirez-Amaya has done some interesting work on learning-related structural plasticity in the hippocampus and he’s also shown that the plasticity-related protein Arc is expressed in a delayed fashion after experience, probably as a part of the process of memory consolidation. Since there’s an emerging role for the dentate gyrus and neurogenesis in long-term memory I’m interested in this poster, which looks at activity-dependent Arc expression in the dentate gyrus and in young neurons after recent and remote(ish) memory retrieval.

3) 101.6/KKK46 – Spatial representation along the proximo- distal axis of CA1
1Kavli Inst. Sys Neurosci, Ctr. Biol of Memory, NTNU, Trondheim, Norway; 2Univ. Arizona, NSMA, Tuscon, AZ

The hippocampus is a convenient structure to study because its anatomical boundaries are distinct – the dentate gyrus doesn’t abut any other principal cell layers. CA3 and CA1 are easily distinguished from each other based on cell packing density. Probably for this reason there has emerged the assumption that these subregions are homogeneous in function. However, at least for the dentate gyrus it has become clear that it’s two blades are very different. And now, this abstract reports that the CA1 neurons that border region CA3 carry more spatial information than those at the other end, near the subiculum. I’m not entirely sure why I’m interested in this, but it may be because it suggests a certain level of care must be taken in future experiments (e.g. being consistent in where measurements are made) and it argues for better reporting in methods sections as to how measurements were made (because we now know that not all areas of CA1 are equivalent).

Old news gets the shaft

I was recently reading a number of old papers on memory and synaptic tagging and found myself wondering whether they were bloggable. My instincts said yes but the more I thought about it the more I realized they’re several years old and that is ancient by the standards of Twitter and the blogosphere*. I enjoyed reading them but would my readers enjoy them? Is it useful to report on “old” science? If it is then why is it so rare? Continue reading Old news gets the shaft

Increased neurogenesis is not (necessarily) the opposite of reduced neurogenesis

Two recent papers have attracted a lot of media attention because they draw direct links between adult neurogenesis and behavioral disorders: Noonan et al. showed that rats lacking adult neurogenesis (stopped with irradiation) are more susceptible to cocaine addiction. Jin et al. showed that mice lacking adult neurogenesis (using a transgenic model) suffer greater infarct size and have more severe motor deficits after stroke.

While the papers themselves have important implications, what caught my attention was the angle taken by press releases: both articles studied the effects of reducing neurogenesis but the media focused on potential benefits of increasing neurogenesis. See speculation that antidepressants, by increasing neurogenesis, might be stroke-protective here. And, from Science Daily:

While the research specifically focused on what happens when neurogenesis is blocked, the scientists said the results suggest that increasing adult neurogenesis might be a potential way to combat drug addiction and relapse.

It may very well be the case that increasing neurogenesis is good in the same way decreasing neurogenesis is bad but it shouldn’t be assumed – maybe we have all the neurogenesis we need and, while completely arresting neurogenesis could be harmful, increasing neurogenesis beyond normal levels is just redundant. Continue reading Increased neurogenesis is not (necessarily) the opposite of reduced neurogenesis

The first example of functional neurogenesis? I recently became re-acquainted with the neurogenesis literature while writing the last post, re-finding data in papers whose gist, but not details, I had remembered. I reached out a little bit, asking others if I had forgot any studies and indeed I had, including this study by Okano, Pfaff and Gibbs from 1993.

I’ve been interested in new neuron function since 1999 and so I’m actually quite surprised I missed this study until so recently. In 1999 the neurogenesis literature was so scant that it was easy to know ALL of the studies, even the early Altman, Kaplan and Nottebohm studies from the 1960s through 1980s. Even studies that were not interesting were interesting, because there was nothing else to read! So, had I known about it back then, I would have been pretty interested in this study by Okano et al. if only for its focus on cell cycle markers. But I really would have been interested in it because it has a small functional experiment that was way ahead of it’s time:

Continue reading The first example of functional neurogenesis?