Tag Archives: Leutgeb

#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.

Do new neurons go through a critical period and then retire, never to be used again?

ResearchBlogging.org And here we have the latest, craziest hypothesis of granule cell function. Crazy not because the authors have lost their minds but because the story of the dentate gyrus, where adult neurogenesis occurs, is becoming more peculiar every day. The underlying premise of this paper by Alme et al. (which we will examine later) is that granule neurons go through a critical period during their development when they are more likely to contribute to memory encoding. Here it’s hypothesized that, once the critical period is over, they shut down. Forever. Hundreds of thousands of neurons never to be used again. It’s not every day you get to read such bold and novel ideas. Their hypothesis has similarities with that proposed by Aimone 2006, that adult neurogenesis causes different cohorts of neurons to be immature at different phases of an animal’s life, thereby separating memories according to time. The question here is whether these neurons can be reactivated once their critical period is over. Continue reading Do new neurons go through a critical period and then retire, never to be used again?