#SFN10 Itinerary Pt. 2

Continuing on…

1) 31.20/C37 – Dentate network activity modulates integration of newborn granule cells
*F. KLEINE BORGMANN¹, J. GRÄFF², N. TONI³, I. M. MANSUY^4,5, S. JESSBERGER¹;
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?
F. T. SPARKS*¹, E. A. MANKIN*², B. SLAYYEH², R. J. SUTHERLAND¹, *J. K. LEUTGEB²;
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
*G. D. CLEMENSON, JR, F. H. GAGE;
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.