#SFN10 Intinerary Pt. 3 – Mossy Fibers!

…and now for what is probably my final pre-SFN post. Posters dealing with mossy fiber function!

1) 405.14/MMM34Mossy fiber input for pattern separation and pattern completion
*T. NAKASHIBA1, J. CUSHMAN2, K. A. PELKEY3, C. J. MCBAIN3, M. S. FANSELOW2, S. TONEGAWA1;
1The RIKEN-MIT Ctr. For Neural Circuit Genetics, The Picower Inst. For Lear, CAMBRIDGE, MA; 2Dept. of Psychology, UCLA, Los Angeles, CA; 3NICHD, NIH, Bethesda, MD

So by inserting, like, 27 transgenes a mouse was created where the mossy fibers, the axons that connect the dentate gyrus to CA3, can be inducibly silenced. Since there are a number of pathways that connect the cortex to CA3 this looks like an effective way to determine the importance of this one pathway for behavior and physiology. It appears that the mossy fiber pathway promotes a pattern completion function rather than a pattern separation function. Using discriminative contextual fear paradigms, mice lacking mossy fiber functionality were better at discriminating related contexts, and worse at a task that required them to treat related contexts differently.

2) 709.24/MMM74 – Increased connectivity with inhibitory interneurons underlies functional integration of newborn neurons in the dentate gyrus of the hippocampus
*L. RESTIVO1, M. SAKAGUCHI1, P. W. FRANKLAND1,2,3;
1Program in Neurosciences & Mental Hlth., The Hosp. For Sick Children, Toronto, ON, Canada; 2Inst. of Med. Sci., 3Dept. of Physiol., Univ. of Toronto, Toronto, ON, Canada

Using a GFP retrovirus, this looks to be latest of only a few studies of the mossy fiber output of new neurons. And the only one that has looked at new neuron mossy fiber synaptogenesis in response to learning (recently it was shown that learning alters afferent synaptogenesis in new neurons). Basically, it appears that new neurons, after water maze training, have increased synaptogenesis onto inhibitory interneurons without any change in the number and size of synapses onto excitatory principal CA3 neurons. Neat-O.

3) 100.8/KKK24 – Encoding to consolidation: An optogenetic probe reveals continuous modulation of hippocampal information processing by behavioral state
*C. KEMERE1, M. F. CARR1, M. P. KARLSSON2, F. ZHANG3, K. DEISSEROTH4, L. M. FRANK1;
1UCSF, San Francisco, CA; 2HHMI-Janelia Farm, Ashburn, VA; 3Society of Fellows, Harvard Univ., Cambridge, MA; 4Stanford Univ., Stanford, CA

The results are a little vague but the question and method are both pretty interesting here. Directing channelrhodopsin to dentate gyrus neurons and using a probe that can both light-activate those neurons and simultaneously record from downstream CA3 and CA1 these authors examined how dentate gyrus activation modulates activity in CA3/CA1 during different behavioral states. And they argue that information processing does not simply alternate between discrete states during locomotion vs. stillness/sleep, but rather that there is a continuum between these states that varies with how fast the animal is moving.