Robert C. Froemke, PhD
Assistant Professor of Physiology and Neuroscience
Ph.D., 2004 University of California, Berkeley
Developmental neurobiology, Neuronal Plasticity, Sensory Systems
Neuroscience, Physiology, Brain Repair, Plasticity
New York University School of Medicine
540 First Avenue, Floor 5, Room 9
New York, NY 10016
Tel: (212) 263-4082
Fax: (212) 263-7760
Transplantation of stem cells or progenitor cells into host tissue may be a promising method for repairing aged, damaged, or diseased organs. This is especially true for neural circuits of the cerebral cortex, which are believed to lack endogenous neural stem cells of their own in adult humans. Brain damage that occurs after stroke, chronic epilepsy, or in Alzheimers and Parkinsons patients may be reversible after cell transplantation, but knowledge of how cellular grafts interact with and affect native tissues is sorely lacking.
We study the efficacy of interneuron progenitor cell transplants for brain repair in rodent models. Previously we have discovered that transplantation of tissue from the embryonic medial ganglionic eminence- a main source of interneuron precursors for the developing cerebral cortex- leads to functional integration of these new cells into recipient neural networks. Compared to young brains, neural circuits in older animals are normally less plastic, i.e., have less capacity to change, to be modified by sensory experience, and to withstand and recover from injury or disruptive episodes. However, transplantation of embryonic progenitor cells rejuvenates the cortex, and opens a new period of heightened neuroplasticity in adult animals (Southwell et al., Science 2010; Southwell et al., Nature 2012).
We currently use a combination of methods, including electrophysiology (recording from pairs of native and transplanted cells), molecular biology and pharmacology (to disrupt or induce specific signaling pathways or gene expression), and computational approaches to ask two main questions related to the incorporation of new neurons into extant circuitry.
First, how many new cells can be supported by the existing tissue? After overloading the adult cortex with many more interneuron precursors, the majority of these new cells are culled within several days, although a large fraction is maintained indefinitely. We aim to determine what factors and activity patterns allow certain progenitor cells to fully and persistently integrate into the rest of the cortex, while other cells do not survive.
Second, how does the addition of new interneurons promote plasticity within neural networks? We hypothesize that a switch from a smaller number of relatively strong synapses (before transplantation) to a larger number of relatively weak synapses (as we discovered after transplantation) is critical, keeping the total synaptic drive relatively constant, while making it much easier for any one particular synapse to be changed by variations in sensory experience.
A future project will involve testing the effects of interneuron transplantation in behaving animals, to ask whether such cell grafts can directly enhance sensory perception (particularly in aged animals with degraded sensory representations), or might lead to gains in task performance.
- Froemke, R.C., et al. (2013). Long-term modification of cortical synapses improves sensory perception. Nature Neuroscience 16, 79-88. PMID: 23178974
- Southwell, D.G., et al. (2012). Intrinsically determined cell death of developing cortical interneurons. Nature 491, 109-113. PMID: 23041929
- Dorrn, A.L., Yuan, K., Barker, A.J., Schreiner, C.E., and Froemke, R.C. (2010). Developmental sensory experience balances cortical excitation and inhibition. Nature 465, 932-936. PMID: 20559387
- Southwell, D.G., Froemke, R.C., Alvarez-Buylla, A., Stryker, M.P., and Gandhi, S.P. (2010). Cortical plasticity induced by inhibitory neuron transplantation. Science 327, 1145-1148. PMID: 20185728
- Froemke, R.C.,Merzenich, M.M., and Schreiner, C.E. (2007). A synaptic memory trace for cortical receptive field plasticity. Nature 450, 425-429. PMID: 18004384