Steve M. Potter, PhD - US grants

This study explores the potentials of a new organotypic culture system as a model for in vivo neural transplants, and as a tool for studying the morphological correlates of synaptic plasticity. I will study the development of embryonic rat hippocampal neurons transplanted to cultured hippocampal slices from neonatal rats. I will observe the process of transplant integration while it happens, using time-lapse 2-photon microscopy. I will observe the effects of slice age and transplant location on the neurite outgrowth of transplanted CA1 and CA3 pyramidal neurons. I will quantify dynamic morphological parameters of the transplanted cells, such as neurite growth and retraction rates, branch formation, and cell body migration, in comparison to those of the host cells. Depolarizing agents will be applied to slices during timelapse imaging to see how the overall level of spontaneous activity in the slice influences neural morphology. The findings will be useful to those interested in the bases of learning and memory, and the potential for hippocampal transplants to ameliorate the effects of neurodegenerative disorders, such as Alzheimer's disease.

At present, there is a large gap between in vivo behavioral studies of learning and memory, and in vitro studies of the cellular mechanisms of synaptic plasticity. A neuroscience research tool will be created that bridges this gap by providing a network of cultured cortical neurons with a computer-simulated body, and a virtual reality in which to behave. This new paradigm for studying learning in vitro is enabled by recent advances in computing power and multi-electrode array substrates. A long-term, 2-way interface between a computer and a cultured neural network will be created. Software tools that recognize emergent patterns of network activity will be developed, and used to trigger distributed patterns of electrical stimulation in real time. The effects of this sensory-motor feedback loop will be studied at the millisecond time scale by optical recording using our custom high-speed CCD camera. Changes in neuronal connectivity and morphology will be followed on the scale of minutes, hours and days using our 2-photon laser scanning microscope. Two-photon microscopy allows extended high- resolution imaging of living cells without harming them or bleaching the fluorescent label. It is clear that neural systems process and store information in a distributed fashion. Single-unit neurophysiology research is likely to miss many of the emergent properties of distributed information processing. By combining many-unit electrophysiology and optical recording with non-destructive 2-photon imaging in an in vitro system capable of behaving and learning, it will be possible to observe changes in subcellular, cellular, and network properties that underlie learning and memory. By studying the mechanisms of information processing and storage in small networks of neurons, models of mental impairment from disease or aging can be examined with unprecedented detail. Information about how living neural networks function will promote the creation of more human-like computing systems.