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Neuronal Imaging

One important application area of the hole-refilling technique is neuronal imaging. Self phase modulation (SPM) is sensitive to material structure and we therefore expect SPM properties of neurons to change during neuronal firing. Using the hole-refilling technique we have demonstrated novel intrinsic nonlinear signatures of neuronal activation in hippocampal brain slices of rats with an average power below 500 µW.

Figure 1 displays the experimental setup used to image the response of hippocampal brain slices subject to chemical stimulation. The brain slice is immersed in an artificial CerebroSpinal fluid (ACSF) buffer solution during the experiments. We probe localized regions of hippocampal brain slices as shown in figure 2, and have been typically targeting CA1 neurons. During the experiment, ACSF is continuously flowed through the sample holder. At specific times, a 200µM glutamate solution (glutamate is a neurotransmitter) is introduced to induce neuronal activity for a short period of time. The SPM signals are continuously recorded during the time course of the experiment. We are capable of recording several activations in an experimental run (see figure 3). Since induced scattering changes affect our measurements, we simultaneously record the transmitted light as a way to estimate the contributions of scattering to our signals. Figures 3a and b illustrate that we are capable of extracting the SPM response of neurons subject to chemical stimulation.

Figure 1. Part of the experimental setup used to probe hippocampal brain slices.

Figure 2. (a) Diagram of a hippocampal brain slice showing regions containing different neurons. (b) CA1 neurons are typically targeted in our imaging experiments.

Figure 3. (a) SPM and (b) scattering coefficient changes in a hippocampal brain slice subject to several glutamate stimulations.

Another interesting result of our measurements is depicted in figure 4. Since we are capable of measuring a relatively large area during the time course of the experiment, we have analyzed the spatial dependence of SPM signals and transmitted light before and during glutamate stimulations. Figures 4a and b illustrate that the SPM response is fairly localized before and during chemical activation. This is indicative of possible structural changes that occur in the CA1 region when glutamate-induced neuronal firing events are taking place. The lack of features in the scattered light response and the suppression of activity when an inhibitor is introduced (tetrodotoxin – TTX) further support the fact that we are measuring an SPM response that is localized within the sample. The ability to gain access to this fundamentally new intrinsic contrast mechanism with modest power levels suggests a new approach to in vivo functional imaging.

Figure 4. SPM and transmitted light signals measured at different positions in the sample when (a) only buffer solution is present in the sample and (b) glutamate solution is injected into the sample.


	The Warren Research Group at Duke University Home Research LASERS NMR Publications Personnel Useful Links Contact Neuronal Imaging One important application area of the hole-refilling technique is neuronal imaging. Self phase modulation (SPM) is sensitive to material structure and we therefore expect SPM properties of neurons to change during neuronal firing. Using the hole-refilling technique we have demonstrated novel intrinsic nonlinear signatures of neuronal activation in hippocampal brain slices of rats with an average power below 500 µW. Figure 1 displays the experimental setup used to image the response of hippocampal brain slices subject to chemical stimulation. The brain slice is immersed in an artificial CerebroSpinal fluid (ACSF) buffer solution during the experiments. We probe localized regions of hippocampal brain slices as shown in figure 2, and have been typically targeting CA1 neurons. During the experiment, ACSF is continuously flowed through the sample holder. At specific times, a 200µM glutamate solution (glutamate is a neurotransmitter) is introduced to induce neuronal activity for a short period of time. The SPM signals are continuously recorded during the time course of the experiment. We are capable of recording several activations in an experimental run (see figure 3). Since induced scattering changes affect our measurements, we simultaneously record the transmitted light as a way to estimate the contributions of scattering to our signals. Figures 3a and b illustrate that we are capable of extracting the SPM response of neurons subject to chemical stimulation. Figure 1. Part of the experimental setup used to probe hippocampal brain slices. Figure 2. (a) Diagram of a hippocampal brain slice showing regions containing different neurons. (b) CA1 neurons are typically targeted in our imaging experiments. Figure 3. (a) SPM and (b) scattering coefficient changes in a hippocampal brain slice subject to several glutamate stimulations. Another interesting result of our measurements is depicted in figure 4. Since we are capable of measuring a relatively large area during the time course of the experiment, we have analyzed the spatial dependence of SPM signals and transmitted light before and during glutamate stimulations. Figures 4a and b illustrate that the SPM response is fairly localized before and during chemical activation. This is indicative of possible structural changes that occur in the CA1 region when glutamate-induced neuronal firing events are taking place. The lack of features in the scattered light response and the suppression of activity when an inhibitor is introduced (tetrodotoxin – TTX) further support the fact that we are measuring an SPM response that is localized within the sample. The ability to gain access to this fundamentally new intrinsic contrast mechanism with modest power levels suggests a new approach to in vivo functional imaging. Figure 4. SPM and transmitted light signals measured at different positions in the sample when (a) only buffer solution is present in the sample and (b) glutamate solution is injected into the sample. Website concerns - contact mike.conti@duke.edu