Functional optical coherence tomography of rat olfactory bulb with periodic odor stimulation

Abstract

Abstract:In rodent olfactory bulb (OB), optical intrinsic signal imaging (OISI) is commonly used to investigate functional maps to odorant stimulations. However, in such studies, the spatial resolution in depth direction (z-axis) is lost because of the integration of light from different depths. To solve this problem, we propose functional optical coherence tomography (fOCT) with periodic stimulation and continuous recording. In fOCT experiments of in vivo rat OB, propionic acid and m-cresol were used as odor stimulus presentations. Such a periodic stimulation enabled us to detect the specific odorresponses from highly scattering brain tissue. Swept source OCT operating at a wavelength of 1334 nm and a frequency of 20 kHz, was employed with theoretical depth and lateral resolutions of 6.7 μm and 15.4 μm, respectively. We succeeded in visualizing 2D cross sectional fOCT map across the neural layer structure of OCT in vivo. The detected fOCT signals corresponded to a few glomeruli of the medial and lateral parts of dorsal OB. We also obtained 3D fOCT maps, which upon integration across z-axis agreed well with OISI results. We expect such an approach to open a window for investigating and possibly addressing toward inter/intra-layer connections at high resolutions in the future. 181-192 (1997). 33. Y. Nakamichi, V. A. Kalatsky, H. Watanabe, U. M. Rajagopalan, and M. Tanifuji, "3D structure of the orientation column in cat primary cortex revealed by functional optical coherence tomography," Abstr. Soc. Neurosci. 270. 01 (2011), http://www.abstractsonline.com/Plan/ViewAbstract.aspx?sKey=d023089b-a64b-4aa9-b3cb-6129bde54e45&cKey=09b7566c-c153-4692-8113-1a04e1af0b1d&mKey=%7b8334BE29-8911-4991-8C31- 3067-3086 (2012).

Optical coherence tomography imaging of evoked neural activity in sciatic nerve of rat

“…Haemodynamic effects were not present in the current study because the subjects were recently deceased cadavers. Phase [13][14][15][16] and retardation [25,32] signals observed in previous studies were not visible above the noise level in the current study. One possible reason for this lack of signal is the use of unmyelinated nerve tissue or neurons in previous studies.…”

“…Depth dimension processing. Four signal properties were analysed for neural activity based on existing studies: intensity [11,14], phase retardation [25], phase [13][14][15], and frequency spectra [33]. To determine these properties for each A-scan, raw data from each polarisation channel was Hanning windowed, zero-padded to 2 14 points, then Fourier transformed to produce complex signals of the form:…”

“…Slow changes caused by haemodynamics occur in the order of seconds and have been imaged in cortex using intravascular tracer [22], doppler [23], and spectroscopic [24] based OCT techniques which analyse the properties of several temporally spaced B-scans. While fast changes caused by electrical activity occur in the order of milliseconds, and have been imaged in abdominal ganglion of sea slug and in unmyelinated axons of squid and crayfish using intensity [11,14], birefringence [25], and phase [13][14][15] based OCT techniques applied to images with one spatial (depth) and one temporal dimension, called an M-scan, or in one study [25] with temporally spaced Bscans. Researchers have also measured both the hemodynamic and electrophysiological changes in mammalian cortical tissue using intensity-based OCT techniques by employing prolonged stimulus durations [26][27][28] and during artificially induced epileptiform activity [29].…”

“…Researchers have also measured both the hemodynamic and electrophysiological changes in mammalian cortical tissue using intensity-based OCT techniques by employing prolonged stimulus durations [26][27][28] and during artificially induced epileptiform activity [29]. While the results of these studies [11,[13][14][15][22][23][24][25][26][27][28][29] demonstrate great promise for OCT in functional imaging of neural activity, in several studies [11,[13][14][15]25] the tissues were non-mammalian and so are not easily translatable to clinical applications for humans, and in all studies the tissues were unmyelinated and so differ in cytostructure from myelinated fibres, figures 1(a) and (b). Expanding functional imaging with OCT from unmyelinated fibres and neurons to myelinated fibres is important because the latter have distinct roles in communication within the central and peripheral nervous systems, and unique pathologies, such as multiple sclerosis [30].…”

Extended-focus optical coherence microscopy for high-resolution imaging of the murine brain

“…The method must be non-contact for the comfort of the animal (reduction of extraneous uncontrollable stimuli) and support high ergonomics in the imaging system-especially by maintaining a sufficiently long working distance to manipulate the imaging subject and thus perform multiple imaging sessions using the same animal. Previous literature shows that optical coherence microscopy (OCM) has a considerable potential in comprehensive rodent brain imaging, can deliver extensive useful information about its structure [8] and function [9,10], and fulfills most of the mentioned prerequisites. Additionally, it has been successfully utilized in many diverse aspects of brain research [11].…”