Revealing speckle obscured living human retinal cells with artificial intelligence assisted adaptive optics optical coherence tomography

BACKGROUND

In vivo imaging of the human retina using adaptive optics optical coherence tomography (AO-OCT) has transformed medical imaging by enabling visualization of 3D retinal structures at cellular-scale resolution, including the retinal pigment epithelial (RPE) cells, which are essential for maintaining visual function. However, because noise inherent to the imaging process (e.g., speckle) makes it difficult to visualize RPE cells from a single volume acquisition, a large number of 3D volumes are typically averaged to improve contrast, substantially increasing the acquisition duration and reducing the overall imaging throughput.

METHODS

Here, we introduce parallel discriminator generative adversarial network (P-GAN), an artificial intelligence (AI) method designed to recover speckle-obscured cellular features from a single AO-OCT volume, circumventing the need for acquiring a large number of volumes for averaging. The combination of two parallel discriminators in P-GAN provides additional feedback to the generator to more faithfully recover both local and global cellular structures. Imaging data from 8 eyes of 7 participants were used in this study.

RESULTS

We show that P-GAN not only improves RPE cell contrast by 3.5-fold, but also improves the end-to-end time required to visualize RPE cells by 99-fold, thereby enabling large-scale imaging of cells in the living human eye. RPE cell spacing measured across a large set of AI recovered images from 3 participants were in agreement with expected normative ranges.

CONCLUSIONS

The results demonstrate the potential of AI assisted imaging in overcoming a key limitation of RPE imaging and making it more accessible in a routine clinical setting.

Visualization of erythrocyte stasis in the living human eye in health and disease

Blood cells trapped in stasis have been reported within the microcirculation, but their relevance to health and disease has not been established. In this study, we introduce an in vivo imaging approach that reveals the presence of a previously-unknown pool of erythrocytes in stasis, located within capillary segments of the CNS, and present in 100% of subjects imaged. These results provide a key insight that blood cells pause as they travel through the choroidal microvasculature, a vascular structure that boasts the highest blood flow of any tissue in the body. Demonstration of clinical utility using deep learning reveals that erythrocyte stasis is altered in glaucoma, indicating the possibility of more widespread changes in choroidal microvascular than previously realized. The ability to monitor the choroidal microvasculature at the single cell level may lead to novel strategies for tracking microvascular health in glaucoma, age-related macular degeneration, and other neurodegenerative diseases.

Photoreceptor and Retinal Pigment Epithelium Relationships in Eyes With Vitelliform Macular Dystrophy Revealed by Multimodal Adaptive Optics Imaging

Purpose

To assess the structure of cone photoreceptors and retinal pigment epithelial (RPE) cells in vitelliform macular dystrophy (VMD) arising from various genetic etiologies.

Methods

Multimodal adaptive optics (AO) imaging was performed in 11 patients with VMD using a custom-assembled instrument. Non-confocal split detection and AO-enhanced indocyanine green were used to visualize the cone photoreceptor and RPE mosaics, respectively. Cone and RPE densities were measured and compared across BEST1-, PRPH2-, IMPG1-, and IMPG2-related VMD.

Results

Within macular lesions associated with VMD, both cone and RPE densities were reduced below normal, to 37% of normal cone density (eccentricity 0.2 mm) and to 8.4% of normal RPE density (eccentricity 0.5 mm). Outside of lesions, cone and RPE densities were slightly reduced (both to 92% of normal values), but with high degree of variability in the individual measurements. Comparison of juxtalesional cone and RPE measurements (<1 mm from the lesion edge) revealed significant differences in RPE density across the four genes (P < 0.05). Overall, cones were affected to a greater extent than RPE in patients with IMPG1 and IMPG2 pathogenic variants, but RPE was affected more than cones in BEST1 and PRPH2 VMD. This trend was observed even in contralateral eyes from a subset of five patients who presented with macular lesions in only one eye.

Conclusions

Assessment of cones and RPE in retinal locations outside of the macular lesions reveals a pattern of cone and RPE disruption that appears to be gene dependent in VMD. These findings provide insight into the cellular pathogenesis of disease in VMD.

Visualizing retinal cells with adaptive optics imaging modalities using a translational imaging framework

Adaptive optics reflectance-based retinal imaging has proved a valuable tool for the noninvasive visualization of cells in the living human retina. Many subcellular features that remain at or below the resolution limit of current in vivo techniques may be more easily visualized with the same modalities in an ex vivo setting. While most microscopy techniques provide significantly higher resolution, enabling the visualization of fine cellular detail in ex vivo retinal samples, they do not replicate the reflectance-based imaging modalities of in vivo retinal imaging. Here, we introduce a strategy for imaging ex vivo samples using the same imaging modalities as those used for in vivo retinal imaging, but with increased resolution. We also demonstrate the ability of this approach to perform protein-specific fluorescence imaging and reflectance imaging simultaneously, enabling the visualization of nearly transparent layers of the retina and the classification of cone photoreceptor types.

Real-time pixelwise phasor analysis for video-rate two-photon fluorescence lifetime imaging microscopy

Two-photon fluorescence lifetime imaging microscopy (FLIM) is a widely used technique in biomedical optical imaging. Presently, many two-photon time-domain FLIM setups are limited by long acquisition and postprocessing times that decrease data throughput and inhibit the ability to image fast sub-second processes. Here, we present a versatile two-photon FLIM setup capable of video-rate (up to 25 fps) imaging with graphics processing unit (GPU)-accelerated pixelwise phasor analysis displayed and saved simultaneously with acquisition. The system uses an analog output photomultiplier tube in conjunction with 12-bit digitization at 3.2 GHz to overcome the limited maximum acceptable photon rate associated with the photon counting electronics in many FLIM systems. This allows for higher throughput FLIM acquisition and analysis, and additionally enables the user to assess sample fluorescence lifetime in real-time. We further explore the capabilities of the system to examine the kinetics of Rhodamine B uptake by human breast cancer cells and characterize the effect of pixel dwell time on the reduced nicotinamide adenine dinucleotide and reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) autofluorescence lifetime estimation accuracy.

In-vivo sub-diffraction adaptive optics imaging of photoreceptors in the human eye with annular pupil illumination and sub-Airy detection

Adaptive optics scanning light ophthalmoscopy (AOSLO) allows non-invasive visualization of the living human eye at the microscopic scale; but even with correction of the ocular wavefront aberrations over a large pupil, the smallest cells in the photoreceptor mosaic cannot always be resolved. Here, we synergistically combine annular pupil illumination with sub-Airy disk confocal detection to demonstrate a 33% improvement in transverse resolution (from 2.36 to 1.58 μm) and a 13% axial resolution enhancement (from 37 to 32 μm), an important step towards the study of the complete photoreceptor mosaic in heath and disease. Interestingly, annular pupil illumination also enhanced the visualization of the photoreceptor mosaic in non-confocal detection schemes such as split detection AOSLO, providing a strategy for enhanced multimodal imaging of the cone and rod photoreceptor mosaic.

Integrating adaptive optics-SLO and OCT for multimodal visualization of the human retinal pigment epithelial mosaic

In vivo imaging of human retinal pigment epithelial (RPE) cells has been demonstrated through multiple adaptive optics (AO)-based modalities. However, whether consistent and complete information regarding the cellular structure of the RPE mosaic is obtained across these modalities remains uncertain due to limited comparisons performed in the same eye. Here, an imaging platform combining multimodal AO-scanning light ophthalmoscopy (AO-SLO) with AO-optical coherence tomography (AO-OCT) is developed to make a side-by-side comparison of the same RPE cells imaged across four modalities: AO-darkfield, AO-enhanced indocyanine green (AO-ICG), AO-infrared autofluorescence (AO-IRAF), and AO-OCT. Co-registered images were acquired in five subjects, including one patient with choroideremia. Multimodal imaging provided multiple perspectives of the RPE mosaic that were used to explore variations in RPE cell contrast in a subject-, location-, and even cell-dependent manner. Estimated cell-to-cell spacing and density were found to be consistent both across modalities and with normative data. Multimodal images from a patient with choroideremia illustrate the benefit of using multiple modalities to infer the cellular structure of the RPE mosaic in an affected eye, in which disruptions to the RPE mosaic may locally alter the signal strength, visibility of individual RPE cells, or even source of contrast in unpredictable ways.

High-speed label-free two-photon fluorescence microscopy of metabolic transients during neuronal activity

The brain is an especially active metabolic system, requiring a large supply of energy following neuronal activation. However, direct observation of cellular metabolic dynamics associated with neuronal activation is challenging with currently available imaging tools. In this study, an optical imaging approach combining imaging of calcium transients and the metabolic co-enzyme nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) is utilized to track the metabolic dynamics in hippocampal neuron cultures. Results show distinct cellular components for the NAD(P)H response following neuronal activity, where notable differences in the NAD(P)H dynamics between neurons and astrocytes can be directly observed. Additionally, tracking of these responses across a large field of view is demonstrated for metabolic profiling of neuronal activation. Observation of neuronal dynamics using these methods allows for closer examination of the complex metabolic machinery of the brain, and may lead to a better understanding of the cellular metabolism of neuronal activation.

Video-rate multimodal multiphoton imaging and three-dimensional characterization of cellular dynamics in wounded skin

To date, numerous studies have been performed to elucidate the complex cellular dynamics in skin diseases, but few have attempted to characterize these cellular events under conditions similar to the native environment. To address this challenge, a three-dimensional (3D) multimodal analysis platform was developed for characterizing in vivo cellular dynamics in skin, which was then utilized to process in vivo wound healing data to demonstrate its applicability. Special attention is focused on in vivo biological parameters that are difficult to study with ex vivo analysis, including 3D cell tracking and techniques to connect biological information obtained from different imaging modalities. These results here open new possibilities for evaluating 3D cellular dynamics in vivo, and can potentially provide new tools for characterizing the skin microenvironment and pathologies in the future.

Tracking metabolic dynamics of apoptosis with high-speed two-photon fluorescence lifetime imaging microscopy

Programmed cell death, or apoptosis, is an essential process in development and homeostasis, and disruptions in associated pathways are responsible for a wide variety of diseases such as cancer, developmental abnormalities, and Alzheimer's disease. On the other hand, cell death, in many cases, is the desired outcome of therapeutic treatments targeting diseases such as cancer. Recently, metabolic imaging based on two-photon fluorescence microscopy has been developed and shown to be highly sensitive to certain cell death processes, most notably apoptosis, thus having the potential as an advanced label-free screening tool. However, the typically low acquisition rates of this imaging technique have resulted in a limited throughput approach, allowing only a small population of cells to be tracked at well-separated time points. To address this limitation, a high-speed two-photon fluorescence lifetime imaging microscopy (2P-FLIM) platform capable of video-rate imaging is applied to study and further characterize the metabolic dynamics associated with cell death. Building upon previous work demonstrating the capabilities of this system, this microscope is utilized to study rapid metabolic changes during cell death induction, such as dose-dependency of metabolic response, response in invasive vs. noninvasive cancer cells, and response in an apoptosis-resistant cell line, which is further shown to undergo autophagy in response to toxic stimuli. Results from these experiments show that the early apoptosis-related metabolic dynamics are strongly correlated with important cellular parameters including responsiveness to apoptosis-inducing stimuli. The high speed and sensitivity of the presented imaging approach enables new investigations into this highly dynamic and complex process.

Digital staining through the application of deep neural networks to multi-modal multi-photon microscopy

Deep neural networks have been used to map multi-modal, multi-photon microscopy measurements of a label-free tissue sample to its corresponding histologically stained brightfield microscope colour image. It is shown that the extra structural and functional contrasts provided by using two source modes, namely two-photon excitation microscopy and fluorescence lifetime imaging, result in a more faithful reconstruction of the target haematoxylin and eosin stained mode. This modal mapping procedure can aid histopathologists, since it provides access to unobserved imaging modalities, and translates the high-dimensional numerical data generated by multi-modal, multi-photon microscopy into traditionally accepted visual forms. Furthermore, by combining the strengths of traditional chemical staining and modern multi-photon microscopy techniques, modal mapping enables label-free, non-invasive studies of in vivo tissue samples or intravital microscopic imaging inside living animals. The results show that modal co-registration and the inclusion of spatial variations increase the visual accuracy of the mapped results.

High-speed imaging of transient metabolic dynamics using two-photon fluorescence lifetime imaging microscopy

Two-photon fluorescence lifetime imaging microscopy (2P-FLIM) of autofluorescent metabolic coenzymes has been widely used to investigate energetic perturbations in living cells and tissues in a label-free manner with subcellular resolution. While the currently used state-of-the-art instruments are highly sensitive to local molecular changes associated with these metabolic processes, they are inherently slow and limit the study of dynamic metabolic environments. Here, a sustained video-rate 2P-FLIM imaging system is demonstrated for time-lapse lifetime imaging of reduced nicotinamide adenine dinucleotide, an autofluorescent metabolic coenzyme involved in both aerobic and anaerobic processes. This system is sufficiently sensitive to differences in metabolic activity between aggressive and nonaggressive cancer cell lines and is demonstrated for both wide field-of-view autofluorescence imaging as well as sustained video-rate image acquisition of metabolic dynamics following induction of apoptosis. The unique capabilities ofthis imaging platform provide a powerful technological advance to further explore rapid metabolic dynamics in living cells.

In Vivo Assessment of Engineered Skin Cell Delivery with Multimodal Optical Microscopy

The healing process is often significantly impaired under conditions of chronic or large area wounds, which are often treated clinically using autologous split-thickness skin grafts. However, in many cases, harvesting of donor tissue presents a serious problem such as in the case of very large area burns. In response to this, engineered biomaterials have emerged that attempt to mimic the natural skin environment or deliver a suitable therapy to assist in the healing process. In this study, a custom-built multimodal optical microscope capable of noninvasive structural and functional imaging is used to investigate both the engineered tissue microenvironment and the in vivo wound healing process. Investigation of various engineered scaffolds show the strong relationship among the microenvironment of the scaffold, the organization of the cells within the scaffold, and the delivery pattern of these cells onto the healing wound. Through noninvasive tracking of these processes and parameters, multimodal optical microscopy provides an important tool in the assessment of engineered scaffolds both in vitro and in vivo.

Wavefront measurement using computational adaptive optics

In many optical imaging applications, it is necessary to correct for aberrations to obtain high quality images. Optical coherence tomography (OCT) provides access to the amplitude and phase of the backscattered optical field for three-dimensional (3D) imaging samples. Computational adaptive optics (CAO) modifies the phase of the OCT data in the spatial frequency domain to correct optical aberrations without using a deformable mirror, as is commonly done in hardware-based adaptive optics (AO). This provides improvement of image quality throughout the 3D volume, enabling imaging across greater depth ranges and in highly aberrated samples. However, the CAO aberration correction has a complicated relation to the imaging pupil and is not a direct measurement of the pupil aberrations. Here we present new methods for recovering the wavefront aberrations directly from the OCT data without the use of hardware adaptive optics. This enables both computational measurement and correction of optical aberrations.

Investigating the healing mechanisms of an angiogenesis-promoting topical treatment for diabetic wounds using multimodal microscopy

Impaired skin wound healing is a significant comorbid condition of diabetes that is caused by poor microcirculation, among other factors. Studies have shown that angiogenesis, a critical step in the wound healing process in diabetic wounds, can be promoted under hypoxia. In this study, an angiogenesis-promoting topical treatment for diabetic wounds, which promotes angiogenesis by mimicking a hypoxic environment via inhibition of prolyl hydroxylase resulting in elevation or maintenance of hypoxia-inducible factor, was investigated utilizing a custom-built multimodal microscopy system equipped with phase-variance optical coherence tomography (PV-OCT) and fluorescence lifetime imaging microscopy (FLIM). PV-OCT was used to track the regeneration of the microvasculature network, and FLIM was used to assess the in vivo metabolic response of mouse epidermal keratinocytes to the treatment during healing. Results show a significant decrease in the fluorescence lifetime of intracellular reduced nicotinamide adenine dinucleotide, suggesting a hypoxic-like environment in the wounded skin, followed by a quantitative increase in blood vessel density assessed by PV-OCT. Insights gained in these studies could lead to new endpoints for evaluation of the efficacy and healing mechanisms of wound-healing drugs in a setting where delayed healing does not permit available methods for evaluation to take place.

A quantitative framework for the analysis of multimodal optical microscopy images

BACKGROUND

Multimodal optical microscopy, a set of imaging techniques based on unique, yet complementary contrast mechanisms and spatially and temporally co-registered data acquisition, has emerged as a powerful biomedical tool. However, the analysis of the dense, high-dimensional datasets acquired by these instruments remains mostly qualitative and restricted to analysis of each modality individually.

METHODS

Using a custom-built multimodal nonlinear optical microscope, high dimensional datasets were acquired for automated classification of functional cell states as well as identification of histopathological features in tissues slices. Supervised classification of cell death modes was performed through support vector machines (SVM) and semi-supervised classification of tissue slices was performed through the use of the expectation maximization (EM) algorithm.

RESULTS

Applications of these techniques to the automated classification of cell death modes as well as to the identification of tissue components in fixed ex vivo tissue slices are presented. The analysis techniques developed provide a direct link between multimodal image contrast and biological structure and function, resulting in highly accurate classification in both settings.

CONCLUSIONS

Quantification of multimodal optical microscopy images through statistical modeling of the high dimensional data acquired gives a strong correlation between biological structure and function and image contrast. These methods are sensitive to the identification of diagnostic, cellular-level features important in a variety of clinical settings.

Label-free in vivo cellular-level detection and imaging of apoptosis

Cell death plays a critical role in health and homeostasis as well as in the pathogenesis and treatment of a broad spectrum of diseases and can be broadly divided into two main categories: apoptosis, or programmed cell death, and necrosis, or acute cell death. While these processes have been characterized extensively in vitro, label-free detection of apoptosis and necrosis at the cellular level in vivo has yet to be shown. In this study, for the first time, fluorescence lifetime imaging microscopy (FLIM) of intracellular reduced nicotinamide adenine dinucleotide (NADH) was utilized to assess the metabolic response of in vivo mouse epidermal keratinocytes following induction of apoptosis and necrosis. Results show significantly elevated levels of both the mean lifetime of NADH and the intracellular ratio of protein bound-to-free NADH in the apoptotic compared to the necrotic tissue. In addition, the longitudinal profiles of these two cell death processes show remarkable differences. By identifying and extracting these temporal metabolic signatures, apoptosis in single cells can be studied in native tissue environments within the living organism.

In vivo evaluation of adipose- and muscle-derived stem cells as a treatment for nonhealing diabetic wounds using multimodal microscopy

Impaired skin wound healing is a significant comorbid condition of diabetes, which often results in nonhealing diabetic ulcers due to poor peripheral microcirculation, among other factors. The effectiveness of the regeneration of adipose-derived stem cells (ADSCs) and muscle-derived stem cells (MDSCs) was assessed using an integrated multimodal microscopy system equipped with two-photon fluorescence and second-harmonic generation imaging. These imaging modalities, integrated in a single platform for spatial and temporal coregistration, allowed us to monitor in vivo changes in the collagen network and cell dynamics in a skin wound. Fluorescently labeled ADSCs and MDSCs were applied topically to the wound bed of wild-type and diabetic (db/db) mice following punch biopsy. Longitudinal imaging demonstrated that ADSCs and MDSCs provided remarkable capacity for improved diabetic wound healing, and integrated microscopy revealed a more organized collagen remodeling in the wound bed of treated mice. The results from this study verify the regenerative capacity of stem cells toward healing and, with multimodal microscopy, provide insight regarding their impact on the skin microenvironment. The optical method outlined in this study, which has the potential for in vivo human use, may optimize the care and treatment of diabetic nonhealing wounds.

Intraoperative optical coherence tomography for assessing human lymph nodes for metastatic cancer

Background

Evaluation of lymph node (LN) status is an important factor for detecting metastasis and thereby staging breast cancer. Currently utilized clinical techniques involve the surgical disruption and resection of lymphatic structure, whether nodes or axillary contents, for histological examination. While reasonably effective at detection of macrometastasis, the majority of the resected lymph nodes are histologically negative. Improvements need to be made to better detect micrometastasis, minimize or eliminate lymphatic disruption complications, and provide immediate and accurate intraoperative feedback for in vivo cancer staging to better guide surgery.

Methods

We evaluated the use of optical coherence tomography (OCT), a high-resolution, real-time, label-free imaging modality for the intraoperative assessment of human LNs for metastatic disease in patients with breast cancer. We assessed the sensitivity and specificity of double-blinded trained readers who analyzed intraoperative OCT LN images for presence of metastatic disease, using co-registered post-operative histopathology as the gold standard.

Results

Our results suggest that intraoperative OCT examination of LNs is an appropriate real-time, label-free, non-destructive alternative to frozen-section analysis, potentially offering faster interpretation and results to empower superior intraoperative decision-making.

Conclusions

Intraoperative OCT has strong potential to supplement current post-operative histopathology with real-time in situ assessment of LNs to preserve both non-cancerous nodes and their lymphatic vessels, and thus reduce the associated risks and complications from surgical disruption of lymphoid structures following biopsy.

Longitudinal in vivo tracking of adverse effects following topical steroid treatment

Topical steroids are known for their anti-inflammatory properties and are commonly prescribed to treat many adverse skin conditions such as eczema and psoriasis. While these treatments are known to be effective, adverse effects including skin atrophy are common. In this study, the progression of these effects is investigated in an in vivo mouse model using multimodal optical microscopy. Utilizing a system capable of performing two-photon excitation fluorescence microscopy (TPEF) of reduced nicotinamide adenine dinucleotide (NADH) to visualize the epidermal cell layers and second harmonic generation (SHG) microscopy to identify collagen in the dermis, these processes can be studied at the cellular level. Fluorescence lifetime imaging microscopy (FLIM) is also utilized to image intracellular NADH levels to obtain molecular information regarding metabolic activity following steroid treatment. In this study, fluticasone propionate (FP)-treated, mometasone furoate (MF)-treated and untreated animals were imaged longitudinally using a custom-built multimodal optical microscope. Prolonged steroid treatment over the course of 21 days is shown to result in a significant increase in mean fluorescence lifetime of NADH, suggesting a faster rate of maturation of epidermal keratinocytes. Alterations to collagen organization and the structural microenvironment are also observed. These results give insight into the structural and biochemical processes of skin atrophy associated with prolonged steroid treatment.

Effect of recombinant interleukin-12 on murine skin regeneration and cell dynamics using in vivo multimodal microscopy

Interleukin-12 (IL-12) is a pro-inflammatory cytokine known for its role in immunity, and previous studies have shown that IL-12 provides mitigation of radiation injury. In this study, we utilize a multimodal microscopy system equipped with second harmonic generation (SHG) and fluorescence lifetime imaging microscopy (FLIM) to examine the effect of IL-12 on collagen structure and cellular metabolic activity in vivo during skin wound healing. This preliminary study illustrates the highly dynamic and heterogeneous in vivo microenvironment of the wounded skin. In addition, results suggest that IL-12 triggers a significantly more rapid and greater cellular metabolic response in the wounded animals. These results can elucidate insights into the response mechanism of IL-12 in both wound healing and acute radiation syndrome.

Enhancement of optical coherence microscopy in turbid media by an optical parametric amplifier

We report the enhancement in imaging performance of a spectral-domain optical coherence microscope (OCM) in turbid media by incorporating an optical parametric amplifier (OPA). The OPA provides a high level of optical gain to the sample arm, thereby improving the signal-to-noise ratio of the OCM by a factor of up to 15 dB. A unique nonlinear confocal gate is automatically formed in the OPA, which enables selective amplification of singly scattered (ballistic) photons against the multiply-scattered light background. Simultaneous enhancement in both imaging depth and spatial resolution in imaging microstructures in highly light-scattering media are demonstrated with the combined OPA-OCM setup. Typical OCM inteferograms (left) and images (right) without and with OPA.

Computed optical interferometric tomography for high-speed volumetric cellular imaging

Three-dimensional high-resolution imaging methods are important for cellular-level research. Optical coherence microscopy (OCM) is a low-coherence-based interferometry technology for cellular imaging with both high axial and lateral resolution. Using a high-numerical-aperture objective, OCM normally has a shallow depth of field and requires scanning the focus through the entire region of interest to perform volumetric imaging. With a higher-numerical-aperture objective, the image quality of OCM is affected by and more sensitive to aberrations. Interferometric synthetic aperture microscopy (ISAM) and computational adaptive optics (CAO) are computed imaging techniques that overcome the depth-of-field limitation and the effect of optical aberrations in optical coherence tomography (OCT), respectively. In this work we combine OCM with ISAM and CAO to achieve high-speed volumetric cellular imaging. Experimental imaging results of ex vivo human breast tissue, ex vivo mouse brain tissue, in vitro fibroblast cells in 3D scaffolds, and in vivo human skin demonstrate the significant potential of this technique for high-speed volumetric cellular imaging.

In vivo multimodal microscopy for detecting bone-marrow-derived cell contribution to skin regeneration

Bone-marrow (BM)-derived cells have been shown to be capable of aiding skin regeneration in vivo by differentiating into keratinocytes. However, the conditions under which this occurs are not fully understood. Characterizing innate mechanisms of skin regeneration by stem cells in vivo is important for the area of stem cell biology. In this study, we investigate the use of novel in vivo imaging technology for characterizing the contribution of BM-derived cells to regeneration of the epidermis in mouse skin in vivo. In vivo imaging provides the ability to non-invasively observe the spatial positions and morphology of the BM-derived cells. Using a GFP BM-transplanted mouse model and in vivo multimodal microscopy, BM-derived cells can be observed in the skin. Our in vivo imaging method was used to search for the presence and identify the 3D spatial distribution of BM-derived cells in the epidermis of the skin under normal conditions, following wound healing, and after syngeneic skin grafting. We did not observe any evidence of BM-derived keratinocytes under these conditions, but we did observe BM-derived dendritic cells in the skin grafts. In vivo multimodal imaging has great potential for characterizing the conditions under which BM-derived cells contribute to skin regeneration.

In vivo multimodal microscopy for detecting bone-marrow-derived cell contribution to skin regeneration

Bone-marrow (BM)-derived cells have been shown to be capable of aiding skin regeneration in vivo by differentiating into keratinocytes. However, the conditions under which this occurs are not fully understood. Characterizing innate mechanisms of skin regeneration by stem cells in vivo is important for the area of stem cell biology. In this study, we investigate the use of novel in vivo imaging technology for characterizing the contribution of BM-derived cells to regeneration of the epidermis in mouse skin in vivo. In vivo imaging provides the ability to non-invasively observe the spatial positions and morphology of the BM-derived cells. Using a GFP BM-transplanted mouse model and in vivo multimodal microscopy, BM-derived cells can be observed in the skin. Our in vivo imaging method was used to search for the presence and identify the 3D spatial distribution of BM-derived cells in the epidermis of the skin under normal conditions, following wound healing, and after syngeneic skin grafting. We did not observe any evidence of BM-derived keratinocytes under these conditions, but we did observe BM-derived dendritic cells in the skin grafts. In vivo multimodal imaging has great potential for characterizing the conditions under which BM-derived cells contribute to skin regeneration.

Abstract P1-01-23: Intraoperative optical coherence tomography for the assessment of metastatic disease in human lymph nodes

The status of lymph nodes is an important factor in staging cancer since the transport of primary cancer cells via the lymphatic system is one of the main pathways of metastasis to distant organs. During cancer surgery, lymph node status is evaluated via sentinel lymph node biopsy (SLNB), which involves the removal and analysis of the first (or sentinel) nodes along the lymphatic chain of nodes draining the primary tumor. The sentinel nodes are identified through the accumulation of a radioactive agent (technetium-99) and/or isosulfan blue dye within the nodes, frequently resulting in the resection of multiple nodes for subsequent, often time-consuming, histopathological analysis. The majority of these resected nodes are found by histological analysis to be normal, leading to unnecessary complications, including increased risk of lymphedema. Thus, a method for the in situ assessment of node status could reduce the number of normal lymph nodes that are resected. In this study we evaluated the sensitivity and specificity of three-dimensional optical coherence tomography (OCT) for the intraoperative assessment of metastatic disease in lymph nodes.

OCT is the optical analogue to ultrasound imaging, except images are based on the optical scattering properties of near-infrared light. Real-time OCT with micron-scale resolution affords optical biopsies of tissue for immediate feedback. Intraoperative OCT imaging was conducted on human lymph nodes resected from 49 subjects during breast and, head and neck cancer surgeries. Three-dimensional OCT datasets were recorded ex vivo from one or more locations per node, and marked with surgical ink for subsequent correlation to histology. These lymph nodes then underwent the standard histological processing.

A double-blinded study was performed comparing the assessment of OCT datasets to the co-registered histological findings. Three-dimensional -OCT datasets from 206 sites were independently analyzed by six observers and classified as cancerous or non-cancerous. Seventy-nine sets were identified as unsuitable for OCT analysis due to insufficient nodal tissue within the imaged field-of-view. Early training classification results from three of the six observers resulted in a sensitivity of 64.8% and a specificity of 73.3% for identifying metastatic lymph nodes intraoperatively, in real-time, compared to the gold standard of post-operative histopathology. Final study results are expected to improve with observer training and a decision tree for interpreting OCT images.

Our initial imaging studies of resected lymph nodes in human cancer subjects demonstrate the potential of OCT as a technique for real-time optical biopsy of lymph nodes for the intraoperative staging of cancer.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-01-23.

Imaging and tracking of bone marrow-derived immune and stem cells

Bone marrow (BM)-derived stem and immune cells play critical roles in maintaining the health, regeneration, and repair of many tissues. Given their important functions in tissue regeneration and therapy, tracking the dynamic behaviors of BM-derived cells has been a long-standing research goal of both biologists and engineers. Because of the complex cellular-level processes involved, real-time imaging technologies that have sufficient spatial and temporal resolution to visualize them are needed. In addition, in order to track cellular dynamics, special attention is needed to account for changes in the microenvironment where the cells reside, for example, tissue contraction, stretching, development, etc. In this chapter, we introduce methods for real-time imaging and longitudinal tracking of BM-derived immune and stem cells in in vivo three-dimensional (3-D) tissue environments with an integrated optical microscope. The integrated microscope combines multiple imaging functions derived from optical coherence tomography (OCT) and multiphoton microscopy (MPM), including optical coherence microscopy (OCM), microvasculature imaging, two-photon excited fluorescence (TPEF), and second harmonic generation (SHG) microscopy. Short- and long-term tracking of the dynamic behavior of BM-derived cells involved in cutaneous wound healing and skin grafting in green fluorescent protein (GFP) BM-transplanted mice is demonstrated. Methods and algorithms for nonrigid registration of time-lapse images are introduced, which allows for long-term tracking of cell dynamics over several months.

BDNF and NT3 extend the critical period for developmental climbing fibre plasticity

The effect on neonatal brain plasticity of two neurotrophins, brain derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), was studied using the rat olivocerebellar projection as a model. Unilateral transection of climbing fibres (CFs) in the rat before postnatal day 7 induces reinnervation of the deafferented hemicerebellum, but this does not occur if the transection is performed after postnatal day 10. Eleven-day-old day rats underwent unilateral CF transection followed by neurotrophin injection into the denervated cerebellar cortex 24 h later. The exogenous neurotrophins induced CF reinnervation of the denervated hemicerebellum. However BDNF was more efficacious than NT-3. Thus two neurotrophins can extend the window of neonatal brain plasticity, therefore suggesting potential therapeutic use after brain trauma.

Localization of low affinity nerve growth factor receptor in the rat inferior olivary complex during development and plasticity of climbing fibres

The rat olivocerebellar pathway has a precise topography from an inferior olive (IOC) to Purkinje cells in the contralateral hemicerebellum. While its development and plasticity have been documented, the molecular mechanisms underlying these events are not fully elucidated. Neurotrophins are a family of growth factors with diverse roles in development and neuronal plasticity, acting through a two-receptor system, including a low affinity receptor (LNGFR) which binds all neurotrophins with similar affinity. Since neurotrophins are present in the cerebellum during early postnatal development when LNGFR is synthesized in the IOC, they may act as target-derived trophic agents for climbing fibres during development and plasticity. To assess this, standard immunohistochemistry was used to document the distribution of LNGFR in the rat IOC during climbing fibre development and until cerebellar development was complete at postnatal day 28 (P28). LNGFR immunoreactivity (LNGFR-IR) was detected in the IOC from P0 until P15, however after P7 it diminished in intensity and distribution, a change which indicates a relationship between cerebellar neurotrophins and climbing fibre development. After denervation of the left hemicerebellum, there was an apparent increase in inferior olivary LNGFR-IR that was concurrent with climbing fibre re-innervation. Thus the results of this study support the hypothesis that neurotrophins are involved in climbing fibre development and suggest a possible contribution to the plasticity of the olivocerebellar pathway.

Changes in the numbers of neurons and astrocytes during the postnatal development of the rat inferior olive

In the developing nervous system, cell death is an important component of refining axonal projections. In the developing rat inferior olive, previous studies have demonstrated cell death as temporally incongruent with both initial axon-target interactions and subsequent axon collateral regression. Furthermore, these studies identified a late rise in neuron numbers that is concurrent with climbing fibre regression. As axonal regression has not previously been associated with increasing neuron numbers, and since immature neurons and glia have similar morphological characteristics, it was decided to reassess the timing of cell death within the inferior olive in animals in which neurons and glia had been differentially stained. Glia were identified by the presence of glial cytoskeletal proteins, S100, or glial fibrillary acidic protein, and stereological counts were made of both neurons and glia in the inferior olive from rats of ages 0, 5, 10, 15, and 30 days. The number of inferior olivary neurons was approximately 22,000 between birth and day 10, which decreased to about 17,500 by day 30 (P<0.05). In contrast, the number of glia rose from about 5,000 at birth to approximately 15,000 by day 10 (P<0.001), after which there was no further increase. The changes in neurons and glia caused the neuron-to-glia ratio to fall to approximately 1.5 by the time of functional maturation within the olive. These results confirm that there is neuronal death in the inferior olive but that it is temporally correlated with both climbing fibre regression and functional maturation of the olivocerebellar projection.

Role of afferents in the development and cell survival of the vertebrate nervous system

1. During normal development of the vertebrate central nervous system, a considerable number of neurons die. The factors controlling which neurons die and which survive are not fully understood. 2. Target populations are known to maintain their innervating neurons. However, the role of afferents in maintaining their targets is still under review. 3. In the developing nervous system, deafferentation of a neuron population is difficult to achieve because plasticity (structural re-organization) can cause re-innervation of the area. Re-innervation alters, rather than removes, the afferent supply. 4. Afferent input is important for neuronal survival during development because deafferentation increases neuronal death by 20-30% and increasing input diminishes neuronal death. 5. Deafferented neurons die at the normal time for cell death for any given population. This occurs after the arrival of afferent axons but before the completion of connectivity and the onset of function. 6. Neuronal survival is maintained by any input, such as reinnervation by inappropriate fibres, but for optimal survival, morphological maturation and the acquisition of normal physiology, the correct input is required. 7. Afferents maintain their target neurons via a combination of electrical activity and delivery of trophic agents, which adjust intracellular calcium, thereby facilitating protein synthesis, mitochondrial function and suppressing apoptosis. 8. Evidence from animal and in vitro experiments indicates that afferents play an extremely important role in the survival of developing neurons in the immature vertebrate nervous system.

Changes in the hippocampus induced by glucose in thiamin deficient rats detected by MRI

Using T2-weighted Magnetic Resonance Imaging (MRI) in a pyrithiamin-treated, thiamin deficient (TD) rat model of Wernicke's encephalopathy (WE), we have observed hyperintensity in the thalamus, hypothalamus, collicular bodies and hippocampus which was enhanced 40 min after a glucose load. Hyperintensity was not evident in these structures in thiamin replete rats receiving glucose nor was it enhanced in TD rats administered 2-deoxyglucose. Residual hyperintensity was still evident in the hippocampus as long as 30 days after thiamin administration and was increased by repeat glucose challenge at that time. These data indicate that the hippocampus is as vulnerable as the thalamus to some persistent pathological change when glucose is metabolised in a state of thiamin deficiency.

Acute neuronal and vascular changes following unilateral cerebellar pedunculotomy in the neonatal rat

During development of the central nervous system (CNS) both deafferentation and axotomy induce increased neuronal death and result in a smaller brain with diminished function at maturity. Unilateral cerebellar pedunculotomy has been used as a model to study the relative importance of these 2 types of lesion on the survival of developing CNS neurons. Within the cerebellum, unilateral pedunculotomy causes deafferentation of the hemicerebellum and axotomy in the efferent pathway from the ipsilateral deep cerebellar nuclei. This results in a smaller hemicerebellum with normal cortical laminae but no extracerebellar outflow. In order to identify the sequence of events which leads to this altered structure and therefore to understand the relative importance of afferent versus target-derived trophic support, unilateral cerebellar pedunculotomy was performed on neonatal rat pups, aged between 1 and 3 days. The cerebella were analysed for histological and vascular changes after survival times of 0, 3, 6, 9, 12, 18, 21, 24 and 48 h. The results show that the effects of axotomy on the deep cerebellar nuclear neurons begin within 3 h of the lesion and apoptotic neuronal degeneration occurs within 48 h. However, the cerebellar cortical neurons continue to undergo normal histological development for at least 48 h after deafferentation. In addition, since ischaemia induces similar effects, a study of the vascular tree was made. The results indicate that the pedunculotomy does not alter the blood supply to the cerebellum, nor induce ischaemia of the cerebellar neurons. From this it may be hypothesised that target-derived trophic support is more crucial for the survival of immature neurons than is the trophic effect of afferent input.

MRI demonstration of impairment of the blood-CSF barrier by glucose administration to the thiamin-deficient rat brain

Contrast-enhanced T1-weighted spin-echo magnetic resonance imaging (MRI) has demonstrated that Gd-diethylenetriaminepentaacetate (Gd-DTPA), which normally does not cross the blood-brain or blood-CSF barriers, does so approximately 40 min after administration of glucose to a vitamin B1 deficient rat. The period of the onset of this blood-CSF or blood-brain barrier dysfunction coincides with our previous observations of accumulation of glutamate or glutamate derivatives following an equivalent glucose load under identical conditions of thiamin deficiency, consistent with a relationship between these two observations. The dysfunction was reversed when a thiamin deficient animal was made thiamin replete.

Plasticity in the adult and neonatal central nervous system

The adult nervous system is capable of plastic change; studies have shown that plasticity is part of normal adaptation to daily life as well as being part of the response to trauma. The structural substrates of plastic change are described, and the hypotheses for explaining functional recovery in adults following trauma are reviewed. Events in normal brain development are summarized, and experiments designed to investigate the processes involved are described. The brain of the neonate is a much more plastic structure than that of the adult, both in normal development and in response to trauma. Activity in pathways is an essential component for consolidation of connections, whether normal or compensatory. Experiments which elucidate the mechanisms of axonal/target recognition are described. Recent work on the possible development of therapeutic agents to enhance recovery from trauma, in both adults and neonates, is reviewed. An attempt is made to link the findings from basic research to the clinical field.

Cerebellar afferents in early postnatal rats: a retrograde fluorescence study

The development of afferent projections to the cerebellum was studied by making small (20 nl) injections of True blue into the cerebella of neonatal rats under general anaesthesia. Neurones in all main precerebellar nuclei were labelled even in rats less than one day old. With the exception of the disappearance of small numbers of ipsilateral olivocerebellar projections, no qualitative differences were seen after injections in animals one or two weeks older.

Effects of partial truncal vagotomy on intragastric pressure responses to vagal stimulation and gastric distension in ferrets

Changes in intragastric pressure after dorsal truncal vagotomy, investigated by stimulation of the surviving vagal branches and by step inflation of the stomach, were divided into an early phase lasting five days, and a late phase continuing for at least three months. During the early phase the amplitude of vagal evoked contraction was diminished but the resting pressure and the response to gastric inflation were increased. After the fifth day vagal evoked contractions doubled in amplitude but the resting pressure and the response to step inflation of the stomach returned to control levels. Ventral vagotomy did not produce any substantial changes. Alterations to gastric and body weight, or to the relation between resting pressure and evoked contraction and relaxation were excluded as causes of the enhanced vagal effectiveness. Sprouting of axons into denervated territory occurred too late to explain the changes, but an increase in synaptic density within the innervated territory has not been ruled out.

An ipsilateral olivocerebellar pathway in the normal neonatal rat demonstrated by the retrograde transport of true blue

Neonatal rats, aged less than 24 h, were anaesthetised and 25 nl of 2% True blue was injected into the lateral part of the left cerebellar hemisphere. After 48-60 h, the brains were fixed by perfusion and 30 micron thick frozen sections were prepared of the brainstem and cerebellum. Only animals in which the injection sites were clearly unilateral were studied. In the contralateral inferior olive numerous True blue-labelled neurones were seen. In addition, the ipsilateral olive in all animals contained True blue-labelled neurones. This demonstrates that in these neonatal animals there is an ipsilateral olivocerebellar pathway.

An electron microscope study of vagus nerve composition in the ferret

The total number of axons in the cervical and abdominal vagus nerves of the ferret was counted. The ratio of myelinated to non-myelinated, and afferent to efferent axons was determined. The fibre diameter spectrum of myelinated axons was measured. The total number of axons in the ferret cervical vagus is similar to other mammals (approximately 28,000); the majority of axons are afferent (approx. 24,000) and also the majority of axons are nonmyelinated (approx. 27,000). The dorsal abdominal trunk is about twice the size of the ventral trunk although both trunks have the same number of efferent axons. The abdominal vagal trunks are over 90% afferent.

The effect of unilateral cerebellar pedunculotomy on the vascular development of the neonatal rat cerebellum

After cerebellar pedunculotomy the density of the blood vessel network in the cerebellar cortex was not different from that in the control animals. But the pattern of the blood vessels was different, being less organized in the operated animals.

Rate of degeneration of a neonatal ipsilateral olivocerebellar pathway revealed by unilateral cerebellar pedunculotomy in the rat

This series of experiments tested the rate of degeneration of a recently demonstrated ipsilateral olivocerebellar pathway that followed unilateral cerebellar pedunculotomy in the neonatal rat. Animals aged either 3 or 10 days were anesthetized and subjected to a left cerebellar pedunculotomy; at the same time [3H]leucine was injected into the right inferior olive. The results indicated that there was climbing fiber labeling in the cerebellum, the extent of which depended on the age at which the experimental procedures were carried out.

Innervation of the adult rat cerebellar hemisphere by fibres from the ipsilateral inferior olive following unilateral neonatal pedunculotomy: an autoradiographic and retrograde fluorescent double-labelling study

A left cerebellar pedunculotomy was carried out in neonatal rats of different ages to deprive the left cerebellar hemisphere of its normal climbing fibre input. In control adult animals this is totally crossed and thus arises only from the contralateral (right) inferior olive. After pedunculotomy, only the left inferior olive was intact, the right being degenerated. The remaining olivocerebellar pathway was investigated using anterograde autoradiographic or retrograde fluorescent double-labelling techniques. The anterograde autoradiographic technique showed that, in these animals, the remaining left inferior olive had an aberrant climbing fibre projection which travelled via the intact right inferior cerebellar peduncle to the denervated left hemicerebellum. If the pedunculotomy was carried out at 3 days of age (P3), this aberrant projection closely mirrored the normal pathway to the opposite hemisphere; pedunculotomy at P7 produced a different pattern of projection; while if the operation was done at P10 there was no new projection. True blue (TB) and diamidino yellow (DY) were injected into the denervated (left) and normal (right) cerebellar hemispheres respectively. Retrograde transport of these tracers confirmed both the aberrant ipsilateral projection and the normal crossed projection from neurons in the remaining inferior olive. Most of the ipsilaterally projecting neurons were in the medial accessory olive. As none of them were double-labelled, it was concluded that the new projection is not a collateral of normally projecting olivary neurons, but arises from a separate population of cells. The significance of these findings in relation to earlier work on this system is discussed.

An ipsilateral olivocerebellar connection: an autoradiographic study in the unilaterally pedunculotomised neonatal rat

Using autoradiographic techniques the olivocerebellar pathway was investigated in neonatal rats which had undergone a left cerebellar pedunculotomy on postnatal day 7 (p7). Tritiated (3H) leucine was injected into the right inferior olive at the same time as the pedunculotomy and the animals were allowed to survive for two or four days. Autoradiographs were then made of the brainstem and the cerebellum. Only those animals which had had a total left cerebellar pedunculotomy and in which the 3H-leucine did not spill into the left inferior olive were included in the experiment. The results showed the presence of climbing fibres in the cerebellar hemisphere ipsilateral to the injection site, arranged in sagittal bands and topographically organised. The only route for those fibres to enter the cerebellum is through the inferior cerebellar peduncle ipsilateral to the injected olive which is a pathway not present in the adult animal. The possible explanations for these results are discussed.

Brainstem connections of vagal afferent nerves in the ferret: an autoradiographic study

Using an autoradiographic technique the central connections of vagal afferent fibres in the ferret were studied. The results show that the principal site of termination is the ipsilateral nucleus of the tractus solitarius with smaller projections to the contralateral tractus nucleus, the dorsal motor nucleus of the vagus and the area postrema and subpostrema. The fibres cross the midline via the commissural nucleus of Cajal. No evidence of vagal afferent fibres was found in the reticular formation, the spinal tract of the trigeminal nerve, the external cuneate nucleus or the dorsal horns of the first and second cervical spinal segments. The findings from all studies using axon tracing techniques on vagal afferent fibres are summarised.

Rat cerebellar afferents after unilateral pedunculotomy. A retrograde fluorescent double-labelling study

Cerebellar afferents from the lateral reticular nucleus (LRN) and inferior olive (IO) were investigated using retrograde fluorescent labelling in rats subjected to a unilateral inferior cerebellar pedunculotomy at 6-8 days of age. The remaining (ipsilateral) IO of the operated group was essentially the same as in control animals but the remaining (contralateral) LRN in the operated group had a greater percentage of neurones with collaterals to both sides of the cerebellum.

The effects of neonatal pedunclectomy on [3H]noradrenaline uptake and the development of beta-adrenergic receptors in the rat cerebellum

A newly developed method for cutting the cerebellar peduncles in neonatal rats has allowed the study of the development of cerebellar beta-adrenergic receptors in the absence of noradrenergic afferents. Cutting the cerebellar peduncles of neonatal animals did not affect the pattern of development of the beta-adrenergic receptors, nor their final numbers. Pedunclectomy induced a decline in the ability of slices of cerebellar cortex to accumulate [3H]noradrenaline although high-affinity noradrenaline uptake, was never completely abolished. It is suggested that the remaining high-affinity noradrenaline uptake cannot be attributed to noradrenergic fibres from the locus coeruleus.

An autoradiographic study of the brainstem projections of vagal visceral afferent fibres in the domestic hen

Using an autoradiographic technique, the central brainstem connections of vagal visceral afferent fibres were studied. The results show that there is a large projection of vagal afferent fibres to the ipsilateral nucleus of the tractus solitarius and a smaller, sparser projection to the contralateral nucleus of the tractus solitarius. That vagal afferent fibres across the mid-line via the commissural nucleus of Cajal is confirmed. In addition, a second, more rostrally placed decussation of vagal afferent fibres is shown. Associated with this more rostral decussation is an area of termination of vagal afferent fibres in the contralateral ventromedial reticular formation. No direct projection of vagal afferent fibres to the dorsal motor nucleus of the vagus was seen.