Wilbrand knee.

Wilbrand and Saenger(1) studied optic chiasms after unilateral enucleation, noting inferonasal crossing fibers curved anteriorly into the contralateral optic nerve (Wilbrand knee; figure, A). This explains contralateral superotemporal visual field defects (junctional scotomas) with optic nerve lesions at the chiasmal junction. However, Wilbrand knee may be an enucleation artifact.(2) The anisotropic light-reflecting properties of myelinated axons permitted imaging of normal human chiasms. Thin sections (25 µm) were illuminated and digitally imaged from 3 incident angles. Each of the images was pseudocolored (red, green, or blue) and merged, revealing an anomalously oriented fiber tract (appearing white) that reversed direction at the optic nerve-chiasm junction, found in inferior (figure, C) but not in superior sections (figure, B), consistent with Wilbrand and Saenger's original description.

Coherence-gated Doppler: a fiber sensor for precise localization of blood flow.

Miniature optical sensors that can detect blood vessels in front of advancing instruments will significantly benefit many interventional procedures. Towards this end, we developed a thin and flexible coherence-gated Doppler (CGD) fiber probe (O.D. = 0.125 mm) that can be integrated with minimally-invasive tools to provide real-time audio feedback of blood flow at precise locations in front of the probe. Coherence-gated Doppler (CGD) is a hybrid technology with features of laser Doppler flowmetry (LDF) and Doppler optical coherence tomography (DOCT). Because of its confocal optical design and coherence-gating capabilities, CGD provides higher spatial resolution than LDF. And compared to DOCT imaging systems, CGD is simpler and less costly to produce. In vivo studies of rat femoral vessels using CGD demonstrate its ability to distinguish between artery, vein and bulk movement of the surrounding soft tissue. Finally, by placing the CGD probe inside a 30-gauge needle and advancing it into the brain of an anesthetized sheep, we demonstrate that it is capable of detecting vessels in front of advancing probes during simulated stereotactic neurosurgical procedures. Using simultaneous ultrasound (US) monitoring from the surface of the brain we show that CGD can detect at-risk blood vessels up to 3 mm in front of the advancing probe. The improved spatial resolution afforded by coherence gating combined with the simplicity, minute size and robustness of the CGD probe suggest it may benefit many minimally invasive procedures and enable it to be embedded into a variety of surgical instruments.

A forward-imaging needle-type OCT probe for image guided stereotactic procedures.

A forward-imaging needle-type optical coherence tomography (OCT) probe with Doppler OCT (DOCT) capability has the potential to solve critical challenges in interventional procedures. A case in point is stereotactic neurosurgery where probes are advanced into the brain based on predetermined coordinates. Laceration of blood vessels in front of the advancing probe is an unavoidable complication with current methods. Moreover, cerebrospinal fluid (CSF) leakage during surgery can shift the brain rendering the predetermined coordinates unreliable. In order to address these challenges, we developed a forward-imaging OCT probe (740 µm O.D.) using a gradient-index (GRIN) rod lens that can provide real-time imaging feedback for avoiding at-risk vessels (8 frames/s with 1024 A-scans per frame for OCT/DOCT dual imaging) and guiding the instrument to specific targets with 12 µm axial resolution (100 frames/s with 160 A-scans per frame for OCT imaging only). The high signal-to-background characteristic of DOCT provides exceptional sensitivity in detecting and quantifying the blood flow within the sheep brain parenchyma in real time. The OCT/DOCT dual imaging also demonstrated its capability to differentiate the vessel type (artery/vein) on rat's femoral vessels. We also demonstrated in ex vivo human brain that the location of the tip of the OCT probe can be inferred from micro-anatomical landmarks in OCT images. These findings demonstrate the suitability of OCT guidance during stereotactic procedures in the brain and its potential for reducing the risk of cerebral hemorrhage.

Environmental neurotoxin-induced progressive model of parkinsonism in rats.

OBJECTIVE: Exposure to a number of drugs, chemicals, or environmental factors can cause parkinsonism. Epidemiologic evidence supports a causal link between the consumption of flour made from the washed seeds of the plant Cycas micronesica by the Chamorro population of Guam and the development of amyotrophic lateral sclerosis/parkinsonism dementia complex. METHODS: We now report that consumption of washed cycad flour pellets by Sprague-Dawley male rats induces progressive parkinsonism. RESULTS: Cycad-fed rats displayed motor abnormalities after 2 to 3 months of feeding such as spontaneous unilateral rotation, shuffling gait, and stereotypy. Histological and biochemical examination of brains from cycad-fed rats revealed an initial decrease in the levels of dopamine and its metabolites in the striatum (STR), followed by neurodegeneration of dopaminergic (DAergic) cell bodies in the substantia nigra (SN) pars compacta (SNc). alpha-Synuclein (alpha-syn; proteinase K-resistant) and ubiquitin aggregates were found in the DAergic neurons of the SNc and neurites in the STR. In addition, we identified alpha-syn aggregates in neurons of the locus coeruleus and cingulate cortex. No loss of motor neurons in the spinal cord was found after chronic consumption of cycad flour. In an organotypic slice culture of the rat SN and the striatum, an organic extract of cycad causes a selective loss of dopamine neurons and alpha-syn aggregates in the SN. INTERPRETATION: Cycad-fed rats exhibit progressive behavioral, biochemical, and histological hallmarks of parkinsonism, coupled with a lack of fatality.

Nrf2 activators provide neuroprotection against 6-hydroxydopamine toxicity in rat organotypic nigrostriatal cocultures.

Oxidative stress and inflammation appear to play a critical role in the progression of Parkinson's disease. As a result, there has been growing interest in antioxidant pathways and how these pathways might be exploited to slow the progressive loss of dopamine neurons. One such pathway that has garnered attention recently is mediated by the transcription factor Nrf2 and is integral in orchestrating cells' antiinflammatory defense. Nrf2 controls the inducible expression of numerous antioxidant and phase 2 detoxification genes, such as glutathione S-transferase, heme oxygenase-1, and NAD(P)H:quinone oxidoreductase 1 (NQO1). Once activated, these genes work synergistically to maintain intracellular redox homeostasis. In this study, we test the hypothesis that Nrf2 activation can protect dopaminergic neurons against 6-hydroxydopamine (6-OHDA)-induced toxicity. Treatment of organotypic nigrostriatal cocultures with either tert-butylhydroquinone (tBHQ) or sulforaphane, known activators of Nrf2, mitigated dopaminergic cell loss. The observed protection appeared to be mediated, at least in part, by an increase in antioxidant activity. Simultaneous treatment of cultures with tBHQ and 6-OHDA increased NQO1 expression 17-fold compared with controls. Overall, these results suggest that Nrf2 may play an important role in cellular protection in neurodegenerative diseases and may be a viable therapeutic target in the future.

Optical coherence tomography guided neurosurgical procedures in small rodents.

The delivery of therapeutic agents directly to targets deep within the brain is becoming an important tool in the treatment of a variety of neurological disorders. Currently, the standard method to accomplish this is by using stereotactic procedures. While this existing method is adequate for many experimental situations, it is essentially a blind procedure that cannot provide real-time feedback on whether the actual location deviated from the intended location or whether the therapeutic agent was actually delivered. Here we describe an optical guidance technique that is designed to work in conjunction with existing stereotactic procedures to provide the needed real-time feedback for therapeutic delivery in live animals. This real-time feedback is enabled by a technology called catheter-based optical coherence tomography (OCT). In this study we show that OCT can provide real-time position feedback based on microanatomic landmarks from the live rodent brain. We show that OCT can provide the necessary guidance to perform microsurgery such as the selective transection of the Schaffer collateral inputs to the CA1 region of the hippocampus with minimal perturbation of overlying structures. We also show that OCT allows visual monitoring of the successful delivery of viral vectors to specific subregions of the hippocampus.

Optical coherence tomography imaging of the inner ear: a feasibility study with implications for cochlear implantation.

Cochlear implantation is now being performed in ears with residual hearing. Those implant recipients who keep residual hearing may benefit from improved pitch resolution through both electrical and acoustic hearing. Preservation of cochlear function after implantation is a challenging task for the surgeon. Current topics of hearing preservation research include electrode design and surgical technique. To maintain hearing, surgeons strive to create a cochleostomy and place the electrode in a minimally traumatic fashion. In this study, we examine a novel catheter-based real-time imaging modality with 10- to 15-microm resolution, optical coherence tomography (OCT), on the inner ear. We demonstrate the capability of OCT to allow visualization of inner ear structures through bone in live mice. We additionally used OCT to image the inner ear in a human temporal bone. Optical coherence tomography was able to delineate soft tissue structures within the cochlea and may be useful as an adjunct to cochlear implantation. Other potential otologic applications of OCT are discussed.

Growth-compromised HSV-2 vector Delta RR protects from N-methyl-D-aspartate-induced neuronal degeneration through redundant activation of the MEK/ERK and PI3-K/Akt survival pathways, either one of which overrides apoptotic cascades.

We have previously shown that intrastriatal injection of Delta RR, the growth-compromised herpes simplex virus type 2 (HSV-2) vector for the antiapoptotic protein ICP10PK, prevents apoptosis caused by the excitotoxin N-methyl-D-aspartate (NMDA) in a mouse model of glutamatergic neuronal cell death (Golembewski et al. [2007] Exp. Neurol. 203:381-393). Because apoptosis regulation is stimulus and cell type specific, our studies were designed to examine the mechanism of Delta RR-mediated neuroprotection in striatal neurons. Organotypic striatal cultures (OSC) that retain much of the synaptic circuitry of the intact striatum were infected with Delta RR or a growth-compromised HSV-2 vector that lacks ICP10PK (Delta PK) and examined for neuroprotection-associated signaling. The mutated ICP10 proteins (p175 and p95) were expressed in 70-80% of neurons from Delta RR- and Delta PK-infected cultures, respectively, as determined by double-immunofluorescent staining with antibodies to ICP10 and NeuN or GAD65. Delta RR- but not Delta PK-treated OSC were protected from NMDA-induced apoptosis, as verified by ethidium homodimer staining, TUNEL, caspase-3 activation, and poly(AD-ribose) polymerase (PARP) cleavage. Neuroprotection was through ICP10PK-mediated activation of the survival pathways MEK/ERK and PI3-K/Akt, up-regulation of the antiapoptotic proteins Bag-1 and Bcl-2, and phosphorylation (inactivation) of the proapoptotic protein Bad. It was blocked by the MEK inhibitor U0126 or the PI3-K inhibitor LY294002, suggesting that either pathway can prevent NMDA-induced apoptosis. The data indicate that Delta RR-delivered ICP10PK stimulates redundant survival pathways that override proapoptotic cascades. Delta RR is a promising gene therapy platform against glutamatergic cell death.

Catheter-based infrared light scanner as a tool to assess conduit quality in coronary artery bypass surgery.

OBJECTIVES: Endothelial disruption within saphenous vein and radial artery grafts increases thrombosis risk. However, no clinically applicable method for imaging the intima currently exists. We used a novel infrared imaging technology, optical coherence tomography (OCT; LightLab Imaging, Inc, Westford, Mass), to visualize the intima within harvested conduits. METHODS: Conduits were procured endoscopically (37 saphenous vein grafts and 8 radial artery grafts) or with the open technique (9 radial artery grafts) from 50 patients. Surplus segments were analyzed by means of OCT for evidence of preexisting pathology or traumatic injury. Focal plaques in radial artery grafts and the intimal hyperplasia area in saphenous vein grafts were quantified as having an intimal/medial thickness ratio of greater than 0.5. Biopsy specimens were obtained for histologic confirmation and to analyze matrix metalloproteinase 2 levels (saphenous vein grafts) and prostacyclin/nitric oxide metabolites (radial artery grafts). Interobserver kappa coefficients and a Bland-Altman analysis were used to determine the reproducibility and accuracy of OCT interpretations. RESULTS: Radial artery imaging revealed plaque in 76%. Endoscopically harvested vessels showed intraluminal clot (38%) and intimal tears ranging from severe (6%) to mild (88%). In saphenous vein grafts intimal thickening was detected in 86% and intraluminal clotting in 68%. The intimal/medial thickness ratio determined by means of OCT correlated directly with matrix metalloproteinase 2 levels (R = 0.6804) in saphenous vein grafts and inversely with metabolites of prostacyclin (R = -0.55) and nitric oxide (R = -0.58) in radial artery grafts. OCT imaging was reproducible (interobserver kappa coefficients of >0.81 for the characterization of plaque types) and showed a strong correlation with histology (R = 0.8, P < .001). CONCLUSIONS: OCT imaging provides an accurate, real-time, and reproducible means for assessing saphenous vein graft and radial artery graft bypass conduits. As a quality assurance tool, this technology might afford a more objective basis for conduit selection.

Optical coherence tomography in the diagnosis and treatment of neurological disorders.

Optical contrast is often the limiting factor in the imaging of live biological tissue. Studies were conducted in postmortem human brain to identify clinical applications where the structures of interest possess high intrinsic optical contrast and where the real-time, high-resolution imaging capabilities of optical coherence tomography (OCT) may be critical. Myelinated fiber tracts and blood vessels are two structures with high optical contrast. The ability to image these two structures in real time may improve the efficacy and safety of a neurosurgical procedure to treat Parkinson's disease called deep brain stimulation (DBS). OCT was evaluated as a potential optical guidance system for DBS in 25 human brains. The results suggest that catheter-based OCT has the resolution and contrast necessary for DBS targeting. The results also demonstrate the ability of OCT to detect blood vessels with high sensitivity, suggesting a possible means to avoid their laceration during DBS. Other microscopic structures in the human brain with high optical contrast are pathological vacuoles associated with transmissible spongiform encephalopathy (TSE). TSE include diseases such as Mad Cow disease and Creutzfeldt-Jakob disease (CJD) in humans. OCT performed on the brain from a woman who died of CJD was able to detect clearly the pathological vacuoles.