Multi-DNA-Modified Double-Network Hydrogel with Customized Microstructure: A Novel System for Living Circulating Tumor Cells Capture and Real-Time Detection.

The precise and effective isolation of living circulating tumor cells (CTCs) from peripheral blood, followed by their real-time monitoring, is crucial for diagnosing cancer patients. In this study, a cell-imprinted double-network (DN) hydrogel modified with circular multi-DNA (CMD), coined the CMD-imprinted hydrogel with fixed cells as templates (CMD-CIDH), was developed. The hydrogel featured a customized surface for proficient capture of viable CTCs and in situ real-time fluorescent detection without subsequent release. The customized surface, constructed using polyacrylamide/chitosan DN hydrogel as the matrix on the cell template, had a dense network structure, thereby ensuring excellent stability and a low degradation rate. Optimal capture efficiencies, recorded at 93 ± 3% for MCF-7 cells and 90 ± 2% for Hela cells, were achieved by grafting the CMD and adjusting the nodule size on the customized surface. The capture efficiency remained significantly high at 67 ± 11% in simulated breast cancer patient experiments even at a minimal concentration of 5 cells mL-1. Furthermore, CMD grafted onto the surface produced a potent fluorescence signature, enabling in situ real-time fluorescent detection of the target cell's growth state even in complex environments. The customized surface is highly efficient for screening CTCs in peripheral blood and has promising potential for setting up the CTCs culture.

Dengzhanshengmai capsule alleviates heart failure and concomitantly decreases phenylacetylglutamine level, interacting with the intestinal microflora in rats.

Heart failure (HF) is an advanced stage of most heart diseases. Some studies reported that Dengzhanshengmai (DZSM) capsule may improve HF, but its mechanisms are unclear. This study attempts to determine the function of DZSM in treating HF and investigates its potential mechanism. We demonstrated that DZSM can considerably reduce systemic inflammation, improve intestinal barrier functions and enhance cardiac functions in HF rats. Further investigations displayed that the beneficial effects of DZSM were related to the reduction of gut microbiota metabolite phenylacetylglutamine (PAGln) levels in serum and heart tissue. In addition, we demonstrated that PAGln can exacerbate the severity of HF in rats, and the serum PAGln levels in HF patients were higher than in healthy subjects. Moreover, by using microbial sequencing, we found that DZSM could alter the composition and function of the intestinal microbiota in HF rats, including decreased relative abundance of Turicibacter and Turicibacter_sp.TS3, and regulated the gene expression of PAGln synthesis-related enzymes. Therefore, our findings have contributed novel perspectives on the involvement of DZSM in treating HF, specifically in its regulation of intestinal flora and associated detrimental metabolites. Furthermore, our results have offered empirical evidence supporting the utilization of DZSM as a therapeutic approach for HF.

Validation of combined AFP, AFP-L3, and PIVKA II for diagnosis and monitoring of hepatocellular carcinoma in Chinese patients.

Background: In this study, we aimed to investigate the performance of GALAD, GALAD-C, and GAAP models in Chinese population in comparison to our newly build statistical model. Methods: In this study, we built the AALP model based on age, α-fetoprotein (AFP), AFP-L3, and prothrombin induced by vitamin K absence-II (PIVKA II) to differentiate between patients with HCC and patients with CLD. We then compared the serum levels of AFP-L3 and PIVKA II in patients with HCC who were defined as remission or progression and showed the prognostic value of combined biomarkers. Results: The AUC value of the AALP model for HCC detection was 0.939 and AALP model exhibited a sensitivity of 81 % and a high specificity of 95 %. AALP model also exhibited good performance in the subgroups of patients with CLD. Furthermore, we demonstrated the consistency between imaging results and serum levels of AFP-L3 and PIVKA II. Conclusions: The AALP model achieved a good diagnostic performance and a high sensitivity for predicting HCC patients. Our research also showed that AFP-L3 and PIVKA II are complementary to each other but irreplaceable in the clinical detection and monitoring of HCC.

Hepatic transcriptome analysis reveals that elovl5 deletion promotes PUFA biosynthesis and deposition.

The safe and low-cost acquisition of polyunsaturated fatty acids (PUFAs) has become a research hotspot. Fatty acyl elongase 5 (Elovl5), a rate-limiting enzyme for fatty acid elongation, is principally in charge of extending C18 and C20 PUFA substrates. However, the role of elovl5 in regulating pathways and genes involved in PUFA synthesis remain largely unknown. Here, hepatic transcriptome analysis of wild-type and elovl5 knockout (elovl5-/-) zebrafish was performed to identify the potential regulatory targets related to PUFA deposition and synthesis. There were 1579 differentially expressed genes (DEGs), of which 787 had their expression levels increased while 792 had the opposite effect. Peroxisome proliferators-activated receptors (PPAR) signaling pathway was considerably enriched in DEGs, according to the KEGG analysis, in which fatp2, fabp7, and pparδ were engaged in PUFA absorption and deposition. Additionally, transcriptome analysis also revealed that cyp46a1 and cyp2r1 were implicated in the synthesis of bile acids and the metabolism of vitamin D, thus indirectly participating in PUFA biosynthesis and deposition. Finally, the DEGs, which improve PUFA level following elovl5 deletion, were verified through feeding experiment with two prepared diets soybean oil diet and linolenic acid oil diet. This study revealed potential regulatory targets that improve PUFA level after elovl5 deletion in teleosts.

Enoyl-CoA hydratase/3-hydroxyacyl CoA dehydrogenase is essential for the production of DHA in zebrafish.

Compared with other species, freshwater fish are more capable of synthesizing DHA via same biosynthetic pathways. Freshwater fish have a "Sprecher" pathway to biosynthesize DHA in a peroxisome-dependent manner. Enoyl-CoA hydratase/3-hydroxyacyl CoA dehydrogenase (Ehhadh) is involved in the hydration and dehydrogenation reactions of fatty acid ß-oxidation in peroxisomes. However, the role of Ehhadh in the synthesis of DHA in freshwater fish remains largely unclear. In this study, the knockout of Ehhadh significantly inhibited DHA synthesis in zebrafish. Liver transcriptome analysis showed that Ehhadh deletion significantly inhibited SREBF and PPAR signaling pathways and decreased the expression of PUFA synthesis-related genes. Our results from the analysis of transgenic zebrafish (Tg:Ehhadh) showed that Ehhadh overexpression significantly increased the DHA content in the liver and significantly upregulated the expression of genes related to PUFA synthesis. In addition, the DHA content in the liver of Tg:Ehhadh fed with linseed oil was significantly higher than that of wildtype, but the expression of PUFA synthesis-related genes fads2 and elovl2 were significantly lower, indicating that Ehhadh had a direct effect on DHA synthesis. In conclusion, our results showed that Ehhadh was essential for DHA synthesis in the "Sprecher" pathway, and Ehhadh overexpression could promote DHA synthesis. This study provides insight into the role of Ehhadh in freshwater fish.

ARID1A has prognostic value in acute myeloid leukemia and promotes cell proliferation via TGF-ß1/SMAD3 signaling.

Previous studies have shown that the gene AT-rich interactive domain-containing protein 1A (ARID1A) is a subunit of SWI/SNF chromatin remodeling complex that acts as a tumor suppressor gene in several cancers and plays a vital role in tumorigenesis. However, its biological functions in acute myeloid leukemia (AML) are still unclear. Here, we tried to elaborate the expression of ARID1A in patients with AML, in leukemia cells, as well as the molecular mechanisms. Our results indicated that the expression of ARID1A was significantly downregulated in the bone marrow of patients with AML and relapsed patients compared with healthy subjects and patients in complete remission. Meantime, receiver operating characteristic curve analysis showed that the expression of ARID1A could be used to discriminate between patients with AML and patients in complete remission. We further constructed a knockdown cell model to determine the regulatory mechanisms of ARID1A in AML cells. We found that the decreased expression of ARID1A promoted cell proliferation, suppressed cellular apoptosis, and impeded cell cycle arrest via TGF-ß1/SMAD3 signaling pathway. These results revealed that the reduced expression of ARID1A promoted cell proliferation via the TGF-ß1/SMAD3 cascade and served as a prognostic biomarker for AML and therapeutic targets.

The reticular lamina and basilar membrane vibrations in the transverse direction in the basal turn of the living gerbil cochlea.

The prevailing theory of cochlear function states that outer hair cells amplify sound-induced vibration to improve hearing sensitivity and frequency specificity. Recent micromechanical measurements in the basal turn of gerbil cochleae through the round window have demonstrated that the reticular lamina vibration lags the basilar membrane vibration, and it is physiologically vulnerable not only at the best frequency but also at the low frequencies. These results suggest that outer hair cells from a broad cochlear region enhance hearing sensitivity through a global hydromechanical mechanism. However, the time difference between the reticular lamina and basilar membrane vibration has been thought to result from a systematic measurement error caused by the optical axis non-perpendicular to the cochlear partition. To address this concern, we measured the reticular lamina and basilar membrane vibrations in the transverse direction through an opening in the cochlear lateral wall in this study. Present results show that the phase difference between the reticular lamina and basilar membrane vibration decreases with frequency by ~ 180 degrees from low frequencies to the best frequency, consistent with those measured through the round window. Together with the round-window measurement, the low-coherence interferometry through the cochlear lateral wall demonstrates that the time difference between the reticular lamina and basilar membrane vibration results from the cochlear active processing rather than a measurement error.

An outer hair cell-powered global hydromechanical mechanism for cochlear amplification.

It is a common belief that the mammalian cochlea achieves its exquisite sensitivity, frequency selectivity, and dynamic range through an outer hair cell-based active process, or cochlear amplification. As a sound-induced traveling wave propagates from the cochlear base toward the apex, outer hair cells at a narrow region amplify the low level sound-induced vibration through a local feedback mechanism. This widely accepted theory has been tested by measuring sound-induced sub-nanometer vibrations within the organ of Corti in the sensitive living cochleae using heterodyne low-coherence interferometry and optical coherence tomography. The aim of this short review is to summarize experimental findings on the cochlear active process by the authors' group. Our data show that outer hair cells are able to generate substantial forces for driving the cochlear partition at all audible frequencies in vivo. The acoustically induced reticular lamina vibration is larger and more broadly tuned than the basilar membrane vibration. The reticular lamina and basilar membrane vibrate approximately in opposite directions at low frequencies and in the same direction at the best frequency. The group delay of the reticular lamina is larger than that of the basilar membrane. The magnitude and phase differences between the reticular lamina and basilar membrane vibration are physiologically vulnerable. These results contradict predictions based on the local feedback mechanism but suggest a global hydromechanical mechanism for cochlear amplification. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.

The origin of mechanical harmonic distortion within the organ of Corti in living gerbil cochleae.

Although auditory harmonic distortion has been demonstrated psychophysically in humans and electrophysiologically in experimental animals, the cellular origin of the mechanical harmonic distortion remains unclear. To demonstrate the outer hair cell-generated harmonics within the organ of Corti, we measured sub-nanometer vibrations of the reticular lamina from the apical ends of the outer hair cells in living gerbil cochleae using a custom-built heterodyne low-coherence interferometer. The harmonics in the reticular lamina vibration are significantly larger and have broader spectra and shorter latencies than those in the basilar membrane vibration. The latency of the second harmonic is significantly greater than that of the fundamental at low stimulus frequencies. These data indicate that the mechanical harmonics are generated by the outer hair cells over a broad cochlear region and propagate from the generation sites to their own best-frequency locations.

Effect of Cochlear Implantation on the Endocochlear Potential and Stria Vascularis.

HYPOTHESIS: Animals with cochlear implantation-induced hearing loss will have a lower endocochlear potential (EP) and decreased strial vascular density. BACKGROUND: The cause of residual hearing loss following cochlear implantation remains poorly understood. Recent work from our lab has shown a correlation between vascular changes in the cochlear lateral wall and postimplantation hearing loss, suggesting a role of the stria vascularis and EP. METHODS: Fourteen young, normal-hearing male albino guinea pigs underwent cochlear implantation using either a cochleostomy (CI-c, n = 9) or an extended round window (CI-eRW, n = 5) approach. Hearing sensitivity was assessed pre- and postoperatively using auditory brainstem response thresholds. Three weeks after implantation, EP measurements were obtained from the first and second turns. Hair cell counts and stria vascularis capillary density measurements were also obtained. RESULTS: The implanted group experienced significant threshold elevations at 8 to 24 kHz (mean threshold shift 9.1 ±â€Š1.1 dB), with a more robust threshold shift observed in the CI-eRW group compared to the CI-c group. Implanted animals had a significantly lower first turn EP (81.4 ±â€Š5.1 mV) compared with controls (87.9 ±â€Š6.1 mV). No differences were observed in the second turn (75.8 ±â€Š12.0 mV for implanted animals compared to 76.5 ±â€Š7.0 mV for controls). There were no significant correlations between turn-specific threshold shifts, EP measurements, or strial blood vessel density. CONCLUSIONS: Reliable EP measurements can be obtained in chronically implanted guinea pigs. Hearing loss after implantation is not explained by changes in strial vascular density or reductions in EP.

Polyunsaturated fatty acids synthesized by freshwater fish: A new insight to the roles of elovl2 and elovl5 in vivo.

At present, fish provide an important supply of long-chain polyunsaturated fatty acids (LC-PUFAs) for human consumption. Previous studies have shown that fatty acyl elongase 2 (elovl2) and elovl5 play important roles in fish LC-PUFA synthesis. Generally, freshwater fish have a stronger ability to synthesize LC-PUFAs than marine fish. However, the roles of elovl2, elovl5 and elovl2 + elovl5 in LC-PUFA synthesis of freshwater fish in vivo are not very clear. In this study, the elovl2 knockout zebrafish (elovl2-/-), elovl5 knockout zebrafish (elovl5-/-) and the double gene knockout zebrafish (DKO) were generated by CRISPR/Cas9 technology for the first time. Compared with wild type zebrafish (WT), elovl5-deletion zebrafish showed a significant increase in C22 PUFA content, which might be due to the up-regulation expressions of elovl4b and elovl2. elovl5 expressed at very low levels in livers of elovl2-/- relative to WT, indicating that elovl5 may be an "assistant attacker" of elovl2 in LC-PUFA synthesis of zebrafish. Moreover, there were no significant differences in levels of C18-C22 PUFAs between DKO and WT, indicating that besides elovl2 + elovl5 path, LC-PUFA synthesis in zebrafish could be performed by other paths. In addition, the hepatic lipidomic analysis results revealed that the contents of C22:6n-3 in phosphatidyl ethanolamine (PE-DHA) and PE-C22 PUFAs were more easily affected by the absence of elovl2 and elovl5. Our results suggest that the elovl2+elovl5 path is not the only path for LC-PUFA synthesis in zebrafish, and provide novel insights into the roles of elovl2 and elovl5 in LC-PUFA synthesis of freshwater fish.

Leukocyte telomere length: a potential biomarker for the prognosis of coronary artery disease.

Aim: This study aimed to explore the prognostic value of leukocyte telomere length (LTL) in patients with coronary artery disease (CAD). Materials & methods: We enrolled 366 CAD patients and 76 healthy subjects in this study. LTL was measured. All subjects were followed up for 6 months for further analysis regarding major adverse cardiac events (MACEs). Results: CAD patients had a significantly shortened LTL compared with healthy subjects (p < 0.05). The area under the curve for LTL prediction of MACEs was 0.769 (p < 0.001), with a shorter LTL being an independent predictor of MACEs (Cox proportional hazards regression, hazard ratio: 2.866; p < 0.001). Conclusion: LTL could be considered as an independent predictor of short-term MACEs in CAD.

Clinical significance of circulating tumor cells and metabolic signatures in lung cancer after surgical removal.

BACKGROUND: Lung cancer (LC) remains the deadliest form of cancer globally. While surgery remains the optimal treatment strategy for individuals with early-stage LC, what the metabolic consequences are of such surgical intervention remains uncertain. METHODS: Negative enrichment-fluorescence in situ hybridization (NE-FISH) was used in an effort to detect circulating tumor cells (CTCs) in pre- and post-surgery peripheral blood samples from 51 LC patients. In addition, targeted metabolomics analyses, multivariate statistical analyses, and pathway analyses were used to explore surgery-associated metabolic changes. RESULTS: LC patients had significantly higher CTC counts relative to healthy controls with 66.67% of LC patients having at least 1 detected CTC before surgery. CTC counts were associated with clinical outcomes following surgery. In a targeted metabolomics analysis, we detected 34 amino acids, 147 lipids, and 24 fatty acids. When comparing LC patients before and after surgery to control patients, metabolic shifts were detected via PLS-DA and pathway analysis. Further surgery-associated metabolic changes were identified when comparing LA (LC patients after surgery) and LB (LC patients before surgery) groups. We identified SM 42:4, Ser, Sar, Gln, and LPC 18:0 for inclusion in a biomarker panel for early-stage LC detection based upon an AUC of 0.965 (95% CI 0.900-1.000). This analysis revealed that SM 42:2, SM 35:1, PC (16:0/14:0), PC (14:0/16:1), Cer (d18:1/24:1), and SM 38:3 may offer diagnostic and prognostic benefits in LC. CONCLUSIONS: These findings suggest that CTC detection and plasma metabolite profiling may be an effective means of diagnosing early-stage LC and identifying patients at risk for disease recurrence.

Two-tone distortion in reticular lamina vibration of the living cochlea.

It has been demonstrated that isolated auditory sensory cells, outer hair cells, can generate distortion products at low frequencies. It remains unknown, however, whether or not motile outer hair cells are able to generate two-tone distortion at high frequencies in living cochleae under the mechanical loads caused by surounding tissues and fluids. By measuring sub-nanometer vibration directly from the apical ends of outer hair cells using a custom-built heterodyne low-coherence interferometer, here we show outer hair cell-generated two-tone distortion in reticular lamina motion in the living cochlea. Reticular-lamina distortion is significantly greater and occurs at a broader frequency range than that of the basilar membrane. Contrary to expectations, our results indicate that motile outer hair cells are capable of generating two-tone distortion in vivo not only at the locations tuned to primary tones but also at a broad region basal to these locations.

Clinical significance of circulating tumor cells and tumor markers in the diagnosis of lung cancer.

BACKGROUND: Lung cancer has the highest fatality rate of all cancer types. To improve patients' survival and life quality, it is therefore very important to screen for and detect it at an early stage. METHODS: A negative enrichment-fluorescence in situ hybridization (NE-FISH) approach was used to detect circulating tumor cells (CTCs) in lung cancer patients, and levels of lung cancer-associated serum markers were also measured in the peripheral blood of these same patients. The correlation between CTCs, serum cancer markers (carcinoembryonic antigen [CEA], CA 125, CYFRA 21-1, and SCC), and clinicopathological characteristics was then investigated. Moreover, the potential clinical use of the combination of CTCs and tumor markers for the diagnosis of lung cancer, especially at early stages, was also explored. RESULTS: CTC frequencies in lung cancer patients were significantly higher than in healthy control volunteers or patients with benign lung disease, and the area under the receiver operating characteristics curve for the control group was 0.846 (95% CI 0.796-0.887, P < 0.001). The rate of CTC positivity in lung cancer patients was 68.29% when the CTC cutoff value was 2, and the sensitivity of this means of lung cancer detection rose to 82.93% by combining CTC-based detection with measurements of serum tumor markers. Similarly, the diagnostic sensitivity of this approach in early-stage lung cancer patients (I-II) was improved from 63.93% to 78.69%. Detection of CTCs can thus assist with the identification of benign and malignant pulmonary nodules. CONCLUSIONS: It is potentially helpful and effective to employ a combination of CTCs and serum tumor markers for the clinical diagnosis of lung cancer.

A mechanoelectrical mechanism for detection of sound envelopes in the hearing organ.

To understand speech, the slowly varying outline, or envelope, of the acoustic stimulus is used to distinguish words. A small amount of information about the envelope is sufficient for speech recognition, but the mechanism used by the auditory system to extract the envelope is not known. Several different theories have been proposed, including envelope detection by auditory nerve dendrites as well as various mechanisms involving the sensory hair cells. We used recordings from human and animal inner ears to show that the dominant mechanism for envelope detection is distortion introduced by mechanoelectrical transduction channels. This electrical distortion, which is not apparent in the sound-evoked vibrations of the basilar membrane, tracks the envelope, excites the auditory nerve, and transmits information about the shape of the envelope to the brain.

Timing of the reticular lamina and basilar membrane vibration in living gerbil cochleae.

Auditory sensory outer hair cells are thought to amplify sound-induced basilar membrane vibration through a feedback mechanism to enhance hearing sensitivity. For optimal amplification, the outer hair cell-generated force must act on the basilar membrane at an appropriate time at every cycle. However, the temporal relationship between the outer hair cell-driven reticular lamina vibration and the basilar membrane vibration remains unclear. By measuring sub-nanometer vibrations directly from outer hair cells using a custom-built heterodyne low-coherence interferometer, we demonstrate in living gerbil cochleae that the reticular lamina vibration occurs after, not before, the basilar membrane vibration. Both tone- and click-induced responses indicate that the reticular lamina and basilar membrane vibrate in opposite directions at the cochlear base and they oscillate in phase near the best-frequency location. Our results suggest that outer hair cells enhance hearing sensitivity through a global hydromechanical mechanism, rather than through a local mechanical feedback as commonly supposed.

Improvement of sensitive and specific detection of circulating tumor cells using negative enrichment and immunostaining-FISH.

BACKGROUND: Circulating tumor cells (CTCs) provide an opportunity to obtain pivotal biological information required for the development of personalized medicine. However, the current assays of CTCs' detection face serious challenges regarding specificity and sensitivity. METHODS: In this study, we developed a novel strategy that combined negative enrichment (NE), immunocytochemistry CD45 staining and fluorescence in situ hybridization (FISH) to identify, enumerate and characterize CTCs. CTCs were identified as DAPI+/CD45-/Chromosome multiploid. The assay was evaluated with different cancer cell lines including lung, breast, esophageal and gastric cancer. And then, the developed assay was applied in cancer patients to explore the possibility of clinical application and whether CTC number was related to clinicopathological factors. RESULTS: The average recover rate of esophageal cancer cell line Eca-109 using negative enrichment was higher than 80% and the multiploid cells rate of four cancer cell lines were >96%, which demonstrate the NE-FISH platform is favorable for CTCs detection. CTCs count was significantly higher in lung cancer patients than healthy controls and benign lung disease with an area under ROC curve of 0.905 (95% confidence interval 0.866-0.944, P < .001). Using a cutoff value of 2 CTCs, the positive rate of detecting lung, gastric, breast and esophageal cancer patients were 71.33%, 86.21%, 76.77% and 78.35%, respectively. Besides, CTCs could be detected in stage I with the positive rate of 64.15% for lung cancer, 83.33% for gastric cancer, 78.95% for breast cancer and 68.18% for esophageal cancer, which may promote the early diagnose and influence the treatment decision for better management of those cancer in clinic. CONCLUSIONS: Our study showed that CTCs could be detected in diverse cancers using the novel NE-FISH platform with high sensitivity and specificity. Therefore, analysis of CTCs with NE-FISH has a clear potential to improve the management of cancer patients in clinical use.

Reticular lamina and basilar membrane vibrations in living mouse cochleae.

It is commonly believed that the exceptional sensitivity of mammalian hearing depends on outer hair cells which generate forces for amplifying sound-induced basilar membrane vibrations, yet how cellular forces amplify vibrations is poorly understood. In this study, by measuring subnanometer vibrations directly from the reticular lamina at the apical ends of outer hair cells and from the basilar membrane using a custom-built heterodyne low-coherence interferometer, we demonstrate in living mouse cochleae that the sound-induced reticular lamina vibration is substantially larger than the basilar membrane vibration not only at the best frequency but surprisingly also at low frequencies. The phase relation of reticular lamina to basilar membrane vibration changes with frequency by up to 180 degrees from ∼135 degrees at low frequencies to ∼-45 degrees at the best frequency. The magnitude and phase differences between reticular lamina and basilar membrane vibrations are absent in postmortem cochleae. These results indicate that outer hair cells do not amplify the basilar membrane vibration directly through a local feedback as commonly expected; instead, they actively vibrate the reticular lamina over a broad frequency range. The outer hair cell-driven reticular lamina vibration collaboratively interacts with the basilar membrane traveling wave primarily through the cochlear fluid, which boosts peak responses at the best-frequency location and consequently enhances hearing sensitivity and frequency selectivity.

Minimally invasive surgical method to detect sound processing in the cochlear apex by optical coherence tomography.

Sound processing in the inner ear involves separation of the constituent frequencies along the length of the cochlea. Frequencies relevant to human speech (100 to 500 Hz) are processed in the apex region. Among mammals, the guinea pig cochlear apex processes similar frequencies and is thus relevant for the study of speech processing in the cochlea. However, the requirement for extensive surgery has challenged the optical accessibility of this area to investigate cochlear processing of signals without significant intrusion. A simple method is developed to provide optical access to the guinea pig cochlear apex in two directions with minimal surgery. Furthermore, all prior vibration measurements in the guinea pig apex involved opening an observation hole in the otic capsule, which has been questioned on the basis of the resulting changes to cochlear hydrodynamics. Here, this limitation is overcome by measuring the vibrations through the unopened otic capsule using phase-sensitive Fourier domain optical coherence tomography. The optically and surgically advanced method described here lays the foundation to perform minimally invasive investigation of speech-related signal processing in the cochlea.