Recent development of in vivo cryotechnique to cryobiopsy for living animals

Immunohistochemical and morphofunctional studies of skeletal muscle tissues with electric nerve stimulation by in vivo cryotechnique

In this study, morphological and immunohistochemical alterations of skeletal muscle tissues during persistent contraction were examined by in vivo cryotechnique (IVCT). Contraction of gastrocnemius muscles was induced by sciatic nerve stimulation. The IVCT was performed immediately, 3 min or 10 min after the stimulation start. Prominent ripples of muscle fibers or wavy deformation of sarcolemma were detected immediately after the stimulation, but they gradually diminished to normal levels during the stimulation. The relative ratio of sarcomere and A band lengths was the highest in the control group, but it immediately decreased to the lowest level and then gradually recovered at 3 min or 10 min. Although histochemical intensity of PAS reaction was almost homogeneous in muscle tissues of the control group or immediately after the stimulation, it decreased at 3 min or 10 min. Serum albumin was immunolocalized as dot-like patterns within some muscle fibers at 3 min stimulation. These patterns became more prominent at 10 min, and the dots got larger and saccular in some sarcoplasmic regions. However, IgG1 and IgM were immunolocalized in blood vessels under nerve stimulation conditions. Therefore, IVCT was useful to capture the morphofunctional and metabolic changes of heterogeneous muscle fibers during the persistent contraction.

Immunohistochemical distribution of serum proteins in living mouse heart with In vivo cryotechnique

In vivo cryotechnique (IVCT), which immediately cryofixes target organs in situ, was used to clarify the morphological features of beating heart tissue of living mice. IVCT was performed for diastolic heart tissue under the condition of monitoring with electrocardiogram (ECG). Other mouse hearts were prepared with conventional perfusion-fixation (PF-DH) or immersion-fixation followed by dehydration (IM-DH), and quick-freezing of resected heart tissues (FQF). Immunolocalizations of albumin, immunoglobulin G1 (IgG1), intravenously injected bovine serum albumin (BSA), and connexin 43 were examined after different intervals of BSA injection. In the case of IVCT, the exact stop time of beating mouse hearts was recorded by ECG, and open blood vessels with flowing erythrocytes were observed with less artificial tissue shrinkage than with conventional preparation methods. Both albumin and BSA were well preserved in intercalated discs and t-tubules of cardiomyocytes in addition to blood vessels and interstitial matrices. IgG1 was immunolocalized in interstitial matrices of heart tissues in addition to their blood vessels. At 4 hr after BSA injection, it was immunolocalized in the intercalated discs of cardiomyocytes and lost later at 8 hr. IVCT should prove to be more useful for the morphofunctional examination of dynamically changing heart tissue than conventional preparation methods.

Immunohistochemical detection of hypoxia in mouse liver tissues treated with pimonidazole using "in vivo cryotechnique"

To evaluate hypoxic cells in live mouse liver tissues, immunohistochemistry for protein adducts of reductively activated pimonidazole (PARaPi) was performed using the "in vivo cryotechnique (IVCT)" followed by freeze-substitution fixation. This method was used because cryotechniques have some merits for examining biological events in living animal organs with improved time-resolution compared to conventional perfusion and/or immersion chemical fixation. Pimonidazole was intraperitoneally injected into living mice, and then after various times of hypoxia, their livers were quickly frozen by IVCT. The frozen liver tissues were freeze-substituted in acetone containing 2% paraformaldehyde, and routinely embedded in paraffin wax. De-paraffinized sections were immunostained for PARaPi. In liver tissues of mice without hypoxia, almost no immunostained cells were detected. However, in liver tissues with 30 s of hypoxia, some hepatocytes in the pericentral zones were strongly immunostained. After 60 s of hypoxia, many hepatocytes were immunostained with various degrees of staining intensity in all lobular zones, indicating different reactivities of pimonidazole in the hepatocytes to hypoxia. At this time, the general immunoreactivity also appeared to be stronger around the central veins than other portal areas. Although many hepatocytes were immunostained for PARaPi in the liver tissues with perfusion fixation via heart, those with perfusion via portal vein were not immunostained. Thus, IVCT is useful to detect time-dependent hypoxic states with pimonidazole treatment in living animal organs.