Localizaci ´on del Bactenecin respecto la membrana

3.3.8.1 Pancreas preparation and quantitative stereological analyses

Following prefixation to allow manipulation of the organ without damaging the tissue, the pancreas (without left lobe) was cut into 1 cm thick slices, slices were tilted to their left side and covered by a 1 cm2 _{point-counting grid which was used for area-} weighted subsampling of pancreas tissue for quantitative stereological analyses. As pancreas slices were of the same thickness this procedure represents volume- weighted subsampling. The total number of points hitting pancreas tissue was determined. One tenth of the total number of points hitting pancreas tissue yielded the total sample number. For determination of the sites of sample collection, a random number (X) between one and the quotient of total hitting points and total sample number (Y) was determined. Pieces with a volume of 0.5 cm3 were taken at the sites X+Y; X+2*Y; X+3*Y … Selected samples were placed in an embedding cassette with the right cut surface facing downwards, fixed in 10% neutral buffered formalin at room temperature overnight, routinely processed and embedded in paraffin. From half of the paraffin embedded samples a series of sections of approximately 4 µm thickness was cut with a HM 315 microtome (Microm). One section from each series was mounted on a glass slide for hematoxylin and eosin

silane-treated glass slide for immunohistochemistry. All H&E stained sections as well as a sheet of millimeter paper for calibration purposes were photocopied at a final magnification of 400% on a commercial photocopier showing the complete cut surface of all pancreas slices. Morphometric evaluation was carried out on a Videoplan® image analysis system (Zeiss-Kontron, Eching, Germany) attached to a microscope by a color video camera. The cross-sectional area of the pancreas was determined planimetrically by circling the cut surfaces on the photocopies. Planimetric measurements of islet profiles were performed on H&E stained sections while β-cell areas were determined on immunohistochemically stained sections (see 3.3.8.3) by circling their outlines with a cursor on a digitizing tablet of the image analysis system. Images were displayed on a color monitor at an 850x final magnification. The volume of the pancreas (V(Pan)) before embedding was calculated by the quotient of the pancreas weight and the specific weight of the pig pancreas (1.07 g/cm3). The specific weight was determined by the submersion method (Scherle 1970). The volume density of the islets in the pancreas (Vv(Islet/Pan)) was calculated by dividing the total islet area (A(Islet)) by the total pancreas area (A(Pan)). The total volume of islets in the pancreas (V(Islet, Pan)) was determined as the product of Vv(Islet/Pan) and V(Pan). Accordingly, the volume density of β-cells in the pancreas (Vv(β-cell/Pan)) was obtained as the quotient of the total area of β-cells (A(β-cells)) and

A(Pan). Here, total area of β-cells included total area of β-cells in the islets and total area of isolated β-cells in the pancreas. Further, the total volume of β-cells in the pancreas was determined as the product of Vv(β-cell/Pan) and V(Pan). Division of A(β-cell)

by A(Islet) yielded the volume density of the β-cells in the islets (Vv(β-cell/Islet)) and the

product of Vv(β-cell/Islet) and V(Islet, Pan) resulted in the total volume of β-cells in the islets

(V(β-cell, Islet)).

Isolated β-cells (insulin positive single cells and small clusters of insulin positive cells not belonging to established islets) were quantified separately. The volume density of isolated β-cells in the pancreas was obtained by division of the total profile areas of isolated β-cells by A(Pan). The total volume of isolated β-cells was determined as the product of their volume density in the pancreas and the total volume of the pancreas.

Figure 3.6: Pancreas preparation for islet isolation and quantitative stereological analyses

White arrows indicate the separation site of the left pancreatic lobe from the rest of the organ using the left pancreatic lobe for islet isolation and the remnant organ for quantitative stereological analyses.

3.3.8.2 Hemalaun & Eosin staining

After incubation overnight at 37°C in an incubator, sections were deparaffinized in xylene for 15 minutes, rehydrated in a descending alcohol series and washed in distilled water. Subsequently nuclear staining was carried out by incubation of the slides in Meyer’s Hemalaun solution for four minutes. Then tissue sections were washed with tap water for five minutes and dipped four to five times in eosin solution. Sections were dehydrated in an ascending alcohol series, cleared in xylene and mounted under coverslips using Eukitt® (Electron Microscopy Sciences).

3.3.8.3 Immunohistochemistry for insulin

The indirect immunoperoxidase technique was applied to localize insulin containing cells. Sections were deparaffinized in xylene, rehydrated in a descending alcohol series and washed in distilled water. Endogenous peroxidase activity was blocked using 1% hydrogen peroxide in TBS buffer (pH 7.4). After that sections were washed in TBS (pH 7.4) for ten minutes and pre-incubated with normal rabbit serum (MP Biomedicals) for 30 minutes to reduce non-specific binding. Subsequently, slides

porcine insulin antibody (dilution 1:1000 in TBS) (Dako Cytomation). Thereafter slides were washed in TBS buffer for ten minutes, followed by an incubation step with horseradish peroxidase conjugated polyclonal rabbit anti-guinea pig IgG (dilution 1:50 in TBS buffer containing 5% (vol/vol) porcine serum) for one hour. The slides were washed again in TBS buffer for ten minutes and immunoreactivity was visualized using 3,3´ diaminobenzidine tetrahydrochloride dehydrate (Sigma-Aldrich) as chromogen and 1% hydrogen peroxide as substrate. Mayer’s hemalaun solution was used for counterstaining. Tissue sections were then dehydrated in an ascending alcohol series, cleared in xylene and mounted under coverslips using Eukitt®.

Specificity controls included substitution of primary antisera with nonimmune serum and omission of the secondary antiserum.