FIG. 2.

Mouse thyroid transmission electron microscopy. Thyroid lobes were fixed in 2.5% glutaraldehyde in 0.1 M cacodylate buffer for 1.5 hours, post-fixed in 1% osmium tetroxide for 1 hour, and embedded in LX112 resin (Ladd Research Industries, Burlington, VT). (A) Thin sections (0.5 μm) were stained with toluidine blue and analyzed for morphology by light microscopy. (B) Ultrathin sections were prepared and stained with uranyl acetate and lead citrate and examined with an electron microscope Zeiss EM169 (Carl Zeiss, Oberkochen, Germany). (C) Ultrastructural distribution of ¹²⁷I by secondary ion mass spectrometry (SIMS) imaging. Semi-thin sections were prepared, and the ultrastructural distribution of the iodide natural isotope (¹²⁷I) was obtained through imaging by SIMS, using the NanoSIMS 50 system. Maps were acquired under standard analytic conditions: a Cs+ primary beam with impact energy of 16 keV and a probe with current intensity of 1 pA. The analyzed surface was 30×30 μm. Under these conditions, a lateral resolution of 100 nm is expected. All images were acquired in 256×256 pixels with a counting time of 20 milliseconds per pixel. White areas correspond to iodine detection. ¹²⁷I is homogeneously distributed in the follicular lumina and in a few intracytoplasmic vesicles. Reproduced with permission from Senou et al. (20).