Objective: To study the feasibility of using combined morphology and terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick-end labeling (TUNEL) for apoptosis detection and the impact of cryopreservation on this process.
Materials and methods:We conducted this investigation using a porcine animal model. Bilateral oophorectomy was performed in eight sows. The ovarian tissues were divided into two parts; one part was immediately fixed while the other was cryopreserved. The cryopreserved specimens were subsequently thawed and then fixed. All the specimens were sectioned, fixed and stained with H&E. The ovarian follicles were counted, histologically categorized as healthy and atretic and evaluated for the presence of apoptosis. Then, in situ examination of apoptosis was performed using TUNEL assay. Results: In the cryopreserved tissues: 1) the count of the primordial follicle was significantly reduced as compared to freshly-fixed samples (4.9±5.3 vs. 7.2±5.4, p=0.03 respectively) and 2) the mean values of apoptosis were insignificantly higher when compared to the freshly-fixed group (p=0.74). Moreover: 1) apoptosis was found in the atretic, but not in the healthy follicles (primordial, primary and secondary); 2) the nuclei of the granulosa cells, but not those of theca or stromal cells, were TUNEL positive; 3) some cells with histological features of necrosis and apoptosis were TUNEL negative, and 6) The distribution of apoptosis was not different between cryopreserved tissue and freshly fixed tissue. Conclusions: the presence of apoptosis in the atretic follicles may suggest its involvement in follicular atresia; and 2) combined histology and TUNEL assay may be a useful method for detection of apoptosis. Key words: Apoptosis/ovarian cryopreservation/Morphology/TUNEL assay.In 1885, the first observation of apoptosis in the ovary was made following morphological analysis of granulosa cells in the rabbit ovary (1). This form of cell death is involved in the ovarian homeostasis (2) and its regulation depends on a balance between (3,4). Morphologically, apoptosis is characterized by specific changes, such as cytoplasmic vacuolization, chromatin condensation and formation of apoptotic bodies (5, 6). Biochemically, apoptosis is characterized by DNA fragmentation into oligonucleosome-sized fragments (6). This DNA fragmentation has been examined in the pig ovarian tissues; using DNA fluorescence flowcytometry (7) and autoradiography (8-10). However, these methods have the following limitations 1) they require large amounts of DNA and 2) they do not allow identification of apoptotic changes in specific tissue compartments or at the single cell level.
163Although morphology provided the original criteria for apoptosis and therefore remains as a reliable indicator, detection of early apoptotic changes may be beyond the scope of histological examination. Alternatively, it is well known that apoptosis may occur without evidence of DNA fragmentation (11) and therefore its detection becomes beyond the scope...