Research Article: Spatial distribution of preantral follicles in the equine ovary

Date Published: June 13, 2018

Publisher: Public Library of Science

Author(s): Benner G. Alves, Kele A. Alves, Gustavo D. A. Gastal, Melba O. Gastal, José R. Figueiredo, Eduardo L. Gastal, Peter J. Hansen.

http://doi.org/10.1371/journal.pone.0198108

Abstract

Comprehensive studies on spatial distribution of preantral follicles in the ovary are scarce. Considering that preantral follicles represent the main ovarian reserve, harvesting of these follicles is crucial for the development/use of assisted reproductive techniques. Therefore, knowledge on follicle spatial distribution can be helpful for targeting areas with richer number of preantral follicles through biopsy procedures. The aim of this study was to assess the distribution and localization of equine preantral follicles according to: (i) age, (ii) ovarian portion (lateral and intermediary) and region (dorsal and ventral), (iii) distance from the geometric center, and (iv) follicular class. Ovaries from young and old mares (n = 8) were harvested in a slaughterhouse and submitted to histological processing for further evaluation. For data analyses, a novel methodology was developed according to the geometric center of each histological section for a precise determination of preantral follicle distribution. Results indicated that (i) equine preantral follicles are clustered and located near to the ovarian geometric center, and that aging induced their dispersion through the ovarian cortex; (ii) the distance from the geometric center was shorter for developing follicles than primordial; and (iii) secondary follicles were more distant from the geometric center but closer to the ovulation fossa. In conclusion, the spatial distribution of preantral follicles was successfully determined in the equine ovary and was affected by age, region, and portion.

Partial Text

During the reproductive lifespan, a rich and finite number of gametes (primordial follicles) are available and represent the main oocyte ovarian reserve of an individual. Early folliculogenesis in vivo is a complex dynamic process featured by follicular quiescence [1], activation and growth [2], follicular migration [3], and cell interactions [4]. Once these events occur simultaneously in the ovarian parenchyma [5], studies related to preantral follicle spatial distribution can potentially help to clarify important anatomical-physiological mechanisms involved in folliculogenesis.

Young and old mares had similar (P > 0.05) ovary measurements (length, 48.8 ± 3.5 vs. 48.6 ± 3.3 mm; height, 35.7 ± 2.4 vs. 30.7 ± 2.4 mm; and width, 31.1 ± 2.5 vs. 28.0 ± 2.2, respectively). A total of 240 ovarian maps were evaluated (15 per ovary) and 9,284 preantral follicles were recorded in lateral (n = 4,901) and intermediary (n = 4,383) ovarian portions. The frequency distribution of preantral follicles on ovarian portions and regions (dorsal and ventral) is shown (Table 1). Overall, 58% of the total number of preantral follicles were observed on the ovarian dorsal region. Ovarian portions within the same region had a similar (P < 0.05) frequency of preantral follicles. The present study developed a novel methodology for objective and accurate assessment of the preantral follicle spatial distribution in the equine ovarian parenchyma using histology, computational image analysis, and mathematical calculations. Furthermore, the influence of age on preantral follicle spatial distribution was observed. Results herein described have the potential to be translated to animals of the equidae family, and to advance our knowledge towards characterization of mechanisms involved in ovarian plasticity [28] with migration of preantral follicles throughout the ovarian parenchyma during the early phases of folliculogenesis.   Source: http://doi.org/10.1371/journal.pone.0198108

 

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