Role of the testicular capsule in seasonal modulation of the testis

Abstract

While the seasonal testicular cycle has been well studied regarding internal components, no attention has been given to the testicular capsule (tunica albuginea and tunica serosa). This study elucidated the structure‐function modulations of intra‐testicular functions by its capsule in the finch red munia (Amandava amandava) during the annual testicular cycle. The birds were studied during breeding (preparatory and breeding) and nonbreeding (regressive and quiescent) reproductive phases using hematoxylin‐eosin and acridine orange‐ethidium bromide capsule staining, hormonal ELISA (LH and testosterone) and immunohistochemical expression of neuropeptides (GnRH, GnIH) and androgen receptor (AR). The thickness of the tunica albuginea was significantly increased with multiple myoid layers during the nonbreeding phases (p < 0.05). The thickness of the tunica serosa was not altered, although characteristics and distribution of squamous cells showed significant seasonal alterations. Immunoreactive (‐ir) AR and GnIH cells were differentially localized on both layers of the capsule. Strong AR‐ir cells on tunica serosa during breeding phases showed increased expression of the receptor; a significant increase in plasma LH and testosterone was also observed during the breeding cycle (p < 0.01). Contrarily, intense GnIH‐ir cells on both the capsular layers peaked during testicular regression. Differential structural alterations of the testicular capsule provide mechanical support and help maintain internal homeostasis in tune with changing seasons. The seasonal expressions and alterations of reproduction‐related receptors, hormones, and neuropeptides provide evidence for the potential regulatory roles of the capsule in the peripheral modulation of intratesticular functions.

Seasonality of Reproduction in a Subtropical Free-Living Finch <i>Amandava amandava</i>: Plasticity of Adenohypophyseal Gonadotropes, Lactotropes, and Thyrotropes

“…Seasonality of reproduction in the tropical/subtropical birds has mostly been interpreted from the variation in the plasma levels of reproduction-related hormones and the impact on gonadal maturation as reflected in size and histological alterations [18, 23‒27]. However, less is understood of the mechanism of entrainment of the environmental cues (not specifically photoperiod) for setting in of active reproductive status and transition to other life-history stages.…”

“…Significant increase in the number of ir-LH gonadotropes in the PT and PD, and intense immunoreactivity coincided with a surge of the LH in the plasma during the breeding phase in this bird. We have recently reported the peak plasma LH and testosterone levels along with drastic increase in size of the testis (weight and volume) during the breeding season of this bird [18]. Pituitary secretion of LH in concert with FSH orchestrates gonad growth and the release of sex steroids such as testosterone during the breeding phase in the seasonally breeding temperate zone birds [25].…”

“…The immunointensity of the expressed hormones in situ (LH, PRL, and TSH) was quantified by Image J 1.32 j as reported before [18]. In brief, the optical density (OD) of 50 cells selected at random from each of the five mid-sagittal sections of every bird (300 cells for each phase) was measured and the value was corrected by subtraction of the back ground OD of the same section for determination of mean OD.…”

“…Notwithstanding the significance of this, the variation in the expression of hormones in the adenohypophyseal cells (PD and PT) in any free-living vertebrates of tropical/subtropical regions during annual reproductive cycle has been least studied. Seasonal modulation of the reproduction was mainly understood correlating the gonadal development with the alterations in the plasma levels of various hormones including that of the pituitary [17, 18]. In domesticated avian species (turkey hen), the alteration of lactotropes (PRL cells), somatotropes (GH cells), and gonadotropes (GTH cells) in the PD of the pituitary with respect to various physiological conditions like incubation, broodiness, and moulting, etc., was demonstrated [19].…”

“…On the basis of testicular development, the annual reproductive cycle of Red Munia was divided into four phases: preparatory/pre-breeding phase, breeding phase, post-breeding/regressive phase, and quiescent phase. The preparatory and the breeding phases constituted the breeding cycle (June to November), while the post-breeding regressive and the quiescent phases constitute the nonbreeding cycle (December to end May) [18].…”