Chapter 31 Puberty in the Sheep © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.1 Growth based upon body weight from birth through the initiation of ovulation for sheep (mean) and human beings (50th percentile). Note the different x-axes. Growth during the first 30 weeks is shown (inset). From Ref. 7, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.2 Development of the response to the stimulatory feedback action of estradiol on LH secretion in the female sheep. Estradiol was administered (arrows) subcutaneously by Silastic cap- sules for 96 h at each age in the same lambs. From Ref. 10, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.3 Rapid administration of LH induces ovulation in the immature sheep. Circulating LH and estradiol concentrations are shown at various times before and during hourly injections (arrows) of purified ovine LH in an individual female. High LH values between hours 22 and 24 reflect the initial portion of a preovulatory LH surge that was followed by an 11-day luteal phase with three corpora lutea. From Ref. 25, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.4 Mean (± SEM) LH pulse frequency (top panel) and amplitude (bottom panel) during the prepubertal period (striped bars) and the first postpubertal follicular phase (solid bars). Values for weeks 4–5 and 6–7 were combined to increase the number of observations contributing to the means. Each mean frequency was based on values from 7 or 8 lambs. Because of the absence of LH pulses during some collection periods, mean pulse amplitudes were based on values from 4 (weeks 3, 6–7, 8); 5 (weeks 2, 4–5); or 7 (week 1, follicular phase) lambs. Redrawn from Ref. 26, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.5 Patterns of circulating LH in the same ovariectomized (OVX) lamb in the presence (weeks 9, 15, 21, 27, 33) and absence (weeks 6, 12, 18, 24, 30) of exogenous estradiol (E, 2 pg/ml by implant). Samples were collected 3 weeks after insertion (top) or removal (bottom) of implant. Ovariectomy was at 3 weeks of age. From Ref. 36, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.6 Response to estradiol inhibition of tonic LH secretion decreases during puberty. Top: Onset of reproductive cycles in untreated lambs based upon the appearance of luteal-phase concen- trations of circulating progesterone. Bottom: Mean (± SEM) concentrations of circulating LH and estra- diol (E2 ) in ovariectomized lambs treated chronically with Silastic implants of estradiol from the time of ovariectomy (arrow); undetectable LH values (open circles). From Ref. 42, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.7 Effects of naloxone on serum LH concentrations in developing estradiol-treated OVX lambs at 15, 21, and 27 weeks of age. Data from four representative individuals are shown. During each naloxone test, the first 4 h served as a control period; four intrave- nous injections of naloxone (1 mg/kg body weight) were administered hourly for 4 h (arrows). Top: Two individuals (748 and 747) were raised on a permissive photoperiod; note the age-related increase in LH pulse frequency during the control periods. Bottom: Two individuals (762 and 761) were raised on an inhibitory photoperiod; note that LH secre- tion remains low in the control periods throughout the experiment. Redrawn from Ref. 53, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.8 Changes in LH pulse frequency and kisspeptin during pubertal development. Panels C and D of this figure are reproduced in color in the color plate section. Panel A: LH pulse frequency in prepubertal and postpubertal female lambs that were either gonad-intact (Intact) or ovariectomized (OVX). Postpubertal intact lambs were in the early follicular phase. LH pulse frequency was higher in intact postpubertal female lambs than in intact prepubertal female lambs and rose following ovariectomy in the prepubertal, but not postpubertal, lambs. Panel B: Kisspeptin-immunopositive cell numbers were greater in postpubertal intact females than prepubertal intact females and increased with ovari- ectomy in the prepubertal, but not postpubertal, lambs. Panels C and D: GnRH neuron from a prepubertal female (panel C) and postpubertal female (panel D). Heavy arrows indicate point of contact between kisspeptin-containing varicosities and the GnRH neuron. Lighter arrows depict kisspeptin-positive nerve fibers. Panels E and F: The percentage of GnRH neurons exhibiting at least one kisspeptin close contact (panel E) was greater in intact postpubertal females than intact prepubertal females. This percentage increased with ovariectomy in the prepubertal, but not postpubertal, group. Numbers of contacts per GnRH neuron (panel F) did not differ among groups. Redrawn from Ref. 72, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.9 Analogous phases of sexual maturation based on the control of LH secretion in the monkey and sheep. The times of birth for each within the maturational scheme are indicated. Central to the hypothesis is that the sheep is born at a relatively advanced stage of sexual maturation, one that is comparable to that developed by the monkey shortly before menarche. From Ref. 91, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.10 Growth and the timing of puberty. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.11 Partitioning of metabolic fuel during develop- ment in the sheep. The circles represent increasing body mass from birth (inner circle) to maturity (outer circle). Each circle is divided into four quadrants to represent the estimated relative proportion of energy allocated at each stage of development. Modified from Bucholtz DC [Ph.D. Thesis]. University of Michigan. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.12 Patterns of LH secretion in representative gonad- ectomized, estradiol-treated male sheep before and after treatment with recombinant human leptin (12.5 μg/kg sc every 4 h). Top: LH pulse frequency is reduced in adults fasted for 48 h (left); 48 h of leptin treatment while continuing the fast increases LH secretion (right). Bot- tom: LH pulse frequency is low in nonfasted, growing lambs at 6 weeks of age (left); pulsatile LH secretion is increased after 72 h of leptin treat- ment (right) although responses were variable (see text for discussion). Data from Ref. 146. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.13 Central mechanisms controlling pulsatile LH secretion in the nutritionally growth-restricted female lamb. See text for explanation of insets. Top: Pattern of GnRH in pituitary portal blood of a representative growth-retarded lamb (left). Mean (±SEM) hypotha- lamic GnRH content in lambs fed restricted (Rest) and ad libitum (Ad lib) diets; POA/AH, preoptic area/anterior hypothalamus; MBH/M, mediobasal hypothalamus/median eminence (right). Bottom: Patterns of LH secretion in a representative growth-restricted lamb injected with NMDA (5 mg/kg BW) (left). Mean (±SEM) LH concentrations in lambs injected with GnRH (5 ng/kg BW, n = 15) (right). Redrawn from Ref. 173; portal GnRH data from Ref. 174. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.14 Photoperiod and the timing of puberty. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.15 Interplay among rhythms timing puberty involv- ing day length, the pineal gland, electrical activity of GnRH neurons, and GnRH/LH secretion. LD, long day; SD, short day; RHT, retinohy- pothalamic tract; SCN, suprachiasmatic nucleus; PVN, paraventricular nucleus; SCG, superior cervical ganglion. Redrawn from Ref. 233. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.16 Delay in puberty in autumn-born lambs due to inappropriate photoperiod during development. Shown are the ages and months at first ovulation in spring-born and autumn-born females raised in natural photoperiod (first three panels) and in autumn-born females reared in an artificial, seasonally reversed photoperiod (last two panels). Ovulations were initiated in spring-born females dur- ing the age range of 26–35 weeks (dashed rectangle). From Ref. 20, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.17 Timing of puberty, as evidenced by the first rise in circulating progesterone to luteal phase concentrations in lambs of the D’man breed and of the Sardi breed. Lambs were born either in winter (top) or summer (bottom) and raised in natural environmental conditions in Morocco. Data from Ref. 234, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.18 LH patterns at different ages in a lamb maintained in a permissive photope- riod sequence for puberty (top two panels) and in a lamb maintained in an inhibitory photope- riod sequence for puberty (bottom two panels). For each lamb, upper panels depict LH patterns 3 weeks after replacement of a constant release estradiol capsule; lower panels depict LH pat- terns 3 weeks after removal of estradiol. From Ref. 44, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31. 19 Alternate photoperiods initiate reproductive cycles FIGURE 31.19 Alternate photoperiods initiate reproductive cycles. Spring-born lambs were raised entirely in artificial short days of 9 h light: 15 h dark (9L:15D) or with 10 weeks, 5 weeks, or 1 week of long days of 15 h light: 9 h dark (15L:9D). Reproductive cycles with normal luteal phases (large blocks); cycles with short luteal phases (small blocks); photoperiod (broken lines). Each horizontal line shows data for an individual lamb, except in the top panel, which indicates that seven of 10 lambs remained anovulatory. From Ref. 42, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.20 Change in melatonin pattern after shift from long days to short days. Circulating melatonin (mean ± SEM, n = 8) is shown during a 24-h period for 7-week-old lambs (left) and their mothers (right) on long days (Day −1), on the day of the shift to short days (Day 0), and on Days 4 and 13; periods of darkness (shaded areas). From Ref. 252, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.21 Denervation of the pineal gland of the lamb pre- vents onset of repetitive reproductive cycles at the normal age in natural environment (bottom). The 24-h pattern of circulating melato- nin (mean ± SEM (insets)) is shown at 40 weeks in lambs in which the superior cervical ganglia were removed bilaterally at 6 weeks of age (bottom); also shown is the melatonin pattern in unoperated postpu- bertal lambs that were exhibiting normal reproductive cycles (top) (see Figure 31.19 for details of coding of luteal phases). From Ref. 25, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.22 Circulating prolactin con- Birth Female centrations in female lambs in a 12L:12D, born to mothers maintained in a 16L:8D (open circles) or 8L:16D (solid circles) during late gestation. Values are mean ± SEM; n = 7. From Ref. 262, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.23 Season and growth influence timing of onset of reproduc- tive cycles in female lambs (top, mean (±SEM) BW and age at first luteal phase; bottom, cumulative % ovulating for each group). Lambs were born in spring (March) and were raised outdoors (bro- ken line, photoperiod). They were either fed ad libitum after weaning at 10 weeks of age (Group A), or were placed on a restricted diet of similar composition (Groups B, C, D); at various ages (arrows), feeding ad libitum was begun in food- restricted lambs. From Ref. 231, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.24 Increase in mean (± SEM) circulating LH in rapidly- growing estradiol-treated, ovariectomized lambs exposed to either natural photoperiod (open circles, n = 7) or to decreasing artificial pho- toperiod (solid circles, n = 8) from birth. Artificial photoperiod data from Ref. 268. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.25 Sex differences in the timing of the pubertal increase in GnRH secretion and gonadal activation. Mean (± SEM) LH concentrations (solid circles) in gonadectomized female (top) and male (bottom) sheep treated chronically with a constant level of estra- diol by subcutaneous Silastic implant. The time of the increase in LH secretion is associated with the onset of ovulatory cycles (shaded his- togram) in intact females, and testicular growth and spermatogenesis (shaded line) in intact males. Redrawn from Ref. 270. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.26 Prenatal exposure to testosterone (panels a-f) or DHT (panel g) and its effect on external genitalia (left), the developmen- tal pattern of tonic LH secretion (middle), and the LH surge (right). The lambs were gonadectomized within 3 weeks after birth and implanted with a Silastic capsule containing estradiol. Redrawn from Ref. 270. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.27 Photoperiodic regulation of the timing of puberty in male, female, and prenatally testosterone-treated female (shaded symbols) sheep. Symbols indicate timing of pubertal LH rise. Top: Animals raised indoors in a simulated natural photoperiod. Bottom: Animals raised indoors in a reverse natural photoperiod. Puberty was delayed in females in the reverse natural photoperiod beyond the end of the study. Redrawn from Ref. 270. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.28 Integrated model for internal and external determinants tim- ing the onset of puberty in the sheep. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 31.29 Model for integration of signals and control mechanisms timing puberty through the regulation of GnRH secre- tion. A genetically linked developmental clock is proposed to signal when it is first possible to produce the pubertal increase in GnRH secretion but the actual time when it occurs is fine-tuned by mul- tiple permissive signals that provide information about internal and external environments. These signals regulate steroid-dependent and steroid-independent feedback control of GnRH pulse frequency. From Ref. 287, with permission. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition