State the 3 definitions of puberty in the female (which is most practical?)
Age at first estrus (heat)
Age at first ovulation
Age at which a female can support pregnancy without deleterious effects (most practical, as "timely" offspring is the end goal)
State the 5 definitions of puberty in the male and identify which one is most practical
Age at which behavioral traits are expressed
Age at first ejaculation
Age when spermatozoa first appear in the ejaculate
Age when spermatozoa first appear in the urine
Age when ejaculate contains a threshold number of spermatozoa (most practical, leads to successful fertilization)
Development of specific GnRH neurons in the hypothalamus to support gametogenisis is influenced by what 3 factors?
The development of threshold body size/plane of nutrition
Exposure to a variety of environmental and social cues
The genetics of the animal/individual
Describe how E2 defeminizes the brain in the male but not the female
Testosterone from the fetal testis in the male fetus is converted to estradiol, which crosses the blood-brain barrier and defeminizes the hypothalamus, thus minimizing surge center function.
This does not occur in the female because estradiol from the ovaries binds to a protein called alpha-feto protein, preventing it from crossing the blood-brain barrier. Alpha-feto protein is a glycoprotein synthesized by the embryonic yolk sac and later the fetal liver
What endocrine mechanism supresses the release of GnRH in the prepubertal a) female and b) male
FB from the tonic center E2 in females and T in males
What are the 3 plausible signals whereby metabolic signals are converted to hypothalamic neural activity
1) Leptin sensitive neurons - adipocytes produce leptin that enters the blood and may stimulate neuropeptide Y neurons or directly stimulate GnRH neurons. Blood leptin is proportional to the amount of fat, thus reflecting the nutritional status of the animal
2) Glucose sensitive neurons - blood glucose levels (another indicator of metabolic status) might stimulate glucose sensing neurons that in turn stimulate GnRH neurons
3) Fatty acid sensitive neurons - blood fatty acids may stimulate neurons that in turn stimulate the GnRH neurons. Blood fatty acids would be an indicator of nutritional status of the animal
Describe the difference in the secretory pattern of LH in males versus females
LH does not surge in male, but maintains consistent episodic patterns of secretion every 2-6 hours in the post pubertal animal. Steady GnRH results in steady LH and therefore steady pulsative testosterone release.
LH and estradiol surge about every 20 days in the female, varying among species and lengths of estrous cycles. Low amplitude LH pulses are present between the surges.
Describe how social cues alter the onset of puberty in the gilt
Social cues impact the onset of puberty, including olfactory recognition of pheromones in the urine. Gilts housed in small groups have delayed puberty as opposed to gilts housed in groups of 10 or more. The presence of a male, whether through visual or physical contact, will hasten the onset of puberty in gilts, even more so than those housed in large groups.
Describe the influence of growth rate and bull exposure on the age of puberty in beef heifers
Exposure to a bull accelerates the onset of puberty in beef heifers. Heifers with a high growth rate reached puberty 74 days earlier when exposed to a bull. Heifers with a moderate growth rate reached puberty 53 days earlier when exposed to a bull, as opposed to their counter parts without exposure to a bull, but with the same high or moderate growth rates.
Briefly explain why age of puberty in girls is decreasing
The likely explanation is that nutrition today is much better and more energy is available in wealthy countries. The body weight of the average 12 year old at menarche is the same as the 17 year old examples from the mid 1800's in Norway. In poorer countries where nutrition is not adequate, puberty continues to occur at older ages
Why must the endangered captive clouded leopards (male and female) be housed together before they reach puberty (and why is this not the case in the wild)
The male will become aggressive and injure or kill the female, however, this is a captive anomoly.
What was done to maintain the soprano or alto voices of boys choirs
Castration, because puberty "ruined" their high pitched clear voices, and orchidectomy made them retain their voices through adulthood