Adolescence and Puberty 11/12/03

1. What is adolescence? 2. Describe reproductive function from adolescence through adulthood. 3. What is the difference between puberty and adolescence? 4. Why is reproductive function so late to mature? 5. What is the gondal function in children? 6. Review!!: What is the negative feedback loop of gondal regulation? 7. What is the paradox in children in terms of the negative feedback loop regulation versus adults? 8. What happens during puberty to influence the limbic system which will eventually impact reproductive function? 9. AT birth and in childhood, what organ is proportionately more developed than other organs? 10.How does the CNS mature from birth until late childhood? 11.What is the significance of the maturation of the reproductive function is limbic system? 12.What are some of the functions of the limbic system mentioned in lecture? 13. What are some of the majors structures of the limbic system? What are some the major pathways? 14.Give some evidence that it is the immaturity of the limbic-hypothalmic system that is responsible for reproductive immaturity? 15. At puberty the hypothalamus changes its “gonadostat” threshold. What happens? 16.If there are low levels of sex steroids, why wouldn’t there be secretion of GnRH from the hypothalamus in children? 17.So you saw a bunch of graph and figures in lecture that somehow related the electrical regulation of amygdala to hypothalamus regulation. There was some talk about maturation changes evoke potential in amygdala and hypothalamus of developing rats This time table of maturation was metioned: Eyes Open (10 days)  21 days (weaning)  39 days reproductive maturation  Adult What was the point of hearing about Dr. Timiras’ PhD student’s research?

1. Adolescence is the period extending from the onset of reproductive function until adulthood. It is a gradual development which serves as a time period when bodily function mature into optimal functioning in adulthood. 2. In males and females, reproductive function starts during (as opposed to by) adolescence. In males, it persists through life. In females, it ceases at menopause. 3. Puberty is maturation of the reproductive system. Adolescence is the maturation of all bodily function. Puberty is just one of the physiological changes that occur during adolescence. 4. Immaturity of the reproductive system is not at the level of the gonads or anterior pituitary but at the level of the brain. Translation: It’s not that the ovaries can’t produce mature ova or testis sperm – they can – so what’s the problem? Basically, the brain, particularly the limbic system and hypothalamus, must have matured sufficiently in order for reproductive function to occur. Puberty cannot occur until the brain is mature enough to regulate reproductive function.  Immaturity of reproductive system happens at the: i. hypothalamus: YES! ii. Anterior pituitary: NO! iii. Gonads: NO! iv. Level of limbic – hypothalamic pathways: Yes! Extra Logic: From an evolutionary perspective, you need to be able to provide for your offspring in order to get genes to be passed and stick around long enough to be passed on again. The relative late development of reproductive function in humans helps protect against pregnancy before males and females are able to provide for a child successfully.

5. In boys and girls, there are secondary sex organs that have some functionality. In boys, the testis produce low levels of testosterone and in girls, the ovaries produce low levels of estrogen. There are also very low levels of GnRH from the hypothalamus and very low levels of FSH/LH from the anterior pituitary. In essence, there are hormones but at very low levels because the negative feedback of hormone regulation that we all know and love does not function during childhood (because the brain is immature).

6. Review of negative feedback loop 

7. In children, there are low FSH, low LH, low GnRH  Low sex hormones. This does not happen in adults. Low levels of sex hormones usually means there are high levels of the regulatory hormones which stimulate the production of sex hormones. 8. During puberty, the limbic system matures which leads to GnRH neurons to increase responsiveness to changes in sex hormone levels. In essence, this means that the cells are now sensitive to steroid hormones and the negative feedback loop begins to function as it does in adults. 9. The BRAIN!! 10.The CNS matures progressively by # of different means including:  Developing better communication between neurons through increases in dendritic branches and # of synapses  Increasing the # of glial cells  better metabolism, neurotransmission, myelination, faster and more efficient neuronal communication to specific stimulus  The threshold to stimulus decreases  Limbic system maturation (can you pick up the reoccurring theme?!)

11.Basically, the limbic So what is the limbic system again? It’s a collective term for the system tells the various brain structures at or near the edge (limbus) of the medial hypothalamus what wall of the cerebral hemisphere, including hippocampus, amygdala, to do. The amygdala and fornicate gyrus; also refers to the interconnections of these structures, which includes organs like the hypothalamus. The limbic has fibers extending system’s most important influence is on the endocrine and to the autonomic motor systems; its functions also appear to affect hypothalamus. Until motivational, sexual and mood states. this connection is made, there is no regulation of the hypothalamus  no secretion of GnRH  no secretion of FSH/LH  no stimulus for gonads to produce sex steroids. During puberty, these connective fibers are laid down. 12.Cognition, affect, conation (urge to take action – hmmmm could this mean I often have a problem with my limbic system…), sexual behavior (copulation, coordinate events that lead to pregnancy – yeah, I’m just going to leave that one out of the commentary…), fear and rage, and motivation 13. Limbic Structures: amygala, hippocampus, septal nuclei, Pathways: stria terminalis, Amygdala – hypothalmic fibers 14.  Gonads from immature animal transplanted into adult animals  produce ova or sperm immediately and normally  Pituitary from immature animal  adult animal regulates normal reproductive function  A messed-up hypothalamus (lesions, alterations, trauma) and specifc areas of the limbic system(amygdala and hippocampus) will PREVENT puberty from occurring

15.During adolescence, the threshold for low sex hormones decreased  inducing stimulation of GnRH release from the hypothalamus  cascade of anterioir-pituiatary and gonadal hormone release AND negative feedback regulation 16.Before puberty, the secretion of GnRh and Gns is inhibited by very low levels of gondal function. This is the OPPOSITE of what happends in adults. At puberty, decreased sensitivity to negative feedback of gonadal hormones on GnRH and FSH/LH  normal reproductive function. 17.THE POINT: the relationship between the limbic system and the hypothalamus is an intimate relationship which impacts on reproductive function. No maturation of limbic-hypothalamic pathway  No puberty