<Endocrine System> combination of neural and glandular mechanisms which control physiological functions/behavior via the secretion of hormones. Often endocrine cells are clumped together into a well defined gland (e.g. pituitary, thyroid, adrenal, testes, ovaries). Study of <Epigenetic Effects> Explanations that go beyond a pure genetic determination of traits. epi = above, genetics = the genotype
<Hormones> chemical signaling molecules secreted by the body at one site which cause changes in physiology at other sites. Such changes may affect behavior by altering neural substrates directly (organizational effects) or by altering their present function (activational effects).
<Neurohormone> refers to a compound that is released into the bloodstream at specialized neurohemal release sites. It binds to receptors anywhere in the body and thereby coordinates disparate biochemical responses.They are released from glands, transported via the circulatory system and influence the activity of target organs.
Target Organs receives hormones via blood stream, respond directly or release their own hormones in response (steroid hormones), and these hormones circulate back to turn off hormonal secretion: endocrine feed back loops.
Compensatory hypertrophy: feedback loops control levels of activity, systems are upregulated until they achieve sufficient functional effects (e.g. thyroxine and goiter)
Organizational effects
Hormonal influences during critical periods produce fairly permanent changes in nervous and endocrine systems; chromosomal Sex-determination (mammals, birds) or environmental (turtles, fish)
Mammals: hormonal cascade of events takes an individual down one of two paths (default is female). testes determining factor (tdf) in mammals or Sexchromosomal Abnormalities: Turner syndrome (XO monosomy), Klinefelter syndrome (XXY trisomy), XYY syndrome ("supermale"), Multi-X syndrome ("superfemale"), XX Male syndrome (SRY gene transference) XY Female syndrome (SRY gene missing)
Birds: Males are homogametic (ZZ), females are heterogametic (ZW)
Turtles: temperature
Fish: social stimuli
<Maternal effects>: atributes influenced by effects of the mother that are not due to direct genetic inheritance
Positional effects in the mammalian uterus
Activational effects
Hormonal secretion or its inhibition leads to a rather rapid response, they do not change behavior directly but lead to other hormonal changes. Hormones influence Sensory perception (human visual, rat odor, preference in castrated vs. intact)
Hypothalamus / Pituitary
Hypothalamus assesses the internal state: thirst, hunger
sends neurosecretory cell axons to the posterior pituitary (e.g. Oxytocin - following release from the posterior pituitary it travels the body via the general circulation and produces the physiological effects of milk-ejection (milk let-down) in the mammary gland or contraction in the uterus during parturition (child-birth). It also has powerful emotional effects (affective states) functioning in parental behavior and maternal competence)
secretes stimulatory / inhibitory releasing factors into anterior pituitary portal system
Pituitary receives releasing factors from hypothalamus and manufactures and secretes hormones (tropins): Prolactin, Follicle stimulating hormone (FSH), Luteinizing hormone (LH); receives, stores and releases neurohormones from hypothalamus
Sex behaviors: gonadotropin releasing hormone (GnRH) -> gonadotropin -> gonad maturation and gonadal steroid production -> feed back to brain
Sex steroids: Steroids initiate the basic female and male anatomies (i.e., organizing effects in sexual differentiation cascade) but also allow animals to later respond to activational effects. Expression of sex differences in behavior also requires that steroids activate many aspects of the phenotype during maturation. Reproductive Neuroendocrinology of Ring Doves (Streptopelia risoria): monogamous, sexually monomorphic, parental care from both male and female (incubate eggs, crop "milk"); Lordosis in female hamsters: female soliciting behavior.Lee-Boot effect - estrous cycles slow and stop in female mice housed together; Whitten effect - individuals start cycling again in synchrony if exposed to male odor; Vandenbergh effect - acceleration of onset of puberty in female rat when exposed to odor of male; Bruce effect - failure of recent pregnancy of female rat when exposed to male who is not the father.
Hormonal Control of Arthropod Molting: Brain: releases ecdysiotropin which stimulates release of molting hormone (MH) from Prothoracic Gland; Corpora allata: Juvenile Hormone (JH) suppresses metamorphosis; Prothoracic Gland; Corpora allata: Juvenile Hormone (JH) suppresses metamorphosis
