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Lecture 12

Psych 2220A Lecture 12

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Department
Psychology
Course
Psychology 2220A/B
Professor
Scott Mac Dougall- Shackleton
Semester
Fall

Description
Psych 2220A Lecture 12 Neuroendocrinology • Hormones and Behaviour – Endocrine System – Classes of Hormones – Control of Hormones – Sexual Differentiation –Aromitization and Neural Sex Differences – Levels of Sexual Determination – Hormones and Stress Hormones • “Secretory blood-borne product” • Internal chemical messengers •An organic chemical messenger released from endocrine cells that travels through the blood system to interact with cells at some distance away and causes a biological response • Molecules that have effects on cells (like NT) • Can have effects on distant tissues due to blood transportation • Important parts: Chemical messenger, travels through blood*, endogenous compound, released from endocrine cells*, interact with target cells at some distance away * Endocrine Glands • Ductless glands • Exocrine glands have ducts – E.g. sweat glands, mammary glands, scent glands Chemical Communication • Endocrine – Secreting cell --> Blood vessel --> Target cell Target Cells • Hormones require receptors to have actions Endocrine vs. Nervous Hormones Neurotransmitters Released from endocrine gland Released from presynaptic neuron Travels through blood Travels across synaptic cleft Received at distant target organ Received at postsynaptic neuron Psych 2220A Lecture 12 Neurohormones • Released from neurons (neurosecretory cells) • Travel through blood • Received at distant target organ • Not hormones; not produced by an endocrine gland. Produced by neurosecretory cells Chemical messengers • Hormones • Neurohormones • Neurotransmitters • The same molecule may act as more than one type, depending on nature of secretory cell •Adrenaline aka epinephrine; released by the adrenal medulla HormoneAction • Hormone action via 2 main processes • Water soluble hormones (e.g. peptides) – Cannot cross cell membranes on their own; bind to receptors on the external part of the cells • Fat soluble hormones (e.g. steroids) – Liophilic; trouble getting transported in blood plasma. No problem going through cell membrane Water Soluble Hormones • Cannot cross cell membranes • Bind to membrane receptors • Initiate 2nd messenger system within cell – Pretty much like a neurotransmitter binding to a metabotropic receptor! Fat Soluble Hormones • E.g. steroid hormones • Freely cross cell membrane • Bind to intracellular receptors • Steroid-receptor complex modifies cell •Act as transcription factors (change gene transcription) • Need protein to help dissolve so they can go through the blood; at the target tissue they can go through. Float in cytoplasm waiting to bind to receptor. Steroid and receptor bind to form complex (acts as transcription factor). Enter cell and bind to promotor regions to effect the transcription of genes Hormones and Behaviour • How can hormones affect behaviour? • Hormone receptors found on – effector organs (e.g. muscles) – Sensory organs – The central nervous system! • Main target for most hormones are the brain. Hormones MODIFY how the nervous system is Psych 2220A Lecture 12 working (neuromodulator) • Hormones modulate behaviour by affecting how the nervous system works * • Hormones do not directly cause a behaviour • For a behavior to occur you need a functioning CNS leading to a potential change in behavior • Hormones change the probability or intensity of a behaviour in the appropriate context • How can hormones affect behaviour? 1 - Development long term effects (organizational effects) 2 - Short term change in adulthood (activational effects) -->Activate behavior happening now Organizational effects • Example: urinary posture in dogs • Sex difference in posture (male lifts leg) –Adult castration does not make male urinate like female – Early testosterone treatment induces females to urinate like males • Hormone effects during early stage of development. Later in the life the hormone doesn't need to be there as the change has already taken place. Eventually don't "need" the hormones around • Hormones can alter the development of the nervous system, effector organs, and sensory system * Activational Effects • Short term changes in behaviour • Neurons can have hormone receptors • Hormones induce change in activity of nervous system – Mammals: suckling leads to oxytocin release which leads to milk letdown (released from the pituitary gland) – Stress response, stress hormones released in minutes • Rodents: sexual behavior is hormone dependent. Male won't mount female unless he has circulating testosterone. To exhibit behavior he needs to be exposed to testosterone in early development. Treat female with testosterone? She won't mount. BOTH activational and organizational Classes of Hormones • Peptide/ protein hormones – Direct product of gene transcription. Water soluble (growth hormone, comes through expression of gene) • Steroid hormones – Lipid soluble; derivative of cholesterol. Gene for enzyme to take cholesterol to testosterone, no gene for testosterone • Monoamines • Lipid-based hormones (but don’t affect behaviour directly in vertebrates • Usually only one class produced by any given gland * Psych 2220A Lecture 12 Sex steroid hormones •All steroids are derivatives of cholesterol • Enzymes convert steroids into different molecules in a series of steps Sex steroids • Produced primarily by the gonads, the adrenal cortex, and the brain!! Steroids •Androgens ≠ male hormones • Estrogens ≠ female hormones • Varies by ratio of hormone present Hypothalamus • Subdivided into many nuclei multiple afferents and efferents • Integration of environmental cues • Endocrine output via neurosecretory cells Pituitary • “Master gland” • Two glands sitting behind the “stalk” •Aka hypophysis •Actually 2 distinct glands –Anterior = adenohypophysis (Travel through blood supply in the stock. Neurohormones bind to receptors and release hormones from anterior pituitary. Endocrine gland) Psych 2220A Lecture 12 – Posterior = neurohypophysis (Neurons axons project all the way down the stalk. Terminals of neurons in posterior. Release products into the blood stream.Axon synaptic terminals from the hypothalamus) Anterior Pituitary • Hypothalamus secretes neurohormones in portal blood stream – Releasing hormones, inhibiting hormones • Stimulate release of tropic hormones from anterior pituitary – E.g. growth hormone, follicle stimulating hormone Posterior Pituitary • Receives projections from hypothalamic neurosecretory cells •Acts as reservoir for oxytocin and vasopressin Cyclic vs. Steady Gonadal Hormone Levels • Female hormones go through a ~28- day cycle, the menstrual cycle • Male hormone levels are more constant, but still have pulsatile release and circadian cycles • Cyclic release of anterior pituitary hormones under control of hypothalamus Control of the Pituitary by the Hypothalamus • Posterior – neural input from hypothalamus – Vasopressin – antidiuretic hormone – Oxytocin – labor and lactation – Synthesized in hypothalamic paraventricular and supraoptic nuclei – These nuclei have terminals in the posterior pituitary •Anterior pituitary – hypothalamopituitary portal system carries hormones from the hypothalamus to the anterior pituitary Discovery of Hypothalamic Releasing Hormones • Thyrotropin-releasing hormone first isolated from the hypothalamus of sheep and then pigs • Triggers the release of thyrotropin from the anterior pituitary • Thyrotropin then stimulates release of hormones from the thyroid gland Regulation of Hormone Levels • Neural –All endocrine glands (except the anterior pituitary) receive neural signals – From cerebral or autonomic neurons • Hormonal – Tropic hormones, negative feedback • Nonhormonal chemicals – Glucose, Ca2+, Na+ Pulsatile Hormone Release • Hormones tend to be released in pulses • Leads to often large minute-to- minute fluctuations in levels of hormones Psych 2220A Lecture 12 See Figure 13.5 - Neural signals project to hypothalamus - Integration of environmental cues - Environmental output - Travels through portal to anterior pituitary - Gonads release steroid hormones, which are released into body tissues Sex differences • Sex differences are ubiquitous • By definition sexes differ in behaviour • How are sexes determined through development? • How does this process give rise to sex differences in behaviour? Levels of Sex Determination • Genetic sex • Chromosomal sex • Gonadal sex • Gametic sex • Hormonal sex • Morphological sex • Behavioural sex • Genetic sex • Human specific: – Gender identity – Gender role – Legal sex Sexual Differentiation Mammals • Genetic sex determination • XX (female) versus XY (male) • SRY gene – Sex determining Region of the Y chromosome Genetic sex • Developing embryo has a bipotent gonad • In XY embryo, expression of SRY in the gonad produces TDF (testis determining factor) – Default developmental pathway to become an ovary when TDF is absent • TDF binds to other genes results in development of testis • In absence of TDF gonad develops into ovaries • Mice that are XY, but lack SRY gene develop as female • XX mice transgenically given SRY gene develop as male • Mammals only • Bipotent: become either testicular tissue or ovarian tissue Psych 2220A Lecture 12 Morphological sex • Differentiated gonads produce hormones • Testis produces androgens – Organization of morphology and brain to male phenotype • Ovaries produce more estrogens than androgens – Development of female phenotype – Even in absence of gonads • Remove ovaries early in development you get typical female development. "Default pathway" --> happens in the absence of testosterone • Female development “default”, however requires low levels of estrogens for normal development • Embryonic bipotent gonads • Embryonic dual sexual ducts Müllerian ducts • Develop into female sexual ducts unless told otherwise – Fallopian tubes, uterus and cervix • Development proceeds in presence of ovaries, or absence of gonad • Testes produce MIH (Müllerian Inhibiting Hormone) which induces regression of Müllerian ducts Wolffian ducts • Develop into male sexual ducts – Seminal vessicles, vas deferens • In presence of ovaries or absence of gonad Wolffian ducts regress • In presence of androgens (from testes) Wolffian ducts develop Psych 2220A Lecture 12 Morphological sex • Genitalia, bipotent genital tissue • Genital folds – Form labia or scrotum • Genital tubercle – Forms clitoris or penis • Masculiniz
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