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Hormones and Stress
Hormones
Classifying Hormones by StructureSteroid Hormones
Fat-soluble chemical messenger synthesized from cholesterol
Examples: gonadal (sex) hormones, thyroidPeptide Hormones
Chemical messenger synthesized by cellular DNA that acts to affect the target cell’s physiology
Examples: insulin, growth hormone
Hormones
Classifying Hormones by FunctionHormones that maintain homeostasis
State of internal metabolic balance and regulation of physiological systems in an organism
Gonadal (sex) hormones Control reproductive functions and sexual appearance
and identity
Stress hormones (e.g., glucocorticoids) Secreted in times of stress (fight or flight); important in
protein and carbohydrate metabolism
HormonesHierarchical Control
Four LevelsHypothalamusPituitary GlandTarget Endocrine GlandsTarget Organs and Tissues
HormonesHierarchical Control
Hormones affect almost every neuron in the brain
Hormones Neurons Genes Proteins
HormonesHomeostatic Hormones
Homeostasis of intracellular and extracellular environments are essential to life
Diabetus mellitus Caused by a failure of the pancreas to secrete
enough (or any) insulin Hyperglycemia: High blood-glucose levels; cells
are not using glucose and therefore are not able to function properly
Hypoglycemia: Low blood-glucose levels
HormonesGonadal Hormones
Sex hormones begin to affect us before we are born and continue to affect us throughout our life
Organizational Hypothesis Proposal that actions of hormones during
development alter tissue differentiation Example: Testosterone masculinizes the brain
Biological effects of sex hormones
organizational effects: permanent structural changes elicited by sex hormones during critical period of embryonic / fetal life
activational effects: reversible effects of sex hormones (e.g. estrus)
Steroid Hormones Act Through Gene Expression
hormone
Hormone receptor
hormoneHormone receptor
Gene products
Synthesizes transcription factor
mRNA
HormonesGonadal Hormones
Sex hormones contribute to brain differences: Male brain is slightly larger than female after
correcting for body size Right hemisphere is larger than the left hemisphere
in men Female brains have higher rates of cerebral blood
flow and glucose utilization Parts of the corpus callosum are larger in women Language areas of the brain are somewhat larger in
women
Copyright © 2004 Allyn and Bacon
Neural Control of Sexual Behavior Brain Mechanisms
Sexually dimorphic nucleus (SDN): A nucleus in the preoptic area that is much larger in males
than in females; first observed in rats; plays a role in male sexual behavior.
Periaqueductal gray matter (PAG): The region of the midbrain that surrounds the cerebral
aqueduct; plays an essential role in various species-typical behaviors, including female sexual behavior.
Copyright © 2004 Allyn and Bacon
HormonesGonadal Hormones
Sex hormones contribute to differences in cognitive performance: Men tend to excel on spatial tasks whereas women
tend to excel on verbal tasks Performance of women differs during the course of
menstruation Low female sex hormones: Better spatial performance High female sex hormones: Better verbal performance
Differences between pre- and postmenopause, and during various stages of pregnancy
Gender differences in brain structure & function
less lateralization of cerebral hemispheres in women (in men, left more concerned with verbal skills, right with visual-spatial function)
larger fiber tracts in female corpus callosum “sexually dimorphic nucleus” present in hypothalamus
(also: INAH 3)
Males > FemalesFemales > Males
Difference in Solving Intellectual Problems
• Boys and girls different way of developing brains.
• Difference between boys and girls lies in patterns of ability rather than in overall level of intelligence (IQ).
***
Townsend et al. 2004
Hormonal Control of Sexual Behavior of Laboratory Animals Males
Oxytocin: A hormone secreted by the posterior pituitary gland; causes
contraction of the smooth muscle of the milk ducts, the uterus, and the male ejaculatory system.
Prolactin: A hormone of the anterior pituitary gland, necessary for
production of milk; has an inhibitory effect on male sexual behavior.
Copyright © 2004 Allyn and Bacon
Hormonal Control of Sexual Behavior Hormonal Control of Female
Reproductive Cycles
Corpus luteum: A cluster of cells that develops from
the ovarian follicle after ovulation; secretes estradiol and progesterone.
Progesterone: A steroid hormone produced by the
ovary that maintains the endometrial lining of the uterus during the later part of the menstrual cycle and during pregnancy.
Organizational Effects of Androgens on Behavior:Masculinization and Defeminization Effects of Pheromones
Pheromone: A chemical released by one animal that affects the behavior
or physiology of another animal; usually smelled or tasted.
Lee-Boot effect: The slowing and eventual cessation of estrous cycles in
groups of female animals that are housed together; caused by a pheromone in the animals urine.
Organizational Effects of Androgens on Behavior:Masculinization and Defeminization Effects of Pheromones
Whitten effect: The synchronization of the menstrual or estrous cycle of a
group of females, which occurs only in the presence of a pheromone in a male’s urine.
Vandenbergh effect: The earlier onset of puberty seen in female animals that are
housed with males; caused by a pheromone in the male’s urine.
HormonesStress HormonesStressor
A stimulus that challenges the body’s homeostasis and triggers arousal
Stress Response The physiological and behavioral arousal and any
attempt to reduce the stress Two sequences
Fast-acting: Activation of sympathetic nervous system; “fight-or-flight” response
Slow-acting: Activation of parasympathetic nervous system; “rest-and-digest” response
Stress Disorders
Stress: A general, imprecise term that can refer either to a stress
response or to a stressor (stressful situation).
Stressor: A stimulus (or situation) that produces a stress response.
Stress Disorders
Fight-or-flight response: A species-typical response preparatory to fighting or fleeing;
thought to be responsible for some of the deleterious effects
of stressful situations on health.
Stress Disorders Physiology of Stress
Glucocorticoid: One of a group of hormones of the adrenal cortex that are
important in protein and carbohydrate metabolism, secreted
especially in times of stress.
Stress Disorders Physiology of Stress
Corticotropin-releasing hormone (CRH): A hypothalamic hormone that stimulates the anterior
pituitary gland to secrete ACTH.
Adrenocorticotropic hormone (ACTH): A hormone released by the anterior pituitary gland in
response to CRH; stimulates the adrenal cortex to produce
glucocorticoids.
Copyright © 2004 Allyn and Bacon
CRF and the Hypothalamus
PVN
CRH
AnteriorPituitary
Glucocorticiods
AdrenalCTX
ACTH
Target Organs
PVN
CRH
AnteriorPituitary
Glucocorticiods
AdrenalCTX
ACTH
Systemic effects:
Fight or flight responses
↑BP ↑HR ↑O2 ↑Blood sugar
LH
Lateral horn
Adrenalmedulla
Epi/NE
Functions
BASAL LEVELS (Proactive)Circadian rhythmMoodSleepSensory perceptionLearning
ELAVATED LEVELS (Reactive)Stress Reponses
CRH Feedback
RapidpvnIntermediateCort (pvn/pituitary)DelayedHigher brain areas
PVN
CRH
AnteriorPituitary
Glucocorticiods
AdrenalCTX
ACTH
Hippocampus
CRH
CORT
SeptumBNST
Somatostatin
BRAKE
INHIBIT CRH
Release
Receptors
-
PVN
CRH
AnteriorPituitary
Glucocorticiods
AdrenalCTX
ACTH
CRF Receptor types
CRF Receptor types
TYPE 1 (MR) High affinity Binds CORT and
aldosterone Stabilizes excitability Stress Sensitivity
TYPE 2 (GR) Low affinity Binds only CORT Suppresses
excitability Recovery from stress
CRF receptor distribution
CRF cellular effects
CRF cellular effects
Chronic Stress
Both Receptors down regulatedEnlarged Adrenal glandReduced neuronal activityReduced neurogenesisReduced metabolic activityInhibited Glucose uptake
Chronic Stress and Hypothalamic integration
Stress and Depression Hypothesis
Depression is predicated by
deregulation of the HPA axis
PVN
CRH
AnteriorPituitary
Glucocorticiods
AdrenalCTX
ACTH
Hippocampus
CRH
CORT
SeptumBNST
Somatostatin
BRAKE
INHIBIT CRH
Release
Receptors
-
Stress and Depression Hypothesis
Stress and Depression Hypothesis
After depression treatment Cort secretion returns to normal
Cushing Disease- always depressed
High CORT and CRH disregulates 5ht, causing Learned Helplessness
Symptomology matches CRH functions
Dexamethasone Test
Stress and Depression Hypothesis
CRH/Depression leads to behavioral symptoms and inability to learn new coping strategies
Therapy or SSRI Drug treatment allows for the brake to become functional again
Prozac—BDNF ---ROS-neurogenesisTherapeutic lag = Mrna CORT rebalancing
PVN
CRH
AnteriorPituitary
Glucocorticiods
AdrenalCTX
ACTH
HippocampusAMYGDALA
NE
CORT Receptors
MemoryStorage
NE
Stress Disorders Psychoneuroimmunology
Psychoneuroimmunology: The branch of neuroscience involved with interactions
between environmental stimuli, the nervous system, and the immune system.
Antigen: A protein present on a microorganism that permits the
immune system to recognize the microorganism as an invader.
Stress Disorders Psychoneuroimmunology
Antibody: A protein produced by a cell of the immune system that
recognizes antigens present on invading microorganisms.
B-lymphocyte: A white blood cell that originates in the bone marrow; part of
the immune system.
Stress Disorders Psychoneuroimmunology
Immunoglobulin: An antibody released by B-lymphocytes that bind with
antigens and help to destroy invading microorganisms.
T-lymphocytes: A white blood cell that originates in the thymus gland; part of
the immune system.
Stress Disorders Psychoneuroimmunology
Cytokine: A category of chemicals released by certain white blood
cells when they detect the presence of an invading microorganism; causes other white blood cells to proliferate and mount an attack against the invader.
HormonesEnding a Stress Response
Normally, stress responses are briefStress responses are turned on and off in
the brainSapolsky (2003)
Hippocampus is involved in turning off the stress response
Too much cortisol will damage neurons in the hippocampus
Vicious cycle involving prolonged stress, cortisol levels, and hippocampal functioning
HormonesEnding a Stress Response
Posttraumatic Stress Disorder Syndrome characterized by physiological
arousal symptoms related to recurring memories and dreams related to a traumatic event – for months or years after the event