Hormones and BehaviorAlison BellAnimal BiologyUniversity of Illinois

Todays lectureHormonesWhat are they?Where are they made?What do they do?

Hormones and behaviorOrganization-activationRelative plasticity hypothesis In utero and parental effectsChallenge hypothesis

Hormones: What are they?Chemical substances, formed in a specialized gland or group of cells, released into the blood that affect target cells in another organ.

Distinct from:Neurotransmitters, substances released by neurons that are received by adjacent neurons & alter their membrane potential.Pheromones, substances released by an individual as scent signals for another.

Hormones: What are they?Chemically, they can be:Lipids (e.g. steroids such as testosterone)Peptides/proteins (e.g. vasopressin)Amines/other small molecules (e.g. epinephrine)Testosterone

Hormones: Where are they made?Peripherally Endocrine glands, e.g. adrenal gland, thyroid glandGonads, e.g. testes, ovariesCentrallyNeurohormones are produced within the brain, but travel to target via bloodstreame.g. hypothalamus, neurosteroidogenic cells

Hormones: What do they do?Many physiological effects: regulation of reproduction, growth, osmotic balance, heart rate, etc.In the brain: influence neuronal responsiveness, or activity of certain genes within the neuron, thus altering the biochemistry of the brain to alter behaviorNonsteroid hormones: cant enter cellSteroid hormones: pass right through

Hormone regulation:Important vertebrate pathways Hypothalamus-pituitary-gonad (HPG)Hypothalamus-pituitary-adrenal (HPA)

Hormone regulation:Synthesis and metabolismBells and whistles:ReceptorsPlasma binding proteinsEnzymes

How to study hormones?Remove the glandAdd hormoneMeasure circulating levelsBlock receptor

Sexual Behavior: FemalesEstradiol and miceOVX mice: eliminates female sexual behavior (lordosis)Can be restored by treatment with estradiol followed by progesteroneEstradiol

Sexual Behavior: MalesRed deer stagSept/Oct become aggressive, begin courting femalesTestes generate sperm and release testosteroneCastrated males do not fight or mateTestosterone implants restore behavior

HormonesBehaviorIf a male and female ring dove are placed in a cage containing a bowl and nesting material, and kept in simulated spring, they will initiate the following sequence:bow and coo display, where the male bows and coos to the femaleselect a nest site, marked by the female sitting on itbuild the nest takes one weekcopulate during nest buildingfemale lays eggs, 2 eggs over 2 daysincubate the eggs takes two weeksthe young hatch and the parents feed the young by producing a crop milk and regurgitating it for the young takes two weeksinitiate sequence againRole of progesteroneLehrman 1964

Important pointMany shared mechanisms, BUT mechanisms often differ between species/groupsDifferent selection pressures result in modifications of the hormonal mechanisms of behaviorHunt et al 1995

Modes of Hormone Action Activational effects Short-term, reversible effects that occur in the fully developed organism (e.g. alteration of transmission in neural networks that respond to certain aspects of the environment)Organizational effectsLong-term, irreversible effects on tissue differentiation and development (e.g. brain, ovary) that can either directly (brain) or indirectly (ovary) influence behaviorCritical or sensitive period

Activational EffectOxytocin and maternal behavior in micePre-maternal mice fear pups and will attack themOxytocin injections induce maternal behavior

Another activational exampleOxytocin and maternal behavior in sheepStimulation of birth canal during parturition results in oxytocin release in brainOxytocin injections cause non-pregnant females to accept alien lambs in 30 seconds!Dolly the sheep and her surrogate mom

Organizational EffectSexual differentiation via exposure to steroids during developmentFigure 1. Sexual dimorphisms in the brain.(a,b) The sexually dimorphic nucleus of the preoptic area (SDN-POA) is larger in male rats (a) than in females (b) because the testes secrete testosterone during the perinatal sensitive period. After that time, testosterone has little effect on SDN-POA volume. (c,d) In contrast, the volume of the rat posterodorsal medial amygdala (MePD), which is about 1.5 times larger in males (c) than in females (d), retains its responsiveness to testosterone throughout life. (e,f) In zebra finches, the robustus archistriatum (RA) nucleus is crucial for song production and has a greater volume in males (e) than in females (f). Like the rat SDN-POA, exposure to steroid hormones early in life is essential for the RA to develop a masculine phenotype. For the RA, however, the steroids may not originate from the testes, but are rather synthesized locally in the brain itself. SCN, suprachiasmatic nucleus; 3V, third ventricle; ot, optic tract. All scale bars = 250 mum. Morris et al 2004

Applying organization-activation theory to alternative phenotypesThe relative plasticity hypothesisAlternative phenotypes within-sex variation in phenotype (morphology, behavior), e.g. sneakers vs territorial males

Fixed: individual permanently, irreversibly differentiated into one or the other type and doesnt change phenotype during lifetime, e.g. satellite vs territorial ruffs, hooknose or jack salmon

Plastic: individual can change phenotype, e.g. calling vs intercepting frogs depending on local conditions

Moore et al 1998

The relative plasticity hypothesis

Moore et al 1998

Effects of exposure to hormones on behavioral developmentMice and aggressivenessSubtle differences in the hormonal environment during embryonic development influence adult behaviorE.g. Males: 2M more aggressive later on.E.g. Females: 2M more aggressive (correlated with territory size as adults)Vom Saal et al

Another interesting way in which developing embryos are exposed to hormonesGil et al 1999, zebra finchesFemales mated to relatively attractive males deposited more testosterone in their eggs compared to females mated to unattractive males

The differential allocation hypothesis (Burley 1988)

Testosterone in male birds

What explains the dynamics (change over time) of T?

Costs of TTLevel of behaviorAggressionParental behavior

The challenge hypothesis

In species where males provide direct parental care (feed the chicks), males should increase T only when needed, e.g. when challenged, but then return T to level B. In contrast, in species where males do not provide direct parental care and spend most of their time defending the territory, males should have high, relatively unchanging, levels of T.

Wingfield et al 1990

Closer to home: hormones and human behavior

Undoubtedly, hormones involved in organizing and activating human sexual behavior

What about unique human behaviors?

Testosterone and aggressionSome studies find higher T in CSF of aggressive malesMeta-analysis of 45 studies: weak, positive correlation between T & aggressivenessMay be more related to dominanceSerotonin may be more important in aggressionRitualized aggression? Men experience a surge in T after team/individual wins in sportsWorld Cup soccer fans show increased T if their team wins