Hormones and Behavior

Alison Bell

Animal Biology

University of Illinois

Today’s lecture

• Hormones– What are they?– Where are they made?– What do they do?

• Hormones and behavior– Organization-activation

• Relative plasticity hypothesis

– In utero and parental effects– Challenge 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

gland– Gonads, e.g. testes, ovaries

• Centrally– ‘Neurohormones’ are produced within the

brain, but travel to target via bloodstream• e.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 behavior

Nonsteroid hormones: can’t enter cell Steroid hormones: pass right through

Hormone regulation:Important vertebrate pathways

Hypothalamus-pituitary-gonad (HPG) Hypothalamus-pituitary-adrenal (HPA)

Hormone regulation:Synthesis and metabolism

Bells and whistles:

Receptors

Plasma binding proteins

Enzymes

How to study hormones?

•Remove the gland

•Add hormone

•Measure circulating levels

•Block receptor

Sexual Behavior: Females

• Estradiol and mice– OVX mice: eliminates

female sexual behavior (lordosis)

– Can be restored by treatment with estradiol followed by progesterone Estradiol

Sexual Behavior: Males

Red deer stag– Sept/Oct become

aggressive, begin courting females

– Testes generate sperm and release testosterone

– Castrated males do not fight or mate

– Testosterone implants restore behavior

Hormones BehaviorIf 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 again

Role of progesterone…Lehrman 1964

Important point

• Many shared mechanisms, BUT mechanisms often differ between species/groups– Different selection

pressures result in modifications of the hormonal mechanisms of behavior

Hunt 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 effects– Long-term, irreversible effects on tissue

differentiation and development (e.g. brain, ovary) that can either directly (brain) or indirectly (ovary) influence behavior• Critical or sensitive period

Activational Effect

• Oxytocin and maternal behavior in mice– Pre-maternal mice fear

pups and will attack them– Oxytocin injections induce

maternal behavior

Another activational example

• Oxytocin and maternal behavior in sheep– Stimulation of birth

canal during parturition results in oxytocin release in brain

– Oxytocin 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 development

Figure 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 phenotypes

The 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 doesn’t 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 development

Mice and aggressiveness– Subtle differences in the

hormonal environment during embryonic development influence adult behavior

– E.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 hormones…Gil et al 1999, zebra finches

Females 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 T

T

Level of behavior

Aggression

Parental 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?

• Some studies find higher T in CSF of aggressive males– Meta-analysis of 45 studies:

weak, positive correlation between T & aggressiveness

– May be more related to “dominance”

– Serotonin may be more important in aggression

• Ritualized aggression? – Men experience a surge in T

after team/individual wins in sports

– World Cup soccer fans show increased T if their team wins

Testosterone and aggression