A summary of the theory discussed during the lectures of the course Behavioural Endocrinology and explained in the textbook. Covered textbook pages can be found in the course guide.
Behavioral endocrinology = the scientific study of the interaction between hormones and behavior. This
interaction is bidirectional: hormones can influence behaviour, and vice versa. Hormones = chemical
messengers released by endocrine glands, which travel through the blood system to affect target organs,
and to influence the nervous system and regulate the physiology and behavior of individuals, e.g. gene
expression, cellular function, occurrence of a behavior in response to a certain stimulus. Hormones
coordinate the physiology and behavior of animals by regulating, integrating and controlling body functions.
Behavioral endocrinologists are interested in the interactions between hormones and behavior. NB:
hormones do not cause behavioral changes per se; they change the probability that a specific behavior will
occur in response to certain environmental stimuli.
The knowledge of the existence of interactions between hormones and behavior has been known for
centuries, e.g. Hippocrates described the story of a woman that started to masculinize and stopped
menstruating. This was because of an excessive production of testosterone from the adrenal gland; the
adrenal gland was not able to convert testosterone into cortisol. (questa storiella può essere un exam
question!!!). Ernest Henry Starling was the first to identify that there are organs/glands that produce
messenger molecules (hormones). In recent years, there have been improvements for measurement of
hormone levels, isolation and purification of hormones, identification of their chemical structure etc.
Berthold’s experiment (DA SAPERE) à first formal study of
endocrinology. He took 3 groups of chicks: chicks in group 1 were
castrated, and the animal didn’t develop into a rooster but into a capon
(cappone) with no typical rooster behavior or appearance; chicks in group
2 were castrated and one of their testes was reimplanted in the
abdominal cavity, and they developed into normal roosters (appearance
and behavior); chicks in group 3 were castrated and a testis from another
chick was reimplanted in them, and they also developed into a normal
rooster. 3 major conclusions were made: 1) the testes are transplantable
organs; 2) transplanted testes can function and produce sperm; 3) since
the testes functioned normally after all nerves were cut, there are no
specific nerves directing testicular function. Berthold concluded that a
product of the testes (now we know it’s testosterone) was responsible for the normal development and
behavior of roosters.
NB: hormones can directly influence only cells that have specific receptors for that hormone. Cells that have
these receptors are called target cells. The interaction of the hormone with its receptors starts a series of
reactions that will affect gene expression, protein synthesis etc. For hormones to have effect, it is important
that the concentration of hormone produced is sufficient but also that there are enough receptors for it.
When studying behavior, it is important to distinguish between relevant behaviors from trivial (not
significant) behaviors. An important step is to investigate the cause of the behaviors, e.g. why do birds
sing? The answer to the question “what causes animal A to emit behavior X?” can have different answers
based on 4 different levels of analysis (Tinbergen 4 questions):
- Immediate causation: refers to the physiological mechanisms underlying behavior, explain how the
organism works to make a behavior happen. These mechanisms are usually mediated by the
nervous and endocrine system. E.g. high estrogen concentrations in blood and increased rate of
neural activity are immediate causes of singing in birds.
, - Development: refers to how experience and development (changes in the individual) affect
behavior of animals. E.g. newborn animals have rudimentary behavior, that become more
sophisticated as they develop and learn. E.g. birds might sing because they reached puberty or
because they learned songs from their parents.
- Evolution: refers to how evolution of a species affects its behavior. The study of the evolution of
behavior is based on comparing related species. E.g. we can say that birds sing because they
evoluted from a common ancestor that could sing.
- Adaptive function: refers to the role of behavior in the adaptation of animals to their environment
and their fitness. E.g. we can say that birds sing because it increases the chance to attract a partner.
These 4 levels of analysis can help in understanding why certain behaviors
occur. The 4 levels of analysis can be grouped into 2 groups (figura):
- “how” questions or questions of proximate causation, i.e. how does
an animal engage in a certain behavior? What
processes/mechanisms are involved? (immediate causation and
development)
- “why” questions or questions of ultimate causation, i.e. why does
an animal engage in a certain behavior? (evolution and adaptive
function)
How might hormones affect behavior? How might behavior affect hormones?
In terms of behavior, animals are made of 3 interacting components: the
input systems (sensory systems), integrators (the central nervous
system), and output systems or effectors (e.g. muscles, or the organs
that are affected by the hormones). Hormones will affect these 3 systems,
and this results in a certain behavior. Again, hormones don’t cause
behavioral changes but influence these 3 systems so that specific external
stimuli can cause certain behavioral responses based on the context. E.g.
only male zebra finches (birds) sing in nature. If the testes are removed,
they reduce singing but they continue to sing if the testes are
reimplanted or if birds are provided with testosterone or estradiol (an estrogen). Since testosterone can be
converted into estrogen, probably the presence of estrogens is important for singing. E.g. high levels of
estrogens can make environmental stimuli that elicit singing more salient; estrogens can also affect neuron
function; estrogens can also affect the effector organs (muscles in this case) that allow to sing.
Not only hormones affect behavior, but behavior can affect hormone production. E.g. the sight of a
territorial intruder can increase testosterone levels in males (behavior affects hormones) and consequently
stimulate singing or fighting (hormones affect behavior). Another example: watching a football match
increase testosterone and cortisol levels in male fans compared to when they were not watching a match
(females were not affected). Another example: behavior of pups affects hormonal levels in the mother, and
consequently affect maternal behavior and lactation.
Per esame saper dare esempi di hormones affecting behavior, and behaviors affecting hormones.
Classes of evidence for determining hormone-behavior interactions (SAPERE)
,To establish that a certain hormone affects a certain behavior or vice versa we need evidence. When doing
experiments to find links between hormones and behavior, generally 3 conditions have to be satisfied (i.e.
we need to find evidence about these 3 things) before we can say that a h ormone is linked to a certain
behavior:
1. A behavior that depends on a hormone should disappear when the source of hormone is removed
or the actions of the hormone are blocked. E.g. if you block the production of testosterone,
behaviors associated with it should stop
2. When you restore the missing source of hormone or the hormone itself, the behavior should start
appearing again. E.g. if you stop blocking testosterone, the behavior associated should appear
again
3. The hormone concentrations and the behavior should be covariant, i.e. the behavior should be
observed only when hormone levels are relatively high and never/rarely when levels are low.
LECTURE CL2 – THE ENDOCRINE SYSTEM (p. 35-76, ch2 book)
Hormones are produced by endocrine glands and secreted in blood. They travel in blood to target organs
containing specific receptors. Hormones interact with the receptors, and initiate biochemical events that
can activate genes to affect certain responses. In some cases, genes are not involved and we call these
nongenomic effects of hormones.
Chemical communication
There are different ways of chemical communication in the body (vedi figura p. 36 per capire meglio):
- Intracrine mediation: hormones or growth factors act inside the cells that produced them, without
going out of the cell first.
- Autocrine mediation: autocrine cells produce a messenger molecule that is released outside the
cell but then acts on that cell (feedback mechanism).
- Paracrine mediation: paracrine cells produce messenger molecules that affect adjacent cells.
- Ectocrine or interspecific mediation: substances are released from an individual into the outside
world and induce a biological response in another animal, e.g. pheromones.
- Endocrine mediation: endocrine cells produce hormones that are secreted in the bloodstream, and
travel to distant target cells.
All the chemical mediators are involved in the endocrine (hormones), nervous (neurotransmitters) or
immune system (cytokines). These substances all interact with each other to
generate a response.
General features of the endocrine system
Endocrinology = the study of endocrine glands and their hormones. In some
cases, hormones are neurohormones, which are released in blood by
neurosecretory cells instead of endocrine cells. Neuroendocrinology = study of
transduction of neural signals into hormonal signals.
General features of the endocrine system:
, - Endocrine glands have no ducts. While endocrine glands have no ducts and secrete their products
directly in blood, exocrine glands have ducts or tubes from which their products are released, e.g.
salivary, sweat and mammary glands are exocrine glands (figura).
- Some hormones are water-soluble proteins or peptides that are stored in the endocrine cells into
secretory granules or vesicles, which then release the hormones in the extracellular space via
exocytosis when there is a stimulus, and then enter blood. Other hormones (e.g. steroids) are fat-
soluble (non water-soluble); since they can easily move out of the cell’s phospholipid membrane,
they are not stored in endocrine cells but are produced only when there is a stimulus and secreted
immediately.
- Endocrine glands have a rich blood supply. This helps reach the target cells faster.
- Hormones are secreted in the bloodstream. While water-soluble hormones are soluble in blood,
fat-soluble hormones are not so they bind to carrier proteins while circulating in blood.
- Hormones can travel to virtually every cell in the body and can interact with any cell that has the
right receptors.
- Hormone receptors are specific binding sites in the cell membrane or other parts of the cell, that
interact with specific hormones. When blood concentration of hormones is high and all specific
receptors are occupied, hormones can bind to receptors that are more specific for other hormones
(but similar). When not enough receptors are available (e.g. because of medical condition), the
biological response may not occur. Sometimes when individuals have problems it is not because
they don’t produce enough hormones, but because they don’t produce enough receptors so the
hormones cannot work. E.g. a deficiency in androgen receptors can prevent development of male
traits even if the individual produces enough testosterone.
Classes of hormones
There are 4 main classes of hormones: Most hormones are proteins!!
- Monoamines, e.g. catecholamines (epinephrine, norepinephrine, dopamine), indoleamines
(melatonin, serotonin), T3/T4. They derive from a single aminoacid
- Polypeptides/proteins, e.g. GH, prolactin, oxytocin
- Glycoproteins, e.g. TSH, FSH, LH. They are proteins with a carbohydrate chain
- Steroids, e.g. progesterone, testosterone, estradiol, cortisol, all corticoids in general. Cholesterol is
the precursor of all steroids.
(There is actually another class of lipid-based hormones, e.g. prostaglandins, that derive from lipids but are
not steroids).
LEARN THE 4 CLASSES WELL, POSSIBLE EXAM QUESTION, WITH EXAMPLES!
NB: the different types of hormones are transported differently in the blood. Protein hormones are water-
soluble so they can be stored in the endocrine cell, then they are released in the bloodstream via exocytosis
when needed, and they can be soluble in blood. On the other hand, steroids and some monoamines (e.g.
T3, T4) are fat-soluble (non water-soluble) so they are not stored in the endocrine cells because they would
easily pass the cell membrane made of phospholipids. They are produced when needed and released in
blood immediately after. Since they cannot be soluble in blood, they have to bind to carrier proteins in
blood that are water-soluble to be transported through blood. THIS CAN ALSO BE AN EXAM QUESTION!!
(how are the different classes of hormones transported in blood?).
The metabolisms of a hormone is measured in terms of its biological half-life, i.e. the time needed to
remove half of the hormone from the blood.
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