This document is a concise summary of subjects in the book 'an introduction to behavioral endocrinology' noted of importance for the course HAP21806. It is quite concise as I did not have enough time to work through the whole book extensively and should used more as an overview of important matter.
Behavioral Endocrinology
Introduction to behavioral endocrinology book
Chapter 1
Behavioral endocrinology = the study of the interaction between hormones and behavior.
Hormones = chemical messengers released from endocrine glands. They affect gene expression,
cellular function rate, and influence the likelihood of a behavior occurring in the presence of stimuli.
Certain chemicals can mimic hormones and therefore affect behavior.
Hormones change the probability that a behavior will occur within an appropriate behavioral or
social context. What is considered appropriate depends on nurture factors.
Testes produce and secrete testosterone which influences sexual behavior, aggression, territoriality,
hibernation and migration.
Castration has been the most common manipulation of the endocrine system.
One of the first formal endocrinology studies one performed in roosters. Castrated roosters didn’t
develop properly. Berthold who conducted this experiment had two concepts:
- various parts of the body release specific agents into the blood.
- these agents travel through the bloodstream to target organs.
Berthold illustrated that the effects of the testes were due to a substance they produced which
circulated the blood.
Ernest starling coined the term ‘hormone’.
Hormones have a similar function to neurotransmitters, but operate over a greater distance and
temporal range.
Hormones can affect target cells that have specific receptors for them.
Hormone concentration is important to reach a threshold however once this threshold has been
passed concentration does not influence reaction or reaction strength.
Interactions hormone and behavior are bidirectional.
Effector = hormone outputting organ
Problems in behavioral research;
- Bias.
- Subjective observation (ascribing emotions to certain patterns)
- What behaviors are relevant for the research question?
- Behaviors that are looked at should be described elaborately and in a way all observers will
score and recognize it in the same way.
To entangle environmental and hormonal influences on an indivudiual experiments are usually
conducted on similar individuals.
Using simple behaviors for research:
Ease of replication and quantification.
Subtle but important interactiosn will go unnoticed.
Generic behaviorist research question: what causes animal A to emit behavior B?
Four different levels of analysis:
- Immediate causation. Proximate mechanisms responsible for behavior. Mediated by
nervous- and endocrine system. Influence moment-to-moment behavior. Environmental
stimuli are highly influential. Short term regulation of behavior.
- Development . Covers an animals lifetime. Hormonal influences in prepubescent and
pubescent kids etc.
, - Evolution. This approach involves multiple generations. Studies evolutionary bases of
behavior to learn why it may vary between species.
- Adaptive function. This approach studies the role of behaviors in adaptation of a species to
an environment.
The first to are proximate ‘why’ questions, the last to ultimate ‘how’ questions.
Animals are made up of three components; an input system, integrators and an output
system/effector. Hormones influence these three systems.
Behavior can affect hormone levels. For example animals that lost in combat have lowered
testosterone levels for a period of time. Sexual intercourse can also cause testosterone to increase.
Conditions for a causal link between hormone and behavior to be established:
- A hormonally dependent behavior should disappear when the source of the hormone is
removed or the actions of the hormone are blocked.
- After the behavior stops, restoration of the missing hormonal source or its hormone
should reinstate the absent behavior.
- Hormone concentrations and the behavior in question should be covariant. (difficult to
obtain, for example because hormones are released pulsatile.)
Chapter 2
Systems of chemical mediation:
- Intracrine: regulate intracellular events.
- Autocrine: secreted extracellular and influence the same cells that secreted them.
- Paracrine: these cells secrete chemicals that influence adjacent cells.
- Endocrine: chemicals are secreted into the bloodstream.
- Ectocrine: chemicals released into the environment to influence other individuals.
(pheromones)
Chemical communication terminology:
Chemical messenger = any substance produced by a cell that affects the function of another cell.
Cytokine = a chemical messenger that evokes proliferation of other cells, especially the immune
system.
Hormone = a chemical messenger that is released into the bloodstream or tissue fluid system that
affects target cells.
Neurohormone = a hormone produced by a neuron.
Neuromodulator = a hormone that changes the response of a neuron to other factors/
Neuropeptide = a peptide hormone produced by a neuron.
Neurotransmitter = a chemical messenger that acts across the neural synapse.
Neurohormones are released into the blood by neurosecretory cells. Neurons in the hypothalamic
median secrete releasing and inhibiting hormones.
Features endocrine system:
- Endocrine glands are ductless
- Endocrine glands have rich blood supply
- Hormones are secreted into the bloodstream
- Hormones can travel in the blood to every cell in the body and can interact with all cells
with the right receptors
- Hormone receptors are specific binding sites, embedded in the cell membrane elsewhere
in the cell, that interact with particular hormones or hormone classes
Exocrine glands do have ducts that lead to the external environment.
,The most active endocrine organ is the brain. Some water soluble hormones and small peptides are
stored in secretory granules called vesicles. In response to a stimulus a vesicle can fuse with a cell
membrane and hormones are released into the cell. This is called exocytosis.
Lipid soluble molecules can easier pass the cell membrane. These molecules are not stored in the
endocrine cell but are released as soon as they are produced.
The precursor cholesterol can be stored in the cell in the form of lipid droplets.
Soluble in blood: protein and peptide hormones
Not soluble in blood: steroid hormones. (these bond with a carrier protein)
Carrier proteins are of importance for mediating steroid hormone actions.
Hormones and receptors can have very high affinity for each other. This makes it possible for
hormones to still exert effects when they are present in very low concentration. If receptors aren’t
present or available no response will occur. This lead to endocrine deficiency even though hormone
levels are sufficient. A high receptor count can cause an overly strong reaction in response to a
relatively normal/low concentration of hormones.
, Endocrine glands:
Biological half-life = the amount of time required to remove half of the hormone form the blood
through excretion or degradation.
Protein and peptide hormones
A peptide hormone is a protein hormone only a few amino acids in length. These hormones can be
stored in endocrine cells and are released by exocytosis. They are soluble in blood.
Hormones
The hypothalamus consists of several nuclei (collections of nerve cell bodies). At the base are
neurosecretory cells, axons terminals release neurotransmitters into blood vessels in the pituitary
gland.
Hypothalamic Thyrotropin-releasing Stimulates release of TSH and prolactin
hormone/TRH
Growth hormone-releasing Stimulates secretion of GH
hormone/GHRH
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