PSYC 304 - Midterm 2.22

Hormones 1

Hormones

Chemicals secreted by cells in one part of the body that travel through the bloodstream + acts on targets in other parts of the body 

Endocrine glands

 Release hormones inside the body 

• Other tissues secrete hormones too

Exocrine glands

Use ducts to secrete fluids outside the body (tears, sweat, saliva)

Key DIfferences Between NT and Hormones

NT: 

• Local effect (across short distance of synaptic cleft) 

• Fast + short-lived (ends when NTs are broken down/reabsorbed 

• Enables precise, point–to-point communication between specific cells 

Hormones: 

• Systemic effect: Travel throughout body via bloodstream to reach distant target organs/tissues

• Slower + long-lasting: act over seconds-hours. But produce persistent effects 

  • Coordinate physiological processes such as growth, metabolism, and stress responses

Major Endocrine Glands + Functions

• Hypothalamus: Control of hormone secretion 

• Pineal gland: Reproductive maturation, body rhythms

• Anterior Pituitary gland: hormone secretion by thyroid, adrenal cortex, and gonads

• Posterior pituitary gland: water balance, lactation

Chemical Communication Within the Body

• Autocrine: Released chemical acts on releasing cell. Cell affects own activity!

  • Most local 

  • Ex. dopaminergic neurons release dopamine, some of the dopamine binds to its own D2 autoreceptors to reduce further dopamine release + regulate their activity 

Chemical Communication with Others

• Semiochemicals

• pheromones

• allomones/kairomones/synomones

Semiochemicals

Chemical substances that convey information between individual organisms

• Released into the environment!

Pheromones

• Chemical used to communicate between individuals of same species

  • Standardized message: meaning does not vary between individuals of a  given species

  • Common in insect communication 

  • Benefits both sender + receiver

Allomones, kairomones, and synomones

• Chemicals released by one species to affect the behaviour of another species 

  • Function may be defensive (repellent) or attractive 

  • Allomone: Benefits emitter of chemical substance, but not the receiver

  • Kairomone: Benefits receiver but not emitter

Synomone: Benefits both emitter and receiver (reciprocal!)

Initial Experiments in Behavioural Endocrinology

Adolf Berthold

• Observation: Castrated roosters did not develop appearance + behavior of typical adult rooster 

• Test: Transplant testis into body cavity of castrated young rooster (immediately after testes removed) restored normal development of male anatomy + behaviour!

  • Nerve innervation of implanted testis: none, therefore could not be a neural impulse triggering characteristics 

• Conclusion: Effect had to be chemical

  • Testes release chemical into bloodstream that affects male behavior and body structure → testosterone  

  • Only worked because testes was put back while they were still young, body did not develop without effects. Organizational effect of testosterone requires it to be present at a specific time

Ontogenetic Effects

• Organizational Effects: Permanent changes in brain and body structure caused by hormone exposure early in development 

• Hormones in adulthood activates behaviour!

  • Effects are less dramatic and short-lived (“activational” effects) 

General Principles of Hormone Action

• Gradual 

  • Behavioural + physiological response occurs hours-weeks after entering bloodstream 

  • Changes may persist for days/weeks/years after hormone release is over

• Change probability/Intensity of behavior 

• Reciprocal relationship with behaviour 

  • Hormone change behavior, and behaviour changes hormone levels 

• Multiplicity of action

  • Hormone may have multiple effects + one behavior may be affected by several hormones

• Pulsatile Secretion Pattern 

  • Often secreted in bursts

• Rhythmic changes in levels throughout the day

  • Some hormones are controlled by circadian clocks in the brain  

• Can interact with other hormones + change their effects

• Only affects cells with a receptor protein for that hormone

Neuroendocrine Cells

Neurons that release hormones directly into the bloodstream 

• Located in hypothalamus

• Crucial for brian control of endocrine glands

• Receive AP, vesicles release hormones instead of NT. close to blood vessels, hormones diffuse inside + released into blood

• Release hormones into the blood from the brain!

Neuropeptides

Peptides used by neurons. Can act as neuromodulators + alter sensitivity to transmitters

Neuromodulators

Can modify the receptivity of cells to specific transmitters

• Act more slowly than NT + have longer lasting effects 

Peptide

Soluble in water, cannot pass membrane covering cell (cant enter cells!)

Amine

Usually cannot enter the cell (exception → thyroid). Need receptors outside of cell to function 

Steroid

• Sex + stress hormones

• Can cross lipid bilayer that surrounds the cell + change cell’s functions! 

Do hormones bind to receptor molecules?

Yes!

• Same as NTs, hormones fit like a lock-and-key to repectors 

• Receptors or hormones typically only in certain cells + tissues (only specific targets respond to that hormone) 

• Peptide + amine hormones bind to receptors on cell surface → trigger second messenger pathways that alter cellular activity 

• Steroid hormones pass through cell membrane + bind to receptors inside the cell 

Peptide + Amine Hormones

• G protein-coupled receptors

• Hormone binds to receptor + changes receptors shape, activates G-protein complex that splits into subunits

• Starts cascade of messengers, gives out effects depending on cell 

• Cyclic AMP or cAMP is a second messenger that transmits messages of many hormones

  • Different effects depending on target cell type, location, and biochemical activity inside the cell 

• Specificity of hormonal effects is largely determined by select of receptors 

  • Fast-acting: seconds - minutes (fast for hormones, much slower than neural activity) 

Steroid Hormones

• Act slowly (hours) 

• Diffuse passively into cells 

• Receptors within target cells 

• Steroid-receptor complexes alter protein production, producing long-lasting effects

• Steroid-receptor complex binds to DNA + acts as a transcription factor, altering gene expression

Steroid Receptor Cofactors 

• May be necessary for the cell to respond to the steroid-receptor complexes 

• Different cells can have different types of coactivators! 

• Same hormone can cause different effects in different cells, depending on which coactivators are present

Genomic effects

• Involve steroid/thyroid hormones binding to intracellular receptors

• Alter gene transcription, leading to changes in protein synthesis 

• Usually slow (days - hours) to manifest

Non-genomic effects

• Do not involve direct changes in gene expression 

• Often mediated by membrane receptors 

• Produce rapid responses 

Steroids can have both genomic and non-genomic effects!