Behavioral Endocrinology Introduction and the Hypothalamus

Behavioral Endocrinology

The Study of Interactions between Hormones and Behavior. Hormones are long lasting chemical messengers that are released from endocrine glands throughout the body. These messengers act on target tissue throughout development and across the lifespan.

Endocrine System

Glands secrete chemicals into blood stream. Travel to target tissues in chemical form. Produce long lasting responses over time. Influence metabolism and development.

Nervous System

Nervous system cells. Travel to target tissues via electrical current. Produce fast responses. Influences acute changes in body systems.

Hormone Chemicals

Produced and released from differentiated cell types to affect other cells in the body and brain. Interactions occur through blood circulation to target. Depending on the Chemical Composition effects are fast (adrenaline) or slow (Steroids).

Intracrine

Within the cell

Autocrine

With its own cell surface

Paracrine

Between cells

Endocrine (system of communication)

With distant target cells

Ectocrine

Between animals

Behavior

Any output from an organism that can be observed in response to a stimulus.

Endocrine Communication and Behavioral Changes

Hormones do not produce behavior directly but alter the probability and expression of behaviors in response to specific stimuli.

Inputs

Environment and Sensory Systems

Integration

Central Nervous System Processing

Outputs

Effectors in the Periphery

Endocrinology

The Study of Hormones. Major Features: Glands, Blood Supply, Target Cells, Receptors.

Bioregulatory Organization

The endocrine axis starts with the hypothalamus communicating with the pituitary (HPA). The pituitary secretions affect other glands, (i.e., the thyroid, adrenals, gonads and liver). NOT ALL BIOREGULATION IS UNDER INFLUENCE OF BRAIN/PITUITARY.

Independent Bioregulation

Parathyroid, Thymus, Endocrine pancreas, GI tract.

The Hypothalamus (PVN and SON)

The PVN and SON project to the posterior pituitary.

CNS Control of Pituitary — Neural Transmission (Form and Function)

Dendrites, Soma, Axon Hillock, Axon, Terminal.

Posterior Pituitary

The magnocellular cells of the PVN and SON produce Oxytocin & Vasopressin.

Vasopressin and Oxytocin

Small peptide hormones that differ by very few amino acids. Bind to each other's receptor proteins.

Oxytocin (females)

Oxytocin plays a role in reproductive behavior in females. Lactation.

Oxytocin (females and males)

Oxytocin plays a role in reproductive behavior in females and Males. Reflexes produced in the cervix, vagina, uterus and areola release OXT via neural input to the Hypothalamus. OXT increases in plasma during ovulation, parturition, and sex. Estrogen increases the synthesis of OXT and lowers the threshold for OXT release. Males show increased OXT during ejaculation and orgasm. OXT correlates with sexual satiety in both sexes.

Oxytocin and Sexual Behavior (Carter 1990)

Small amounts of oxytocin (and vasopressin) or initial exposure to oxytocin could facilitate pre-copulatory events, including sexual arousal or excitement. Oxytocin, released centrally during early stages of sexual excitement could, through positive feedback, prime the nervous system to permit a larger, pulsatile release of oxytocin. When adequate priming has been achieved, electrical coupling among oxytocin-producing cells would be possible. Large dosage of oxytocin can inhibit sexual activity in rodents so oxytocin might be involved in sexual "satiety". Oxytocin released during or after coitus could influence the development of subsequent social attachments. Sex and/or species difference in oxytocin and differential effects of steroid hormones could modulate sex differences, species differences and individual differences in sexual responses.

Complex Synchonization

The Hypothalamus exerts both tropic and trophic effects on pituitary cells via the median Eminence.

TRH

Thyroid releasing hormone (also stimulates prolactin secretion)

GnRH

Gonadotropin releasing hormone (FSH & LH) – whether or not gonadotroph cells releases FSH or LH depends on the frequency of stimulation by GnRH

GHRH

Growth hormone releasing hormone

SRIH

Somatotropin release-inhibiting hormone – inhibits GH

CRH

Corticotropin releasing hormone

Hypothalamic Pituitary Adrenal Axis

Stress activates HPA axis.

Acute stress (HPA Axis)

Increases gluconeogenesis, prevent buildup of fat reserves, inhibit immune system.

Chronic stress (HPA Axis)

Lose muscle, inhibit reproductive system, immune suppression; negative feedback acts at all levels.

True or False: Hormones directly cause behavior.

False — hormones do not produce behavior directly; they alter the probability and expression of behaviors in response to specific stimuli.

True or False: The nervous system and endocrine system communicate the same way.

False — the nervous system uses fast electrical transmission for acute changes; the endocrine system uses chemical messengers through the bloodstream for long-lasting effects.

True or False: Endocrine communication is the only way cells signal to each other.

False — there are 5 systems: Intracrine, Autocrine, Paracrine, Endocrine, and Ectocrine, each acting at a different scope/distance.

True or False: All hormone effects happen at the same speed.

False — speed depends on chemical composition; e.g., adrenaline acts quickly, steroids act slowly.

True or False: All bioregulation is controlled by the brain/pituitary.

False — some systems regulate independently, including the parathyroid, thymus, endocrine pancreas, and GI tract.

True or False: Oxytocin only plays a role in female reproductive behavior.

False — oxytocin plays a role in reproductive behavior in both females and males (e.g., males show increased OXT during ejaculation and orgasm).

True or False: Vasopressin and oxytocin are structurally very different.

False — they are small peptide hormones that differ by only a few amino acids and can even bind to each other's receptors.

True or False: Large doses of oxytocin always increase sexual activity.

False — per Carter (1990), large doses of oxytocin can actually inhibit sexual activity in rodents, suggesting a role in sexual "satiety."

True or False: GnRH always causes the same hormone (either FSH or LH) to be released.

False — whether FSH or LH is released depends on the frequency of GnRH stimulation.

True or False: Acute and chronic stress have the same effects on the body via the HPA axis.

False — acute stress increases gluconeogenesis and prevents fat buildup; chronic stress causes muscle loss, reproductive suppression, and immune suppression.

A hormone acts fast, like adrenaline. What does this suggest about its chemical composition?

Its chemical composition allows for fast action (unlike steroid hormones, which act more slowly).

If a signaling molecule affects the very cell that released it, via that cell's own surface, which system of communication is this?

Autocrine

If a signaling molecule acts within the same cell without leaving it, what is this called?

Intracrine

If a chemical signal is released by one animal and affects another animal's behavior or physiology (e.g., pheromones), what type of communication is this?

Ectocrine

Which brain structure begins the endocrine axis by communicating with the pituitary, forming the HPA?

The hypothalamus

Which two hypothalamic nuclei project to the posterior pituitary?

The PVN (paraventricular nucleus) and SON (supraoptic nucleus)

Which two hormones are produced by the magnocellular cells of the PVN and SON?

Oxytocin and Vasopressin

Through what structure does the hypothalamus exert tropic and trophic effects on the pituitary?

The median eminence

Which hypothalamic hormone also stimulates prolactin secretion, in addition to its main role?

TRH (thyroid releasing hormone)

What determines whether GnRH triggers FSH or LH release from the pituitary?

The frequency of GnRH stimulation

Which hormone inhibits growth hormone (GH) release?

SRIH (somatotropin release-inhibiting hormone)

Which hormone controls the release of stress-related hormones from the pituitary?

CRH (corticotropin releasing hormone)

What physiological events are associated with spikes in plasma oxytocin?

Ovulation, parturition (birth), and sex

Which hormone increases OXT synthesis and lowers the threshold for its release?

Estrogen

Per Carter (1990), what might oxytocin released during/after coitus influence long-term?

The development of subsequent social attachments

What are the 3 components of the hormone-behavior interaction model?

Inputs (environment/sensory systems), Integration (CNS processing), Outputs (effectors in the periphery)

Name 4 organs/glands that regulate independently of brain/pituitary control.

Parathyroid, thymus, endocrine pancreas, GI tract

How does the immune system respond differently to acute vs. chronic stress?

Acute stress inhibits the immune system temporarily; chronic stress causes ongoing immune suppression.

What is the key structural relationship between oxytocin and vasopressin?

They are small peptide hormones differing by only a few amino acids, and they can bind to each other's receptor proteins.

Compare the speed and duration of endocrine vs. nervous system signaling.

Endocrine signaling is slower but longer-lasting; nervous system signaling is fast but produces acute, short-term changes.