Hormonal Control of Behavior 4

Endocrine System

  • Hormone: A chemical substance secreted in one part of the body that causes change in other parts of the body.
  • Endocrine gland: Ductless glands that secrete their products into the space between cells, allowing them to diffuse into the bloodstream. This contrasts with exocrine glands, which have ducts and produce substances like saliva and sweat.
  • Hormones are produced by endocrine glands and transported via the bloodstream to their distant target sites.

Major Types of Hormones

  1. Peptide hormones:

    • Chains of 3 to 300 amino acids.
    • Bind to receptors on cell surfaces due to being water-soluble.
    • Short half-life.
    • Act quickly via second messengers, often cyclic AMP (cAMP).
    • Example: Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) produced by the anterior pituitary gland.

  2. Steroid hormones:

    • A group of closely related hormones secreted mainly by the gonads and adrenal glands.
    • Fat-soluble, allowing them to enter cell membranes.
    • Long half-life.
    • Act slowly, over hours or days.
    • Move into cells and eventually into the nucleus, where they turn genes on or off in DNA.
    • Affect gene expression and protein synthesis.
    • Four types, all chemically derived from cholesterol and structurally similar.
    • Include sex steroids (progesterone, androgen, and estrogen) and corticosteroids.

Major Axis of Hormonal Control in Vertebrates

The hormonal control pathway typically follows this sequence:

  • Hypothalamus → Hypophysis (pituitary) → Target tissues in the body (adrenals, pancreas, gonads, thyroid).
  • The hypothalamus releases neurosecretions (monoamines).
  • The hypophysis releases peptides (monoamines).
  • The target tissues produce steroids and monoamines.

Examples of pituitary (hypophysial) hormones important in behavior:

  • LH & FSH (gonadotropins): involved in reproduction and development.
    • LH: Luteinizing hormone
    • FSH: Follicle-stimulating hormone
  • ACTH (adrenocorticotrophic hormone): involved in stress responses via the adrenal glands.
  • Prolactin: involved in brooding behavior, milk production, amphibian metamorphosis, and fish migration.
  • Melatonin: involved in pigment modification and biological rhythmicity.

How Hormones Influence Behavior

Hormones influence behavior through three main mechanisms:

  1. Sensory or perceptual mechanisms: Influences the ability to detect stimuli, response to stimuli, and preference for stimuli.
  2. Development or activity of neurons: Influences the CNS to affect brain/CNS neuron development.
  3. Muscles involved in the execution of behavior: Affects muscle/motor neurons.

Examples of Hormonal Influence

  1. Sensory or Perceptual Mechanisms:

    • Example: Pheromones and mate attraction in pigs (Sus scrofa).
    • Male pigs produce boar pheromone but cannot detect it themselves.
    • Females are highly sensitive to boar pheromone and, when exposed, solicit copulations.
    • Castrated males injected with estradiol respond to boar pheromones as if female.

  2. Development or activity of neurons:

    • Example: Singing in Zebra Finches (Taeniopygia guttata).
    • Male finches sing, while females do not.
    • Sex differences exist in brain nuclei that control song production.
    • These differences are established at the time of hatching due to differences in hormone levels.
    • Females can develop male song nuclei if given testosterone.

  3. Muscles involved in execution of behavior:

    • Example: Calling behavior in African clawed frogs (Xenopus laevis).
    • Males produce complex advertisement calls; females respond with rapping or tick calls.
    • Rapping calls indicate the female is receptive.
    • Tick calls indicate the female is unreceptive.
    • Male larynx muscles contract/relax more than 10 times faster than female larynx muscles.
    • During development, the presence of androgen in males causes sex-specific differences in the muscles of the larynx to develop.

Studying Hormone-Behavior Relationships

Two primary methods:

  1. Interventional: Experimental manipulation of hormones to test effects on behavior.
  2. Correlational: Looking for parallels between natural hormonal level fluctuations and changes in behavior.

1. Interventional Studies

  • Removal of endocrine gland.
  • Hormone replacement therapy.
  • Manipulate hormone levels.
  • Genetic knockouts.
Examples of Interventional Studies
  • Green Anole (Anolis carolinensis)
    • Castration (removal of the endocrine gland producing testosterone/androgen) to observe the effects of hormone removal on behavior.
    • Androgen replacement—hormone replacement restored mating behavior (but not all competitive behavior).
  • Manipulation - Excess hormone provision:
    • How does behavior change if the level of hormone present is increased?
  • Agonist provisions & anti-hormones:
    • Agonist – analog for hormone, binds to same receptor, leads to same biochemical reaction, and mimics hormone actions
    • Anti-hormones (Antagonist) – binds to the same receptor or inhibits binding of hormone to receptor, prevents biochemical reaction/inhibits behavior.
  • Genetic Knockouts:
    • Knock out gene coding for hormone.
    • Knock out gene coding for receptor for hormone.
    • Example: Male PRKO mice lacking progesterone receptors rarely attack pups.
      • PRKO = Progesterone receptor knockout.

2. Correlational Studies

  • Bioassays.
  • Sample blood/feces/urine from individuals and observe behaviors to find correlations.
Examples of Correlational Studies
  • Male Song Sparrows (Melospiza melodia)
    • Wingfield (1984) captured and banded males.
    • Took blood samples 5-10 times during the breeding season and observed behavior.
    • Found a correlation between peak in territorial aggression and peak in testosterone concentrations.
    • Concluded there was a link between testosterone and territoriality in male sparrows.

Organizational vs. Activational Effects

  • Organizational effects: Hormonal influences occur during early development with lasting effects.
  • Activational effects: Hormonal influences occur later in life, and effects may be temporary.

1. Organizational Effects

  • Steroids organize neural pathways responsible for certain patterns of behavior (e.g., singing in male Zebra Finches).
  • Occurs EARLY in life (before birth/hatching or just afterwards).
  • Generally PERMANENT (structural changes in the brain, long-term cellular changes, etc.).
Example: Sex Differences in Norway Rats:
  • Lordosis posture (copulation solicitation pose).
Example: Uterine Position in Mice
  • The position of female mice in the uterus can affect their adult behavior.
  • Females that develop between two males (2M females) are exposed to higher levels of testosterone in utero, which affects their behavior.
  • 2M females tend to be more aggressive and have larger home ranges compared to females that develop between two sisters (0M females).
  • The home range sizes were compared to males in the spring and fall, showing the influence of prenatal hormone exposure on behavior.
    Percentage attacking strangerPercentage \ attacking \ stranger, Area (m2)Area \ (m^2)

2. Activational Effects

  • Occur in adulthood.
  • Generally TRANSIENT (lasting as long as hormone levels are high).
  • Involved in subtle changes in previously established connections.
  • E.g., ‘flight or fight’ response to danger due to increased epinephrine levels.

3. Facultative Effects

  • A possible 3rd category of hormonal effects (besides organization and activational effects).
  • Challenge hypothesis: Levels of hormones that regulate aggression/dominance are influenced by the social environment of the animal.
Example: Song Sparrows and Territorial Aggression
  • Correlation between aggression and testosterone (Wingfield’s work and other studies).
  • Testosterone levels ONLY rise after initial aggression.

Patterns of Hormonal Interactions With The Environment

  1. Associative reproductive pattern: Gonadal growth/increase in sex hormone production activate mating activity.
  2. Dissociated reproductive pattern: Gonadal activity occurs only after the mating season (in preparation for the next season).
  3. Constant (opportunistic) reproductive pattern: Mature gametes/high levels of sex hormones are maintained for a long time/constantly.