Behavioral Endocrinology Overview

Behavioral Endocrinology

• Study of interaction between hormones and behavior
• Interaction is bidirectional: hormones affect behavior, and behavior influences hormone levels

Key Concepts

• Hormones are chemical messengers affecting sensory systems, neural integration, behavioral outputs.
• Environmental chemicals can mimic hormones, influencing behavior in humans and animals.
• Behavior isn't limited to movement; changes in appearance (e.g., color in chameleons) are also considered as behavioral outputs influenced by hormones (e.g., MSH).

Examples

Example 1: Testosterone and Aggression

• Mechanism: Testosterone, produced by testes (males) and adrenal glands (both sexes), increases aggression by influencing brain regions like the amygdala and prefrontal cortex.
• Behavioral Outcome: Higher testosterone levels in humans are associated with aggression, risk-taking, and competitive behavior.
• Sensory System Involvement: Testosterone may heighten sensitivity to sensory cues (visual or auditory) related to social competition in preparation for interactions.

Example 2: Oxytocin and Bonding

• Mechanism: Oxytocin, often called the "bonding hormone," is released by the posterior pituitary gland and acts on the limbic system (particularly the hypothalamus and amygdala).
• Behavioral Outcome: Oxytocin promotes trust, empathy, and bonding, especially during childbirth, breastfeeding, and social interactions.
• Sensory System Involvement: Tactile stimulation (e.g., breastfeeding) triggers oxytocin release, strengthening mother-infant bonding and enhancing caregiving behaviors.

How Behavior Affects Hormones

Example 1: Exercise and Endorphins

• Mechanism: Physical activity stimulates the hypothalamus to release endorphins, and adrenal glands to release cortisol/adrenaline.
• Hormonal Outcome: Endorphins reduce stress and promote well-being.
• Sensory System Involvement: Proprioceptive input (muscle movements) inform the brain about physical exertion, triggering hormonal changes.

Example 2: Social Stress and Cortisol

• Mechanism: Social rejection or competition activates the hypothalamus, triggering CRH release, and subsequent cortisol secretion.
• Hormonal Outcome: Cortisol levels rise, increasing alertness and preparing the body for stress.
• Sensory System Involvement: Sensory cues (hearing/seeing threats) amplify stress responses and cortisol release.

Environmental Chemicals Mimic Hormones

Example 1: Bisphenol A (BPA)

• Mechanism: BPA, found in plastics, mimics estrogen by binding to estrogen receptors.
• Behavioral Effect: BPA exposure is linked to altered reproductive behaviors (impaired mating preferences) in animals and humans.
• Sensory System Involvement: BPA's effects on sensory systems may influence mating behaviors.

Example 2: Polychlorinated Biphenyls (PCBs)

• Mechanism: PCBs mimic thyroid hormones, and interfere with their signaling pathways.
• Behavioral Effect: PCB exposure during development can lead to cognitive impairments and developmental delays.
• Sensory System Involvement: Thyroid hormone disruptions can affect sensory function.

Historical Roots of Behavioral Endocrinology

• A blend of sciences: psychology, endocrinology, neuroscience, zoology, and genetics.
• Collaboration across fields helps understand how hormones influence behavior.
• Emergence as a distinct area of study in the mid-20th century.
• Key milestones:
• 1967: Launch of the journal "Hormones and Behavior."
• 1996: Creation of the Society for Behavioral Neuroendocrinology.

Berthold's Experiment

• First formal study of endocrinology (1849)
• Demonstrated that substances from testes travel through the bloodstream to influence behaviors.
• Marked the beginning of both endocrinology and behavioral endocrinology.
• Experimental design showed that castrated animals had different behaviors and physical features. Replanting testes restored their normal characteristics

What Are Hormones?

• Chemical messengers traveling through the bloodstream or tissue fluid to target organs or tissues.
• Crucial for regulating bodily functions, including metabolism, reproduction, and coordinating physiological changes (ex. mating/activity).
• Example: metabolic hormones elevate blood glucose before waking, preparing the body for activity.

Hormonal Regulation and Behavior

• Hormones modify the likelihood of specific behaviors being elicited instead of causing the behavior itself.
• The influence of hormones may be related to the correct context.

Common Techniques in Behavioral Endocrinology

• Ablation and Replacement: Removing a hormone-producing gland, and replacing it to study hormonal influences on behavior.
• Immunoassays: Using antibodies to measure hormone levels/concentrations.
• Enzyme-linked Immunosorbent Assay (ELISA): A common type of immunoassay for quantitative measurements of hormones and other substances.
• Non-invasive Hormone Measurement: Techniques like measuring hormone levels in saliva, feces, and hair without blood draw.
• Immunocytochemistry/Immunohistochemistry: Localizing hormones or hormone receptors in tissues using antibodies.
• Blot Tests (Southern, Northern, Western): Separating and detecting specific proteins/nucleic acids to study hormone-related molecules.
• In Situ Hybridization: Determining location of mRNA (messenger ribonucleic acid) encoding proteins using labelled probes.
• Cannulation: Inserting hollow tubes into specific brain areas to introduce substances or collect samples.
• Parabiosis: Connecting circulatory systems of two animals to study interactions between their hormones.
• Genetic Manipulations: Inactivating or overexpressing specific genes to observe impacts on hormone and behavior.
• Electrical Recording/Stimulation: Monitoring neural activity in response to hormonal exposure and/or stimulating neurons directly.
• Optogenetics: Precisely activating neurons to study their responses to hormonal cues using light-sensitive proteins.

Key Components of Animal Behavior

• Input Systems: Sensory systems detecting environmental stimuli.
• Integrators: CNS processes and integrates sensory input.
• Output Systems: Effectors (muscles) producing behavioral responses.
• Hormones: Influence the likelihood of specific behaviors in given situations.

Estrogen's Potential Effects on Zebra Finch Singing

• Testosterone and estrogen play roles in zebra finch singing behavior.
• Estrogen levels correlate with singing frequency
• Estrogen may enhance sensory perception and improve CNS processing.
• Estrogen affects muscles controlling vocalizations (like syrinx).

Human Aggression

• Testosterone may increase sensitivity to stimuli, making threats appear more aggressive.
• Testosterone impacts brain areas (amygdala) involved in aggression and decision-making.
• Testosterone may also increase efforts towards dominance and assertion.
• Testosterone changes can influence physical responses (e.g., muscle tone, posture, and expressions).

How Behavior Affects Hormones

• Describes how various behaviors affect hormone production/levels.
• Examples include; physical exercise, social support, competition, parenting behaviors, emotional expression, social exclusion, romantic interaction, meditation, laughter and mindset impacting hormone levels.
• Hormones are influenced and affected by these behaviors through complex interconnected pathways.