Topic 9 Hormones and the brain

Background

Hormones are…

• Chemicals secreted into blood
• Act on specific target tissues via receptors
• Produce specific effects

Can a substance be a hormone AND a neurotransmitter?

Yes, if the substances are 1) released by neurons, 2) bind to neurons, and 3) bind to other cells in the body.

Substances that are both hormones and neurotransmitters

• Melatonin
• Epinephrine/adrenaline
• Oxytocin
• Vasopressin

Physiological responses and behaviors under hormonal influence

• Ingestive (eating/ drinking)
  • Fluid levels
  • Na, K, Ca levels
  • Digestion
  • Blood glucose levels

Figure 9.1: Snails mating: http://2.bp.blogspot.com/-LziO1SbCVbU/UeqmTPOCJiI/AAAAAAAACUI/u7mCG4vlf_U/s1600/reprodution.JPG+51.jpg

• Reproduction
  • Sexual Maturation
  • Mating
  • Birth
  • Care giving

• Responses to threat/challenge
  • Metabolism
  • Heart rate, blood pressure
  • Digestion
  • Arousal

Commonalities

• Biological imperatives
• Events restricted in space and time

Differences: Neural vs. hormonal communication

• Point to point vs.“broadcast”
  • Wider broadcast than neuromodulators
  • Everywhere in body via bloodstream
• Fast vs. slow-acting
• Short-acting vs. long-acting
• Digital (yes-no) vs. analog (graded)
• Voluntary control vs. involuntary

Similarities: Neural vs. hormonal communication

• Chemical messengers stored for later release
• Release follows stimulation
• Action depends on specific receptors
• 2nd messenger systems common

Biology

• Rest of body
  • Thyroid
  • Adrenal (ad=adjacent, renal=kidney) gland
    • Adrenal cortex
    • Adrenal medulla
  • Gonads (testes/ovaries)
• CNS
  • Hypothalamus
  • Pituitary
    • Anterior
    • Posterior
  • Pineal gland

Two hypothalamus/pituitary release systems

• Direct
• Indirect

Direct hormone release into bloodstream

• Hypothalamus (paraventricular nucleus, supraoptic nucleus) to
• Posterior pituitary
  • Oxytocin
  • Arginine Vasopressin (AVP, vasopressin), also known as anti-diurectic hormone (ADH)

Figure 9.2: Posterior pituitary: https://upload.wikimedia.org/wikipedia/commons/thumb/7/70/1807_The_Posterior_Pituitary_Complex.jpg/594px-1807_The_Posterior_Pituitary_Complex.jpg

Indirect release (multiple steps before end organs)

• Hypothalamus -> releasing hormones
• Anterior pituitary -> tropic hormones
• Blood stream ->
• End organs

Case studies

Case 1: Responses to threat or challenge

• Neural response
  • Sympathetic Adrenal Medulla (SAM) response
  • Sympathetic NS activation of adrenal medulla, other organs
  • Releases NE and Epi

Figure 9.3: Deussing and Chen (2018)

• Endocrine response
  • Hypothalamic Pituitary Adrenal (HPA) axis
• Hypothalamus
  • Corticotropin Releasing Hormone (CRH)
• Anterior pituitary
  • Adrenocorticotropic hormone (ACTH)
• Adrenal cortex
  • Glucocorticoids (e.g., cortisol)
    • increases blood glucose, anti-inflammatory
    • negative consequences of prolonged exposure
  • Mineralocorticoids (e.g. aldosterone)
    • Regulates Na (and water) retention in kidneys

Cortisol-related receptors widespread in brain

Figure 9.4: Deussing and Chen (2018)

• Cortisol release affects the brain

Case 2: Reproductive behavior – the milk letdown reflex

• Hypothalamus releases oxytocin into posterior pituitary
• Targets milk ducts in breast tissue

Oxytocin’s multiple roles

• Sexual arousal
• Released in bursts during orgasm
• Stimulates uterine, vaginal contraction
• Links to social interaction, bonding: Weisman and Feldman (2013)
• Alters face processing in autism: Domes et al. (2013)

But, can oxytocin treat social impairments in autism?

Figure 9.5: Sikich et al. (2021)

What are effects of “knocking-out” oxytocin receptors

Figure 9.6: Ledford (2023)

References

Deussing, Jan M, and Alon Chen. 2018. “The Corticotropin-Releasing Factor Family: Physiology of the Stress Response.” Physiological Reviews 98 (4): 2225–86. https://doi.org/10.1152/physrev.00042.2017.

Domes, Gregor, Markus Heinrichs, Ekkehardt Kumbier, Annette Grossmann, Karlheinz Hauenstein, and Sabine C. Herpertz. 2013. “Effects of Intranasal Oxytocin on the Neural Basis of Face Processing in Autism Spectrum Disorder.” Biological Psychiatry 74 (3): 164–71. https://doi.org/http://dx.doi.org/10.1016/j.biopsych.2013.02.007.

Ledford, Heidi. 2023. “CRISPR Voles Can’t Detect ‘Love Hormone’ Oxytocin — but Still Mate for Life.” http://dx.doi.org/10.1038/d41586-023-00197-9. https://doi.org/10.1038/d41586-023-00197-9.

Sikich, Linmarie, Alexander Kolevzon, Bryan H King, Christopher J McDougle, Kevin B Sanders, Soo-Jeong Kim, Marina Spanos, et al. 2021. “Intranasal Oxytocin in Children and Adolescents with Autism Spectrum Disorder.” The New England Journal of Medicine 385 (16): 1462–73. https://doi.org/10.1056/NEJMoa2103583.

Weisman, Omri, and Ruth Feldman. 2013. “Oxytocin Effects on the Human Brain: Findings, Questions, and Future Directions.” Biological Psychiatry 74 (3): 158–59. https://doi.org/http://dx.doi.org/10.1016/j.biopsych.2013.05.026.