[NS14] Chemical Control of the Brain and Behavior

Introduction

Communication in the nervous system

• point-to-point communication
  • Influence of one neuron is targeted to a small number of other neurons.
  • Tightly constrained in both space and time (a few msec)
  • e.g. sensory or motor systems.
• Communication with many cells
  • Slowly (seconds~minutes)

1. The Secretory Hypothalamus

1.1. An Overview of the Hypothalamus

hypothalamus:

• Location: Below the thalamus, along the walls of the third ventricle (forebrain)
• Integrates somatic and visceral responses if needed.
• Regulates internal condition of the body in response to a changing external environment: homeostasis.

1.1.1. Homeostasis

• Homeostasis: The maintenance of the body’s internal environment within a narrow physiological range.
• example:
  • Temperature regulation
    • Low
      • Blood vessles constrict => heat is conserved.
      • Sweat glands do not secrete fluid.
      • Turn blue: shunt blood away from surface tissues => keep sensitive core of the body warmer.
      • Shiver (involuntary contraction of muscles => generate heat in the muscles)
      • Goose bumps (a futile attempt to fluff up your nonexistent fur for better insulation. a reflexive remnant from harrier ancestors)
    • High
      • Blood vessles dilate => heat loss to env.
      • Sweat glands secrete fluid. (evaporate => heat is lost from the body)
      • Turn red: shunt blood to surface tissues where heat can radiate away.

1.1.2. Structure and Connections of the Hypothalamus

3 zones:

• lateral, medial

  Extensive connections with…

  • the brain stem
  • the telencephalon

  regulate certain types of behavior.

• periventricular
  • Location: Right next to the wall of the third ventricle.
  • Complex mix of neurons. e.g.
    • Supra Chiasmatic Nucleus (SCN)
      • Location: just above the optic chiasm.
      • Input: direct retinal innervation
      • Fn: Sync. circadian rhythms with daily light-dark cycle.
    • neurosecretory neurons
      • Control ANS
      • regulate pituitary gland.

1.2. Pathways to the pituitary (Posterior and Anterior)

1.2.1. Hypothalamic Control of the Posterior Potuitary

• Neurohormones: Substances released into the blood by neurons.
• the subfornical organ: a part of the telencephalong that lacks a BBB.

magnocellular neurosecretory cells

• extend axons down the stalk of the pituitary and into the posterior lobe.

release 2 kinds of neurohormones directly into the capillaries of the posterior lobe.

They have the following properties:

• peptides
• a chain of 9 aa.s

1. Oxytocin
   1. rise when…
      1. sexual/intimate behaviors
      2. somatic sensations generated by a suckling baby
         1. cortex informed by somatic, visual, or auditory pathways stimulates the hypothalamus to release oxytocin.
   2. Function
      1. Promote social bonding
      2. Cause the uterus to contract => facilitate the delivery
      3. Stimulates ejection of milk from the mammary glands
2. Vasopressin (antidiuretic hormone, ADH)
   1. Trigger: (low blood volume <=> P, high blood salt concentration)
      1. Pressure receptors in the cardiovascular system (P is low => hypothalamus)
      2. Salt concentration-sensitive cells in the hypothalamus (C is high)
   2. Fn (Regulates blood volume and salt concentration)
      1. water retention
      2. reduced urine production
   3. Process
      1. low blood P in kidney
      2. kidney release renin
      3. renin converts Angiotensin from liver to angiotensin I => angiotensin II.
      4. Angiotensin II…
         1. Direct effect on kidneys & blood vessels
         2. Detected by the subfornical organ =>
            1. Activate ADH-containing neurosecretory cells in the hypothalamus (control of visceral organs)
            2. Activate cells in the lateral hypothalamus => Promote thirst (control of behavorial responses)

1.2.2. Hypothalamic Control of the Anterior Pituitary

Terms:

• hypophysiotropic hormone

  A peptide hormone releasd into the blood by the parvocellular neurosecretory cells of the hypothalamus; stimulates/inhibits the secretion of hormones from the anterior pituitary

• hypothalamo-pituitary portal circulation

  A system/network of blood vessels that carries hypophysiotropic hormones from the hypothalamus to the anterior pituitary.

• adrenal cortex
• adrenal medulla

Anterior Pituatary

• body’s “master gland” (traditionally)
• NOT a part of the brain(CNS)
• Controlled by parvocellular neurosecretory cells of the periventricular hypothalamus by releasing the hypophysiotropic hormones. (“true master gland”)

Example

• adrenal cortex produce cortisol (steroid)
• fn:
  • mobilize(=use) energy reserves of body
  • suppress immune system => cope with life’s various stress.
• good stimulus for release: stress
  • physiological strss e.g. loss of blood
  • positive emotional stimulation. e.g. falling in love
  • phychological stress; anxity over an upcoming exam.
• stress is determined by the parvocellular neurosecrtory cells (by the release of cortisol) that control the adrenal cortex

Process

1. parvocellular neurosecrtory cells release Corticotropin-Releasing Hormone (CRH) into the blood of the portal circulation.
2. CRH travels to the anterior pituitary. stimulates the release of corticotropin(=adrenocorticotropic hormone (ACTH)) into the general circulation.
3. ACTH travels to the adrenal cortex, stimulating cortisol release.

Hormone	Target	Action
FSH; Follicle-Stimulating Hormone	Gonads	Ovulation, spermatogenesis
LH; Lutenizing Hormone	Gonads	Ovarian and sperm maturation
TSH; Thyroid-Stimulating Hormone (=thyrotropin)	Thyroid	Thyroxin secretion ( => inc metabolic rate)
ACTH(adreno cortico tropic hormone) (=corticotropin)	Adrenal cortex	Cortisol secretion (mobilize E stores, inhibits immune system, etc.)
GH; growth hormone	All Cells	Stimulation of protein synthesis
Prolactin	Mammary glands	Growth and milk secretion

(portal circulation <-> general circulation)

Regulation of the adrenal glands

2. The Autonomic Nervous System

2.1. ANS Circuits

2.2. ntms & the Pharmacology of Autonomic Fn.

3. The Diffuse Modulatory Systems of the Brain

3.1. Anatomy & Functions of the Diffuse Modulatory Systems

3.2. Drugs & the Diffuse Modulatory Systems