Chemical Control of Brain and Behavior Flashcards
Overview of this chapter
Overview of diffuse modulatory systems
- Found only in CNS
- Highly divergent axonal projections
- Defined by the NT they use
What is the purpose of diffuse modulatory systems?
To coordinate activation states of neurons encompassing broad brain regions
Core neurons in the diffuse modulatory systems?
Small set (several thousand)
Origin of neurons in diffuse modulatory systems
Most arise from the brainstem nuclei
Most neurons in the diffuse modulatory systems arise in the ___
Brainstem nuclei
Axons of neurons in diffuse modulatory systems
Core neurons give rise to widely divergent axons that can form up to 100,000 synapses, each spreading throughout the brain
NT release in diffuse modulatory systems
Diffuse NT release affecting many neurons, and may also regulate NTs into extracellular fluid so they can mediate effects beyond a single synaptic cleft
Describe receptor activation in diffuse modulatory systems
Typically metabotropic receptors in the CNS
Classification of diffuse modulatory systems
Can be classified by NT (name of system is (NT)-ergic)
Diagram of projections in noradrenergic (NE) system
Origin of neurons noradrenergic system
Locus coeruleus
Projection of neurons in noradrenergic system
Throughout brain, including cortex, thalamus, and cerebellum (extremely wide projections)
Purposes of the noradrenergic system
- Locus coeruleus neurons strongly activated by novel, unexpected, nonpainful stimuli in the environment
- When activated, may generally increase brain responsiveness and increase speed/efficiency of information processing
- May be involved in sleep/wake cycles
NE system and stimulands
The noradrenergic system’s efficacy is enhanced by stimulants, such as cocaine and amphetamine
Peter the tiny horse is trying to severely impede the noradrenergic system by targeting one of its main nuclei.
Which would he target and why? What general effects would you see?
a) Raphe nuclei, slowed eating
b) Periventricular Hypothalamus, less sleep
c) Locus Coeruleus, generally less excitation
d) Substantia Nigra, less movement
Answer: C, this is the source nucleus for the Noradrenergic System
Diagram of projections in serotonergic (5-HT) system
Origin of neurons in the serotonergic system
Raphe nuclei throughout brainstem
Projections of neurons in serotonergic system
Large projections to forebrain & spinal cord
Purposes of the serotonergic system
- Rostral raphe nuclei innervate forebrain
○ Fires most during wakefulness and least during sleep
○ Controls sleep/wake cycles - Caudal raphe nuclei innervate the spinal cord
○ Modulates pain - Works with locus coeruleus for reticular activating system:
○ Arouses and awakens forebrain - Control of mood: SSRIs are effective drugs against clinical depression
When do the raphe nuclei innervating the forebrain fire the most and least? (Serotonergic system)
Fire most during wakefulness and least during sleep
Rostral raphe nuclei innervate the ___
Forebrain
Caudal raphe nuclei innervate the ___
Spinal cord
Serotonergic system and hallucinogens such as LSD
Hallucinogens such as LSD are 5-HT agonists:
- LSD binds to 5-HT receptors on raphe nuclei neurons → inhibits raphe firing → reduces outflow of serotonergic system (this also happens during dreaming!
Diagram of projections in dopaminergic (DA) system
Origin of neurons in dopaminergic system
Substantia nigra
Projections of neurons in DA system
Striatum (caudate and putamen)
Purpose of DA system
Initiate voluntary movement (degenerates during Parkinson’s), especially in response to environmental stimuli
Origin of neurons in mesocorticolimbic system (DA)
Ventral tegemental area (VTA)
Projection of neurons mesocorticolimbic system (DA)
Frontal cortex, nucleus accumbens, and parts of the limbic system (emotional nervous system)
Purpose of mesocorticolimbic system
- Reward system that reinforces adaptive behaviors
- Normal rewarding/reinforced behaviors and addictive drugs all increase DA release from VTA to nucleus accumbens
Stimulants and mesocorticolimbic system
Stimulants enhance the effect of this system (along with noradrenergic)
Two parts of the cholinergic (ACh) system
- Basal forebrain complex
- Pontomesencephalotegmental complex
Diagram of projections in basal forebrain complex of cholinergic system
Origin of neurons in basal forebrain complex
- Cholinergic neurons scattered around forebrain (medial and ventral to basal ganglia)
- E.g. medial septal nuclei, basal nucleus of Meynert
Projections of neurons in basal forebrain complex
- Medial septal nuclei innervate hippocampus
- Basal nuclei of Meynert innervates neocortex
Medial septal nuclei innervate ___
Hippocampus
Basal nucleus of Meynert innervates ___
Neocortex
Purpose of basal forebrain complex
- Mainly unknown but system is among the first to degenerate in Alzheimer’s
- Implicated in regulating general brain excitability during arousal and sleep-wake cycles
- May be involved in learning and memory formation
Origin of neurons complex
Cells in pons and midbrain tegmentum
Projections and purpose of pontomesencephalotegmental system
- To dorsal thalamus, where it (along with serotonergic and noradrenergic systems) regulates excitability of sensory relay nuclei
- To telencephalon to provide cholineric link between brainstem and basal forebrain complexes
Summary table of diffuse modulatory systems
Your friend feeds you what looks to be an innocent-looking sandwich. However, she later reveals that it actually contains LSD and that you’ve been entered into her top-secret science experiment.
Before you enter the nether world, what effects would you warn your friend about?
a) LSD acts on the substantia nigra to promote increased sleepiness, so you’re going to enter a period of diminished activity
b) LSD will interfere with your noradrenergic signalling and make you more irritable
c) LSD acts as a stimulant that overall increases your activity and ability to perceive your surroundings
d) LSD is a 5-HT agonist, and will inhibit raphe nuclei firing and reduce outflow of the dopaminergic system
e) None of the above
E. “D” would be correct if dopaminergic is replaced with serotonergic
Oh no! Something is wrong in my housemate’s diffuse modulatory systems, and she no longer has normal sleep/wake cycles. Choose all of the following areas that might be damaged.
a) Locus coeruleus
b) Raphe nucleus
c) Substantia Nigra
d) Basal forebrain complex
e) A,B,C
f) None of the above
Answer: E
A (noradrenergic system), B (serotonergic system), D (cholinergic system)
ACh, NE, and 5-HT all influence sleep/wake cycles
Diagram of hypothalamus
Lateral and medial hypothalamus
Ends projections to brainstem and telencephalon → involved in regulating certain behaviors (more on this later)
Periventricular hypothalamus (communicates more with body)
- Receives input from lateral and medial hypothalamus
- Outflow of ANS (sympathetic vs. parasympathetic) mediates things like fight/flight/freeze response
- Includes variety of neurons, including supraoptic nucleus (magnocellular secretory neurons) and suprachiasmatic nucleus (circadian rhythms)
- Also contains neurosecretory neurons involved in pituitary signaling
Which of the following best describes the role of the hypothalamus in neuroendocrine communication?
A. It directly secretes all hormones into the bloodstream without involving any other gland.
B. It integrates signals from the nervous system and regulates hormone release via the pituitary gland.
C. It only controls digestive enzymes and is not involved in hormone regulation.
D. It functions exclusively as a receptor for peripheral nervous system signals.
B. It integrates signals from the nervous system and regulates hormone release via the pituitary gland.
Diagram of pituitary gland
Location of pituitary gland
Found at base of brain (right above roof of mouth)
How does the hypothalamus control the two lobes of the pituitary?
- Parvocellular secretory neuron from hypothalamus → anterior lobe of pituitary
- Magnocellular secretory neuron from hypothalamus → posterior lobe of pituitary
Parvo ≠ posterior
Summary table of anterior and posterior pituitary
Which of the following correctly distinguishes the role of parvocellular and magnocellular cells in the pituitary gland?
A. Parvocellular cells regulate short-term reflexes, while magnocellular cells exclusively control metabolism.
B. Parvocellular cells release hormones into the posterior pituitary, while magnocellular cells act on the anterior pituitary.
C. Parvocellular cells release regulatory hormones into the portal system for the anterior pituitary, while magnocellular cells release hormones directly into the bloodstream from the posterior pituitary.
D. Both parvocellular and magnocellular cells function exclusively within the anterior pituitary
C. Parvocellular cells release regulatory hormones into the portal system for the anterior pituitary, while magnocellular cells release hormones directly into the bloodstream from the posterior pituitary.
Vole species
- Prairie voles are monogamous (prairie = pair)
- Montane voles do not pair (mon means mono, alone ):
Receptors in female and male prairie voles
- Female prairie voles have higher oxytocin receptor density in the nucleus accumbens and prefrontal cortex (PFC)
- Male prairie voles have higher vasopressin receptor density in the ventral pallidum (VP)
Female prairie voles have higher ___ receptor density in the ___ and ___
Oxytocin, nucleus accumbens, prefrontal cortex
Male prairie voles have higher ___ receptor density in the ___
Vasopressin, ventral pallidum (VP)
Mv
Manipulating vole behavior
- Oxytocin receptor antagonists in nucleus accumbens can prevent partner preference in F prairie voles
- Administering vasopressin before a male meets a new female will make him strongly prefer her
- Vasopressin receptor antagonists in VP of M prairie voles before mating prevents pair-bonding
- Adding vasopressin receptors can make montane voles monogamous
What manipulation can make montane voles monogamous?
Adding vasopressin receptors
What manipulation can prevent partner preference in female prairie voles?
Administering oxytocin receptor antagonists in nucleus accumbens
What manipulation can make male prairie voles strongly prefer their partner?
Administering vasopressin before a male meets a new female will make him strongly prefer her
What manipulation prevents pair bonding in male prairie voles?
Administering vasopressin antagonists in VP
Mechanisms of ADH
- Body is deprived of water
- 2 effects
a. Blood volume decreases → sensed by pressure receptors in cardiovascular system
b. Blood salt concentration increases → sensed by salt concentration-sensitive cells in hypothalamus) - Vasopressin-containing magnocellular secretory neurons release vasopressin into posterior lobe
- Vasopressin acts on kidney to increase water retention and reduce urine production
Where are the osmoreceptors that detect salt concentration?
Hypothalamus
What is the overall effect of vasopressin on the kidney?
It acts on the kidney to increase water retention and reduce urine production
HPA axis diagram
HPA axis flow chart with feedback
Hypothalamus Pituitary Adrenal (HPA) axis
- Involves the steroid/glucocorticoid cortisol (anterior pituitary hormone)
- Sequence:
○ Hypothalamus releases
○ Pituitary releases ACTH to adrenal cortex (on kidney)
○ Adrenal cortex releases cortisol into the bloodstream
Negative feedback in HPA axis
Cortisol inhibits release of CRH (from hypothalamus) and ACTH (from anterior pituitary)
How can chronic stress throw off the HPA axis?
- Elevated levels of cortisol have long-term effects:
- Chronic stress and chronic cortisol release cause decay of hippocampal dendrites
- Chronic stress results in cell death and reduction in hippocampal size
HPA axis and anxiety disorders
- The hippocampus regulates HPA axis and anxiety disorders
- Normal pathway: Amygdala excites HPA axis → HPA axis releases cortisol → cortisol excites hippocampus → hippocampus inhibits HPA axis
- Chronic stress can eliminate this negative feedback → may be basis for stress disorders
Diagram of hippocampus-HPA-amygdala connection in normal state
Diagram of hippocampus-HPA-amygdala connection in stressed state
Key features of ANS (autonomic nervous system)
- Commands every muscle that isn’t skeletal muscle fibers
- Actions of ANS are multiple, widespread, and relatively slow
- Balances synaptic excitation and inhibition for widely coordinated and graded control
What parts of the body does the ANS interact with?
Secretory glands, heart and blood vessels, bronchi of lungs, digestive system, excretory system, genitals and reproductive organs, immune system
ANS diagram
Somatic motor vs. ANS control
- Somatic motor control is monosynaptic (alpha motor neuron → muscle fibers)
- ANS control is disynaptic (preganglionic fiber from CNS → synapses onto autonomic ganglion, which sends out postganglionic fiber → smooth muscle/cardiac muscle/glands)
Is ANS control mono- or di-synaptic?
Disynaptic
What parts of the brain are important for autonomic control?
Hypothalamus (mainly) and nucleus of solitary tract in medulla are important for autonomic control (regulator of autonomic preganglionic neurons)
Table comparing sympathetic and parasympathetic systems
Features of sympathetic NS
- From middle 1/3 of spinal cord
sympathetic chain (intermediolateral gray matter) - Preganglionic fibers release ACh onto autonomic ganglion
- Ganglion further from target
- Postganglionic fibers release NE onto target
- Innervate smooth muscle, cardiac muscle, gland cells
Similarities between sympathetic NS and parasympathetic NS
- In both, preganglionic fibers release ACh onto autonomic ganglion
- Both innervate smooth muscle, cardiac muscle, gland cells
Features of parasympathetic NS
- From brainstem and sacral spinal cord
- Preganglionic fibers release ACh onto autonomic ganglion
- Ganglion closer to target
- Postganglionic fibers release ACh onto target (muscarinic)
Table of effects of sympathetic vs. parasympathetic NS
Which of the following statements are TRUE about the Parasympathetic vs Sympathetic nervous systems?
a) Preganglionic fibers release ACh onto autonomic ganglia in both systems
b) The ganglion is closer to the CNS in the Sympathetic whereas it’s further away in the
Parasympathetic
c) Both types of ganglia release norepinephrine
d) These systems innervate somatic muscles and gland cells
e) The effects of these systems are opposing
Answer: A, B, E - what’s wrong about the other answers?
Does this statement describe the sympathetic or parasympathetic NS?
Ganglia are further from target
Sympathetic
Does this statement describe the sympathetic or parasympathetic NS?
Ganglia are closer to target
Parasympathetic
Does this statement describe the sympathetic or parasympathetic NS?
Postganglionic fibers release ACh onto target (muscarinic)
Parasympathetic
Does this statement describe the sympathetic or parasympathetic NS?
Postganglionic fibers release NE onto target
Sympathetic
Does this statement describe the sympathetic or parasympathetic NS?
From brainstem and sacral spinal cord
Parasympathetic
Does this statement describe the sympathetic or parasympathetic NS?
From middle 1/3 of spinal cord sympathetic chain (inermediolateral gray matter)
Sympathetic
Corticotropin-releasing hormone (CRH)
a) travels through the blood to the adrenal glands and stimulates the release of cortisol
b) is released into the blood in the posterior pituitary
c) travels through the blood to the anterior pituitary triggering the release of adrenocorticotropic hormone (ACTH)
d) binds to neurons in the hypothalamus and causes an increase in feeding behavior
c) travels through the blood to the anterior pituitary triggering the release of adrenocorticotropic hormone (ACTH)
Anterior pituitary hormones
a) are released from axon terminals
b) are released in response to the presence of releasing factors
c) include glutamate and GABA
d) stimulate parvocellular neurons in the hypothalamus
b) are released in response to the presence of releasing factors
Blocking acetylcholine receptors in the ganglia of the autonomic nervous system would cause
a) Decreased activity in sympathetic axons
b) Decreased activity in parasympathetic axons
c) Decreased activity in motor neurons innervating skeletal muscle
d) More than one of the above
e) All of the above
d) More than one of the above
a and b are both correct because ACh is used in both the symp and parasymp systems
Hypophysiotropic hormones are released into the ___
hypothalamo-hypophyseal portal system
