Neurotransmitters and Inhibitory Actions

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Questions and Answers

What is the role of glutamine synthetase?

Releasing glutamate from synaptic vesicles

Activating ionotropic receptors

Converting glutamate to glutamine (correct)

Converting glutamine to glutamate

Which of the following is NOT a type of ionotropic receptor?

GABA (correct)

AMPA

NMDA

What happens when NMDA receptors are activated?

Only Na+ and K+ are allowed to pass through

Only Ca2+ is allowed to pass through

No ions are allowed to pass through

Ca2+, Na+, and K+ are allowed to pass through (correct)

What is the function of VGLUT?

Achieving high concentrations of glutamate in synaptic vesicles (A) Signup and view all the answers

What is the effect of domoic acid on the body?

It causes abdominal cramps, vomiting, diarrhea, and seizure (A) Signup and view all the answers

What is the characteristic of AMPA receptors that lack the GluA2 subunit?

They are permeable to Na+, K+, and Ca2+ (D) Signup and view all the answers

What is the major inhibitory neurotransmitter in the brain?

GABA (A) Signup and view all the answers

What is the effect of Picrotoxins on GABA receptors?

It blocks the effect of GABA (A) Signup and view all the answers

What type of receptors do neurotransmitters involved in diffuse neuronal systems mainly act on?

Metabotropic receptors (B) Signup and view all the answers

What is the function of inhibitory neurotransmitters?

They inhibit the cascade of action potential (A) Signup and view all the answers

Which of the following is an example of an amino acid neurotransmitter?

Glutamate (D) Signup and view all the answers

What is the process by which glutamate is released into the synaptic cleft?

Ca2+ dependent exocytosis (C) Signup and view all the answers

What is a characteristic of neuropeptides in the CNS?

They are involved in a wide range of CNS functions (D) Signup and view all the answers

What is the effect of a lack of orexin or its receptors in animals?

Narcolepsy and disrupted sleep-wake patterns (D) Signup and view all the answers

What is the primary use of Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)?

Treatment of pain disorders including neuropathies and fibromyalgia (D) Signup and view all the answers

What is the primary function of endocannabinoids in the brain?

Activating a specific cannabinoid receptor (D) Signup and view all the answers

What is a common symptom of Major Depressive Disorder?

Disturbances in sleep and appetite (D) Signup and view all the answers

What is the characteristic of fluvoxamine?

Potent inhibitor of CYP2D6 (D) Signup and view all the answers

What is the enantiomer of citalopram?

Escitalopram (A) Signup and view all the answers

What is the role of orexin neurons in the sleep-wake cycle?

They exhibit firing patterns associated with wakefulness (C) Signup and view all the answers

What is a function of somatostatin, a type of neuropeptide?

Involvement in reproduction (A) Signup and view all the answers

What is the primary use of Tricyclic Antidepressants (TCAs)?

Treatment of depression that is unresponsive to more commonly used antidepressants (C) Signup and view all the answers

What is the characteristic of trazodone?

Weak but selective inhibitor of SERT with little effect on NET (C) Signup and view all the answers

What is the characteristic of paroxetine?

Selective Serotonin Reuptake Inhibitor (C) Signup and view all the answers

What is a common thought pattern in individuals with depression?

Thoughts of guilt, worthlessness, and suicide (C) Signup and view all the answers

What is a common comorbidity associated with depression?

Coronary artery disease, diabetes, and stroke (C) Signup and view all the answers

What is the primary use of antidepressants?

Treatment of major depressive disorder (MDD) (C) Signup and view all the answers

What is the role of neurotrophic factors in the neurotrophic hypothesis of depression?

Enhancement of synaptic connectivity and neurotrophic support (A) Signup and view all the answers

What is the hippocampus primarily responsible for?

Regulation of contextual memory and hormone release (B) Signup and view all the answers

What is the outcome of effective antidepressant therapies on neurogenesis and synaptic connectivity?

Increased neurogenesis and synaptic connectivity (A) Signup and view all the answers

Study Notes

Glutamate and Glial Cells

Released glutamate acts on post-synaptic glutamate receptors.
Glutamate is converted to glutamine in glial cells by the enzyme glutamine synthetase.
In glia, glutamine is converted back to glutamate by the enzyme glutaminase.

Vesicular Transport and Excitation

High concentrations of glutamate in synaptic vesicles are maintained by the vesicular glutamate transporter (VGLUT).
Nearly all tested neurons are excited by glutamate through activation of ionotropic and metabotropic receptors.

Ionotropic Receptors

Three main types of ionotropic receptors: AMPA, Kainic Acid (KA), and NMDA.
AMPA receptors (contain GluA2 subunit) are permeable to Na+ and K+, but not Ca2+; some interneurons without GluA2 are Ca2+ permeable.
KA receptors are permeable to Na+ and K+, and can be Ca2+ permeable depending on subunit composition.
Domoic acid from shellfish can cause poisoning through excitatory action on KA and AMPA receptors, leading to symptoms like seizures.
NMDA receptors are ubiquitous in the CNS, allowing Na+, K+, and Ca2+ permeability; they require extreme depolarization to open.

Inhibitory Neurotransmitters

GABA and Glycine serve as primary inhibitory neurotransmitters.
GABA is the major neurotransmitter in the brain, while Glycine is predominant in the spinal cord.
Picrotoxins block GABA's effects by binding to GABA-A receptors causing convulsions.

Diffuse Neuronal Systems

These systems have broad distribution and varied activities, innervating multiple CNS regions.
Neurotransmitters involved include norepinephrine, dopamine, and serotonin (5HT), affecting a range of functions like sleep, attention, and emotional states.
Primarily activate metabotropic receptors for long-lasting synaptic effects.

Neurotransmitter Categories

Excitatory neurotransmitters trigger action potentials.
Inhibitory neurotransmitters inhibit action potential transmission.
Major amino acid neurotransmitters include glutamate, GABA, and glycine.

Neuropeptides and Functions

Neuropeptides co-exist with conventional neurotransmitters, influencing functions such as reproduction, social behavior, appetite, pain, and learning.
Opioid peptides like enkephalins and endorphins are included.

Orexin/Hypocretins

Produced in the hypothalamus, orexins are excitatory neurotransmitters that regulate wakefulness and energy homeostasis.
Lack of orexin or its receptors leads to narcolepsy and disturbed sleep patterns.

Other Signaling Substances

Endocannabinoids are psychoactive compounds affecting cognition and pain perception.
Nitric oxide and purines (ATP, UTP, adenosine) also act as signaling molecules in the CNS.

Antidepressant Agents

Major Depressive Disorder (MDD) presents with persistent depressed mood, loss of interest, sleep and appetite disturbances, and cognitive deficits.
Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine and escitalopram have varying half-lives and inhibit cytochrome P450 enzymes.
Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs) include venlafaxine and duloxetine, treating pain disorders and anxiety.

Tricyclic Antidepressants (TCAs)

TCAs like imipramine and amitriptyline are used for treatment-resistant depression.
5HT2 receptor modulators such as trazodone block 5HT2A receptors and are often prescribed as sleep aids.

Tetracyclic and Unicyclic Antidepressants

Similar to TCAs but infrequently prescribed.
Depression increases risks for coronary artery disease, diabetes, and stroke.

MDD Pathophysiology

Monoamine hypothesis suggests low monoamine levels in MDD.
Neurotrophic hypothesis emphasizes the role of neurotrophic factors in neural plasticity and resilience.
Brain-derived neurotrophic factor (BDNF) links effective antidepressant therapy to neurogenesis and synaptic connectivity, particularly in the hippocampus, which is crucial for memory and hormone release regulation.

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Description

This quiz covers the role of inhibitory neurotransmitters like GABA and Glycine, and how drugs interact with them, leading to effects like convulsions.