Glycine Transporters and Hereditary Hyperekplexia Quiz

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Questions and Answers

Which of the following is NOT a known transporter involved in regulating glycine levels at the synapse?

SMHT (correct)

VIAAT

GLYT1

GLYT2

Where is GLYT2 primarily expressed?

Postsynaptic terminals

Axons and presynaptic terminals (correct)

Presynaptic terminals

Astrocytes

Which of the following is NOT true about the degradation of glycine?

Glycine degradation is initiated by the SMHT enzyme. (correct)

Glycine degradation occurs in mitochondria.

Glycine degradation is a crucial step in the removal of glycine from the synaptic cleft.

Glycine degradation uses the glycine cleavage system (GCS).

What is the function of GLYT1 in the forebrain?

Regulating NMDAR transmission. Signup and view all the answers

Which of the following is TRUE about the expression of GLYT1?

GLYT1 is expressed in both neurons and astrocytes. Signup and view all the answers

What is the primary function of GLYT1 and GLYT2?

Removing glycine from the synaptic cleft. Signup and view all the answers

Which of the following statements ACCURATELY describes the relationship between glycine and the NMDA receptor?

Glycine is a co-agonist of the NMDA receptor. Signup and view all the answers

Which of the following is TRUE regarding the synthesis of glycine?

Glycine synthesis occurs from serine by the enzyme serine hydroxymethyltransferase (SMHT). Signup and view all the answers

Why does GLYT1 exist in different isoforms?

Different isoforms of GLYT1 allow for tissue-specific regulation of glycine levels. Signup and view all the answers

Which of the following statements is TRUE regarding the symptoms of hereditary hyperekplexia in older individuals?

Older individuals with hereditary hyperekplexia may experience periodic rigidity, significantly affecting their movements, but their startle response often diminishes. Signup and view all the answers

Based on the provided text, what is the most likely cause of the transient breathing difficulties experienced by infants with hereditary hyperekplexia?

The rigidity induced by the startle response can restrict chest movements necessary for proper respiration. Signup and view all the answers

Which of the following is a TRUE statement about the progression of hereditary hyperekplexia?

The characteristic hypertonia is a defining feature throughout an individual's life, albeit at a lesser intensity in adulthood. Signup and view all the answers

Based on the text, the statement that hereditary hyperekplexia is characterized by hypertonia 'except when they are sleeping' implies that:

Sleep induces a relaxation of muscles, thus temporarily mitigating the hypertonia associated with hereditary hyperekplexia. Signup and view all the answers

Given the symptoms and progression of hereditary hyperekplexia, which of the following statements is the LEAST likely explanation for the observed fading of symptoms by age 1?

The condition inherently has a self-limiting course, where symptoms naturally subside over time, regardless of biological or neurological factors. Signup and view all the answers

Which substance is identified as the main inhibitory neurotransmitter in the adult nervous system?

GABA Signup and view all the answers

What is synthesized by the enzyme glutamic acid decarboxylase?

GABA Signup and view all the answers

Which of the following substances is mentioned as being seized at breweries in London?

Sulphuric acid Signup and view all the answers

What is a primary conclusion of William Black regarding the brewing of porter?

They are required to achieve the desired taste and flavor. Signup and view all the answers

According to William Black, what contributes to the intoxicating qualities of porter?

The presence of certain drugs mixed with it Signup and view all the answers

Which of the following drugs is specifically mentioned as having been used in brewing?

Cocculus indicus Signup and view all the answers

What effect does the quantity of stupefying ingredients have on porter according to historical claims?

It affects the intoxicating strength of the beer. Signup and view all the answers

What characterizes GABAC receptors in terms of agonist activation?

They are activated by cis-4-aminobut-2-enoate (CACA). Signup and view all the answers

Which statement is true regarding the composition of GABAA receptors?

They can consist of more than 2000 different subunit combinations. Signup and view all the answers

Which GABAA receptor subtype exhibits the most prevalence in the brain?

α1β2γ2 Signup and view all the answers

In which brain regions are GABAA receptors containing the α2 subunit most abundant?

Hippocampus and striatum. Signup and view all the answers

What is the primary basis for differentiating GABAA and GABAC receptors?

Pharmacological grounds related to their agonists. Signup and view all the answers

What is the stoichiometry of the major GABAA receptor subtype found in the brain?

α1β2γ2 Signup and view all the answers

What type of receptor is GABAA categorized as?

Ionotropic receptor. Signup and view all the answers

Which of the following statements about GABAC receptors is correct?

They are a homomeric complex of rho subunits. Signup and view all the answers

What can be concluded about the relationship between GABAC receptors and GABAA receptors?

GABAC receptors show considerable amino acid sequence homology with GABAA receptors. Signup and view all the answers

Which of the following statements regarding glycine receptors is TRUE?

They are allosterically modulated by certain alcohols and anesthetics. Signup and view all the answers

Why can glycine act as an excitatory neurotransmitter in the embryonic nervous system?

The Cl- reversal potential is more positive in embryonic neurons. Signup and view all the answers

What is the primary mechanism by which alcohols modulate glycine receptors?

Allosteric modulation of the receptor. Signup and view all the answers

Based on the provided information, which of the following neurotransmitters can be considered both excitatory and inhibitory depending on the developmental stage?

Glycine Signup and view all the answers

In the context of embryonic nervous system development, what likely happens to the Cl- reversal potential as the nervous system matures?

It becomes more negative. Signup and view all the answers

Which of these factors contributes to the transition of glycine from an excitatory neurotransmitter to an inhibitory one during development?

Increased expression of the KCC2 transporter. Signup and view all the answers

Based on the provided information, what is the MOST likely reason that β-mRNA is abundant in the CNS but does not alone create glycine receptors?

β-mRNA requires the presence of other specialized molecules for proper glycine receptor formation. Signup and view all the answers

Select the option that is TRUE about the relationship between glycine receptors and inherited hyperekplexia.

Hyperekplexia results from non-functional glycine receptors. Signup and view all the answers

Which of the following drugs, based on the information given, is LIKELY to have an effect on glycine receptors?

Ketamine (an NMDA receptor antagonist) Signup and view all the answers

Which of the following is a REASONABLE inference regarding the role of KCC2 transporter in the development of the nervous system?

KCC2 plays a crucial role in the maturation of inhibitory neurotransmission. Signup and view all the answers

Study Notes

GABA & Glycine

GABA and glycine are neurotransmitters, crucial for inhibitory functions in the adult nervous system.
Ironically, the precursor to GABA is glutamate, a major excitatory neurotransmitter.
GABA is synthesized via the enzyme glutamic acid decarboxylase (GAD).
GAD (65 and/or 67) is localized specifically on GABAergic neurons.
GABA is present throughout the brain in diverse inhibitory interneurons (e.g., basket, stellate) and projection neurons (e.g., Purkinje).
GABA is transported back into GABAergic terminals via dedicated GABA transporters.
GABA is also buffered by astrocytes where it is degraded by GABA transaminase (GABA-T).
This process results in a net flow of GABA from neuronal to astrocytic compartments.
Compensatory flow of a GABA precursor is needed to maintain this balance.
GABA-related proteins like GAD, GABA-T, and GATs have specific locations and functions.
GABA receptors (GABAA, GABAB, GABAC) have diverse roles and are modulated by various substances (e.g., alcohol, anaesthetics, benzodiazepines, etc).

Receptor Nomenclature

GABA receptors form complexes with different subunits (homomeric and heteromeric), and their respective types.
GABA_A, GABA_B, and GABA_C receptors have differing properties including the types of ions involved, their locations, and their roles in the nervous system.
The Greek letters denote subunit families, each with significant homology in amino acid sequence (specifically about 70%).
The related homology between families is around 30-40%.
GABAA receptors are chloride channels, while GABAB is a G protein-coupled receptor.
GABA_C receptors are homomeric, containing only rho subunits.

Drugs Affecting GABAergic Transmission

Drugs can modulate GABAergic transmission through various mechanisms.
Agonists often enhance GABAergic activity, and antagonists reduce it.
Different drugs target different GABA receptors.
Examples of drugs impacting relevant receptors include benzodiazepines, barbiturates, and some anaesthetics.

Case Study - Adulteration

The case study involving the adulteration of beer exemplifies the use of various substances to alter flavour and perceived strength, including toxins and other harmful compounds.
Brewers used different products, such as cocculus indicus in an attempt to enhance flavour and masking of poor products.
Authorities took measures to control these adulteration practices.

Case Study - Performance Enhancement

Historically, substances like strychnine were used as performance enhancers.
Strychnine is a potent convulsant, and its use in sports competitions was a significant concern.
Athletic performance enhancers have ethical and legal implications.
Contemporary athletic guidelines address the use of performance-enhancing substances.

Glycine in Synaptic Transmission

Glycine is a major neurotransmitter in the nervous system, and it has similar characteristics to GABA.
Glycine is synthesized from serine by serine hydroxymethyltransferase (SMHT).
Glycine is packaged into vesicles, transported in the synaptic cleft by uptake transporters on astrocytes and presynaptic terminals (GLYT1 and GLYT2).
GLYT1 and GLYT2 are expressed throughout the brain, performing a crucial role.
Degradation occurs through the glycine cleavage system in mitochondria. Glycine receptors are impacted by various drugs.

Glycine Receptors

Glycine receptors are a class of ionotropic receptors, with specific subunit compositions and functions.
Glycine receptors are related to nicotinic cholinergic and 5-HT3 receptors, possessing a pentameric structure.
Glycine receptors are activated by glycine and are inhibited by strychnine.
Glycine receptors have specific regional and developmental regulation, notably with the alpha subunits determining location, influencing the physiological roles of glycine.

Ethanol and GABA/Glycine Receptors

Ethanol enhances GABA_A receptor-mediated synaptic inhibition.
Ethanol affects GABA_A receptor function and consequently increases efficacy of glycine.
Blocking GABA_B receptors enhances effect of ethanol.
Ethanol may impact other neurotransmitter systems like glutamate in different ways.

GABA and Disease

GABAergic neurotransmission plays a role in various neuropsychiatric disorders, including epilepsy, Huntington's disease, tardive dyskinesia, alcoholism and sleep disorders.
In some conditions, imbalances in GABA neurotransmission can affect neuronal activity, contributing to disease processes.

GABAergic System Deficiency

GABA transaminase (GABA-T) deficiency, a genetic disorder, leads to recurrent seizures, uncontrolled movements and other complications in infants.
Symptoms are present early in infancy.
These patients have difficulty thriving and developing.

Embryonic Nervous System and GABA/Glycine

GABA and glycine can cause depolarization in the embryonic nervous system, which contrasts to their inhibitory role in the adult nervous system.
In early stages of development, GABA can affect neuron activity in an excitatory way.
This early excitatory role is essential for CNS development.

Receptor Modulation

Glycine receptors are allosterically modulated.
Alcohol impacts glycine receptors and GABA receptors in different ways.

Additional Notes (from various pages)

Strychnine: a substance historically used as a performance enhancer, now forbidden in sports competition due to its convulsive properties.
Several case studies provide historical examples of substances used or abused in the past in an attempted performance enhancement which often highlighted ethical considerations.
Learning Outcomes: Specific outcomes mentioned include discussing various transmitters, their actions, and agonists/antagonists, along with examining associated diseases and case studies.
There's a specific concern with learning outcomes tied to performance enhancement.
The pharmacology of GABA and glycine is crucial for understanding diverse neurological and psychiatric conditions.

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Description

Test your knowledge on glycine transporters GLYT1 and GLYT2, their functions, and their role in conditions like hereditary hyperekplexia. This quiz covers key concepts related to glycine regulation at the synapse and the implications of transporters in neurological function. Challenge yourself with a variety of true/false questions and in-depth inquiries.