TRANSMISSÃO ADRENÉRGICA - AULA NEUROFISIOLOGIA #4

Summary

In this video, neuroscientist Bruno explains the complex process of adrenergic neurotransmission, which is crucial for the sympathetic nervous system. He details how the amino acid tyrosine is converted into key neurotransmitters, including dopamine, norepinephrine, and adrenaline, and describes their synthesis, release, and reuptake mechanisms. Bruno also covers the role of different adrenergic receptors and how they affect various tissues in the body, from the heart to the muscles. Additionally, he explains the importance of enzymes like MAO and COMT in regulating these neurotransmitters and their relevance in treating certain psychiatric disorders and drug abuse. The video provides an accessible yet thorough understanding of adrenergic neurotransmission.

Takeaways

• 😀 The script explains the fundamentals of adrenergic neurotransmission, a crucial process in the sympathetic nervous system.
• 😀 The neurotransmitters involved in adrenergic transmission are dopamine, noradrenaline, and adrenaline, collectively known as catecholamines.
• 😀 Tyrosine is the precursor amino acid for the synthesis of these catecholamine neurotransmitters, which occurs through several enzymatic reactions.
• 😀 The process involves the enzyme tyrosine hydroxylase (TH) converting tyrosine into L-DOPA, which is then transformed into dopamine.
• 😀 Dopamine can further be converted into noradrenaline (or norepinephrine) by the enzyme dopamine beta-hydroxylase, and noradrenaline can be converted into adrenaline.
• 😀 Adrenaline is considered a hormone and is primarily produced in the adrenal glands, whereas noradrenaline acts as a neurotransmitter in both the central and peripheral nervous systems.
• 😀 Adrenergic synaptic transmission begins with the uptake of tyrosine by a transporter and the formation of dopamine, followed by its conversion to noradrenaline in adrenergic neurons.
• 😀 The release of neurotransmitters occurs via exocytosis triggered by calcium influx into the cell, facilitated by voltage-dependent calcium channels.
• 😀 Catecholamines can be reabsorbed into the presynaptic neuron, degraded by enzymes such as MAO and COMT, or diffuse out of the synaptic cleft.
• 😀 The script also explains the role of drugs like cocaine and reserpine, which affect neurotransmitter availability by either inhibiting reuptake or vesicular uptake, respectively.

Q & A

What is the focus of this video?

The video focuses on explaining adrenergic neurotransmission, its physiological mechanisms, and the role of different neurotransmitters and receptors in the sympathetic nervous system.

What amino acid is a precursor to key catecholamines?

The amino acid tyrosine is the precursor to several catecholamines, including dopamine, noradrenaline (norepinephrine), and adrenaline (epinephrine).

What enzyme is responsible for the conversion of tyrosine into L-DOPA?

The enzyme responsible for converting tyrosine into L-DOPA is tyrosine hydroxylase (TH).

How is dopamine converted into noradrenaline?

Dopamine is converted into noradrenaline through the action of the enzyme dopamine beta-hydroxylase (DBH).

What distinguishes noradrenaline from adrenaline in terms of function?

Noradrenaline primarily functions as a neurotransmitter in both the central and peripheral nervous systems, while adrenaline is more commonly considered a hormone produced by the adrenal glands.

What is the role of the enzyme phenylethanolamine N-methyltransferase (PNMT)?

PNMT is responsible for converting noradrenaline into adrenaline in the adrenal glands.

What happens during the release of neurotransmitters in adrenergic synapses?

When an action potential arrives, voltage-gated calcium channels open, allowing calcium to enter the neuron, triggering exocytosis, which releases neurotransmitters such as noradrenaline into the synaptic cleft.

How are neurotransmitters like noradrenaline reabsorbed after their release?

Noradrenaline is reabsorbed into the presynaptic neuron via the norepinephrine transporter (NET), which regulates the neurotransmitter's availability in the synaptic cleft.

What effect does cocaine have on adrenergic neurotransmission?

Cocaine inhibits the norepinephrine transporter (NET), increasing the availability of noradrenaline in the synaptic cleft and enhancing its effects.

What role do enzymes like MAO and COMT play in neurotransmitter degradation?

Monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) degrade catecholamines like dopamine, noradrenaline, and adrenaline into inactive metabolites, which are then excreted from the body.

How do adrenergic receptors differ in terms of their signaling mechanisms?

Adrenergic receptors can be coupled with different G proteins (Gs, Gi, Gq), which initiate distinct signaling cascades involving second messengers like cAMP or inositol trisphosphate (IP3), affecting cellular responses such as contraction, relaxation, or secretion.