Question

Which of these statements about catecholamines is false? a. They include norepinephrine, epinephrine, and dopamine. b. Their effects are increased by action of the enzyme catechol- O-methyltransferase. c. They are inactivated by monoamine oxidase. d. They are inactivated by reuptake into the presynaptic axon. e. They may stimulate the production of cyclic AMP in the postsynaptic axon.

Short answer

The false statement about catecholamines is: b. Their effects are increased by the action of the enzyme catechol-O-methyltransferase.

Step-by-step solution

Evaluate statement a

Statement a says that norepinephrine, epinephrine, and dopamine are catecholamines. This statement is true, as catecholamines are a group of neurotransmitters including norepinephrine, epinephrine, and dopamine.

Evaluate statement b

Statement b mentions that the effects of catecholamines are increased by the action of the enzyme catechol-O-methyltransferase. This statement is actually false, as the enzyme catechol-O-methyltransferase (COMT) is involved in the inactivation and degradation of catecholamines. It decreases their effects, not increases them.

Evaluate statement c

Statement c states that catecholamines are inactivated by monoamine oxidase. This statement is true, as monoamine oxidase (MAO) is another enzyme responsible for the degradation and inactivation of catecholamines.

Evaluate statement d

Statement d says that catecholamines are inactivated by reuptake into the presynaptic axon. This statement is accurate, as the reuptake of catecholamines into the presynaptic axon is one of the primary mechanisms for terminating their action.

Evaluate statement e

Statement e mentions that catecholamines may stimulate the production of cyclic AMP (cAMP) in the postsynaptic axon. This statement is true, as catecholamines can bind to adrenergic receptors in the postsynaptic neuron, which often lead to the activation of adenylate cyclase and the subsequent increase in cAMP levels. Based on the evaluation of all statements, we can conclude that statement b is the false statement.

Key concepts

Neurotransmitters

Neurotransmitters are the body's chemical messengers that transmit signals across the synapse from one neuron to another. They play a crucial role in the central nervous system by influencing our mood, arousal, and cognitive functions. Catecholamines like norepinephrine, epinephrine, and dopamine fall under this category and are particularly involved in the body's response to stress or fear, often referred to as the 'fight or flight' response.

Understanding neurotransmitters is fundamental, as they are key to how neurons communicate with each other. Each neurotransmitter has specific receptors it binds to, initiating various effects in the receiving cell and ultimately influencing numerous bodily and mental functions.

Catechol-O-methyltransferase

Catechol-O-methyltransferase (COMT) is one of the key enzymes that help regulate neurotransmitter levels in the brain, particularly those of catecholamines. Although it might seem intuitive that enzymes affecting neurotransmitters would boost their activity, COMT actually does the opposite. It inactivates catecholamines by transferring a methyl group, essentially breaking them down.

This process helps maintain appropriate levels of neurotransmitters, preventing excessive signaling that could lead to a range of cognitive and psychological problems. An understanding of COMT is important for students as it emphasizes the balance necessary in our nervous system's chemistry.

Monoamine Oxidase

Monoamine oxidase (MAO) is another enzyme crucial for neurotransmitter regulation. Specifically, MAO works by breaking down excess monoamine neurotransmitters, including catecholamines, in the synaptic cleft.

There are two types of MAO: MAO-A and MAO-B. Each type has a preference for different neurotransmitters. The action of MAO ensures that neurotransmitters do not accumulate excessively in the brain, which could disrupt normal brain function. Medications known as MAO inhibitors (MAOIs) block this enzyme and are sometimes used to treat certain neurological and psychiatric conditions, showcasing the significance of MAO in neural processes.

Neural Reuptake

Neural reuptake is a process where neurotransmitters that have been released into the synapse are reabsorbed back into the presynaptic neuron. This mechanism is crucial for clearing the synapse from excess neurotransmitters and is a key step in terminating the signal.

Reuptake carries neurotransmitters away from the synaptic cleft and either recycles them for future use or disposes of them through degradation. This is not only important for turning off the signal but also for regulating the amount of neurotransmitters available for future communication. Drugs that inhibit reuptake, such as certain antidepressants, prolong the action of neurotransmitters, which underlines the importance of reuptake in neural function.

Cyclic AMP

Cyclic AMP (cAMP) is a secondary messenger used widely in various biological signaling processes. In the context of neurotransmitters, once a neurotransmitter binds to its receptor, it can activate an enzyme called adenylate cyclase, which then converts ATP (adenosine triphosphate) to cAMP.

cAMP acts as a signal amplification system, whereby a single neurotransmitter binding event can result in the generation of multiple cAMP molecules, leading to a robust cellular response. This process can modulate various physiological responses, such as heart rate, energy metabolism, and even long-term memory formation in neurons.