Class 11 - Neuropeptides & Neurotransmitter Receptors

What are neuropeptides?

Neuropeptides are large signaling molecules that act as neurotransmitters and are synthesized in the cell body.

How are neuropeptides synthesized?

Neuropeptides are synthesized as pre-propeptides in the rough endoplasmic reticulum, processed into propeptides, and then converted into mature neuropeptides in vesicles.

What distinguishes neuropeptide transmission from classical neurotransmission?

Neuropeptide transmission involves slower, longer-lasting effects and can diffuse broadly over larger distances, unlike the rapid, localized effects of classical neurotransmitters.

What type of receptors do nearly all neuropeptides act upon?

Nearly all neuropeptides act on G-protein coupled receptors (GPCRs).

What is the role of NPY receptors?

NPY receptors are implicated in the initiation and maintenance of feeding behavior and are associated with satiety and obesity.

What characterizes the storage of neuropeptides at the synapse?

Neuropeptides are stored in large dense-core vesicles and require a larger influx of calcium for release compared to classical neurotransmitters.

What is unique about peptide catabolism?

There is no reuptake for neuropeptides; their action is terminated by peptidases that cleave the peptides into inactive fragments.

What are the major classes of opioid peptides?

Opioid peptides fall into three classes: endorphins, enkephalins, and dynorphins.

What is the primary effect of GABA-A receptors in the nervous system?

GABA-A receptors are ligand-gated ion channels that mediate inhibitory neurotransmission by allowing chloride ions to flow into the cell.

How do metabotropic receptors differ from ionotropic receptors?

Metabotropic receptors do not have ion channels as part of their structure; they require second messengers to open channels and are generally slower than ionotropic receptors.

What neurotransmitter is primarily excitatory in the CNS?

Glutamate is the primary excitatory neurotransmitter in the CNS.

What happens to the NMDA receptor when the membrane is depolarized?

Depolarization dislodges Mg2+ from the NMDA receptor, allowing ion flow when glutamate and glycine are bound.

What are autoreceptors and their function?

Autoreceptors respond to neurotransmitters released by the same neuron and commonly inhibit further neurotransmitter release or synthesis.

What are some examples of modulatory neurotransmitters that use metabotropic receptors?

Examples include serotonin (5-HT), dopamine (DA), norepinephrine (NE), and acetylcholine (ACh).

Identify the two main classes of neurotransmitter receptors.

The two main classes are ionotropic receptors (ligand-gated) and metabotropic receptors (G-protein coupled).

What consequence does excessive glutamate signaling have in the nervous system?

Excessive glutamate signaling can lead to neuronal hyper-excitability and excitotoxicity, causing damage to neurons.

How do GABA-B receptors function in terms of synaptic response?

GABA-B receptors are metabotropic and facilitate longer-lasting effects by linking to potassium or calcium channels via second messengers.

What distinguishes classical neurotransmitters from neuropeptides at synapses?

Classical neurotransmitters are stored in small synaptic vesicles and are rapidly recycled, while neuropeptides are stored in large dense-core vesicles and are not rapidly recycled after release.

What characterizes the structure of ionotropic receptors?

Ionotropic receptors are usually multimeric proteins with multiple subunits forming a channel pore.

What roles do endogenous cannabinoids typically have in the nervous system?

Endogenous cannabinoids, like anandamide and 2-arachidonoylglycerol, regulate numerous physiological functions and modulate neurotransmitter release.

What is the importance of the glycine binding site on NMDA receptors?

The glycine binding site is necessary for effective opening of the NMDA receptor channel in conjunction with glutamate.

What effect does glutamate binding have on NMDA receptors?

Glutamate binding to NMDA receptors promotes the opening of the channel, allowing Na+ and Ca2+ influx and K+ efflux.

What is the function of autoreceptors in neurotransmitter signaling?

Autoreceptors provide a mechanism for feedback inhibition, reducing neurotransmitter release when activated.

What role do muscarinic acetylcholine receptors play in the body?

Muscarinic receptors mediate a variety of functions in the parasympathetic nervous system, including slowing heart rate and stimulating smooth muscle contraction.

What distinguishes ionotropic GABA receptors from metabotropic GABA receptors?

Ionotropic GABA receptors (GABA-A) are ligand-gated chloride channels, while metabotropic GABA receptors (GABA-B) are G-protein coupled and have slower, modulatory effects.