Pre- and postganglionic terminals release neuropeptides that function directly onto the target tissue or have a modulatory role.

Pre- and postganglionic terminals release neuropeptides that function directly onto the target tissue or have a modulatory role.

• A. Acetylcholine as the sole transmitter
• B. Norepinephrine as the primary transmitter
• C. Neuropeptides that function directly onto the target tissue or have a modulatory role
• D. Gamma-aminobutyric acid as an inhibitory transmitter

Answer: (C)

The question hinges on co-transmission in autonomic neurons. Pre- and postganglionic terminals don’t rely solely on a single fast transmitter; they can release neuropeptides that act directly on the target tissue or modulate the effect of the classical transmitter. These neuropeptides are stored in dense-core vesicles and are released with higher-frequency activity, producing slower, longer-lasting responses via metabotropic receptors. Examples include neuropeptides that accompany norepinephrine to enhance or prolong vasoconstriction, or peptides that accompany acetylcholine to shape glandular or smooth muscle responses. This combination of direct tissue effects and modulatory roles is why the statement about neuropeptides functioning directly on target tissue or modulating transmission best captures what happens at these terminals. The other options describe only a single classic transmitter or a transmitter not typical of autonomic peripheral neurons, and thus don’t reflect the co-transmission reality.

The question hinges on co-transmission in autonomic neurons. Pre- and postganglionic terminals don’t rely solely on a single fast transmitter; they can release neuropeptides that act directly on the target tissue or modulate the effect of the classical transmitter. These neuropeptides are stored in dense-core vesicles and are released with higher-frequency activity, producing slower, longer-lasting responses via metabotropic receptors. Examples include neuropeptides that accompany norepinephrine to enhance or prolong vasoconstriction, or peptides that accompany acetylcholine to shape glandular or smooth muscle responses. This combination of direct tissue effects and modulatory roles is why the statement about neuropeptides functioning directly on target tissue or modulating transmission best captures what happens at these terminals. The other options describe only a single classic transmitter or a transmitter not typical of autonomic peripheral neurons, and thus don’t reflect the co-transmission reality.