Write the name of neurotransmitter which act as neuromodulator as well as inhibitor of neurotransmitter

One of the best-known neurotransmitters that shows both neuromodulatory and inhibitory functions is GABA (Gamma-Aminobutyric Acid). It is a major chemical messenger in the central nervous system (CNS) and plays a vital role in regulating brain activity. GABA is unique because it not only participates in fast synaptic transmission as an inhibitory neurotransmitter but also acts more broadly as a neuromodulator that controls the excitability of entire neural circuits.

1. GABA as a Neuromodulator

As a neuromodulator, GABA works at a slower and more widespread level than fast synaptic transmission. Instead of targeting a single postsynaptic neuron, it can influence large groups of neurons or entire regions of the brain. Neuromodulatory action of GABA usually happens through GABA-B receptors, which are metabotropic and linked with second messenger systems.

Through these pathways, GABA can regulate the activity of other neurotransmitter systems like:
  • Glutamate (main excitatory neurotransmitter)
  • Dopamine (involved in mood and reward)
  • Serotonin (involved in emotion and sleep)
This kind of modulation helps in maintaining emotional stability, attention control, sleep-wake cycles and stress regulation. For example, in the limbic system and prefrontal cortex, GABA modulates circuits related to anxiety and decision-making. In this way, GABA does not always act by directly inhibiting action potentials but adjusts the general tone of neural activity.

2. GABA as an Inhibitory Neurotransmitter

In its classical role, GABA functions as the main inhibitory neurotransmitter in the CNS. It is released at synapses by inhibitory interneurons. It binds mainly to:
  • GABA-A receptors, which are ionotropic and allow chloride ions (Cl⁻) to enter the neuron, making the inside more negative (hyperpolarization).
  • GABA-B receptors, which are metabotropic and open potassium (K⁺) channels and close calcium (Ca²⁺) channels, also leading to inhibition.
This inhibition prevents the postsynaptic neuron from reaching threshold and firing an action potential. As a result, GABA helps maintain the balance between excitation and inhibition in the nervous system, and prevents problems like seizures, overstimulation and anxiety.



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