Name an inhibitory neurotransmitter.

Explanation

**Step-by-Step Solution:**

1. **Understanding Neurotransmitters**: Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. They can be classified as excitatory or inhibitory based on their effects on the target neuron.

2. **Identifying Inhibitory Neurotransmitters**: Inhibitory neurotransmitters are those that decrease the likelihood of the firing action potential in the receiving neuron. This means they reduce neuronal excitability.

3. **Naming an Inhibitory Neurotransmitter**: One of the most well-known inhibitory neurotransmitters is gamma-aminobutyric acid, commonly abbreviated as GABA.

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