Which of the following does NOT represent an inhibitory mechanism in the brain?

The option that does not represent an inhibitory mechanism in the brain is excitatory neurotransmission. This concept pertains to the process through which certain neurotransmitters, such as glutamate, bind to receptors on the postsynaptic neuron, leading to depolarization and an increased likelihood of generating an action potential. Essentially, excitatory neurotransmission enhances the activity of neurons, making them more likely to fire.

In contrast, mechanisms such as GABA release and inhibitory postsynaptic potentials serve to decrease neuronal excitability. GABA (gamma-aminobutyric acid) is the primary inhibitory neurotransmitter in the brain; its release leads to hyperpolarization of the postsynaptic neuron, making it less likely to fire. This hyperpolarization is the result of increased permeability of the membrane to chloride ions, which stabilizes the membrane potential and reduces the chances of action potentials occurring.

Overall, while some options indicate processes that diminish neuronal activity, excitatory neurotransmission clearly functions to promote and facilitate neuron firing, distinguishing it from the other inhibitory mechanisms listed.