Which of the following is NOT a role of glutamate in the central nervous system?

Glutamate primarily functions as the major excitatory neurotransmitter in the central nervous system, playing a crucial role in synaptic transmission and plasticity, which is vital for learning and memory processes. It is involved in various neural circuits and is essential for cognitive functions.

Regarding its role in bipolar cells, glutamate can act as an inhibitory neurotransmitter in specific contexts, such as the visual system where it is involved in the processing of light signals. This is particularly relevant in low-light conditions, where glutamate signaling affects the response of bipolar cells.

Facilitating synaptic plasticity is another important role of glutamate, as it enables the strengthening of synapses, which is critical for the mechanisms underlying learning and memory.

In contrast, initiating the fight-or-flight response primarily involves other neurotransmitters and hormones, such as norepinephrine and epinephrine, which are released by the sympathetic nervous system in response to stress or perceived threats. Thus, while glutamate plays a critical role in various central nervous system processes, it is not involved in the direct initiation of the fight-or-flight response.