Which amino acid neurotransmitter functions primarily to excite neurons and plays a role in learning and memory?

Glutamate is the primary amino acid neurotransmitter responsible for exciting neurons and is crucial for synaptic plasticity, which underlies learning and memory processes. It binds to various receptors throughout the central nervous system, including NMDA (N-methyl-D-aspartate) receptors and AMPA receptors. This interaction significantly enhances neuronal excitability, promoting communication between neurons.

The role of glutamate in cognitive functions, such as learning and memory, has been extensively studied; it is essential for long-term potentiation (LTP), a process involved in strengthening synapses based on recent patterns of activity. Elevated levels of glutamate in the synaptic cleft lead to various signaling cascades that contribute to the formation and retention of memories.

In contrast, glycine primarily serves as an inhibitory neurotransmitter in the spinal cord and brainstem and is not directly involved in excitatory signaling or memory. Histamine plays roles in wakefulness and regulation of the sleep-wake cycle, while cysteine is more of a precursor for the synthesis of other important molecules rather than functioning itself as a neurotransmitter in the same context as glutamate.