Q. 38 Which one of the following is NOT a neurotransmitter?
(A) Adrenaline
(B) Glutamate
(C) Histamine
(D) Histidine
Adrenaline is not primarily recognized as a neurotransmitter, unlike the other options which function in neural signaling. This multiple-choice question tests knowledge of neurochemistry basics relevant to exams like NEET or undergraduate biology.
Correct Answer
(A) Adrenaline
Option Breakdown
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(A) Adrenaline: Functions mainly as a hormone released by the adrenal glands into the bloodstream to trigger fight-or-flight responses, not as a synaptic neurotransmitter in the central nervous system.
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(B) Glutamate: Serves as the primary excitatory neurotransmitter in the brain, involved in over 90% of synaptic connections and critical for learning, memory, and synaptic plasticity.
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(C) Histamine: Acts as a neurotransmitter in the brain, modulating sleep-wake cycles, appetite, and cognition through histaminergic neurons.
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(D) Histidine: An amino acid precursor to histamine but does not function directly as a neurotransmitter itself.
Why Adrenaline Stands Out
Neurotransmitters release at synapses for rapid neuron-to-neuron communication, while hormones like adrenaline circulate systemically for broader effects. Though adrenaline (epinephrine) can act neuromodulatorily in peripheral nerves, textbooks classify it primarily as a hormone, distinguishing it here. Glutamate, histamine, and even histidine-derived compounds fit neurotransmitter roles, making adrenaline the clear outlier.
