Neurotransmitters in the central nervous system: Basic knowledge revisited

Abstract

The chemistry within us This elegant experiment performed by Otto Loewi is considered to be the Rosetta stone of chemical transmission concept and has provided the first evidence that nerves do not influence the heart directly, but liberate specific chemical substances from their terminals. Today, when neurotransmitters are inseparable part of theories of how our brain works, it is difficult to understand that it took more than thirty years of scientific disputes between neurophysiologists and pharmacologists to prove that synaptic transmission is chemical rather than electrical. The great victory of pharmacologists in a war called "the war of sparks and soups" [2,3] happened in 1936, when Otto Loewi and Sir Henry Dale were awarded the Nobel Prize for establishing chemical synaptic transmission.Given the fact that acetylcholine was the first neurotransmitter to be discovered [4], it is not surprising that the classic criteria for neurotransmitters were based on the properties of this particular molecule.Although conventional definition describes a neurotransmitter as a substance that satisfies the following criteria [5,6]:1. It is synthesized and stored within the presynaptic neuron 2. It is released by nerve stimulation in a calcium-dependent manner 3. It binds to specific receptor(s) localized presinaptically or postsinaptically 4. Its exogenous application mimics the postsynaptic effect of presynaptic stimulation 5. Specific receptor antagonists block the effects of endogenous (synaptically released) or exogenous (externally applied) substance 6. Its action(s) can be terminated in enzyme-mediated way or by the cellular uptake mechanism, the increasing knowledge in the field of neuroscience has been continually modifying the understanding of the term "neurotransmitter". Nowadays, we are faced with at least two questions that may sound like a rather perplexing word game, but still need to be properly addressed: Are only neurotransmitters-neurotransmitters? Are neurotransmitters only neurotransmitters?