Neurotransmission is necessarily difficult to investigate in the brain, particularly in the human brain. However the striking development of anatomical, biochemical and electrophysiological technics now enables a more accurate analysis of the neurones, the neuronal systems and the synapses. The neurones can no longer be considered as unipolarized transmitting nerve units only. They inform other neurones through thousands of nerve terminals, but also receive informations through a great number of afferences the regulation of which involves dendritic release of neurotransmitters. The neurones spread in such spread in such intricated networks that a change in the activity of one neuronal system has an immediate effect on all parts of the brain. We begin to understand the biochemical events taking place within the synapses due to the development of molecular biology, particularly in studies that have characterized the receptor site. The complexity of the organization of the synaptic cleft appears greater inasmuch that one considers the evidence of various types and even sub-groups of defined neurotransmitter receptors (i.e. pre- and postsynaptic, linked or not linked to cyclic-AMP) as well as the discovery of a new class of putative neurotransmitters (the neuropeptides).
在大脑中，尤其是在人类大脑中，神经传递必然难以研究。然而，解剖学、生物化学和电生理学技术的显著发展，现在能够对神经元、神经元系统和突触进行更精确的分析。神经元不再仅仅被视为单极化的神经传导单位。它们通过数千个神经末梢向其他神经元传递信息，但也通过大量的传入信息接收信息，其调节涉及树突释放神经递质。神经元分布在如此错综复杂的网络中，以至于一个神经元系统活动的变化会立即影响大脑的所有部分。由于分子生物学的发展，特别是在对受体位点进行表征的研究中，我们开始了解突触内发生的生化事件。考虑到已确定的神经递质受体的各种类型甚至亚组（即突触前和突触后，与环磷酸腺苷相关或不相关）的证据，以及一类新的假定神经递质（神经肽）的发现，突触间隙组织的复杂性似乎更大。
