Spinal Excitatory Synaptic Transmission: Mediators, Modulators and Second Messengers

生物活性物质介导的细胞间通讯几乎存在于所有的多细胞系统中。脊椎动物神经系统中的化学神经传递是这类信号的一种形式。快速化学信号(毫秒内)，神经递质在被称为突触的特殊神经元连接处释放，刺激突触后细胞中受体控制的离子通道的打开。有证据表明，谷氨酸和天冬氨酸可能是许多中枢神经元使用的主要快速递质。然而，一些化学介质的作用是缓慢的(作用几秒钟甚至几分钟)，例如神经肽，它们作为突触传递的调节器在功能上很重要。由于哺乳动物脊髓中兴奋性突触递质的化学性质尚不清楚，本研究项目将在体外分析大鼠脊髓背角的细胞机制。这些实验将针对兴奋性氨基酸突触介体(L-谷氨酸及其类似物)、兴奋性氨基酸受体的作用、速激肽(P物质和神经激肽A)的作用以及兴奋性氨基酸和速激肽激活细胞内第二信使系统(光肌醇)的作用。具体研究目标为：1)大鼠脊髓切片制备中快、慢兴奋性突触后电位的药理特性和离子机制。由于缺乏关于NMDA受体在初级传入传递中的作用的信息，因此将重点放在NMDA受体上：2)第二信使系统(磷脂酰肌醇和环核苷酸)参与调节兴奋性氨基酸和速激肽在大鼠脊髓背角传入突触的作用的可能性；3)用膜片微电极全细胞电压钳技术研究兴奋性氨基酸、速激肽和第二信使对急性分离的大鼠背角神经元钙电导的调节作用。这些研究将有助于更好地了解神经系统内通过化学媒介传递的突触信号。

Intercellular communication mediated by bioactive substances occurs in virtually all multicellular systems. Chemical neurotransmission in the vertebrate nervous system represents a form of this type of signalling. Fast chemical signalling (within milliseconds), in which the neurotransmitter is released at specialized neuronal junctions, called synapses, stimulates the opening of receptor-controlled ion channels in the post- synaptic cell. There is evidence that the amino acids, glutamate and aspartate, may represent the principal fast transmitters used by many central neurons. However, the actions of some chemical mediators, for instance neuropeptides, are slow (acting over seconds or even minutes) and they are functionally important as modulators of synaptic transmission. Since the chemical nature of excitatory synaptic transmitters in the mammalian spinal cord is still unknown, this research project will analyze cellular mechanisms underlying the rat spinal dorsal horn in vitro. The experiments will be directed at the role of excitatory amino acid synaptic mediators (l-glutamate and its analogues), receptors for excitatory amino acids, the role of tachykinins (substance P and neurokinin A), and the activation of intracellular second messenger systems (phoshoinositides) by excitatory amino acids and the tachykinins. Specific objectives to be examined are: 1) the pharmacological properties and ionic mechanisms of fast and slow excitatory postsynaptic potentials in the rate spinal cord slice preparation. The emphasis will be on NMDA receptors, since information about their role in primary afferent transmission is lacking; 2) the possibility of the involvement of second messenger systems (phosphoinositides and cyclic nucleotides) in the regulation of actions of excitatory amino acids and tachykinins at afferent synapses in the rat spinal dorsal horn; and 3) modulation of voltage-dependent calcium conductance of acutely-isolated rat dorsal horn neurons by excitatory amino acids, tachykinins and second messengers using whole-cell voltage clamp technique with a patch microelectrode. These studies will provide for a better understanding of synaptic signalling via chemical mediators within the nervous system.