Llewellyn-Smith I J, Arnolda L F, Pilowsky P M, Chalmers J P, Minson J B
Cardiovascular Medicine and Centre for Neuroscience, Flinders University, Bedford Park, South Australia, Australia.
J Auton Nerv Syst. 1998 Jul 15;71(2-3):96-110. doi: 10.1016/s0165-1838(98)00069-1.
Our previous work suggests that virtually all of the synapses on sympathetic preganglionic neurons projecting to the rat adrenal medulla are immunoreactive for either the inhibitory amino acid, gamma-aminobutyric acid (GABA) or the excitatory amino acid, L-glutamate. To investigate whether or not this is true for other groups of sympathetic preganglionic neurons, and to determine whether or not the proportion of inputs containing each type of amino acid neurotransmitter is the same for different groups of sympathetic preganglionic neurons, we retrogradely labelled rat and rabbit sympathetic preganglionic neurons projecting to the superior cervical ganglion and used post-embedding immunogold on ultrathin sections to localise GABA- and glutamate-immunoreactivity. The cell bodies and dendrites of both rat and rabbit sympathetic preganglionic neurons projecting to the superior cervical ganglion received synapses and direct contacts from nerve fibres immunoreactive for GABA and from nerve fibres immunoreactive for glutamate. In the rat, GABA was present in 48.9% of the inputs to sympathetic preganglionic neurons projecting to the superior cervical ganglion, and glutamate was present in 51.7% of inputs. Double immunogold labelling for glutamate and GABA on the same section, as well as labelling of consecutive serial sections for the two antigens, indicated that GABA and glutamate occur in separate populations of nerve fibres that provide input to rat sympathetic preganglionic neurons projecting to the superior cervical ganglion. We now have shown that GABA or glutamate is present in virtually all of the inputs to sympathetic preganglionic neurons projecting to the superior cervical ganglion and in essentially all of the inputs to sympathetic preganglionic neurons supplying the adrenal medulla. These findings are consistent with the hypothesis that all fast synaptic transmission in central autonomic pathways may be mediated by either excitatory or inhibitory amino acids. Furthermore, we showed a statistically significant difference in the proportion of glutamate-immunoreactive inputs between sympathetic preganglionic neurons projecting to the superior cervical ganglion and sympathoadrenal neurons (data from Llewellyn-Smith et al. [Llewellyn-Smith, I.J., Phend, K.D., Minson, J.B., Pilowsky, P.M., Chalmers, J.P., 1992. Glutamate immunoreactive synapses on retrogradely labelled sympathetic neurons in rat thoracic spinal cord. Brain Res. 581, 67-80]), with preganglionics supplying the adrenal medulla receiving more excitatory inputs than those supplying the superior cervical ganglion. This increased excitatory input to sympathoadrenal neurons may explain the predominant activation of these neurons following baroreceptor unloading.
我们之前的研究表明，投射至大鼠肾上腺髓质的交感神经节前神经元上，几乎所有的突触对抑制性氨基酸γ-氨基丁酸（GABA）或兴奋性氨基酸L-谷氨酸均呈免疫反应性。为了研究其他交感神经节前神经元群体是否也是如此，并确定不同交感神经节前神经元群体中，含有每种氨基酸神经递质的输入比例是否相同，我们对投射至上颈神经节的大鼠和兔交感神经节前神经元进行逆行标记，并在超薄切片上采用包埋后免疫金法来定位GABA和谷氨酸的免疫反应性。投射至上颈神经节的大鼠和兔交感神经节前神经元的胞体和树突，接受了对GABA呈免疫反应性的神经纤维以及对谷氨酸呈免疫反应性的神经纤维的突触和直接接触。在大鼠中，投射至上颈神经节的交感神经节前神经元的输入中，48.9%存在GABA，51.7%存在谷氨酸。在同一切片上对谷氨酸和GABA进行双重免疫金标记，以及对两种抗原的连续系列切片进行标记，表明GABA和谷氨酸存在于为投射至上颈神经节的大鼠交感神经节前神经元提供输入的不同神经纤维群体中。我们现在已经表明，投射至上颈神经节的交感神经节前神经元的几乎所有输入以及供应肾上腺髓质的交感神经节前神经元基本上所有的输入中，均存在GABA或谷氨酸。这些发现与以下假说一致：中枢自主神经通路中的所有快速突触传递可能由兴奋性或抑制性氨基酸介导。此外，我们发现投射至上颈神经节的交感神经节前神经元与交感肾上腺神经元之间，谷氨酸免疫反应性输入的比例存在统计学上的显著差异（数据来自Llewellyn-Smith等人[Llewellyn-Smith, I.J., Phend, K.D., Minson, J.B., Pilowsky, P.M., Chalmers, J.P., 1992. Glutamate immunoreactive synapses on retrogradely labelled sympathetic neurons in rat thoracic spinal cord. Brain Res. 581, 67 - 80]），供应肾上腺髓质的节前神经元比供应上颈神经节的节前神经元接受更多的兴奋性输入。交感肾上腺神经元兴奋性输入的增加，可能解释了压力感受器卸载后这些神经元的主要激活现象。
