Chemical Effects of Kainic Acid Injection into the Rat Superior Olivary Region.

Donald A Godfrey, Jami L Park, Jon D Dunn, C David Ross
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Abstract

Kainic acid injections have been used to destroy neuron somata in particular regions without damaging fiber tracts. We injected a solution of kainic acid into the region of the rat superior olivary complex in an effort to destroy its cholinergic projections to the cochlea and cochlear nucleus, which derive especially from the lateral superior olivary nucleus and ventral nucleus of the trapezoid body. In the lateral superior olivary nucleus, there were relatively small but fairly consistent decreases of choline acetyltransferase (ChAT) activity, larger decreases of acetylcholinesterase (AChE) activity, and consistent decreases of malate dehydrogenase activity, as a marker for oxidative metabolism. Other superior olivary regions were less affected by the kainic acid injections, but most showed overall significant decreases of AChE activity. Our results suggest that the cholinergic neurons giving rise to the centrifugal pathways to the cochlea and cochlear nucleus are more resistant to the effects of kainic acid than are those that receive major ascending input from the cochlear nucleus and project to higher levels of the auditory system. Comparison with published anatomical studies suggests that this resistance to the effects of kainic acid is related to relatively little glutamatergic input to the somata and proximal dendrites of these neurons. We also found a consistent approximately 16 % decrease of ChAT activity in the injected-side facial nerve root, which is most easily explained as a small effect of kainic acid on the facial nerve fibers passing through the injection site.
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Kainic酸注射大鼠上橄榄区的化学作用。
Kainic酸注射已被用于破坏特定区域的神经元体而不破坏纤维束。我们在大鼠上橄榄复合体区域注射了一种kainic酸溶液,试图破坏其对耳蜗和耳蜗核的胆碱能投射,特别是来自外侧上橄榄核和梯形体腹侧核。在侧上橄榄核中,胆碱乙酰转移酶(ChAT)活性下降幅度相对较小,但相当一致,乙酰胆碱酯酶(AChE)活性下降幅度较大,苹果酸脱氢酶(作为氧化代谢的标志)活性下降幅度一致。其他上橄榄区受kainic酸注射的影响较小,但大多数显示AChE活性总体显着降低。我们的研究结果表明,产生通往耳蜗和耳蜗核的离心通路的胆碱能神经元比那些接受来自耳蜗核的主要上行输入并投射到更高水平听觉系统的神经元更能抵抗kainic酸的影响。与已发表的解剖学研究的比较表明,这种对kainic酸作用的抵抗与相对较少的谷氨酸能输入到这些神经元的体细胞和近端树突有关。我们还发现,在注射侧面神经根,ChAT活性持续下降约16%,这最容易解释为kainic酸对穿过注射部位的面神经纤维的小影响。
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Chemical Effects of Kainic Acid Injection into the Rat Superior Olivary Region.
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