Saint Marie R L, Ostapoff E M, Morest D K, Wenthold R J
Department of Anatomy, University of Connecticut Health Center, Farmington, 06032.
J Comp Neurol. 1989 Jan 15;279(3):382-96. doi: 10.1002/cne.902790305.
Neurons in the lateral superior olive are optimally excited by stimulation of the ipsilateral ear, as are those in the inferior colliculus by stimulation of the contralateral ear. This reversal of ear dominance may result, in part, from distinct crossed excitatory and uncrossed inhibitory pathways ascending from the lateral superior olive. To explore this possibility, immunoreactivity for two putative inhibitory neurotransmitters, glycine and GABA, was examined in projection neurons that retrogradely transported horseradish peroxidase from the cat inferior colliculus. The results suggest that the projection from the lateral superior olive can be segregated, immunocytochemically, into three components: 1) a crossed, glycine-negative (-) projection; 2) an uncrossed, glycine-positive (+) projection; and 3) an uncrossed, glycine(-) projection. Additional evidence suggests that the terminal fields of the two uncrossed projections may distribute differently within the inferior colliculus. Glycine(+) or glycine(-) projection neurons, crossed or uncrossed, do not differ in the size, shape, or location of their somata. However, most glycine(-) neurons are heavily encrusted with glycine(+) endings; glycine(+) neurons have 40-60% fewer of these endings. Glycine(-) neurons located in the lateral limb have fewer glycine (+) perisomatic endings than those in the medial limb. Few projection neurons are GABA(+), and GABA(+) perisomatic endings are rare in the lateral superior olive. Thus, there is a heavy uncrossed projection from the cat lateral superior olive to the inferior colliculus that may be glycinergic and inhibitory. Furthermore, there is a bilateral projection that is not glycinergic or GABAergic, which may be excitatory. The potential contribution of these pathways to contralateral ear dominance in the inferior colliculus is discussed.
外侧上橄榄核中的神经元在同侧耳受到刺激时会得到最佳兴奋，而下丘中的神经元在对侧耳受到刺激时会得到最佳兴奋。这种耳优势的逆转可能部分源于从外侧上橄榄核上升的不同的交叉兴奋性和不交叉抑制性通路。为了探究这种可能性，我们在从猫下丘逆向运输辣根过氧化物酶的投射神经元中检测了两种假定的抑制性神经递质甘氨酸和γ-氨基丁酸（GABA）的免疫反应性。结果表明，从外侧上橄榄核发出的投射在免疫细胞化学上可分为三个部分：1）交叉的、甘氨酸阴性（-）投射；2）不交叉的、甘氨酸阳性（+）投射；3）不交叉的、甘氨酸阴性（-）投射。其他证据表明，两种不交叉投射的终末场所在下丘内的分布可能不同。交叉或不交叉的甘氨酸阳性（+）或甘氨酸阴性（-）投射神经元在其胞体的大小、形状或位置上没有差异。然而，大多数甘氨酸阴性（-）神经元被大量甘氨酸阳性（+）终末所覆盖；甘氨酸阳性（+）神经元的这些终末要少40% - 60%。位于外侧肢的甘氨酸阴性（-）神经元的胞体周围甘氨酸阳性（+）终末比内侧肢的少。很少有投射神经元是γ-氨基丁酸阳性（GABA+），并且γ-氨基丁酸阳性（GABA+）的胞体周围终末在外侧上橄榄核中很少见。因此，从猫外侧上橄榄核到下丘有大量不交叉投射，可能是甘氨酸能且具有抑制性。此外，还有一种双侧投射，既不是甘氨酸能也不是γ-氨基丁酸能，可能是兴奋性的。本文讨论了这些通路对下丘中对侧耳优势的潜在贡献。
