Feldblum S, Dumoulin A, Anoal M, Sandillon F, Privat A
INSERM U-336, Ecole Nationale Superieure de Chimie, Montpellier, France.
J Neurosci Res. 1995 Dec 15;42(6):742-57. doi: 10.1002/jnr.490420603.
Gamma-aminobutyric acid (GABA) synthesis can result from the action of at least two glutamic acid decarboxylase (GAD) isoforms, GAD65 and GAD67, possibly involved in distinct mechanisms. We have made the hypothesis that GAD65 may respond to short-term changes and is present in neurons with a phasic activity, while GAD67 may rather provide GABA for the metabolic pool and for supporting tonic levels of synaptic transmission (Erlander et al.: Neuron 7:91-100, 1991; Feldblum et al.: J Neurosci Res 34:689-706, 1993). In the present work we have tested this hypothesis in the rat spinal cord where both types of activities have been identified. The correlation of GABA immunodetection with the distribution of GAD65 and GAD67 mRNAs and proteins has evinced in the dorsal horn a differential regulation of the two isoforms. In situ hybridization has revealed, in the dorsal horn, relatively higher levels of GAD67 mRNA than of GAD65, while immunodetection of the proteins demonstrated numerous punctate profiles with both GAD antisera. Reverse transcription-polymerase chain reaction (RT-PCR) data confirmed the abundance of the GAD67 transcripts compared to GAD65 in the rat spinal cord. In contrast, within the ventral horn, there was a greter number of GAD67-immunoreactive (IR) profiles mostly located around motoneurons. The paucity of GAD65 immunoreactivity in the ventral horn cannot be related to a different accessibility of the antigens to the epitopes since on the same section a dense GAD65 staining was detected in the dorsal horn. Hence, a number of biochemical and electrophysiological data support the concept of the involvement of glycine as the major inhibitory system within the ventral horn which may explain the low levels of GAD transcription in this region. The paucity of GAD65 in the ventral horn may also reflect a functional difference, suggesting a predominance of GAD67 in neurons under tonic activity. In the dorsal horn, where neurons with phasic and tonic firing patterns have been disclosed, GAD65 may, in addition, provide GABA for responses to short-term changes.
γ-氨基丁酸（GABA）的合成可能源于至少两种谷氨酸脱羧酶（GAD）同工型GAD65和GAD67的作用，它们可能参与不同的机制。我们提出了一个假说，即GAD65可能对短期变化做出反应，并存在于具有相位性活动的神经元中，而GAD67可能主要为代谢池提供GABA，并支持突触传递的紧张性水平（Erlander等人：《神经元》7：91 - 100，1991；Feldblum等人：《神经科学研究杂志》34：689 - 706，1993）。在本研究中，我们在已鉴定出这两种活动类型的大鼠脊髓中对该假说进行了验证。GABA免疫检测与GAD65和GAD67 mRNA及蛋白质分布的相关性表明，在背角中这两种同工型存在差异调节。原位杂交显示，在背角中GAD67 mRNA水平相对高于GAD65，而蛋白质免疫检测表明两种GAD抗血清均呈现出众多点状分布。逆转录 - 聚合酶链反应（RT - PCR）数据证实，与GAD65相比，大鼠脊髓中GAD67转录本更为丰富。相反，在腹角内，有更多GAD67免疫反应性（IR）分布，大多位于运动神经元周围。腹角中GAD65免疫反应性的缺乏与抗原对表位的不同可及性无关，因为在同一切片上背角中检测到浓密的GAD65染色。因此，许多生化和电生理数据支持甘氨酸作为腹角内主要抑制系统的概念，这可能解释了该区域GAD转录水平较低的原因。腹角中GAD65的缺乏也可能反映了一种功能差异，表明在紧张性活动的神经元中GAD67占主导地位。在已发现具有相位性和紧张性放电模式神经元的背角中，则GAD65可能还为对短期变化的反应提供GABA。
