Soltesz I, Lightowler S, Leresche N, Crunelli V
Department of Pharmacology, St George's Hospital Medical School, London, U.K.
Neuroscience. 1989;33(1):23-33. doi: 10.1016/0306-4522(89)90307-2.
Intracellular recordings were performed from projection cells of the cat dorsal lateral geniculate nucleus in vitro to investigate the properties and origin of optic tract evoked inhibitory postsynaptic potentials mediated by GABAB receptors and their relationship to the physiologically different cell classes present in this nucleus. In all three main laminae of the dorsal lateral geniculate nucleus, stimulation of the optic tract evoked an excitatory postsynaptic potential followed by two inhibitory postsynaptic potentials. The first is a GABAA receptor mediated inhibitory postsynaptic potential since it was blocked by bicuculline, reversed in polarity following intracellular Cl- injection and had a reversal potential similar to the bicuculline sensitive hyperpolarizing effect of GABA. The second is a GABAB receptor mediated inhibitory postsynaptic potential. Its amplitude was not linearly related to membrane potential (maximal amplitude at -60 mV), it decreased when using frequencies of stimulation higher than 0.05 Hz and it was reversibly increased by addition of bicuculline to the perfusion medium. The reversal potential of GABAB inhibitory postsynaptic potentials was dependent on the extracellular K+ concentration but did not change in the presence of bicuculline or when recording with Cl- filled microelectrodes. While GABAA inhibitory postsynaptic potentials always abolished repetitive firing of projection cells, GABAB inhibitory postsynaptic potentials were able to block weak firing but unable to decrease strong activation of projection cells evoked by direct current injection. Optic tract evoked GABAB (as well as GABAA) inhibitory postsynaptic potentials could be recorded in slices which did not include the perigeniculate nucleus, thus indicating that they are generated by the interneurons of the dorsal lateral geniculate nucleus. Using intracellular injection of horseradish peroxidase, we have found that the GABAB inhibitory postsynaptic potentials are present in projection cells showing many different types of neuronal morphologies. In conclusion, GABA released from interneurons in the dorsal lateral geniculate nucleus is capable of evoking an early, short-lasting GABAA and a late, long-lasting GABAB inhibitory postsynaptic potential in projection cells with diverse morphology, indicating that the late inhibition in the dorsal lateral geniculate nucleus can no longer be associated exclusively with the recurrent inhibitory pathway through the perigeniculate nucleus.
为了研究由GABAB受体介导的视束诱发抑制性突触后电位的特性、起源及其与该核中生理上不同细胞类型的关系，在体外对猫背外侧膝状核的投射细胞进行了细胞内记录。在背外侧膝状核的所有三个主要层中，对视束的刺激诱发了一个兴奋性突触后电位，随后是两个抑制性突触后电位。第一个是GABAA受体介导的抑制性突触后电位，因为它被荷包牡丹碱阻断，在细胞内注射Cl-后极性反转，并且其反转电位类似于GABA对荷包牡丹碱敏感的超极化效应。第二个是GABAB受体介导的抑制性突触后电位。其幅度与膜电位不是线性相关（在-60 mV时幅度最大），当使用高于0.05 Hz的刺激频率时其幅度减小，并且通过向灌流介质中添加荷包牡丹碱可使其可逆性增加。GABAB抑制性突触后电位的反转电位取决于细胞外K+浓度，但在存在荷包牡丹碱时或用充满Cl-的微电极记录时不变。虽然GABAA抑制性突触后电位总是消除投射细胞的重复放电，但GABAB抑制性突触后电位能够阻断微弱放电，但不能降低由直流注入诱发的投射细胞的强烈激活。在不包括膝周核的切片中可以记录到视束诱发的GABAB（以及GABAA）抑制性突触后电位，因此表明它们是由背外侧膝状核的中间神经元产生的。通过细胞内注射辣根过氧化物酶，我们发现GABAB抑制性突触后电位存在于显示许多不同类型神经元形态的投射细胞中。总之，背外侧膝状核中间神经元释放的GABA能够在具有不同形态的投射细胞中诱发早期、短暂的GABAA和晚期、持久的GABAB抑制性突触后电位，这表明背外侧膝状核中的晚期抑制不再能仅仅与通过膝周核的回返抑制途径相关联。
