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A few investigations have been reported about pretectal suppressive influences on the optic tectum of frog, but characteristics of tectal activity to pretectal input are left unknown. We made intracellular recordings to demonstrate the unexpected complexity in synaptic mechanisms involved in the suppressive influences of pretecal stimulation on the tectal cells.
In the present study, we investigated the neuronal activity evoked by pretectal (Lpd/P) nuclei stimulation using intracellular recording technique.
The pretectal stimulation mainly elicited two types of responses in the ipsilateral tectum: an excitatory postsynaptic potential (EPSP) followed by an inhibitory postsynaptic potential (IPSP) and a pure IPSP. The latter predominated in the tectal cells responding to pretectal stimulation. In a few cells, biphasic hyperpolarization appeared under stronger stimulus intensities. The spikes of tecto-pretectal projecting cells elicited by antidromical stimulation were recorded in the ipsilateral tectum, which revealed reciprocal connections between the tectum and particular pretectal nuclei. The synaptic natures underlying pretecto-tectal information transformation have also been demonstrated. EPSPs with short latencies were concluded to be monosynaptic. Most IPSPs were generated through polysynaptic paths, but monosynaptic IPSPs were also recorded in the tectum. Nearly 98% of impaled tectal cells (except for antidromically projecting cells) showed inhibitory responses to pretectal stimulation.
The results provide strong evidence that pretectal cells broadly inhibit tectal neurons as that has suggested by behavioral and extracellular recording studies.
已有许多研究报告了青蛙的前视盖对视顶盖起抑制作用, 但关于此神经活动的特性尚不清楚。 本研究探讨了这种复杂的神经活动的机理。
前视盖的电刺激在同侧视顶盖主要唤起了两种神经反应: 一种是兴奋性(excitatory postsynaptic potential, EPSP)和抑制性突触后电位(an inhibitory postsynaptic potential, IPSP)同时出现, 另一种是单纯的IPSP, 后者在本记录中占主导地位。 另外我们也记录到了某些投射到前视盖的视盖投射细胞的神经电位。 它揭示了视顶盖和前视盖之间存在着交叉性的相互作用。短潜时的EPSP可能是通过单突触进行传导的, 而大多数的IPSP是通过多突触方式进行神经信息传递的。几乎98%被记录的视盖细胞对前视盖的刺激显示出了 抑制性反应。