Unitary and Minimal Postsynaptic Potentials (Literature Review)

Abstract

The natural continuation of our study at this stage seems to be the application of the microelectrode technique to analysis of LTP mechanisms. Various variants of this technique had been successfully used for studies of the CNS by many workers (see references in the Introduction). Up to recent times, mainly stimulations of peripheral receptors, nerve trunks or structures which produced activity of a large number of afferent fibres were used while recording from CNS neurones. However, it is sometimes more useful to analyze postsynaptic potentials (PSPs) generated in a target (postsynaptic) neurone by activation of a small number of afferent (presynaptic) fibres. I shall term such PSPs “minimal” PSPs or MPSPs. Even a more precise method is a recording of PSPs generated by activation of a single afferent fibre. These PSPs are termed “elementary, “individual” or “unitary” PSPs (UPSPs). Initial detailed studies of UPSPs at neuro-neuronal synapses have been done with intracellular stimulation of giant axons in both invertebrates [305, 409, 951, 1073] and in some non-mammalian vertebrates [56, 673, 674, 844] though first related publications with recordings from spinal motoneurones are dated back to the early 1960s [488, 570, 571]. Due to more recent improvements in methods of stimulation, recording and analysis, the studies in this field have attracted considerably more attention. I shall mention here the following improvements which make it easier to collect data and interpret results related to the analysis of MPSP and UPSP at the level of vertebrate CNSs: elaboration of the methods of stimulation of single afferent fibres [462, 570, 708]; intracerebral microstimulation [48, 47, 60, 393, 468, 540, 820, 893]; improvement of methods of intracellular recording due to bevelling of the microelectrodes [77, 724, 377]; intracellular staining [77, 354, 484, 750]; elaboration of new isolated preparations including brain slices, isolated spinal cord and cell culture. More recently, recordings of postsynaptic currents (PSCs) instead of PSPs became available due to development of the whole-cell patch technique ([139, 307, 677]; see also Sect. 2.2.6). The last but not least improvement is the growing use of computers, specifically, the averaging technique which permits low-amplitude signals to be distinguished from technical and synaptic noises.