1. Dual intracellular recordings were made from synaptically coupled pyramidal cell-tointerneurone pairs (n = 5) of the cat visual cortex in vitro. Pre-and postsynaptic neurones were labelled with biocytin, followed by correlated light and electron microscopic analysis to determine all sites of synaptic interaction. 2. Pyramidal neurones in layers II-III elicited monosynaptic EPSPs in three distinct classes of smooth dendritic local-circuit neurones, namely basket cells (n = 3), a dendrite-targeting cell (n = 1) and a double bouquet cell (n = 1). Unitary EPSPs in basket cells were mediated by one, two, and two synaptic junctions, whereas the pyramid-to-dendrite-targeting cell and pyramidto-double bouquet cell interaction were mediated by five and seven synaptic junctions, respectively. Recurrent synaptic junctions were found on all somato-dendritic compartments, with a tendency to be clustered close to the soma on the double bouquet and dendrite-targeting cells. The latter interneurones were reciprocally connected with pyramidal cells. 3. Unitary EPSPs had an average peak amplitude of 1005 + 518 1sV, fast rise times (10-90%; 0-67 + 0-25 ms) and were of short duration (at half-amplitude, 4-7 + 1.0 ms). Their decay was monoexponential (T = 7-8 + 4-3 ms) at hyperpolarized membrane potentials and appeared to be shaped by passive membrane properties (T = 9-2 + 8-5 ms). All parameters of concomitantly recorded spontaneous EPSPs were remarkably similar (mean amplitude, 981 + 433 ,sV; mean rise time, 0-68 + 0-18 ms; mean duration, 4-7 + 1-7 ms). 4. In all three pyramidal-to-basket cell pairs, closely timed (10-50 ms) pairs of presynaptic action potentials resulted in statistically significant paired-pulse depression, the mean of the averaged second EPSPs being 80 + 11 % of the averaged conditioning event. The overall degree of paired-pulse modulation was relatively little affected by either the amplitude of the preceding event or the inter-event interval.5. The probability density function of the peak amplitudes of the unitary EPSPs could be adequately fitted with a quantal model. Without quantal variance, however, the minimum number of components in the model, excluding the failures, exceeded the number of electron microscopically determined synaptic junctions for all five connections. In contrast, incorporating quantal variance gave a minimum number of components which was compatible with the number of synaptic junctions, and which fitted the data equally well as models incorporating additional components but no quantal variance. For this model with quantal variance with the minimum number of components the estimate of the quantal coefficient of variation ranged between 0 33 and 0-46, and the corresponding quantal sizes ranged between 260 and 657 ,sV. The peak EPSP amplitudes in two of the four connections with more than one synaptic junction could be adequately described by a uniform binomial model for transmitter release. 6. In conclusion, at least three distinct interneurone classes receive local excitatory pyramid...

Basket and bistratified cells form two anatomically distinct classes of GABAergic local‐circuit neurons in the CA1 region of the rat hippocampus. A physiological comparison was made of intracellularly recorded basket (n = 13) and bistratified neurons (n = 6), all of which had been anatomically defined by their efferent target profile (Halasy et al., 1996). Basket cells had an average resting membrane potential of −64.2 ± 7.2 vs. −69.2 ± 4.6 mV in bistratified cells. The latter had considerably higher mean input resistances (60.2 ± 42.1 vs. 31.3 ± 10.9 MO) and longer membrane time constants (18.6 ± 8.1 vs. 9.8 ± 4.5 ms) than basket cells. Differences were also apparent in the duration of action potentials, those of basket cells being 364 ± 77 and those of bistratified cells being 527 ± 138 μs at half‐amplitude. Action potentials were generally followed by prominent, fast afterhyperpolarizing potentials which in basket cells were 13.5 ± 6.7 mV in amplitude vs. 10.5 ± 5.1 in bistratified cells. The differences in membrane time constant, resting membrane potential, and action potential duration reached statistical significance (P < 0.05). Extracellular stimulation of Schaffer collateral/commissural afferents elicited short‐latency excitatory postsynaptic potentials (EPSPs) in both cell types. The average 10–90% rise time and duration (at half‐amplitude) of subthreshold EPSPs in basket cells were 1.9 ± 0.5 and 10.7 ± 5.6 ms, compared to 3.3 ± 1.3 and 20.1 ± 9.7 ms in bistratified cells, the difference in EPSP rise times being statistically significant. Basket and bistratified EPSPs were highly sensitive to a bath applied antagonist of non‐N‐methyl‐D‐aspartate (NMDA) receptors, whereas the remaining slow‐rise EPSP could be abolished by an NMDA receptor antagonist. Increasing stimulation intensity elicited biphasic inhibitory postsynaptic potentials (IPSPs) in both basket and bistratified cells. In conclusion, basket and bistratified cells in the CA1 area show prominent differences in several of their membrane and firing properties. Both cell classes are activated by Schaffer collateral/commissural axons in a feedforward manner and receive inhibitory input from other, as yet unidentified, local‐circuit neurons. © 1996 Wiley‐Liss, Inc.

The first step in building a realistic computational neuron model is to produce a passive electrical skeleton on to which active conductances can be grafted. For this, anatomically accurate morphological reconstructions of the desired cell type are required. In this study compartmental models were used to compare from a functional perspective three on-line archives of rat hippocampal CA1 pyramidal cell morphologies. The topological organization of cells was found to be similar for all archives, but several morphometric differences were observed. The three-dimensional size of the cells, the diameter and tortuosity of dendrites, and the electrotonic length of the main apical dendrite and of the branches in stratum lacunosum moleculare were dissimilar. The experimentally measured kinetics of somatically recorded inhibitory postsynaptic currents evoked in the stratum lacunosum moleculare (data from the literature) could be reproduced only using the archives that contained cells with an electrotonically short main apical dendrite. In the amplitude attenuation of the simulated postsynaptic currents and the voltage escape from the command potential under voltage clamp conditions, a two- to three-fold difference was observed among archives. Upon activation of a single model synapse on distal branches, cells with low dendritic diameter showed a voltage escape larger than 15 mV. The diameter of the dendrites influenced greatly the results, emphasizing the importance of methods that allow an accurate measurement of this parameter. Our results indicate that there are functionally significant differences in the morphometric data available in different archives even if the cell type, brain region and species are the same.

Although Ca2+ ion plays an essential role in cellular physiology, calcium-binding proteins (CaBPs) were long used for mainly as immunohistochemical markers of specific cell types in different regions of the central nervous system. They are a heterogeneous and wide-ranging group of proteins. Their function was studied intensively in the last two decades and a tremendous amount of information was gathered about them. Girard et al. compiled a comprehensive list of the gene-expression profiles of the entire EF-hand gene superfamily in the murine brain. We selected from this database those CaBPs which are related to information processing and/or neuronal signalling, have a Ca2+-buffer activity, Ca2+-sensor activity, modulator of Ca2+-channel activity, or a yet unknown function. In this way we created a gene function-based selection of the CaBPs. We cross-referenced these findings with publicly available, high-quality RNA-sequencing and in situ hybridization databases (Human Protein Atlas (HPA), Brain RNA-seq database and Allen Brain Atlas integrated into the HPA) and created gene expression heat maps of the regional and cell type-specific expression levels of the selected CaBPs. This represents a useful tool to predict and investigate different expression patterns and functions of the less-known CaBPs of the central nervous system.