1 ± 0.2 collaterals/branchpoint, Selleckchem INCB024360 range 1–3, n = 22, Figures 1A and 1B). Axon collaterals were on average 3-fold smaller in diameter compared to the parent axons (collaterals, 0.43 ± 0.02 μm; first internodes, 1.2 ± 0.06 μm; paired t test p < 0.001, n = 8). The average distance from the base of the soma to the first branchpoint was 128.2 ± 5.4 μm (range 85–173 μm, n = 22) while the second node was located at 200 ± 24 μm from the soma (n = 5, biocytin staining). Some axon parameters (e.g., diameter) are dependent on the size of the cell (Sloper and Powell, 1979). To test whether the variability
in location of the node can be explained by cell size, the branchpoint location was plotted against the somatic surface area (Figure 1C). The results show that the first branchpoint distance from the soma was linearly related to the soma size, with larger neurons having the first node located more distally (r2 = 0.53, p < 0.001, n = 22). These data show that the Dolutegravir manufacturer first branchpoint in L5 neurons is on average located at ∼130 μm and within a range of ∼90–180 μm from the soma. As a first step to test the functional contribution of the node to AP generation, the somatically recorded
firing properties were compared between neurons with an intact axon, including a first branchpoint, and L5 neurons with axons cut proximal to the branchpoint during the slice preparation procedure (Figure 2A). Axon lengths were either ad hoc determined in the bright-field/fluorescence image
or post hoc with biocytin staining (soma-bleb distance range, 15–1590 μm; n = 69). A commonly observed characteristic of L5 neocortical pyramidal neurons is the existence of two subpopulations generating distinct firing patterns called intrinsic bursts (IBs), characterized by a first interspike interval (ISI) less than 10 ms (firing frequency ≥ 100 Hz) or regular spiking (RS) with nonadapting ISI of ∼100–200 ms (Chagnac-Amitai et al., 1990, Mason and Larkman, 1990 and Williams and Stuart, 1999). Figure 2A shows a typical Rutecarpine example of a L5 neuron with the axon cut proximally to the first node at a distance of 98 μm. In response to constant suprathreshold current injections, the neuron responded with RS patterns (9.7 Hz at threshold). In contrast, many instances of IB firing were found when recording from neurons with axons cut at more distal locations (e.g., 750 μm, Figure 2A). The collected results revealed a striking dependence of the intrinsic excitability on the remaining axon length; L5 neurons with axons cut proximal to the average first branchpoint location (<130 μm) only generated RS output patterns (frequency ∼10.7 ± 0.6 Hz, range 5.3–15.6 Hz, n = 22), whereas L5 neurons with longer primary axons responded with both RS (8.2 ± 0.6 Hz, n = 23) and IB firing (234.0 ± 11.5 Hz, n = 24, Figures 2B and 2C). The probability of burst firing with axons cut proximal was 0%, compared to 50% in longer axons (χ2 test p < 0.