|Hippocampus CA1 pyramidal cell||Middle apical dendrite||I Na,t||.||Na impulses may underly "fast prepotentials" that boost distal EPSPs (Spencer WA and Kandel ER, 196175 ). Na action potentials support backpropagating impulses (Spruston N et al, 1995 [mammal ]57 ), and can activate Ca action potentials (Spruston N et al, 1995 [mammal ]57 ). Patch recordings yield an approximate channel density of 28 pS/micron^2 in juvenile rats < 4 wks of age, rising to 61 pS/micron^2 in older rats. Channel density was similar in other dendritic compartments (Magee JC and Johnston D, 1995 [rat ]140 ).
Tsubokawa H et al, 2000180 .
Inactivation of dendritic Na channel contributes to the attenuation of activity-dependent backpropagation of APs (Jung HY et al, 1997435 ). Slow inactivation of sodium channels in dendrites and soma will modulate neuronal excitability in a way that depends in a complicated manner on the resting potential and previous history of action potential firing (Mickus T et al, 1999436 ). Dendritic can fire sodium spikes that can precede somatic action potentials (APs), the probability and amplitude of which depend on previous synaptic and firing history. Some dendritic spikes could occur in the absense of somatic APs, indicating that their propagation to soma is unreliable (Golding NL and Spruston N, 1998437 ). Single action potential backpropagations show dichotomy of either strong attenuation (26-42%) or weak attenuation (71-87%). The dichotomy seems to be conferred primarily by differences in distribution, density, etc. of voltage dependent sodium and potassium channel (A-type, especially ) along the somatodendritic axis (Golding NL et al, 2001439 )