Somatic spikes regulate dendritic signaling in small neurons in the absence of backpropagating action potentials - PubMed (original) (raw)

Action potentials in SCs elevate dendritic calcium. Recordings of P17–P19 SCs were made with pipettes containing a green calcium-sensitive indicator (fluo-5F, 50 μ

m

) and a red calcium-insensitive dye (Alexa 594, 50 μ

m

). Action potentials were evoked in current clamp from an initial potential of −80 mV (black traces) or −60 mV (gray traces), and calcium was measured at a dendritic site 50 μm from the soma. Representative calcium transients evoked by single action potentials (C, H) are averages of 12–16 trials, whereas transients evoked by 2 s 100 Hz trains (D, I) are averages of 3–5 trials. A–E and F–J represent ∼80% and 20% of neurons, respectively. In images of example neurons (A, F), axons were removed for clarity. In a cell representing the majority of neurons (A), a single action potential (B, left) elevated dendritic calcium by 10 n

m

, regardless of the initial potential (C, left). TTX eliminated the action potential (B, right) and substantially reduced the dendritic calcium elevations (C, right). D, Action potential trains (2 s, 100 Hz) elevated dendritic calcium to 300 n

m

(left). TTX reduced the calcium elevations evoked by trains (right). E, Recordings as in A–D are summarized (n = 5 neurons). In a cell representing the remaining neurons (F), a single action potential generated an afterdepolarization when evoked from −80 mV but not when evoked from −60 mV (G, left). Single action potentials elevated dendritic calcium to 40 and 10 n

m

when evoked from initial potentials of −80 mV and −60 mV, respectively (H, left). TTX eliminated the action potential but did not substantially reduce the afterdepolarization (G, right) or the calcium elevation (H, right) for an initial potential of −80 mV. However, calcium elevations were reduced when the initial potential was −60 mV. I, Action potential trains elevated dendritic calcium to 300 n

m

in control conditions, regardless of the initial potential (left). TTX reduced calcium elevations evoked by trains (right). J, Recordings as in F–I are summarized (n = 5 neurons).