Аннотация
Coherent network oscillations in the brain are correlated with different
behavioural states. Intrinsic resonance properties of neurons provide
a basis for such oscillations. In the hippocampus, CA1 pyramidal
neurons show resonance at theta (theta) frequencies (2-7 Hz). To
study the mechanisms underlying theta-resonance, we performed whole-cell
recordings from CA1 pyramidal cells (n = 73) in rat hippocampal slices.
Oscillating current injections at different frequencies (ZAP protocol),
revealed clear resonance with peak impedance at 2-5 Hz at approximately
33 degrees C (increasing to approximately 7 Hz at approximately 38
degrees C). The theta-resonance showed a U-shaped voltage dependence,
being strong at subthreshold, depolarized (approximately -60 mV)
and hyperpolarized (approximately -80 mV) potentials, but weaker
near the resting potential (-72 mV). Voltage clamp experiments revealed
three non-inactivating currents operating in the subthreshold voltage
range: (1) M-current (I(M)), which activated positive to -65 mV and
was blocked by the M/KCNQ channel blocker XE991 (10 microM); (2)
h-current (I(h)), which activated negative to -65 mV and was blocked
by the h/HCN channel blocker ZD7288 (10 microM); and (3) a persistent
Na$^+$ current (I(NaP)), which activated positive to -65 mV and
was blocked by tetrodotoxin (TTX, 1 microM). In current clamp, XE991
or TTX suppressed the resonance at depolarized, but not hyperpolarized
membrane potentials, whereas ZD7288 abolished the resonance only
at hyperpolarized potentials. We conclude that these cells show two
forms of theta-resonance: "M-resonance" generated by the M-current
and persistent Na$^+$ current in depolarized cells, and "H-resonance"
generated by the h-current in hyperpolarized cells. Computer simulations
supported this interpretation. These results suggest a novel function
for M/KCNQ channels in the brain: to facilitate neuronal resonance
and network oscillations in cortical neurons, thus providing a basis
for an oscillation-based neural code.
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