Figure 1.

I_h varies systematically along the dorsoventral axis. (A) A brain slice containing the MSO with Alexa-488-filled neurons (green) verifies the distribution of the patched neurons along the dorsoventral axis (red: MAP-2). (B) Pharmacologically isolated I_h current traces were elicited by depolarizing and hyperpolarizing voltage steps from −60.5 mV to potentials between −40.5 mV and −120.5 mV for 1 s in 5 mV step increment and then to −100.5 mV for 0.5 s to elicit the tail current to determine the voltage dependence of I_h activation. Current traces are representative for the dorsal, the intermediate and the ventral part of the MSO. (C) I-V relationships of steady-state (red arrow in B) I_h density for ventral (n = 15), intermediate (n = 12) and dorsal (n = 18) neurons emphasize that I_h density amplitudes are smallest in dorsal neurons and largest in ventral neurons (C1). I_h density amplitudes for a voltage step to −110.5 mV (C2). (D) Weighted activation time constants at −110.5 mV (D1). The weighted activation time constants are voltage dependent and largest in the dorsal part of the MSO (D2). (E) The voltage-dependence of I_h activation was measured from the tail current 20 ms after the end of the voltage steps (red arrow) (E1). Values were fitted with a Boltzmann function to obtain the half-maximal activation voltage. In dorsal neurons the I_h activation curve is shifted to more negative voltages (E2). Half-maximal activation voltage was measured in each experiment and averaged (E3). Black symbols: dorsal neurons; gray symbols: intermediate neurons; white symbols: ventral neurons. ^**P < 0.01, ^***P < 0.001, single-factor ANOVA test followed by a Scheffe's post-hoc test.