Figure 5.

A, immunohistological localisation of the small-conductance calcium-activated potassium channel SK3 in the MHb of mouse brain. Inset a, a small area in A is enlarged showing SK3 staining in greater detail. B, no staining for SK3 channels is observed when primary antibody is omitted. C, application of 20 μm NS309, an activator of small conductance Ca²⁺-activated K⁺ channels (SK1–3), hyperpolarised all the spontaneously depolarised silent and DLAMO-generating MHb neurones tested (n = 8). During the hyperpolarisation, the DLAMOs recorded under control conditions initially transformed into full APs upon NS309 wash-in and eventually, in the presence of full steady state NS309 concentration, the cell became silent when hyperpolarised below the AP threshold. During wash-out of NS309, this cell initially depolarised to the AP threshold level and fired full APs. The cell then returned to the baseline and displayed DLAMOs (see enlarged epochs in grey rectangles). D, the NS309-induced hyperpolarisations persisted in the presence of 1 μm TTX which blocks AP-dependent synaptic communication, suggesting a direct effect of NS309 on the cells (n = 5). In D, two traces are shown from the same cell. E, overall, NS309 (20 μm) significantly hyperpolarised all the MHb neurons tested by 14.9 ± 2.8 mV. This suggests that reduction in small conductance Ca²⁺-dependent K⁺ currents contributes to the depolarised MHb cell states. Scale bars in A and B are 200 μm. 3V, third ventricle. Paired t test, **P < 0.01.