Figure 3. Properties of lateral inhibition.

A, depolarization of an intact terminal from −70 to −10 mV for 200 ms evoked the lateral IPSC in a neighbouring (26.0 μm apart) axotomized terminal voltage clamped at −90 mV (left). Depolarization of the axotomized terminal elicited the reciprocal IPSC in itself, but failed to induce a detectable response in the intact terminal voltage clamped at −90 mV (right). E_Cl was −55 mV. B, the relationship between the lateral Q_IPSC/200 ms at −90 mV and the inter-terminal distance (circles; n= 64 pairs). Data were fitted to a single exponential function (λ = 62.1 μm). The grey circle indicates the lateral Q_IPSC shown in A. C, voltage dependence of lateral inhibition (n= 4–8 pairs). An intact terminal was depolarized from −70 mV to various membrane potentials for 200 ms, and the lateral Q_IPSC/400 ms was obtained from a nearby (<60 μm) axotomized terminal voltage clamped at −90 mV. The lateral Q_IPSC is normalized to the value at −10 mV in each recording. D, after bath application of 10 μm mefloquine for 2 h, depolarization of an intact terminal (intact 1) from −70 to −10 mV for 200 ms evoked the reciprocal IPSC, but failed to elicit the lateral IPSC in a nearby intact terminal (intact 2; 34.0 μm apart) voltage clamped at −90 mV. E, Ca²⁺ uncaging experiment. Paired recordings were performed from an intact terminal filled with 5 mm DM-nitrophen and a nearby (57.8 μm apart) axotomized terminal voltage clamped at −90 mV. Depolarization of the intact terminal from −70 to −10 mV for 200 ms elicited the lateral IPSC in the axotomized terminal (left). UV laser flash applied to the intact terminal voltage clamped at −90 mV evoked the reciprocal IPSC in the terminal but failed to evoke the lateral IPSC in the axotomized terminal (right). The bath solution contained 100 μm l-2-amino-4-phosphonobutyric acid (l-AP4) to reduce artefacts of the UV flash. IPSC was obtained as the difference between the current responses before and during bath application of 200 μm picrotoxin (grey traces). The reduction of the resting current by picrotoxin was not included for calculation of the IPSCs. F, summary of Q_IPSC/400 ms in unstimulated terminals in paired recordings (<60 μm apart). Stimulated terminals were 16 axotomized terminals (P < 0.001), 52 intact terminals, eight mefloquine-treated intact terminals (P < 0.001), and five Ca²⁺ uncaged intact terminals (P < 0.001). P-values are calculated by Welch's t test with Bonferroni correction.