Figure 1.
Exposure to synaptic excitation regulates membrane excitability in aCC/RP2. A, The number of action potentials (APs) fired, for a given depolarizing input (10 pA/500 msec), is inversely related to endogenous synaptic excitation in aCC/RP2 (line coefficient, 0.92). All of the determinations of AP firing were from a maintained RMP of -60 mV (see Materials and Methods). Input resistances did not differ significantly between genotypes shown. Synaptic current amplitude shown is the average current magnitude recorded from at least eight cells for each genotype (n > 200 currents). Neurons exposed to greater than normal synaptic excitation (WT, 76 ± 3.3 pA) exhibit reduced membrane excitability and vice versa. APs fired are means (n ≥ 8cells). Pan-neuronal expression of TeTx-A results in aCC/RP2 neurons firing 28 ± 2.4 APs while exhibiting no evoked synaptic currents (see also Baines et al., 2001). This “nonphysiological” condition is not shown because it markedly deviates from the line of best fit shown. This is most likely because this frequency of AP firing represents the physiological maximum for these cells at this developmental stage. B, Representative traces for injection of 10 pA/500 msec for the two genotypes stated. C, Endogenous synaptic currents, recorded in voltage clamp (Vh =-60 mV) for the same two genotypes. Three excitatory synaptic currents are shown overlaid in each example. Genotypes are as follows: (1) RN2-O × UAS-PKAinh, (2) B19-GAL4, (3) Canton-S, (4) RN2-O × UAS-dCREBact (1157-19), (5) rut1, (6) dnc2, (7) RN2-O × UAS-PKAact, (8) RN2-O × UAS-dCREBact (1157-51), (9) dnc2, (10) RN2-O × UAS-dCREBinh (9), and (11) 1407-GAL4 × UAS-rut.