Fig. 7.
Calcium-dependent spontaneous hyperexcitability in FrCasE RNs. A: records of spontaneous firing in RNs. Top: spontaneous firing in FrCasE RNs characterized by bursts and silent periods. Bursts were defined as continuous firing (≥2.5 Hz) for at least 2 s, followed by a quiescent period ≥ 1 s. Middle: Fr57E RN with low levels of spontaneous spiking and regions of accumulating depolarization (asterisks) but no suprathreshold bursts. Bottom: uninfected RN with subthreshold synaptic potentials (asterisks) without accumulating depolarization and low spontaneous spiking. Postnatal ages and RPs: FrCasE: P13, −62 mV; Fr57E: P14, −59 mV; uninfected, P14, −58 mV. B: spontaneous firing in a P13 FrCasE RN with 11 mM EGTA-5 mM Ca in the internal recording solution at <1 min (top) and 5 min (bottom) after whole cell access. Note that spontaneous firing is lost but subthreshold synaptic potentials remain (asterisks). C: D-APV (100 μM) does not reduce spontaneous firing or the prolonged depolarizations observed between spikes (asterisks) in a FrCasE RN. P14; RP −59 mV. Top: recording prior to bath application of D-APV. D, left: spontaneous firing in ICC RNs averaged over the whole recording window. Data pooled over P11–P16. No. of cells: 9 FrCasE, 8 uninfected, 7 Fr57E. Means and SD. ANOVA, ***P < 0.05. Right: spontaneous spike rates in uninfected and FrCasE sustained-regular cells are shown for comparison (t7 = 0.68; P = 0.52; n = 4 uninfected, 4 FrCasE). E: burst spike frequency in ICC RNs under the conditions outlined in A–C; effects at −90 mV membrane potential are included. Data pooled over P11–P16. Means and SD. No. of cells: ACSF: 9 FrCasE, 8 uninfected, 7 Fr57E; 4 FrCasE APV (100 μM); 6 FrCasE EGTA; 5 FrCasE. ANOVA: uninfected vs. Fr57E, P = 0.36; uninfected vs. FrCasE, P < 0.00001; FrCasE APV vs. control, P = 0.13; FrCasE EGTA vs. control, P = 0.00002; FrCasE normal RP vs. −90 mV, P < 0.000001. F, left and center: confocal image stack of a P13 FrCasE RN that showed spontaneous firing and PIR loss filled with biocytin during recording and detected with Alexa Fluor 488 conjugated-streptavidin postfixation. Arrows, areas of dendritic swelling. Right: biocytin-filled RN from an uninfected ICC showing normal morphology.