Figure 1.

Spontaneous and depolarization-evoked bursting of representative HEGCs. The recordings shown were obtained at 22-24 ° during superfusion at ≈3 mL/min with artificial cerebrospinal fluid that contained 122 mM NaCl, 25 mM NaHCO₃, 3.1 mM KCl, 1.8 mM CaCl₂, 1.2 mM MgSO₄, 0.4 mM KH₂PO₄, and 10 mM D-glucose, equlibrated with 95% O₂ / 5% CO₂. A cellular burst was defined as two or more action potentials superimposed on a single depolarizing wave. No such events were detected in recordings from any GC-SE or CGC made under these conditions. Cellular bursts are indicated by asterisks (*) in panels A, B. A: Gramicidin perforated patch recording in current clamp mode. Spontaneous action potentials and cellular bursts were recorded at the resting membrane potential of −65 mV. B: Whole-cell patch clamp recording in current clamp mode obtained soon after break-in. Spontaneous action potentials and bursts were recorded at the resting membrane potential of −62 mV. The expanded trace shows the fourth spontaneous burst in greater detail. C,D: Depolarization-evoked burst recorded during whole-cell patch clamp recording in current clamp mode. C: Membrane currents were monitored for 5 minutes during cell-attached recording in voltage clamp mode at a holding potential of −70 mV. No currents associated with spontaneous bursting were recorded from this cell. D: After achieving whole cell access, membrane potential was monitored during successive injections of depolarizing current from −0.5 to +1.9 nA for 1 second each. The cell’s minimal response was a burst of action potentials first recorded during depolarization to −56 mV from a resting membrane potential of −71 mV. E,F: Lack of depolarization-evoked bursting in another recorded HEGC. E: Again, no currents associated with spontaneous bursting were observed by cell-attached recording. In addition, no spontaneous bursts were recorded at the resting membrane potential upon achieving whole cell access. F: Depolarization of this cell to −56 mV from a resting membrane potential of −71 mV evoked no response. Its minimal response was a single action potential first recorded during depolarization to −43 mV. In these respects, this nonbursting HEGC resembled closely all recorded GC-SEs and CGCs. CGC, normotopic granule cell from control rat; GC-SE, normotopic granule cell from rat that had experienced status epilepticus; HEGC, hilar ectopic granule cell from rat that had experienced status epilepticus.