Article Figures & Data
Figures
- Fig. 1.
Diagram of hippocampal slice preparation and experimental configuration. The granule cell layer is shown divided into three regions: inner blade, apex, and outer blade. The electrode used for antidromic electrical stimulation of dentate granule cells is represented with its tip located in the region of the hilus. Pipettes for the application of glutamate microdrops (glutamate pipette) are shown positioned on both sides (tip andapex) of a recording electrode in the inner blade.
- Fig. 2.
Photomicrographs of the dentate gyrus from a control (A) and a kainate-treated (B) rat. Combined cresyl violet (blue) and Timm’s stains (brown) were used to reveal granule cell bodies and mossy fiber boutons simultaneously. In the control slice, Timm’s stain labeled the hilar region and mossy fiber projections to the CA3 area. In the slice from the kainate-treated rat (B), Timm’s stain also marked a thick band in the inner molecular layer. The data presented in Figure 12, A and B, were obtained from the slice in B.
- Fig. 3.
Comparison of electrically evoked responses in the granule cell layer of slices from a control rat (A) and kainate-injected rats 4 d (B) and 10 months (C) after treatment in 10 μmbicuculline and 6 mm[K+]o. A1–A3, B1–B3, Antidromic (hilar) electrical stimulation evoked one population spike in the granule cell layer. C, Antidromic electrical stimulation evoked bursts of action potentials in a granule cell that were synchronized with bursts of population spikes superimposed on long negative shifts. The pairs of traces are simultaneous intracellular (top) and extracellular (bottom) recordings obtained in the outer blade. The extracellular electrode was positioned near the intracellular electrode. The intracellular recording was performed at resting membrane potential (−73 mV). The cell input resistance was 60 MΩ. Composition of the perfusion solution was identical in A–C.Arrows show the time of the electrical stimulation. In this and subsequent figures, dashed lines represent baseline.
- Fig. 4.
Antidromic (hilar) electrical stimulation of granule cells evoked bursts of EPSPs. A, Pairs of traces (1–3) are simultaneous intracellular (top) and extracellular (lower) recordings obtained in the outer blade. The granule cell input resistance was 40 MΩ, and the resting membrane potential was −70 mV. The cell membrane potential was hyperpolarized to −90 mV with intracellular current injection to block action-potential firing. Note that an antidromic action potential could be evoked with a stimulation intensity of 100 μA (3, truncated). Note also the decrease in the delay between the stimulation artifact (arrows) and the beginning of the burst of EPSPs, when the stimulation intensity was increased from 20 μA to 30 μA.B, Delayed EPSPs in a granule cell were synchronized with delayed bursts of antidromically evoked population spikes. Top traces (1, 2) are intracellular recordings at resting membrane potential (−68 mV) from a granule cell located in the inner blade. Cell input resistance was 100 MΩ. Bottom traces are extracellular recordings obtained also in inner blade. Note the slight delay between the beginning of the extracellular bursts and the rising phase of the EPSPs. Arrows show stimulation artifact.
- Fig. 5.
Hyperpolarization of membrane potential with intracellular current injection blocked action-potential firing in a granule cell but did not modify the frequency of the spontaneous bursts. In all panels, top traces are intracellular recordings of a granule cell in the outer blade, and bottom traces are extracellular recordings obtained in the same region. Between each pair of traces, 6 sec periods were deleted during which no activity was detected. Hyperpolarizing the cell membrane potential from resting potential (−70 mV) to −120 mV blocked action potentials and revealed EPSPs but did not change the spontaneous bursting frequency (∼0.15 Hz). The cell input resistance was 100 MΩ.
- Fig. 6.
Spontaneous long-duration bursts became shorter when their frequency increased. Traces are extracellular recordings of successive spontaneous bursts obtained with the recording electrode positioned in the apical region of the granule cell layer. Time shown between traces is the time elapsed between the beginning of each successive burst.
- Fig. 7.
Electrical stimulation of the hilar region could evoke long bursts with tonic and clonic phases. A, Evoked burst recorded in the apical region. Note the large amplitude of the negative shift. The insets illustrate the progressive change of the firing pattern of population spikes from fast and regular at the beginning of the burst to slower and clustered at the end of the burst.B, Both extracellular (top) and intracellular (bottom) recordings were obtained in the outer blade of a slice from a different kainate-treated rat. Note the exact synchronization between population spikes and action potentials. Cell resting membrane potential was −75 mV. Stimulus intensity was 100 μA in A and B (arrows).
- Fig. 8.
During long bursts, progressively synchronized EPSPs underscored the clustering of the action-potential firing. Intracellular recording of a granule cell located in the inner blade. The thick bars under the top trace show sections enlarged in the bottom traces. Hilar electrical stimulation (arrow) intensity was 250 μA. Action potentials are truncated in traces 1–4. Cell input resistance was 80 MΩ; resting membrane potential was −80 mV.
- Fig. 9.
Glutamate microstimulation of the granule cell layer evoked an abrupt increase of EPSP size and frequency in a granule cell. Intracellular recording of a granule cell located in the inner blade is shown at resting membrane potential (−73 mV) while a glutamate microdrop was applied 250 μm from the recorded cell toward the side of the tip of the inner blade. Arrow shows the artifact produced by the microdrop touching the slice. Time indicates the beginning of each trace. Traces are consecutive. The bottom traces are an enlargement of the area underlined by thethick bar. Cell input resistance was 80 MΩ.
- Fig. 10.
A, Plot of the percentage of cells responding to glutamate microstimulation by an increase in EPSPs as a function of their location in the granule cell layer. All of the granule cells tested with microapplications of glutamate were grouped according to the arbitrarily defined region where they were located: inner blade (IB), outer blade (OB), and apical region (apex). B, Histogram of the distances between granule cells and glutamate microstimulations. The distance was measured between the point of entry of the recording electrode in the slice and the application site of the glutamate microdrop. The number of stimulations (n = 41) includes only one application for a given distance in each side of the granule cell and therefore excludes repeated applications of the same site.
- Fig. 11.
Glutamate microstimulations of areas in both sides of a granule cell evoked an increase in EPSP frequency. The distance between glutamate microdrop and recording electrode was 200 μm in A and 250 μm in B. The cell was located in the inner blade. Cell input resistance was 50 MΩ; resting membrane potential was −80 mV. Traces are consecutive in A andB. Arrows show the artifact produced by the microdrops touching the slice.
- Fig. 12.
Local glutamate microstimulation evoked an increase of the excitatory input in a higher percentage of granule cells in slices showing long antidromically evoked bursts.A, A granule cell located in the outer blade showed an increase in EPSPs in response to a glutamate microdrop applied 400 μm from the recording electrode in the side of the tip of the outer blade (slice shown in Fig. 2B). B, After removal of the intracellular recording electrode, an extracellular recording electrode was positioned in the same region, and antidromic (hilar) electrical stimulation evoked a long burst. The cell input resistance was 50 MΩ, and resting membrane potential was −82 mV. C, Plot of the percentage of cells responding to glutamate microstimulation by an increase in EPSPs as a function of the duration of the antidromically evoked extracellular burst. For each granule cell tested with glutamate microstimulations, extracellular burst recordings were obtained in the same area. All of the granule cells tested were grouped in three categories depending on the duration of the extracellularly recorded burst: <3 sec, 3–10 sec, and >10 sec.
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