Article Figures & Data
Figures
- Fig. 1.
TEA-, Ba-, and TTX-containing Krebs (TEA Krebs) evoke synchronous oscillations in membrane potential, action potentials, and extracellular field potentials. A, Thetop trace shows an intracellular recording of membrane potential (dashed line is −60 mV), and the bottom trace shows a recording of field potentials with an extracellular electrode. The larger deflections are action potentials that were evoked at the peak of the depolarizing phase of oscillations. In this cell, the largest oscillations in membrane potential were <25 mV.B, Expanded time scale of the period indicated by theopen box in A. The action potentials and oscillations in membrane potential were synchronous with field potentials. An example of an oscillation is marked with anasterisk and is illustrated at an expanded time base inC. C, Expanded time scale of an intracellular recording of an oscillation (indicated by the asterisk inB), an action potential that arose at the peak of an oscillation, and an extracellular spike (indicated by the solid triangle in B).
- Fig. 2.
Oscillations of membrane potential are independent of voltage and extracellular potassium concentration. A, Spontaneous activity was examined at −60, −80, and −120 mV, and the extracellular potassium was increased from 2.5 to 10 mm. At −60 mV, an action potential was evoked at the peak of each oscillation. The hyperpolarization after the action potential is therefore the combination of an AHP and the hyperpolarizating phase of the oscillation. The spontaneous oscillations were not affected by increasing extracellular potassium.B, The waveforms of evoked action potentials were tested at −60, −80, and −120 mV in 2.5 and 10 mmK+. In this case, the AHP reversed polarity at hyperpolarized potentials, and this reversal was dependent on the extracellular K+. C, The waveforms of a spontaneous oscillation (Spontaneous) and an action potential (Evoked) are illustrated with the same time scale. The initial membrane potential is −80 mV for both traces.D, Plot of the amplitude of the hyperpolarizing component of the oscillations (open symbols) compared with the AHP (solid symbols) at different membrane potentials and in different potassium concentrations (2.5 mm,circles; 6.5 mm, squares; 10 mm, triangles). Thelines are the best fits using a least-squares analysis. Error bars indicate the SEM (n = 6).
- Fig. 3.
Dual intracellular recordings show synchronous action potentials. This experiment was made from intracellular recordings from two cells: top trace from cell 1 andbottom trace from cell 2. In TEA, BaCl2, and TTX solution, two individual cells show synchronous action potentials (solid triangles) and oscillations (open triangles) of the membrane potential.
- Fig. 4.
Synchronous activity is found throughout the LC cell body region but not outside that area. The extent of synchronous oscillations was examined by recording field potentials from various positions either inside or outside the LC. Membrane potential was measured intracellularly from the point marked by the X.Top trace (I) shows membrane potential, and bottom trace (E) shows field potential of each panel. The schematic illustrates the cell body region of LC in a slice. The boundary of the fourth ventricle is shown (4V); the numbers show positions from which extracellular field potential recordings were made, inside (1–3) and outside (4–6) the cell body region of the LC.
- Fig. 5.
Field potentials are synchronous in the entire cell body area of the LC. Field potentials were recorded from two positions inside the LC using two extracellular electrodes. The schematic illustrates the positions at which field potentials were recorded. One electrode was fixed at the place indicated by theX (potentials illustrated with the dotted lines). A second electrode was placed close (C), intermediate (I), or far (F) (potentials illustrated with the solid line). Sample records are shown at close, intermediate, and far position. This experiment was carried out in recordings from eight slices obtained from five animals.
- Fig. 6.
Barium and enkephalin modulate the frequency of synchronous activity. A, Top trace shows potential, and bottom trace shows current. Dotted line shows −60 mV. TEA (10 mm) and TTX (1 μm) were present throughout the experiment. Thebar indicates the period of superfusion of BaCl2 (1 mm). BaCl2 induced the membrane potential oscillations that were present even at −120 mV. This effect was reversible on washout. B, Top trace (I) shows membrane potential, and bottom trace (E) shows field potential. This experiment was carried out in the presence of TEA (10 mm), TTX (1 μm), and BaCl2 (100 μm).Met-Enkephalin (10 μm) was added to the bath solution during the period showing an open bar. Enkephalin decreased the frequency of oscillations. Current injection was used to evoke action potentials in the cell recorded intracellularly, but those action potentials were not detected with the extracellular electrode.
- Fig. 7.
Carbenoxolone and acidification disrupt synchronous activity. A, Top trace(I) shows membrane potential, middle trace(E) shows field potential, and bottom trace shows current. The dashed line indicates −60 mV. Before perfusion of carbenoxolone, synchronous action potentials and field activity were observed. After perfusion of carbenoxolone (100 μm, 90 min), spontaneous action potentials were observed at the zero current level, but no oscillations in membrane potential or field potentials were observed. The effect of carbenoxolone was irreversible. B, Low-pH solution was perfused during the period indicated by the bar. Cell acidification reversibly depolarized the cell and blocked field potential activity, despite the presence of action potentials observed with intracellular recordings. C, In the same cell as shown in B, superfusion of AMPA (0.5 μm) depolarized the neuron and increased the rate of action potentials, oscillations, and extracellular field potential activity. The firing remained synchronous during the depolarization induced by AMPA.
- Fig. 8.
Dendrites extend beyond the cell body region of the LC in the rostral and caudal directions. Left, Confocal image of 10 Cy5-filled neurons. This image highlights the extent of the dendritic arbor of these cells. To avoid saturation of the detection system in the cell body region, images in this area were collected with lower-intensity illumination. Thus, the dendrites in the area proximal to the cell body region are not clearly visualized. Right, Catecholamine fluorescence image of the same slice to indicate the extent of the cell body region. The ventrical is on theright, and rostral is toward the top.Bottom, A voltage recording illustrating the typical spontaneous activity observed in these control slices.
- Fig. 9.
In resectioned slices, oscillations in membrane potential induced by TEA are small, erratic, and of low frequency.Top, The catecholamine fluorescence in the resectioned area of a slice. The top and bottom of this section were the cut regions of the slice caudal and rostral to the cell body region, respectively. The fourth ventrical is to the left.Middle, A confocal image of the area indicated by thebox at the top to illustrate the cut dendrites that extended rostrally. In this slice, six cells were filled with Cy5.Bottom, A voltage record from a resectioned slice (951206) to illustrate the small size and erratic frequency of the oscillations in membrane potential that were commonly found in resection slices. Thedots indicate where changes in membrane potential were counted as oscillations.
Tables
Cell Oscillations ME current Number in 5 min Frequency (Hz) At −60 mV (pA) Reversal potential (mV) Control slices 950928 40 0.13 950929 25 0.083 951010 22 0.073 951019 22 0.073 951020 21 0.07 951027 17 0.057 951121 40 0.13 (FromTravagli et al., 1995) (300–400) (−132 ± 3.2) Resectioned slices 951130 21 0.07 174 951201 1 0.003 98 951204 0 0 94 −110 951205 7 0.02 70 −110 951206 6 0.02 70 −111 951212 15 0.05 123 −136 951218 1 0.003 86 −115 960226a 145 −119 960226b 141 −106 Resectioned slices are those in which knife cuts were made rostral and caudal to the cell body region of the locus coeruleus.
