Article Figures & Data
Figures
- Fig. 1.
Histological criteria used to identify CE and intercalated recording sites. A, Identification of amygdala nuclei in transilluminated slices. The area delimited byblack corners is expanded in C.B, Varicose axon collateral of a Neurobiotin-filled intercalated neuron. This axonal segment was observed in theCEM . C, Neurobiotin-filled neurons recorded in the CEL ,CEM , and intercalated cell masses (small neurons located between the dashed lines). Axon collaterals are marked by the letter a. Note the correspondence between the mediolateral position of intercalated cells and that of their axon collaterals in the CE nucleus.EC, External capsule.
- Fig. 2.
CEM neurons are responsive to electrical stimulation of the BL nucleus. A, Scheme showing the position of the stimulating electrode array (dots). B, Graph plotting the peak amplitude of the postsynaptic potentials elicited by stimuli (0.2 msec) of three different intensities (0.2 mA, continuous line; 0.5 mA, dashed line; 1 mA, dotted line) delivered through neighboring stimulating electrodes. The numbers in the x-axis correspond to those marking the stimulation sites in the scheme of A. Four stimuli were delivered at each intensity and stimulation site. Evoked responses were averaged, excluding suprathreshold responses. For clarity, error bars are only indicated for responses evoked by the 1 mA stimuli. C, Examples of evoked responses elicited by stimuli delivered at selected sites (numbers on the left,arrows in B) and at the three stimulation intensities (superimposed single sweeps). The truncated spike in C measured 92 mV. During these tests, the cell was depolarized to −65 mV (0.06 nA). Rest was −86 mV.GP, Globus pallidus; OT, optic tract;PU, putamen; V, ventricle.
- Fig. 3.
CEL neurons are responsive to stimulation of the LA and basal nuclei. A, Graph plotting the peak amplitude of the postsynaptic potentials elicited in a CEL (continuous line) and aCEM (dashed line) neuron by stimuli (0.2 msec; 0.5 mA) delivered through neighboring stimulating electrodes. The numbers in the x-axis correspond to those marking the stimulation sites in the scheme of Figure 2A. Both neurons were recorded in the same slice. B, Example of evoked responses elicited in a CEL neuron by stimuli delivered at selected sites (numbers in the middle). Responses are shown with a slow (B1) and fast (B2) time base. The CEL cell was depolarized to −65 mV (0.04 nA). Rest was −76 mV.
- Fig. 4.
Intercalated neurons are responsive to stimulation of the LA and basal nuclei. A, Scheme showing the position of the stimulating electrode array and of the intercalated neurons (arrowheads and letters) depicted in the rest of the figure. B1, C1,D, Graphs plotting the peak amplitude of the postsynaptic potentials elicited in three intercalated neurons by electrical stimuli (0.2 msec; 0.5 mA) delivered through neighboring stimulating electrodes. Four stimuli were delivered at each site and averaged. The numbers in the x-axes correspond to those marking the stimulation sites in the scheme of A.B2–3, C2–3, Examples of evoked responses elicited by single stimuli delivered at selected sites (numbers on the left,arrows in B1 and C1). Responses are shown at a slow (2) and a fast (3) time base. During these tests, intercalated neurons were depolarized to −65 mV with 0.02, 0.01, and 0.01 nA inB–D, respectively. Rest was −80 mV, −75, and −76 inB, C, D, respectively.GP, Globus pallidus; OT, optic tract;PU, putamen; V, ventricle.
- Fig. 5.
Average response profiles of CEM(B), CEL (C), and intercalated (ITC;D,E) neurons to stimulation of the basolateral complex. A, Scheme showing the position of the stimulating electrode array and of the intercalated neurons (arrowheads and letters) depicted in the rest of the figure. B–E, Graphs plotting the peak amplitude (left axis) and latency (○,right axis) of the postsynaptic potentials elicited in central and intercalated neurons by electrical stimuli (0.2 msec; 0.5 mA) delivered through neighboring stimulating electrodes. The graphs shown in B–E were obtained by normalizing and averaging the responses of 14, 6, 5, and 6 cells, respectively. Four stimuli were delivered at each site and averaged. The numbers in thex-axes correspond to those marking the stimulation sites in the scheme of A.
- Fig. 6.
Intercalated neurons generate feedforward IPSPs in CEM cells. A, Depolarization discloses BL-evoked IPSPs in CEM cells dialyzed with QX-314. The same BL stimuli were applied at various Vm values (indicated on the right) in control Ringer's solution (A1), in the presence of bicuculline (A2) or, after recovery, in picrotoxin (A3).B, Scheme illustrating the approach used to test the effect of local pressure application of NBQX on CEMresponses to BL stimuli (dots). The horizontal arrows on the left indicate the direction of the flow of Ringer's solution. The ejection pipette was first positioned in the CEM and, after a period of recovery (10 min), close to intercalated cells. The effect of NBQX pulses (1 sec, 10 PSI) in the CEM and in the intercalated cell mass is shown in C1 and C2, respectively. Each trace is the average response to four BL stimuli delivered at 0.1 Hz in control conditions (dashed line) or preceded by an NBQX pulse (dashed line; pulse-shock interval of 100 msec).
- Fig. 7.
Stimuli having no direct effects on CEM neurons can enhance or reduce BL-evoked CEMresponses by modulating intercalated neurons. A, The BL-evoked responses of CEM neurons (Control) are enhanced when BL stimuli are preceded by a LA shock (Paired). To carry out these tests, this cell was depolarized to −65 mV (with 0.01 nA), and the BL stimulation intensity gradually decreased just below firing threshold.B, Same protocol as in A but with a pipette solution containing QX-314. This CEM cell was depolarized to −49 mV by current injection (0.06 nA). Averages of four paired and unpaired (Control) responses.C, Different CEM neuron depolarized to −51 mV (0.05 nA). The intensity of BL stimuli was gradually reduced to minimize the amplitude of the evoked IPSP. The recording pipette contained QX-314. Averages of four paired and unpaired (Control) responses.
- Fig. 8.
Synaptic interactions postulated to explain the modulation of CEM responses by intercalated neurons (ITC). Glutamatergic (GLU) and GABAergic (GABA) neurons are represented by ○ and ●, respectively. Stimulation sites are indicated by symbols: BL(▾), L (▵), BM (□). In the three panels, the top two traces represent the responses of CEM neurons, and the two bottom traces represent the responses of intercalated cells.Left, In control conditions, BL inputs exciteCEM and intercalated cells. The feedforward inhibition thus generated in CEM cells reduces their likelihood of responding with orthodromic spikes.Middle, Inputs from the LA inhibit intercalated neurons projecting to the CEM via the activation of other intercalated neurons located laterally. As a result, less feedforward inhibition is elicited inCEM cells by BL inputs, resulting in a higher probability of orthodromic spiking. Right,BM inputs produce a subthreshold depolarization in intercalated neurons projecting to the CEM . Simultaneous BL inputs thus elicit more feedforward inhibition in CEM neurons, leading to a decreased likelihood of orthodromic spiking. See Pitkänen et al. (1997) for a review of intra-amygdaloid pathways.
