Table 1.
Electrophysiological Properties of IL Neurons.
Figure 1.
The intrinsic excitability of IL pyramidal neurons increased within 4 hours after extinction and reversed with the spontaneous recovery of fear.
A. Percent of time that rats spent freezing to the tone in groups that were conditioned (Cond; n = 13 rats, black), and fear extinguished (Ext-0; n = 9 rats, red; Ext-4; n = 6 rats, blue; SR; n = 8 rats, green). The Ext-0 group was sacrificed immediately after extinction, and the Ext-4 group was sacrificed 4 hours after extinction. B. Average freezing of the SR group on day 3 and day 21 to two tones. SR rats were sacrificed immediately after testing on day 21. C. Sample traces showing responses of IL neurons from each group to a 200 pA depolarizing current step. D. Number of spikes evoked in IL neurons by increasing depolarizing steps in the Cond (n = 34), Ext-0 (n = 22), Ext-4 (n = 18), and SR (n = 18) groups. E. Average maximum number of spikes evoked in each group. F. Average first interspike interval (ISI). ***p<0.001, *p<0.05.
Figure 2.
Spontaneous recovery reverses the decrease in fAHP induced by fear extinction.
A. Sample traces for each group showing fAHP measured within gray bar. Traces have been aligned to overlap at the spike threshold. B. Average of the fAHP for each group. C. Correlation between maximum number of spikes and fAHP for all neurons. D. Sample traces showing sAHP measured within gray bar. E. Average of the sAHP for each group. F. Lack of correlation between number of spikes and sAHP for all neurons. *p<0.05.
Figure 3.
IL neurons of naïve age-matched rats are more excitable than IL neurons of the SR rats.
The number of spikes, ISI, fAHP, and sAHP of IL neurons (n = 15) of P50 naïve rats (n = 5) are shown normalized to the average values of the SR group. Dashed line indicates values of SR group.
Figure 4.
Summary and model of the changes in IL intrinsic excitability at different behavioral time-points.
A. Average values of the measured intrinsic parameters. C = COND, E0 = EXT-0, E4 = EXT-4, E24 = 24 hours after extinction, SR = Spontaneous Recovery. Dash-line indicates values of naïve group. Naïve and E24 values used with permission from the Journal of Neuroscience (Santini et al., 2008). B. Schematic representation of IL and amygdala interactions at different behavioral time-points.