Anatomical placement of tetrodes.

<p>(A) Coronal sections representing all of the tetrode placements included in the data analysis. (B) Serial sections from one DELAY animal showing tetrodes in both the IL and PrL; these placements are shown as filled gray circles in (A).</p

Peri-event time histograms illustrating CS-evoked activity in the IL (A) and PrL (B) during behavioral training.

<p>The number of neurons contributing to each average (Z>0 within 200 ms) is indicated in the panels. (A) For the IL, there was no difference between the IMMED and DELAY groups in firing to tones during the baseline (BL) session (p>0.05) and early extinction (EXT). During the extinction session, only DELAY rats decreased their firing to the CS (p<0.05). Firing to tone CSs was significantly higher in IMMED rats compared to DELAY rats during the test session (TEST, p<0.05). (B) For the PrL, there was no difference between groups in any of the behavioral phases. The 2-sec tone CS period is shaded in gray.</p

Fear recall suppresses mPFC population level single-unit activity.

<p><b>(A)</b> Day 2 design. <b>(B)</b> Upon tone presentation on Day 2, signaled (red) and unsignaled rats (blue) displayed opposing freezing patterns. (<b>C, D</b>) Average normalized firing rate data from PL and IL are binned in 5 sec increments for the duration of the session. Gray dashed lines indicate tone onset (tone response is the bar immediately to the right of dashed line) for the 5 tones. Signaled rats exhibited robust tone-evoked responses that are superimposed on the overall suppression of neural activity in both PL and IL, as compared to the general increase in firing in unsignaled PL and IL. <b>(E)</b> Heat maps plotting tone-evoked responses for neurons from signaled and unsignaled rats. <b>(F)</b> Normalized tone-evoked histogram averages plotted in 100 msec bins for PL and IL. Previously signaled rats showed robust tone-evoked responses in both PL and IL around tone onset (first 200 msec) compared to unsignaled rats. No difference was observed between brain regions when comparing within a shock group. All values are means ± SEM.</p

Differential firing in PL versus IL predicts freezing behavior.

<p><b>(A</b>) Freezing (circles) was similar across Days 1 (3 min post-shock period) and 2 (tones 4 and 5) in signaled rats, whereas it decreased markedly on Day 2 in unsignaled animals. Relative neural activity (PL minus IL) was similar in magnitude (and positive) across days for the same time periods in signaled rats, but also decreased in magnitude markedly on Day 2 in unsignaled animals. <b>(B)</b> Linear regression analysis showing the PL vs IL difference during tones 4 and 5 plotted against freezing levels for the same time period. This analysis revealed a strongly positive correlation between the two variables when including rats from both shock groups. All values are means ± SEM. *<i>p</i> < 0.01.</p

Neuronal bursting in the IL (A) and the PrL (B) divisions of the medial prefrontal cortex.

<p>(A) The frequency of IL bursting (mean ± SEM) during the 2-s CS (filled circles) and the 1-min ITI (moving average of 5 sec) is shown for rats in the IMMED and DELAY groups; the number of neurons showing bursting in each session is indicated in the panels. During extinction, bursting was greater in the DELAY rats. (B) There was no significant difference in PrL bursting between the IMMED and DELAY groups for trial-related bursting across different behavioral phases (all ps>0.05).</p

Number of neurons recorded in each behavior session.

<p>Number of neurons recorded in each behavior session.</p

Signaled and unsignaled footshock modulates mPFC single-unit activity.

<p><b>(A)</b> Day 1 experimental design; histological placement of the center of each electrode array in mPFC is shown. Each array targeted both PL (8 wires) and IL (8 wires) in the right hemisphere. Coronal sections represent (left to right) coordinates +3.2 and +2.8 relative to bregma in the anteroposterior plane. <b>(B)</b> Signaled (red) and unsignaled rats (blue) displayed no significant difference in freezing behavior during the post-shock 15 min stimulus-free period. The spontaneous firing rate of all neurons was normalized to the pre-conditioning baseline for each brain region and shock group. Normalized firing rate for PL and IL for signaled and unsignaled, (time 0 is immediately after the last shock). <b>(C)</b> Heat maps showing shock-induced changes in firing rate for individual neurons split by group and brain region. Data during the shock trials were not recorded. All values are means ± SEM.</p

ZIP in BLA Disrupts Inhibitory Avoidance Memory

<p>Latency to enter the dark compartment during the acquisition and retention phases of inhibitory avoidance. Retention was tested 24 h after acquisition, 2 h after the bilateral BLA injections (sal, <i>n</i> = 7; scr-ZIP, <i>n</i> = 15; and ZIP, <i>n</i> = 16). The latency to enter the dark compartment was similar across groups during acquisition, but not during retention. The interaction between group and phase of the inhibitory avoidance task was significant (<i>F</i>_2,35 = 4.28; <i>p</i> = 0.02). ZIP impaired retention of inhibitory avoidance compared to the animals treated with saline and scr-ZIP, which were indistinguishable. The asterisk (*) indicates <i>p</i> < 0.01, ZIP relative to saline and scr-ZIP. All data are presented as averages, with error bars indicating standard errors of the mean.</p

Chelerythrine in DH Disrupts Place Avoidance Memory

<p>Naive rats rapidly entered the shock zone on the first training trial but learned to avoid the location for several minutes by the eighth training trial. Chelerythrine (chel) or vehicle (veh) was injected in the DH 2 h before testing retention of 24-h memory. Chelerythrine, but not saline, eliminated retention of the memory, causing avoidance to drop to the level of when the rats were naive (F_2,21 = 14.2; <i>p</i> = 0.0001; an asterisk (*) indicates <i>p</i> < 0.05, chel relative to veh). All data are presented as averages, with error bars indicating standard errors of the mean.</p

ZIP in DH Disrupts Spatial Memory

<div><p>(A) Performance of the eight-arm radial maze task. Learning across 6 d (ten trials per day) was followed by a single retention trial after a 24-h interval. Two hours before the retention trial, each rat received a bilateral DH injection of either saline (sal, <i>n</i> = 9), the control peptide (scr-ZIP, <i>n</i> = 9), or ZIP (<i>n</i> = 8). The ZIP injection impaired overall performance ([A]; <i>F</i>_2,23 = 14.80; <i>p</i> = 10⁻⁵) by increasing reference memory errors ([C]; <i>F</i>_2,23 = 9.30; <i>p</i> = 0.001) without increasing working memory errors ([B]; <i>F</i>_2,23 = 1.16; <i>p</i> = 0.33).</p> <p>(D–G) Performance of the water maze task (D) during training (two four-trial blocks per day) and (E–G) during the unreinforced swim retention test after a 24-h interval. Each rat received a bilateral DH infusion of saline (<i>n</i> = 7), scr-ZIP (<i>n</i> = 7), or ZIP (<i>n</i> = 10) 2 h before the retention test. (E) Percent time in the target quadrant, (F) number of times the position of the escape platform was crossed, and (G) the color-coded time-in-location map for each treatment group during the retention trial. The same blue-to-red scale is used for each map, where the minimum time in the peak, red category is 0.9 s. ZIP impaired retention of spatial accuracy (<i>F</i>_2,21 = 3.96; <i>p</i> = 0.03), but not the spatial search procedure (<i>F</i>_2,21 = 2.08; <i>p</i> = 0.15). All data are presented as averages, with error bars indicating standard errors of the mean. An asterisk (*) indicates <i>p</i> < 0.05, ZIP relative to saline and scr-ZIP.</p></div