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A temporal shift in the circuits mediating retrieval of fear memory.

Do-Monte FH, Quiñones-Laracuente K, Quirk GJ - Nature (2015)

Bottom Line: In contrast, silencing of PL inputs to the basolateral amygdala impaired retrieval at early, but not late, time points, indicating a time-dependent shift in retrieval circuits.Retrieval at late time points also activated PVT neurons projecting to the central nucleus of the amygdala, and silencing these projections at late, but not early, time points induced a persistent attenuation of fear.Thus, the PVT may act as a crucial thalamic node recruited into cortico-amygdalar networks for retrieval and maintenance of long-term fear memories.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Psychiatry, University of Puerto Rico School of Medicine, PO Box 365067, San Juan 00936, Puerto Rico [2] Department of Anatomy &Neurobiology, University of Puerto Rico School of Medicine, P.O. Box 365067, San Juan 00936, Puerto Rico.

ABSTRACT
Fear memories allow animals to avoid danger, thereby increasing their chances of survival. Fear memories can be retrieved long after learning, but little is known about how retrieval circuits change with time. Here we show that the dorsal midline thalamus of rats is required for the retrieval of auditory conditioned fear at late (24 hours, 7 days, 28 days), but not early (0.5 hours, 6 hours) time points after learning. Consistent with this, the paraventricular nucleus of the thalamus (PVT), a subregion of the dorsal midline thalamus, showed increased c-Fos expression only at late time points, indicating that the PVT is gradually recruited for fear retrieval. Accordingly, the conditioned tone responses of PVT neurons increased with time after training. The prelimbic (PL) prefrontal cortex, which is necessary for fear retrieval, sends dense projections to the PVT. Retrieval at late time points activated PL neurons projecting to the PVT, and optogenetic silencing of these projections impaired retrieval at late, but not early, time points. In contrast, silencing of PL inputs to the basolateral amygdala impaired retrieval at early, but not late, time points, indicating a time-dependent shift in retrieval circuits. Retrieval at late time points also activated PVT neurons projecting to the central nucleus of the amygdala, and silencing these projections at late, but not early, time points induced a persistent attenuation of fear. Thus, the PVT may act as a crucial thalamic node recruited into cortico-amygdalar networks for retrieval and maintenance of long-term fear memories.

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Conditioning levels for cFos experiments, and the effects of PL inactivation at early vs. late timepoints(a) Freezing levels for conditioned (n= 4) and unshocked control (n= 5) groups during fear conditioning and retrieval at 6 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,35)= 76.12, P< 0.001). (b) Freezing levels for conditioned (n= 3) and control (n= 4) groups during fear conditioning and retrieval at 24 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,25)= 40.07, P< 0.001). (c) Freezing levels for conditioned (n= 5) and control (n= 6) groups during fear conditioning and retrieval at 7 d timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,45)= 49.88, P< 0.001). Rats were sacrificed and perfused for cFos immunocytochemistry 90 min after the fear retrieval test. Repeated-measures ANOVA followed by Tukey post hoc test. (d, upper) Representative micrograph showing the site of fluorescent MUS injection into PL. (d, lower) Orange areas represent the minimum (darker) and the maximum (lighter) spread of muscimol into PL. (e) PL inactivation impaired fear retrieval at 6 h (F(1,11)= 7.92, P= 0.01, SAL: n= 6; MUS: n= 7) (f) In separate animals, PL inactivation also impaired fear retrieval at 7 d after conditioning (F(1,14)= 13.8, P= 0.002, SAL: n= 8; MUS: n= 8). The retrieval test was performed 30 min after infusion of SAL or MUS (black arrows). One-way ANOVA followed by Tukey post hoc test. Data are shown as mean ± SEM in blocks of two trials; *P< 0.05. Legend: Hab= habituation, Cond= conditioning.
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Figure 7: Conditioning levels for cFos experiments, and the effects of PL inactivation at early vs. late timepoints(a) Freezing levels for conditioned (n= 4) and unshocked control (n= 5) groups during fear conditioning and retrieval at 6 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,35)= 76.12, P< 0.001). (b) Freezing levels for conditioned (n= 3) and control (n= 4) groups during fear conditioning and retrieval at 24 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,25)= 40.07, P< 0.001). (c) Freezing levels for conditioned (n= 5) and control (n= 6) groups during fear conditioning and retrieval at 7 d timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,45)= 49.88, P< 0.001). Rats were sacrificed and perfused for cFos immunocytochemistry 90 min after the fear retrieval test. Repeated-measures ANOVA followed by Tukey post hoc test. (d, upper) Representative micrograph showing the site of fluorescent MUS injection into PL. (d, lower) Orange areas represent the minimum (darker) and the maximum (lighter) spread of muscimol into PL. (e) PL inactivation impaired fear retrieval at 6 h (F(1,11)= 7.92, P= 0.01, SAL: n= 6; MUS: n= 7) (f) In separate animals, PL inactivation also impaired fear retrieval at 7 d after conditioning (F(1,14)= 13.8, P= 0.002, SAL: n= 8; MUS: n= 8). The retrieval test was performed 30 min after infusion of SAL or MUS (black arrows). One-way ANOVA followed by Tukey post hoc test. Data are shown as mean ± SEM in blocks of two trials; *P< 0.05. Legend: Hab= habituation, Cond= conditioning.

Mentions: Next, we used the neural activity marker cFos to determine when dMT is activated by conditioning. Following training, exposure to conditioned tones induced robust freezing at 6 h, 24 h and 7 d timepoints (Extended Data Fig. 3a–c), but triggered different patterns of neuronal activation (Fig. 2a,b). The mediodorsal subdivision of dMT (MD) showed no conditioned activation at any timepoint, whereas PL showed activation at all three timepoints. This suggests that PL is necessary for retrieval at both early and late timepoints, which we confirmed with muscimol (Extended Data Fig. 3d–f). Retrieval at 6 h activated PL and BLA, but not PVT neurons, whereas retrieval at 7 d activated PL and PVT, but not BLA neurons. Retrieval at 7 d also activated the medial portion of the central amygdala (CeM), suggesting that retrieval at 7 d may involve PL-PVT and PVT-CeA pathways. At 24 h, however, both targets of PL (BLA and PVT) were activated (Fig. 2b,c), suggesting a gradual shift in retrieval circuits from PL-BLA to PL-PVT.


A temporal shift in the circuits mediating retrieval of fear memory.

Do-Monte FH, Quiñones-Laracuente K, Quirk GJ - Nature (2015)

Conditioning levels for cFos experiments, and the effects of PL inactivation at early vs. late timepoints(a) Freezing levels for conditioned (n= 4) and unshocked control (n= 5) groups during fear conditioning and retrieval at 6 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,35)= 76.12, P< 0.001). (b) Freezing levels for conditioned (n= 3) and control (n= 4) groups during fear conditioning and retrieval at 24 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,25)= 40.07, P< 0.001). (c) Freezing levels for conditioned (n= 5) and control (n= 6) groups during fear conditioning and retrieval at 7 d timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,45)= 49.88, P< 0.001). Rats were sacrificed and perfused for cFos immunocytochemistry 90 min after the fear retrieval test. Repeated-measures ANOVA followed by Tukey post hoc test. (d, upper) Representative micrograph showing the site of fluorescent MUS injection into PL. (d, lower) Orange areas represent the minimum (darker) and the maximum (lighter) spread of muscimol into PL. (e) PL inactivation impaired fear retrieval at 6 h (F(1,11)= 7.92, P= 0.01, SAL: n= 6; MUS: n= 7) (f) In separate animals, PL inactivation also impaired fear retrieval at 7 d after conditioning (F(1,14)= 13.8, P= 0.002, SAL: n= 8; MUS: n= 8). The retrieval test was performed 30 min after infusion of SAL or MUS (black arrows). One-way ANOVA followed by Tukey post hoc test. Data are shown as mean ± SEM in blocks of two trials; *P< 0.05. Legend: Hab= habituation, Cond= conditioning.
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Figure 7: Conditioning levels for cFos experiments, and the effects of PL inactivation at early vs. late timepoints(a) Freezing levels for conditioned (n= 4) and unshocked control (n= 5) groups during fear conditioning and retrieval at 6 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,35)= 76.12, P< 0.001). (b) Freezing levels for conditioned (n= 3) and control (n= 4) groups during fear conditioning and retrieval at 24 h timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,25)= 40.07, P< 0.001). (c) Freezing levels for conditioned (n= 5) and control (n= 6) groups during fear conditioning and retrieval at 7 d timepoint. The conditioned group showed a significant increase in freezing compared to controls (F(5,45)= 49.88, P< 0.001). Rats were sacrificed and perfused for cFos immunocytochemistry 90 min after the fear retrieval test. Repeated-measures ANOVA followed by Tukey post hoc test. (d, upper) Representative micrograph showing the site of fluorescent MUS injection into PL. (d, lower) Orange areas represent the minimum (darker) and the maximum (lighter) spread of muscimol into PL. (e) PL inactivation impaired fear retrieval at 6 h (F(1,11)= 7.92, P= 0.01, SAL: n= 6; MUS: n= 7) (f) In separate animals, PL inactivation also impaired fear retrieval at 7 d after conditioning (F(1,14)= 13.8, P= 0.002, SAL: n= 8; MUS: n= 8). The retrieval test was performed 30 min after infusion of SAL or MUS (black arrows). One-way ANOVA followed by Tukey post hoc test. Data are shown as mean ± SEM in blocks of two trials; *P< 0.05. Legend: Hab= habituation, Cond= conditioning.
Mentions: Next, we used the neural activity marker cFos to determine when dMT is activated by conditioning. Following training, exposure to conditioned tones induced robust freezing at 6 h, 24 h and 7 d timepoints (Extended Data Fig. 3a–c), but triggered different patterns of neuronal activation (Fig. 2a,b). The mediodorsal subdivision of dMT (MD) showed no conditioned activation at any timepoint, whereas PL showed activation at all three timepoints. This suggests that PL is necessary for retrieval at both early and late timepoints, which we confirmed with muscimol (Extended Data Fig. 3d–f). Retrieval at 6 h activated PL and BLA, but not PVT neurons, whereas retrieval at 7 d activated PL and PVT, but not BLA neurons. Retrieval at 7 d also activated the medial portion of the central amygdala (CeM), suggesting that retrieval at 7 d may involve PL-PVT and PVT-CeA pathways. At 24 h, however, both targets of PL (BLA and PVT) were activated (Fig. 2b,c), suggesting a gradual shift in retrieval circuits from PL-BLA to PL-PVT.

Bottom Line: In contrast, silencing of PL inputs to the basolateral amygdala impaired retrieval at early, but not late, time points, indicating a time-dependent shift in retrieval circuits.Retrieval at late time points also activated PVT neurons projecting to the central nucleus of the amygdala, and silencing these projections at late, but not early, time points induced a persistent attenuation of fear.Thus, the PVT may act as a crucial thalamic node recruited into cortico-amygdalar networks for retrieval and maintenance of long-term fear memories.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Psychiatry, University of Puerto Rico School of Medicine, PO Box 365067, San Juan 00936, Puerto Rico [2] Department of Anatomy &Neurobiology, University of Puerto Rico School of Medicine, P.O. Box 365067, San Juan 00936, Puerto Rico.

ABSTRACT
Fear memories allow animals to avoid danger, thereby increasing their chances of survival. Fear memories can be retrieved long after learning, but little is known about how retrieval circuits change with time. Here we show that the dorsal midline thalamus of rats is required for the retrieval of auditory conditioned fear at late (24 hours, 7 days, 28 days), but not early (0.5 hours, 6 hours) time points after learning. Consistent with this, the paraventricular nucleus of the thalamus (PVT), a subregion of the dorsal midline thalamus, showed increased c-Fos expression only at late time points, indicating that the PVT is gradually recruited for fear retrieval. Accordingly, the conditioned tone responses of PVT neurons increased with time after training. The prelimbic (PL) prefrontal cortex, which is necessary for fear retrieval, sends dense projections to the PVT. Retrieval at late time points activated PL neurons projecting to the PVT, and optogenetic silencing of these projections impaired retrieval at late, but not early, time points. In contrast, silencing of PL inputs to the basolateral amygdala impaired retrieval at early, but not late, time points, indicating a time-dependent shift in retrieval circuits. Retrieval at late time points also activated PVT neurons projecting to the central nucleus of the amygdala, and silencing these projections at late, but not early, time points induced a persistent attenuation of fear. Thus, the PVT may act as a crucial thalamic node recruited into cortico-amygdalar networks for retrieval and maintenance of long-term fear memories.

Show MeSH
Related in: MedlinePlus