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. 2004 Mar 3;24(9):2328-34.
doi: 10.1523/JNEUROSCI.1622-03.2004.

Intra-amygdala administration of polyamines modulates fear conditioning in rats

Maribel A Rubin  1 , Daiane B Berlese, Juliano A Stiegemeier, Márcio A Volkweis, Denise M Oliveira, Telma L B dos Santos, Ana C Fenili, Carlos F Mello
Affiliations

Intra-amygdala administration of polyamines modulates fear conditioning in rats

Maribel A Rubin et al. J Neurosci. .

Abstract

Amygdalar NMDA receptor activation has been implicated in the acquisition of fear memories in rats. However, little is known about the role of endogenous modulators of the NMDA receptor, such as polyamines, in pavlovian fear-conditioning learning. Therefore, in the present study we investigated whether the immediate pretraining or post-training bilateral infusion of arcaine, an antagonist of the NMDA receptor polyamine-binding site, or spermidine, an agonist of the NMDA receptor polyamine-binding site, into the amygdala affected classical fear conditioning in rats. Bilateral microinjections of arcaine (0.0002-0.2 nmol) decreased, whereas spermidine (0.002-20 nmol) increased, contextual and auditory fear conditioning. Arcaine coadministration, at a dose that had no effect per se, reversed the facilitatory effect of spermidine. These results provide evidence that endogenous and exogenous polyamines modulate the acquisition or early consolidation (or both) of the fear-conditioning task in the amygdala.

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Figures

Figure 1.
Figure 1.
Drawing adapted from Paxinos and Watson (1986) showing the area (black) where the infusions were considered correctly placed. Note that infusions were bilateral.
Figure 2.
Figure 2.
Effect of pretraining intra-amygdala arcaine administration on freezing to context (A) and to tone (B). *p < 0.05 compared with vehicle by the Student-Newman-Keuls test. Data are the means + SEM percentage of freezing averaged across all context (A) or tone (B) trials (n = 9-11 animals in each group).
Figure 3.
Figure 3.
Effect of immediate post-training intra-amygdala arcaine administration on freezing to context (A) and to tone (B). *p < 0.05 compared with vehicle by the Student-Newman-Keuls test. Data are the means + SEM percentage of freezing averaged across all context (A) or tone (B) trials (n = 7-13 animals in each group).
Figure 4.
Figure 4.
Effect of pretraining intra-amygdala spermidine administration on freezing to context (A) and to tone (B). *p < 0.05 compared with vehicle by the Student-Newman-Keuls test. Data are the means + SEM percentage of freezing averaged across all context (A) or tone (B) trials (n = 9-14 animals in each group).
Figure 5.
Figure 5.
Effect of immediate post-training intra-amygdala spermidine administration on freezing to context (A) and to tone (B). *p < 0.05 compared with vehicle by the Student-Newman-Keuls test. Data are the meana + SEM percentage of freezing averaged across all context (A) or tone (B) trials (n = 12-14 animals in each group).
Figure 6.
Figure 6.
Effect of the pretraining intra-amygdala coadministration of arcaine (0.002 nmol) and spermidine (0.02 nmol) on the percentage of freezing to context (A) and to tone (B). PBS represents vehicle treatment. *p < 0.05 compared with vehicle by the Student-Newman-Keuls test. Data are the means + SEM averaged across all context (A) or tone (B) trials (n = 17-18 animals in each group).
Figure 7.
Figure 7.
Effect of the immediate post-training intra-amygdala coadministration of arcaine (0.0002 nmol) and spermidine (0.2 or 2 nmol) on the percentage of freezing to context (A) and to tone (B). PBS represents vehicle treatment. *p < 0.05 compared with vehicle by the Student-Newman-Keuls test. Data are means + SEM averaged across all context (A) or tone (B) trials (n = 9-13 animals in each group).
Figure 8.
Figure 8.
Effect of intra-amygdala administration of spermidine (0.02 nmol) or arcaine (0.02 nmol) on foot shock sensitivity. PBS represents vehicle treatment. Data are the means + SEM flinch, jump, and vocalization thresholds expressed in milliamps (n = 8-10 animals in each group).
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