Involvement of amygdalar protein kinase A, but not calcium/calmodulin-dependent protein kinase II, in the reconsolidation of cocaine-related contextual memories in rats

Abstract

Rationale: Contextual control over drug relapse depends on the successful reconsolidation and retention of context-response-cocaine associations in long-term memory stores. The basolateral amygdala (BLA) plays a critical role in cocaine memory reconsolidation and subsequent drug context-induced cocaine-seeking behavior; however, less is known about the cellular mechanisms of this phenomenon.

Objectives: The present study evaluated the hypothesis that protein kinase A (PKA) and calcium/calmodulin-dependent protein kinase II (CaMKII) activation in the BLA is necessary for the reconsolidation of context-response-cocaine memories that promote subsequent drug context-induced cocaine-seeking behavior.

Methods: Rats were trained to lever-press for cocaine infusions in a distinct context, followed by extinction training in a different context. Rats were then briefly re-exposed to the previously cocaine-paired context or an unpaired context in order to reactivate cocaine-related contextual memories and initiate their reconsolidation or to provide a similar behavioral experience without explicit cocaine-related memory reactivation, respectively. Immediately after this session, rats received bilateral microinfusions of vehicle, the PKA inhibitor, Rp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt (Rp-cAMPS), or the CaMKII inhibitor, KN-93, into the BLA or the posterior caudate putamen (anatomical control region). Rats were then tested for cocaine-seeking behavior (responses on the previously cocaine-paired lever) in the cocaine-paired context and the extinction context.

Results: Intra-BLA infusion of Rp-cAMPS, but not KN-93, following cocaine memory reconsolidation impaired subsequent cocaine-seeking behavior in a dose-dependent, site-specific, and memory reactivation-dependent fashion.

Conclusions: PKA, but not CaMKII, activation in the BLA is critical for cocaine memory re-stabilization processes that facilitate subsequent drug context-induced instrumental cocaine-seeking behavior.

Figure 1

(A) Photographic and (B–D) schematic depiction of cannula placements for infusion of Rp-cAMPS or KN-93 into the BLA or pCPu. The most ventral point of injector cannula tracks are shown for rats that received (B) Rp-cAMPS or 1X phosphate buffered saline vehicle (VEH) into the BLA or pCPu after cocaine-paired context re-exposure, (C) Rp-cAMPS or VEH into the BLA after unpaired context exposure, or (D) KN-93 or 20% DMSO VEH into the BLA after cocaine-paired context re-exposure. Numbers denote distance from bregma in mm on the schematics modified from the rat brain atlas of Paxinos and Watson (1997). The length of the scale bar in (A) is 1 mm.

Figure 2

Effects of intra-BLA Rp-cAMPS administration following cocaine memory reactivation on subsequent drug context-induced cocaine-seeking behavior. (A) Schematic depicting the timeline for experiment 1: cocaine self-administration training (COC SA), extinction training (EXT), re-exposure to the previously cocaine-paired context (cocaine memory reactivation, MR), and the test of cocaine-seeking behavior in the EXT and cocaine-paired (COC-paired) contexts. (B) Active and inactive lever responses (mean ± SEM/2 h) during each phase of the experiment for rats that had received VEH (0.5 μl/hemisphere, clear symbols) or the selective PKA inhibitor, Rp-cAMPS (9 μg/0.5 μl per hemisphere, light gray symbols; 18 μg/0.5 μl per hemisphere, dark gray symbols) into the BLA immediately after the MR session. (C) Time course of active lever responding at test in the COC-paired context. Symbols represent statistically significant difference (P < 0.05) relative to the EXT context (*), relative to VEH(^{†, ‡}), or relative to intervals 2–6(^#).

Figure 3

Effects of intra-BLA Rp-cAMPS administration without explicit cocaine memory reactivation on subsequent drug context-induced cocaine-seeking behavior. (A) Schematic depicting the timeline for experiment 2: cocaine self-administration training (COC SA), extinction training (EXT), exposure to an unpaired context (no memory reactivation, No MR), and the test of cocaine-seeking behavior in the EXT and cocaine-paired (COC-paired) contexts. (B) Active and inactive lever responses (mean ± SEM/2 h) during each phase of the experiment for rats that had received VEH (0.5 μl/hemisphere, clear symbols) or Rp-cAMPS (18 μg/0.5 μl per hemisphere, dark gray symbols) into the BLA immediately after the No MR session. Symbols represent statistically significant difference (P < 0.05) relative to the EXT context (*).

Figure 4

Effects of intra-pCPu Rp-cAMPS administration following cocaine memory reactivation on subsequent drug context-induced cocaine-seeking behavior. (A) Schematic depicting the timeline for experiment 3 (same as in experiment 1). (B) Active and inactive lever responses (mean ± SEM/2 h) during each phase of the experiment for rats that had received VEH (0.5 μl/hemisphere, clear symbols) or Rp-cAMPS (18 μg/0.5 μl per hemisphere, dark gray symbols) into the pCPu immediately after the MR session. Symbols represent statistically significant (P < 0.05) difference relative to the EXT context (*).

Figure 5

Effects of intra-BLA KN-93 administration following cocaine memory reactivation on subsequent drug context-induced cocaine-seeking behavior. (A) Schematic depicting the timeline for experiment 4 (same as in experiment 1). (B) Active and inactive lever responses (mean ± SEM/2 h) during each phase of the experiment for rats that had received VEH (0.5 μl/hemisphere, clear symbols) or KN-93 (5 μg/0.5 μl per hemisphere, light gray symbols; 10 μg/0.5 μl per hemisphere, dark gray symbols) into the BLA immediately after the MR session. Symbols represent statistically significant (P < 0.05) difference relative to the EXT context (*).