Context-driven cocaine-seeking in abstinent rats increases activity-regulated gene expression in the basolateral amygdala and dorsal hippocampus differentially following short and long periods of abstinence

Abstract

In this study, the expression patterns of zif268 and activity-regulated cytoskeleton-associated gene (arc) were investigated in the basolateral amygdala (BLA) and dorsal hippocampal (dHPC) subregions during context-induced drug-seeking following 22 h or 15 d abstinence from cocaine self-administration. Arc and zif/268 mRNA in BLA and dHPC increased after re-exposure to the cocaine-paired chamber at both timepoints; however, only the BLA increases (with one exception-see below) were differentially affected by the presence or absence of the cocaine-paired lever in the chamber. Following 22 h of abstinence, arc mRNA was significantly increased in the BLA of cocaine-treated rats re-exposed to the chamber only with levers extended, whereas following 15 d of abstinence, arc mRNA in the BLA was increased in cocaine-treated rats returned to the chamber with or without levers extended. In contrast, zif268 mRNA in the BLA was greater in cocaine-treated rats returned to the chamber with levers extended vs. levers retracted only after 15 d of abstinence. In the dentate gyrus (DG) following 22 h of abstinence, zif268 mRNA was greater in rats returned to the chamber where levers were absent regardless of drug treatment whereas arc mRNA was increased in CA1 (cell bodies and dendrites) and CA3 only in cocaine-treated groups. Following 15 d of abstinence, arc mRNA was significantly greater in CA1 and CA3 of both cocaine-treated groups returned to the chamber than in those placed into a familiar, non-salient alternate environment; however, only in CA1 cell bodies the cocaine context-induced increases significantly greater than in yoked-saline controls. In contrast, zif/268 mRNA in all dHPC regions was significantly greater in both cocaine-treated groups returned to the cocaine context than in the cocaine-treated group returned to an alternative environment or saline-treated groups. These data suggest that the temporal dynamics of arc and zif268 gene expression in the BLA and dHPC encode different key elements of drug context-induced cocaine-seeking.

Figure 1

Experimental design and active lever pressing during 1 h context-induced test of drug-seeking. (A) Schematic representing the experimental design for experiment 1 and 2 (adapted from Hearing et al. 2008). SA and CA rats were not included in the design of experiment 1 because exposure to an alternate environment on day 1 of abstinence would have constituted a novel experience. In experiment 2, all rats were habituated to the alternate environment before the test day. (B) Mean number of active lever presses in the 1 h test following 22 h and 15 d of abstinence expressed in 15 min time bins. ^§p<0.05, ^§§§p<.001 22 h cocaine vs saline; ^ΦΦΦp<.001 15 d cocaine vs saline.

Figure 2

After 22 h of abstinence, arc and zif268 mRNA in the BLA of cocaine-treated rats with access to the levers was increased during context re-exposure. Representative coronal hemi-sections illustrating the expression pattern and quantitative analysis of the integrated density of the hybridization signal for arc (A, B) and zif268 (C, D) mRNA in the BLA. Region of interest selected for measurement (white outline) in the BLA is indicated. ^@@@p<0.001 vs. CN; ^^p<0.01, ^^^p<0.001 vs. SL. SN, saline-no levers; SL, saline-levers available; CN, cocaine-no levers; CL, cocaine-levers available; BLA, basolateral amygdala; ID, integrated density.

Figure 3

After 15 d of abstinence, arc and zif268 mRNA in the BLA was increased differentially, depending on lever availability during 1 h re-exposure to the cocaine-paired context. Representative coronal hemi-sections illustrating the expression pattern and quantitative analysis of the integrated density of the hybridization signal for arc (A,B) and zif268 (C,D) in the BLA. **p<0.01, ***p<0.001 vs. CA; ^@@p<0.01 vs. CN; ^^p<0.01, ^^^p<0.001 vs. SL; ^$$$p<0.001 vs. SN. SA, saline-alternate environment; CA, cocaine-alternate environment; SN, saline-no levers; SL, saline-levers available; CN, cocaine-no levers; CL, cocaine-levers available; BLA, basolateral amygdala; ID, integrated density.

Figure 4

After 22 h of abstinence, arc mRNA in CA1 and CA3, and zif268 in CA1, CA3 and DG subregions of the dHPC were increased during 1 h re-exposure to the cocaine-associated context. Representative coronal hemi-sections illustrating the expression pattern and quantitative analysis of the integrated density of the hybridization signal for arc (A,B) and zif268 (C,D) in the dorsal hippocampus. Regions of interest selected for measurement (white outlines) in CA1 pyramidal cells and apical dendrites, CA3, and DG are shown. ^p<.05, ^^p<0.01 vs. SL; ^##p<.01 vs. CL; ^€€p<.01, ^€€€p<.001 cocaine (CN, CL) vs saline (SN, SL). Saline-no levers; SL, saline-levers available; CN, cocaine-no levers; CL, cocaine-levers available; CA1cb, CA1 cell body (pyramidal) layer; CA1d, CA1 dendritic (stratum radiatum) layer; ID, integrated density.

Figure 5

After 15 d of abstinence, arc and zif268 mRNA in CA1, CA3, and DG of the dorsal hippocampus was increased during 1 h re-exposure to the cocaine-associated context. Representative coronal hemi-sections illustrating the expression pattern and quantitative analysis of the integrated density of the hybridization signal for arc (A,B) and zif268 (C,D) in the dorsal hippocampus. *p<0.05, **p<0.01, ***p<0.001 vs. CA; ^$p<0.05, ^$$$p<0.001 vs. SN; ^p<0.05, ^^p<0.01, ^^^p<0.001 vs. SL; ⁺p<0.05, ⁺⁺p<0.01 vs. SA. SA, saline-alternate environment; CA, cocaine-alternate environment; SN, saline-no levers; SL, saline-levers available; CN, cocaine-no levers; CL, cocaine-levers available; CA1cb, CA1 cell body (pyramidal) layer; CA1d, CA1 dendritic (stratum radiatum); ID, integrated density.