Neuronal pentraxins modulate cocaine-induced neuroadaptations

Abstract

Neuronal pentraxins (NPs) function in the extracellular matrix to bind alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Three NPs have been described, neuronal activity-regulated pentraxin (Narp), which is regulated as an immediate early gene, NP1, and neuronal pentraxin receptor (NPR). Narp and NP1 enhance synaptogenesis and glutamate signaling by clustering AMPA receptors, whereas NPR contributes to removing AMPA receptors during group I metabotropic glutamate receptor-dependent long-term depression. Here, we examine mice with genetic deletions [knockout (KO)] of each NP to assess their contributions to cocaine-induced neuroplasticity. Consistent with a shared AMPA receptor clustering function for Narp and NP1, deletion of either NP caused similar behavioral alterations. Thus, although both Narp and NP1 deletion promoted cocaine-induced place preference, NPR deletion was without effect. In addition, although Narp and NP1 KO showed reduced time in the center of a novel environment, NPR KO mice spent more time in the center. Finally, although Narp and NP1 KO mice showed blunted locomotion after AMPA microinjection into the accumbens 3 weeks after discontinuing repeated cocaine injections, the AMPA response was augmented in NPR KO. Likewise, endogenous glutamate release elicited less motor activity in Narp KO mice. Consistent with reduced AMPA responsiveness after chronic cocaine in Narp KO mice, glutamate receptor 1 was reduced in the PSD fraction of Narp KO mice withdrawn from cocaine. These data indicate that NPs differentially contribute to cocaine-induced plasticity in a manner that parallels their actions in synaptic plasticity.

Fig. 1

Narp and NP1 KO mice show enhanced cocaine-induced conditioned place preference. A, cocaine induces place conditioning in Narp KO but not in WT mice. Cocaine place conditioning is expressed as mean ± S.E.M. occupancy difference in seconds (post-test time – pretest time). The number of determinations is shown in the bars. B, cocaine (20 mg/kg i.p.) elicited place preference in NP1 KO but not NPR KO or the NP1/NPR WT. *, p < 0.05 comparing saline-with cocaine-treated animals within each genotype using a Dunnett’s test (A) or Bonferroni post hoc test (B).

Fig. 2

The deletion of NP genes altered spontaneous behavior in a novel open field. A, spontaneous locomotor activity, estimated by distance traveled, was not affected by Narp gene deletion, was greatly elevated in NPR KO, and was elevated during the first 10 min in NP1 KO. B, amount of time spent in the center of the open field was reduced in Narp and NP1 KO and increased in NPR KO. Data are shown as mean ± S.E.M., and the number of determinations in each group is shown in parentheses. *, p < 0.05, comparing KO with respective WT using a Bonferroni post hoc or main effect of genotype (Narp KO versus WT).

Fig. 3

The deletion of NP genes altered the development, but not the expression, of cocaine-induced behavioral sensitization. Mice were injected once a day for 7 days with either saline or cocaine (1 × 15, 5 × 30, 1 × 15 mg/kg). A, Narp deletion reduced the acute response to cocaine and delayed the development of full sensitization relative to WT by showing reduced motor activity on day 7 versus day 28. The numbers of determinations in each group were WT/saline = 10, Narp-KO/saline = 10, WT/cocaine = 11, and Narp-KO/cocaine = 12. B, lack of effect by Narp gene deletion on caffeine-induced motor activity. n = 9 for Narp-KO and n = 6 for WT. C, NP1 deletion reduced the development of sensitization to daily cocaine relative to WT by showing reduced motor activity on day 7 versus day 28. The numbers of determinations in each group were WT/saline = 8, WT/cocaine = 10, NP1-KO/cocaine = 10, and NPR-KO/cocaine = 9. All data are expressed as mean ± S.E.M. distance traveled (centimeters). *, p < 0.05 comparing saline with cocaine- or caffeine-treated animals within each genotype. +, p < 0.05 comparing KO to corresponding WT; #, p < 0.05, comparing genotypes on day 1.

Fig. 4

Narp and NP1 gene deletion inhibit AMPA-induced motor activity. A, AMPA microinjection into the nucleus accumbens produced a dose-dependent increase in motor activity only in mice withdrawn from daily cocaine, and Narp KOs show reduced locomotor activity to the lowest dose of AMPA. The data are shown as mean ± S.E.M. total distance traveled (centimeters) during 2 h after AMPA. B, time course for AMPA-induced locomotion in WT and Narp KO. C, NP1 KO inhibits locomotor responding to AMPA relative to WT, whereas NPR KO shows enhanced responding. D, time course for AMPA-induced locomotion in WT, NP1 KO, and NPR KO. *, p < 0.05 compared with saline infusion within each genotype using a oneway ANOVA followed by a Bonferroni post hoc test (A and C). Main effect of KO versus WT (B and D). +, p < 0.05 comparing KO with corresponding WT using a oneway ANOVA followed by a Dunnett’s post hoc (A and C) or a least significant difference post hoc (D).

Fig. 5

Narp KOs show deficits in the motor response elicited by glutamate released endogenously after DHPG injection into the accumbens. A, dose-dependent induction of motor activity by DHPG in WT is absent in Narp KO mice. B, time course of DHPG-induced (2.5 nmol) locomotor activity revealed a marked genotypic difference. C, DHPG induced an equivalent dose-dependent release of glutamate between WT and Narp KO when reverse dialyzed into the accumbens. D, time course of DHPG-induced changes in extracellular glutamate. *, p < 0.05, comparing between genotypes. +, p < 0.05, comparing with baseline or saline injection within genotypes.

Fig. 6

Withdrawal from chronic cocaine reduces GluR1 in the Narp KO but not WT mice. A, levels of GluR1 are reduced after withdrawal from chronic cocaine in the PSD subfraction of Narp KO but not WT mice. GluR1 was not reduced by cocaine in the non-PSD subfraction. B, representative immunoblots of GluR1. C, internal standard control (see Materials and Methods); 1, non-PSD, 2, PSD; Sa, chronic saline; Co, chronic cocaine; M, protein standard; WS, WT/saline; WC, WT/cocaine; KS, KO/saline; KC, KO/cocaine. *, p < 0.05, comparing chronic cocaine with saline treatments within each genotype.