Abstract

Background:

Opiate addiction is associated with complex cognitive impairment, which contributes to the development of compulsive drug use and relapses. Dopamine and N-methyl-D-aspartate (NMDA) receptors play critical roles in opiate-induced cognitive deficits. However, the roles of D1 and D3 receptors in the NMDA/glycineB receptor-regulated cognitive behaviors induced by morphine remain unknown.

Methods:

The 5-choice serial reaction time task (5-CSRTT) was used to investigate the cognitive profiles associated with repeated morphine administration in D1 (D1-/-)- and D3 (D3-/-)-receptor knockout mice. The expression of phosphorylated NR1, CaMKII and CREB in the brain was examined by Western blotting. D1-/- and D3-/- mice were treated with the NMDA/glycineB site agonist ACPC and the antagonist L-701,324 to chronically disrupt NMDA receptor function and to investigate their effects on morphine-induced cognitive changes.

Results:

Repeated morphine administration impaired attentional function and caused impulsive and compulsive behaviors. D1-/- mice exhibited hardly any premature nosepokes. D3-/- mice showed robustly increased morphine-induced impulsive behavior. The numbers of premature responses were decreased by L-701,324 administration and increased by ACPC administration; these effects were completely abolished in D1-/- mice due to their inability to perform reward-based tasks. In contrast, the inhibitory effects of L-701,324 on impulsive behavior were significantly augmented in D3-/- mice.

Conclusions:

NMDA/glycineB site functions may contribute to morphine-induced cognitive deficits, especially those related to impulsive behavior. D1 and D3 receptors may have contrasting effects with respect to modulating impulsive behavior. D3 receptors have inhibitory effects on impulsive behaviors, and these effects are clearly mediated by NMDA/glycineB receptor and μ-opioid receptor interactions.

Author notes

Correspondence: Jianghua Lai, PhD. College of Forensic Science, Xi’an Jiaotong University, Xi’an, Shaanxi, 710061, China. E-mail: laijh1011@mail.xjtu.edu.cn Tel: 86-29-82655473; Fax: 86-29-8265511
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