Virus-mediated shRNA knockdown of prodynorphin in the rat nucleus accumbens attenuates depression-like behavior and cocaine locomotor sensitization.

Ami Cohen,Max Kreifeldt,Olivier George,Timothy W Whitfield,Candice Contet,Brigitte L Kieffer,George F Koob,Pascale Koebel,Veronique Sgambato-Faure

doi:10.1371/journal.pone.0097216

Abstract

Dynorphins, endogenous opioid peptides that arise from the precursor protein prodynorphin (Pdyn), are hypothesized to be involved in the regulation of mood states and the neuroplasticity associated with addiction. The current study tested the hypothesis that dynorphin in the nucleus accumbens (NAcc) mediates such effects. More specifically, we examined whether knockdown of Pdyn within the NAcc in rats would alter the expression of depressive-like and anxiety-like behavior, as well as cocaine locomotor sensitization. Wistar rats were injected with adeno-associated viral (AAV) vectors encoding either a Pdyn-specific short hairpin RNA (AAV-shPdyn) or a scrambled shRNA (AAV-shScr) as control. Four weeks later, rats were tested for anxiety-like behavior in the elevated plus maze test and depressive-like behavior in the forced swim test (FST). Finally, rats received one daily injection of saline or cocaine (20 mg/kg, i.p.), followed by assessment of locomotion for 4 consecutive days. Following 3 days of abstinence, the rats completed 2 additional daily cocaine/saline locomotor trials. Pdyn knockdown in the NAcc led to a significant reduction in depressive-like behavior in the FST, but had no effect on anxiety-like behavior in the elevated plus maze. Pdyn knockdown did not alter baseline locomotor behavior, the locomotor response to acute cocaine, or the initial sensitization of the locomotor response to cocaine over the first 4 cocaine treatment days. However, following 3 days abstinence the locomotor response to the cocaine challenge returned to their original levels in the AAV-shPdyn rats while remaining heightened in the AAV-shScr rats. These results suggest that dynorphin in a very specific area of the nucleus accumbens contributes to depressive-like states and may be involved in neuroadaptations in the NAcc that contribute to the development of cocaine addiction as a persistent and lasting condition.

Highlights

Dynorphins, a class of opioid peptides that arise from the precursor protein prodynorphin, have been implicated in emotional control and stress responses in general [1], and in the negative emotional states associated with drug addiction in particular [2]
The recombinant adeno-associated viral (rAAV)-sequence targeted at the Pdyn transcript (shPdyn) vector led to a significant knockdown of Pdyn mRNA expression in the transduced region compared to the rAAV-shScr vector (79% reduction; t34 = 3.92; P,0.001; Fig 3)
This study was designed to examine the role of dynorphin in the nucleus accumbens (NAcc) in functions related to mood regulation and the stimulatory effects of cocaine, as it has been suggested that dynorphin mediates negative mood states and the dependence-related effects of repeated exposure to cocaine [1,2]

Summary

Introduction

Dynorphins, a class of opioid peptides that arise from the precursor protein prodynorphin (encoded by the Pdyn gene), have been implicated in emotional control and stress responses in general [1], and in the negative emotional states associated with drug addiction in particular [2]. Dynorphins are the primary endogenous ligands of kappa opioid receptors (KOR) and systemic or central KOR activation produces dysphoria in humans [3,4] and depressive-like behaviors in rodents, including increased elevated reward thresholds in the intracranial self-stimulation test (ICSS) [5], and increased immobilization in the forced swim test (FST) [6]. The dynorphin/KOR system appears to be involved in anxiety, as systemic administration of KOR antagonists to rodents dose-dependently reduces anxiety-like behavior in the elevated plus maze [10,11], the open field [11], and the fear-potentiated startle paradigm [10]. Studies making use of Pdyn KO mice showed mixed results, with some studies demonstrating anxiolytic-like behavior in the elevated plus maze, and open field test [12], while others showed increased anxiety-like behavior [13]

Methods

Results

Conclusion