Cocaine self-administration alters transcriptome-wide responses in the brain’s reward circuitry

Walker et al., Biological Psychiatry, 2018

Global changes in gene expression underlying circuit and behavioral dysregulation associated with cocaine addiction remain incompletely understood. Here, we show how a history of cocaine self-administration (SA) “re-programs” transcriptome-wide responses throughout the brain’s reward circuitry at baseline and in response to context and/or cocaine re-exposure after prolonged withdrawal (WD). We assigned male mice to one of six groups: saline/cocaine SA + 24 hr WD; or saline/cocaine SA + 30 d WD + an acute saline/cocaine challenge within the previous drug-paired context. RNA-sequencing was conducted on six interconnected brain reward regions. Using pattern analysis of gene expression and factor analysis of behavior, we identified genes that are strongly associated with addiction-related behaviors and uniquely altered by a history of cocaine SA. We then identified potential upstream regulators of these genes. We focused on three Patterns of gene expression that reflect responses to: a) acute cocaine, b) context re-exposure, and c) drug + context re-exposure. These Patterns revealed region-specific regulation of gene expression. Further analysis revealed that each of these gene expression Patterns correlated with an “Addiction Index”—a composite score of several addiction-like behaviors during cocaine SA—in a region-specific manner. CREB and nuclear receptor families were identified as key upstream regulators of genes associated with such behaviors. This comprehensive picture of transcriptome-wide regulation in the brain’s reward circuitry by cocaine SA and prolonged WD provides new insight into the molecular basis of cocaine addiction, which will guide future studies of the key molecular pathways involved.

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Granulocyte-colony stimulating factor controls neural and behavioral plasticity in response to cocaine

Calipari et al., Nature Communications, 2018

Cocaine addiction is characterized by dysfunction in reward-related brain circuits, leading to maladaptive motivation to seek and take the drug. There are currently no clinically available pharmacotherapies to treat cocaine addiction. Through a broad screen of innate immune mediators, we identify granulocyte-colony stimulating factor (G-CSF) as a potent mediator of cocaine-induced adaptations. Here we report that G-CSF potentiates cocaine-induced increases in neural activity in the nucleus accumbens (NAc) and prefrontal cortex. In addition, G-CSF injections potentiate cocaine place preference and enhance motivation to selfadminister cocaine, while not affecting responses to natural rewards. Infusion of G-CSF neutralizing antibody into NAc blocks the ability of G-CSF to modulate cocaine’s behavioral effects, providing a direct link between central G-CSF action in NAc and cocaine reward. These results demonstrate that manipulating G-CSF is sufficient to alter the motivation for cocaine, but not natural rewards, providing a pharmacotherapeutic avenue to manipulate addictive behaviors without abuse potential.

  Fig. 1 Serum multiplex analysis after self- and experimenter-administered cocaine in mice .  a  Timeline of experimenter-administered chronic cocaine injections.  b  Cocaine resulted in robust locomotor sensitization.  c  Timeline of cocaine self-administration in mice.  d  Average daily intake of cocaine across self-administration sessions.  e  Multiplex serum analysis of 32 chemokines, cytokines, and growth factors after experimenter- or self-administered cocaine. For each analyte, the heatmap depicts fold-change values compared to the respective saline group. Correlation heatmap of individual analyte levels with either locomotor sensitization (Day 10/Day 1) or daily intake of cocaine

Fig. 1 Serum multiplex analysis after self- and experimenter-administered cocaine in mice. a Timeline of experimenter-administered chronic cocaine injections. b Cocaine resulted in robust locomotor sensitization. c Timeline of cocaine self-administration in mice. d Average daily intake of cocaine across self-administration sessions. e Multiplex serum analysis of 32 chemokines, cytokines, and growth factors after experimenter- or self-administered cocaine. For each analyte, the heatmap depicts fold-change values compared to the respective saline group. Correlation heatmap of individual analyte levels with either locomotor sensitization (Day 10/Day 1) or daily intake of cocaine

  Fig. 5 G-CSF levels are increased by the selective activation of mPFC to NAc projections.   a  Experimental design of projection-specific DREADD stimulation. Mice were injected with a retrograde traveling CAV2-Cre virus in the NAc and a Cre-dependent hM3Dq-DREADD virus in either the mPFC or the VTA to allow for the specific stimulation of either mPFC to NAc or VTA to NAc.  b  Csf3 (G-CSF) mRNA levels in the NAc were increased after mPFC to NAc stimulation.  c  Csf3r (G-CSFR) mRNA levels in the NAc were increased only after mPFC to NAc stimulation.  d  Peripheral G-CSF serum levels were not affected by stimulation. 

Fig. 5 G-CSF levels are increased by the selective activation of mPFC to NAc projections. a Experimental design of projection-specific DREADD stimulation. Mice were injected with a retrograde traveling CAV2-Cre virus in the NAc and a Cre-dependent hM3Dq-DREADD virus in either the mPFC or the VTA to allow for the specific stimulation of either mPFC to NAc or VTA to NAc. b Csf3 (G-CSF) mRNA levels in the NAc were increased after mPFC to NAc stimulation. c Csf3r (G-CSFR) mRNA levels in the NAc were increased only after mPFC to NAc stimulation. d Peripheral G-CSF serum levels were not affected by stimulation. 

 
 

Dopaminergic Dynamics underlying sex-specific cocaine reward 

Calipari et al., Nature Communications, 2017

Although both males and females become addicted to cocaine, females transition to addiction faster and experience greater difficulties remaining abstinent. We demonstrate an oestrous cycle-dependent mechanism controlling increased cocaine reward in females. During oestrus, ventral tegmental area (VTA) dopamine neuron activity is enhanced and drives post translational modifications at the dopamine transporter (DAT) to increase the ability of cocaine to inhibit its function, an effect mediated by estradiol. Female mice conditioned to associate cocaine with contextual cues during oestrus have enhanced mesolimbic responses to these cues in the absence of drug. Using chemogenetic approaches, we increase VTA activity to mechanistically link oestrous cycle-dependent enhancement of VTA firing to enhanced cocaine affinity at DAT and subsequent reward processing. These data have implications for sexual dimorphism in addiction vulnerability and define a mechanism by which cellular activity results in protein alterations that contribute to dysfunctional learning and reward processing.

  Proposed schematic highlighting a potential mechanism for the activity-dependent changes in reward processing that occur during oestrus.  (1) The VTA to NAc pathway comprises dopaminergic neurons (purple) and other neuronal subpopulations (grey). (2) Dopamine neuron firing is enhanced during oestrus. (3) The increased activity of this pathway leads to downstream ERK activation and concomitant phosphorylation of Thr53 (blue) on DAT. (4) These changes in DAT lead to alterations in cocaine affinity, whereby cocaine is more able to bind to DAT and increase extracellular dopamine levels. This increased cocaine binding leads to increased dopamine levels in the NAc. (5) In vivo this drives increased associations between cocaine and contextual cues, which leads to enhanced cocaine CPP due to differences in the perceived rewarding value of cocaine.

Proposed schematic highlighting a potential mechanism for the activity-dependent changes in reward processing that occur during oestrus. (1) The VTA to NAc pathway comprises dopaminergic neurons (purple) and other neuronal subpopulations (grey). (2) Dopamine neuron firing is enhanced during oestrus. (3) The increased activity of this pathway leads to downstream ERK activation and concomitant phosphorylation of Thr53 (blue) on DAT. (4) These changes in DAT lead to alterations in cocaine affinity, whereby cocaine is more able to bind to DAT and increase extracellular dopamine levels. This increased cocaine binding leads to increased dopamine levels in the NAc. (5) In vivo this drives increased associations between cocaine and contextual cues, which leads to enhanced cocaine CPP due to differences in the perceived rewarding value of cocaine.

  Figure 5.  Download manuscript PDF below. 

Figure 5. Download manuscript PDF below. 

 

In vivo imaging identifies temporal signature of D1 and D2 Medium Spiny Neurons in cocaine reward

Calipari et al, Proceedings of the national academy of science, USA, 2016

The reinforcing and rewarding properties of cocaine are attributed to its ability to increase dopaminergic transmission in nucleus accumbens (NAc). This action reinforces drug taking and seeking and leads to potent and long-lasting associations between the rewarding effects of the drug and the cues associated with its availability. The inability to extinguish these associations is a key factor contributing to relapse. Dopamine produces these effects by controlling the activity of two subpopulations of NAc medium spiny neurons (MSNs) that are defined by their predominant expression of either dopamine D1 or D2 receptors. Previous work has demonstrated that optogenetically stimulating D1 MSNs promotes reward, whereas stimulating D2 MSNs produces aversion. However, we still lack a clear understanding of how the endogenous activity of these cell types is affected by cocaine and encodes information that drives drug-associated behaviors. Using fiber photometry calcium imaging we define D1 MSNs as the specific population of cells in NAc that encodes information about drug associations and elucidate the temporal profile with which D1 activity is increased to drive drug seeking in response to contextual cues. Chronic cocaine exposure dysregulates these D1 signals to both prevent extinction and facilitate reinstatement of drug seeking to drive relapse. Directly manipulating these D1 signals using designer receptors exclusively activated by designer drugs prevents contextual associations. Together, these data elucidate the responses of D1- and D2-type MSNs in NAc to acute cocaine and during the formation of context-reward associations and define how prior cocaine exposure selectively dysregulates D1 signaling to drive relapse.

  This work outlined the temporally signature of D1 and D2 medium spiny neuron encoding of reward information and how it is dysregulated by cocaine exposure to drive addictive behaviors. 

This work outlined the temporally signature of D1 and D2 medium spiny neuron encoding of reward information and how it is dysregulated by cocaine exposure to drive addictive behaviors. 

  Figure 2.  Download manuscript PDF below. 

Figure 2. Download manuscript PDF below.