Noradrenaline enhances the excitatory effects of dopamine on medial prefrontal cortex pyramidal neurons in rats

Noradrenergic regulation of cue-guided decision making and impulsivity is doubly dissociable across frontal brain regions

RATIONALE

Win-paired stimuli can promote risk taking in experimental gambling paradigms in both rats and humans. We previously demonstrated that atomoxetine, a noradrenaline reuptake inhibitor, and guanfacine, a selective α2A adrenergic receptor agonist, reduced risk taking on the cued rat gambling task (crGT), a rodent assay of risky choice in which wins are accompanied by salient cues. Both compounds also decreased impulsive premature responding.

OBJECTIVE

The key neural loci mediating these effects were unknown. The lateral orbitofrontal cortex (lOFC) and the medial prefrontal cortex (mPFC), which are highly implicated in risk assessment, action selection, and impulse control, receive dense noradrenergic innervation. We therefore infused atomoxetine and guanfacine directly into either the lOFC or prelimbic (PrL) mPFC prior to task performance.

RESULTS

When infused into the lOFC, atomoxetine improved decision making score and adaptive lose-shift behaviour in males, but not in females, without altering motor impulsivity. Conversely, intra-PrL atomoxetine improved impulse control in risk preferring animals of both sexes, but did not alter decision making. Guanfacine administered into the PrL, but not lOFC, also altered motor impulsivity in all subjects, though in the opposite direction to atomoxetine.

CONCLUSIONS

These data highlight a double dissociation between the behavioural effects of noradrenergic signaling across frontal regions with respect to risky choice and impulsive action. Given that the influence of noradrenergic manipulations on motor impulsivity could depend on baseline risk preference, these data also suggest that the noradrenaline system may function differently in subjects that are susceptible to the risk-promoting lure of win-associated cues.

Social defeat stress enhances the rewarding effects of cocaine through α1A adrenoceptors in the medial prefrontal cortex of mice

Various stressors potentiate the rewarding effects of cocaine and contribute to cocaine cravings. However, it remains unclear whether psychosocial stress enhances the rewarding effects of cocaine. Accordingly, this study employed a cocaine-conditioned place preference (CPP) paradigm combined with social defeat (SD) exposure to investigate the effects of acute SD stress on cocaine reward in male mice. We found that SD stress immediately before the posttest significantly increased cocaine CPP, and systemic blockade of α1 adrenoceptors, but not β adrenoceptors, suppressed this increase. Fiber photometry recordings with GRABNE1m sensors revealed increased noradrenaline (NA) levels in the medial prefrontal cortex (mPFC) in test mice in response to attacks by aggressor mice during SD. Moreover, the SD stress-induced enhancement of CPP was effectively suppressed by intra-mPFC infusion of an α1 adrenoceptor antagonist. In vitro whole-cell recordings demonstrated that silodosin, an α1A, but not α1B or α1D, adrenoceptor antagonist, inhibited NA-induced depolarizing currents and facilitation of excitatory synaptic transmissions. Consistently, intra-mPFC silodosin infusion significantly suppressed the SD stress-induced CPP enhancement. Conversely, intra-mPFC infusion of α1A adrenoceptor agonist augmented cocaine CPP in the absence of stress exposure. Additionally, intranasal silodosin administration attenuated the SD stress-induced enhancement of CPP, and chemogenetic inhibition of mPFC excitatory neurons also suppressed the SD stress-induced CPP enhancement. Together, these findings suggest that NA stimulation of α1A adrenoceptors and the subsequent activation of mPFC pyramidal cells may contribute to SD stress-induced amplification of the rewarding effects of cocaine, and intranasal silodosin administration may hold therapeutic potential for mitigating stress-associated cocaine craving.

Noradrenergic stimulation of α1 adrenoceptors in the medial prefrontal cortex mediates acute stress-induced facilitation of seizures in mice

Stress is one of the critical facilitators for seizure induction in patients with epilepsy. However, the neural mechanisms underlying this facilitation remain poorly understood. Here, we investigated whether noradrenaline (NA) transmission enhanced by stress exposure facilitates the induction of medial prefrontal cortex (mPFC)-originated seizures. In mPFC slices, whole-cell current-clamp recordings revealed that bath application of picrotoxin induced sporadic epileptiform activities (EAs), which consisted of depolarization with bursts of action potentials in layer 5 pyramidal cells. Addition of NA dramatically shortened the latency and increased the number of EAs. Simultaneous whole-cell and field potential recordings revealed that the EAs are synchronous in the mPFC local circuit. Terazosin, but not atipamezole or timolol, inhibited EA facilitation, indicating the involvement of α₁ adrenoceptors. Intra-mPFC picrotoxin infusion induced seizures in mice in vivo. Addition of NA substantially shortened the seizure latency, while co-infusion of terazosin into the mPFC inhibited the effect of NA. Finally, acute restraint stress shortened the latency of intra-mPFC picrotoxin infusion-induced seizures, whereas prior infusion of terazosin reversed this stress-induced shortening of seizure latency. Our findings suggest that stress facilitates the induction of mPFC-originated seizures via NA stimulation of α₁ adrenoceptors.

Spatial contextual recognition memory updating is modulated by dopamine release in the dorsal hippocampus from the locus coeruleus

Detecting novelty is critical to consolidate declarative memories, such as spatial contextual recognition memory. It has been shown that stored memories, when retrieved, are susceptible to modification, incorporating new information through an updating process. Catecholamine release in the hippocampal CA1 region consolidates an object location memory (OLM). This work hypothesized that spatial contextual memory updating could be changed by decreasing catecholamine release in the hippocampal CA1 terminals from the locus coeruleus (LC). In a mouse model expressing Cre-recombinase under the control of the tyrosine hydroxylase (TH) promoter, memory updating was impaired by photoinhibition of the CA1 catecholaminergic terminals from the LC (LC-CA1) but not from the ventral tegmental area (VTA-CA1). In vivo microdialysis confirmed that the extracellular concentration of both dopamine (DA) and noradrenaline (NA) decreased after photoinhibition of the LC-CA1 terminals (but not VTA-CA1) during the OLM update session. Furthermore, DA D1/D5 and beta-adrenergic receptor antagonists disrupted behavior, but only the former impaired memory updating. Finally, photoinhibition of LC-CA1 terminals suppressed long-term potentiation (LTP) induction in Schaffer's collaterals as a plausible mechanism for memory updating. These data will help understand the underpinning mechanisms of DA in spatial contextual memory updating.

Noradrenergic circuits and signaling in substance use disorders

The central noradrenergic system innervates almost all regions of the brain and, as such, is well positioned to modulate many neural circuits implicated in behaviors and physiology underlying substance use disorders. Ample pharmacological evidence demonstrates that α1, α2, and β adrenergic receptors may serve as therapeutic targets to reduce drug -seeking behavior and drug withdrawal symptoms. Further, norepinephrine is a key modulator of the stress response, and stress has been heavily implicated in reinstatement of drug taking. In this review, we discuss recent advances in our understanding of noradrenergic circuitry and noradrenergic receptor signaling in the context of opioid, alcohol, and psychostimulant use disorders.

Role of noradrenergic transmission within the ventral bed nucleus of the stria terminalis in nicotine withdrawal-induced aversive behavior

AIM

Cessation of smoking induces nicotine withdrawal symptoms such as anxiety, depression, and dysphoria, which could lead to smoking relapse. In the present study, we examined the role of noradrenergic transmission within the ventral bed nucleus of the stria terminalis (vBNST) on nicotine withdrawal-induced aversive behavior.

METHODS

Nicotine dependence in rats was established by subcutaneous implantation with a nicotine-filled osmotic minipump on day 1. Nicotine withdrawal was precipitated by administration of the nicotine receptor antagonist, mecamylamine (3.0 mg/kg, s.c.), on day 15. Nicotine withdrawal-induced intra-vBNST noradrenaline release and aversive behavior were examined by in vivo microdialysis and a conditioned place aversion (CPA) test, respectively.

RESULTS

Intra-vBNST noradrenaline release was significantly increased during nicotine withdrawal. Nicotine withdrawal induced aversive behavior, which was attenuated by intra-vBNST injection of the β-adrenoceptor antagonist, timolol.

CONCLUSIONS

These results suggest that enhanced noradrenergic transmission via β-adrenoceptors in the vBNST plays a crucial role in nicotine withdrawal-induced aversive behavior.

Medial prefrontal cortical control of reward- and aversion-based behavioral output: Bottom-up modulation

How does the brain guide our actions? This is a complex issue, where the medial prefrontal cortex (mPFC) plays a crucial role. The mPFC is essential for cognitive flexibility and decision making. These functions are related to reward- and aversion-based learning, which ultimately drive behavior. Though, cortical projections and modulatory systems that may regulate those processes in the mPFC are less understood. How does the mPFC regulate approach-avoidance behavior in the case of conflicting aversive and appetitive stimuli? This is likely dependent on the bottom-up neuromodulation of the mPFC projection neurons. In this review, we integrate behavioral-, pharmacological-, and viral-based circuit manipulation data showing the involvement of mPFC dopaminergic, noradrenergic, cholinergic, and serotoninergic inputs in reward and aversion processing. Given that an incorrect balance of reward and aversion value could be a key problem in mental diseases such as substance use disorders, we discuss outstanding questions for future research on the role of mPFC modulation in reward and aversion.

Role of 5-HT1A receptor-mediated serotonergic transmission in the medial prefrontal cortex in acute restraint stress-induced augmentation of rewarding memory of cocaine in mice

Stress enhances cocaine craving. We recently reported that acute restraint stress increases cocaine conditioned place preference (CPP) in mice; however, the underlying mechanisms remain unclear. This study aimed to examine the role of serotonergic transmission in the medial prefrontal cortex (mPFC) in cocaine CPP enhancement by acute restraint stress, which increases extracellular serotonin (5-HT) levels in the mPFC. Intra-mPFC infusion of the selective serotonin reuptake inhibitor (S)-citalopram prior to the test session significantly increased the cocaine CPP score under non-stressed conditions. This is indicative of the substantial role of increased mPFC 5-HT levels in cocaine CPP enhancement. Moreover, intra-mPFC and systemic administration of the 5-HT_1A receptor antagonist WAY100635 immediately before restraint stress exposure significantly attenuated stress-induced cocaine CPP enhancement. Our findings suggest that enhanced serotonergic transmission via 5-HT_1A receptors in the mPFC is involved in acute stress-induced augmentation of rewarding memory of cocaine; moreover, the 5-HT_1A receptor could be a therapeutic target for stress-induced cocaine craving.

Noradrenaline enhances the excitatory effects of dopamine on medial prefrontal cortex pyramidal neurons in rats

Aim

Our previous studies showed that exposure to acute restraint stress enhanced cocaine‐induced conditioned place preference (cocaine‐CPP) and suggested the possibility that co‐activation of adrenergic transmission boosts the increase in medial prefrontal cortex (mPFC) neuronal activity by the activation of dopaminergic transmission. To examine this possibility, the effects of the co‐treatment with dopamine (DA) and noradrenaline (NA) on mPFC neurons were compared with those of treatment with DA alone using whole‐cell patch‐clamp recordings.

Methods

The effects of DA alone and a mixture of DA and NA on the membrane potentials and spontaneous excitatory postsynaptic currents (sEPSCs) were examined by electrophysiological recordings of mPFC pyramidal neurons in brain slices of male Sprague Dawley rats. Extracellular DA and NA levels in the mPFC during and after restraint stress exposure were also examined by in vivo microdialysis.

Results

Dopamine significantly produced depolarizing effects on mPFC neurons and tended to increase sEPSC frequency. Co‐administration of NA with DA produced stronger depolarizing effects and significantly increased sEPSC frequency. The findings suggest that the additional depolarizing effect of NA on DA‐responsive neurons, rather than the excitation of DA‐nonresponsive neurons by NA, contributes to the stronger effect of co‐treatment of NA with DA.

Conclusion

The present study suggests that NA released by restraint stress exposure cooperates with DA to stimulate DA‐responsive neurons in the mPFC, thereby causing the stress‐induced enhancement of cocaine‐CPP.

Our previous studies showed that exposure to acute restraint stress enhanced cocaine‐induced conditioned place preference (cocaine‐CPP). The present study revealed that noradrenaline enhanced the excitatory effects of dopamine on medial prefrontal cortex (mPFC) pyramidal neurons in rats. Noradrenaline released by restraint stress exposure may cooperate with dopamine to stimulate dopamine‐responsive neurons in the mPFC, thereby causing the stress‐induced enhancement of cocaine‐CPP.