Noradrenergic inputs from locus coeruleus to posterior ventral tegmental area are essential to support ethanol reinforcement

Noradrenergic mechanisms and circuitry of hyperkatifeia in alcohol use disorder

Hyperkatifeia, the manifestation of emotional distress or pain, is a conceptual framework gaining traction throughout the alcohol and other substance use fields as an important driver of addiction. It is well known that previous or current negative life experiences can serve as powerful motivators for excessive alcohol consumption and precipitate the development of an alcohol use disorder (AUD). A major hallmark of later stages of AUD is the emergence of hyperkatifeia during withdrawal, which can persist well into protracted abstinence to drive relapse. Given these complex interactions, understanding the specific neuroadaptations that lie at the intersection of hyperkatifeia and AUD can inform ongoing therapeutic development. Of particular interest is the monoamine norepinephrine (NE). Noradrenergic dysfunction is implicated in AUD, anxiety, chronic stress, depression, and emotional and physical pain. Importantly, there are key sexual dimorphisms within the noradrenergic system that are thought to differentially impact the development and trajectory of AUD in women and men. The present review discusses past and recent work on noradrenergic influences at each stage of the AUD cycle (binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation) through the lens of hyperkatifeia. Evidence from these studies support the prioritization of NE-specific drug development to treat AUD and the identification of AUD subpopulations that may benefit the most from these therapies (e.g., women and people with comorbid chronic pain or anxiety/stress disorders).

Response of nitrergic system in the brain of rat conditioned to intracranial self-stimulation

The role of nitrergic system in modulating the action of psychostimulants on reward processing is well established. However, the relevant anatomical underpinnings and scope of the involved interactions with mesolimbic dopaminergic system have not been clarified. Using immunohistochemistry, we track the changes in neuronal nitric oxide synthase (nNOS) containing cell groups in the animals conditioned to intracranial self-stimulation (ICSS) via an electrode implanted in the lateral hypothalamus-medial forebrain bundle (LH-MFB) area. An increase in the nNOS immunoreactivity was noticed in the cells and fibers in the ventral tegmental area (VTA) and nucleus accumbens shell (AcbSh), the primary loci of the reward system. In addition, nNOS was up-regulated in the nucleus accumbens core (AcbC), vertical limb of diagonal band (VDB), locus coeruleus (LC), lateral hypothalamus (LH), superficial gray layer (SuG) of the superior colliculus, and periaqueductal gray (PAG). The brain tissue fragments drawn from these areas showed a change in nNOS mRNA expression, but in opposite direction. Intracerebroventricular (icv) administration of nNOS inhibitor, 7-nitroindazole (7-NI) showed decreased lever press activity in a dose-dependent manner in ICSS task. While an increase in the dopamine (DA) and 3, 4-dihydroxyphenylacetic acid (DOPAC) efflux was noted in the microdialysates collected from the AcbSh of ICSS rats, pre-administration of 7-NI (icv route) attenuated the response. The study identifies nitrergic centers that probably mediate sensory, cognitive, and motor components of the goal-directed behavior.

Dopaminergic regulation of hippocampal plasticity, learning, and memory

The hippocampus is responsible for encoding behavioral episodes into short-term and long-term memory. The circuits that mediate these processes are subject to neuromodulation, which involves regulation of synaptic plasticity and local neuronal excitability. In this review, we present evidence to demonstrate the influence of dopaminergic neuromodulation on hippocampus-dependent memory, and we address the controversy surrounding the source of dopamine innervation. First, we summarize historical and recent retrograde and anterograde anatomical tracing studies of direct dopaminergic projections from the ventral tegmental area and discuss dopamine release from the adrenergic locus coeruleus. Then, we present evidence of dopaminergic modulation of synaptic plasticity in the hippocampus. Plasticity mechanisms are examined in brain slices and in recordings from in vivo neuronal populations in freely moving rodents. Finally, we review pharmacological, genetic, and circuitry research that demonstrates the importance of dopamine release for learning and memory tasks while dissociating anatomically distinct populations of direct dopaminergic inputs.

In-house fabrication of bipolar electrode-cannula assembly for electrical stimulation and drug delivery at the same site in rat brain

Strategies drawn at understanding the functional attributes of specific neural circuits often necessitate electrical stimulation and pharmacological manipulation at the same anatomical site. We describe a simple, inexpensive and reliable method to fabricate a bipolar electrode-cannula assembly for delivery of electric pulses and administration of neuroactive agents at the same site in the rat brain. The assembly consisting of a guide cannula, dummy cannula, internal cannula and bipolar electrode was fabricated using syringe needles, wires and simple electronic components. To test the usefulness of the device, it was implanted on the skull of a rat specifically targeting the posterior ventral tegmental area (pVTA). The rat was conditioned to press the lever in intracranial self-stimulation (ICSS) protocol in an operant chamber. The number of lever presses in a 30 min task was monitored. Intra-pVTA administration with bicuculline (GABA_A receptor antagonist) increased the lever press activity, while muscimol (GABA_A receptor agonist) had opposite effect. The results confirm that the group of neurons responding to the electrical stimulation probably receive GABAergic inputs. The device is light in weight, costs less than a dollar and can be fabricated from readily available components. It can serve a useful purpose in electrically stimulating any given target in the brain - before, during or after pharmacological manipulation at the same locus and may find application in neuropharmacological and neurobehavioral studies.

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.

Neurobiological Bases of Alcohol Consumption After Social Stress

The urge to seek and consume excessive alcohol is intensified by prior experiences with social stress, and this cascade can be modeled under systematically controlled laboratory conditions in rodents and non-human primates. Adaptive coping with intermittent episodes of social defeat stress often transitions to maladaptive responses to traumatic continuous stress, and alcohol consumption may become part of coping responses. At the circuit level, the neural pathways subserving stress coping intersect with those for alcohol consumption. Increasingly discrete regions and connections within the prefrontal cortex, the ventral and dorsal striatum, thalamic and hypothalamic nuclei, tegmental areas as well as brain stem structures begin to be identified as critical for reacting to and coping with social stress while seeking and consuming alcohol. Several candidate molecules that modulate signals within these neural connections have been targeted in order to reduce excessive drinking and relapse. In spite of some early clinical failures, neuropeptides such as CRF, opioids, or oxytocin continue to be examined for their role in attenuating stress-escalated drinking. Recent work has focused on neural sites of action for peptides and steroids, most likely in neuroinflammatory processes as a result of interactive effects of episodic social stress and excessive alcohol seeking and drinking.

Neuropeptide CART modulates dopamine turnover in the nucleus accumbens: Insights into the anatomy of rewarding circuits

Neuropeptide cocaine- and amphetamine-regulated transcript (CART) is known to influence the activity of the canonical mesolimbic dopaminergic pathway and modulate reward seeking behaviour. CART neurons of the lateral hypothalamus (LH) send afferents to the ventral tegmental area (VTA) and paraventricular thalamic nucleus (PVT) and these nuclei, in turn, send secondary projections to nucleus accumbens. We try to dissect the precise sites of CART's action in these circuits in promoting reward. Rats were implanted with bipolar electrode targeted at the lateral hypothalamus-medial forebrain bundle (LH-MFB) and trained to press the lever through intracranial self-stimulation (ICSS) protocol. CART (55-102) administered directly into posterior VTA (pVTA) or PVT of the conditioned rats significantly increased the number of lever presses, indicating reward-promoting activity of the peptide. Concomitant increase in dopamine (DA) and 3, 4-dihydroxyphenylacetic acid (DOPAC) efflux was noted in the microdialysate collected from the nucleus accumbens shell (AcbSh). On the other hand, immunoneutralization of endogenous CART with CART antibodies injected directly in the pVTA or PVT reduced the lever press activity as well as DA and DOPAC efflux in the AcbSh. Injection of CART (1-39) in pVTA or PVT was ineffective. We suggest that CART cells in the LH-MFB area send afferents to (a) pVTA and influence dopaminergic neurons projecting to AcbSh and (b) PVT, from where the secondary neurons may feed into the AcbSh. Excitation of the CARTergic pathway to the pVTA as well as the PVT seems to promote DA release in the AcbSh and contribute to the generation of reward.

Stress Alters the Effect of Alcohol on Catecholamine Dynamics in the Basolateral Amygdala

The current rodent study applied in vivo fast-scan cyclic voltammetry (FSCV), paired with a pharmacological approach, to measure the release of the catecholamines (CA) dopamine (DA) and norepinephrine (NE) in the basolateral amygdala (BLA) following locus coeruleus (LC) stimulation. The primary goal was to determine if exposure to either social (social defeat) or non-social (forced swim) stress altered LC-evoked catecholamine release dynamics in the BLA. We used idazoxan (α2 adrenergic receptor antagonist) and raclopride (D₂ dopamine receptor antagonist) to confirm the presence of NE and DA, respectively, in the measured CA signal. In non-stressed rats, injection of idazoxan, but not raclopride, resulted in a significant increase in the detected CA signal, indicating the presence of NE but not DA. Following exposure to either stress paradigm, the measured CA release was significantly greater after injection of either drug, suggesting the presence of both NE and DA in the LC-induced CA signal after social or non-social stress. Furthermore, acute administration of alcohol significantly decreased the CA signal in stressed rats, while it did not have an effect in naïve animals. Together, these data reveal that, while LC stimulation primarily elicits NE release in the BLA of control animals, both social and non-social stress unmask a novel dopaminergic component of LC catecholamine signaling. Future studies will be needed to identify the specific neural mechanism(s) responsible for these plastic changes in LC-BLA catecholamine signaling and to assess the possible contribution of these changes to the maladaptive behavioral phenotypes that develop following exposure to these stressors.

Autophagy status as a gateway for stress-induced catecholamine interplay in neurodegeneration

The catecholamine-containing brainstem nuclei locus coeruleus (LC) and ventral tegmental area (VTA) are critically involved in stress responses. Alterations of catecholamine systems during chronic stress may contribute to neurodegeneration, including cognitive decline. Stress-related catecholamine alterations, while contributing to anxiety and depression, might accelerate neuronal degeneration by increasing the formation of toxic dopamine and norepinephrine by-products. These, in turn, may impair proteostasis within a variety of cortical and subcortical areas. In particular, the molecular events governing neurotransmission, neuroplasticity, and proteostasis within LC and VTA affect a variety of brain areas. Therefore, we focus on alterations of autophagy machinery in these nuclei as a relevant trigger in this chain of events. In fact, these catecholamine-containing areas are mostly prone to autophagy-dependent neurodegeneration. Thus, we propose a dynamic hypothesis according to which stress-induced autophagy alterations within the LC-VTA network foster a cascade towards early neurodegeneration within these nuclei.

Altered Extended Locus Coeruleus and Ventral Tegmental Area Networks in Boys with Autism Spectrum Disorders: A Resting-State Functional Connectivity Study

INTRODUCTION

Previous studies have suggested that cerebral projections of the norepinephrine (NE) and dopamine (DA) systems have important etiology and treatment implications for autism spectrum disorder (ASD).

METHODS

We used functional magnetic resonance imaging to evaluate spontaneous resting state functional connectivity in boys aged 7-15 years with ASD (n=86) and age-, intelligence quotient-matched typically developing boys (TD, n=118). Specifically, we investigated functional connectivity of the locus coeruleus (LC) and ventral tegmental area (VTA), the main source projection of neurotransmitters NE and DA, respectively.

RESULTS

1) Both the LC and VTA showed reduced connectivity with the postcentral gyrus (PoCG) in boys with ASD, reflecting the potential roles of NE and DA in modulating the function of the somatosensory cortex in boys with ASD. 2) The VTA had increased connectivity with bilateral thalamus in ASD; this alteration was correlated with repetitive and restrictive features. 3) Altered functional connectivity of both the LC and VTA with brain regions such as the angular gyrus (AG), middle temporal gyrus visual area (MT/V5), and occipital face area (OFA) in ASD group.

DISCUSSION

Our findings implicate the role of LC-NE and VTA-DA systems from the perspective of functional neuroimaging and may shed light on pharmacological studies targeting NE and DA for the treatment of autism in the future.

Behavioral, neurobiological, and neurochemical mechanisms of ethanol self-administration: A translational review

Alcohol use disorder has multiple characteristics including excessive ethanol consumption, impaired control over drinking behaviors, craving and withdrawal symptoms, compulsive seeking behaviors, and is considered a chronic condition. Relapse is common. Determining the neurobiological targets of ethanol and the adaptations induced by chronic ethanol exposure is critical to understanding the clinical manifestation of alcohol use disorders, the mechanisms underlying the various features of the disorder, and for informing medication development. In the present review, we discuss ethanol's interactions with a variety of neurotransmitter systems, summarizing findings from preclinical and translational studies to highlight recent progress in the field. We then describe animal models of ethanol self-administration, emphasizing the value, limitations, and validity of commonly used models. Lastly, we summarize the behavioral changes induced by chronic ethanol self-administration, with an emphasis on cue-elicited behavior, the role of ethanol-related memories, and the emergence of habitual ethanol seeking behavior.

Autophagy-Based Hypothesis on the Role of Brain Catecholamine Response During Stress

Stressful events, similar to abused drugs, significantly affect the homeostatic balance of the catecholamine brain systems while activating compensation mechanisms to restore balance. In detail, norepinephrine (NE)- and dopamine (DA)-containing neurons within the locus coeruleus (LC) and ventral tegmental area (VTA), are readily and similarly activated by psychostimulants and stressful events involving neural processes related to perception, reward, cognitive evaluation, appraisal, and stress-dependent hormonal factors. Brain catecholamine response to stress results in time-dependent regulatory processes involving mesocorticolimbic circuits and networks, where LC-NE neurons respond more readily than VTA-DA neurons. LC-NE projections are dominant in controlling the forebrain DA-targeted areas, such as the nucleus accumbens (NAc) and medial pre-frontal cortex (mPFC). Heavy and persistent coping demand could lead to sustained LC-NE and VTA-DA neuronal activity, that, when persisting chronically, is supposed to alter LC-VTA synaptic connections. Increasing evidence has been provided indicating a role of autophagy in modulating DA neurotransmission and synaptic plasticity. This alters behavior, and emotional/cognitive experience in response to drug abuse and occasionally, to psychological stress. Thus, relevant information to address the role of stress and autophagy can be drawn from psychostimulants research. In the present mini-review we discuss the role of autophagy in brain catecholamine response to stress and its dysregulation. The findings here discussed suggest a crucial role of regulated autophagy in the response and adaptation of LC-NE and VTA-DA systems to stress.

Modulation of serotonin and noradrenaline in the BLA by pindolol reduces long-term ethanol intake

Repeated cycles of binge-like alcohol consumption and abstinence change the activity of several neurotransmitter systems. Some of these changes are consolidated following prolonged alcohol use and are thought to play an important role in the development of dependence. We have previously shown that systemic administration of the dual beta-adrenergic antagonist and 5-HT_1A/1B partial agonist pindolol selectively reduces long-term but not short-term binge-like consumption of ethanol and alters excitatory postsynaptic currents in basolateral amygdala (BLA) principal neurons. The aim of this study was to investigate the effects of pindolol microinfusions in the BLA on long-term ethanol intake using the drinking-in-the-dark paradigm in mice. We also microinfused RU24969 (5-HT_1A/1B receptor partial agonist) and CGP12177 (β_1/2 adrenergic antagonist) following long-term ethanol intake and determined the densities of 5-HT_1A/1B receptors and β_1/2 adrenergic in the BLA following short-term (4 weeks) and long-term ethanol (12 weeks) consumption. We show that intra-BLA infusion of pindolol (1000 pmol/0.5 μl), RU24969 (0.3 and 3 pmol/0.5 μl) and CGP12177 (500 pmol/0.5 μl) produce robust decreases in long-term ethanol consumption. Additionally, we identified reduced β_1/2 adrenergic receptor expression and no change in 5-HT_1A/1B receptor density in the BLA of long-term ethanol-consuming mice. Collectively, our data highlight the effects of pindolol on voluntary, binge-like ethanol consumption behavior following long-term intake.

Cocaine- and amphetamine-regulated transcript (CART): A multifaceted neuropeptide

Over the last 35 years, the continuous discovery of novel neuropeptides has been the key to the better understanding of how the central nervous system has integrated with neuronal signals and behavioral responses. Cocaine and amphetamine-regulated transcript (CART) was discovered in 1995 in the rat striatum but later was found to be highly expressed in the hypothalamus. The widespread distribution of CART peptide in the brain complicated the understanding of the role played by this neurotransmitter. The main objective of the current compact review is to piece together the fragments of available information about origin, expression, distribution, projection, and function of CART peptides. Accumulative evidence suggests CART as a neurotransmitter and neuroprotective agent that is mainly involved in regulation of feeding, addiction, stress, anxiety, innate fear, neurological disease, neuropathic pain, depression, osteoporosis, insulin secretion, learning, memory, reproduction, vision, sleep, thirst and body temperature. In spite of the vast number of studies about the CART, the overall pictures about the CART functions are sketchy. First, there is a lack of information about cloned receptor, specific agonist and antagonist. Second, CART peptides are detected in discrete sets of neurons that can modulate countless activities and third; CART peptides exist in several fragments due to post-translational processing. For these reasons the overall picture about the CART peptides are sketchy and confounding.

CART modulates the effects of levodopa in rat model of Parkinson's disease

Parkinson's disease (PD) is an age-related disorder characterized by a progressive degeneration of dopaminergic neurons of substantia nigra (SN). The neuropeptide cocaine- and amphetamine-regulated transcript (CART) is known to closely interact with the dopamine system and regulate psychomotor activity. We screened the effectiveness of CART in reversing the symptoms of PD in a rat model. PD like condition was induced by administering 6-hydroxydopamine (6-OHDA) directly in the SN of the right side. Fifteen days later, intraperitoneal (IP) treatment with apomorphine hydrochloride to these rats, resulted in contralateral rotations in the rotation test chamber suggesting induction of PD-like symptoms. This action of apomorphine was significantly attenuated by intracerebroventricular (ICV) treatment with CART and potentiated by CART antibody. IP treatment with levodopa also produced contralateral rotation in PD induced rats, and showed anti-Parkinson-like action. Prior treatment with CART via ICV route potentiated the anti-Parkinsonian effects of levodopa, while CART antibody produced opposite effects. CART treatment per se, to PD induced rats produced ipsilateral rotations, suggesting that the peptide may promote the endogenous release of dopamine from intact neurons. While CART-immunoreactivity in arcuate nucleus, paraventricular nucleus, striatum, substantia nigra, ventral tegmental area and locus coeruleus was reduced in the PD induced rats, levodopa treatment restored the expression of CART-immunoreactivity in these nuclei. These results suggest that endogenous CART might closely interact with the dopamine containing SN-striatal pathway which is known to profoundly influence the motor system. The study underscores the importance of CART as a potential therapeutic agent in the treatment of PD.