The subthalamic nucleus keeps you high on emotion: behavioral consequences of its inactivation

A role for the subthalamic nucleus in aversive learning

The subthalamic nucleus (STN) is critical for behavioral control; its dysregulation consequently correlated with neurological and neuropsychiatric disorders, including Parkinson's disease. Deep brain stimulation (DBS) targeting the STN successfully alleviates parkinsonian motor symptoms. However, low mood and depression are affective side effects. STN is adjoined with para-STN, associated with appetitive and aversive behavior. DBS aimed at STN might unintentionally modulate para-STN, causing aversion. Alternatively, the STN mediates aversion. To investigate causality between STN and aversion, affective behavior is addressed using optogenetics in mice. Selective promoters allow dissociation of STN (e.g., Pitx2) vs. para-STN (Tac1). Acute photostimulation results in aversion via both STN and para-STN. However, only STN stimulation-paired cues cause conditioned avoidance and only STN stimulation interrupts on-going sugar self-administration. Electrophysiological recordings identify post-synaptic responses in pallidal neurons, and selective photostimulation of STN terminals in the ventral pallidum replicates STN-induced aversion. Identifying STN as a source of aversive learning contributes neurobiological underpinnings to emotional affect.

Peer presence and familiarity as key factors to reduce cocaine intake in both rats and humans: an effect mediated by the subthalamic nucleus

RATIONALE

Stimulant use, including cocaine, often occurs in a social context whose influence is important to understand to decrease intake and reduce associated harms. Although the importance of social influence in the context of drug addiction is known, there is a need for studies assessing its neurobiological substrate and for translational research.

OBJECTIVES

Here, we explored the influence of peer presence and familiarity on cocaine intake and its neurobiological basis. Given the regulatory role of the subthalamic nucleus (STN) on cocaine intake and emotions, we investigated its role on such influence of social context on cocaine intake.

METHODS

We first compared cocaine consumption in various conditions (with no peer present or with peers with different characteristics: abstinent peer or drug-taking peer, familiar or not, cocaine-naive or not, dominant or subordinate) in rats (n = 90). Then, with a translational approach, we assessed the influence of the social context (alone, in the group, in a dyad with familiar or non-familiar peers) on drug intake in human drug users (n = 77).

RESULTS

The drug consumption was reduced when a peer was present, abstinent, or drug-taking as well, and further diminished when the peer was non-familiar. The presence of a non-familiar and drug-naive peer represents key conditions to diminish cocaine intake. The STN lesion by itself reduced cocaine intake to the level reached in presence of a non-familiar naive peer and affected social cognition, positioning the STN as one neurobiological substrate of social influence on drug intake. Then, the human study confirmed the beneficial effect of social presence, especially of non-familiar peers.

CONCLUSION

Our results indirectly support the use of social interventions and harm reduction strategies and position the STN as a key cerebral structure to mediate these effects.

Evidence for a vocal signature in the rat and its reinforcing effects: a key role for the subthalamic nucleus

Although rodents have a well-structured vocal form of communication, like humans and non-human primates, there is, to date, no evidence for a vocal signature in the well-known 50- and 22-kHz ultrasonic vocalizations (USVs) emitted by rats. Here, we show that rats can recognize the identity of the USV emitter since they choose to preferentially self-administer playback of 50-kHz USVs emitted by a stranger rat over those of their cagemate. In a second experiment, we show that only stranger, but not familiar, 50-kHz USVs reduce cocaine self-administration. Finally, to study the neurobiological substrate of these processes, we have shown that subthalamic nucleus (STN)-lesioned rats did not lever press much for any USV playback, whatever their emotional valence, nor did they seem able to differentiate familiar from stranger peer. Advocating for the existence of a vocal signature in rats, these results highlight the importance of ultrasonic communication in the socio-affective influence of behaviour, such as the influence of proximal social factors on drug consumption and confirm the role of the STN on this influence.

Evidence for a vocal signature in the rat and its reinforcing effects: a key role for the subthalamic nucleus

Although rodents have a well-structured vocal form of communication, like humans and non-human primates, there is, to date, no evidence for a vocal signature in the well-known 50- and 22-kHz ultrasonic vocalizations (USVs) emitted by rats. Here, we show that rats can recognize the identity of the USV emitter since they choose to preferentially self-administer playback of 50-kHz USVs emitted by a stranger rat over those of their cagemate. In a second experiment, we show that only stranger, but not familiar, 50-kHz USVs reduce cocaine self-administration. Finally, to study the neurobiological substrate of these processes, we have shown that subthalamic nucleus (STN)-lesioned rats did not lever press much for any USV playback, whatever their emotional valence, nor did they seem able to differentiate familiar from stranger peer. Advocating for the existence of a vocal signature in rats, these results highlight the importance of ultrasonic communication in the socio-affective influence of behaviour, such as the influence of proximal social factors on drug consumption and confirm the role of the STN on this influence.

Clinical Impact of Deep Brain Stimulation on the Autonomic System in Patients with Parkinson's Disease

Background

The role of deep brain stimulation (DBS) in the management of motor symptoms in patients with Parkinson's disease is well defined. However, it is becoming increasingly clear that DBS can either improve or worsen a number of non-motor phenomena.

Objectives

We examined the published literature to better understand the effects on autonomic symptoms following DBS of the subthalamic nucleus and the globus pallidus interna.

Methods

We conducted a PubMed search of studies regarding the effects of DBS on the autonomic system published from January 2001. We searched for the following terms and their combinations: Parkinson's disease, deep brain stimulation, subthalamic nucleus, globus pallidus interna, autonomic dysfunction.

Results

Most studies reported in the literature focus on DBS targeting the subthalamic nucleus, with particular emphasis on favorable outcomes regarding gastrointestinal function and bladder control. However, the emergence or worsening of autonomic symptoms in subgroups of patients has also been documented. More controversial is the effect of stimulation on the cardiovascular, pulmonary, and thermo-regulatory systems as well as sexual functioning. Data regarding the influence of DBS on the autonomic system when the target is the globus pallidus interna is less forthcoming, with target selection varying according to centre and clinical indication.

Conclusions

DBS appears to affect the autonomic nervous system, with varying degrees of influence, which may or may not be clinically beneficial for the patient. A better understanding of these effects could help personalize stimulation for individual patients with autonomic disorders and/or avoid autonomic symptoms in susceptible patients.

Subthalamic nucleus mediates the modulation on cocaine self-administration induced by ultrasonic vocalization playback in rats

Drug intake is known to be under the influence of social context. We have recently shown that presence of a peer influences drug intake in both rats and humans. Whether or not social acoustic communications between the peers play a role during cocaine or sucrose self-administration (SA) was investigated here using playback of ultrasonic vocalizations (USVs) at 50 and 22 kHz, conveying, respectively, positive and negative internal affective states in adult rats. To assess the neurobiological substrate of a potential USV influence on drug and food intake, we tested the effects of subthalamic nucleus (STN) lesions, given its role in emotional and motivational processes. In sham-control rats, playback of USV associated with positive affective states induced long-term decreased cocaine consumption, while USV associated with negative affective states induced short-term increase. Interestingly, no effect of USV playback was observed on sucrose intake, whatever the frequency. STN lesions abolished the influence of USV on cocaine intake, highlighting the influence of STN in emotional processes induced by USV emitted by a peer. These results show how acoustic social communication is important to regulate drug intake in rats and how STN modulation could interfere with addiction processes.

Posttraumatic Stress Disorder is associated with altered reward mechanisms during the anticipation and the outcome of monetary incentive cues

BACKGROUND

Recent studies suggest that Posttraumatic Stress Disorder (PTSD) might be associated with dysfunctional reward circuitry. However, further research is needed to understand the key role of the reward system in PTSD symptomatology.

METHODS

Twenty participants with PTSD and 21 Trauma-Exposed matched Controls (TECs) completed the Monetary Incentive Delay (MID) task during an MRI session. Reaction times (RTs) and hit rates were recorded. Brain activity was investigated during the anticipation and the outcome of monetary gains and losses.

RESULTS

During the anticipation of monetary loss, PTSD participants had higher RTs than TECs. However, the groups did not differ at the neurofunctional level. During successful avoidance of monetary loss, PTSD patients showed higher activation than TECs in the left caudate nucleus. During the anticipation of monetary gains, no differences in RTs were found between groups. PTSD patients had specific activations in the right amygdala, nucleus accumbens, putamen, and middle frontal gyrus (p < 0.05 family-wise error (FWE)-corrected), while TECs had specific activation in the anterior cingulate cortex. When obtaining monetary gains, PTSD patients had specific activation in the caudate nucleus, while TECs had specific activations in the right hypothalamus, subthalamic nucleus, and left inferior frontal gyrus.

CONCLUSION

For the first time, functional brain activation during both the anticipation and the outcome of monetary rewards is reported altered in PTSD patients. These alterations might be associated with the complex symptomatology of PTSD.

Translating striatal activity from brain slice to whole animal neurophysiology: A guide for neuroscience research integrating diverse levels of analysis

An important goal of this review is highlighting research in neuroscience as examples of multilevel functional and anatomical analyses addressing basic science issues and applying results to the understanding of diverse disorders. The research of Dr. Michael Levine, a leader in neuroscience, exemplifies this approach by uncovering fundamental properties of basal ganglia function and translating these findings to clinical applications. The review focuses on neurophysiological research connecting results from in vitro and in vivo recordings. A second goal is to utilize these research connections to produce novel, accurate descriptions for corticostriatal processing involved in varied, complex functions. Medium spiny neurons in striatum act as integrators combining input with baseline activity creating motivational "events." Basic research on corticostriatal synapses is described and links developed to issues with clinical relevance such as inhibitory gating, self-injurious behavior, and relative reward valuation. Work is highlighted on dopamine-glutamate interactions. Individual medium spiny neurons express both D₁ and D₂ receptors and encode information in a bivalent manner depending upon the mix of receptors involved. Current work on neurophysiology of reward processing has taken advantage of these basic approaches at the cellular and molecular levels. Future directions in studying physiology of reward processing and action sequencing could profit by incorporating the divergent ways dopamine modulates incoming neurochemical signals. Primary investigators leading research teams should mirror Mike Levine's efforts in "climbing the mountain" of scientific inquiry by performing analyses at different levels of inquiry, integrating the findings, and building comprehensive answers to problems unsolvable without this bold approach.

Social modulation of drug use and drug addiction

This review aims to demonstrate how social science and behavioral neurosciences have highlighted the influence of social interactions on drug use in animal models. In neurosciences, the effect of global social context that are distal from drug use has been widely studied. For human and other social animals such as monkeys and rodents, positive social interactions are rewarding, can overcome drug reward and, in all, protect from drug use. In contrast, as other types of stress, negative social experiences facilitate the development and maintenance of drug abuse. However, interest recently emerged in the effect of so-called "proximal" social factors, that is, social interactions during drug-taking. These recent studies have characterized the role of the drug considered, the sharing of drug experience and the familiarity of the peer which interaction are made with. We also examine the few studies regarding the sensorial mediator of social behaviors and critically review the neural mediation of social factors on drug use. However, despite considerable characterization of the factors modulating distal influences, the mechanisms for proximal influences on drug use remain largely unknown. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Subthalamic nucleus high frequency stimulation prevents and reverses escalated cocaine use

One of the key features of addiction is the escalated drug intake. The neural mechanisms involved in the transition to addiction remain to be elucidated. Since abnormal neuronal activity within the subthalamic nucleus (STN) stands as potential general neuromarker common to impulse control spectrum deficits, as observed in obsessive-compulsive disorders, the present study recorded and manipulated STN neuronal activity during the initial transition to addiction (i.e., escalation) and post-abstinence relapse (i.e., re-escalation) in rats with extended drug access. We found that low-frequency (theta and beta bands) neuronal oscillations in the STN increase with escalation of cocaine intake and that either lesion or high-frequency stimulation prevents the escalation of cocaine intake. STN-HFS also reduces re-escalation after prolonged, but not short, protracted abstinence, suggesting that STN-HFS is an effective prevention for relapse when baseline rates of self-administration have been re-established. Thus, STN dysfunctions may represent an underlying mechanism for cocaine addiction and therefore a promising target for the treatment of addiction.

High-Frequency Stimulation of the Subthalamic Nucleus Blocks Compulsive-Like Re-Escalation of Heroin Taking in Rats

Opioid addiction, including addiction to heroin, has markedly increased in the past decade. The cost and pervasiveness of heroin addiction, including resistance to recovery from addiction, provide a compelling basis for developing novel therapeutic strategies. Deep brain stimulation may represent a viable alternative strategy for the treatment of intractable heroin addiction, particularly in individuals who are resistant to traditional therapies. Here we provide preclinical evidence of the therapeutic potential of high-frequency stimulation of the subthalamic nucleus (STN HFS) for heroin addiction. STN HFS prevented the re-escalation of heroin intake after abstinence in rats with extended access to heroin, an animal model of compulsive heroin taking. STN HFS inhibited key brain regions, including the substantia nigra, entopeduncular nucleus, and nucleus accumbens shell measured using brain mapping analyses of immediate-early gene expression and produced a robust silencing of STN neurons as measured using whole-cell recording ex vivo. These results warrant further investigation to examine the therapeutic effects that STN HFS may have on relapse in humans with heroin addiction.

Mu-opioid receptor activation in the medial shell of nucleus accumbens promotes alcohol consumption, self-administration and cue-induced reinstatement

Endogenous opioid signaling in ventral cortico-striatal-pallidal circuitry is implicated in elevated alcohol consumption and relapse to alcohol seeking. Mu-opioid receptor activation in the medial shell of the nucleus accumbens (NAc), a region implicated in multiple aspects of reward processing, elevates alcohol consumption while NAc opioid antagonists reduce it. However, the precise nature of the increases in alcohol consumption, and the effects of mu-opioid agonists on alcohol seeking and relapse are not clear. Here, we tested the effects of the mu-opioid agonist [D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin (DAMGO) in rat NAc shell on lick microstructure in a free-drinking test, alcohol seeking during operant self-administration, extinction learning and expression, and cue-reinforced reinstatement of alcohol seeking. DAMGO enhanced the number, but not the size of drinking bouts. DAMGO also enhanced operant alcohol self-administration and cue-induced reinstatement, but did not affect extinction learning or elicit reinstatement in the absence of cues. Our results suggest that mu-opioid agonism in NAc shell elevates alcohol consumption, seeking and conditioned reinforcement primarily by enhancing the incentive motivational properties of alcohol and alcohol-paired cues, rather than by modulating palatability, satiety, or reinforcement.

The Good and Bad Differentially Encoded within the Subthalamic Nucleus in Rats(1,2,3)

The subthalamic nucleus (STN) has only recently been added into the reward circuit. It has been shown to encode information regarding rewards (4% sucrose, 32% cocaine). To investigate the encoding of negative value, STN neurons were recorded in rats performing a task using discriminative stimuli predicting various rewards and especially during the replacement of a positive reinforcer (4% sucrose) by an aversive reinforcer (quinine). The results show that STN neurons encode information relative to both positive and aversive reinforcers via specialized subpopulations. The specialization is reset when the context is modified (change from a favorable context (4% vs 32% sucrose) to an unfavorable context (quinine vs 32% sucrose). An excitatory response to the cue light predicting the reward seems to be associated with the preferred situation, suggesting that STN plays a role in encoding the relative value of rewards. STN also seems to play a critical role in the encoding of execution error. Indeed, various subpopulations of neurons responding exclusively at early (i.e., "oops neurons") or at correct lever release were identified. The oops neurons respond mostly when the preferred reward (32% sucrose) is missed. Furthermore, STN neurons respond to reward omission, suggesting a role in reward prediction error. These properties of STN neurons strengthen its position in the reward circuit as a key cerebral structure through which reward-related processes are mediated. It is particularly important given the fact that STN is the target of surgical treatment for Parkinson's disease and obsessive compulsive disorders, and has been suggested for the treatment of addiction as well.

[Surgical strategy to rescue the addicts]

Since its successful application for the treatment of neurological disorders, deep brain stimulation (DBS) is currently also applied for the treatment of psychiatric disorders such as obsessive compulsive disorders or depression. DBS is being considered, or even applied, as a treatment for certain forms of addiction. We review here the cerebral structures aimed for such a strategy and discuss their respective positive and negative aspects.