Dopamine is differentially involved in the locomotor hyperactivity produced by manipulations of opioid, GABA and glutamate receptors in the median raphe nucleus

The Role of Vesicular Glutamate Transporter Type 3 in Social Behavior, with a Focus on the Median Raphe Region

Social behavior is important for our well-being, and its dysfunctions impact several pathological conditions. Although the involvement of glutamate is undeniable, the relevance of vesicular glutamate transporter type 3 (VGluT3), a specific vesicular transporter, in the control of social behavior is not sufficiently explored. Since midbrain median raphe region (MRR) is implicated in social behavior and the nucleus contains high amount of VGluT3+ neurons, we compared the behavior of male VGluT3 knock-out (KO) and VGluT3-Cre mice, the latter after chemogenetic MRR-VGluT3 manipulation. Appropriate control groups were included. Behavioral test battery was used for social behavior (sociability, social discrimination, social interaction, resident intruder test) and possible confounding factors (open field, elevated plus maze, Y-maze tests). Neuronal activation was studied by c-Fos immunohistochemistry. Human relevance was confirmed by VGluT3 gene expression in relevant human brainstem areas. VGluT3 KO mice exhibited increased anxiety, social interest, but also aggressive behavior in anxiogenic environment and impaired social memory. For KO animals, social interaction induced lower cell activation in the anterior cingulate, infralimbic cortex, and medial septum. In turn, excitation of MRR-VGluT3+ neurons was anxiolytic. Inhibition increased social interest 24 h later but decreased mobility and social behavior in aggressive context. Chemogenetic activation increased the number of c-Fos+ neurons only in the MRR. We confirmed the increased anxiety-like behavior and impaired memory of VGluT3 KO strain and revealed increased, but inadequate, social behavior. MRR-VGluT3 neurons regulated mobility and social and anxiety-like behavior in a context-dependent manner. The presence of VGluT3 mRNA on corresponding human brain areas suggests clinical relevance.

The Dopaminergic Cells in the Median Raphe Region Regulate Social Behavior in Male Mice

According to previous studies, the median raphe region (MRR) is known to contribute significantly to social behavior. Besides serotonin, there have also been reports of a small population of dopaminergic neurons in this region. Dopamine is linked to reward and locomotion, but very little is known about its role in the MRR. To address that, we first confirmed the presence of dopaminergic cells in the MRR of mice (immunohistochemistry, RT-PCR), and then also in humans (RT-PCR) using healthy donor samples to prove translational relevance. Next, we used chemogenetic technology in mice containing the Cre enzyme under the promoter of the dopamine transporter. With the help of an adeno-associated virus, designer receptors exclusively activated by designer drugs (DREADDs) were expressed in the dopaminergic cells of the MRR to manipulate their activity. Four weeks later, we performed an extensive behavioral characterization 30 min after the injection of the artificial ligand (Clozapine-N-Oxide). Stimulation of the dopaminergic cells in the MRR decreased social interest without influencing aggression and with an increase in social discrimination. Additionally, inhibition of the same cells increased the friendly social behavior during social interaction test. No behavioral changes were detected in anxiety, memory or locomotion. All in all, dopaminergic cells were present in both the mouse and human samples from the MRR, and the manipulation of the dopaminergic neurons in the MRR elicited a specific social response.

Therapeutic Effects of Quetiapine and 5-HT1A Receptor Agonism on Hyperactivity in Dopamine-Deficient Mice

Some diseases that are associated with dopamine deficiency are accompanied by psychiatric symptoms, including Parkinson’s disease. However, the mechanism by which this occurs has not been clarified. Previous studies found that dopamine-deficient (DD) mice exhibited hyperactivity in a novel environment. This hyperactivity is improved by clozapine and donepezil, which are used to treat psychiatric symptoms associated with dopamine deficiency (PSDD). We considered that DD mice could be used to study PSDD. In the present study, we sought to identify the pharmacological mechanism of PSDD. We conducted locomotor activity tests by administering quetiapine and drugs that have specific actions on serotonin (5-hydroxytryptamine [5-HT]) receptors and muscarinic receptors. Changes in neuronal activity that were induced by drug administration in DD mice were evaluated by examining Fos immunoreactivity. Quetiapine suppressed hyperactivity in DD mice while the 5-HT_1A receptor antagonist WAY100635 inhibited this effect. The number of Fos-positive neurons in the median raphe nucleus increased in DD mice that exhibited hyperactivity and was decreased by treatment with quetiapine and 5-HT_1A receptor agonists. In conclusion, hyperactivity in DD mice was ameliorated by quetiapine, likely through 5-HT_1A receptor activation. These findings suggest that 5-HT_1A receptors may play a role in PSDD, and 5-HT_1A receptor-targeting drugs may help improve PSDD.

Identification of novel target molecules of l-menthol

The present study used a binding assay to identify novel target biomolecules of l-menthol ([−]-menthol) that promote mouse ambulation. Among 88 different ligands to specific biomolecules examined, 0.1 mM l-menthol inhibited the binding of 13 ligands with relatively high inhibition rates. The assays showed that l-menthol acts on calcium channels, sodium channels, γ-aminobutyric acid type A (GABA_A) receptor, GABA transporter, dopamine transporter, dopamine D4 receptor, adenosine A2a receptor, α2A-adrenergic receptor, histamine H2 receptor, bombesin receptor, angiotensin AT1 receptor, vasopressin V2 receptor, and leukotriene B4 receptor over a similar concentration range. The inhibition constant (K_i) for l-menthol inhibition of binding of [³H]-WIN35,428 to the human recombinant dopamine transporter was 6.15 × 10⁻⁴ mol/L. The K_i for l-menthol inhibition of binding of [³H]-ethynylbicycloorthobenzoate (EBOB), a ligand of GABA_A receptor picrotoxin site, was 2.88 × 10⁻⁴ mol/L. These results should aid future research by providing clues for investigating the mechanisms underlying l-menthol activities, including the ambulation-promoting effect. The present results suggest that the dopamine transporter, adenosine A2a receptor, dopamine D4 receptor, α2A-adrenergic receptor, and GABA_A receptor are promising candidate molecules that are involved in the mechanisms underlying the psychostimulant-like effect of l-menthol.

Self-reported Health Diagnoses and Demographic Correlates With Kratom Use: Results From an Online Survey

OBJECTIVES

To determine whether diagnosed pre-existing health conditions correlate with Kratom demographics and use patterns.

METHODS

A cross-sectional, anonymous US national online survey was conducted among 8049 Kratom users in October, 2016 to obtain demographic, health, and Kratom use pattern information.

RESULTS

People who use Kratom to mitigate illicit drug dependence self-reported less pain and better overall health than individuals who used Kratom for acute/chronic pain. Self-reported improvements in pre-existing mental health symptoms (attention deficit and hyperactivity disorder/attention deficit disorder, anxiety, bipolar disorder, post-traumatic stress disorder, and depression) attributed to Kratom use were greater than those related to somatic symptoms (back pain, rheumatoid arthritis, acute pain, chronic pain, fibromyalgia). Demographic variables, including female sex, older age, employment status, and insurance coverage correlated with increased likelihood of Kratom use.

CONCLUSIONS

Kratom use may serve as a self-treatment strategy for a diverse population of patients with pre-existing health diagnoses. Healthcare providers need to be engaging with patients to address safety concerns and potential limitations of its use in clinical practice for specific health conditions.

Spontaneous Early Withdrawal Behaviors after Chronic 24-hour Free-Choice Access to Ethanol

AIMS

Abstinence after chronic alcohol consumption leads to withdrawal symptoms, which are exacerbated after repeated cycles of relapse. This study examined withdrawal-like behaviors after chronic ethanol drinking, with or without repeated cycles of deprivation.

METHODS

Male alcohol-preferring (P) rats had access to continuous ethanol (CE), chronic ethanol with repeated deprivation (RD), or remained ethanol naïve (EN). The RD group experienced seven cycles of 2 weeks of deprivation and 2 weeks of re-exposure to ethanol after an initial 6 weeks of ethanol access. Withdrawal was measured after an initial 24 h of ethanol re-exposure in the RD group, which coincided with the same day of ethanol access in the CE group. Withdrawal-like behavior was measured by (a) ethanol intake during the initial 24 h of re-exposure, (b) locomotor activity (LMA) in a novel field 9-13 h after removal of ethanol at the beginning of the fifth re-exposure cycle and (c) acoustic startle responding (ASR) 8-15 h after removal of ethanol at the beginning of the sixth re-exposure cycle.

RESULTS

The RD rats displayed a 1-h alcohol deprivation effect (ADE) (temporary ethanol increase), relative to CE rats, during the first to fourth and seventh re-exposure cycles. RD and CE rats displayed significant increases in LMA than EN rats. Regarding ASR, RD rats displayed significantly greater ASR relative to EN rats.

CONCLUSION

This study confirms that P rats meet the animal model criterion for ethanol-associated dependence, without a reliance on either behavioral (limited fluid access) or pharmacological (seizure threshold manipulation) challenges.

Mu Opioid Receptor Agonist DAMGO Produces Place Conditioning, Abstinence-induced Withdrawal, and Naltrexone-Dependent Locomotor Activation in Planarians

Unlike the behavioral effects planarians display when exposed to cocaine, amphetamines, cathinones, ethanol and sucrose, effects of opioid receptor agonists, especially mu opioid receptor agonists, are poorly defined in these flatworms. Here, we tested the hypothesis that planarians exposed to a selective mu opioid receptor agonist, DAMGO (0.1, 1, 10 µM), would display a triad of opioid-like effects (place conditioning, abstinence-induced withdrawal, and motility changes). DAMGO was selected versus morphine because of its greater mu opioid receptor selectivity. In place conditioning and abstinence experiments, the planarian light/dark test (PLDT) was utilized (i.e., planarians are placed into a petri dish containing water that is split into light and dark compartments and time spent in the compartments is determined). Planarians conditioned with DAMGO (1 µM) spent more time on the drug-paired side compared to water controls. In abstinence experiments, planarians exposed to DAMGO for 30 min were removed and then placed into water, where light avoidance (e.g. defensive responding) and depressant-like effects (i.e., decreased motility) were quantified. Compared to water controls, DAMGO-withdrawn planarians spent less time in the light (10 µM) and displayed decreased motility (1, 10 µM). Acute DAMGO exposure (1 µM) produced hypermotility that was antagonized by naltrexone (1, 10, 100 µM). In contrast, acute exposure to the kappa opioid receptor agonist U50,488H (0.1, 1, 10 µM) resulted in decreased motility. Our results show that a mu opioid agonist produces mammalian-like behavioral responses in planarians that may be related to addiction and suggest opioid-like behavioral effects are conserved in invertebrates.

The Psychoactive Agent Crocin Can Regulate Hypothalamic-Pituitary-Adrenal Axis Activity

Post-traumatic stress disorder (PTSD) occurs following life-threatening events. The activity of the hypothalamic-pituitary-adrenal (HPA) axis, which serves as the first line of defense against stress, is dysfunctional in this disorder. The current study aimed to investigate the role of Crocin in normalizing HPA function in an animal model of PTSD induced by electric foot shock. Rats were treated with Crocin 5 min prior to stress induction. The stimulus was re-introduced after 21 days, and we measured individual behaviors such as sniffing, rearing, grooming, and freezing. Enzyme-linked immunosorbent assays were performed to measure plasma levels of Corticosterone. On day 28, after rats were weighed and sacrificed, the adrenal and thymus glands were removed and subjected to real-time polymerase chain reaction to quantify the gene expression of corticotrophin-releasing hormone (CRH), glucocorticoid receptor (GluR), and arginine vasopressin (AVP). Our results demonstrate that rats re-exposed to a stressor developed characteristic symptoms of PTSD, but these were attenuated by Crocin. Treated rats showed significant changes in CRH expression in the hypothalamus, GluR expression in the pituitary, plasma Corticosterone levels, and freezing behavior. Together, these findings suggest that Crocin can regulate HPA axis activity in PTSD. It may serve an appropriate treatment for subjects who experience a traumatic event.

Sodium oxybate treatment in narcolepsy and its effect on muscle tone

AIMS

To estimate the effect of the compound sodium oxybate (SO) on chin muscle tone in sleep, a re-analysis of the results of the international multicenter study SXB-15 was performed, applying a validated semi-automatic analysis of muscle tone. This analysis distinguishes short (<0.5 s) and long (>0.5 s) muscle activity indices per hour (SMI, LMI) in 116 patients with narcolepsy-cataplexy. While stable stimulant medication was permitted, tricyclics and SSRIs were withdrawn. Polysomnographies were performed at baseline (V5), four weeks after titration of SO to 4.5 g, 6 g, or 9 g or placebo (V6) and after another four weeks on stable SO dose (V7).

RESULTS

SMI and LMI decreased significantly during light sleep. LMI remained stable in all SO groups during slow wave sleep (SWS), but decreased significantly during REM sleep. SMI decreased non-significantly, but consistently during SWS and REM in the 9 g group only. A subgroup analysis of patients who stayed on stimulants showed that they had higher SMIs and LMIs in all groups. Patients who had been treated with anticataplectic medication prior to study inclusion had lower LMIs in the 9 g group during REM sleep in all visits.

CONCLUSION

SO has a differential effect on muscle tone that is dose and sleep stage dependent. Low dosages increase short muscle activity, possibly enabling the occurrence of parasomnias. High doses are especially efficacious in REM sleep, suggesting that SO could be used to treat REM sleep behavior disorder. Comedication with stimulants and prior medication with anticataplectic medication exerts an influence on muscle tone.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Chemogenetic inhibition of cells in the paramedian midbrain tegmentum increases locomotor activity in rats

Pronounced hyperactivity can be produced by lesions or pharmacological inhibition of cells in the median raphe nucleus (MR) located in the paramedian midbrain tegmentum. In the current study we examined whether a similar effect can be seen after chemogenetic inhibition of cells in this region using the DREADD (Designer Receptors Exclusively Activated by Designer Drugs) approach. We found that the DREADD ligand clozapine-N-oxide (CNO) increased locomotor activity in animals expressing the inhibitory DREADD hM4Di, but not those injected with a control virus in the MR. The effect was of rapid onset and short duration and persisted for at least four months after virus injections. Histological examination of the brains indicated that labeled fibers followed the known projection patterns of the MR to a variety of forebrain and midbrain structures. These findings confirm the role of the MR region in the control of locomotion and suggest that the DREADD technique may be a useful approach to the study of the functional architecture of this complex area. Methodological and interpretive aspects of DREADD studies are discussed.

γ-Aminobutyric acid neural signaling in the lateroanterior hypothalamus modulates aggressive behavior in adolescent anabolic/androgenic steroid-treated hamsters

Male Syrian hamsters (Mesocricetus auratus) treated with anabolic/androgenic steroids (AAS) during adolescence (P27-P56) display highly escalated and mature forms of offensive aggression correlated with increased γ-aminobutyric acid (GABA) afferent development as well as decreased GABAA receptors in the lateroanterior hypothalamus (LAH) - an area of convergence for developmental and neuroplastic changes that underlie offensive aggressive behaviors in hamsters. This study investigated whether microinfusion of a GABAA receptor agonist (muscimol; 0.01-1.0 pmol/l) or antagonist (bicuculline; 0.04-4.0 pmol/l) directly into the LAH modulate adolescent AAS-induced offensive aggression. Activation of LAH GABAA receptors enhanced adolescent AAS-induced offensive aggression, beginning at the 0.1 pmol/l dose, when compared with AAS-treated animals injected with saline into the LAH. Importantly, GABAA receptor agonism within the LAH significantly increased the frequency of belly/rear attacks, while simultaneously decreasing the frequency of frontal attacks. These data identify a neuroanatomical locus where GABAA receptor activation functions to enhance aggression in adolescent AAS-treated animals, while also promoting the display of mature forms of aggression and suppressing juvenile play behaviors.

Ingestive and locomotor behaviours induced by pharmacological manipulation of <Alpha>-adrenoceptors into the median raphe nucleus

The present study evaluated the involvement of α-adrenoceptors of the median raphe nucleus (MRN) in satiated rats, in food and water intake and motor behaviour. Control groups were treated with saline (SAL) or adrenaline (ADR), injected into the MRN seven minutes after injection of the vehicle used to solubilize the antagonists, propylene glycol (PLG) or SAL. Experimental groups were treated with an α-adrenoceptor antagonist, prazosin (α1, 20 or 40 nmol) or yohimbine (α2, 20 or 40 nmol) or phentolamine (non-selective α, 20 or 40 nmol), followed (later) by injection of ADR or SAL. Behaviour was recorded for 30 min. The injection of ADR and the blockade of α1 receptors resulted in hyperphagia whereas blocking α2 or α1 and α2 simultaneously did not change feeding behaviour. Pre-treatment with prazosin, followed by injection of ADR was not able to cause an increase in the amount of food ingested, while the higher dose of the α1 antagonist reduced the latency to start feeding. Pre-treatment with prazosin also caused hyperactivity. However, pre-treatment with phentolamine or yohimbine was able to block ADR-induced feeding. The present study supports the hypothesis that there is a tonic activation of α1-adrenoceptors in the MRN in satiated rats, which activates an inhibitory influence in areas that control food intake. Injection of ADR seems to activate α2 receptors, resulting in a decrease in the availability of endogenous catecholamines, which reduces the release of the signal that inhibits food intake, leading to hyperphagia.