Panicolytic-like effects caused by substantia nigra pars reticulata pretreatment with low doses of endomorphin-1 and high doses of CTOP or the NOP receptors antagonist JTC-801 in male Rattus norvegicus

Kappa-opioid receptor blockade in the inferior colliculus of prey threatened by pit vipers decreases anxiety and panic-like behaviour

The dorsal midbrain comprises dorsal columns of the periaqueductal grey matter and corpora quadrigemina. These structures are rich in beta-endorphinergic and leu-enkephalinergic neurons and receive GABAergic inputs from substantia nigra pars reticulata. Although the inferior colliculus (IC) is mainly involved in the acoustic pathways, the electrical and chemical stimulation of central and pericentral nuclei of the IC elicits a vigorous defensive behaviour. The defensive immobility and escape elicited by IC activation is commonly related to panic-like emotional states. To investigate the role of κ-opioid receptor of the IC in the antiaversive effects of endogenous opioid receptor blockade in a dangerous situation, male Wistar rats were pretreated in the IC with the κ-opioid receptor-selective antagonist nor-binaltorphimine at different concentrations and submitted to the non-enriched polygonal arena for a snake panic test in the presence of a rattlesnake and, after 24 h, prey were resubmitted to the experimental context. The snakes elicited in prey a set of antipredatory behaviours, such as the anxiety-like responses of defensive attention and risk assessment, and the panic-like reactions of defensive immobility and either escape or active avoidance during the elaboration of unconditioned and conditioned fear-related responses. Pretreatment of the IC with microinjections of nor-binaltorphimine at higher concentrations significantly decreased the frequency and duration of both anxiety- and panic-attack-like behaviours. These findings suggest that κ-opioid receptor blockade in the IC causes anxiolytic- and panicolytic-like responses in threatening conditions, and that kappa-opioid receptor-selective antagonists can be a putative coadjutant treatment for panic syndrome treatment.

Neostriatum neuronal TRPV1-signalling mediates striatal anandamide at high concentration facilitatory influence on neostriato-nigral dishinhibitory GABAergic connections

RATIONALE

Several lines of evidence have demonstrated that the cannabinoid type 1 receptor (CB₁) is found in the caudate nucleus and putamen (CPu) in addition to the substantia nigra pars reticulata (SNpr). Here, we investigated the role of endocannabinoid neuromodulation of striato-nigral disinhibitory projections on the activity of nigro-collicular GABAergic pathways that control the expression of unconditioned fear-related behavioural responses elicited by microinjections of the GABA_A receptor selective antagonist bicuculline (BIC) in the deep layers of the superior colliculus (dlSC).

METHODS

Fluorescent neural tract tracers were deposited in either CPu or in SNpr. Wistar rats received injection of vehicle, anandamide (AEA), either at low (50 pmol) or high (100 pmol) concentrations in CPu followed by bicuculline microinjections in dlSC.

RESULTS

Connections between CPu, the SNpr and dlSC were demonstrated. The GABA_A receptor blockade in dlSC elicited panic-like behaviour. AEA at the lowest concentration caused a panicolytic-like effect that was antagonised by the CPu pretreatment with AM251 at 100 pmol. AEA at the highest concentration caused a panicogenic-like effect that was antagonised by the CPu pretreatment with 6-iodonordihydrocapsaicin (6-I-CPS) at different concentrations (0.6, 6, 60 nmol).

CONCLUSION

These findings suggest that while pre-synaptic CB1-signalling subserves an indirect facilitatory effect of AEA on striato-nigral pathways causing panicolytic-like responses through midbrain tectum enhanced activity, post-synaptic TRPV₁-signalling in CPu mediates AEA direct activation of striato-nigral disinhibitory pathways resulting in increasing dlSC neurons activity and a panicogenic-like response. All these actions seem to depend on the interface with the nigro-collicular inhibitory GABAergic pathways.

Augmented anandamide signalling in the substantia nigra pars reticulata mediates panicolytic-like effects in mice confronted by Crotalus durissus terrificus pit vipers

RATIONALE

The endocannabinoid modulation of fear and anxiety due to the on-demand synthesis and degradation is supported by a large body of research. Although it has been proposed that anandamide (AEA) in the substantia nigra pars reticulata (SNpr) seems to be important for the organisation of innate fear-related behaviours, a role for endogenous AEA has yet to be clarified.

METHODS

Mice were treated with the fatty acid amide hydrolase (FAAH) selective inhibitor URB597 at different concentrations (0.01, 0.1, 1 nmol/0.1 µL) in the SNpr and confronted by rattlesnakes (Crotalus durissus terrificus). The most effective dose of URB597 (1 nmol) was also preceded by microinjections of the CB₁ receptor antagonist AM251 (0.1 nmol) into the SNpr, and mice were then confronted by the venomous snake.

RESULTS

URB597 (0.1 and 1 nmol) in the SNpr decreased the expression of defensive behaviours such as defensive attention, escape, and time spent inside the burrow of mice confronted by rattlesnakes. Moreover, pretreatment of SNpr with AM251 suppressed these antiaversive effects of URB597 in this midbrain structure.

CONCLUSION

Overall, these data clearly indicate that the panicolytic consequences of endogenous AEA enhancement in the SNpr are mediated by CB1 receptor signalling.

The modulation of striatonigral and nigrotectal pathways by CB1 signalling in the substantia nigra pars reticulata regulates panic elicited in mice by urutu-cruzeiro lancehead pit vipers

Cannabinoid receptor type 1 (CB₁R) is widely distributed in the substantia nigra pars reticulata (SNpr). However, the role of CB₁R at the SNpr level in threatening situations is poorly understood. We investigated the role of CB₁R in the SNpr on the expression of fear responses in mice confronted with urutu-cruzeiro pit vipers. First, a bidirectional neurotracer was injected into the SNpr; then, immunostaining of the vesicular GABA transporter was conducted at the levels of the striatum (CPu) and deep layers of the superior colliculus (dlSC). In addition, CB₁R immunostaining and GABA labelling were performed in the SNpr. Using a prey-versus-snake paradigm, mice were pretreated with the CB₁R antagonist AM251 (100 pmol) and treated with the endocannabinoid anandamide (AEA, 5 pmol) in the SNpr, followed by bicuculline (40 ng) in the dlSC, and were then confronted with a snake. Bidirectional neural tract tracers associated with immunofluorescence showed the GABAergic striatonigral disinhibitory and nigrotectal inhibitory pathways. Furthermore, we showed that CB₁R labelling was restricted to axonal fibres surrounding SNpr GABAergic cells. We also demonstrated a decrease in the defensive behaviours of mice treated with AEA in the SNpr, but this effect was blocked by pre-treatment with AM251 in this structure. Taken together, our results show that the panicolytic consequences of the AEA enhancement in the SNpr are signalled by CB₁R, suggesting that CB₁R localised in axon terminals of CPu GABAergic neurons in the SNpr modulates the activity of the nigrotectal GABAergic pathway during the expression of defensive behaviours in threatening situations.

Chronic aerobic exercise: Autoradiographic assessment of GABA(a) and mu-opioid receptor binding in adult rats

Exercise programs have shown great potential for both the prevention and treatment of substance use disorder (SUD). As exercise has been shown to have potent effects on physical and psychological health, it is reasonable to examine the mechanism of how exercise can be used as an adjunct treatment for addiction. The present study examined the effects of chronic aerobic (treadmill) exercise on both GABA(a) and mu-opioid receptor levels in the brains of male and female rats. GABA(a) receptor binding, measured by [³H] Flunitrazepam, was increased in the cingulate cortex following exercise, but only in females. Mu-opioid receptor expression, measured by [³H] ([D-Ala², N-MePhe⁴, Gly-ol]-enkephalin) (DAMGO), showed no effect of exercise while showing an effect of sex, with increased [³H] DAMGO binding in the brains of sedentary males compared to that of sedentary females. Our findings support the potential role for GABA(a) signaling in the cingulate cortex as part of the mechanism of action of aerobic exercise. These data, along with prior reports, aid our understanding of the neurochemical impact and mechanism of chronic aerobic exercise on neuropsychiatric disease, particularly regarding addiction.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Panicolytic-like effect of µ1-opioid receptor blockade in the inferior colliculus of prey threatened by Crotalus durissus terrificus pit vipers

BACKGROUND

The endogenous opioid peptide system has been implicated in the neural modulation of fear and anxiety organised by the dorsal midbrain. Furthermore, previous results indicate a fundamental role played by inferior colliculus (IC) opioid mechanisms during the expression of defensive behaviours, but the involvement of the IC µ₁-opioid receptor in the modulation of anxiety- and panic attack-related behaviours remains unclear. Using a prey-versus-snake confrontation paradigm, we sought to investigate the effects of µ₁-opioid receptor blockade in the IC on the defensive behaviour displayed by rats in a dangerous situation.

METHODS

Specific pathogen-free Wistar rats were treated with microinjection of the selective µ₁-opioid receptor antagonist naloxonazine into the IC at different concentrations (1.0, 3.0 and 5.0 µg/0.2 µL) and then confronted with rattlesnakes ( Crotalus durissus terrificus). The defensive behavioural repertoire, such as defensive attention, flat back approach (FBA), startle, defensive immobility, escape or active avoidance, displayed by rats either during the confrontations with wild snakes or during re-exposure to the experimental context without the predator was analysed.

RESULTS

The blockade of µ₁-opioid receptors in the IC decreased the expression of both anxiety-related behaviours (defensive attention, FBA) and panic attack-related responses (startle, defensive immobility and escape) during the confrontation with rattlesnakes. A significant decrease in defensive attention was also recorded during re-exposure of the prey to the experimental apparatus context without the predator.

CONCLUSION

Taken together, these results suggest that a decrease in µ_1-opioid receptor signalling activity within the IC modulates anxiety- and panic attack-related behaviours in dangerous environments.

Understanding the role of dopamine in conditioned and unconditioned fear

Pharmacological and molecular imaging studies in anxiety disorders have primarily focused on the serotonin system. In the meantime, dopamine has been known as the neurotransmitter of reward for 60 years, particularly for its action in the nervous terminals of the mesocorticolimbic system. Interest in the mediation by dopamine of the well-known brain aversion system has grown recently, particularly given recent evidence obtained on the role of D2 dopamine receptors in unconditioned fear. However, it has been established that excitation of the mesocorticolimbic pathway, originating from dopaminergic (DA) neurons from the ventral tegmental area (VTA), is relevant for the development of anxiety. Among the forebrain regions innervated by this pathway, the amygdala is an essential component of the neural circuitry of conditioned fear. Current findings indicate that the dopamine D2 receptor-signaling pathway connecting the VTA to the basolateral amygdala modulates fear and anxiety, whereas neural circuits in the midbrain tectum underlie the expression of innate fear. The A13 nucleus of the zona incerta is proposed as the origin of these DA neurons projecting to caudal structures of the brain aversion system. In this article we review data obtained in studies showing that DA receptor-mediated mechanisms on ascending or descending DA pathways play opposing roles in fear/anxiety processes. Dopamine appears to mediate conditioned fear by acting at rostral levels of the brain and regulate unconditioned fear at the midbrain level.

The endogenous opioid system modulates defensive behavior evoked by Crotalus durissus terrificus: Panicolytic-like effect of intracollicular non-selective opioid receptors blockade

BACKGROUND

There is a controversy regarding the key role played by opioid peptide neurotransmission in the modulation of panic-attack-related responses.

AIMS

Using a prey versus rattlesnakes paradigm, the present work investigated the involvement of the endogenous opioid peptide-mediated system of the inferior colliculus in the modulation of panic attack-related responses.

METHODS

Wistar rats were pretreated with intracollicular administration of either physiological saline or naloxone at different concentrations and confronted with rattlesnakes ( Crotalus durissus terrificus). The prey versus rattlesnake confrontations were performed in a polygonal arena for snakes. The defensive behaviors displayed by prey (defensive attention, defensive immobility, escape response, flat back approach and startle) were recorded twice: firstly, over a period of 15 min the presence of the predator and a re-exposure was performed 24 h after the confrontation, when animals were exposed to the experimental enclosure without the rattlesnake.

RESULTS

The intramesencephalic non-specific blockade of opioid receptors with microinjections of naloxone at higher doses decreased both anxiety- (defensive attention and flat back approach) and panic attack-like (defensive immobility and escape) behaviors, evoked in the presence of rattlesnakes and increased non-defensive responses. During the exposure to the experimental context, there was a decrease in duration of defensive attention.

CONCLUSIONS

These findings suggest a panicolytic-like effect of endogenous opioid receptors antagonism in the inferior colliculus on innate (panic attack) and conditioned (anticipatory anxiety) fear in rats threatened by rattlesnakes.

JTC-801 inhibits the proliferation and metastasis of the Hep G2 hepatoblastoma cell line by regulating the phosphatidylinositol 3-kinase/protein kinase B signalling pathway

The increased worldwide mortality rate due to liver cancer may be attributed to the aggressive nature of the disease. Signal transduction through G-protein-coupled receptors (GPCRs) can affect a number of aspects of cancer biology, including invasion, migration and vascular remodelling. JTC-801, a novel GPCR antagonist, has demonstrated promising anticancer effects in adenocarcinoma and osteosarcoma cells. In the present study, the effect of JTC-801 on the proliferation and migration of hepatoblastoma Hep G2 cells was investigated. The Cell Counting Kit-8 assay revealed that JTC-801 markedly suppressed the growth of the Hep G2 cells. Additionally, JTC-801 significantly inhibited cell invasion and migration in a Transwell assay. Furthermore, the expression of anti-apoptotic protein B-cell lymphoma 2 decreased and the expression of the pro-apoptotic proteins active caspase-3 and apoptosis regulator BAX increased in the Hep G2 cells following JTC-801 treatment. Additionally, JTC-801 suppressed the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signalling pathway in the Hep G2 cells. Therefore, the present study revealed that JTC-801 can induce the apoptosis of Hep G2 cells by regulating the PI3K/AKT signalling pathway, which suggests that JTC-801 may be a potential novel drug target for clinical liver cancer treatment.