Maladaptive responses to stress adversely affect human behavior, yet the signaling mechanisms underlying stress-responsive behaviors remain poorly understood. Using a conditional gene knockout ...approach, the α isoform of p38 mitogen-activated protein kinase (MAPK) was selectively inactivated by AAV1-Cre-recombinase infection in specific brain regions or by promoter-driven excision of p38α MAPK in serotonergic neurons (by
Slc6a4-Cre or
ePet1-Cre) or astrocytes (by
Gfap-CreERT2). Social defeat stress produced social avoidance (a model of depression-like behaviors) and reinstatement of cocaine preference (a measure of addiction risk) in wild-type mice, but not in mice having p38α MAPK selectively deleted in serotonin-producing neurons of the dorsal raphe nucleus. Stress-induced activation of p38α MAPK translocated the serotonin transporter to the plasma membrane and increased the rate of transmitter uptake at serotonergic nerve terminals. These findings suggest that stress initiates a cascade of molecular and cellular events in which p38α MAPK induces a hyposerotonergic state underlying depression-like and drug-seeking behaviors.
► p38α MAPK is for stress-induced behaviors including depression and addiction ► Selective p38α MAPK deletion in serotonergic neurons produces stress resilience ► p38α MAPK activation translocates the serotonin transporter ► Stress-induced dysphoria is caused by hyposerotoninergic tone
Astrocytes are a subpopulation of glial cells that directly affect neuronal function. This review focuses on the potential functional roles of astrocytes in the development of behavioral ...sensitization and rewarding effects induced by chronic treatment with drugs of abuse. In vitro treatment of cortical neuron/glia cocultures with either methamphetamine or morphine caused activation of astrocytes via protein kinase C (PKC). Purified cortical astrocytes were markedly activated by methamphetamine, whereas morphine had no such effect. Methamphetamine, but not morphine, caused a long-lasting astrocytic activation in cortical neuron/glia cocultures. Morphine-induced behavioral sensitization, assessed as hyperlocomotion, was reversed by 2 months of withdrawal from intermittent morphine administration, whereas behavioral sensitization to methamphetamine-induced hyperlocomotion was maintained even after 2 months of withdrawal. In vivo treatment with methamphetamine, which was associated with behavioral sensitization, caused PKC-dependent astrocytic activation in the mouse cingulate cortex and nucleus accumbens. Furthermore, the glial modulator propentofylline dramatically diminished the activation of astrocytes and the rewarding effect induced by methamphetamine and morphine. On the other hand, intra-nucleus accumbens and intra-cingulate cortex administration of astrocyte-conditioned medium aggravated the development of rewarding effects induced by methamphetamine and morphine. Furthermore, astrocyte-conditioned medium, but not methamphetamine itself, clearly induced differentiation of neural stem cells into astrocytes. These findings provide direct evidence that astrocytes may, at least in part, contribute to the development of the rewarding effects induced by drugs of abuse in the nucleus accumbens and cingulate cortex.
In this study, we investigated the role of orexinergic systems in dopamine-related behaviors induced by the mu-opioid receptor agonist morphine in rodents. Extensive coexpression of tyrosine ...hydroxylase with orexin receptors was observed in the mouse ventral tegmental area (VTA). The levels of dopamine and its major metabolites in the nucleus accumbens were markedly increased by the microinjection of orexin A and orexin B into the VTA. The subcutaneous morphine-induced place preference and hyperlocomotion observed in wild-type mice were abolished in mice that lacked the prepro-orexin gene. An intra-VTA injection of a selective orexin receptor antagonist SB334867A 1-(2-methylbenzoxazol-6-yl)-3-1.5naphthyridin-4-yl urea significantly suppressed the morphine-induced place preference in rats. Furthermore, the increased level of dialysate dopamine produced by morphine in the mouse brain was significantly decreased by deletion of the prepro-orexin gene. These findings provide new evidence that orexin-containing neurons in the VTA are directly implicated in the rewarding effect and hyperlocomotion induced by morphine through activation of the mesolimbic dopamine pathway in rodents.
The κ-opioid receptor is a widely expressed G-protein-coupled receptor that has been implicated in biological responses to pain, stress, anxiety, and depression, and its potential as a therapeutic ...target in these syndromes is becoming increasingly apparent. However, the prototypical selective κ-opioid antagonists have very long durations of action that have been attributed to c-Jun N-terminal kinase (JNK) 1 activation in vivo. To test generality of this proposed noncompetitive mechanism, we used C57BL/6 wild type mice to determine the durations of antagonist action of novel κ-opioid receptor ligands and examined their efficacies for JNK1 activation compared with conventional competitive antagonists. Of the 12 compounds tested, 5 had long durations of action that positively correlated with JNK activation: RTI-5989-97 (3S)-7-hydroxy-N-(1S)-1-(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinylmethyl}-(2-methylpropyl-2-methyl-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide, RTI-5989-194 (3R)-7-hydroxy-N-(1S)-1-(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinylmethyl}-(2-methylbutyl-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide, RTI-5989-241 (3R)-7-hydroxy-N-(1S)-1-{(3R,4R)-4-(3-methoxyphenyl)-3,4-dimethyl-1-piperidinylmethyl}-2-methylpropyl-1,2,3,4-tetrahydroisoquinoline-3-carboxamide), nor-binaltorphimine (nor-BNI); and (3R)-7-hydroxy-N-((1S)-1-{(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinylmethyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide (JDTic). Seven had short durations of action and did not increase phospho-JNK-ir: RTI-5989-212(3R)-N-(1S)-1-(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinylmethyl}-(2-methylpropyl-7-methoxy-1,2,3,4-tetrahydroisoquinoline-3-carboxamide, RTI-5989-240 (3R)-7-hydroxy-N-(1S)-1-(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethylpiperidin-1-ylmethyl}-(2-methylpropyl-3-methyl-1,2,3,4-tetrahydroisoquinoline-3-carboxamide, JSPA0658 (S)-3-fluoro-4-(4-((2-(3,5-dimethylphenyl)pyrrolidin-1-yl)methyl)phenoxy)benzamide, JSPA071B (S)-3-fluoro-4-(4-((2-(3,5-bis(trifluoromethyl)phenyl)pyrrolidin-1-yl)methyl)phenoxy)benzamide. PF-4455242 2-methyl-N-((2'-(pyrrolidin-1-ylsulfonyl)biphenyl-4-yl)methyl)propan-1-amine, PF-4455242 2-methyl-N-((2'-(pyrrolidin-1-ylsulfonyl)biphenyl-4-yl)methyl)propan-1-amine, FP3FBZ (S)-3-fluoro-4-(4-((2-(3-fluorophenyl)pyrrolidin-1-yl)methyl)phenoxy)benzamide, and naloxone. After long-acting antagonist treatment, pJNK-ir did not increase in mice lacking the κ-opioid receptor; increased pJNK-ir returned to baseline by 48 h after treatment; and a second challenge with nor-BNI 72 h after the first did not increase pJNK-ir. Long-lasting antagonism and increased phospho-JNK-ir were not seen in animals lacking the JNK1 isoform. These results support the hypothesis that the duration of action of small molecule κ-opioid receptor antagonists in vivo is determined by their efficacy in activating JNK1 and that persistent inactivation of the κ-receptor does not require sustained JNK activation.
The present study was undertaken to evaluate the implication of δ‐opioid receptor function in neurogenesis and neuroprotection. We found that the stimulation of δ‐opioid receptors by the selective ...δ‐opioid receptor agonist SNC80 (+)‐4‐(αR)‐α‐((2S,5R)‐4‐allyl‐2,5‐dimethyl‐1‐piperazinyl)‐3‐methoxybenzyl‐N,N‐diethylbenzamide (10 nm) promoted neural differentiation from multipotent neural stem cells obtained from embryonic C3H mouse forebrains. In contrast, either a selective µ‐opioid receptor agonist, d‐Ala2, N‐Me‐Phe4, Gly5‐ol‐enkephalin (DAMGO), or a specific κ‐opioid receptor agonist, (–)‐trans‐(1S,2S)‐U‐50488 hydrochloride (U50,488H), had no such effect. In addition to neural differentiation, the increase in cleaved caspase 3‐like immunoreactivity induced by H2O2 (3 µm) was suppressed by treatment with SNC80 in cortical neuron/glia co‐cultures. These effects of SNC80 were abolished by a Trk‐dependent tyrosine kinase inhibitor: (8R*,9S*,11S*)‐(–)‐9‐hydroxy‐9‐methoxycarbonyl‐8‐methyl‐2,3,9,10‐tetrahydro‐8,11‐epoxy‐1H,8H,11H‐2,7b,11a‐triazadibenzo(a,g)cycloocta(cde)trinden‐1‐one (K‐252a). The SNC80‐induced neural differentiation was also inhibited by treatment with the protein kinase C (PKC) inhibitor, phosphatidylinositol 3‐kinase (PI3K) inhibitor, mitogen‐activated protein kinase kinase (MEK) inhibitor or Ca2+/calmodulin‐dependent protein kinase II (CaMKII) inhibitor. These findings raise the possibility that δ‐opioid receptors play a crucial role in neurogenesis and neuroprotection, mainly through the activation of Trk‐dependent tyrosine kinase, which could be linked to PI3K, PKC, CaMKII and MEK.
KOR activation of Gβγ dependent signaling results in analgesia, whereas the dysphoric effects of KOR agonists are mediated by a different pathway involving G protein receptor kinase and non-visual ...arrestin. Based on this distinction, a partial KOR agonist that does not efficiently activate arrestin-dependent biased signaling may produce analgesia without dysphoria. No KOR-selective partial agonists are currently available, and preclinical assessment is complicated by sequence differences between rodent (r) and human (h) KOR. In this study, we compared the signaling initiated by the available partial agonists. Pentazocine was significantly more potent at activating p38 MAPK in hKOR than rKOR expressed in HEK293 cells but equally potent at arrestin-independent activation of ERK1/2 in hKOR and rKOR. Similarly, butorphanol increased phospho-p38-ir in hKOR-expressing cells but did not activate p38 in rKOR-HEK293. Like pentazocine, butorphanol was equally efficacious at activating ERK1/2 in rKOR and hKOR. In contrast, levorphanol, nalorphine, and U50,488 did not distinguish between hKOR and rKOR in p38 MAPK activation. Consistent with its low potency at p38 activation, pentazocine did not produce conditioned place aversion in mice. hKOR lacks the Ser-369 phosphorylation site in rKOR required for G protein receptor kinase/arrestin-dependent p38 activation, but mutation of the Ser-358 to asparagine in hKOR blocked p38 activation without affecting the acute arrestin-independent activation of ERK1/2. This study shows that hKOR activates p38 MAPK through a phosphorylation and arrestin-dependent mechanism; however, activation differs between hKOR and rKOR for some ligands. These functional selectivity differences have important implications for preclinical screening of partial KOR agonists.
Background: Dysphoric effects of κ-opioid receptor (KOR) agonists require p38 MAPK activation in mice, but sequence differences in human KOR may affect this mechanism.
Results: Differences in p38 activation were observed between human and rodent KOR for pentazocine and butorphanol.
Conclusion: Species differences affect signaling.
Significance: Rodent models may not predict adverse effects of KOR agonists in humans.
Ketamine, one of the dissociative anaesthetic agents, has been shown to produce psychotomimetic effects. It has been well documented that activation of sigma receptors is responsible for the ...pathogenesis of some psychiatric disorders. In the present study, the effects of NE‐100, a putative sigma 1 receptor antagonist, was investigated in rats trained to discriminate between ketamine (5 mg/kg, i.p.) from saline under a fixed‐ratio 10 food‐reinforced procedure. Here we report for the first time that NE‐100 (1 mg/kg) produced a shift to the right in the dose–response curve for ketamine's discriminative stimulus effects. These results suggest that the sigma 1 receptor is, at least in part, involved in the discriminative stimulus effects of ketamine.
It has been widely recognized that chronic pain could cause physiological changes at supraspinal levels. The δ‐opioidergic system is involved in antinociception, emotionality, immune response and ...neuron‐glia communication. In this study, we show that mice with chronic pain exhibit anxiety‐like behavior and an increase of astrocytes in the cingulate cortex due to the dysfunction of cortical δ‐opioid receptor systems. Using neural stem cells cultured from the mouse embryonic forebrain, astrocyte differentiation was clearly observed following long‐term exposure to the selective δ‐opioid receptor antagonist, naltrindole. We also found that micro‐injection of either activated astrocyte or astrocyte‐conditioned medium into the cingulate cortex of mice aggravated the expression of anxiety‐like behavior. Our results indicate that the chronic pain process promotes astrogliosis in the cingulate cortex through the dysfunction of cortical δ‐opioid receptors. This phenomenon may lead to emotional disorders including aggravated anxiety under chronic pain‐like state.
GTP binding regulatory protein (G protein)-coupled receptors can activate MAPK pathways via G protein-dependent and -independent mechanisms. However, the physiological outcomes correlated with the ...cellular signaling events are not as well characterized. In this study, we examine the involvement of G protein and β-arrestin 2 pathways in kappa opioid receptor-induced, extracellular signal-regulated kinase 1/2 (ERK1/2)-mediated proliferation of both immortalized and primary astrocyte cultures. As different agonists induce different cellular signaling pathways, we tested the prototypic kappa agonist, U69593 as well as the structurally distinct, non-nitrogenous agonist, C(2)-methoxymethyl salvinorin B (MOM-Sal-B). In immortalized astrocytes, U69593, activated ERK1/2 by a rapid (min) initial stimulation that was sustained over 2 h and increased proliferation. Sequestration of activated Gβγ subunits attenuated U69593 stimulation of ERK1/2 and suppressed proliferation in these cells. Furthermore, small interfering RNA silencing of β-arrestin 2 diminished sustained ERK activation induced by U69593. In contrast, MOM-Sal-B induced only the early phase of ERK1/2 phosphorylation and did not affect proliferation of immortalized astrocytes. In primary astrocytes, U69593 produced the same effects as seen in immortalized astrocytes. MOM-Sal-B elicited sustained ERK1/2 activation which was correlated with increased primary astrocyte proliferation. Proliferative actions of both agonists were abolished by either inhibition of ERK1/2, Gβγ subunits or β-arrestin 2, suggesting that both G protein-dependent and -independent ERK pathways are required for this outcome.
GTP binding regulatory protein (G protein)-coupled receptors can activate MAPK pathways via G protein-dependent and -independent mechanisms. However, the physiological outcomes correlated with the ...cellular signaling events are not as well characterized. In this study, we examine the involvement of G protein and beta -arrestin 2 pathways in kappa opioid receptor-induced, extracellular signal-regulated kinase 1-2 (ERK1-2)-mediated proliferation of both immortalized and primary astrocyte cultures. As different agonists induce different cellular signaling pathways, we tested the prototypic kappa agonist, U69593 as well as the structurally distinct, non-nitrogenous agonist, C(2)-methoxymethyl salvinorin B (MOM-Sal-B). In immortalized astrocytes, U69593, activated ERK1-2 by a rapid (min) initial stimulation that was sustained over 2h and increased proliferation. Sequestration of activated G beta gamma subunits attenuated U69593 stimulation of ERK1-2 and suppressed proliferation in these cells. Furthermore, small interfering RNA silencing of beta -arrestin 2 diminished sustained ERK activation induced by U69593. In contrast, MOM-Sal-B induced only the early phase of ERK1-2 phosphorylation and did not affect proliferation of immortalized astrocytes. In primary astrocytes, U69593 produced the same effects as seen in immortalized astrocytes. MOM-Sal-B elicited sustained ERK1-2 activation which was correlated with increased primary astrocyte proliferation. Proliferative actions of both agonists were abolished by either inhibition of ERK1-2, G beta gamma subunits or beta -arrestin 2, suggesting that both G protein-dependent and -independent ERK pathways are required for this outcome.
PDF
