Tramadol and Tapentadol Induce Conditioned Place Preference with a Differential Impact on Rewarding Memory and Incubation of Craving

Tramadol and tapentadol, synthetic opioids commonly prescribed for moderate-to-severe pain, have a unique pharmacology that optimizes their analgesia and safety. However, they are not devoid of risks, presenting addictive, abuse, and dependence potential. While tramadol-reinforcing properties have been documented by various studies with human and animal models, including conditioned place preference (CPP) assays, no similar studies have been performed with tapentadol. In the present study, we performed CPP assays by intraperitoneally administering Wistar rats with a tramadol/tapentadol therapeutic dose. Animal permanence and the number of entries in the CPP compartments were recorded in the preconditioning phase and then 1 (T1), 7 (T7), and 14 (T14) days after conditioning. Both opioids induced a change in place preference (T1), suggesting that they have short-term reinforcing properties. However, only tramadol was associated with place preference retention (T7 and T14), with an increase in the number of entries in the opioid-paired compartment (T1 and T7), showing that it causes rewarding memory and incubation of craving. The results indicate that at therapeutic doses: (1) both drugs cause short-term rewarding effects and (2) as opposed to tramadol, tapentadol does not cause CPP retention, despite its higher central nervous system activity and stricter scheduling.

Tapentadol: A Review of Experimental Pharmacology Studies, Clinical Trials, and Recent Findings

Tapentadol is an analgesic compound that acts centrally to attenuate pain. Previous studies have shown that tapentadol has dual mechanisms of action as a mu-opioid receptor agonist and noradrenaline re-uptake inhibition. Therefore, tapentadol provides a great advantage over classic opioids in pain management from nociceptive to neuropathic. Cumulative evidence from in vitro data suggests that tapentadol effect of norepinephrine re-uptake could be a new target that overcomes other classic opioids in chronic neuropathic pain. Compared to tramadol and other opioids, tapentadol is associated with fewer adverse effects than tramadol. Tapentadol is a new alternative to treat acute, chronic, and neuropathic pain. Thus, this review article was focused on understanding the studies that led to the development of tapentadol as a novel analgesic drug and its advantages over conventional opioids. Thus, tapentadol is a good alternative with fewer adverse effects and is available for human use.

Co-Evolution of Opioid and Adrenergic Ligands and Receptors: Shared, Complementary Modules Explain Evolution of Functional Interactions and Suggest Novel Engineering Possibilities

Cross-talk between opioid and adrenergic receptors is well-characterized and involves second messenger systems, the formation of receptor heterodimers, and the presence of extracellular allosteric binding regions for the complementary ligand; however, the evolutionary origins of these interactions have not been investigated. We propose that opioid and adrenergic ligands and receptors co-evolved from a common set of modular precursors so that they share binding functions. We demonstrate the plausibility of this hypothesis through a review of experimental evidence for molecularly complementary modules and report unexpected homologies between the two receptor types. Briefly, opioids form homodimers also bind adrenergic compounds; opioids bind to conserved extracellular regions of adrenergic receptors while adrenergic compounds bind to conserved extracellular regions of opioid receptors; opioid-like modules appear in both sets of receptors within key ligand-binding regions. Transmembrane regions associated with homodimerization of each class of receptors are also highly conserved across receptor types and implicated in heterodimerization. This conservation of multiple functional modules suggests opioid–adrenergic ligand and receptor co-evolution and provides mechanisms for explaining the evolution of their crosstalk. These modules also suggest the structure of a primordial receptor, providing clues for engineering receptor functions.

Repeated Administration of Clinically Relevant Doses of the Prescription Opioids Tramadol and Tapentadol Causes Lung, Cardiac, and Brain Toxicity in Wistar Rats

Tramadol and tapentadol, two structurally related synthetic opioid analgesics, are widely prescribed due to the enhanced therapeutic profiles resulting from the synergistic combination between μ-opioid receptor (MOR) activation and monoamine reuptake inhibition. However, the number of adverse reactions has been growing along with their increasing use and misuse. The potential toxicological mechanisms for these drugs are not completely understood, especially for tapentadol, owing to its shorter market history. Therefore, in the present study, we aimed to comparatively assess the putative lung, cardiac, and brain cortex toxicological damage elicited by the repeated exposure to therapeutic doses of both prescription opioids. To this purpose, male Wistar rats were intraperitoneally injected with single daily doses of 10, 25, and 50 mg/kg tramadol or tapentadol, corresponding to a standard analgesic dose, an intermediate dose, and the maximum recommended daily dose, respectively, for 14 consecutive days. Such treatment was found to lead mainly to lipid peroxidation and inflammation in lung and brain cortex tissues, as shown through augmented thiobarbituric acid reactive substances (TBARS), as well as to increased serum inflammation biomarkers, such as C reactive protein (CRP) and tumor necrosis factor-α (TNF-α). Cardiomyocyte integrity was also shown to be affected, since both opioids incremented serum lactate dehydrogenase (LDH) and α-hydroxybutyrate dehydrogenase (α-HBDH) activities, while tapentadol was associated with increased serum creatine kinase muscle brain (CK-MB) isoform activity. In turn, the analysis of metabolic parameters in brain cortex tissue revealed increased lactate concentration upon exposure to both drugs, as well as augmented LDH and creatine kinase (CK) activities following tapentadol treatment. In addition, pneumo- and cardiotoxicity biomarkers were quantified at the gene level, while neurotoxicity biomarkers were quantified both at the gene and protein levels; changes in their expression correlate with the oxidative stress, inflammatory, metabolic, and histopathological changes that were detected. Hematoxylin and eosin (H & E) staining revealed several histopathological alterations, including alveolar collapse and destruction in lung sections, inflammatory infiltrates, altered cardiomyocytes and loss of striation in heart sections, degenerated neurons, and accumulation of glial and microglial cells in brain cortex sections. In turn, Masson's trichrome staining confirmed fibrous tissue deposition in cardiac tissue. Taken as a whole, these results show that the repeated administration of both prescription opioids extends the dose range for which toxicological injury is observed to lower therapeutic doses. They also reinforce previous assumptions that tramadol and tapentadol are not devoid of toxicological risk even at clinical doses.

β2 and α2 adrenergic receptors mediate the proneurogenic in vitro effects of norquetiapine

Positive modulation of adult hippocampal neurogenesis may contribute to the therapeutic effects of clinically relevant antidepressant drugs, including atypical antipsychotics. Quetiapine, an antipsychotic which represents a therapeutic option in patients who are resistant to classical antidepressants, promotes adult hippocampal neurogenesis in preclinical studies. Norquetiapine, the key active metabolite of quetiapine in humans, has a distinctive receptor profile than the parent compound. The drug is indeed a high affinity norepinephrine transporter inhibitor and such activity has been proposed to contribute to its antidepressant effect. At present, no information is available on the effects of norquetiapine on adult neurogenesis. We extensively investigated the activity of quetiapine and norquetiapine on adult murine neural stem/progenitor cells and their progeny. Additionally, selective antagonists for β₂/α₂ adrenergic receptors allowed us to evaluate if these receptors could mediate quetiapine and norquetiapine effects. We demonstrated that both drugs elicit in vitro proneurogenic effects but also that norquetiapine had distinctive properties which may depend on its ability to inhibit norepinephrine transporter and involve β₂/α₂ adrenergic receptors. Animal care and experimental procedures were approved by the Institutional Animal Care and Use Committees (IACUC) at University of Piemonte Orientale, Italy (approval No. 1033/2015PR) on September 29, 2015.

Neonatal therapy with clenbuterol and salmeterol restores spinogenesis and dendritic complexity in the dentate gyrus of the Ts65Dn model of Down syndrome

Down syndrome (DS), a neurodevelopmental disorder caused by triplication of chromosome 21, is characterized by intellectual disability. In DS, defective neurogenesis causes an overall reduction in the number of neurons populating the brain and defective neuron maturation causes dendritic hypotrophy and reduction in the density of dendritic spines. No effective therapy currently exists for the improvement of brain development in individuals with DS. Drug repurposing is a strategy for identifying new medical use for approved drugs. A drug screening campaign showed that the β2-adrenergic receptor (β2-AR) agonists clenbuterol hydrochloride (CLEN) and salmeterol xinafoate (SALM) increase the proliferation rate of neural progenitor cells from the Ts65Dn model of DS. The goal of the current study was to establish their efficacy in vivo, in the Ts65Dn model. We found that, at variance with the in vitro experiments, treatment with CLEN or SALM did not restore neurogenesis in the hippocampus of Ts65Dn mice treated during the postnatal (P) period P3-P15. In Ts65Dn mice treated with CLEN or SALM, however, dendritic spine density and dendritic arborization of the hippocampal granule cells were restored and the lowest dose tested here (0.01 mg/kg/day) was sufficient to elicit these effects. CLEN and SALM are used in children as therapy for asthma and, importantly, they pass the blood-brain barrier. Our study suggests that treatment with these β2-AR agonists may be a therapy of choice in order to correct dendritic development in DS but is not suitable to rescue neurogenesis.

Indices of dentate gyrus neurogenesis are unaffected immediately after or following withdrawal from morphine self-administration compared to saline self-administering control male rats

Opiates - including morphine - are powerful analgesics with high abuse potential. In rodents, chronic opiate exposure or self-administration negatively impacts hippocampal-dependent function, an effect perhaps due in part to the well-documented opiate-induced inhibition of dentate gyrus (DG) precursor proliferation and neurogenesis. Recently, however, intravenous (i.v.) morphine self-administration (MSA) was reported to enhance the survival of new rat DG neurons. To reconcile these disparate results, we used rat i.v. MSA to assess 1) whether a slightly-higher dose MSA paradigm also increases new DG neuron survival; 2) how MSA influences cells in different stages of DG neurogenesis, particularly maturation and survival; and 3) if MSA-induced changes in DG neurogenesis persist through a period of abstinence. To label basal levels of proliferation, rats received the S-phase marker bromodeoxyuridine (BrdU, i.p.) 24 -h prior to 21 days (D) of i.v. MSA or saline self-administration (SSA). Either immediately after SA (0-D) or after 4 weeks in the home cage (28-D withdrawal), stereology was used to quantify DG proliferating precursors (or cells in cell cycle; Ki67+ cells), neuroblast/immature neurons (DCX+ cells), and surviving DG granule cells (BrdU+ cells). Analysis revealed the number of DG cells immunopositive for these neurogenesis-relevant markers was similar between MSA and SSA rats at the 0-D or 28-D timepoints. These negative data highlight the impact experimental parameters, timepoint selection, and quantification approach have on neurogenesis results, and are discussed in the context of the large literature showing the negative impact of opiates on DG neurogenesis.

Salmeterol, a β2 Adrenergic Agonist, Promotes Adult Hippocampal Neurogenesis in a Region-Specific Manner

Neurogenesis persists in the subgranular zone of the hippocampal formation in the adult mammalian brain. In this area, neural progenitor cells (NPCs) receive both permissive and instructive signals, including neurotransmitters, that allow them to generate adult-born neurons which can be functionally integrated in the preexisting circuit. Deregulation of adult hippocampal neurogenesis (ahNG) occurs in several neuropsychiatric and neurodegenerative diseases, including major depression, and represents a potential therapeutic target. Of interest, several studies suggested that, both in rodents and in humans, ahNG is increased by chronic administration of classical monoaminergic antidepressant drugs, suggesting that modulation of this process may participate to their therapeutic effects. Since the established observation that noradrenergic innervations from locus coeruleus make contact with NPC in the dentate gyrus, we investigated the role of beta adrenergic receptor (β-AR) on ahNG both in vitro and in vivo. Here we report that, in vitro, activation of β₂-AR by norepinephrine and β₂-AR agonists promotes the formation of NPC-derived mature neurons, without affecting NPC survival or differentiation toward glial lineages. Additionally, we show that a selective β₂-AR agonist able to cross the blood-brain barrier, salmeterol, positively modulates hippocampal neuroplasticity when chronically administered in adult naïve mice. Indeed, salmeterol significantly increased number, maturation, and dendritic complexity of DCX⁺ neuroblasts. The increased number of DCX⁺ cells was not accompanied by a parallel increase in the percentage of BrdU⁺/DCX⁺ cells suggesting a potential prosurvival effect of the drug on neuroblasts. More importantly, compared to vehicle, salmeterol promoted ahNG, as demonstrated by an increase in the actual number of BrdU⁺/NeuN⁺ cells and in the percentage of BrdU⁺/NeuN⁺ cells over the total number of newly generated cells. Interestingly, salmeterol proneurogenic effects were restricted to the ventral hippocampus, an area related to emotional behavior and mood regulation. Since salmeterol is commonly used for asthma therapy in the clinical setting, its novel pharmacological property deserves to be further exploited with a particular focus on drug potential to counteract stress-induced deregulation of ahNG and depressive-like behavior.

[The therapeutic potential of acetyl-L-carnitine in the treatment of cognitive and depressive disorders in the elderly]

The review is based on the assessment of the therapeutic potential of acetyl-L-carnitine (carnicetin) in the treatment of cognitive and depressive disorders in the elderly. The review describes the range of biochemical activity and mechanisms of action of acetyl-L-carnitine, assesses the efficacy and safety of acetyl-L-carnitine in gerontological practice. The results of preclinical and clinical studies of the use of acetyl-L-carnitine in world medical practice are analyzed.

Chronic administration of quetiapine stimulates dorsal hippocampal proliferation and immature neurons of male rats, but does not reverse psychosocial stress-induced hyponeophagic behavior

Quetiapine, an atypical antipsychotic, has been used for the treatment of several neuropsychiatric disorders. However, the underlying mechanism of the broad therapeutic range of quetiapine remains unknown. We previously reported that several aversive conditions affect dorsal/ventral hippocampal neurogenesis differentially. This study was aimed to elucidate the positive effects of chronic treatment with quetiapine on regional differences in hippocampal proliferation and immature neurons and behavioral changes under psychosocial stress using the Resident-Intruder paradigm. Twenty-three male Sprague-Dawley rats were intraperitoneally administered a vehicle or quetiapine (10 mg/kg) once daily for 28 days. Two weeks after starting the injections, animals were exposed to intermittent social defeat (four times over two weeks). The behavioral effects of stress and quetiapine were evaluated by the Novelty-Suppressed Feeding (NSF) test. The stereological quantification of hippocampal neurogenesis was estimated using immunostaining with Ki-67 and doublecortin (DCX). Chronic quetiapine treatment stimulated the Ki-67- and DCX-positive cells in the dorsal hippocampus, but not in the ventral subregion. The stress-induced changes in neurogenesis and hyponeophagic behavior were not reversed by repeated administration of quetiapine. Future study with additional behavioral tests is needed to elucidate the functional significance of the quetiapine-induced increase in dorsal hippocampal neurogenesis.

Tapentadol: an analgesic that differs from classic opioids due to its noradrenergic mechanism of action

Chronic pain treatment represents one of the most complex clinical challenges and even though opioids exhibit particular efficacy on nociceptive pain, their use must be controlled to avoid the risk of adverse reactions. A useful approach, aimed at maintaining analgesia and mitigating side effects, is represented by the use of a new class of analgesics endowed of µ-opioid (MOR) receptor agonism and noradrenaline reuptake inhibition (NRI) mechanisms. Tapentadol is the progenitor of this new class of drugs called MOP-NRI. A literature review has been conducted to gain information about the efficacy and the tolerability profile of tapentadol shifting from MOR agonism (acute pain) to NRI activity (chronic pain). The tolerability and therapeutic safety of tapentadol in neuropathic pain models, as well as in clinical settings, has been analyzed showing a good gastrointestinal tolerability profile, a moderate effect on hormone levels (in healthy volunteers and in patients) and on cognitive performance, a lack of significant alteration of the electrocardiogram recording and no changes of the QT/QTc interval, a minimal effect on serotonin reuptake in vivo with a low risk of serotonin syndrome, a longer time for the onset of analgesic tolerance and a less occurrence of abuse liability compared to formulations containing other comparator compounds. Tapentadol represents a great innovation in chronic pain therapy with a unique analgesic profile different form classical opioids, therefore, thanks to its synergistic MOR-NRI action, it may be a good option for the treatment of chronic, neuropathic and mixed pain.

Adult Cellular Neuroadaptations Induced by Adolescent THC Exposure in Female Rats Are Rescued by Enhancing Anandamide Signaling

BACKGROUND

In rodent models, chronic exposure to cannabis' psychoactive ingredient, Δ9-tetrahydrocannabinol, during adolescence leads to abnormal behavior in adulthood. In female rats, this maladaptive behavior is characterized by endophenotypes for depressive-like and psychotic-like disorders as well as cognitive deficits. We recently reported that most depressive-like behaviors triggered by adolescent Δ9-tetrahydrocannabinol exposure can be rescued by manipulating endocannabinoid signaling in adulthood with the anandamide-inactivating enzyme FAAH inhibitor, URB597. However, the molecular mechanisms underlying URB597's antidepressant-like properties remain to be established.

METHODS

Here we examined the impact of adult URB597 treatment on the cellular and functional neuroadaptations that occurred in the prefrontal cortex and dentate gyrus of the hippocampus upon Δ9-tetrahydrocannabinol during adolescence through biochemical, morphofunctional, and electrophysiological studies.

RESULTS

We found that the positive action of URB597 is associated with the rescue of Δ9-tetrahydrocannabinol-induced deficits in endocannabinoid-mediated signaling and synaptic plasticity in the prefrontal cortex and the recovery of functional neurogenesis in the dentate gyrus of the hippocampus. Moreover, the rescue property of URB597 on depressive-like behavior requires the activity of the CB1 cannabinoid receptor.

CONCLUSIONS

By providing novel insights into the cellular and molecular mechanisms of URB597 at defined cortical and hippocampal circuits, our results highlight that positive modulation of endocannabinoid-signaling could be a strategy for treating mood alterations secondary to adolescent cannabis use.

Treatment with corn oil improves neurogenesis and cognitive performance in the Ts65Dn mouse model of Down syndrome

Individuals with Down syndrome (DS), a genetic condition due to triplication of Chromosome 21, are characterized by intellectual disability that worsens with age. Since impairment of neurogenesis and dendritic maturation are very likely key determinants of intellectual disability in DS, interventions targeted to these defects may translate into a behavioral benefit. While most of the neurogenesis enhancers tested so far in DS mouse models may pose some caveats due to possible side effects, substances naturally present in the human diet may be regarded as therapeutic tools with a high translational impact. Linoleic acid and oleic acid are major constituents of corn oil that positively affect neurogenesis and neuron maturation. Based on these premises, the goal of the current study was to establish whether treatment with corn oil improves hippocampal neurogenesis and hippocampus-dependent memory in the Ts65Dn model of DS. Four-month-old Ts65Dn and euploid mice were treated with saline or corn oil for 30 days. Evaluation of behavior at the end of treatment showed that Ts65Dn mice treated with corn oil underwent a large improvement in hippocampus-dependent learning and memory. Evaluation of neurogenesis and dendritogenesis showed that in treated Ts65Dn mice the number of new granule cells of the hippocampal dentate gyrus and their dendritic pattern became similar to those of euploid mice. In addition, treated Ts65Dn mice underwent an increase in body and brain weight. This study shows for the first time that fatty acids have a positive impact on the brain of the Ts65Dn mouse model of DS. These results suggest that a diet that is rich in fatty acids may exert beneficial effects on cognitive performance in individuals with DS without causing adverse effects.

Modelling the dopamine and noradrenergic cell loss that occurs in Parkinson's disease and the impact on hippocampal neurogenesis

Key pathological features of Parkinson's Disease (PD) include the progressive degeneration of midbrain dopaminergic (DA) neurons and hindbrain noradrenergic (NA) neurons. The loss of DA neurons has been extensively studied and is the main cause of motor dysfunction. Importantly, however, there are a range of ‘non‐movement’ related features of PD including cognitive dysfunction, sleep disturbances and mood disorders. The origins for these non‐motor symptoms are less clear, but a possible substrate for cognitive decline may be reduced adult‐hippocampal neurogenesis, which is reported to be impaired in PD. The mechanisms underlying reduced neurogenesis in PD are not well established. Here we tested the hypothesis that NA and DA depletion, as occurs in PD, impairs hippocampal neurogenesis. We used 6‐hydroxydopamine or the immunotoxin dopamine‐β‐hydroxylase‐saporin to selectively lesion DA or NA neurons, respectively, in adult Sprague Dawley rats and assessed hippocampal neurogenesis through phenotyping of cells birth‐dated using 5‐bromo‐2′‐deoxyuridine. The results showed no difference in proliferation or differentiation of newborn cells in the subgranular zone of the dentate gyrus after NA or DA lesions. This suggests that impairment of hippocampal neurogenesis in PD likely results from mechanisms independent of, or in addition to degeneration of DA and NA neurons.

Comparative pharmacology and toxicology of tramadol and tapentadol

Moderate-to-severe pain represents a heavy burden in patients' quality of life, and ultimately in the society and in healthcare costs. The aim of this review was to summarize data on tramadol and tapentadol adverse effects, toxicity, potential advantages and limitations according to the context of clinical use. We compared data on the pharmacological and toxicological profiles of tramadol and tapentadol, after an extensive literature search in the US National Library of Medicine (PubMed). Tramadol is a prodrug that acts through noradrenaline and serotonin reuptake inhibition, with a weak opioid component added by its metabolite O-desmethyltramadol. Tapentadol does not require metabolic activation and acts mainly through noradrenaline reuptake inhibition and has a strong opioid activity. Such features confer tapentadol potential advantages, namely lower serotonergic, dependence and abuse potential, more linear pharmacokinetics, greater gastrointestinal tolerability and applicability in the treatment of chronic and neuropathic pain. Although more studies are needed to provide clear guidance on the opioid of choice, tapentadol shows some advantages, as it does not require CYP450 system activation and has minimal serotonergic effects. In addition, it leads to less side effects and lower abuse liability. However, in vivo and in vitro studies have shown that tramadol and tapentadol cause similar toxicological damage. In this context, it is important to underline that the choice of opioid should be individually balanced and a tailored decision, based on previous experience and on the patient's profile, type of pain and context of treatment.

SIGNIFICANCE

This review underlines the need for a careful prescription of tramadol and tapentadol. Although both are widely prescribed synthetic opioid analgesics, their toxic effects and potential dependence are not completely understood yet. In particular, concerning tapentadol, further research is needed to better assess its toxic effects.

l-Acetylcarnitine: A Mechanistically Distinctive and Potentially Rapid-Acting Antidepressant Drug

Current therapy of mood disorders has several limitations. Although a high number of drugs are clinically available, as of today, nearly two-thirds of individuals do not achieve full symptomatic remission after treatment with conventional antidepressants. Moreover, several weeks of drug treatment are usually required to obtain clinical effects, a limitation that has considerable clinical implications, ranging from high suicide risk to reduced compliance. The characteristic lag time in classical antidepressant effectiveness has given great impulse to the search for novel therapeutics with more rapid effects. l-acetylcarnitine (LAC), a small molecule of growing interest for its pharmacological properties, is currently marketed for treatment of neuropathic pain. Recent preclinical and clinical data suggested that LAC may exert antidepressant effects with a more rapid onset than conventional drugs. Herein, we review data supporting LAC antidepressant activity and its distinctive mechanisms of action compared with monoaminergic antidepressants. Furthermore, we discuss the unique pharmacological properties of LAC that allow us to look at this molecule as representative of next generation antidepressants with a safe profile.

Chronic Treatment with Fluoxetine Induces Sex-Dependent Analgesic Effects and Modulates HDAC2 and mGlu2 Expression in Female Mice

Gender and sex differences in pain recognition and drug responses have been reported in clinical trials and experimental models of pain. Among antidepressants, contradictory results have been observed in patients treated with selective serotonin reuptake inhibitors (SSRIs). This study evaluated sex differences in response to the SSRI fluoxetine after chronic administration in the mouse formalin test. Adult male and female CD1 mice were intraperitoneally injected with fluoxetine (10 mg/kg) for 21 days and subjected to pain assessment. Fluoxetine treatment reduced the second phase of the formalin test only in female mice without producing behavioral changes in males. We also observed that fluoxetine was able to specifically increase the expression of metabotropic glutamate receptor type-2 (mGlu2) in females. Also a reduced expression of the epigenetic modifying enzyme, histone deacetylase 2 (HDAC2), in dorsal root ganglia (DRG) and dorsal horn (DH) together with an increase histone 3 acetylation (H3) level was observed in females but not in males. With this study we provide evidence that fluoxetine induces sex specific changes in HDAC2 and mGlu2 expression in the DH of the spinal cord and in DRGs and suggests a molecular explanation for the analgesic effects in female mice.

Chronic pain and adult hippocampal neurogenesis: translational implications from preclinical studies

Adult hippocampal neurogenesis (ahNG) occurs in the human brain. Adult generated neurons have been proposed to functionally contribute to relevant hippocampal functions such as learning and memory, mood regulation, and stress response. Learning, environmental enrichment, and physical exercise exert positive effects on ahNG. In parallel, these proneurogenic stimuli have been shown to ameliorate cognitive performance and/or depressive-like behavior in animal models. Conversely, aging, social isolation, and chronic stress exert negative effects on ahNG. Interestingly, reduction of hippocampal neurogenesis is suggested to potentially contribute to cognitive decline and mood alterations associated with aging and several neuropsychiatric disorders. Clinical observation demonstrates that patients affected by chronic pain often exhibit increased anxiety and depression, impaired cognitive flexibility, and memory capacities. As of today, our understanding of the molecular and cellular events that may underlie the comorbidity of chronic pain, depression, and cognitive impairment is limited. Herein we review recent preclinical data suggesting that chronic pain may induce profound changes in hippocampal plasticity, including reduced ahNG. We discuss the possibility that deregulated hippocampal neurogenesis in chronic pain may, at least in part, contribute to cognitive and mood alterations. Based on this hypothesis, the mechanisms underlying chronic pain-associated changes in hippocampal neurogenesis and related functions need to be addressed experimentally. One interesting feature of ahNG is its susceptibility to pharmacological modulation. Again, based on preclinical data we discuss the possibility that, at least in principle, distinct analgesic drugs commonly used in chronic pain states (typical and atypical opiates, α2δ ligands, and acetyl-l-carnitine) may differentially impact ahNG and that this aspect could be taken into account to reduce and/or prevent the potential risk of cognitive and emotional side effects in the clinical setting.

Proneurogenic Effects of Trazodone in Murine and Human Neural Progenitor Cells

Several antidepressants increase adult hippocampal neurogenesis (ahNG) in rodents, primates, and, potentially, humans. This effect may at least partially account for their therapeutic activity. The availability of antidepressants whose mechanism of action involves different neurotransmitter receptors represents an opportunity for increasing our knowledge on their distinctive peculiarities and for dissecting the contribution of receptor subtypes in ahNG modulation. The aim of this study was to evaluate, in vitro, the effects of the antidepressant trazodone (TZD) on ahNG by using primary cultures of murine adult hippocampal neural progenitor cells (ahNPCs) and human induced pluripotent stem cell (iPSC)-derived NPCs. We demonstrated that TZD enhances neuronal differentiation of murine as well as human NPCs. TZD is a multimodal antidepressant, which binds with high affinity to 5-HT_2a, α₁, and 5-HT_1a and with lower affinity to 5-HT_2c, α₂ and 5-HTT. We demonstrated that TZD proneurogenic effects were mediated by 5-HT_2a antagonism both in murine and in human NPCs and by 5-HT_2c antagonism in murine cells. Moreover NF-κB p50 nuclear translocation appeared to be required for TZD-mediated proneurogenic effects. Interestingly, TZD had no proneurogenic effects in 5-HT depleted ahNPCs. The TDZ bell-shaped dose-response curve suggested additional effects. However, in our model 5-HT_1a and α₁/α₂ receptors had no role in neurogenesis. Overall, our data also demonstrated that serotoninergic neurotransmission may exert both positive and negative effects on neuronal differentiation of ahNPCs in vitro.

Tapentadol in neuropathic pain cancer patients: a prospective open label study

Many chemotherapy treatments induce peripheral neuropathy (CIPN). These patients often experience neuropathic pain (NP) that reduces the quality of life. The aim of this prospective, open label study was to evaluate the efficacy and tolerability of tapentadol (TP) in patients affected by CIPN. CIPN were consecutively enrolled in a prospective open label study at the Neuro-Oncology Unit of the Regina Elena National Cancer Institute in Rome. During the titration phase, each patient initially received doses of TP 50 mg twice a day. All patients underwent pain intensity (NRS) and DN4. For evaluation of quality of life, patients underwent EORTC QLQ-C30 and EORTC QLQ-CIPN2 QLQ-CIPN20. We enrolled 31 patients, 19 were females with a median age of 60 years. After 3 months of treatment with TP, 22 patients completed the statistical package for social sciences (SPSS). Nineteen patients out of 22 showed a response to treatment (86%). We also observed that TP reduced the NRS and DN4 values from baseline to the last visit in a significant way (p < 0.001, respectively). Seven patients (22.5%) discontinued the TP therapy after the first week of occurrence of side effects. Furthermore, we observed that TP improved also the global health status measured by EORT QLQ-C30. TP is well tolerated and efficacy in the treatment of NP. The important reduction of neuropathic pain, the improvement in NRS and QoL scores after therapy with TP makes it a candidate in the management of patients suffering from neuropathic pain of CIPN also as a first line of therapy.

ALCAR promote adult hippocampal neurogenesis by regulating cell-survival and cell death-related signals in rat model of Parkinson's disease like-phenotypes

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons in the nigrostriatal pathway that leading to progressive motor and nonmotor symptoms. The formation of newborn neurons in the adult hippocampus is affected by many factors such as anxiety, depression and impairment in learning and memory that are commonly observed nonmotor symptoms in PD, indicating the role of adult neurogenesis in PD pathophysiology. Acetyl-l-carnitine (ALCAR), regulate mitochondrial metabolism and has been reported to improve cognitive functions in different neurodegenerative disorders through an unknown mechanism. For the first time, we investigated the effect of ALCAR on adult neurogenesis in the 6-hydroxydopamine (6-OHDA) induced rat model of PD-like phenotypes and also explored the possible underlying mechanism of action. A single unilateral administration of 6-OHDA into the medial forebrain bundle reduced neural progenitor cell (NPC) proliferation, long-term survival and neuronal differentiation in the hippocampus. Interestingly, chronic treatment with ALCAR (100 mg/kg/day, i.p) potentially enhanced proliferation, long term survival and neuronal differentiation of NPCs in rat model of PD-like phenotypes. ALCAR treatment stimulates cell survival related signals (AKT and BCL-2) by inhibiting cell death related cues (GSK-3β and BAX) which might be responsible for a neuroprotective effect of ALCAR in rat model of PD-like phenotypes. We conclude that ALCAR exerts neuroprotective effects against 6-OHDA-induced impairment in hippocampal neurogenesis by regulating cell survival and cell death-related signals.

Opiate Analgesics as Negative Modulators of Adult Hippocampal Neurogenesis: Potential Implications in Clinical Practice

During the past decade, studies of the mechanisms and functional implications of adult hippocampal neurogenesis (ahNG) have significantly progressed. At present, it is proposed that adult born neurons may contribute to a variety of hippocampal-related functions, including specific cognitive aspects and mood regulation. Several groups focussed on the factors that regulate proliferation and fate determination of adult neural stem/progenitor cells (NSC/NPC), including clinically relevant drugs. Opiates were the first drugs shown to negatively impact neurogenesis in the adult mammalian hippocampus. Since that initial report, a vast array of information has been collected on the effect of opiate drugs, by either modulating proliferation of stem/progenitor cells or interfering with differentiation, maturation and survival of adult born neurons. The goal of this review is to critically revise the present state of knowledge on the effect of opiate drugs on the different developmental stages of ahNG, as well as the possible underlying mechanisms. We will also highlight the potential impact of deregulated hippocampal neurogenesis on patients undergoing chronic opiate treatment. Finally, we will discuss the differences in the negative impact on ahNG among clinically relevant opiate drugs, an aspect that may be potentially taken into account to avoid long-term deregulation of neural plasticity and its associated functions in the clinical practice.

Adult Hippocampal Neurogenesis along the Dorsoventral Axis Contributes Differentially to Environmental Enrichment Combined with Voluntary Exercise in Alleviating Chronic Inflammatory Pain in Mice

Cognitive behavioral therapy, such as environmental enrichment combined with voluntary exercise (EE-VEx), is under active investigation as an adjunct to pharmaceutical treatment for chronic pain. However, the effectiveness and underlying mechanisms of EE-VEx remain unclear. In mice with intraplantar injection of complete Freund's adjuvant, our results revealed that EE-VEx alleviated perceptual, affective, and cognitive dimensions of chronic inflammatory pain. These effects of EE-VEx on chronic pain were contingent on the occurrence of adult neurogenesis in the dentate gyrus in a functionally dissociated manner along the dorsoventral axis: neurogenesis in the ventral dentate gyrus participated in alleviating perceptual and affective components of chronic pain by EE-VEx, whereas neurogenesis in the dorsal dentate gyrus was involved in EE-VEx's cognitive-enhancing effects. Chronic inflammatory pain was accompanied by decreased levels of brain-derived neurotrophic factor (BDNF) in the dentate gyrus, which were reversed by EE-VEx. Overexpression of BDNF in the dentate gyrus mimicked the effects of EE-VEx. Our results demonstrate distinct contribution of adult hippocampal neurogenesis along the dorsoventral axis to EE-VEx's beneficial effects on different dimensions of chronic pain.SIGNIFICANCE STATEMENT Environmental enrichment combined with voluntary exercise (EE-VEx) is under active investigation as an adjunct to pharmaceutical treatment for chronic pain, but its effectiveness and underlying mechanisms remain unclear. In a mouse model of inflammatory pain, the present study demonstrates that the beneficial effects of EE-VEx on chronic pain depend on adult neurogenesis with a dorsoventral dissociation along the hippocampal axis. Adult neurogenesis in the ventral dentate gyrus participates in alleviating perceptual and affective components of chronic pain by EE-VEx, whereas that in the dorsal pole is involved in EE-VEx's cognitive-enhancing effects in chronic pain.

Novel insights into the role of NF-κB p50 in astrocyte-mediated fate specification of adult neural progenitor cells

Within the CNS nuclear factor-kappa B (NF-κB) transcription factors are involved in a wide range of functions both in homeostasis and in pathology. Over the years, our and other groups produced a vast array of information on the complex involvement of NF-κB proteins in different aspects of postnatal neurogenesis. In particular, several extracellular signals and membrane receptors have been identified as being able to affect neural progenitor cells (NPC) and their progeny via NF-κB activation. A crucial role in the regulation of neuronal fate specification in adult hippocampal NPC is played by the NF-κB p50 subunit. NF-κB p50KO mice display a remarkable reduction in adult hippocampal neurogenesis which correlates with a selective defect in hippocampal-dependent short-term memory. Moreover absence of NF-κB p50 can profoundly affect the in vitro proneurogenic response of adult hippocampal NPC (ahNPC) to several endogenous signals and drugs. Herein we briefly review the current knowledge on the pivotal role of NF-κB p50 in the regulation of adult hippocampal neurogenesis. In addition we discuss more recent data that further extend the relevance of NF-κB p50 to novel astroglia-derived signals which can influence neuronal specification of ahNPC and to astrocyte-NPC cross-talk.

Effect of Opioid on Adult Hippocampal Neurogenesis

During the past decade, the study of the mechanisms and functional implications of adult neurogenesis has significantly progressed. Many studies focus on the factors that regulate proliferation and fate determination of adult neural stem/progenitor cells, including addictive drugs such as opioid. Here, we review the most recent works on opiate drugs' effect on different developmental stages of adult hippocampal neurogenesis, as well as the possible underlying mechanisms. We conclude that opiate drugs in general cause a loss of newly born neural progenitors in the subgranular zone of dentate gyrus, by either modulating proliferation or interfering with differentiation and maturation. We also discuss the consequent impact of regulation of adult neurogenesis in animal's opioid addiction behavior. We further look into the future directions in studying the convergence between the adult neurogenesis field and opioid addiction field, since the adult-born granular cells were shown to play a role in neuroplasticity and may help to reduce the vulnerability to drug craving and relapse.

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).

Statins Promote Long-Term Recovery after Ischemic Stroke by Reconnecting Noradrenergic Neuronal Circuitry

Inhibitors of HMG-CoA reductase (statins), widely used to lower cholesterol in coronary heart and vascular disease, are effective drugs in reducing the risk of stroke and improving its outcome in the long term. After ischemic stroke, cardiac autonomic dysfunction and psychological problems are common complications related to deficits in the noradrenergic (NA) system. This study investigated the effects of statins on the recovery of NA neuron circuitry and its function after transient focal cerebral ischemia (tFCI). Using the wheat germ agglutinin (WGA) transgene technique combined with the recombinant adenoviral vector system, NA-specific neuronal pathways were labeled, and were identified in the locus coeruleus (LC), where NA neurons originate. NA circuitry in the atorvastatin-treated group recovered faster than in the vehicle-treated group. The damaged NA circuitry was partly reorganized with the gradual recovery of autonomic dysfunction and neurobehavioral deficit. Newly proliferated cells might contribute to reorganizing NA neurons and lead anatomic and functional recovery of NA neurons. Statins may be implicated to play facilitating roles in the recovery of the NA neuron and its function.

Loss of the mu opioid receptor induces strain-specific alterations in hippocampal neurogenesis and spatial learning

Alterations in hippocampal neurogenesis affect spatial learning, though, the relative contributions of cell proliferation and cell survival on this process are poorly understood. The current study utilized mu opioid receptor (MOR-1) knockout (KO) mice on two background strains, C57BL/6 and 129S6, to assess cell survival as well as determine the impact on spatial learning using the Morris water maze. These experiments were designed to extend prior work showing that both C57BL/6 and 129S6 MOR-1 KO mice have an increased number of proliferating cells in the dentate gyrus (DG) when compared to wild-type (WT) mice. The current study indicates that newly born neurons in the DG of C57BL/6 MOR-1 KO mice exhibit enhanced survival when compared to WT mice, while new neurons in the DG of 129S6 MOR-1 KO mice do not. In addition, C57BL/6 MOR-1 KO mice have a lower number of apoptotic cells in the DG compared to WT mice while, in contrast, 129S6 MOR-1 KO mice have a higher number of apoptotic cells in this region. These alterations collectively contribute to an increase in the granule cell number in the DG of C57BL/6 MOR-1 KO mice, while the total number of granule cells in 129S6 MOR-1 KO mice is unchanged. Thus, although C57BL/6 and 129S6 MOR-1 KO mice both exhibit increased cell proliferation in the DG, the impact of the MOR-1 mutation on cell survival differs between strains. Furthermore, the decrease in DG cell survival displayed by 129S6 MOR-1 KO mice is correlated with functional deficits in spatial learning, suggesting that MOR-1-dependent alterations in the survival of new neurons in the DG, and not MOR-1-dependent changes in proliferation of progenitor cells in the DG, is important for spatial learning.

The mu-opioid receptor agonist/noradrenaline reuptake inhibition (MOR-NRI) concept in analgesia: the case of tapentadol

Tapentadol is a novel, centrally-acting analgesic drug, with an analgesic efficacy comparable to that of strong opioids such as oxycodone and morphine. Its high efficacy has been demonstrated in a range of animal models of acute and chronic, nociceptive, inflammatory, and neuropathic pain as well as in clinical studies with moderate to severe pain arising from a number of different etiologies. At the same time, a favorable gastrointestinal tolerability has been demonstrated in rodents and humans, and advantages over morphine regarding tolerance development and physical dependence were shown in animal studies. Furthermore, a low level of abuse and diversion is beginning to emerge from first post-marketing data. Tapentadol acts as a μ-opioid receptor (MOR) agonist and noradrenaline reuptake inhibitor (NRI). Both mechanisms of action have been shown to contribute to the analgesic activity of tapentadol and to produce analgesia in a synergistic manner, such that relatively moderate activity at the two target sites (MOR and noradrenaline reuptake transporter) is sufficient to produce strong analgesic effects. It has been suggested that tapentadol is the first representative of a proposed new class of analgesics, MOR-NRI. This review presents the evidence that has led to this suggestion, and outlines how the pharmacology of tapentadol can explain its broad analgesic activity profile and high analgesic potency as well as its favorable tolerability.