Preclinical evidence of the effects of sweet flavors: Sweetness increases nicotine intake and seeking.

INTRODUCTION: The influence of early exposure to sweet and fruit flavors on subsequent nicotine use behaviors during adolescence remains poorly understood. To address this gap, we utilized a rodent model to simulate childhood flavor exposure and examine its effects on later nicotine use behaviors. METHODS: We employed a two-bottle choice paradigm in weanling rats to mimic human childhood flavor exposure. Subsequently, we investigated the impact of early exposure to sweet (saccharin) and cherry fruit (benzaldehyde) flavors on adolescent nicotine use behaviors. This included assessing subsequent nicotine acquisition, maintenance, and seeking behaviors using intraoral flavor and intravenous nicotine self-administration. RESULTS: Our findings reveal that rats exposed to saccharin during early development exhibited altered patterns of nicotine intake and seeking behaviors during adolescence. Specifically, rats demonstrated increased nicotine intake and seeking of saccharin flavored solutions when paired with nicotine, indicating a potential predisposition towards nicotine use following childhood flavor exposure. Intraoral benzaldehyde did not affect nicotine reinforcement in early sessions of self-administration, but significantly decreased nicotine reinforcement during later sessions. Both saccharin exposure alone or in combination with benzaldehyde promoted nicotine reinforcement. No significant sex differences in nicotine-related behaviors were observed. CONCLUSIONS: This study highlights the significance of early flavor exposure in shaping adolescent nicotine use behaviors. The findings suggest that childhood exposure to sweet flavors may contribute to heightened susceptibility to nicotine use and addiction later in life. Understanding these early influences is crucial for developing targeted interventions to prevent the onset of nicotine addiction during adolescence. IMPLICATIONS: Our study highlights the importance of how sweetness can contribute to and possibly even alter the effects of the flavor itself. The sweetness of a tobacco product does not solely stem from sweeteners, but it is also influenced by other components such as the PG/VG ratio (e.g., higher VG) and the inclusion of flavors associated with sweetness (e.g., vanillin and ethyl maltol). Therefore, sweet-associated constituents in tobacco products should be investigated further to inform regulatory policy. We believe that our findings can inform regulatory decisions on controlling sweet associated constituents in tobacco products.

The influence of ovarian hormones on the putative mechanisms that promote female nicotine use.

Nicotine use is driven by pleasurable effects, but following chronic exposure, nicotine use becomes largely driven by the desire need to avoid withdrawal symptoms. Current cessation strategies focusing on alleviating withdrawal, but current cessation interventions are less effective for women than men. Also, hormone fluctuations across the menstrual cycle appear to impact use patterns, withdrawal severity, and treatment efficacy. This raises important questions regarding optimal quit dates and the application of hormone interventions to alleviate withdrawal in women. This review surveys the existing literature assessing the impact of ovarian hormones on nicotine withdrawal severity. This is an important issue because women seeking cessation treatments may be using hormone-based contraceptives or hormone replacement post-menopause. Hormone interventions may also offer a novel treatment avenue that is more effective than current cessation approaches. Future work in this area is important for reducing health disparities produced by excessive nicotine use in women.

Impact of vanilla flavor on nicotine taste, choice, intake, and seeking behaviors.

RATIONALE: Flavors can alter the orosensory properties of tobacco products. Specifically, flavors can serve as an oral cue for smokeless tobacco products. OBJECTIVES: We aimed to investigate the impact of oral vanillin, the principal chemical of vanilla flavor in tobacco products, on nicotine's taste, and nicotine choice, intake, and seeking behaviors. METHODS: Experiments were performed in young adult Sprague Dawley rats. We employed a two-bottle free-choice test (2BC) to measure the preference for different concentrations of vanillin and its effect on nicotine preference. To explore the long-term effects of early exposure to sweetened vanillin, we utilized a combined 2BC and intraoral self-administration (IOSA) model. We assessed the nicotine taking and seeking behaviors in the presence or absence of vanillin. We performed a taste reactivity test (TRT) to quantify liking (ingestive) and disliking (aversive) taste responses to oral nicotine with or without vanillin. RESULTS: In 2BC, female rats preferred vanillin containing solutions more than their male counterparts. In IOSA, vanillin alone and in combination with nicotine led to greater IOSA compared to water. Female rats self-administered vanillin plus nicotine more than male rats. Vanillin increased motivation to nicotine taking, but only in females. In TRT, vanillin increased nicotine's ingestive responses but blocked aversive responses in both sexes. CONCLUSIONS: These results indicate that vanilla flavor can increase oral nicotine intake. It can also increase liking and decrease disliking of nicotine's taste. Furthermore, the impact of vanilla flavor on nicotine taste and nicotine choice, intake, and seeking behaviors is concentration and sex dependent.

Chronic oral nicotine exposure decreases aversive taste of nicotine, increases nicotine withdrawal and reinstatement, but cherry flavor does not alter nicotine's effects in adolescent rats.

Although e-cigarette use among youth is recognized as an epidemic, there is limited understanding regarding nicotine's orosensory and chronic use effects in youth, and how fruit e-cigarette flavorings may influence nicotine's effects. We aimed to characterize the orosensory and chronic use effects of nicotine in adolescent rats. We also determined the acute and chronic effects of benzaldehyde, a cherry/berry/almond flavoring, on nicotine's taste, consumption, withdrawal, and reinstatement. Rats were examined for their acute taste responses to the different nicotine concentrations. The effects of chronic exposure on nicotine's taste, withdrawal, and reinstatement were also determined. In addition, impact of benzaldehyde on these nicotine use behaviors was evaluated. While taste responses to low nicotine concentrations did not differ from water, high nicotine concentrations induced aversion. Aversive responses to nicotine that were observed in naïve animals vanished after chronic nicotine exposure, indicating the development of tolerance to nicotine's aversive taste. Additionally, nicotine abstinence after chronic exposure induced withdrawal. Following abstinence, animals reinstated nicotine use. Further, animals showed higher preference to nicotine after reinstatement, compared to preference values before nicotine withdrawal. Benzaldehyde did not alter nicotine's taste reactivity, withdrawal, and reinstatement experiments. Some sex differences were found in benzaldehyde's taste response and choice behavior experiments.

Phosphosulindac (OXT-328) prevents and reverses chemotherapy induced peripheral neuropathy in mice.

Background: Chemotherapy-induced peripheral neuropathy (CIPN), a side effect of chemotherapy, is particularly difficult to treat. We explored whether phosphosulindac (PS), a modified NSAID, could treat CIPN. Methods: CIPN was induced in male C57BL/6 J mice by paclitaxel, vincristine or oxaliplatin. Mechanical allodynia was measured with the von Frey test and cold allodynia with the acetone test. To determine the preventive effect of PS, it was administered 2 days before the induction of CIPN. Mouse Lewis lung carcinoma xenografts were used to determine if PS altered the chemotherapeutic efficacy of paclitaxel. Cultured cell lines were used to evaluate the effect of PS on neuroinflammation. Results: Treatment with each of the three chemotherapeutic agents used to induce CIPN lowered the mechanical allodynia scores by 56 to 85% depending on the specific agent. PS gel was applied topically 3x/day for 16-22 days to the hind paws of mice with CIPN. This effect was dose-dependent. Unlike vehicle, PS returned mechanical allodynia scores back to pre-CIPN levels. PS had a similar effect on paclitaxel-induced CIPN cold allodynia. Sulindac, a metabolite of PS, had no effect on CIPN. PS significantly prevented CIPN compared to vehicle. Given concomitantly with paclitaxel to mice with lung cancer xenografts, PS relieved CIPN without affecting the anticancer effect of paclitaxel. The enantiomers of PS were equally efficacious against CIPN, suggesting the therapeutic suitability of the racemate PS. There were no apparent side effects of PS. PS suppressed the levels of IL-6, IL-10, CXCL1, and CXCL2 induced by paclitaxel in a neuroblastoma cell line, and macrophage activation to the M1 proinflammatory phenotype. Conclusion: Topically applied PS demonstrated broad therapeutic and preventive efficacy against CIPN, preserved the anticancer effect of paclitaxel, and was safe. Its anti-CIPN effect appears to be mediated, in part, by suppression of neuroinflammation. These data support further evaluation of topical PS for the control of CIPN.

Pharmacological characterization of 5-iodo-A-85380, a ß2-selective nicotinic receptor agonist, in mice.

BACKGROUND: Because of their implications in several pathological conditions, α4ß2* nicotinic acetylcholine receptors (nAChRs) are potential targets for the treatment of nicotine dependence, pain, and many psychiatric and neurodegenerative diseases. However, they exist in various subtypes, and finding selective tools to investigate them has proved challenging. The nicotinic receptor agonist, 5-iodo-A-85380 (5IA), has helped in delineating the function of ß2-containing subtypes in vitro; however, much is still unknown about its behavioral effects. Furthermore, its effectiveness on α6-containing subtypes is limited. AIMS: To investigate the effects of 5IA on nociception (formalin, hot-plate, and tail-flick tests), locomotion, hypothermia, and conditioned reward after acute and repeated administration, and to examine the potential role of ß2 and α6 nAChR subunits in these effects. Lastly, its selectivity for expressed low sensitivity (LS) and high sensitivity (HS) α4ß2 receptors is investigated. RESULTS: 5IA dose-dependently induced hypothermia, locomotion suppression, conditioned place preference, and antinociception (only in the formalin test but not in the hot-plate or tail-flick tests). Furthermore, these effects were mediated by ß2 but not α6 nicotinic subunits. Finally, we show that 5-iodo-A-85380 potently activates both stoichiometries of α4ß2 nAChRs with differential efficacies, being a full agonist on HS α4(2)ß2(3) nAChRs, and a partial agonist on LS α4(3)ß2(2) nAChRs and α6-containing subtypes as well.

Persistent sensory changes and sex differences in transgenic mice conditionally expressing HIV-1 Tat regulatory protein.

HIV-associated sensory neuropathies (HIV-SN) are prevalent in >50% of patients aged over 45 years many of which report moderate to severe chronic pain. Previous preclinical studies have investigated the mechanisms by which HIV-1 causes sensory neuropathies and pain-like behaviors. The aim of the present study is to delineate the role of chronic HIV-1 trans-activator of transcription protein (Tat) exposure in the development of neuropathy in mice. The temporal effects of conditional Tat expression on the development of hypersensitivity to mechanical (von Frey filaments) and thermal (heat or cold) stimuli were tested in male and female mice that transgenically expressed HIV-1 Tat in a doxycycline-inducible manner. Inducing Tat expression produced an allodynic response to mechanical or cold (but not heat) stimuli that respectively persisted for at least 23-weeks (mechanical hypersensitivity) or at least 8-weeks (cold hypersensitivity). Both allodynic states were greater in magnitude among females, compared to males, and mechanical increased hypersensitivity progressively in females over time. Acute morphine or gabapentin treatment partly attenuated allodynia in males, but not females. Irrespective of sex, Tat reduced intraepidermal nerve fiber density, the mean amplitude of sensory nerve action potentials (but not conductance), engagement in some pain-related ethological behaviors (cage-hanging and rearing), and down-regulated PPAR-α gene expression in lumbar spinal cord while upregulating TNF-α expression in dorsal root ganglion. Taken together, these data reveal fundamental sex differences in mechanical and cold hypersensitivity in response to Tat and demonstrate the intractable nature in female mice to current therapeutics. Understanding the role of Tat in these pathologies may aid the design of future therapies aimed at mitigating the peripheral sensory neuropathies that accompany neuroHIV.

Genotypic Differences in the Effects of Menthol on Nicotine Intake and Preference in Mice.

Menthol has been shown to exacerbate elements of nicotine addiction in humans and rodents; however, the mechanisms mediating its effects are not fully understood. This study examined the impact of genetic factors in menthol's effects on oral nicotine consumption by comparing two inbred mouse strains with differing sensitivities to nicotine. C57BL/6J (B6J) mice are nicotine-preferring, while DBA/2J (D2J) mice are not. While the effects of menthol on oral nicotine consumption have been highlighted in B6J mice, it is unknown if they extend to the D2J strain as well. Consequently, adolescent (PND 21) and adult (PND 63), male and female D2J mice were subjected to the nicotine two-bottle choice (2BC) paradigm with orally and systemically administered menthol. Then, we evaluated its impact on nicotine pharmacological responses in conditioned reward and nociception after systemic administration and, lastly, investigated the potential involvement of the TAAR1 gene and α7 nAChRs in menthol's effects. Menthol failed to enhance oral nicotine consumption in adult and adolescent female and male D2J mice. Moreover, this lack in effect was not due to nicotine concentration, oral aversion to menthol, or basal preference for nicotine. Menthol also failed to augment nicotine reward or enhance nicotine-induced antinociception in D2J mice, demonstrating that genetic background plays a significant role in sensitivity to menthol's effects on nicotine. Furthermore, TAAR1 or α7 nAChRs did not seem to mediate menthol's differential effects in D2J mice. These findings support the existence of genotype-specific mechanisms that may contribute to the variable effects of menthol in different populations.

Animal Models to Investigate the Impact of Flavors on Nicotine Addiction and Dependence.

BACKGROUND: Tobacco use in humans is a long-standing public health concern. Flavors are common additives in tobacco and alternative tobacco products, added to mask nicotine's harsh orosensory effects and increase the appeal of these products. Animal models are integral for investigating nicotine use and addiction and are helpful for understanding the effects of flavor additives on the use of nicotine delivery products. OBJECTIVE: This review focuses on preclinical models to evaluate the contribution of flavor additives to nicotine addiction. MATERIALS AND METHODS: An electronic literature search was conducted by authors up to May 2022. Original articles were selected. RESULTS: The behavioral models of rodents described here capture multiple dimensions of human flavored nicotine use behaviors, including advantages and disadvantages. CONCLUSION: The consensus of the literature search was that human research on nicotine use behavior has not caught up with fast-changing product innovations, marketing practices, and federal regulations. Animal models are therefore needed to investigate mechanisms underlying nicotine use and addiction. This review provides a comprehensive overvie.

Cholinergic and dopaminergic-mediated motivated behavior in healthy states and in substance use and mood disorders.

Acetylcholine is an important neuromodulator of the mesolimbic dopamine (DA) system, which itself is a mediator of motivated behavior. Motivated behavior can be described by two primary components, termed directional and activational motivation, both of which can be examined and dissociated using effort-choice tasks. The directional component refers to motivated behavior directed towards reinforcing stimuli and away from aversive stimuli. Behaviors characterized by increased vigor, persistence, and work output are considered to reflect activational components of motivation. Disruption of DA signaling has been shown to decrease activational components of motivation, while leaving directional features intact. Facilitation of DA release promotes the activational aspects of motivated behavior. In this review, we discuss cholinergic and DA regulation of motivated behaviors. We place emphasis on effort-choice processes and the ability of effort-choice tasks to examine and dissociate changes of motivated behavior in the context of substance use and mood disorders. Furthermore, we consider how altered cholinergic transmission impacts motivated behavior across disease states, and the possible role of cholinergic dysregulation in the etiology of these illnesses. Finally, we suggest that treatments targeting cholinergic activity may be useful in ameliorating motivational disruptions associated with substance use and comorbid substance use and mood disorders.

Evaluation of Flavor Effects on Oral Nicotine Liking and/or Disliking Using the Taste Reactivity Test in Rats.

INTRODUCTION: Tobacco product flavors may change the sensory properties of nicotine, such as taste and olfactory cues, which may alter nicotine reward and aversion and nicotine taking behavior. The hedonic or aversive value of a taste stimulus can be evaluated by examining affective orofacial movements in rodents. AIMS AND METHODS: We characterized taste responses to various oral nicotine concentrations using the taste reactivity test in rats. We also evaluated the impact of menthol and benzaldehyde (cherry, almond) flavorants on both ingestive and aversive responses to oral nicotine. Adult Sprague-Dawley rats (n = 5-10 per sex per group) were implanted with intraoral catheters and received 20 infusions (200 µl/ea). Nicotine (1-100 µg/mL) was evaluated in taste reactivity test to determine taste responses to nicotine. Later, the effects of menthol (50 µg/mL) and benzaldehyde (100 µg/mL) on the taste responses to nicotine were determined. RESULTS: Nicotine at low concentrations (3 µg/mL in males, 1 µg/mL in females) elicited significantly greater ingestive responses compared with water, whereas higher nicotine concentrations (≥30 µg/mL in males, ≥10 µg/mL in females) elicited significant aversive reactions. Thus, intraoral nicotine induced both hedonic and aversive responses in a concentration- and sex-dependent manner. Females were more sensitive to nicotine's concentration. The addition of menthol or benzaldehyde significantly increased the hedonic responses to nicotine, and significantly decreased the aversive nicotine responses. CONCLUSIONS: Oral nicotine induces both hedonic and aversive taste responses, which may represent liking and disliking. Menthol and benzaldehyde can alter the orosensory experience of nicotine, which may influence nicotine's abuse liability. IMPLICATIONS: Our work represents a model to study impact of flavors on oral nicotine liking and disliking responses in rats. Moreover, our findings show that menthol and benzaldehyde alter the orosensory experience of nicotine, suggesting that both could influence nicotine's abuse liability.

(E)-3-furan-2-yl-N-phenylacrylamide (PAM-4) decreases nociception and emotional manifestations of neuropathic pain in mice by α7 nicotinic acetylcholine receptor potentiation.

Clinical intervention of pain is often accompanied by changes in affective behaviors, so both assays of affective and sensorial aspects of nociception play an important role in the development of novel analgesics. Although positive allosteric modulation (PAM) of α7 nicotinic acetylcholine receptors (nAChRs) has been recognized as a novel approach for the relief of sensorial aspects of pain, their effects on affective components of pain remain unclear. Therefore, we investigated whether PAM-4, a highly selective α7-nAChR PAM, attenuates inflammatory and neuropathic pain, as well as the concomitant depressive/anxiety comorbidities. The anti-nociceptive activity of PAM-4 was assessed in mice using the formalin test and chronic constriction injury (CCI)-induced neuropathic pain model. The anxiolytic- and antidepressant-like activity of PAM-4 was evaluated using the marble burying test and forced swimming test. Acute systemic administration of PAM-4 dose-dependently reversed formalin-induced paw licking behavior and CCI-induced mechanical allodynia without development of any motor impairment. PAM-4 reversed the decreased swimming time and number of buried marbles in CCI-treated mice, suggesting that this ligand attenuates chronic pain-induced depression-like behavior and anxiogenic-like effects. The effects of PAM-4 were inhibited by the α7-selective antagonist methyllycaconitine, indicating molecular mechanism mediated by α7-nAChRs. Indeed, electrophysiological recordings showed the PAM-4 enhances human α7 nAChRs with higher potency and efficacy compared to rat α7 nAChRs. These findings suggest that PAM-4 reduces both sensorial and affective behaviors induced by chronic pain in mice by α7-nAChR potentiation. PAM-4 deserves further investigations for the management of chronic painful conditions with comorbidities.

N-acylethanolamine-hydrolysing acid amidase: A new potential target to treat paclitaxel-induced neuropathy.

BACKGROUND: Although paclitaxel is an effective chemotherapeutic agent used to treat multiple types of cancer (e.g. breast, ovarian, neck and lung), it also elicits paclitaxel-induced peripheral neuropathy (PIPN), which represents a major dose-limiting side effect of this drug. METHODS: As the endogenously produced N-acylethanolamine, palmitoylethanolamide (PEA), reverses paclitaxel-induced mechanical hypersensitivity in mice, the main goals of this study were to examine if paclitaxel affects levels of endogenous PEA in the spinal cord of mice and whether exogenous administration of PEA provides protection from the occurrence of paclitaxel-induced mechanical hypersensitivity. We further examined whether inhibition of N-acylethanolamine-hydrolysing acid amidase (NAAA), a hydrolytic PEA enzyme, would offer protection in mouse model of PIPN. RESULTS: Paclitaxel reduced PEA levels in the spinal cord, suggesting that dysregulation of this lipid signalling system may contribute to PIPN. Consistent with this idea, repeated administration of PEA partially prevented the paclitaxel-induced mechanical hypersensitivity. We next evaluated whether the selective NAAA inhibitor, AM9053, would prevent paclitaxel-induced mechanical hypersensitivity in mice. Acute administration of AM9053 dose-dependently reversed mechanical hypersensitivity through a PPAR-α mechanism, whereas repeated administration of AM9053 fully prevented the development of PIPN, without any evidence of tolerance. Moreover, AM9053 produced a conditioned place preference in paclitaxel-treated mice, but not in control mice. This pattern of findings suggests a lack of intrinsic rewarding effects, but a reduction in the pain aversiveness induced by paclitaxel. Finally, AM9053 did not alter paclitaxel-induced cytotoxicity in lung tumour cells. CONCLUSIONS: Collectively, these studies suggest that NAAA represents a promising target to treat and prevent PIPN. SIGNIFICANCE: The present study demonstrates that the chemotherapeutic paclitaxel alters PEA levels in the spinal cord, whereas repeated exogenous PEA administration moderately alleviates PIPN in mice. Additionally, targeting NAAA, PEA's hydrolysing enzyme with a selective compound AM9053 reverses and prevents the PIPN via the PPAR-α mechanism. Overall, the data suggest that selective NAAA inhibitors denote promising future therapeutics to mitigate and prevent PIPN.

Effect of High Fructose Corn Sirup on Pancreatic Ductal Adenocarcinoma Induced by Dimethyl Benzantracene (DMBA) in Rats.

Increased risk of pancreatic cancer may be associated with consumption of sugar containing foods. The aim of this study was to evaluate the effect of peach nectar containing high fructose corn sirup (HFCS) consumption in a pancreatic carcinogenesis rat model induced by 7,12-Dimethyl benzanthracene (DMBA). Fifty-day-old male Sprague Dawley rats were fed with peach nectar containing HFCS + chow, peach nectar containing sucrose + chow and only chow. After 8 mo, feeding period, each group was divided into two subgroups, in which the rats were implanted with DMBA and no DMBA (sham). Histologic specimens were evaluated according to the routine tissue processing protocol. The animals with ad libitum access to pn-HFCS, pn-sucrose and chow (only) showed significant differences in chow consumption and glucose level. Necropsy and histopathologic findings showed tumor formation in the entire group treated with DMBA. Excluding one rat in chow group, which was classified as poorly differentiated type, the others were classified as moderately differentiated pancreatic ductal adenocarcinoma (PDAC). This study demonstrated that daily intake of HFCS did not increase body weight and there was no effect of peach nectar consumption on the development of PDAC induced by DMBA in rats.

Deficit in voluntary wheel running in chronic inflammatory and neuropathic pain models in mice: Impact of sex and genotype.

Patients with chronic pain report decreased general activity and emotional distress. Therefore, the development of various animal models that encompass different aspects of pain are crucial for the discovery of genetic differences and the assessment of novel analgesics to improve quality of life. C57BL/6J and DBA/2J mice received unilateral intraplantar injections of 100 % CFA, paclitaxel, or CCI surgery to compare their distance traveled in a voluntary wheel running assay, paw edema diameter, and mechanical sensitivity. Mechanical withdrawal thresholds were lower in both strains of mice that received CFA when compared to their vehicle. However, a decrease in distance traveled was observed in CFA-treated C57BL/6J but not DBA/2J mice. In a separate group, chemotherapy agent paclitaxel 8 mg/kg, i.p. was administered to both strains of mice to induce CIPN which was confirmed by lower mechanical thresholds in paclitaxel-treated mice compared to vehicle-treated mice. Only female C57BL/6J mice showed attenuation of distance traveled following treatment, whereas male C57BL/6J and DBA/2J mice did not. Lastly, C57BL/6J mice underwent chronic constriction injury (CCI) or sham surgery to observe the impact of another chronic neuropathic pain model in wheel running assay. CCI mice showed a gradual decrease in mechanical withdrawal threshold and a decrease in distance traveled compared to sham 5 days following the procedure. Comparing these chronic inflammatory and neuropathic pain models in different mouse strains may help us better understand genetic differences underlying pain perception and its impact on reflexive and nonreflexive outcome measures.

Impact of menthol on nicotine intake and preference in mice: Concentration, sex, and age differences.

Menthol has been shown to contribute to the appeal of tobacco products in humans. However, factors such as sex, age and menthol concentration remain unclear in the interaction between menthol and nicotine. To understand these factors, we utilized a mouse model to determine the impact of menthol on oral nicotine consumption. A range of menthol concentrations (oral and systemic) were tested with or without oral nicotine using the two-bottle choice paradigm in adolescent and adult female and male C57BL/6J mice. Moreover, genetically modified mice were used to investigate the role of α7 nicotinic acetylcholine receptors (nAChRs) on the effects of menthol. Menthol addition to nicotine solution increased oral nicotine consumption in C57BL/6J mice in a sex- and menthol concentration-dependent manner. At lower menthol concentrations, female mice demonstrated an enhancement of nicotine consumption and male mice showed a similar behavior at higher menthol concentrations. Menthol drinking alone was only significantly different by sex at 60 µg/ml menthol concentration where female mice had higher menthol intake than males. Menthol administered both orally and systemically (intraperitoneal) increased oral nicotine consumption. Adolescent female mice had a higher nicotine intake at lower menthol concentrations compared to their adult counterparts. While α7 nAChR wild type mice consumed more mentholated nicotine solution than nicotine only solution, this effect was abolished in KO mice. Effects of menthol are concentration-, sex-, age-, and α7 nAChR-dependent. Oral and intraperitoneal menthol increases nicotine intake, suggesting that sensory, peripheral, and/or central mechanisms are involved in effects of menthol on oral nicotine consumption.

Conditional expression of HIV-1 tat in the mouse alters the onset and progression of tonic, inflammatory and neuropathic hypersensitivity in a sex-dependent manner.

BACKGROUND: At least one-third of HIV-1-afflicted individuals experience peripheral neuropathy. Although the underlying mechanisms are not known, they may involve neurotoxic HIV-1 proteins. METHODS: We assessed the influence of the neurotoxic HIV-1 regulatory protein, Tat, on inflammatory and neuropathic nociceptive behaviours using transgenic male and female mice that conditionally expressed (or did not express) HIV-1 Tat1-86 in fibrillary acidic protein-expressing glia in the central and peripheral nervous systems. RESULTS: Tat induction significantly attenuated the time spent paw-licking following formalin injection (2.5%, i.pl.) in both male and female mice. However, significant sex differences were observed in the onset and magnitude of inflammation and sensory sensitivity following complete Freund's adjuvant (CFA) injection (10%, i.pl.) after Tat activation. Unlike female mice, male mice showed a significant attenuation of paw swelling and an absence of mechanical/thermal hypersensitivity in response to CFA after Tat induction. Male Tat(+) mice also showed accelerated recovery from chronic constrictive nerve injury (CCI)-induced neuropathic mechanical and thermal hypersensitivity compared to female Tat(+) mice. Morphine (3.2 mg/kg) fully reversed CCI-induced mechanical hypersensitivity in female Tat(-) mice, but not in Tat(+) females. CONCLUSIONS: The ability of Tat to decrease oedema, paw swelling, and limit allodynia suggests a sequel of events in which Tat-induced functional deficits precede the onset of mechanical hypersensitivity. Moreover, HIV-1 Tat attenuated responses to inflammatory and neuropathic insults in a sex-dependent manner. HIV-1 Tat appears to directly contribute to HIV sensory neuropathy and reveals sex differences in HIV responsiveness and/or the underlying peripheral neuroinflammatory and nociceptive mechanisms.

Aging protects rat cortical slices against to oxygen-glucose deprivation induced damage.

Objective: In present study, we aimed to clarify effect of aging on the susceptibility of brain tissue to neurodegeneration induced by ischemia.Methods: Damage induced by oxygen-glucose deprivation (OGD) followed by reoxygenation (REO) were compared in cortical slices prepared from young (3 months of age) and aged (22-24 months of age) male Sprague Dawley rats.Results: After incubation of the slices in an oxygen and glucose containing control condition, 2,3,5-triphenyl tetrazolium chloride (TTC) staining intensity was found significantly high in aged cortical slices. Although thirty minutes incubation of the slices in OGD medium followed by REO (OGD-REO) caused similar decline in TTC staining in young and aged cortical slices, staining intensity was still significantly higher in the slices prepared from aged animals. Thirty minutes of OGD-REO, on the other hand, also caused more increase in lactate dehydrogenase (LDH) leakage from young slices. While water contents of the slices were almost equal under control condition, it was significantly high in young cortical slices after OGD-REO incubations. In contrary to these findings, OGD and REO caused more increases in S100B output from aged rat cortical slices. S100B levels in brain regions including the cerebral cortex were also found higher in aged rats.Conclusion: All these results indicate that, cortical slices prepared from aged male rats are significantly less responsive to in vitro OGD-REO induced alterations. Since protein S100B outputs were almost doubled from aged cortical slices, a possible involvement of this enhanced S100B output seems to be likely.

Impact of Menthol on Oral Nicotine Consumption in Female and Male Sprague Dawley Rats.

INTRODUCTION: One of the preferable flavors in oral nicotine delivery systems is menthol which masks the harshness of tobacco. However, possible interactions between oral menthol and nicotine on intake and preference remain unclear. Therefore, we aimed to determine the impact of menthol on oral nicotine consumption. METHODS: Adult Sprague Dawley female and male rats (n = 8 per group) were given a choice of water or drug solution by using two-bottle free choice paradigm for 2 weeks: vehicle (5% ethanol), nicotine (20 mg/L), menthol (1 g/L) and mentholated nicotine groups. At the end of the study, plasma nicotine levels were determined. RESULTS: When rats were given a choice of nicotine or water, nicotine intake was similar between female and male rats. Menthol addition to nicotine solution significantly increased nicotine intake and preference in male but not female rats without a considerable effect on total fluid intake and body weight change in either sex. The average nicotine intake in male rats was 0.5 ± 0.05 and 1.4 ± 0.12 mg/kg/day for nicotine and menthol-nicotine combination (p < .05), respectively. The average nicotine intake in female rats was 0.6 ± 0.05 and 0.6 ± 0.03 mg/kg/day for nicotine and menthol-nicotine combination (p > .05), respectively. Plasma nicotine levels were not significantly different between the groups in either male (nicotine group: 20.8 ± 4.9, mentholated nicotine group: 31.9 ± 3.2 ng/mL) or female (nicotine group: 24.0 ± 3.3, mentholated nicotine group: 17.8 ± 2.9 ng/mL) rats (p > .05). CONCLUSIONS: Menthol increases oral nicotine consumption in male, but not female, rats. IMPLICATIONS: This study may provide data on the co-use of menthol and nicotine in smokeless tobacco, particularly oral dissolvable tobacco products.

Pharmacologic Overview of Chlorogenic Acid and its Metabolites in Chronic Pain and Inflammation.

BACKGROUND: Natural phenolic compounds in medicinal herbs and dietary plants are antioxidants which play therapeutic or preventive roles in different pathological situations, such as oxidative stress and inflammation. One of the most studied phenolic compounds in the last decade is chlorogenic acid (CGA), which is a potent antioxidant found in certain foods and drinks. OBJECTIVE: This review focuses on the anti-inflammatory and antinociceptive bioactivities of CGA, and the putative mechanisms of action are described. Ethnopharmacological reports related to these bioactivities are also reviewed. MATERIALS AND METHODS: An electronic literature search was conducted by authors up to October 2019. Original articles were selected. RESULTS: CGA has been shown to reduce inflammation and modulate inflammatory and neuropathic pain in animal models. CONCLUSION: The consensus of the literature search was that systemic CGA may facilitate pain management via bolstering antioxidant defenses against inflammatory insults.