Basal activity level in mice predicts the initial and sensitized locomotor response to nicotine only in high responders

Overestimation of sex differences in psychostimulant activity via comparisons of males and females from different behavioral groups

Background

There are inconsistencies in the observation of sex differences in baseline activity and psychostimulant activity. To address this, we have developed the MISSING (Mapping Intrinsic Sex Similarities as an Integral quality of Normalized Groups) model. MISSING model proposes that sex similarities are observed when we compare similar behavioral groups of males and females, with sex differences occurring when we compare distinct groups of sexes, but this model has not been tested.

Methods

To test this model, we identified within-sex groups of Sprague Dawley rats (male n = 22, female n = 23) by conducted normal mixtures clustering of baseline activity, cocaine activity (as distance traveled in cm over 90 min) and cocaine activity normalized-to-baseline activity (NBA) of all subjects. We employed 2-way ANOVA to determine the impact of within-sex heterogeneity on sex differences. We compared our cluster-based method to current median-split approaches.

Results

Our new cluster-based method revealed three distinct clusters, each consisting of both males and females. We determined there were no sex differences in any of the variables when males and females from the same clusters were compared. The within-sex clusters for females were not defined by estrous phase. Median split analysis was ineffective in accurately identifying within-sex groups.

Conclusions

Our results validate the MISSING model: there are no sex differences in psychostimulant activity except when we compare males and females from different behavioral groups. This has significant implications for how we proceed with research towards understanding the mechanism governing sex differences in psychostimulant activity.

Effect of chronic vapor nicotine exposure on affective and cognitive behavior in male mice

Nicotine use is a leading cause of preventable deaths worldwide, and most of those who attempt to quit will relapse. While electronic cigarettes and other electronic nicotine delivery systems (ENDS) were presented as a safer alternative to traditional cigarettes and promoted as devices to help traditional tobacco smokers reduce or quit smoking, they have instead contributed to increasing nicotine use among youths. Despite this, ENDS also represent a useful tool to create novel preclinical animal models of nicotine exposure that more accurately represent human nicotine use. In this study, we validated a chronic, intermittent, ENDS-based passive vapor exposure model in mice, and then measured changes in multiple behaviors related to nicotine abstinence. First, we performed a behavioral dose curve to investigate the effects of different nicotine inter-vape intervals on various measures including body weight, locomotor activity, and pain hypersensitivity. Next, we performed a pharmacokinetic study to measure plasma levels of nicotine and cotinine following chronic exposure for each inter-vape interval. Finally, we utilized a behavior test battery at a single dosing regimen that produces blood levels equivalent to human smokers in order to characterize the effects of chronic nicotine, vehicle, or passive airflow and identified nicotine-induced impairments in cognitive behavior.

Effect of chronic vapor nicotine exposure on affective and cognitive behavior in male mice

Nicotine use is a leading cause of preventable deaths worldwide, and most of those who attempt to quit will relapse. While electronic cigarettes and other electronic nicotine delivery systems (ENDS) were presented as a safer alternative to traditional cigarettes and promoted as devices to help traditional tobacco smokers reduce or quit smoking, they have instead contributed to increasing nicotine use among youths. Despite this, ENDS also represent a useful tool to create novel preclinical animal models of nicotine exposure that more accurately represent human nicotine use. In this study, we validated a chronic, intermittent, ENDS-based passive vapor exposure model in mice, and then measured changes in multiple behaviors related to nicotine abstinence. First, we performed a behavioral dose curve to investigate the effects of different nicotine inter-vape intervals on various measures including body weight, locomotor activity, and pain hypersensitivity. Next, we performed a pharmacokinetic study to measure plasma levels of nicotine and cotinine following chronic exposure for each inter-vape interval. Finally, we utilized a behavior test battery at a single dosing regimen that produces blood levels equivalent to human smokers in order to characterize the effects of chronic nicotine, vehicle, or passive airflow and identified nicotine-induced impairments in cognitive behavior.

Nicotine Differentially Modulates Emotional-Locomotor Interactions for Adult or Adolescent Rats

Previous research has shown that exposure to nicotine and other drugs of abuse stimulate dopaminergic neurons in the mesolimbic circuit. Sustained activation of this circuit by prolonged exposure to drugs promotes locomotor sensitization. However, there are inconsistent reports about nicotine-induced locomotor sensitization when assessed among different developmental stages. We evaluated exploratory behavior on specific areas of the open field as an indicator of behavioral disinhibition and general locomotor activity as an indicator of nicotine-induced locomotor sensitization, to further explore the mechanisms underlying behavioral adaptations to nicotine exposure in animals from different developmental stages. We found that while adolescent and adult rats are equally responsive to nicotine-induced locomotor sensitization, nicotine disrupts inhibition of risk-related behavior only in adolescent rats. Together, our results suggest that chronic daily exposure to nicotine promotes potentiation of its stimulant effects on locomotor activity. In adolescents, this effect is accompanied by a decreased capacity to inhibit risk-related behaviors under the acute effect of the drug.   How to cite this article: Novoa, C., Solano, J. L., Ballesteros-Acosta, H., Lamprea, R. M., & Ortega, L. A. (2021). Nicotine Differentially Modulates Emotional-Locomotor Interactions for Adult or Adolescent Rats. Revista Colombiana de Psicología, 31(1), 13-22. https://doi.org/10.15446/rcp.v31n1.89822

Variability in nicotine conditioned place preference and stress-induced reinstatement in mice: Effects of sex, initial chamber preference, and guanfacine

Relapse to smoking occurs at higher rates in women compared with men, especially when triggered by stress. Studies suggest that sex-specific interactions between nicotine reward and stress contribute to these sex differences. Accordingly, novel treatment options targeting stress pathways, such as guanfacine, an α2-adrenergic receptor agonist, may provide sex-sensitive therapeutic effects. Preclinical studies are critical for elucidating neurobiological mechanisms of stress-induced relapse and potential therapies, but rodent models of nicotine addiction are often hindered by large behavioral variability. In this study, we used nicotine conditioned place preference to investigate stress-induced reinstatement of nicotine preference in male and female mice, and the effects of guanfacine on this behavior. Our results showed that overall, nicotine induced significant place preference acquisition and swim stress-induced reinstatement in both male and female mice, but with different nicotine dose-response patterns. In addition, we explored the variability in nicotine-dependent behaviors with median split analyses and found that initial chamber preference in each sex differentially accounted for variability in stress-induced reinstatement. In groups that showed significant stress-induced reinstatement, pretreatment with guanfacine attenuated this behavior. Finally, we evaluated neuronal activation by Arc immunoreactivity in the infralimbic cortex, prelimbic cortex, anterior insula, basolateral amygdala, lateral central amygdala and nucleus accumbens core and shell. Guanfacine induced sex-dependent changes in Arc immunoreactivity in the infralimbic cortex and anterior insula. This study demonstrates sex-dependent relationships between initial chamber preference and stress-induced reinstatement of nicotine conditioned place preference, and the effects of guanfacine on both behavior and neurobiological mechanisms.

Mouse strain-specific acute respiratory effects of nicotine unrelated to nicotine metabolism

Plethysmograph measurement of respiratory phenotypes provides a highly sensitive means to study nicotine response in experimental model animals. We measured average respiratory frequency, tidal volume, minute volume and inspiratory time in C3H/HeJ and C57BL/6J mice subcutaneously administered 0.35 and 0.70 mg/kg nicotine. Both mouse strains showed significantly altered respiratory and locomotion phenotypes relative to saline-injected controls when administered the higher dose, but only C57BL/6J responded to the lower nicotine dose. Respiratory and locomotion phenotypes rarely differed significantly by sex. To investigate whether the strain-specific differences in nicotine sensitivity were related to differences in clearance, we followed up by measuring nicotine clearance in C3H/HeJ and C57BL/6J mice (0.35 mg/kg subcutaneous) and found sex differences in both strains, but no difference between strains.

Drug-free and context-dependent locomotor hyperactivity in DBA/2 J mice previously treated with repeated cocaine: Relationship with behavioral sensitization and role of noradrenergic receptors

Drug-associated contexts and discrete cues can trigger motivational states responsible for drug-seeking behavior and relapse. In preclinical research, drug-free conditioned hyperactivity has been used to investigate the expression of memories associated with psychostimulant drug effects. Addictive drugs can produce long-lasting sensitization to their psychomotor actions, a phenomenon known as behavioral sensitization. The neuroplasticity underlying behavioral sensitization appears to be involved in pathological drug pursuit and abuse. In the present study we evaluated drug-free, context-dependent hyperactivity in DBA/2 J mice previously treated with cocaine and we explored whether this conditioned effect was related to behavioral sensitization. Given the role of noradrenergic (NA) neurotransmission in memory retrieval, consolidation and reconsolidation processes, we also investigated whether conditioned hyperactivity in a drug-free state was mediated by NA receptors. Animals underwent a sensitization protocol with six cocaine injections (0, 5, 10 or 20 mg/kg) paired to a particular floor cue. Three days after this sensitization phase, all animals were exposed to the same familiar floor environment without drug treatment. A second test with an unfamiliar floor was conducted 24 h later. Conditioned hyperactivity was also explored after one or three cocaine pairings and was evaluated for its duration (with repeated familiar vs. unfamiliar floor tests). In a series of pharmacological experiments, we evaluated the effects propranolol (a non-selective antagonist of β1- and β2-receptors) and prazosin (α1-receptor antagonist) on conditioned hyperactivity. Cocaine treatment produced both robust sensitization and drug-free conditioned hyperactivity, an effect that lasted up to 17 days (with cocaine 20 mg/kg). A significant correlation between the magnitude of cocaine sensitization and the level of conditioned hyperactivity was found. Propranolol, but not prazosin, blocked context-dependent hyperlocomotion in a drug-free state. Our data, together with a vast body of literature, indicate that the NA system plays a key role in the retrieval and behavioral expression of drug-associated memories.

Chronic infection with Mycobacterium lepraemurium induces alterations in the hippocampus associated with memory loss

Murine leprosy, caused by Mycobacterium lepraemurium (MLM), is a chronic disease that closely resembles human leprosy. Even though this disease does not directly involve the nervous system, we investigated a possible effect on working memory during this chronic infection in Balb/c mice. We evaluated alterations in the dorsal region of the hippocampus and measured peripheral levels of cytokines at 40, 80, and 120 days post-infection. To evaluate working memory, we used the T-maze while a morphometric analysis was conducted in the hippocampus regions CA1, CA2, CA3, and dentate gyrus (DG) to measure morphological changes. In addition, a neurochemical analysis was performed by HPLC. Our results show that, at 40 days post-infection, there was an increase in the bacillary load in the liver and spleen associated to increased levels of IL-4, working memory deterioration, and changes in hippocampal morphology, including degeneration in the four subregions analyzed. Also, we found a decrease in neurotransmitter levels at the same time of infection. Although MLM does not directly infect the nervous system, these findings suggest a possible functional link between the immune system and the central nervous system.

Trace Amine-Associated Receptor 1 Modulates the Locomotor and Sensitization Effects of Nicotine

Trace amine-associated receptor 1 (TAAR1) has emerged as a promising target for addiction treatments because it affects dopamine transmission in the mesolimbic pathway. TAAR1 is involved in the effects of addictive drugs, such as amphetamines, cocaine and ethanol, but the impact of TAAR1 on the effects of nicotine, the psychoactive drug responsible for the development and maintenance of tobacco smoking, has not yet been studied. This study was performed to investigate the possible modulatory action of TAAR1 on the effects of nicotine on locomotor behaviors in rats and mice. Pretreatment with the TAAR1 agonist RO5263397 dose-dependently decreased nicotine-induced hyperlocomotion in rats habituated to locomotor boxes, prevented the development of nicotine sensitization and blocked hypermotility in nicotine-sensitized rats at the highest tested dose (10 mg/kg). The lack of TAAR1 failed to affect the effects of nicotine on the locomotion of mutant mice. Based on the results of the present study, TAAR1 activation attenuates the locomotion-stimulating effects of nicotine on rats. These results further support the previously proposed hypothesis that TAAR1 is a promising target for the prevention and treatment of drug addiction. Further studies aimed at analyzing the effects of TAAR1 agonists on animal models of nicotine addiction are warranted.

Sex differences in the acute locomotor response to methamphetamine in BALB/c mice

Women use methamphetamine more frequently than men and are more vulnerable to its negative psychological effects. Rodent models have been an essential tool for evaluating the sex-dependent effects of psychostimulants; however, evidence of sex differences in the behavioral responses to methamphetamine in mice is lacking. In the present study, we investigated acute methamphetamine-induced (1mg/kg and 4mg/kg) locomotor activation in female and male BALB/c mice. We also evaluated whether basal locomotor activity was associated with the methamphetamine-induced locomotor response. The results indicated that female BALB/c mice displayed enhanced methamphetamine-induced locomotor activity compared to males, while basal locomotor activity was positively correlated with methamphetamine-induced activity in males, but not females. This study is the first to show sex-dependent locomotor effects of methamphetamine in BALB/c mice. Our observations emphasize the importance of considering sex when assessing behavioral responses to methamphetamine.

Cognitive Dysfunction, Affective States, and Vulnerability to Nicotine Addiction: A Multifactorial Perspective

Although smoking prevalence has declined in recent years, certain subpopulations continue to smoke at disproportionately high rates and show resistance to cessation treatments. Individuals showing cognitive and affective impairments, including emotional distress and deficits in attention, memory, and inhibitory control, particularly in the context of psychiatric conditions, such as attention-deficit hyperactivity disorder, schizophrenia, and mood disorders, are at higher risk for tobacco addiction. Nicotine has been shown to improve cognitive and emotional processing in some conditions, including during tobacco abstinence. Self-medication of cognitive deficits or negative affect has been proposed to underlie high rates of tobacco smoking among people with psychiatric disorders. However, pre-existing cognitive and mood disorders may also influence the development and maintenance of nicotine dependence, by biasing nicotine-induced alterations in information processing and associative learning, decision-making, and inhibitory control. Here, we discuss the potential forms of contribution of cognitive and affective deficits to nicotine addiction-related processes, by reviewing major clinical and preclinical studies investigating either the procognitive and therapeutic action of nicotine or the putative primary role of cognitive and emotional impairments in addiction-like features.

Sex differences in dopamine binding and modafinil conditioned place preference in mice

BACKGROUND

Studies in humans and rodents have demonstrated under certain conditions some reinforcing properties of modafinil, a drug being examined clinically for its potential to treat psychostimulant abuse. However, the majority of rodent studies examining the abuse potential of modafinil have used high doses that may not be clinically relevant. In fact, recent work has indicated that doses similar to those administered to humans are not reinforcing in mice.

METHODS

The current study examined sex differences in the ability of low-dose modafinil (0.75mg/kg, IP) to induce a conditioned place preference in mice, and assessed sex-dependent alterations in dopamine D1, D2 and DAT binding sites in reward-related regions in naïve and modafinil-treated mice.

RESULTS

Low-dose modafinil failed to induce a conditioned place preference in male mice, while female mice demonstrated a significant modafinil place preference. Several dopamine binding differences were also detected in naïve and modafinil-treated mice, including sex differences in D1 and D2 availability in reward-related regions, and are discussed in relation to sex-dependent differences in the reinforcing effects of modafinil and psychostimulants in general.

CONCLUSIONS

These findings implicate sex differences in the reinforcing properties of modafinil in mice, and indicate that clinical evaluation of the sex dependence of the reinforcing properties of modafinil in humans is warranted.

Individual differences in the behavioral effects of nicotine: A review of the preclinical animal literature

Not everyone who tries tobacco or other nicotine-containing products becomes a long-term user. Certain traits or factors that are differentially present in these individuals must be able to help health care providers and researchers determine who is more likely to become chronic users of nicotine-containing products. Some of these factors, particularly sensation-seeking/novelty, impulsivity, and anxiety, lend themselves to the creation of animal models of reactivity to nicotine. These models of reactivity to nicotine can improve the translational aspects of preclinical animal research on nicotine-induced behaviors and treatments in order to help reduce negative outcomes in human populations. The goal of this review is to evaluate the current status of animal models of individual differences that serve to predict the later behavioral effects of nicotine. The limited utility and inconsistency of existing novelty models is considered, as well as the promise of impulsivity and anxiety models in preclinical animal populations. Finally, other models that could be employed to extend the benefit of the current research are examined.

Effects of environmental enrichment on ERK1/2 phosphorylation in the rat prefrontal cortex following nicotine-induced sensitization or nicotine self-administration

Rats raised in an enriched condition (EC) exhibit alterations in the neurobiological and behavioral response to nicotine compared with rats reared in an impoverished condition (IC) or a standard condition (SC). The current study determined whether environmental enrichment differentially regulates extracellular signal-regulated kinase1/2 (ERK1/2) activity in the prefrontal cortex in rats following nicotine sensitization or nicotine self-administration. Under the saline control condition, EC rats displayed diminished baseline activity and greater sensitization to repeated administration of nicotine compared with IC and SC rats. After repeated saline injections, the basal levels of phosphorylated ERK1/2 (pERK1/2) were higher in EC compared with IC and SC rats, which was negatively correlated with their respective baseline activities. Repeated nicotine (0.35 mg/kg) injections induced pERK1/2 to similar levels in SC and IC rats; however, the induction of pERK1/2 in EC rats by nicotine was not significantly different from saline controls, owing to their high baseline. In the self-administration paradigm, EC rats self-administered less nicotine (0.03 mg/kg/infusion) relative to IC or SC rats on a fixed ratio-1 schedule of reinforcement. Accordingly, no differences in pERK1/2 were found between EC and IC rats self-administering saline, whereas nicotine self-administration resulted in an increase in pERK1/2 in IC rats but not in EC rats. Furthermore, the levels of pERK1/2 in EC and IC rats were positively correlated with their respective total number of nicotine infusions. Thus, these findings suggest that environmental enrichment alters the basal and nicotine-mediated pERK1/2, which may contribute to enrichment-induced behavioral alterations in response to nicotine.