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Individuals living with human immunodeficiency virus type 1 (HIV-1) exhibit an increased prevalence of neuropsychiatric comorbities (e.g., apathy) relative to their seronegative counterparts. Given the profound functional consequences associated with apathy, characterizing the multidimensional neuropsychiatric syndrome, and associated neural mechanisms, following chronic HIV-1 viral protein exposure remains a critical need. HIV-1-associated apathy was examined by quantifying goal-directed behaviors, indexed using voluntary wheel running, during the diurnal and nocturnal cycle. Apathetic behaviors in the HIV-1 transgenic (Tg) rat were characterized by a profound decrease in the number of running bouts during both the diurnal and nocturnal cycle, supporting a prominent deficit in the self-initiation of spontaneous behaviors. Additionally, HIV-1 Tg animals exhibited a decreased reinforcing efficacy of voluntary wheel running during the nocturnal cycle. Following the completion of voluntary wheel running, synaptic dysfunction in medium spiny neurons (MSNs) of the nucleus accumbens core (NAcc) was examined as a potential neural mechanism underlying HIV-1-associated apathy. HIV-1 Tg animals displayed prominent synaptic dysfunction in MSNs of the NAcc, characterized by enhanced dendritic branching complexity and a population shift towards an immature dendritic spine phenotype relative to control animals. Synaptic dysfunction, which accounted for 42.0% to 68.5% of the variance in the number of running bouts, was strongly associated with the self-initiation of spontaneous behaviors. Establishment of the relationship between synaptic dysfunction and apathy affords a key target for the development of novel therapeutics and cure strategies for affective alterations associated with HIV-1., Competing Interests: Declaration of Competing Interest The authors have no competing interests to declare., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Independently, chronic cocaine use and HIV-1 viral protein exposure induce neuroadaptations in the frontal-striatal circuit as evidenced by both clinical and preclinical studies; how the frontal-striatal circuit responds to HIV-1 infection following chronic drug use, however, has remained elusive. After establishing experience with both sucrose and cocaine self-administration, a pretest-posttest experimental design was utilized to evaluate preference judgment, a simple form of decision-making dependent upon the integrity of frontal-striatal circuit function. During the pretest assessment, male rats exhibited a clear preference for cocaine, whereas female animals preferred sucrose. Two posttest evaluations (3 days and 6 weeks post inoculation) revealed that, independent of biological sex, inoculation with chimeric HIV (EcoHIV), but not saline, disrupted decision-making. Prominent structural alterations in the frontal-striatal circuit were evidenced by synaptodendritic alterations in pyramidal neurons in the medial prefrontal cortex. Thus, the EcoHIV rat affords a valid animal model to critically investigate how the frontal-striatal circuit responds to HIV-1 infection following chronic drug use.

Individuals living with human immunodeficiency virus type 1 (HIV-1) are often plagued by debilitating neurocognitive impairments and affective alterations;the pathophysiology underlying these deficits likely includes dopaminergic system dysfunction. The present review utilized four interrelated aims to critically examine the evidence for dopaminergic alterations following HIV-1 viral protein exposure. First, basal dopamine (DA) values are dependent upon both brain region andexperimental approach (i.e., high-performance liquid chromatography, microdialysis or fast-scan cyclic voltammetry). Second, neurochemical measurements overwhelmingly support decreased DA concentrations following chronic HIV-1 viral protein exposure. Neurocognitive impairments, including alterations in pre-attentive processes and attention, as well as apathetic behaviors, provide an additional line of evidence for dopaminergic deficits in HIV-1. Third, to date, there is no compelling evidence that combination antiretroviral therapy (cART), the primary treatment regimen for HIV-1 seropositive individuals, has any direct pharmacological action on the dopaminergic system. Fourth, the infection of microglia by HIV-1 viral proteins may mechanistically underlie the dopamine deficit observed following chronic HIV-1 viral protein exposure. An inclusive and critical evaluation of the literature, therefore, supports the fundamental conclusion that long-term HIV-1 viral protein exposure leads to a decreased dopaminergic state, which continues to persist despite the advent of cART. Thus, effective treatment of HIV-1-associated apathy/depression and neurocognitive impairments must focus on strategies for rectifying decreases in dopamine function.

Motivational deficits (e.g., apathy) and dysregulation (e.g., addiction) in HIV-1 seropositive individuals, despite treatment with combination antiretroviral therapy, necessitates the development of innovative adjunctive therapeutics. S-Equol (SE), a selective estrogen receptor β agonist, has been implicated as a neuroprotective and/or neurorestorative therapeutic for HIV-1 associated neurocognitive disorders (HAND); its therapeutic utility for motivational alterations, however, has yet to be systematically evaluated. Thus, HIV-1 transgenic (Tg) and control animals were treated with either a daily oral dose of SE (0.2 mg) or vehicle and assessed in a series of tasks to evaluate goal-directed and drug-seeking behavior. First, at the genotypic level, motivational deficits in HIV-1 Tg rats treated with vehicle were characterized by a diminished reinforcing efficacy of, and sensitivity to, sucrose. Motivational dysregulation was evidenced by enhanced drug-seeking for cocaine relative to control animals treated with vehicle. Second, treatment with SE ameliorated both motivational deficits and dysregulation in HIV-1 Tg rats. Following a history of cocaine self-administration, HIV-1 Tg animals treated with vehicle exhibited lower levels of dendritic branching and a shift towards longer dendritic spines with decreased head diameter. Treatment with SE, however, led to long-term enhancements in dendritic spine morphology in HIV-1 Tg animals supporting a potential underlying basis by which SE exerts its therapeutic effects. Taken together, SE restored motivated behavior in the HIV-1 Tg rat, expanding the potential clinical utility of SE to include both neurocognitive and affective alterations.

HIV-1 infection affects approximately 37 million individuals, and approximately 50% of seropositive individuals will develop symptoms of clinical depression and/or apathy. Dysfunctions of both serotonergic and dopaminergic neurotransmission have been implicated in the pathogenesis of motivational alterations. The present study evaluated the efficacy of a SSRI (escitalopram) in the HIV-1 transgenic (Tg) rat. Behavioral, neurochemical, and neuroanatomical outcomes with respect to HIV-1 and sex were evaluated to determine the efficacy of chronic escitalopram treatment. Escitalopram treatment restored function in each of the behavioral tasks that were sensitive to HIV-1-induced impairments. Further, escitalopram treatment restored HIV-1-mediated synaptodendritic damage in the nucleus accumbens; treatment with escitalopram significantly increased dendritic proliferation in HIV-1 Tg rats. However, restoration did not consistently occur with the neurochemical analysis in the HIV-1 rat. Taken together, these results suggest a role for SSRI therapies in repairing long-term HIV-1 protein-mediated neuronal damage and restoring function.

Hydrophobic tissue clearing methods are easily adjustable, fast, and low-cost procedures that allows for the study of a molecule of interest in unaltered tissue samples. Traditional immunolabeling procedures require cutting the sample into thin sections, which restricts the ability to label and examine intact structures. However, if brain tissue can remain intact during processing, structures and circuits can remain intact for the analysis. Previously established clearing methods take significant time to completely clear the tissue, and the harsh chemicals can often damage sensitive antibodies. The iDISCO method quickly and completely clears tissue, is compatible with many antibodies, and requires no special lab equipment. This technique was initially validated for the use in mice tissue, but the current protocol adapts this method to image hemispheres of control and transgenic rat brains. In addition to this, the present protocol also makes several adjustments to preexisting protocol to provide clearer images with less background staining. Antibodies for Iba-1 and tyrosine hydroxylase were validated in the HIV-1 transgenic rat and in F344/N control rats using the present hydrophobic tissue clearing method. The brain is an interwoven network, where structures work together more often than separately of one another. Analyzing the brain as a whole system as opposed to a combination of individual pieces is the greatest benefit of this whole brain clearing method.

The fronto-striatal circuitry, involving the nucleus accumbens, ventral tegmental area, and prefrontal cortex, mediates goal-directed behavior and is targeted by both drugs of abuse and HIV-1 infection. Acutely, both drugs and HIV-1 provoke increased dopamine activity within the circuit. However, chronic exposure to drugs or HIV-1 leads to dysregulation of the dopamine system as a result of fronto-striatal adaptations to oppose the effects of repeated instances of transiently increased dopamine. Specifically, chronic drug use leads to reduced dopaminergic tone, upregulation of dopamine transporters, and altered circuit connectivity, sending users into an allosteric state in which goal-directed behaviors are dysregulated (i.e., addiction). Similarly, chronic exposure to HIV-1, even with combination antiretroviral therapy (cART), dysregulates dopamine and dopamine transporter function and alters connectivity of the fronto-striatal circuit, contributing to apathy and clinical symptoms of HIV-1 associated neurocognitive disorders (HAND). Thus, in a drug user also exposed to HIV-1, dysregulation of the fronto-striatal dopamine circuit advances at an exacerbated rate and appears to be driven by mechanisms unique from those seen with chronic drug use or HIV-1 exposure alone. We posit that the effects of drug use and HIV-1 infection on microglia interact to drive the progression of motivational dysfunction at an accelerated rate. The current review will therefore explore how the fronto-striatal circuit adapts to drug use (using cocaine as an example), HIV-1 infection, and both together; emphasizing proper methods and providing future directions to develop treatments for pathologies disrupting goal-directed behaviors and improve clinical outcomes for affected patients. Graphical Abstract Drug use and HIV-1 in the fronto-striatal circuit. Drugs of abuse and HIV-1 infection both target the fronto-striatal circuit which mediates goal-directed behavior. Acutely, drugs and HIV-1 increase dopamine activity; in contrast chronic exposure produces circuit adaptions leading to dysregulation, addiction and/or apathy. Comorbid drug use and HIV-1 infection may interact with microglia to exacerbate motivational dysregulation.

Between 30 and 60% of HIV-seropositive individuals develop symptoms of clinical depression and/or apathy. Dopamine and serotonin are associated with motivational alterations; however, histamine is less well studied. In the present study, we used fast-scan cyclic voltammetry in HIV-1 transgenic (Tg) rats to simultaneously analyze the kinetics of nucleus accumbens dopamine (DA), prefrontal cortical serotonin (5-HT), and hypothalamic histamine (HA). For voltammetry, subjects were 15 HIV-1 Tg (7 male, 8 female) and 20 F344/N (11 male, 9 female) adult rats. Both serotonergic and dopaminergic release and reuptake kinetics were decreased in HIV-1 Tg animals relative to controls. In contrast, rates of histamine release and reuptake increased in HIV-1 Tg rats. Additionally, we used immunohistochemical (IHC) methods to identify histaminergic neurons in the tuberomammillary nucleus (TMN) of the hypothalamus. For IHC, subjects were 9 HIV-1 Tg (5 male, 4 female) and 9 F344/N (5 male, 4 female) adult rats. Although the total number of TMN histaminergic cells did not differ between HIV-1 Tg rats and F344/N controls, a significant sex effect was found, with females having an increased number of histaminergic neurons, relative to males. Collectively, these findings illustrate neurochemical alterations that potentially underlie or exacerbate the pathogenesis of clinical depression and/or apathy in HIV-1.

Dopamine release in the nucleus accumbens from ventral tegmental area (VTA) efferent neurons is critical for orientation and response to novel stimuli in the environment. However, there are considerable differences between neuronal populations of the VTA and it is unclear which specific cell populations modulate behavioral responses to environmental novelty. A retroDREADDs (designer drugs exclusively activated by designer receptors) technique, comprising designer G protein-coupled receptors exclusively activated by designer drugs and modulated by retrograde transported Cre, was used to selectively stimulate neurons of the VTA which project to the nucleus accumbens shell (AcbSh). First, the selectivity and expression of the human M3 muscarinic receptor-based adeno-associated virus (AAV-hM3D) was confirmed in primary neuronal cell cultures. Second, AAV-CMV-GFP/Cre was infused into the AcbSh and AAV-hSyn-DIO-hM3D(Gq)-mCherry (a presynaptic enhancer in the presence of its cognate ligand clozapine-N-oxide) was infused into the VTA of ovariectomized female Fisher 344 rats to elicit hM3D(Gq)-mCherry production specifically in neurons of the VTA which synapse in the AcbSh. Finally, administration of clozapine-N-oxide significantly altered rodents' response to novelty (e.g. absence of white background noise) by activation of hM3D(Gq) receptors, without altering gross locomotor activity or auditory processing per se. Confocal imaging confirmed production of mCherry in neurons of the posterior aspect of the VTA (pVTA) suggesting these neurons contribute to novelty responses. These results suggest the pVTA-AcbSh circuit is potentially altered in motivational disorders such as apathy, depression, and drug addiction. Targeting the pVTA-AcbSh circuit, therefore, may be an effective target for pharmacological management of such psychopathologies., Competing Interests: The authors have declared that no competing interests exist.

Motivational alterations, such as apathy, in HIV-1+ individuals are associated with decreased performance on tasks involving frontal-subcortical circuitry. We used the HIV-1 transgenic (Tg) rat to assess effect of long-term HIV-1 protein exposure on motivated behavior using sucrose (1-30%, w/v) and cocaine (0.01-1.0 mg/kg/infusion) maintained responding with fixed-ratio (FR) and progressive-ratio (PR) schedules of reinforcement. For sucrose-reinforced responding, HIV-1 Tg rats displayed no change in EC 50 relative to controls, suggesting no change in sucrose reinforcement but had a downward shifted concentration-response curves, suggesting a decrease in response vigor. Cocaine-maintained responding was attenuated in HIV-1 Tg rats (FR1 0.33 mg/kg/infusion and PR 1.0 mg/kg/infusion). Dose-response tests (PR) revealed that HIV-1 Tg animals responded significantly less than F344 control rats and failed to earn significantly more infusions of cocaine as the unit dose increased. When choosing between cocaine and sucrose, control rats initially chose sucrose but with time shifted to a cocaine preference. In contrast, HIV-1 disrupted choice behaviors. DAT function was altered in the striatum of HIV-1 Tg rats; however, prior cocaine self-administration produced a unique effect on dopamine homeostasis in the HIV-1 Tg striatum. These findings of altered goal directed behaviors may determine neurobiological mechanisms of apathy in HIV-1+ patients.

In those who use nicotine, the likelihood of dependence, negative health consequences, and failed treatment outcomes differ as a function of gender. Women may be more sensitive to learning processes driven by repeated nicotine exposure that influence conditioned approach and craving. Sex differences in nicotine's influence over overt behaviors (i.e. hypoactivity or behavioral sensitization) can be examined using passive drug administration models in male and female rats. Following repeated intravenous (IV) nicotine injections, behavioral sensitization is enhanced in female rats compared to males. Nonetheless, characteristics of the testing environment also mediate rodent behavior following drug administration. The current experiment used a within-subjects design to determine if nicotine-induced changes in horizontal activity, center entries, and rearing displayed by male and female rats is detected when behavior was recorded in round vs. square chambers. Behaviors were recorded from each group (males-round: n=19; males-square: n=18; females-square: n=19; and females-round: n=19) immediately following IV injection of saline, acute nicotine, and repeated nicotine (0.05mg/kg/injection). Prior to nicotine treatment, sex differences were apparent only in round chambers. Following nicotine administration, the order of magnitude for the chamber that provided enhanced detection of hypoactivity or sensitization was contingent upon both the dependent measure under examination and the animal's biological sex. As such, round and square testing chambers provide different, and sometimes contradictory, accounts of how male and female rats respond to nicotine treatment. It is possible that a central mechanism such as stress or cue sensitivity is impacted by both drug exposure and environment to drive the sex differences observed in the current experiment. Until these complex relations are better understood, experiments considering sex differences in drug responses should balance characteristics of the testing environment to provide a complete interpretation of drug-induced changes to behavior., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Deficits in prepulse inhibition (PPI), a measure of sensorimotor gating, are observed in neurodevelopmental and neuropsychiatric disorders. Despite the large PPI literature, the majority of studies characteristically employ tests with one interstimulus interval (ISI), of one modality, at one age. In the context of the auditory startle response (ASR), the present study examined (1) the profile for the ontogeny of PPI through adulthood in Long-Evans hooded rats with a reasonably comprehensive ISI function, (2) whether the ontogenetic profile for PPI is sensitive to modality of the prepulse stimulus, as a within-session variable, and (3) whether the maturation of PPI differs for males and females. Despite the basic effect of more pronounced PPI in adult relative to preweanling animals, each sensory modality displayed a unique ontogenetic profile for PPI, without any compelling evidence for major differences between males and females, in accordance with the known temporal course of peripheral and central maturational profiles of sensory systems in the rat. The context for assessing auditory PPI (auditory and tactile vs. auditory and visual prepulses) influenced the overall startle response, i.e., a shift in the height of the entire profile, but did not significantly impact the auditory PPI profile per se. The translational relevance of preclinical sensorimotor assessments to patients with neurodevelopmental and/or neuropsychiatric disorders depends partly on an understanding of the ontogeny of sensorimotor gating in different sensory systems, and can be strengthened with the use of a reasonably comprehensive number of ISIs to provide relatively precise and defined response functions., (© 2015 Wiley Periodicals, Inc.)

In the USA, approximately 15% of women smoke tobacco cigarettes during pregnancy. In utero tobacco smoke exposure produces somatic growth deficits like intrauterine growth restriction and low birth weight in offspring, but it can also negatively influence neurodevelopmental outcomes in later stages of life, such as an increased incidence of obesity and drug abuse. Animal models demonstrate that prenatal nicotine (PN) alters the development of the mesocorticolimbic system, which is important for organizing goal-directed behavior. In the present study, we determined whether intravenous (IV) PN altered the initiation and/or expression of methamphetamine (METH)-induced locomotor sensitization as a measure of mesocorticolimbic function in adult rat offspring. We also determined whether PN and/or METH exposure altered protein levels of BDNF (brain-derived neurotrophic factor) in the nucleus accumbens, the dorsal striatum, and the prefrontal cortex of adult offspring. BDNF was of interest because of its role in the development and maintenance of the mesocorticolimbic pathway and its ability to modulate neural processes that contribute to drug abuse, such as sensitization of the dopamine system. Dams were injected with IV nicotine (0.05 mg/kg/injection) or saline, 3×/day on gestational days 8-21. Testing was conducted when offspring reached adulthood (around postnatal day 90). Following 3 once daily habituation sessions the animals received a saline injection and baseline locomotor activity was measured. PN and prenatal saline (PS)-exposed offspring then received 10 once daily injections of METH (0.3 mg/kg) to induce locomotor sensitization. The animals received a METH injection (0.3 mg/kg) to assess the expression of sensitization following a 14-day period of no injections. A day later, all animals were injected with saline and conditioned hyperactivity was assessed. Brain tissue was harvested 24 h later. PN animals habituated more slowly to the activity chambers compared to PS controls. PN rats treated with METH showed significant enhancement of locomotor behavior compared to PS rats following acute and repeated injections; however, PN did not produce differential initiation or expression of behavioral sensitization. METH produced conditioned hyperactivity, and PN rats exhibited a greater conditioned response of hyperactivity relative to controls. PN and METH exposure produced changes in BDNF protein levels in all three regions, and complex interactions were observed between these two factors. Logistic regression revealed that BDNF protein levels, throughout the mesocorticolimbic system, significantly predicted the difference in the conditioned hyperactive response of the animals: both correlations were significant, but the predicted relationship between BDNF and context-elicited activity was stronger in the PN (r = 0.67) compared to the PS rats (r = 0.42). These findings indicate that low-dose PN exposure produces long-term changes in activity and enhanced sensitivity to the locomotor effects of METH. The enhanced METH-induced contextual conditioning shown by the PN animals suggests that offspring of in utero tobacco smoke exposure have greater susceptibility to learn about drug-related conditional stimuli, such as the context. The PN-induced alterations in mesocorticolimbic BDNF protein lend further support for the hypothesis that maternal smoking during pregnancy produces alterations in neuronal plasticity that contribute to drug abuse vulnerability. The current findings demonstrate that these changes are persistent into adulthood., (© 2016 S. Karger AG, Basel.)

Cigarette smoking prevalence in the HIV-positive individuals is profoundly higher than that in the HIV-negative individuals. We have demonstrated that HIV-1 transgenic rats exhibit attenuated nicotine-mediated locomotor activity, altered cAMP response element binding protein (CREB) and extracellular regulated kinase (ERK1/2) signaling in the mesocorticolimbic regions. This study investigated the role of HIV-1 transactivator of transcription (Tat) protein in the alterations of nicotine-mediated behavior and the signaling pathway observed in the HIV-1 transgenic rats. Rats received bilateral microinjection of recombinant Tat1-86 (25 μg/side) or vehicle directed at ventral tegmental area (VTA) followed by locomotor testing in response to 13 daily intravenous injections of nicotine (0.05 mg/kg, freebase, once/day) or saline. Further, we examined the phosphorylated levels of CREB (pCREB) and ERK1/2 (pERK1/2) in the prefrontal cortex (PFC), nucleus accumbens (NAc) and VTA. Tat diminished baseline activity in saline control rats, and attenuated nicotine-induced behavioral sensitization. Following repeated saline injection, the basal levels of pERK1 in the NAc and VTA and pERK2 in VTA were lower in the vehicle control group, relative to the Tat group. After repeated nicotine injection, pERK1 in NAc and VTA and pERK2 in VTA were increased in the vehicle group, but not in the Tat group. Moreover, repeated nicotine injections decreased pCREB in the PFC and VTA in the Tat group but not in the vehicle group. Thus, these findings indicate that the direct injection of Tat at the VTA may mediate CREB and ERK activity in response to nicotine-induced locomotor activity.

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., (© 2014 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Background: Maternal smoking during pregnancy is correlated with increased substance use in offspring. Research using rodent models shows that gestational nicotine exposure produces enduring alterations in the neurodevelopment of motivational systems, and that rats prenatally treated with nicotine have altered motivation for drug reinforcement on fixed-ratio (FR) schedules of reinforcement., Objective: The present study investigated methamphetamine (METH) self-administration in adult offspring prenatally exposed to intravenous (IV) nicotine or saline using a progressive-ratio (PR) schedule of reinforcement., Methods: Pregnant rats were administered IV prenatal saline (PS) or nicotine (PN; 0.05mg/kg/infusion), 3×/day during gestational days 8-21. At postnatal day 70, offspring acquired a lever-press response for sucrose (26%, w/v; FR1-3). Rats were trained with METH (0.05mg/kg/infusion), and following stable FR responding, animals were tested using a progressive-ratio (PR) schedule for three different doses of METH (0.005, 0.025, and 0.05mg/kg/infusion)., Results: METH infusion, active lever presses, and the ratio breakpoint are reported. PN-exposed animals exhibited more METH-maintained responding than PS controls, according to a dose×prenatal treatment interaction (e.g., infusions). PN rats self-administered more METH infusions between the range of 0.025 and 0.05, but not for the 0.005mg/kg/infusion dose., Conclusions: IV PN-exposure produced enhanced motivation to self-administer METH. These findings indicate that pregnant women who smoke tobacco may impart neurobiological changes in offspring's motivational systems that render them increasingly vulnerable to drug abuse during adulthood., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Background: Approximately 18% of pregnant women continue to smoke tobacco cigarettes throughout pregnancy. Offspring exposed to tobacco smoke in utero exhibit a higher incidence of drug use in later stages of development relative to non-exposed children. Animal models indicate that prenatal nicotine (PN) exposure alone alters the development of the mesocorticolimbic dopamine (DA) system, which, in part, organizes motivated behavior and reward. The orexin/hypocretin neuropeptide system, which originates in the lateral hypothalamus (LH), projects to key areas of the mesocorticolimbic DA pathway. Previous research suggests that orexin exerts a major influence on motivation and reward., Methods: The present experiments determined if intravenous (IV) PN exposure alters (1) the expression of orexin neurons and melanin-concentrating hormone (MCH; positive control) in the LH; and (2) orexin projections from the LH onto DA neurons in the ventral tegmental area (VTA). Dams were injected with IV nicotine (0.05 mg/kg/injection) or saline 3×/day during gestational days 8-21. Tissues from adult male offspring (∼130 days) were examined using immunohistochemistry., Results: Relative to controls, offspring of IV PN exposure showed (1) increased numbers of orexin neurons in the LH, and no changes in the expression of MCH; and (2) increased orexin appositions on DA cells in the VTA., Conclusion: The findings indicate that the influence of PN exposure is enduring, and suggests that the PN-induced modification of orexin expression on mesolimbic circuitry may contribute to the reported changes in motivated behaviors related to food and drug reward observed in offspring prenatally exposed to nicotine., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Background: Prenatal tobacco smoke exposure is associated with alterations in motivated behavior in offspring, such as increased consumption of highly palatable foods and abused drugs. Animal models show that gestational nicotine (GN) exposure mediates changes in responding for sucrose and drug reward., Methods: A novel, intermittent low-dose intravenous (IV) exposure model was used to administer nicotine (0.05 mg/kg/injection) or saline 3×/day to rats on gestational days 8-21. Two experiments investigated the effect of IV GN on (1) the habituation of spontaneous locomotor activity and on (2) sucrose reinforced responding in offspring. For the operant experiments, animals acquired fixed-ratio (FR-3) responding for sucrose, 26% (w/v), and were tested on varying concentrations (0, 3, 10, 30, and 56%; Latin-square) according to a FR-3, and then a progressive-ratio (PR) schedule. Male and female adult offspring were used., Results: IV GN did not alter birth or growth weight, or the number of pups born. No between-group differences in habituation to spontaneous locomotor activity were observed. FR testing produced an inverted U-shaped response curve, and rats showed peak responding for 10% sucrose reinforcement. Neither gestation nor sex affected responding, suggesting equivalent sensitivity to varying sucrose concentrations. PR testing revealed that GN rats showed greater motivation for sucrose reinforcement relative to controls., Conclusions: A low-dose, IV GN exposure model resulted in increased motivation to respond for sucrose reinforcement in adult offspring. This suggests that using a low number of cigarettes throughout pregnancy will result in increased motivation for highly palatable foods in adult, and perhaps, adolescent offspring., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Maternal smoking during pregnancy is associated with increased substance abuse in offspring. Preclinical research shows that in utero exposure to nicotine, the primary psychoactive compound in tobacco smoke, influences the neurodevelopment of reward systems and alters motivated behavior in offspring. The present study determined if prenatal nicotine (PN) exposure altered the sensitivity to the reinforcing and aversive effects of methamphetamine (METH) in offspring using a low dose, intravenous (IV) exposure method. Pregnant dams were administered nicotine (0.05 mg/kg/injection) or prenatal saline (PS) 3×/day on gestational days 8-21, and adult offspring were tested using METH self-administration (experiment 1) or METH-induced conditioned taste aversion (CTA; experiment 2) procedures. For METH self-administration, animals were trained to respond for IV METH (0.05 mg/kg/infusion; fixed-ratio 3) and they were tested on varying doses of the reinforcer (0.0005-1.0 mg/kg/infusion). For METH CTA, rats received three saccharin and METH pairings (0, 0.3, or 0.5 mg/kg, sc) followed by 14 daily extinction trials. Experiment 1: PN and PS animals exhibited inverted U-shaped dose-response curves; however, the PN animal's curve was shifted to the left, suggesting PN animals were more sensitive to the reinforcing effects of METH. Experiment 2: METH CTA was acquired in a dose-dependent manner and the factor of PN exposure was not related to the acquisition or extinction of METH-induced CTA. There were no sex differences in either experiment. These results indicate that IV PN-exposed adult offspring exhibited increased sensitivity to IV METH. This suggests that PN exposure, via maternal smoking, will alter the reinforcing effects of METH during later stages of development, and furthermore, will influence substance use vulnerability in adult human offspring.

Maternal smoking during pregnancy is associated with enduring psychopathology, such as increased likelihood of substance use, in offspring. Various animal models demonstrate that continuous nicotine exposure produces teratogenic effects in offspring, as well. In this experiment, a novel intravenous (IV) exposure model was used to determine if gestational nicotine (GN) treatment produced alterations in methamphetamine-induced sensitization and the expression of brain-derived neurotrophic factor (BDNF) in the mesocorticolimbic dopamine (DA) system of adolescent offspring. Dams were injected with IV saline or nicotine (0.05 mg/kg/injection) three times per day on gestational days 8-21. Habituation was measured on postnatal day (PND) 25-27 and baseline activity on PND 28. On PND 29-35, offspring were injected with saline or methamphetamine (0.3 mg/kg) and locomotor activity was measured after the first and seventh injections. On PND 36, brains were removed, flash frozen, and BDNF protein levels in the nucleus accumbens (NAcc), dorsal striatum (Str), frontal cortex (FC), and hippocampus (Hipp) were analyzed. GN did not affect habituation or the induction of methamphetamine-induced sensitization. Interestingly, GN, but not adolescent methamphetamine treatment, elevated levels of BDNF in the NAcc and Str; however, the GN-induced increase in BDNF in the FC was attenuated by adolescent methamphetamine treatment. Both GN and adolescent methamphetamine treatment increased BDNF in the Hipp. These findings indicate that GN exposure will result in increased levels of BDNF protein throughout the mesocorticolimbic DA system during adolescent development and suggests that methamphetamine abuse will modulate the expression of BDNF in motivational circuitries of adolescent offspring exposed to GN., (Copyright © 2011 Wiley-Liss, Inc.)

One clue regarding the basis of cocaine-induced deficits in attentional processing is provided by the clinical findings of changes in the infants' startle response; observations buttressed by neurophysiological evidence of alterations in brainstem transmission time. Using the IV route of administration and doses that mimic the peak arterial levels of cocaine use in humans, the present study examined the effects of prenatal cocaine on auditory information processing via tests of the auditory startle response (ASR), habituation, and prepulse inhibition (PPI) in the offspring. Nulliparous Long-Evans female rats, implanted with an IV access port prior to breeding, were administered saline, 0.5, 1.0, or 3.0 mg/kg/injection of cocaine HCL (COC) from gestation day (GD) 8-20 (1×/day-GD8-14, 2×/day-GD15-20). COC had no significant effects on maternal/litter parameters or growth of the offspring. At 18-20 days of age, one male and one female, randomly selected from each litter displayed an increased ASR (>30% for males at 1.0 mg/kg and >30% for females at 3.0 mg/kg). When reassessed in adulthood (D90-100), a linear dose-response increase was noted on response amplitude. At both test ages, within-session habituation was retarded by prenatal cocaine treatment. Testing the females in diestrus vs. estrus did not alter the results. Prenatal cocaine altered the PPI response function across interstimulus interval and induced significant sex-dependent changes in response latency. Idazoxan, an α(2)-adrenergic receptor antagonist, significantly enhanced the ASR, but less enhancement was noted with increasing doses of prenatal cocaine. Thus, in utero exposure to cocaine, when delivered via a protocol designed to capture prominent features of recreational usage, causes persistent, if not permanent, alterations in auditory information processing, and suggests dysfunction of the central noradrenergic circuitry modulating, if not mediating, these responses.

The prevalence of tobacco smoking in HIV-1 positive individuals is 3-fold greater than that in the HIV-1 negative population; however, whether HIV-1 viral proteins and nicotine together produce molecular changes in mesolimbic structures that mediate psychomotor behavior has not been studied. This study determined whether HIV-1 viral proteins changed nicotine-induced behavioral sensitization in HIV-1 transgenic (HIV-1Tg) rats. Further, we examined cAMP response element binding protein (CREB) and extracellular regulated kinase (ERK1/2) signaling in the prefrontal cortex (PFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). HIV-1Tg rats exhibited a transient decrease of activity during habituation, but showed attenuated nicotine (0.35mg/kg, s.c.)-induced behavioral sensitization compared to Fisher 344 (F344) rats. The basal levels of phosphorylated CREB and ERK2 were lower in the PFC of HIV-1Tg rats, but not in the NAc and VTA, relative to the controls. In the nicotine-treated groups, the levels of phosphorylated CREB and ERK2 in the PFC were increased in HIV-1Tg rats, but decreased in F344 animals. Moreover, repeated nicotine administration reduced phosphorylated ERK2 in the VTA of HIV-1Tg rats and in the NAc of F344 rats, but had no effect on phosphorylated CREB, indicating a region-specific change of intracellular signaling. These results demonstrate that HIV-1 viral proteins produce differences in basal and nicotine-induced alterations in CREB and ERK signaling that may contribute to the alteration in psychomotor sensitization. Thus, HIV-1 positive smokers are possibly more vulnerable to alterations in CREB and ERK signaling and this has implications for motivated behavior, including tobacco smoking, in HIV-1 positive individuals who self-administer nicotine., (Published by Elsevier Inc.)

Maternal smoking during pregnancy is associated with auditory processing deficits in children; these effects have been confirmed with animal models of continuous high-dose prenatal nicotine exposure. The present experiments utilized a novel, low-dose, intermittent, intravenous (IV) gestational nicotine exposure model to investigate potential deficits on the preattentive process of sensorimotor gating, as indexed by prepulse inhibition (PPI), in preweanling and adult rat offspring. Pregnant dams received bolus IV injections of nicotine (0.05 mg/kg/injection) 3×/day on gestational days 8-21. Auditory and tactile stimulus modalities were probed with tone and air puff prepulse stimuli, respectively. These prepulse stimuli preceded a 100 dB(A) startle tone by six different interstimulus intervals (ISIs; 0, 8, 40, 80, 120, 4000 ms) to define a curve of response inhibition. The magnitude of PPI increased with age, from 59 to 81% inhibition. Preweanlings (PNDs 14 and 18) and adults (PND 75) gestationally exposed to nicotine exhibited altered startle responding relative to controls, but the nature of the deficit became more localized at later ages. The entire curve of response inhibition in preweanlings exposed to prenatal nicotine (PND 14) was shifted up relative to controls, and notably, did not interact with prepulse stimulus modality, suggesting a generalized increased sensorimotor responsiveness as a function of prenatal nicotine. At PND 18, a shift in the response curve across all ISIs was again noted, but varied as a function of prepulse stimulus modality; the increased sensorimotor responsiveness was specific to the auditory, but not tactile, sensory modality. In adulthood, male and female animals prenatally exposed to nicotine were differentially sensitive to modulation by the ISIs, relative to control male and female animals. Specifically, despite robust PPI, adult females exposed to gestational nicotine were relatively insensitive to changes in ISI from 8 to 120 ms; in contrast, the robust PPI of nicotine-exposed males demonstrated a clear focal point of inhibition at 40 ms. These findings indicate that a low, daily dosing of IV prenatal nicotine produces long-lasting alterations in auditory PPI. An important implication of this research is that "chipping" with smoked-tobacco products during pregnancy may produce enduring changes in sensorimotor processing., (Copyright © 2010 ISDN. Published by Elsevier Ltd. All rights reserved.)

Lobeline, a nicotinic receptor antagonist and neurotransmitter transporter inhibitor, is a candidate pharmacotherapy for methamphetamine abuse. meso-Transdiene (MTD), a lobeline analog, lacks nicotinic receptor affinity, retains affinity for vesicular monoamine transporter 2 (VMAT2), and, surprisingly, has enhanced affinity for dopamine (DA) and serotonin transporters [DA transporter (DAT) and serotonin transporter (SERT), respectively]. In the current study, MTD was evaluated for its ability to decrease methamphetamine self-administration in rats relative to food-maintained responding. MTD specifically decreased methamphetamine self-administration, extending our previous work. Classical structure-activity relationships revealed that more conformationally restricted MTD analogs enhanced VMAT2 selectivity and drug likeness, whereas affinity at the dihydrotetrabenazine binding and DA uptake sites on VMAT2 was not altered. Generally, MTD analogs exhibited 50- to 1000-fold lower affinity for DAT and were equipotent or had 10-fold higher affinity for SERT, compared with MTD. Representative analogs from the series potently and competitively inhibited [(3)H]DA uptake at VMAT2. (3Z,5Z)-3,5-bis(2,4-dichlorobenzylidene)-1-methylpiperidine (UKMH-106), the 3Z,5Z-2,4-dichlorophenyl MTD analog, had improved selectivity for VMAT2 over DAT and importantly inhibited methamphetamine-evoked DA release from striatal slices. In contrast, (3Z,5E)-3,5-bis(2,4-dichlorobenzylidene)-1-methylpiperidine (UKMH-105), the 3Z,5E-geometrical isomer, inhibited DA uptake at VMAT2, but did not inhibit methamphetamine-evoked DA release. Taken together, these results suggest that these geometrical isomers interact at alternate sites on VMAT2, which are associated with distinct pharmacophores. Thus, structural modification of the MTD molecule resulted in analogs exhibiting improved drug likeness and improved selectivity for VMAT2, as well as the ability to decrease methamphetamine-evoked DA release, supporting the further evaluation of these analogs as treatments for methamphetamine abuse.

It is well documented that the transition from periadolescence to adulthood produces profound changes in motivated behavior, and furthermore, attenuates the aversive experience of abused drugs. Little is known, however, about adolescent memory for the conditioned aversive effects of abused drugs following retention intervals that span this developmental transition. The present experiment investigated methamphetamine-induced conditioned taste aversion (CTA) in periadolescent rats to determine if the magnitude of conditioning was altered following retention intervals that extend to adulthood. Rats consumed saccharin (0.1%, w/v) and were immediately injected with saline or methamphetamine (3.0mg/kg) either once (PND 40) or three times (PND 38-40), and memory was assessed one or 50 days later on post natal days 41 or 90, respectively. Rats exhibited robust methamphetamine-induced CTA one and 50 days after conditioning, and the strength of responding did not change as a function of retention interval, regardless if animals were trained with one or three saccharin-methamphetamine pairings. These findings indicate that the expression of memory for the aversive effects of methamphetamine was resistant to degradation throughout the developmental period of periadolescence to adulthood., ((c) 2010 Elsevier Inc. All rights reserved.)

Research has indicated a high correlation between psychostimulant use and tobacco cigarette smoking in human substance abusers. The objective of the current study was to examine the effects of acute and repeated nicotine administration on responding for intravenous methamphetamine (0.03 mg/kg/infusion) in a rodent model of self-administration, as well as the potential of nicotine to induce reinstatement of previously extinguished drug-taking behavior in male Sprague-Dawley rats. In addition, it was assessed whether nicotine-induced reinstatement of methamphetamine-seeking behavior and nicotine-induced locomotor sensitization require that nicotine be temporally paired with the methamphetamine self-administration session or the locomotor activity chamber. Nicotine acutely decreased methamphetamine self-administration, but did not persistently alter responding during the maintenance of methamphetamine self-administration. However, following extinction of methamphetamine self-administration, nicotine administration reinstated methamphetamine-seeking behavior only in rats that had previously been administered nicotine. Nicotine-induced reinstatement and expression of locomotor sensitization were not dependent on a temporal pairing of nicotine with either the methamphetamine self-administration session or the locomotor activity chamber, respectively. These results indicate that nicotine may be acting, at least in part, through a non-associative mechanism to reinstate methamphetamine-seeking behavior., (Copyright 2009 Elsevier Ireland Ltd. All rights reserved.)

Lobeline is being tested in clinical trials as a pharmacotherapy for methamphetamine abuse and attention deficit hyperactivity disorder. Preclinical research demonstrates that lobeline produces locomotor hypoactivity apart from its therapeutic effects; however, the hypothesis that there are sex differences in hypoactivity or in the development of tolerance to its locomotor depressant effects has not been investigated. Periadolescent rats were injected with saline to determine baseline locomotor activity. Animals received saline or lobeline (1.0-10mg/kg) daily for 7 consecutive days (post natal days 29-35), and were challenged with saline 24h later to assess baseline activity. Lobeline produced hypoactivity in total horizontal activity and center distance travelled. Tolerance developed to the lobeline-induced hypoactivity and sex differences in lobeline tolerance were observed on both measures. Females acquired tolerance to lobeline 5.6 mg/kg at a slower rate than males. Saline challenge revealed a linear dose-dependent trend of hyperactivity on both measures, which indicates that rats exhibited altered locomotor behavior 24h after the final lobeline treatment. These findings demonstrate sex differences in the hypoactive response to lobeline prior to puberty and suggest that females may experience more locomotor depressant effects than males. Chronic lobeline may induce hyperactivity following cessation of treatment.

The effects of Tat, an HIV-1 protein, on intravenous cocaine-induced locomotor activity were examined in ovariectomized rats. Animals were habituated to activity chambers, administered an i.v. baseline/saline injection, and 24 h later, received bilateral, intra-accumbal microinjections of Tat1-72 (15 microg/microl) or vehicle. Twenty four hours later, rats received the first of 14 daily i.v. cocaine injections (3.0 mg/kg/inj, 1 /day) or saline. Locomotor activity was measured in automated chambers for 30 min following baseline and after the 1st and 14th cocaine injections. Observational time sampling following cocaine was also performed. Following acute cocaine/saline, Tat significantly increased cocaine-induced total activity over the 30-min session, with no significant effects for activity in the central compartment. Repeated cocaine injections produced behavioral sensitization with approximately 2-fold higher levels of total activity, approximately 3-fold higher levels of centrally directed activity, and increased locomotor scores via direct observations. Following repeated cocaine/saline, Tat altered the development of cocaine-induced behavioral sensitization for total activity with prior Tat exposure attenuating the development of cocaine-induced sensitization. Collectively, these data show that bilateral microinjection of Tat into the N Acc alters i.v. cocaine-induced behavior, suggesting that Tat produces behavioral changes by disrupting the mesocorticolimbic pathway.

The novel object recognition task is gaining popularity for its ability to test a complex behavior which relies on the integrity of memory and attention systems without placing undue stress upon the animal. While the task places few requirements upon the animal, it traditionally requires the experimenter to observe the test phase directly and record behavior. This approach can severely limit the number of subjects which can be tested in a reasonable period of time, as training and testing occur on the same day and span several hours. The current study was designed to test the feasibility of automation of this task for adolescent rats using standard activity chambers, with the goals of increased objectivity, flexibility, and throughput of subjects.

Lobelane, a minor alkaloid of Lobelia inflata and a synthetic, des-oxy analog of lobeline, has good affinity for the vesicular monoamine transporter and the dopamine transporter. The current study examined the ability of lobelane to specifically decrease methamphetamine self-administration. Rats were trained on a fixed ratio 5 schedule of reinforcement to self-administer methamphetamine (0.05 mg/kg/infusion, i.v.) or to respond for sucrose pellets. Upon reaching stable responding, rats were pretreated with lobelane (0.1, 1, 3, 5.6, or 10 mg/kg, s.c.) or saline, 15 min prior to the operant session. To assess the effect of repeated lobelane on methamphetamine self-administration, rats were pretreated with lobelane (5.6 or 10 mg/kg, s.c.) for 7 sessions. Behavioral specificity was further investigated by assessing the effects of lobelane (0.1, 1, 3, 5, or 10 mg/kg, s.c.) or saline on locomotor activity. Within the dose range tested, lobelane dose-dependently decreased methamphetamine self-administration, while having no effect on sucrose-maintained responding. Locomotor activity was decreased following only the highest dose of lobelane (10 mg/kg). Across repeated pretreatments, tolerance developed to the effect of lobelane on methamphetamine self-administration, demonstrating that the ability of lobelane to specifically decrease methamphetamine self-administration is a transient effect. Thus, taken together, the results show that although lobelane interacts with the pharmacological targets believed to be responsible for its ability to decrease methamphetamine self-administration, removal of the oxygen functionalities from the lobeline molecule may have afforded a compound with an altered pharmacokinetic and/or pharmacodynamic profile.

Previous research demonstrates that repeated intravenous (i.v.) nicotine injection resulted in increased locomotor sensitization in female relative to male rats. In order to determine if increased nicotine levels are detected in females compared to males the present experiment examined the plasma nicotine levels of male, female, castrated (CAST), and ovariectomized (OVX) rats (n=7-11 rats/group) following repeated i.v. nicotine injection (50 microg/kg/injection). All rats received 14 i.v. nicotine injections, one/day. Approximately 1 min after the 14th nicotine injection, rats were rapidly decapitated and trunk blood was collected immediately. Gas chromatography revealed a sex difference in nicotine content: higher plasma nicotine levels were measured from female rats (>10 x increase) relative to males, and the sex difference was attenuated by gonadectomy. These data suggest that the sex difference in plasma nicotine levels is due to alteration in distribution or nicotine metabolism as a function of circulating gonadal hormones. These findings indicate that gonadal hormones may influence nicotine pharmacokinetics and therefore nicotine-induced sex differences in behavior.

Maternal cocaine abuse is a societal problem with serious impact on both mother and child. Few studies exist that study the mother/offspring dyad of neurological effects of maternal cocaine abuse. The present study was designed to study alterations in D2, D3 and sigma receptor density in nucleus accumbens and striatum of dams and male and female offspring following gestational cocaine. Long-Evans female rats were implanted with an intravenous (i.v.) access port prior to breeding and were administered saline or 3.0 mg/kg of cocaine from gestational day (GD) GD8-20 (1 injection/day-GD8-14, 2 injections/day-GD15-20). Offspring were raised by maternal dams and allowed to mature until postnatal days 31-35, at which time dams and offspring were sacrificed for assay of radioligand binding. In dams, decreased D2 (24.6%) and D3 (36.9%) binding was observed in striatum. Female offspring displayed no differences in receptor binding in either region. Male offspring displayed decreased D2 receptor binding (27.1%) in nucleus accumbens and increased D3 (75.2% and 33.5%) and sigma receptor binding (73.4% and 53.1%) in accumbens and striatum, respectively. Collectively, these data clearly demonstrate that male offspring exhibit significant alterations in D2, D3 and sigma receptor binding. These results suggest that dams and offspring display long-lasting alterations (5 weeks) in dopamine receptor binding. These alterations in dopamine and sigma receptor binding in offspring following prenatal cocaine and rearing by maternal dams are sex specific and could have profound effects on the development of behavior.

The purpose of the present experiment was to examine the effects of acute and repeated intravenous (IV) cocaine on rat behavior in the home cage environment. An observational sampling method was used. Pair-housed, male, female, castrated (CAST), and ovariectomized (OVX) rats were administered daily IV cocaine injections (3.0 mg/kg/injection) in the home cage for 13 consecutive days, and observations occurred after the 1st and 13th injections. The incidence, i.e., occurrence or nonoccurrence of a behavior, was recorded according to a behavioral profile comprised of 11 behaviors. Data were analyzed as locomotor composite and orofacial composite scores. Behaviors not amenable for combination into a composite incidence score were evaluated independently (e.g., still behavior). Females exhibited more locomotor incidence scores than males following acute injection and more still behavior after repeated cocaine administration. Females exhibited more locomotor activity than OVX rats following acute, but not repeated, cocaine injection. There were no differences between the male and CAST rats on days 1 or 13. CAST rats exhibited more still behavior than OVX following only acute cocaine administration. This study indicates that IV cocaine-induced sex differences and the effects of gonadectomy can be measured in the home cage, and furthermore, describes a simple method to screen changes in cocaine-induced locomotor behaviors in the absence of automated equipment.

The present experiment examined the effects of sex and gonadectomy on cocaine-induced locomotor activity via intravenous (IV) cocaine. Male, female, castrated (CAST), and ovariectomized (OVX) rats received daily IV cocaine injections (3.0 mg/kg/injection) for 13 consecutive days. Locomotor activity was measured in automated activity chambers for 60 min following the baseline-saline administration and after the 1st and 13th cocaine injections. Observational time sampling was also performed, and the observational data were grouped into locomotor and orofacial composite incidence scores. Females exhibited more cocaine-induced locomotor activity, rearing, and locomotor incidence compared to males. The orofacial data revealed a sex difference in the expression of behavioral sensitization: females exhibited more orofacial behaviors than males after repeated, but not acute, cocaine injection. Females exhibited more cocaine-induced locomotor activity, rearing, and locomotor incidence compared to OVX rats, but exhibited less orofacial incidence following acute cocaine administration. There were no differences between male and CAST rats. CAST rats showed more locomotor incidence than OVX after repeated, but not acute, cocaine injection. CAST rats exhibited behavioral sensitization, whereas OVX rats' locomotor incidence did not change with repeated cocaine injection. CAST rats showed less orofacial incidence than OVX after acute, but not repeated, cocaine injection. These findings demonstrate sex differences in response to IV cocaine and replicate earlier findings which show that OVX attenuates increased locomotor activity in females. Furthermore, these findings suggest that IV cocaine administration produces behavioral differences between male and female rats in the absence of circulating gonadal hormones.

The present study examined the sex-dependent expression of behavioral sensitization as well as changes of dopamine (DA) transporters and D1, D2, and D3 receptors following repeated intravenous nicotine administration. Male and female Sprague-Dawley rats were implanted with indwelling jugular catheters, equipped with subcutaneous intravenous injection ports. Rats were habituated to activity chambers for 3 days and were subsequently administered 15-s bolus injections of intravenous nicotine (50 microg/kg/ml) 1/day for 21 days. Animals were placed in activity chambers for 60 min immediately after the 1st and 21st nicotine injection. Observational time sampling was also performed. Brains were subsequently removed and frozen for autoradiographic DA transporter/DA receptor analysis on the afternoon females were in proestrus. With one exception, no robust sex differences were observed for locomotor activity or any rearing measures either during baseline or after initial nicotine injection. Females exhibited markedly more behavioral sensitization of locomotor activity, rearing, duration of rearing, and incidence of observed rearing. There were no sex differences in the number of D1 or D2 receptors. Females exhibited an increased number of DA transporters and decreased D3 receptors in the NAcc, relative to males. Multiple regression analyses suggest that D3 receptors and DA transporters in various striatal and NAcc subregions differentially predicted nicotine-induced behaviors for males and females. Collectively, these findings demonstrate that repeated intravenous nicotine produces sex differences in the expression of behavioral sensitization, and suggest that nicotine-induced changes of DA transporters and D3 receptors are partly responsible for increased behavioral sensitization in female rats.

Previous results indicate that pretreatment with lobeline attenuates methamphetamine (METH) self-administration in rats, but not by acting as a substitute reinforcer. Given these findings, it has been suggested that lobeline may serve as a useful pharmacotherapy for psychostimulant abuse. However, because lobeline produces emesis and nausea in humans, the present study examined whether lobeline has direct effects on taste avoidance behavior in rats within the same dose range shown previously to decrease METH self-administration. Two experiments utilized a Pavlovian conditioning procedure to determine if lobeline produces conditioned taste avoidance (CTA) in rats. In Experiments 1 and 2, rats consumed either novel milk or salt solutions, respectively, and within 10 min, were injected with lobeline (0.3-3.0 mg/kg) or METH (0.3-3.0 mg/kg). A single-bottle test conducted 48 h after flavor-drug pairings indicated that the dose of lobeline that reduced METH self-administration in a previous study (i.e., 3.0 mg/kg) also produced reliable CTA for milk and salt solution. These findings suggest a need to develop lobeline analogs that reduce METH self-administration, but do not produce CTA following the consumption of a novel solution.

Rationale: Methamphetamine has been shown to produce neurotoxicity demonstrated by depletions of dopamine and serotonin in the striatum and nucleus accumbens., Objective: The current study examined the effects of neurotoxic doses of methamphetamine on the rewarding effect of subsequent administration of methamphetamine assessed by the conditioned place preference (CPP) procedure., Methods: Male and female rats were treated with a neurotoxic regimen of methamphetamine (4 x 10 mg/kg, s.c., once every 2 h) or saline, and concentrations of dopamine, 3,4-dihydroxyphenylacetic acid, serotonin, and 5-hydroxyindoleacetic acid were measured 15 days later in the striatum, nucleus accumbens, and prefrontal cortex (PFC). In another experiment, male rats were given methamphetamine neurotoxic treatment or saline and were then conditioned 7 days later with methamphetamine (0.1, 0.3, or 1.0 mg/kg, s.c.) or saline using a four-trial CPP procedure. Locomotor activity was also measured during the conditioning sessions to investigate whether or not the neurotoxic methamphetamine treatment altered locomotor activity following a subsequent methamphetamine challenge., Results: Males and females did not differ significantly in the amount of neurochemical depletion produced by methamphetamine in any brain region. Collapsed across sex, dopamine was significantly depleted in nucleus accumbens (25%) and striatum (51%); serotonin was significantly depleted in nucleus accumbens (35%), striatum (34%) and PFC (33%). The methamphetamine challenge dose dependently increased locomotor activity, but the increase was not affected by treatment with neurotoxic doses of methamphetamine. In contrast, treatment with neurotoxic doses of methamphetamine enhanced CPP at the intermediate conditioning dose (0.3 mg/kg)., Conclusions: These results indicate that the rewarding effect of methamphetamine is enhanced by prior treatment with neurotoxic doses of methamphetamine, suggesting either a compensatory hyperfunctioning of spared dopamine neurons or a loss of inhibitory control from serotonergic input.

Rationale: Previous results demonstrated that pretreatment with lobeline attenuates d-methamphetamine self-administration in rats., Objective: The present experiments determined if lobeline serves as a reinforcer, if it decreases d-methamphetamine-induced reinstatement of d-methamphetamine self-administration, and if it activates the mesolimbic and nigrostriatal dopamine (DA) pathways in Sprague-Dawley male rats., Methods: The ability of intravenous (IV) lobeline (0.015-0.15 mg/kg per infusion) to engender responding and the ability of lobeline (0.015 and 0.05 mg/kg per infusion) to substitute for d-methamphetamine was determined using the self-administration paradigm. Experiments were also performed to determine if lobeline (1.0 and 3.0 mg/kg) reinstates responding for d-methamphetamine or alters the ability of d-methamphetamine (1.0 mg/kg per infusion) to reinstate responding following extinction. The effect of lobeline (3.0 mg/kg) or d-methamphetamine (1.0 and 3.0 mg/kg) on DA and dihydroxyphenylacetic acid (DOPAC) levels in the nucleus accumbens and striatum were also determined., Results: Lobeline was not self-administered and did not substitute for d-methamphetamine. Also, lobeline did not reinstate responding for d-methamphetamine following extinction nor did it alter d-methamphetamine-induced reinstatement. Furthermore, lobeline did not alter DA or DOPAC levels in the either the nucleus accumbens or striatum., Conclusions: Taken together, the present results indicate that lobeline decreases d-methamphetamine self-administration by decreasing reward, not by acting as a substitute reinforcer.

Lobeline inhibits [3H]nicotine binding to rat brain membranes and nicotine-induced [3H]dopamine release from superfused rat striatal slices, indicating that lobeline acts as a nicotinic receptor antagonist. To determine whether lobeline also inhibits the effects of nicotine in vivo, the present study assessed the effect of lobeline pretreatment on nicotine-induced hyperactivity and sensitization. For 12 consecutive days, rats were injected subcutaneously with lobeline (3 mg/kg) or saline, followed 10 min later by nicotine (0.3 mg/kg) or saline injection, and activity was monitored. To determine if lobeline inhibits induction of sensitization to nicotine, 1 or 28 days later, rats were pretreated with saline followed by nicotine or saline. Lobeline attenuated nicotine-induced hyperactivity when both drugs were administered repeatedly. Although an initial injection of lobeline produced hypoactivity, tolerance to this effect developed. Importantly, tolerance did not develop to the lobeline-induced attenuation of nicotine hyperactivity. Lobeline attenuated the induction of sensitization to nicotine 1 day, but not 28 days, after the cessation of lobeline treatment. These results demonstrate that systemic administration of lobeline attenuates the locomotor-activating effects of repeated nicotine injection and the sensitization to nicotine, consistent with lobeline inhibition of nicotinic receptors and/or neurotransmitter transporters.

Two experiments using a state-dependent retention (SDR) design determined whether MK-801 blocked the acquisition and retention of an avoidance response. In Experiments 1 and 2, rats were trained and tested 30 min after injections of either saline or MK-801 (0.05 and 0.10 mg/kg, respectively). Two minutes after training, subjects were immediately tested, and in both experiments, the avoidance response was acquired. The 24-h retention tests for Experiment 1 revealed that the data marginally supported a SDR interpretation. In Experiment 2, the dose of MK-801 was increased to 0.10 mg/kg, and the results showed that MK-801 rendered passive avoidance (PA) state-dependent. These experiments indicate that neither the 0.05 nor 0.10 mg/kg doses of MK-801 prevented acquisition of the avoidance response and that the latter dose rendered memory for PA training state-dependent. It is suggested that doses of MK-801 that did not impair PA learning can function as a cue state and influence expression of memory for PA.

alpha-Lobeline inhibits d-amphetamine-evoked dopamine release from striatal slices in vitro, appearing to reduce the cytosolic pool of dopamine available for reverse transport by the dopamine transporter. Based on this neurochemical mechanism of action, the present study determined if lobeline decreases d-methamphetamine self-administration. Rats were surgically implanted with jugular catheters and were trained to lever press on a fixed ratio 5 schedule for intravenous d-methamphetamine (0.05 mg/kg/infusion). To assess the specificity of the effect of lobeline, another group of rats was trained to lever press on a fixed ratio 5 schedule for sucrose reinforcement. Pretreatment of rats with lobeline (0.3-3.0 mg/kg, 15 min prior to the session) decreased responding for both d-methamphetamine and sucrose reinforcement. Following repeated lobeline (3.0 mg/kg) administration, tolerance developed to the decrease in responding for sucrose; however, the lobeline-induced decrease in responding for d-methamphetamine persisted. Furthermore, the lobeline-induced decrease in responding for d-methamphetamine was not surmounted by increasing the unit dose of d-methamphetamine. These results suggest that lobeline produces a nonspecific rate suppressant effect following acute administration, to which tolerance develops following repeated administration. Importantly, the results also suggest that repeated administration of lobeline specifically decreases responding for d-methamphetamine in a noncompetitive manner. Thus, lobeline may be an effective, novel pharmacotherapy for d-methamphetamine abuse.

Induced recovery from amnesia appears similar to disinhibition effects obtained when response strength is weakened in various ways. Therefore, the possibility that reexposure to the amnestic treatment acts as a "disinhibitor" is problematic for a retrieval interpretation of recovery following amnesia. Two experiments examined the question of whether or not hypothermia treatment (i.e., deep body cooling) acts as a disinhibitor for an extinguished fear response in Sprague-Dawley rats. The results of Experiment 1 indicate that deep body cooling did not significantly disinhibit a passive-avoidance response that had previously been extinguished with a 4-min nonreinforced exposure to the shock chamber of the apparatus. Experiment 2 further examined this negative effect by using a modified passive-avoidance procedure and lengthening the extinction session from 4 to 12 min. Similar to Experiment 1, the results of the second experiment also suggested that if the subject's body temperatures were reduced prior to the retention test, no disinhibitory effect of fear conditioning was manifested. These findings support the notion that memory retrieval (i.e., the contextual cue explanation) is the basis for the alleviation of amnesia by reexposure to the amnestic agent.