Understanding how memory, learning and reward work in unison to form adaptive and sometime maladaptive behaviour is at the forefront of modern neuroscience. The largest unmet need in treating maladaptive reward learning behaviours such as addiction is maintaining long-term abstinence and preventing relapse after re-exposure to drug-associated cues. Nicotinic acetylcholine receptors (nAChR) have been implicated in responses to drugs of abuse other than nicotine (Rahman et al., 2015) and the aim of this work was to characterise the role of α7 nAChRs in morphine reward learning using conditioned place preference (CPP). The α7 nAChR antagonist methyllycaconitine (MLA) was used to determine if these receptors contribute to specific stages of drug-paired learning, namely acquisition, expression, reconsolidation or reinstatement of morphine-CPP. In 7-8week old C57BL/6J mice MLA (4mg/kg, s.c), given 20 minutes prior to a conditioning dose of morphine (10mg/kg, i.p) or post-test trial, had no effect on the acquisition, reconsolidation or expression of morphine-CPP. However, when given 20 minutes prior to a priming dose of morphine (5mg/kg, i.p), MLA (4mg/kg, s.c) significantly inhibited drug-induced reinstatement. The mechanisms of this effect were investigated using glutamate receptor autoradiography. Changes in 2-Amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA) and N-methyl-D-aspartate (NMDA) binding were examined in mice treated with either saline or MLA at morphine reinstatement. There were no significant changes in NMDA receptor binding (using [3H]MK-801) but morphine reinstatement significantly increased [3H]AMPA binding in the CA1/2 of the ventral but not dorsal hippocampus, or in any other brain regions examined (including mPFC, nucleus accumbens, amygdala and VTA). The selective increase in the hippocampus was partially antagonised by MLA, linking α7 nAChR activation to glutamatergic synaptic plasticity in the hippocampus. Intracranial infusions of MLA into the ventral but not the dorsal hippocampus or medial prefrontal cortex blocked reinstatement to morphine-CPP in male Wistar rats.

Previous research has suggested that lobeline, a plant alkaloid derived from Lobelia inflate, has potential to be an efficacious pharmacotherapy for the treatment of methamphetamine dependence. In addition to attenuating methamphetamineinduced dopaminergic alterations in vitro, lobeline has been shown to decrease the primary rewarding effects and discriminative stimulus properties of methamphetamine in rats. It is of clinical interest to assess the utility of lobeline to decrease methamphetamine conditioned cues as these cues have been shown to significantly contribute to relapse. The current studies assessed the ability of lobeline to block the acquisition and expression of methamphetamine-induced conditioned place preference in rats. Lobeline blocked the acquisition of methamphetamine-induced conditioned place preference when a low dose of methamphetamine was used during conditioning. However, this blockade was surmounted with higher doses of methamphetamine. Furthermore, the expression of methamphetamine-induced conditioned place preference is attenuated following repeated administration, indicating that lobeline not only blocks the primary reinforcing effects of methamphetamine, but it also blocks the environmental cues that become associated with drug administration. These results provide further evidence that lobeline may be an efficacious treatment for methamphetamine dependence. The rewarding properties of psychostimulants are thought to be mediated, at least in part, by the nucleus accumbens shell. The effects of lobeline on methamphetamine-induced alterations in this dopaminergic region were assessed using microdialysis in rats. Acute lobeline did not have an effect on the methamphetamine-induced increases in dopamine, indicating that repeated lobeline administration may be more efficacious. Interestingly, lobeline potentiated the methamphetamine-induced decrease of the dopamine metabolite, DOPAC. These results suggest that acute lobeline may function to redistribute vesicular dopamine pools within the terminal bouton.

One of the most common childhood disorders, attention-deficit hyperactivity disorder (ADHD) places individuals at a higher risk for nicotine (NIC) dependence. Approximately 37.2% of individuals with ADHD currently smoke compared to the 18.3% of individuals with no record of mental illness. Methylphenidate (MPH; Trade name Ritalin) is the most commonly prescribed treatment for ADHD. Research regarding the synergistic effects of MPH and NIC, however, is divided. Some research indicates that MPH may enhance susceptibility to NIC effects, whereas other studies report that MPH may inhibit sensitization to NIC. The present study examines the effects of pre-exposure to MPH (1.0 mg/kg) on the behavioral effects of NIC (0.5 mg/kg) in adolescent male and female Sprague-Dawley rats. We used behavioral sensitization and conditioned place preference (CPP) on animals postnatal day (P)28-50; this is defined as adolescence in rats. For behavioral sensitization, results revealed a significant interaction between day of testing, drug pre-exposure, and adolescent drug treatment (p = .004). On the other hand, CPP results revealed a significant interaction between adolescent drug treatment and drug pre-exposure (p = .031). Findings suggest that pre-exposure to MPH reduces behavioral sensitization to NIC during adolescence. In addition, results indicate that MPH enhances NIC CPP in adolescent male and female rats, suggesting that MPH may enhance the rewarding effect of NIC.

Research has revealed that schizophrenics are significantly more likely to smoke cigarettes than the general population, and consume nicotine products at a much more prevalent rate. Further exacerbating this issue, it has been previously demonstrated in clinical populations that the type of antipsychotic treatment administered (typical versus atypical) may result in either an increase or a decrease of already heightened smoking behavior within the schizophrenic population. With these clinical issues in mind, the present study sought to examine the effects of antipsychotic treatment upon the associative reward of nicotine within the neonatal quinpirole model of schizophrenia. We found that treatment with the typical antipsychotic haloperidol blocked the associative reward of nicotine. Clozapine, an atypical antipsychotic, merely reduced the rewarding effects. These findings illustrate the centrality of the dopamine system, specifically the D2 receptor subtype, as an underlying mechanism of the rewarding effects of nicotine among rodents neonatally treated with quinpirole.

Indiana University-Purdue University Indianapolis (IUPUI) / Recently, the co-consumption of highly caffeinated energy drinks and alcohol has become a public health concern. Consumption of these beverages has been linked to a wide variety negative consequences including alcohol poisoning, driving under the influence, physical harm, and sexual violence. The more protracted consequences of caffeinated alcohol consumption have received very little attention, however. Some evidence suggests that individuals that frequently consume energy drinks mixed with alcohol are more likely to develop an alcohol use disorder. Interestingly, both caffeine and alcohol use alone have been linked to polydrug abuse. It is therefore of interest whether combined caffeine and alcohol consumption may pose an additive risk for substance abuse. Given that both compounds can positively influence dopamine signaling in mesolimbocortical reward circuitry via different mechanisms, this is an important question to address. Psychostimulants, such as cocaine, are of particular interest considering the significant involvement of dopamine in their effects. The current project explored this possibility employing an established mouse model of binge caffeine and alcohol co-consumption. Male C57BL/6J mice underwent 14 days of daily, 2hr limited access to water, alcohol, caffeine, or combined caffeine and alcohol. Water was freely available after these sessions. In Experiment 1, mice underwent an 11-day locomotor sensitization protocol for cocaine initiating on day 15. Locomotor sensitization has been associated with a greater propensity to self-administer psychostimulants in rodents. Mice were subjected to injections of cocaine (5 or 10 mg/kg; i.p.) or saline every other day, with 15 minute activity monitoring until day 25. In Experiment 2, a separate group of mice underwent an identical drinking procedure. A conditioned place preference (CPP) protocol commenced on day 15. CPP assesses the conditioned rewarding effects of cues associated with drugs of abuse. On day 15, mice received saline injections and were immediately placed onto a neutral floor texture (paper) in the place conditioning box for 15 minutes in order to habituate the animals to the apparatus and injection procedure. Starting on day 16, mice received daily alternating systemic injections of cocaine (1 or 5 mg/kg; i.p.) and saline or saline throughout (naïve controls) and were placed onto one of two particular tactile floor cues: a metal floor with holes punched out or a grid floor made of metal rods. Mice were exposed to the other injection/floor pairing on the alternate days. Mice were placed into these activity monitors for 15 minute conditioning sessions. These sessions alternated drug and vehicle over the course of 8 days so that a total of 4 drug and 4 saline injections were given. The first place preference test occurred on day 24 wherein all mice were injected with saline and offered access to both floor textures. On day 25, mice were returned to the conditioning protocol for another 8 days and a second CPP test on day 33. The results of Experiment 1 suggested that prior caffeine consumption, irrespective of the presence of ethanol, enhanced the initial psychomotor stimulating effect of 10 mg/kg cocaine. However, prior fluid consumption history did not influence the capacity to develop locomotor sensitization. The results of Experiment 2 indicate that prior caffeine and/or ethanol consumption had no influence on the development or expression of CPP for 1 mg/kg or 5 mg/kg cocaine. Collectively, these results suggest that a history of caffeine consumption may increase the stimulant response to a moderate dose of cocaine, perhaps indicating cross-sensitization. Although the conditioned rewarding effects of cocaine were not altered by prior caffeine and/or ethanol consumption, an enhanced stimulant response may be indicative of enhanced cocaine abuse potential. This study demonstrates that moderate caffeine consumption may influence an individual’s early interactions with cocaine which may eventually influence the likelihood of later problematic use.

京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第20759号 / 人健博第49号 / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 木下 彩栄, 教授 三谷 章, 教授 村井 俊哉 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

No description available.

Neuronal nicotinic acetylcholine receptors modulate both cholinergic and non-cholinergic synaptic transmission. Our research concerns α6 and α4 neuronal nicotinic subunits because they often co-assemble with the β2 subunit, which has abundant expression in the CNS and previous work has demonstrated that β2* nAChRs are involved in nicotine and cocaine reward. α6β2* and α4β2* nAChRs are highly expressed in midbrain, which is known to be critical for the incentive salience associated with natural and artificial (drug) reward. Our goal was to assess the role of α6β2* and α4β2* nAChRs in nicotine and cocaine reward using an unbiased conditioned place preference (CPP) test in mice. Adult male C57BL/6J mice or male mice null for the α6 or α4 nicotinic receptor subunit were used. For CPP: On day 1, pre-conditioning scores were recorded; Days 2-4 mice underwent conditioning, where they were randomly assigned to either the black or the white compartment paired with drug, and the opposite chamber paired with saline; Day 5 was a drug-free test day where post conditioning scores were recorded. α-Conotoxin MII[H9A;L15A], a selective antagonist of α6β2* nAChRs, was given centrally either into the lateral ventricle or the nucleus accumbens on conditioning days, which tested for acquisition of CPP, or it was given only once into the lateral ventricle on test day which tested for expression of CPP. Antagonizing α6*nAChRs resulted in a significant attenuation of both nicotine and cocaine place preference. This was complemented with diminished nicotine and cocaine place preference in α6 KO mice compared to WT littermates. Studies with α4 KO mice showed significantly reduced nicotine place preference scores compared to WT littermates. In contrast, α4 KO and WT mice showed significant place preference for 20mg /kg cocaine, suggesting that the α4 subunit is not required for the reward-like effects of cocaine in our behavioral test. Our results implicate α6β2* and α4β2* nAChR involvement in nicotine and cocaine CPP, but only α6β2* nAChR involvement in cocaine CPP. Lithium conditioned place avoidance and food reward were not altered in α6 KO mice or by α-Conotoxin MII[H9A;L15A], thereby validating the specificity of hedonics of targeting α6* nAChRs in CPP. Our studies suggest that α6β2* and α4β2*nAChR should be further characterized for future nicotine cessation therapies, and α6β2* could provide a new target for treating cocaine addiction.

In two experiments, we analyzed the effects of methylphenidate (MPH) on conditioned place preference (CPP) in adolescent male and female rats, and the effects of MPH on the dopamine transporter (DAT). In Experiment 1, male and female rats were conditioned for 5 consecutive days from postnatal day (P)44 to P48 with saline, 1, or 5mg/kg MPH. On the post conditioning preference test, the group administered the 1mg/kg dose of MPH resulted in no significant preference compared to controls, whereas the 5mg/kg dose of MPH produced a robust significant preference for the paired context, but there were no sex differences. Analysis of the DAT revealed that animals conditioned with the 5mg/kg dose of MPH demonstrated a significant decrease of the dopamine transporter (DAT) in the nucleus accumbens and striatum compared to controls. In Experiment 2, animals were conditioned using an every second day paradigm from P33–41 to model a previous MPH treatment regimen that had revealed sex differences in behavioral sensitization. MPH produced an increased preference for the paired context on a post-conditioning preference test in Experiment 2, but as in Experiment 1, no sex differences were observed. These data show that a relatively high dose of MPH has rewarding associative effects in both adolescent male and female rats reliably across two different conditioning paradigms and ages in adolescence, but no sex difference. In addition, MPH results in a significant decrease of the DAT in drug reward brain areas which has implications toward plasticity of the brain's reward system.

This study analyzed the associative properties of nicotine in a conditioned place preference (CPP) paradigm in adolescent rats neonatally treated with quinpirole (NQ) or saline (NS). NQ produces dopamine D2 receptor supersensitivity that persists throughout the animal's lifetime, and therefore has relevance towards schizophrenia. In two experiments, rats were ip administered quinpirole (1mg/kg) or saline from postnatal day (P)1–21. After an initial preference test at P42–43, animals were conditioned for eight consecutive days with saline or nicotine (0.6mg/kg free base) in Experiment 1 or saline or nicotine (1.8mg/kg free base) in Experiment 2. In addition, there were NQ and NS groups in each experiment given the antipsychotic haloperidol (0.05mg/kg) or clozapine (2.5mg/kg) before nicotine conditioning. A drug free post-conditioning test was administered at P52. At P53, the nucleus accumbens (NAc) was analyzed for glial cell-line derived neurotrophic factor (GDNF). Results revealed that NQ enhanced nicotine CPP, but blunted the aversive properties of nicotine. Haloperidol was more effective than clozapine at blocking nicotine CPP in Experiment 1, but neither antipsychotic affected nicotine conditioned place aversion in Experiment 2. NQ increased accumbal GDNF which was sensitized in NQ rats conditioned to nicotine in Experiment 1, but the aversive dose of nicotine reduced GDNF in NQ animals in Experiment 2. Both antipsychotics in combination with the aversive dose of nicotine decreased accumbal GDNF. In sum, increased D2 receptor sensitivity influenced the associative properties and GDNF response to nicotine which has implications towards pharmacological targets for smoking cessation in schizophrenia.