Intracranial self-stimulation-reward or immobilization-aversion had different effects on neurite extension and the ERK pathway in neurotransmitter-sensitive mutant PC12 cells.

Various actions trigger pleasure (reward) or aversion (punishment) as emotional responses. Emotional factors that negatively affect brain neural control processes for long periods of time might cause various mental diseases by inducing neuronal changes. In the present study, newly developed PC12m12 cells which are　highly sensitivity to neurotransmitters such as acetylcholine (ACh), were used. Exposing the cells to plasma from rats that had been subjected to intracranial self-stimulation (ICSS) markedly upregulated neurite outgrowth. In addition, voluntary running in a wheel or forced on a rotating rod was used to induce behavioral excitation in rats, and examinations of their plasma confirmed that the ICSS-induced neurite outgrowth was not associated with the ICSS behavior itself. Furthermore, immunoblotting and treatment with U0126, an ERK (extracellular signal-regulated kinase) antagonist, showed that the ICSS-induced neurite outgrowth was related to neuronal ERK activity. Exposing the same cells to plasma from rats that had been subjected to immobilization (IMM) also increased neurite outgrowth. Although the degree of enhancement was not as great as that seen after the ICSS rat plasma treatment, it was less than that observed after treatment with ACh as a positive control. These results indicate that ICSS or IMM lead to varying degrees of morphological changes, such as enhanced neurite outgrowth, in PC12m12 cells, but the neuronal signal transduction pathways underlying these effects differ; i.e.,the former morphological change might involve the activation of the ERK pathway, whereas the latter changes might not. Using PC12m12 cells which exhibit sensitivity to neurotransmitters, it might be possible to clarify the pathogeneses of mental diseases at the neuronal level and search for therapeutic drugs.

Contrast bath-induced neurite outgrowth in PC12m3 cells via the p38 mitogen-activated protein kinase pathway.

We investigated the differentiation and activation of p38 MAPK induced by contrast bath in drug-hypersensitive PC12m3 mutant cells. The rate of neurite outgrowth in PC12m3 cells induced by contrast bath was much higher than that induced by warming or cooling alone or that induced by two warmings with an interval of room temperature, indicating that contrast bath has a synergistic effect. The results of an experiment using a p38 MAPK inhibitor, SB203580, showed that neurite outgrowth of PC12m3 cells induced by contrast bath is p38 MAPK-dependent. Moreover, p38 MAPK activity induced by contrast bath was greater than that induced by warming or cooling alone, indicating that the synergistic effect of a contrast bath on neurite outgrowth depends on the activity of p38 MAPK. Since calcium ions are involved in the activations of P38 MAPK, we investigated the effect of the TRP ion channel inhibitor (Capsazepine) that inhibits calcium influx in the cells. Neurite outgrowth induced by contrast bath treatment was greatly suppressed by the addition of Capsazepine. These findings suggest that calcium dependent activation of the p38 MAPK pathway induced by contrast bath is responsible for the neurite outgrowth of PC12m3 cells.

C-SH2 point mutation converts p85ß regulatory subunit of phosphoinositide 3-kinase to an anti-aging gene.

Insulin interacts with the insulin receptor, and the activated receptor promotes activity of the phosphoinositide-3 kinase (PI3K) enzyme. A decrease in insulin or insulin-like growth factor 1 (IGF-1) signaling increases the lifespan in mammalian species. We found that a point mutation in the C-SH2 domain of the p85ß regulatory subunit of PI3K results in a prolonged lifespan. In p85ß mutant cells, nerve growth factor (NGF) activates the longevity protein FOXO, and the mutant p85ß gene produces strong resistance to oxidative stress, which contributes to aging. The p85ß gene mutation causes increased serum insulin and low blood glucose in p85ß mutant transgenic mice. Our results indicate that the p85ß mutant allele alters the activity of downstream targets of PI3K by NGF and platelet-derived growth factor (PDGF) but not by insulin. We report that a point mutation in the C-SH2 domain of p85ß transforms p85ß into a novel anti-aging gene by abnormally regulating PI3K.

Intracranial self-stimulation and immobilization had different effects on neurite extension and the p38 MAPK pathway in PC12m3 cells.

AIM: In mammals, rewarding and aversive states are motivational drivers of behavioral expression. However, it is unclear whether such states affect neuronal functions at the level of individual neurons. In the present study, the neuronal effects of rewarding and aversive states were investigated in using PC12 mutant cells (PC12m3 cells) with low sensitivity to nerve growth factor. MAIN METHODS: The intracranial self-stimulation (ICSS) and immobilization (IMM) methods were used to create rewarding and aversive states, respectively, in rats. Furthermore, experiments involving voluntary running on a wheel and forced running on a rotating rod were used to evaluate the effects of behavioral excitement on neurons. Then, the effects of plasma samples collected from the animals on neurite extension were examined microscopically, and p38 mitogen-activated protein kinase (MAPK) activity was assessed using Western blotting. KEY FINDINGS: Plasma samples from the ICSS and IMM rats facilitated neurite outgrowth to different degrees. However, their effects were not influenced by behavioral excitement. Furthermore, the plasma from the ICSS rats also induced upregulated p38 MAPK activity, whereas that from the IMM rats produced the same or slightly lower levels of MAPK activity to the control plasma. SIGNIFICANCE: These findings indicate that rewarding and aversive states might cause morphological changes, such as neurite extension. As for the effects of these states on p38 MAPK activity, the former state might directly increase p38 MAPK activity, but the latter state might have no effect or cause a slight reduction in p38 MAPK activity.

Intracranial self-stimulation-reward induces neurite extension in PC12m3 cells and activation of the p38 MAPK pathway.

Factors that trigger emotional expression may be divided into two patterns according to the type of motivation, acquiring reward (pleasure) and avoiding aversion (punishment). Repeated exposure to certain external stimuli accompanied by aberrant motivation may produce psychiatric diseases such as bipolar disorder and addiction via dysregulation of the central nervous system. However, neurobiological underpinnings of such diseases have not been clarified, especially at the neuronal level. In the present study, plasma from rats undergoing intracranial self-stimulation (ICSS) produced neurite outgrowth in PC12-variant cells (PC12m3). Stimulated PC12m3 cells also exhibited heightened activity of the p38 MAPK pathway. These findings indicate that reward states lead to not only morphological changes but also increases in p38 MAPK activity at the neuronal level in the central nervous system.

Characteristics of the runway model of intracranial self-stimulation behavior and comparison with other motivated behaviors.

Motivation incorporates several psychological aspects that produce reward-related and learning behaviors. Although reward-related behavior is reported to be mediated by the dopaminergic reward pathway, the involvement of dopaminergic systems in motivated behavior has not been fully clarified. Several experimental methodologies for motivational behavior have been reported, but pharmacological characteristics seem to vary among these methodologies. In this review, we attempt to summarize three main concepts:(1) the relationship of dopamine neuron physiology with motivated behavior, (2) the pharmacological characteristics of the runway intracranial self-stimulation model, and (3) the behavioral distinction of disparate motivated behaviors.

Imipramine-induced c-Fos expression in the medial prefrontal cortex is decreased in the ACTH-treated rats.

Previous studies have shown that the antidepressive-like effect of tricyclic antidepressants is blocked by repeated treatments with adrenocorticotropic hormone (ACTH). However, little is known about the neuroanatomy underlying the mechanism of the imipramine treatment-resistant depression model. In the present study, first experimental evidence showed no significant difference of the serum imipramine concentrations between the saline and ACTH-treated rats. In further study, imipramine produced significant increases in the c-Fos expression in the medial prefrontal cortex (mPFC), the dentate gyrus of the hippocampus (DGH), and the central nucleus of the amygdala (CeA), in rats repeatedly treated with saline. The imipramine-increased c-Fos immunoreactivity was suppressed in the mPFC of rats repeatedly treated with ACTH. However, there was no significant difference in c-Fos expression in the DGH and CeA between ACTH- and saline-treated rats. These results suggest that the mPFC is maybe involved in effects of the imipramine in the ACTH-treated rats.

Effect of GBR12909 on affective behavior: distinguishing motivational behavior from antidepressant-like and addiction-like behavior using the runway model of intracranial self-stimulation.

RATIONALE: It was recently demonstrated that the priming stimulation effect (PSE) in the runway model of intracranial self-stimulation (ICSS) can be used as a model system to study the motivational effects of drugs. However, the characteristics of this novel experimental model have not been fully clarified. OBJECTIVE: To elucidate the involvement of dopamine uptake inhibition in motivated behavior and the difference in experimental characteristics between closely related experimental models, we investigated the effects of the dopamine uptake inhibitor GBR12909 in the runway ICSS model, in the forced swimming test (FST), and on conditioned place preference (CPP). In addition, the role of dopamine receptor signaling in the runway model was evaluated using dopamine receptor agonists and antagonists. RESULTS: GBR12909 dose-dependently increased running speed on the runway and decreased immobility time in the FST without affecting the time spent in the drug-associated compartment in CPP tests. The effect of GBR12909 in the runway model was inhibited by pre-treatment with the dopamine receptor antagonists haloperidol and raclopride. The dopamine receptor agonists SKF38393 and quinpirole dose-dependently decreased running speed. CONCLUSIONS: These results demonstrate that GBR12909 displays motivation-enhancing and antidepressant-like effects without place conditioning effects. In addition, the mechanisms of PSE enhancement in the runway ICSS model are different from those underlying closely associated experimental models and are mediated by increases in dopamine signaling.

Differential effects of nomifensine and imipramine on motivated behavior in the runway model of intracranial self-stimulation.

A motivational deficit (the loss of pleasure or interest in previously rewarding stimuli) is one of the core symptoms of major depression, and valid models evaluating the motivational effects of drugs are needed. It was recently demonstrated that the priming stimulation effect in the runway model of intracranial self-stimulation (ICSS) can be used as a model system to study the motivational effects of drugs. However, the characteristics of this novel experimental model have not been fully clarified. In this study, we investigated the effects of nomifensine and imipramine in the runway ICCS model, forced swim tests, and locomotor activity tests to differentiate motivation from affective-like states. Nomifensine dose-dependently increased running speed on the runway and decreased immobility time in the forced swim test. In contrast, imipramine decreased running speed on the runway although it also decreased immobility time in the forced swim test. In addition, the motivation-enhancing effect of nomifesine in the runway model was completely inhibited by pretreatment with the dopamine receptor antagonist haloperidol, although nomifensine-induced increases in locomotion were not affected by haloperidol. These results demonstrate that nomifensine displays motivation-enhancing and antidepressant-like effects. In addition, the motivational effects of nomifensine in the runway ICSS model are primarily mediated by dopamine receptors and enhancements of motivated behavior do not simply reflect hyperlocomotion.

A new method for evaluation of motivational effects of drugs.

Motivation is a process that continuously changes behavior to achieve a goal and can be conceptualized as a series of steps relating to that process. Intracranial self-stimulation (ICSS) behavior is considered to consist of reward and motivational effects. Moreover, priming stimulation of ICSS behavior is known to promote motivational effects. Using the runway method and priming stimulation, rewards and motivational effects of ICSS behavior can be differentiated. We investigated whether the runway method and priming stimulation of ICSS behavior could be used to evaluate motivational effects of a drug. In the ICSS runway model, running speed was considered as a reference of motivational effect. An assessment of pharmacological drugs known to influence motivational states was also undertaken. Using our experimental methods, prominent changes were observed in running speed when animals were administered methamphetamine and nicotine. Based on our results, we conclude that the runway method may be useful for the evaluation of substances that affect motivation. This review introduces 4 types of neuronal processes involved in motivation, reward mechanisms, outlines evaluation methods, and describes motivational properties of psychoactive drugs.

Involvement of dopaminergic receptor signaling in the effects of glutamatergic receptor antagonists on conditioned place aversion induced by naloxone in single-dose morphine-treated rats.

A better understanding of the neurochemical mechanisms mediating the aversive consequences of drug withdrawal is important for understanding drug addiction. We previously demonstrated that the inhibitory effect of glutamate receptor antagonists on the conditioned place aversion (CPA) induced by naloxone-precipitated withdrawal after a single morphine exposure could be blocked by dopamine receptor antagonists. Thus, a glutamatergic-dopaminergic interaction may participate in this phenomenon. The current study was undertaken to further characterize this interaction by employing both D(1) (SCH 23390) and D(2) (raclopride and eticlopride) dopamine receptor antagonists. The influence of these antagonists on the attenuation of CPA by MK-801 (NMDA receptor antagonist), GYKI 52466 (AMPA receptor antagonist), and MCPG (metabotropic glutamate receptor antagonist) was determined in rats receiving a single dose of morphine. The dopamine antagonists showed either a significant reversal or a tendency to reverse the effects of MK-801 on CPA. The effect of GYKI 52466 was also attenuated by the blockade of either D(1) or D(2) receptors. The effect of MCPG, however, was only blocked by D(2) antagonists and not by the D(1) antagonist SCH 23390. These results add evidence to the hypothesis that a glutamatergic-dopaminergic interaction may be involved in the CPA induced by naloxone-precipitated withdrawal following a single morphine exposure and suggest that both D(1) and D(2) dopamine receptor signaling mechanisms play a role in mediating the aversive aspects of acute dependence.

Effect of glutamate receptor antagonists microinjected into the nucleus accumbens on place aversion induced by naloxone in single-dose, morphine-treated rats.

It is well established that acute morphine withdrawal can be observed following opioid receptor antagonism in rodents. Glutamate receptor antagonists can attenuate the conditioning place aversion (CPA) induced by naloxone in single-dose, morphine-treated rats. Anatomically, the nucleus accumbens appears to be involved in opiate dependence. In the present study, we examined the effects of various glutamate receptor antagonists in the nucleus accumbens on naloxone-induced CPA in rats. MK-801 (an NMDA receptor antagonist), GYKI52466 (an AMPA receptor antagonist), and MCPG (a metabotropic glutamate receptor antagonist) significantly attenuated naloxone-induced CPA following microinjection into the accumbens. In contrast, none of the agents showed place conditioning ability on their own in either morphine-exposed or naïve rats. The present study suggests that glutamate receptors in the nucleus accumbens play a key role in the motivational component of withdrawal during acute morphine dependence.

Chronic treatment with imipramine and lithium increases cell proliferation in the hippocampus in adrenocorticotropic hormone-treated rats.

Adult hippocampal neurogenesis is reported to change in animal models of depression and antidepressants. We have used the mitotic marker 5-bromo-2'-deoxyyridine to address the effects of imipramine and lithium on cell proliferation and survival following chronic treatment with adrenocorticotropic hormone (ACTH) in the subgranular zone of the hippocampal dentate gyrus. ACTH treatment for 14 d decreased adult hippocampal cell proliferation and survival. Coadministration of imipramine and lithium for 14 d blocked the loss of cell proliferation but not cell survival resulting from the chronic treatment with ACTH. The coadministration of imipramine and lithium may have treatment-resistant antidepressive properties, which may be attributed, in part, to a normalization of hippocampal cell proliferation.

α7 Nicotinic acetylcholine receptors in the central amygdaloid nucleus alter naloxone-induced withdrawal following a single exposure to morphine.

RATIONALE: Negative motivational withdrawal from acute opiate dependence was induced by an opioid antagonist, and the withdrawal signs prevented by pretreatment with nicotine. OBJECTIVES: The present study was undertaken to examine the mechanism of nicotine-induced attenuation of withdrawal precipitated by naloxone in rats administered a single dose of morphine. METHODS: Conditioned place aversion (CPA) was precipitated by naloxone in rats exposed once to morphine. Nicotinic acetylcholine receptor (nAChR) agonists were microinjected into the central amygdaloid nucleus (CeA) before naloxone was administered. Additionally, c-Fos expression in the amygdala was measured in rats exposed to α7 nAChR ligands. RESULTS: The microinjection of nicotine (0.3 and 1.0 µg/µl) into the CeA dose-dependently inhibited naloxone-induced CPA. This inhibition of CPA was reversed by methyllycaconitine (MLA), an α7 nAChR antagonist. CPA was also significantly attenuated by the microinjection of tropisetron (3.0 µg/µl), an α7 nAChR agonist and 5-hydroxytriptamine 3 (5-HT(3)) receptor antagonist, but not by ondansetron (1.0 and 3.0 µg/µl), a 5-HT(3) receptor antagonist. The microinjection of PNU-282987 (3.0 µg/µl), a selective α7 nAChR agonist, into the CeA also inhibited CPA. Furthermore, nicotine increased c-Fos expression in the CeA, but not the medial or basolateral amygdaloid nucleus. The increase of c-Fos in the CeA was significantly inhibited by MLA. CONCLUSION: Nicotine-induced attenuation of CPA precipitated by naloxone is mediated by the α7 nAChR subtype, and the CeA is one of the regions of the brain involved in the effect of nicotine on acutely opiate-dependent subjects.

Evaluation of motivational effects induced by intracranial self-stimulation behavior.

In the runway model of intracranial self-stimulation (ICSS) experimentation, the experimental animal is timed in running a fixed distance to depress a lever that releases electrical stimulation to an electrode implanted along its medial forebrain bundle. This ICSS has both a reward and a motivational component. Using the runway method and priming stimulation, we designed an experimental method for directly measuring motivation. An assessment of pharmacological agents that are known to influence motivational states was also undertaken. Using the experimental methods that we created, we observed prominent changes in running speed when animals were exposed to methamphetamine and nicotine. According to these data, the runway method employing intracranial self-stimulation behavior may be useful for the evaluation of substances that act on motivation. We review the underlying neuropharmacological and anatomical functions associated with our experimental methods. We hope that this technique will be used to scientifically evaluate the impact of drugs and/or therapeutic interventions on human motivation.

Effects of imipramine and lithium on the suppression of cell proliferation in the dentate gyrus of the hippocampus in adrenocorticotropic hormone-treated rats.

We examined the influence of chronic adrenocorticotropic hormone (ACTH) treatment on the number of Ki-67-positive cells in the dentate gyrus of the hippocampus in rats. ACTH treatment for 14 days decreased the number of such cells. The administration of imipramine or lithium alone for 14 days had no effect in saline-treated rats. The effect of ACTH was blocked by the administration of imipramine. Furthermore, the coadministration of imipramine and lithium for 14 days significantly increased the number of Ki-67-positive cells in both the saline and ACTH-treated rats. The coadministration of imipramine and lithium normalized the cell proliferation in the dentate gyrus of the hippocampus in rats treated with ACTH.

Effects of bupropion on the forced swim test and release of dopamine in the nucleus accumbens in ACTH-treated rats.

The dopamine reuptake inhibitor bupropion has clinically been proven to improve depression and treatment-resistant depression. We examined its influence on the duration of immobility during the forced swim test in adrenocorticotropic hormone (ACTH)-treated rats and further analyzed the possible role of dopamine receptors in this effect. Additionally, the mechanism by which bupropion acts in this model was explored specifically in relation to the site of action through the use of microinjections into the medial prefrontal cortex and nucleus accumbens. Bupropion significantly decreased the duration of immobility in normal and ACTH-treated rats. This effect was blocked by D2 and D3 receptor antagonists in normal rats. Furthermore, infusions of bupropion into the nucleus accumbens, but not medial prefrontal cortex, decreased the immobility of normal and ACTH-treated rats during the forced swim test. Bupropion treatment plus repeated ACTH treatment significantly increased the extracellular dopamine concentration. These findings suggest the antidepressant-like effect of bupropion to be related to levels of dopamine in the rat nucleus accumbens.

Effects of pramipexole on the duration of immobility during the forced swim test in normal and ACTH-treated rats.

The dopamine D2/D3 receptor agonist pramipexole has clinically been proven to improve depression or treatment-resistant depression. However, the involvement of the dopamine receptor system on the effect of pramipexole on depression remains unclear. We examined the influence of pramipexole on the duration of immobility during the forced swim test in normal and adrenocorticotropic hormone (ACTH)-treated rats and further analyzed the possible role of dopamine receptors in this effect. Additionally, the mechanism by which pramipexole acts in this model was explored specifically in relation to the site of action through the use of microinjections into the intramedial prefrontal cortex and nucleus accumbens. Pramipexole (0.3-1 mg/kg) significantly decreased the duration of immobility in normal and ACTH-treated rats. This effect was blocked by L-741,626, a D2 receptor antagonist, and nafadotride, a D3 receptor antagonist, in normal rats. Furthermore, infusions of pramipexole into the intranucleus accumbens, but not the medial prefrontal cortex, decreased the immobility of normal and ACTH-treated rats during the forced swim test. Taken together, the results of these experiments suggested that pramipexole, administered into the intranucleus accumbens rather than the medial prefrontal cortex, exerted an antidepressant-like effect on ACTH-treated rats via the dopaminergic system. The immobility-decreasing effect of pramipexole may be mediated by dopamine D2 and D3 receptors.

Nicotinic acetylcholine alpha4beta2 receptor regulates the motivational effect of intracranial self stimulation behavior in the runway method.

Recently, it was demonstrated that the priming stimulation effect (PSE) of intracranial self-stimulation (ICSS) with the runway method can be used as a model system to study the motivation that contributes to specific behaviors. It was postulated that these behaviors could be used to compare the effects of various drugs on the mechanism of motivation. In the present study, the influences of nicotine, methyllycaconitine (alpha7 nicotine-receptor antagonist), and dihydro-beta-erythroidine (alpha4beta2 nicotine-receptor antagonist) on motivation were examined using the runway method for ICSS. Electrodes were implanted into the medial forebrain bundle of Wistar rats. The rats ran to the goal lever to get the reward (50 - 200 microA, 0.2 ms, 60 Hz) and pretrial electric stimulation (priming stimulation) in the medial forebrain bundle was performed. The experiment measured the running time from the start box until the rat pressed the goal lever for the reward stimulation. Under these reward and priming stimulation conditions, nicotine (0.2 mg/kg) induced a significant increase in running speed. The nicotine receptor antagonist alpha4beta2 rather than alpha7 showed a dose-dependent antagonistic action on the effect of nicotine on running speed. These results demonstrate that nicotine enhances the running speed towards the goal lever via alpha4beta2 nicotinic receptors and suggest that alpha4beta2 nicotinic receptors influence the brain mechanism of motivation.