Sulpiride injections into the medial septum reverse the influence of intra-medial septum injection of L-arginine on expression of place conditioning-induced by morphine in rats

The antipsychotic drug sulpiride in the ventral pallidum paradoxically impairs learning and induces place preference

Sulpiride, as a D2-like dopamine (DA) receptor (D2R) antagonist, is an important antipsychotic drug in the treatment of schizophrenia. Recently, we have shown that the activation of D2Rs in the ventral pallidum (VP) modulates the activity of the ventral tegmental area (VTA) DAergic neurons. According to our hypothesis, intra-VP sulpiride can influence the motivational and learning processes, pervasively modifying the behavior of examined animals. In the present study, sulpiride was microinjected into the VP of male Wistar rats in three different doses. Morris water maze (MWM) test was applied to investigate the effects of sulpiride on spatial learning, while conditioned place preference (CPP) test was used to examine the potential rewarding effect of the drug. In order to show, whether the animals can associate the rewarding effect with an area which can be recognized only on its spatial location, we introduced a modified version of the CPP paradigm, the spatial CPP test. Our results show that the intra-VP sulpiride dose-dependently impairs learning processes. However, the largest dose of sulpiride induces place preference. Results of the spatial CPP paradigm demonstrate that the animals cannot associate the rewarding effect of the drug with the conditioning area based on its spatial location. In the CPP paradigm, locomotor activity decrease could be observed in the sulpiride-treated rats, likely because of a faster habituation with the conditioning environment. In summary, we can conclude that intra-VP sulpiride has a dual effect: it diminishes the hippocampus-dependent spatial learning processes, in addition, it has a dose-dependent rewarding effect.

The D2-like Dopamine Receptor Agonist Quinpirole Microinjected Into the Ventral Pallidum Dose-Dependently Inhibits the VTA and Induces Place Aversion

BACKGROUND

The ventral pallidum (VP) is a dopaminoceptive forebrain structure regulating the ventral tegmental area (VTA) dopaminergic population activity. We have recently demonstrated that in the VP, the D2-like dopamine (DA) receptor agonist quinpirole dose dependently facilitates memory consolidation in inhibitory avoidance and spatial learning. According to our hypothesis, quinpirole microinjected into the VP can modulate the VTA DAergic activity and influence motivation and learning processes of rats.

METHODS

Quinpirole was microinjected at 3 different doses into the VP of male rats, and controls received vehicle. Single unit recordings were employed to assess VTA DAergic activity. To investigate the possible reinforcing or aversive effect of quinpirole in the VP, the conditioned place preference paradigm was used.

RESULTS

Our results showed that intra-VP quinpirole microinjection regulates VTA DAergic neurons according to an inverted U-shaped dose-response curve. The largest dose of quinpirole decreased the population activity and strongly reduced burst activity of the DAergic neurons in the first hour after its application. In contrast, the 2 smaller doses increased DA population activity, but their effect started with a delay 1 hour after their microinjection. The CPP experiments revealed that the largest dose of quinpirole in the VP induced place aversion in the rats. Furthermore, the largest dose of quinpirole induced an acute locomotor activity reduction, while the medium dose led to a long-duration increase in locomotion.

CONCLUSIONS

In summary, quinpirole dose dependently regulates VTA DAergic activity as well as the motivation and motor behavior of the rats at the level of the VP.

The cross-talk between dopaminergic and nitric oxide systems in the medial septal nucleus, and their distinct effects on anxiety-like behaviors in male rats

Anxiety disorders, which have a noticeable global prevalence and may be caused by many factors, include a spectrum of disorders that share features of excessive fear- and anxiety-related behavioral disturbances. Different brain areas and neurotransmitter systems have been under investigation for anxiety-related disorders. In this study, we investigated the possible interaction between the dopaminergic and nitric oxide (NO) neurotransmitter systems in the medial septal nucleus and their roles in anxiety-like behaviors using elevated plus-maze (EPM) test in male rats. Our results showed that: (i) both D1-and D2-like receptor agonists, SKF-38393 and quinpirole, augmented anxiety-like behaviors at their two highest applied doses in the EPM test; (ii) both D1-and D2-like receptor antagonists, SCH- 23390 and sulpiride, reduced anxiety-like behaviors at their two highest applied doses in the EPM test; (iii) L-Arginine, a NO precursor, increased anxiety-like behaviors, but L-NAME, a non-specific nitric oxide synthase (NOS) inhibitor, reduced them in the EPM test; (iv) L-NAME could not reverse the anxiety-like parameters produced by SKF-38393, but it significantly reduced the anxiety-like behaviors induced by quinpirole; (v) Neither SCH- 23390 nor sulpiride changed anxiety-related behaviors induced by L-Arginine. It can be concluded that both dopaminergic and nitric oxide systems in the medial septal nucleus are involved in modulating anxiety-like behaviors. While NO has an involvement in the exerted effects by the D2-like agonist, such effects were not observed at the applied range of the doses for D1-and D2-like antagonists.

Nitric oxide donor molsidomine promotes retrieval of object recognition memory in a model of cognitive deficit induced by 192 IgG-saporin

Nitric oxide (NO) plays a leading role in learning and memory processes. Previously, we showed its ability to modify the deleterious effect of immunotoxin 192 IgG-saporin (192-IgG-SAP) in the cholinergic system. The aim of this study was to analyze the potential of a NO donor (molsidomine, MOLS) to prevent the recognition memory deficits resulting from the septal cholinergic denervation by 192 IgG-SAP in rats. Quantification of neuronal and endothelial nitric oxide synthase (nNOS and eNOS, respectively) expression was evaluated in striatum, prefrontal cortex, and hippocampus. In addition, a choline acetyltransferase immunohistochemical analysis was performed in medial septum and assessed the effect of MOLS treatment on the spatial working memory of rats through a recognition memory test. Results showed that 192-IgG-SAP reduced the immunoreactivity of cholinergic septal neurons (41%), compared with PBS-receiving control rats (p < 0.05). Treatment with MOLS alone failed to antagonize the septal neuron population loss but prevented the progressive abnormal morphological changes of neurons. Those animals exposed to 192-IgG-SAP immunotoxin exhibited a reduction of cortical nNOS expression against the control group, whereas expression was enhanced in the 192-IgG-SAP + MOLS group. The most relevant finding was the recovering of the discrimination index exhibited by the 192-IgG-SAP + MOLS group. When compared with the rats exposed to the 192-IgG-SAP immunotoxin, they reached values similar to those observed in the PBS group. Our results show that although MOLS failed to block the cholinergic neurons loss induced by 192-IgG-SAP, it avoided the neuronal damage progression.

Role of Nitric Oxide on Dopamine Release and Morphine-Dependency

The catastrophic effects of opioids use on public health and the economy are documented clearly in numerous studies. Repeated morphine administration can lead to either a decrease (tolerance) or an increase (sensitization) in its behavioral and rewarding effects. Morphine-induced sensitization is a major problem and plays an important role in abuse of the opioid drugs. Studies reported that morphine may exert its effects by the release of nitric oxide (NO). NO is a potent neuromodulator, which is produced by nitric oxide synthase (NOS). However, the exact role of NO in the opioid-induced sensitization is unknown. In this study, we reviewed the role of NO on opioid-induced sensitization in 2 important, rewarding regions of the brain: nucleus accumbens and ventral tegmentum. In addition, we focused on the contribution of NO on opioid-induced sensitization in the limbic system.

Oxytocin enhances the expression of morphine-induced conditioned place preference in rats

Drug addiction is characterized by drug-seeking and drug-taking and has devastating consequences on addicts as well as on society. Environmental contexts previously associated with drug use can elicit continued drug use and facilitate relapse. Accumulating evidence suggests that the neuropeptide oxytocin might be a potential treatment for behavioral disorders, including drug addiction. Here, we investigated the effects of central oxytocin administration on the acquisition and expression of morphine-induced conditioned place preference (CPP), a model for measuring the rewarding effects of drugs of abuse, in male Wistar rats. Intracerebroventricular (ICV) administration of oxytocin (0.2μg) or the specific oxytocin receptor antagonist (OTA), desGly-NH2, d(CH2)5[Tyr(Me)(2), Thr(4)] OVT, (0.75μg), on the conditioning days did not affect the acquisition of morphine-induced CPP. By contrast, ICV oxytocin, but not OTA, administration immediately prior to the post-conditioning session enhanced the expression of morphine-induced CPP, possibly by activation of oxytocin receptors in the nucleus accumbens shell (NAcSh). The oxytocin enhancement of morphine-induced CPP was not associated with any changes in the locomotor activity of morphine-conditioned rats. Together, these data suggest that central administration of exogenous oxytocin enhances the expression of morphine-induced CPP, at least in part, via activation of oxytocin receptors within the NAcSh.

The role of nitric oxide in the effects of cumin (Cuminum Cyminum L.) fruit essential oil on the acquisition of morphine-induced conditioned place preference in adult male mice

OBJECTIVE: Nitric oxide is a neural messenger molecule in the central nervous system that is generated from L-arginine via the nitric oxide synthase (NOS) and is involved in many important oplold-induced effects. In Iranian ancient medicine, Cuminum cyminum L (green seed) has been used for the treatment of some diseases. In the present study, the effect of intraperitoneal (ip) administration of different doses of cumin fruit essential oil (FEO) on the acquisition of morphine-induced conditioned place preference (GPP) in L-arginine-treated mice was investigated. METHODS: A total of 213 adult male albino Wistar mice were used in these experiments. The CPP paradigm was carried out in 5 continuous days, pre-conditioning, conditioning and post-conditioning. Animals were randomly assigned to one of the two groups for place conditioning. CPP was induced by subcutaneous (sc) injection of morphine (5 mg/kg) in 3 days conditioning schedule. On the test day, conditioning scores and locomotor activity were recorded by Ethovision software. RESULTS: Sole administration of different doses of cumin FEO (0.01%, 0.1%, 0.5%, 1% and 2%; lp) or L-arginine (50, 100 and 200 mg/kg; lp) during the CPP protocol could not induce CPP. Nonetheless, morphine-induced CPP was decreased by different doses of cumin FEO (0.01%-2%), whereas it was increased by L-arginine (50-200 mg/kg) when they were injected before morphine (5 rug/kg) during a 3-day conditioning phase (acquisition period). Additionally, cumin FEO could interestingly attenuate the raising effect of L-arginine on morphine-induced CPP in a dose-dependent manner. CONCLUSIONS: It is suggested that some components of the Cuminum cyminum L. seed attenuate the excessive effect of L-arginine on morphine-induced CPP through the NOS inhibitory mechanism. It seems that cumin FEO possibly acts as a NOS inhibitor.

Ketamine-induced deficit of auditory gating in the hippocampus of rats is alleviated by medial septal inactivation and antipsychotic drugs

RATIONALE

Gating of sensory responses is impaired in schizophrenic patients and animal models of schizophrenia. Ketamine, an N-methyl-D-aspartate receptor antagonist, is known to induce schizophrenic-like symptoms including sensory gating deficits in humans.

OBJECTIVE

This study aims to investigate the mechanisms underlying ketamine's effect on gating of auditory evoked potentials in the hippocampus of freely moving rats.

METHODS

Gating was measured by the ratio of the test-click response (T) to the conditioning-click response (C), or T/C, with T and C measured as peak amplitudes.

RESULTS

Ketamine (1, 3, or 6 mg/kg s.c.) injection dose-dependently increased T/C ratio as compared to saline injection (s.c.). T/C ratio was 0.48 +/- 0.05 after saline injection and 0.73 +/- 0.17 after ketamine (3 mg/kg s.c.) injection. The increase in T/C ratio after ketamine was blocked by prior inactivation of the medial septum with GABA(A) receptor agonist muscimol or by systemic administration of antipsychotic drugs, including chlorpromazine (5 mg/kg i.p.), haloperidol (1 mg/kg i.p.), or clozapine (7.5 mg/kg i.p.). Infusion of muscimol into the medial septum or injection of an antipsychotic drug alone did not affect the T/C ratio. However, rats with selective lesion of the septohippocampal cholinergic neurons by 192 IgG-saporin showed a significantly higher T/C ratio (0.86 +/- 0.10) than sham lesion rats (0.26 +/- 0.07), and ketamine did not further increase T/C ratio in rats with septohippocampal cholinergic neuron lesion.

CONCLUSIONS

Ketamine's disruption of hippocampal auditory gating was normalized by inactivation of the medial septum; in addition, septal cholinergic neurons participate in normal auditory gating.

Morphine sex-dependently induced place conditioning in adult Wistar rats

The present study was conducted to investigate the potential sex-differences in morphine-induced conditioned place preference. A 3-day unbiased conditioning procedure was used to establish conditioned place preference in adult male and female Wistar rats (weighing 200-250 g). The effect of morphine on locomotor activity of subjects was also studied. Naloxone (0.5-2 mg/kg, i.p.), a selective antagonist of mu-opioid receptor or sulpiride (0.5-2 mg/kg, s.c.), a selective antagonist of dopamine D(2) receptor was administered, during conditioning, to indicate the receptor-mediated mechanisms governing upon possible sex-differences to the opioid response. Results show that morphine (0.5-10 mg/kg, s.c.) differently produced a significant place preference in female and male Wistar rats. Although, the opioid maximum response in both sexes was observed at 7.5 mg/kg, but, it was found that female rats acquired conditioned place preference at a lower dose (0.5 mg/kg, s.c.) of morphine compared to male rats. Moreover, the increase in morphine-induced response at higher doses (5-10 mg/kg, s.c.) was more pronounced in females than the males, indicating that female Wistar rats are more sensitive to the place conditioning induced by morphine. Also, the females were more sensitive to locomotor activation induced by morphine at least at one dose (7.5 mg/kg). Animals' body-weight at 10 mg/kg of opioid was increased, the effect that was not dependent to sex. The results also demonstrate that naloxone (1 and 2 mg/kg, i.p.) induced a significant place preference in two sexes with no significant effect on animals' locomotor activity. The antagonist in males but not in females showed a significant effect on animals' body-weight. Naloxone (0.5-2 mg/kg, i.p.) prior-administration to morphine, during conditioning, attenuated the opioid response in two sexes. The attenuation of the morphine response was more pronounced in males than the other sex at the higher dose (2 mg/kg) of the antagonist. In addition, the preadministration of naloxone, during morphine conditioning, both attenuated the drug-induced hyperactivity in females and decreased the animals' body-weight, albeit more effectively in females than the males. Sulpiride injections (1 and 2 mg/kg s.c.), during the conditioning period, induced a significant aversion in males but not in females with no significant effect either on locomotor activity or body-weight in both sexes. When sulpiride (0.5-2 mg/kg, s.c.), during conditioning, was morphine pre-injected, the antagonist at higher doses significantly attenuated the opioid response in males, reflecting the involvement of dopamine D(2) receptor in sex-dependent morphine-conditioned place preference. Prior-injections of sulpiride to morphine produced a significant effect on locomotor activity of females. The effect of the antagonist preinjections on body-weight was also observed in males. Present results indicate sex-differences both in reinforcing and locomotor activity effects of morphine in Wistar rats.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Effects of ultra-low doses of nicotine on the expression of morphine-induced conditioned place preference in mice

In the present study, the effects of acute administration of nicotine, as well as nicotinic and muscarinic acetylcholine receptor antagonists, on the expression of morphine-induced conditioned place preference, have been investigated in male Swiss-Webster mice. Animals received different doses of morphine 5 days after surgical cannulation in the lateral ventricle. Subcutaneous injections of morphine (2-5 mg/kg) in mouse produced place preference in a dose-dependent manner. Furthermore, both intraperitoneal (0.0006-0.1 mg/kg) and intracerebroventricular (0.007-25 ng) nicotine administration significantly reduced the expression of morphine-induced place preference, in a dose-dependent manner. Nicotine, however, was effective over narrow ultra-low dose ranges (0.0012, 0.0025, 0.005 and 0.01 mg/kg; intraperitoneal) and (0.03, 0.1, 0.3 and 0.6 ng/mouse; intracerebroventricular). In addition, locomotor activity was reduced when higher doses of nicotine [both intraperitoneal (0.02, 0.03 and 0.1 mg/kg) and intracerebroventricular (10 and 24 ng/mouse)] were used. Nicotine alone, however, did not cause motivational effects. Intracerebroventricular injection of hexamethonium (0.03, 0.1 and 0.3 mug/mouse; 10 min before nicotine) diminished the effects of nicotine on morphine-induced conditioned place preference. This effect could neither be obtained by intraperitoneal administration of hexamethonium (1, 5 and 10 mg/kg; 30 min before nicotine), nor be reproduced after either intracerebroventricular or intraperitoneal injection of atropine (a muscarinic receptor antagonist). The antagonists, themselves, did not show any motivational effects when used alone and were unable to affect the expression of morphine-induced conditioned place preference. It appears that ultra-low doses of nicotine can reduce the expression of morphine-induced place preference, and that central nicotinic acetylcholine receptors play a role in this regard.

Aversive stimulus properties of the 5-HT2C receptor agonist WAY 161503 in rats

Serotonin2C (5-HT2C) receptors may influence motivation and reward through effects on the mesocorticolimbic dopamine (DA) system. Previous work from this laboratory indicated that 5-HT2C receptor stimulation does not induce place conditioning when animals are tested in a drug-free state, but does result in decreased locomotor activity and increased frequency thresholds for electrical self-stimulation of the ventral tegmental area (VTA). The present study was conducted to determine whether the 5-HT2C receptor agonist WAY 161503 may induce place conditioning in a state-dependent manner and also whether this compound will induce gustatory avoidance conditioning in the conditioned taste aversion (CTA) paradigm. The effects of the 5-HT2C receptor agonist WAY 161503 in the place conditioning and CTA (two-bottle choice test) paradigms were assessed in male Sprague-Dawley rats. Administration of WAY 161503 (3.0 mg/kg) induced a state-dependent conditioned place aversion and a CTA to saccharin. The differential state dependency of 5-HT2C receptor agonists' effects in place conditioning (state dependent) and CTA (non-state dependent) is consistent with the activation of different brain systems in these two paradigms. The state-dependent effects in place conditioning underscore the need to include controls for state dependency in studies of 5-HT receptor related compounds.

Influence of nitric oxide on morphine-induced amnesia and interactions with dopaminergic receptor agents

The interactions of dopaminergic receptors and nitric oxide (NO) with morphine-induced memory of passive avoidance have been investigated in mice. Pre-training administration of morphine (1, 3 and 5 mg/kg, s.c.) dose-dependently decreased the learning of a one-trial passive avoidance task. Pre-training administration of L-arginine, a nitric oxide precursor (50, 100 and 200 mg/kg, i.p.), alone did not affect memory formation. The drug (100 and 200 mg/kg) decreased significantly amnesia induced by pre-training morphine (5 mg/kg). Pre-training administration of L-NAME (N(G)-nitro-L-arginine methyl ester), a nitric oxide synthase (NOS) inhibitor (20 and 30 mg/kg, i.p.), dose-dependently impaired memory formation. In addition, co-pretreatment of different doses of L-NAME (10, 20 and 30 mg/kg) with lower dose of morphine (1 mg/kg), which did not induce amnesia by itself, caused inhibition of memory formation. Pre-training administration of apomorphine, a dopaminergic receptor agonist (0.25, 0.5 and 1 mg/kg, i.p.), alone also did not affect memory formation, but morphine-induced amnesia was significantly inhibited by pretreatment with apomorphine (0.5 and 1 mg/kg, 5 min, i.p.). On the other hand, the inhibition of morphine-induced amnesia by L-arginine (200 mg/kg, i.p.) was significantly decreased by pretreatment with different doses of dopamine D1 receptor antagonist, SCH 23390 (0.001, 0.01 and 0.1 mg/kg, i.p.) or D2 receptor antagonist, sulpiride (12.5, 25, 50 and 100 mg/kg, i.p.). However, the dopamine receptor antagonists could not affect memory formation by themselves. It may be concluded that the morphine-induced impairment of memory formation can be prevented by nitric oxide donor and, in this effect, dopaminergic mechanism is involved.

Role of the cholinergic system in the rat basolateral amygdala on morphine-induced conditioned place preference

The effects of intra-basolateral amygdala (intra-BLA) injections of physostigmine, atropine, nicotine and/or mecamylamine on morphine-induced conditioned place preference (CPP) in rats was investigated by using an unbiased 3-day schedule of place conditioning design. Animals that received 3 daily injections of morphine (0.5-10 mg/kg) subcutaneously (s.c.) or saline (1.0 ml/kg, s.c.) showed a significant preference for compartment paired with morphine. The maximum response was observed with 7.5 mg/kg of the opioid. Administration of the anticholinesterase drug, physostigmine (1, 3 and 5 microg/rat) with an ineffective dose of morphine (0.5 mg/kg) elicited a significant CPP. Injections of antimuscarinic receptor agent, atropine (1, 4 and 7 microg/rat) dose-dependently inhibited the morphine (7.5 mg/kg)-induced place preference. The injections of nicotine (0.75, 1 and 2 microg/rat) potentiated the morphine (0.5 mg/kg)-induced place preference, while the nicotinic receptor antagonist, mecamylamine (1, 3 and 6 microg/rat) dose-dependently inhibited the morphine (7.5 mg/kg)-induced place preference. Furthermore, administration of atropine (7 microg/rat) but not mecamylamine (6 microg/rat) reduced the response induced by different doses of physostigmine plus morphine. Moreover, mecamylamine (6 microg/rat) but not atropine (7 microg/rat) reduced the response induced by different doses of nicotine plus morphine. It is concluded that the muscarinic and nicotinic receptor mechanisms in the BLA may be involved in the acquisition of morphine-induced place preference.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).