Additive effect of histamine and muscimol upon induction of antinociceptive and antidepressant effects in mice.

We investigated the effects of histamine and GABA A receptor agents on pain and depression-like behaviors and their interaction using a tail-flick test and the forced swimming test (FST) in male mice. Our data revealed that intraperitoneal administration of muscimol (0.12 and 0.25 mg/kg) increased the percentage of maximum possible effect (%MPE) and area under the curve (AUC) of %MPE, indicating an antinociceptive response. Intraperitoneal injection of bicuculline (0.5 and 1 mg/kg) decreased %MPE and AUC of %MPE, suggesting hyperalgesia. Moreover, muscimol by reducing the immobility time of the FST elicited an antidepressant-like response but bicuculline by enhancing the immobility time of the FST caused a depressant-like response. Intracerebroventricular (i.c.v.) microinjection of histamine (5 µg/mouse) enhanced %MPE and AUC of %MPE. i.c.v. infusion of histamine (2.5 and 5 µg/mouse) decreased immobility time in the FST. Co-administration of different doses of histamine along with a sub-threshold dose of muscimol potentiated antinociceptive and antidepressant-like responses produced by histamine. Cotreatment of different doses of histamine plus a noneffective dose of bicuculline reversed antinociception and antidepressant-like effects elicited by histamine. Cotreatment of histamine, muscimol, and bicuculline reversed antinociceptive and antidepressant-like behaviors induced by the drugs. The results demonstrated additive antinociceptive and antidepressant-like effects between histamine and muscimol in mice. In conclusion, our results indicated an interaction between the histaminergic and GABAergic systems in the modulation of pain and depression-like behaviors.

GABA-ergic agents modulated the effects of histamine on the behaviour of male mice in the elevated plus maze test.

NEW FINDINGS: What is the central question of this study? Is there an interaction between histamine and the GABAergic system in modulation of anxiety in mice? What is the main finding and its importance? There is a synergistic anxiogenic effect between histamine and bicuculline in mice. This effect may be due to a direct or an indirect effect of the histaminergic system on the GABAergic system. ABSTRACT: It has been documented that both histaminergic and GABAergic systems participate in the neurobiology of anxiety behaviour. In the current research, we investigated the effects of the histaminergic system and GABAA receptor agents on anxiety-related behaviours and their interaction using the elevated plus maze test in mice. Intraperitoneal (i.p.) administration of muscimol (0.12 and 0.25 mg/kg) increased the open arm time (OAT) (P < 0.001) without affecting the open arm entries (OAE) and locomotor activity, showing an anxiolytic effect. i.p. injection of bicuculline (0.5 and 1 mg/kg) decreased OAT (P < 0.001) but not OAE and locomotor activity, suggesting an anxiogenic behaviour. Intracerebroventricular (i.c.v.) microinjection of histamine (2.5 and 5 µg/mouse) resulted in a decline in OAT (P < 0.001) but not OAE and locomotor activity, indicating an anxiogenic response. Co-administration of histamine with GABAergic agents, muscimol (0.06 mg/kg; i.p.) and bicuculline (0.25 mg/kg; i.p.), decreased (P < 0.001) and increased (P < 0.05), respectively, the anxiogenic-like response to the effective dose (5 µg/mouse; i.c.v.) of histamine. In addition, co-treatment of effective doses of histamine (2.5 and 5 µg/mouse;i.c.v.) with an effective dose of muscimol (0.12 mg/kg; i.p.) and a non-effective dose of bicuculline (0.25 mg/kg; i.p.) significantly decreased OAT (P < 0.001), suggesting a likely interaction between the histaminergic and GABAergic systems in the regulation of anxiety. The results demonstrated a synergistic anxiogenic-like effect between histamine and bicuculline in mice. In conclusion, our results present an interaction between the histaminergic and GABAergic systems in anxiolytic/anxiogenic-like behaviours in the elevated plus maze test.

Dopaminergic and nitric oxide systems interact to regulate the electrical activity of neurons in the medial septal nucleus in rats.

Research characterizing the neuronal substrate of anxiety has implicated different brain areas, including the medial septal nucleus (m-SEPT). Previous reports indicated a role of dopamine and nitric oxide (NO) in anxiety-related behaviors. In this study, the extracellular single-unit recording was performed from the m-SEPT in adult male albino Wistar rats. Baseline activity was recorded for 5 min, and the post-injection recording was performed for another 5 min after the microinjection of each drug. The results showed that (1) both D1- and D2-like receptor agonists (SKF-38393 and quinpirole) enhanced the firing rate of m-SEPT neurons; (2) both D1- and D2-like antagonists (SCH-23390 and sulpiride) attenuated the firing rate of m-SEPT neurons; (3) L-arginine (NO precursor) increased the firing rate of m-SEPT neurons, but a non-specific NOS inhibitor, L-NAME, elicited no significant alterations; (4) the non-specific NOS inhibitor reversed the enhanced firing rate produced by SKF-38393 and quinpirole; (5) neither of the dopaminergic antagonists changed the enhanced activity resulted from the application of the NO precursor. These results contribute to our understanding of the complex neurotransmitter interactions in the m-SEPT and showed that both dopaminergic and NO neurotransmission are involved in the modulation of the firing rate of neurons in the m-SEPT.

Synergistic effect between quinpirole and L-NAME as well as sulpiride and L-arginine on the modulation of anxiety and memory processes in the 6-OHDA mouse model of Parkinson's disease: An isobologram analysis.

We evaluated interactions between dopamine D2 receptor and nitric oxide (NO) actions on the regulation of anxiety and memory in the 6-hydroxydopamine (6-OHDA) mouse model of Parkinson's disease (PD). A unilateral guide cannula was stereotaxically implanted over the right striatum. Elevated plus-maze test (EPM) test-retest protocol was employed to evaluate anxiety and memory in mice. The results revealed that injection of L-NAME (9 mg/kg) induced anxiolytic and amnesic effects, while L-arginine (9 mg/kg) produced anxiogenic and memory-improvement effects in the 6-OHDA mouse model of PD. Administration of sulpiride (20 mg/kg) induced anxiogenic and memory-improvement effects, whereas quinpirole (20 mg/kg) caused anxiolytic and amnesic effects in PD mice. Co-injection of sulpiride (5, 10, and 20 mg/kg) plus L-NAME (3 mg/kg) induced anxiolytic and amnesic effects. Co-injection of sulpiride (20 mg/kg) plus L-arginine (3 mg/kg) induced anxiogenic and memory-improvement effects. Co-administrations of quinpirole (20 mg/kg) and L-NAME (3 mg/kg) induced anxiolytic effect, but co-administration of quinpirole (20 mg/kg) plus L-arginine (3 mg/kg) caused anxiogenic and memory-improvement effects. The isobologram analysis revealed that there is a synergistic effect between sulpiride and L-arginine as well as quinpirole and L-NAME upon induction of anxiogenic and anxiolytic effects, respectively in PD mice. Our results suggested: (1) NO and dopamine D2 receptor mechanisms affect anxiety and memory in PD mice; (2) L-NAME reversed anxiogenic and memory-improvement effect induced by sulpiride; (3) Anxiolytic and amnesic effects induced by quinpirole reversed by L-arginine; (4) There is a synergistic effect between dopamine D2 receptor and NO systems on the modulation of anxiety and memory.

Spinal Orexin-2 Receptors are Involved in Modulation of the Lateral Hypothalamic Stimulation-Induced Analgesia.

Role of the orexinergic system in pain modulation is well studied and involvement of the spinal orexin-1 receptors is well documented. In this study, we examined role of the spinal orexin-2 receptors in modulation of inflammatory pain in rat. Fifty-one adult male Wistar rats were implanted unilaterally with a guide cannula into the LH and intrathecal tubing in the lumbar space between L4 and L5. Chemical stimulation of LH by carbachol (250 nM/0.5 µL saline) induced remarkable analgesia during the two phases of formalin test and Intrathecal administration of different doses of TCS OX2 29 (10, 30 and 100 µM/ 0.5 µL DMSO) prior to LH stimulation, dose-dependently antagonized the antinociceptive effect of the LH-stimulation during the two phases of formalin test. The effect size of the TCS OX2 29 was η2 = 0.47 and η2 = 0. 87 for the early and late phases of the test, respectively. Also, intrathecal administration of TCS OX2 29 alone (without stimulation of the LH) had no significant effect on formalin induced pain-related behaviors. Our results showed that spinal orexin-2 receptors are involved in modulation of the LH-stimulation induced analgesia in a persistent inflammatory pain model. These findings may suggest spinal orexin-2 receptors in particular and the orexin system in general as a useful therapeutic target for treatment of chronic pains.

Interaction between citalopram and omega-3 fatty acids on anxiety and depression behaviors and maintaining the stability of brain pyramidal neurons in mice.

This research was done to examine the combination of citalopram, an antidepressant drug, and omega-3 in a mice model of depression. Mice received citalopram (1 and 2 mg/kg) or omega-3 (10 and 20 mg/kg) daily over 30 days. Then, they were exposed to acute and chronic restraint stress to assess the possible increasing effect of omega-3 on the antidepressant and anxiolytic effects of citalopram. Elevated plus-maze (EPM) and forced swimming test (FST) were used to assess anxiety and depression symptoms in non-restraint stress (NRS), acute restraint stress (ARS), and chronic restraint stress (CRS) mice. The results indicated that induction of acute and chronic restraint stress reduced %OAT (Open arm time) and %OAE (Open arm entrance) in the EPM test but enhanced immobility time in the FST, showing anxiogenic- and depressive-like effects. These stresses reduced the stability of pyramidal neurons in the prefrontal cortex (PFC) and hippocampus. Aone and combination administration with citalopram and omega-3 induced anxiolytic- and antidepressant-like effects in NRS, ARS, and CRS mice. This combination usage increased the stability of pyramidal neurons in the PFC and hippocampus. These results suggested an interaction between citalopram and omega-3 upon the induction of anxiolytic- and antidepressant-like effects as well as augmentation of the ratio of pyramidal live to dark neurons in the PFC and hippocampus of the ARS and CRS mice.

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.

Convergence Science to Transform Biomedicine: A Narrative Review.

Recently convergence science was proposed and promoted in a large report from US National Science Foundation and Department of Commerce (NSF/DOC). The report was entitled "converging technologies for improving human performance. "It was dealing with converging of four technologies as: Nanotechnology, Biotechnology, Information technology and Cognitive science (NBIC). The report has gained tremendous popularity throughout the academia and scientific world. On Dec 2015 in a monthly meeting of the department of basic science of Iran Academy of Medical Science, the report of NSF/DOC on NBIC has been discussed. A working group has been established for more discussion and application in Iran. Several seminars in this regard have been performed, and presently this technology has been started as pilot in some technical universities in Iran. After US National Research Council (NCR) in the year 2014 and Massachusetts Institute of Technology (MIT) on convergence in biomedicine, the concept opened a new gate to approach solving medical and health care problems; the convergence technology in biomedical sciences has become interested and gained great popularity among the working group of convergence science in academy of medical science. This technology can lead to advances in fighting chronic diseases such as cancer, dementia, psychiatric disorders, disease of aging and others. The following is summary of proposed discussions in several gathered groups of scientists in this field.

Effect of dextromethorphan on antinociception and tolerance induced by swim-stress in the formalin test.

BACKGROUND: In the present study, the effect of dextromethorphan on antinociception and tolerance induced by water swim-stress in the formalin test was investigated. METHODS: Swim-stress at 8 masculineC induces antinociception in both phases of the formalin test. Intraperitoneal administration of dextromethorphan (60 mg/kg) also induces antinociception in the second phase of the formalin test. The lower doses of dextromethorphan (1.25, 2.5, and 5 mg/kg) which did not induce antinociception alone, but did so in combination with swim- stress (40 second), showed antinociceptive effect in both phases of the test. Exposure to water swimming stress with a period of 20 sec, once daily for three days, altered swim- stress- induced antinociception in the formalin test, when tested on the fourth day. RESULTS: In these animals, exposure to either water swimming stress alone or water swimming stress in combination with dextromethorphan showed potentiation of antinociception induced by swim- stress up to 20 second and decreased the response induced by 40 and 60 second swim- stress, indicating a tolerance induction. Dextromethorphan (20 mg/kg) did not alter the changes induced by three days exposure to swim- stress. CONCLUSION: The results may indicate a possible involvement of n-methyl-d-aspartate receptor mechanism in the antinociception but not tolerance induced by swim- stress at 8 masculineC.

Effects of intrathecal administration of orexin-1 receptor antagonist on antinociceptive responses induced by chemical stimulation of lateral hypothalamus in an animal model of tonic nociception.

Orexins are produced in the restricted regions of the lateral hypothalamus (LH). However, orexinergic receptors and projections are localized in wide regions like nucleus accumbens, ventral tegmental area, periaqueductal gray area and spinal cord which are involved in the pain modulation. This study was carried out to investigate the effects of intrathecal administration of orexin-1 receptor antagonist (SB-334867) in the spinal antinociception induced by intra-LH administration of carbachol (cholinergic receptor agonist) in both early and late phases of pain related behaviors in formalin test. In this study, pain-related behaviors (pain scores) were evaluated using the formalin test during 5-min block intervals for a 60-min period in seventy male Wistar rats were given SB-334867 (3, 10, 30 and 100 µM/10 µl) or vehicle (DMSO 12%; 10 µl) intrathecally following intra-LH administration of carbachol (250 nM/rat). Our data showed that intra-LH injection of carbachol attenuated the formalin-induced biphasic pain responses, and intrathecal administration of SB-334867 dose-dependently decreased LH stimulation-induced antinociceptive responses during both phases. Moreover, administration of different doses of SB-334867 during the early phase were more effective than those during the late phase. The antinociceptive role of orexinergic system in the formalin test through a neural pathway from the LH to the spinal cord provides evidence that orexins can be useful in therapeutic targets for pain relief.

Influence of morphine- or apomorphine-induced sensitization on histamine state-dependent learning in the step-down passive avoidance test.

Effects of morphine- or apomorphine-induced sensitization on histamine state-dependent memory of passive avoidance task were examined in mice. Pre-training intracerebroventricular (i.c.v.) administration of histamine (20 microg/mouse) decreased the learning of a one-trial passive avoidance task. Pre-test administration of histamine (10 and 20 microg/mouse) reversed amnesia induced by pre-training of histamine, with maximum response at 20 microg/mouse. Pre-training histamine-induced amnesia was also reversed in morphine- or apomorphine-sensitized mice that had previously received once daily injections of morphine (20 and 30 mg/kg) or apomorphine (0.5 and 1 mg/kg) for 3 days. The reversion of histamine-induced amnesia in morphine-sensitized mice was decreased by once daily administration of naloxone (0.5 and 1 mg/kg), SCH 23390 (0.05 and 0.1 mg/kg) or sulpiride (25, 50 and 100 mg/kg) prior to injection of morphine (30 mg/kg/day, 3 days). Furthermore, once daily administration of sulpiride (50 and 100 mg/kg) but not SCH 23390 (0.01, 0.05 and 0.1 mg/kg) prior to apomorphine (1 mg/kg, for 3 days) decreased the reversion of pre-training histamine-induced amnesia by apomorphine. The results suggest that apomorphine or morphine sensitization affects the impairment of memory induced by histamine and thus it is postulated that opioid and dopamine receptors may play an important role in this effect.

Effect of lithium on morphine state-dependent memory of passive avoidance in mice.

In the present study, effects of lithium chloride (LiCl) on morphine induced state-dependent memory of passive avoidance task were examined in mice. One-trial step-down paradigm was used for the assessment of memory retention in adult male NMRI mice. Administration of morphine (5 mg/kg) subcutaneously (s.c.) 30 min before training or testing induced impairment of memory performance. Injection of the same dose of the drug 30 min before testing restored memory retention impaired under pre-training morphine effect. Intraperitoneal (i.p.) injection of lithium, 60 min before training or prior to testing also impaired memory performance. Under the pre-training of morphine, the response of the opioid was restored when animals received LiCl (80 and 160 mg/kg) as pre-test injection. Pre-training administration of lower dose of lithium (20 mg/kg), but not the higher doses of the drug (80 and 160 mg/kg) impaired memory retention in passive avoidance test. LiCl-induced impairment of memory retention was restored by pre-test administration of morphine. In the animals receiving pre-training morphine, combined pre-test morphine and LiCl administration increased the restoration of memory by the opioid. It can be concluded that there may be a cross-state dependency between morphine and lithium.

The effects of histaminergic agents in the dorsal hippocampus of rats in the elevated plus-maze test of anxiety.

High levels of histamine are found in the hippocampus. The central histamine system is involved in many physiological behavioural processes including anxiety-related behaviours both in animals and humans. In the present study, we investigated the effects of intra-hippocampal CA1 (intra-CA1) microinjection of histaminergic agents on anxiety-related behaviours in rats, using elevated plus-maze test of anxiety. Intra-CA1 administration of histamine (at the dose of 10 microg/rat) increased open arm time (%OAT) and open arm entry (%OAE) but not locomotor activity, thus showing an anxiolytic response. Intra-CA1 microinjection of pyrilamine (H1 receptor antagonist; at the doses of 10, 20 and 40 microg/rat) in combination with histamine (10 microg/rat) showed a decrease in the %OAT and %OAE. Higher dose of the antagonist (40 microg/rat) by itself increased both %OAT and %OAE, but not locomotor activity, indicating an anxiolytic effect. Intra-CA1 microinjection of ranitidine (H2 receptor antagonist), at the doses of 10, 20 and 40 microg/rat, also reduced the histamine response. Furthermore, the H2 receptor antagonist by itself reduced %OAT and %OAE without affecting locomotor activity. The results may indicate an anxiogenic effect for the antagonist. Our results showed that histamine may modulate anxiety via H1 and H2 receptors in the CA1 region of hippocampus of the rat.

Acute lead exposure and contraction of rat isolated aorta induced by D1-dopaminergic and alpha-adrenergic drugs.

BACKGROUND/OBJECTIVE: In the present study, the effect of acute lead exposure in the presence and absence of dopamine or alpha (alpha)-adrenoceptor agents on contractile response of rat isolated thoracic aorta was studied. METHODS: Male Wistar rats were used in all experiments. Thoracic aorta was carefully removed, cleaned, and cut into 2-mm thick rings. The rings were mounted for measurement of isometric contractions in a tissue bath containing 10 mL of Kreb's solution at 37 - 38 degrees C. The following drugs were used: lead chloride, dopamine, phenylephrine, prazosin, clonidine, yohimbine, and SCH23390. One-way analysis of variance (ANOVA) and Student's t-test were used for statistical analyses. P < 0.05 was considered significant. RESULTS: The alpha1-adrenoceptor antagonist (prazosin), alpha2-adrenoceptor antagonist (yohimbine), or dopamine D1 receptor antagonist (SCH23390), did not elicit any response. Combination of lead with dopamine, phenylephrine, or clonidine did not show any potentiation. SCH23390, prazosin, and yohimbine decreased the contraction induced by lead. SCH23390 decreased the contraction induced by dopamine, or lead plus dopamine. Prazosin reduced the contraction induced by phenylephrine or lead plus phenylephrine. Yohimbine attenuated the response induced by clonidine or lead plus clonidine. CONCLUSION: alpha1, alpha2, and D1 dopamine receptor mechanisms could have a role in lead-induced contraction.

Cross state-dependent retrieval between histamine and lithium.

Histamine and lithium state-dependent (StD) retrieval of passive avoidance task and their interactions was examined in mice. The pre-training or pre-test intracerebroventricular (i.c.v.) injection of histamine (20 microg/mouse) impaired retrieval when it was tested 24 h later. In the animals, in which retrieval was impaired due to histamine pre-training administration, pre-test administration of histamine, with the same dose, restored retrieval. The H1 blocker, pyrilamine (20 microg/mouse, i.c.v.), but not the H(2) blocker; ranitidine prevented the restoration of retrieval by pre-test histamine. The pre-training (5 and 10 mg/kg) or pre-test (5 mg/kg) injection of lithium also impaired retrieval, when it was tested 24 h later. In the animals that received lithium (5 mg/kg) or histamine (20 microg/mouse) as pre-training treatment, administration of histamine, clobenpropit or lithium, respectively, resulted in restoration of memory retrieval. Neither pyrilamine nor ranitidine prevented the restoration of retrieval by pre-test lithium. In conclusion, histamine or lithium can induce state-dependent retrieval and a cross-StD exists between these drugs, which may be mediated through the inositol pathway.

The effects of dopamine receptor agents on naloxone-induced jumping behaviour in morphine-dependent mice.

In the present study, the effects of dopamine receptor agonists and antagonists on naloxone-induced jumping in morphine-dependent mice were examined. Mice were rendered dependent as described in the methods section. Naloxone was injected to elicit jumping (as withdrawal sign). The first group received dopamine receptor drugs before naloxone injection to test the effects of the drugs on the expression of jumping. Administration of the dopamine D1/D2 receptor agonist, apomorphine (0.25, 0.5 and 1 mg/kg), decreased jumping, but not diarrhoea, induced by naloxone. The effect of apomorphine on jumping was reduced by the dopamine D2 receptor antagonist, sulpiride. The dopamine D2 receptor agonist, quinpirole (0.1, 0.3 and 0.5 mg/kg), increased jumping, while it decreased diarrhoea in mice. Different doses of sulpiride did not alter jumping, but one dose of the drug (12.5 mg/kg) decreased jumping. Neither the dopamine D1 receptor agonist, SKF38393 (1-phenyl-7,8-dihydroxy-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride; 8 and 16 mg/kg), nor the dopamine D1 receptor antagonist, SCH23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-benzazepine-7-ol maleate; 5, 10 and 25 mg/kg), altered jumping, but they decreased diarrhoea. The second group of animals received the drugs during the development of dependence. Administration of quinpirole (0.1, 0.3 and 0.5 mg/kg), but not bromocriptine (4, 8 and 16 mg/kg), apomorphine (0.25, 0.5, 1 and 2 mg/kg) or sulpiride (12.5, 25 and 50 mg/kg) decreased naloxone-induced jumping and diarrhoea. A dose of SKF38393 (8 mg/kg) decreased jumping, while both SKF38393 (4 and 16 mg/kg) and SCH23390 (5 and 10 microg/kg) increased diarrhoea. It is concluded that activation of both dopamine D1 and D2 receptors may suppress naloxone-induced jumping in morphine-dependent mice, and that stimulation of dopamine D1 receptors during development of morphine dependence may increase diarrhoea through peripheral mechanism.

Influence of intracerebroventricular administration of dopaminergic drugs on morphine state-dependent memory in the step-down passive avoidance test.

The effects of dopaminergic drugs on morphine state-dependent memory of passive avoidance task were examined in mice. Pre-training administration of morphine (5mg/kg) led to state-dependent learning with impaired memory retrieval on the test day which was reversed by pre-test administration of the same dose of the opiate. The pre-test intracerebroventricular (i.c.v.) administration of the dopamine D1 receptor agonist (SKF38393), dopamine D2 receptor agonist (quinpirole) and dopamine D2 receptor antagonist (sulpiride) not only reversed the effect of pre-training morphine treatment, but also increased this action of the drug. Furthermore, the pre-test i.c.v. administration of dopamine D1 receptor antagonist (SCH23390) prevented the restoration of memory by morphine. In conclusion, the morphine-induced recovery of memory, on the test day, seems to be induced, at least in part, through dopamine receptors.

Influence of intracerebroventricular administration of cannabinergic drugs on morphine state-dependent memory in the step-down passive avoidance test.

The effects of cannabinergic drugs on morphine state-dependent memory of passive avoidance task were examined in mice. Pre-training (0.25, 0.5 and 5 mg/kg) and post-training (5 mg/kg) administration of morphine impaired memory retrieval on the test day. Impairment of memory retrieval by morphine (5 mg/kg) on the test day was reversed by pre-test administration of the same dose of the opioid. The pre-test intracerebroventricular administration of the cannabinoid CB1/CB2 receptor agonist (WIN55,212-2) (0.75 and 1 microg/mouse) not only mimicked the effect of pre-test morphine treatment, but also increased this action of the opioid. Furthermore, the pre-test intracerebroventricular administration of CB1 receptor antagonist (AM251) (20 and 100 ng/mouse) prevented the restoration of memory by morphine. Pre-training administration of WIN55,212-2 (1 microg/mouse) led to state-dependent learning with impaired memory retrieval on the test day as well, which was reversed by pre-test administration of the drug (0.5, 0.75 and 1 microg/mouse) or morphine (1 and 5 mg/kg). Restoration of impairment induced by WIN55,212-2 was decreased by both the opioid receptor antagonists, naloxone (0.01 microg/mouse) and AM251 (20 and 100 ng/mouse). In conclusion, the improvement of memory retrieval by morphine treatment on the test day seems to be induced, at least in part, by the cannabinoid CB1 receptors.

Dopamine receptor mechanism(s) and antinociception and tolerance induced by swim stress in formalin test.

In the present study, involvement of D1 and D2 dopamine receptors in the antinociception and tolerance induced by water swim stress in the formalin test has been investigated. Water swim stress at 20 degrees C temperature induced antinociception in both phases of the formalin test. Intraperitoneal administration of the D2 dopamine receptor antagonist, sulpiride (25 and 50 mg/kg) reduced swim stress-induced antinociception in the second phase of the formalin test. A higher dose of the D1 dopamine receptor antagonist, SCH23390 (0.1 mg/kg, intraperitoneal) also reduced swim stress-induced antinociception in both phases of the test. Exposure to 3 min water swimming stress, once daily for 3 days, induced tolerance to swim stress-induced antinociception in the second phase of the formalin test. Administration of sulpiride (12.5, 25 and 50 mg/kg), during exposure to water swimming stress (once daily for 3 days), decreased tolerance in the second phase, whereas the antagonist (12.5 and 50 mg/kg) increased pain scores in the first phase of the formalin test. Sulpiride (25 mg/kg) treatment however, once daily for 3 days with no water swimming stress, did not alter swim stress-induced antinociception (0.5, 1 and 3 min tests). Similarly, repeated treatment with SCH23390 (0.05 mg/kg) and water swimming stress did not alter tolerance induced by water swimming stress. Repeated administration of the antagonist in the absence of water swimming stress also did not change swim stress-induced antinociception. The results may indicate a possible involvement of both dopamine D1 and D2 receptors in the antinociception induced by swim stress and D2 receptor mechanism in the tolerance induced by repeated swim stress.

Cross-tolerance between antinociception induced by swim-stress and morphine in formalin test.

The present study investigated cross-tolerance between antinociception induced by water swim-stress and morphine in the formalin test. Intraperitoneal administration of morphine (3, 6 and 9 mg/kg) induced dose-dependent antinociception in both phases of the formalin test. Mice treated with a lower dose of morphine (25 mg/kg), once daily for 3 days, showed tolerance to antinociception induced by a lower test dose of morphine (3 mg/kg). Similar repeated treatments with a higher dose of morphine (50 mg/kg) produced tolerance to antinociception induced by different test doses of morphine (3, 6 and 9 mg/kg). Exposure to water swim-stress, once daily for 2 or 3 days in order to induce tolerance, also decreased morphine-induced antinociception. Swim-stress exposure for 2 or 3 days also tends to potentiate tolerance induced by a lower dose of morphine. Acute swim-stress of different durations (0.5, 1 and 3 min) induced antinociception in both phases of the formalin test, which was not reduced by naloxone, but showed even more antinociception in the second phase. The response to swim stress was decreased in mice treated with higher doses of morphine, but not those animals that received swimming stress (3 min) once daily for 2-3 days, in order to induce habituation to swim-stress-induced antinociception. The results may indicate a possible cross-tolerance between antinociception induced by morphine and by swim stress.