Influence of central administration ATP-dependent K+ channel on morphine state-dependent memory of passive avoidance

The Inflammation/NF-κB and BDNF/TrkB/CREB Pathways in the Cerebellum Are Implicated in the Changes in Spatial Working Memory After Both Morphine Dependence and Withdrawal in Rat

We aimed to explore the impact of the cerebellum on the decline in spatial working memory following morphine dependence and withdrawal. Two groups of male Wistar rats received intraperitoneal injections of either saline (1 ml/kg) or morphine (10 mg/kg) twice daily for 10 days, serving as the control and dependent groups. Additionally, a withdrawal group underwent a 30-day withdrawal period after the dependence phase. Spatial working memory was assessed using a Y maze test. ELISA and western blot were used to assess protein levels in the cerebellum. On day 1, morphine impaired spatial working memory, deteriorated further after 10 days of morphine use, and nearly returned to its initial level following a 30-day withdrawal period. On day 10, significant increases in TNF-α, IL-1β, and CXCL12 and a notable decrease in IL-10 levels were detected in the morphine-dependent group, which did not completely restore in the withdrawal group. The protein levels of CXCR4, TLR4, P2X7R, and NF-κB sharply increased in the morphine-dependent group. However, these levels almost returned to normal after withdrawal. In the morphine-dependent group, BDNF decreased, while TrkB and CREB1 increased noticeably. Nevertheless, after withdrawal, TrkB and CREB1 but not BDNF levels returned to normal. In the morphine-dependent group, both CACNA1 and KCNMA1 decreased significantly and after withdrawal, only KCNMA1 showed partial restoration, while CACNA1 did not. It can be concluded that inflammation/NF-κB and BDNF/TrkB/CREB pathways play key roles in neural adaptation within the cerebellum, contributing to the decline in spatial working memory after both morphine dependence and withdrawal.

Subclinical Doses of ATP-Sensitive Potassium Channel Modulators Prevent Alterations in Memory and Synaptic Plasticity Induced by Amyloid-β

In addition to coupling cell metabolism and excitability, ATP-sensitive potassium channels (KATP) are involved in neural function and plasticity. Moreover, alterations in KATP activity and expression have been observed in Alzheimer's disease (AD) and during amyloid-β (Aβ)-induced pathology. Thus, we tested whether KATP modulators can influence Aβ-induced deleterious effects on memory, hippocampal network function, and plasticity. We found that treating animals with subclinical doses (those that did not change glycemia) of a KATP blocker (Tolbutamide) or a KATP opener (Diazoxide) differentially restrained Aβ-induced memory deficit, hippocampal network activity inhibition, and long-term synaptic plasticity unbalance (i.e., inhibition of LTP and promotion of LTD). We found that the protective effect of Tolbutamide against Aβ-induced memory deficit was strong and correlated with the reestablishment of synaptic plasticity balance, whereas Diazoxide treatment produced a mild protection against Aβ-induced memory deficit, which was not related to a complete reestablishment of synaptic plasticity balance. Interestingly, treatment with both KATP modulators renders the hippocampus resistant to Aβ-induced inhibition of hippocampal network activity. These findings indicate that KATP are involved in Aβ-induced pathology and they heighten the potential role of KATP modulation as a plausible therapeutic strategy against AD.

Effect of naloxone and morphine on arcaine-induced state-dependent memory in rats

RATIONALE

Arcaine is a competitive antagonist of the polyamine binding site at the N-methyl-D-aspartic acid receptor which induces state-dependent recall. However, no study has addressed the involvement of other neurotransmitter/neuromodulators in arcaine-induced state dependency.

OBJECTIVES

The current study investigates whether the opioid system is involved in arcaine-induced state-dependent memory retrieval of the inhibitory avoidance task (IA) in rats.

RESULTS

The systemic administration of arcaine (30 mg/kg, intraperitoneally (i.p.)) or morphine (5 mg/kg, i.p.) 0, 3, 6, or 9 h post-training, reduced step-down latencies at testing. Arcaine (30 mg/kg, i.p.) or morphine (5 mg/kg, i.p.) injection 30 min before testing reversed the performance deficit induced by administration of arcaine or morphine 0, 3 or 6, but not 9 h post-training. The reversal of arcaine-induced impairment of IA performance was completely transferred to morphine and vice versa. The association of low and ineffective doses of morphine and arcaine (10 and 1.5 mg/kg, respectively) were additive and caused state dependency. Naloxone (2 mg/kg, 3 min post-training, or 1 mg/kg, 1 h pre-test, i.p.) reversed the amnesia and the state dependency induced by morphine and arcaine.

CONCLUSION

These results suggest that state dependency induced by arcaine involves the opioid system.

INVOLVEMENT OF NMDA RECEPTORS IN MORPHINE STATE–DEPENDENT LEARNING IN MICE

In the present study, the effects of intracerebroventricular (i.c.v.) injection of NMDA receptor agonist and antagonist on impairment of memory formation and the state-dependent learning by morphine have been investigated in mice. Pretraining administration of morphine (5 mg/kg; s.c.) decreased the learning of one-trial passive avoidance task. Pretest administration of morphine (5 mg/kg) induced state-dependent learning acquired under pretraining morphine influence. Pretest administration of NMDA receptor agonist, L-glutamate (0.00001 and 0.0001 and 0.001 microg/mouse, i.c.v.) following pretraining saline treatment did not affect retention. Amnesia induced by pretraining morphine was significantly reversed by pretest administration of L-glutamate (0.0001 and 0.001 microg/mouse, i.c.v.). Pretest administration of noncompetitive NMDA receptor antagonist, MK-801 (0.5, 1, and 2 microg/mouse, i.c.v.) significantly impaired memory formation. Amnesia induced by pretraining morphine was increased by pretest administration of MK-801 (2 microg/mouse, i.c.v.). Pretest coadministration of L-glutamate (0.0001 and 0.001 microg/mouse, i.c.v.) or MK-801 (0.5, 1, and 2 microg/mouse, i.c.v.) with morphine (5 mg/kg, s.c.) increased and decreased morphine state-dependent learning, respectively. The results suggest that NMDA receptors are involved in morphine state-dependent learning in mice.

Morphine-induced sensitization in mice: changes in locomotor activity by prior scheduled exposure to GABAA receptor agents

This study investigated the effects of a gamma-amino-butyric acid type A (GABAA) receptor agonist and antagonist on morphine-induced locomotor sensitization in male albino mice. Subcutaneous administration to mice of a high dose of morphine (30 mg/kg), but not lower doses (5, 10 and 20 mg/kg) increased locomotion. The maximum locomotor activity was achieved during a 20-min measurement period. The locomotor response to a low dose of morphine (5 mg/kg, subcutaneously) given on day 9 was enhanced in mice pretreated with morphine (7.5, 15 and 30 mg/kg/day x 3 days), indicating that sensitization had developed. Three-day intracerebroventricular (i.c.v.) administration of the GABAA receptor agonist, muscimol (0.025, 0.05, 0.1 and 0.2 microg/mouse/day) significantly decreased both morphine-induced motor stimulation and locomotor sensitization. On the other hand, a 3-day pretreatment with the GABAA-receptor antagonist, bicuculline (0.25, 0.5 and 1 microg/mouse/day) reduced morphine (15 mg/kg)-induced locomotor sensitization. Repeated i.c.v. injections of a lower dose of bicuculline (0.25 microg/mouse/day x 3 days) by itself also decreased morphine-induced locomotion. Furthermore, repeated i.c.v. administration of bicuculline (0.25, 0.5 and 1 microg/mouse/day x 3 days) decreased the effect of i.c.v. injection of muscimol (0.1 microg/mouse/day x 3 days) on locomotor activity induced by morphine (5 mg/kg) in both control and sensitized mice. The magnitude of this response was, however, variable. The results indicate that GABAA receptors might be involved in the acquisition of morphine-induced sensitization.

Involvement of glucose and ATP-sensitive potassium (K+) channels on morphine-induced conditioned place preference

In the present study, the effects of glucose and ATP-sensitive K+ channel compounds on the acquisition of morphine-induced place preference in male mice were investigated. Subcutaneous administration of different doses of morphine (2.5-7.5 mg/kg) produced a dose-dependent conditioned place preference. With a 3-day conditioning schedule, it was found that glucose (100, 200, 500 and 1000 mg/kg), diazoxide (15, 30 and 60 mg/kg) or glibenclamide (3, 6 and 12 mg/kg) did not produce significant place preference or place aversion. Intraperitoneal administration of the glucose (1000 mg/kg) or glibenclamide (6 and 12 mg/kg) with a lower dose of morphine (0.5 mg/kg) elicited the significant conditioned place preference. The response of glibenclamide (6 mg/kg) was reversed by diazoxide (15, 30 and 60 mg/kg). Drug injections had no effects on locomotor activity during the test sessions. It is concluded that glucose and the ATP-sensitive K+ channel may play an active role in morphine reward.

Effects of Clozapine and Sulpiride on Morphine State-Dependent Memory in the Step-Down Passive Avoidance Test

The effects of antipsychotic drugs sulpiride and clozapine on morphine state-dependent memory of passive avoidance task were examined in mice. Post-training administration of morphine (5 mg/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 opioid (5 mg/kg). In animals where memory was impaired by post-training morphine, the administration of either sulpiride or clozapine before pre-test morphine reduced the improvement of memory produced by the opioid. Co-administration of sulpiride with clozapine did not potentiate their antagonistic response. In conclusion, the inhibition of improvement of memory retrieval by morphine treatment on the test day by the two dopamine receptor antagonists seems to be induced through two different receptor mechanisms.

Influence of ATP-sensitive potassium channels on lithium state-dependent memory of passive avoidance in mice

The effects of ATP-sensitive potassium channels on lithium induced state-dependent memory of passive avoidance task were examined in mice. The pre-training (5 mg/kg) and pre-test (5 mg/kg) injection of lithium impaired memory retrieval on the test day. Impairment of pre-training lithium was restored by pre-test administration of lithium (5 mg/kg), diazoxide, an ATP-sensitive potassium channel opener, (15, 30 and 60 mg/kg) or glibenclamide, an ATP-sensitive potassium channel blocker, (6 and 18 mg/kg). Pre-test administration of inactive doses of lithium (2.5 and 10 mg/kg) plus lower and inactive dose of glibenclamide (2 mg/kg) or diazoxide (1.5 mg/kg) also reversed the amnesia induced by pre-training lithium (5 mg/kg). In conclusion, the ATP-sensitive potassium channel opener or blocker not only mimicked the effect of lithium in state-dependent learning in the absence of lithium on the test day, but also potentiated the effect of low dose of lithium in restoration of memory. Therefore, ATP-sensitive potassium channels may have a modulatory influence on lithium response.

Anxiolytic properties of green tea polyphenol (−)-epigallocatechin gallate (EGCG)

Naturally occurring polyphenols are potent antioxidants. Some of these compounds are also ligands for the GABA(A) receptor benzodiazepine site. This feature endows them with sedative properties. Here, the anxiolytic activity of the green tea polyphenol (-)-epigallocatechin gallate (EGCG) was investigated after acute administration in mice, using behavioral tests (elevated plus-maze and passive avoidance tests) and by electrophysiology on cultured hippocampal neurons. Patch-clamp experiments revealed that EGCG (1-10 muM) had no effect on GABA currents. However, EGCG reversed GABA(A) receptor negative modulator methyl beta-carboline-3-carboxylate (beta-CCM) inhibition on GABA currents in a concentration dependent manner. This was also observed at the level of synaptic GABA(A) receptors by recording spontaneous inhibitory synaptic transmission. In addition, EGCG consistently inhibited spontaneous excitatory synaptic transmission. Behavioral tests indicated that EGCG exerted both anxiolytic and amnesic effects just like the benzodiazepine drug, chlordiazepoxide. Indeed, EGCG in a dose-dependent manner both increased the time spent in open arms of the plus-maze and decreased the step-down latency in the passive avoidance test. GABA(A) negative modulator beta-CCM antagonized EGCG-induced amnesia. Finally, state-dependent learning was observable after chlordiazepoxide and EGCG administration using a modified passive avoidance procedure. Optimal retention was observed only when animals were trained and tested in the same state (veh-veh or drug-drug) and significant retrieval alteration was observed in different states (veh-drug or drug-veh). Moreover, EGCG and chlordiazepoxide fully generalized in substitution studies, indicating that they induced indistinguishable chemical states for the brain. Therefore, our data support that EGCG can induce anxiolytic activity which could result from an interaction with GABA(A) receptors.

Sigma1 receptor ligands and related neuroactive steroids interfere with the cocaine-induced state of memory

The present series of experiments examined the involvement of the sigma(1) receptor and related neuroactive steroids in the memory state induced by a very low dose of cocaine. Using a modified passive avoidance procedure in mice, we examined whether cocaine induces state-dependent (StD) learning. Animals trained and tested with saline or the same dose of cocaine (0.1 or 0.3 mg/kg) showed correct retention, measured using two independent parameters: the retention latency and a ratio between the retention latency and the last training latency. Animals trained with cocaine (0.1 mg/kg) and tested with saline or cocaine (0.03, 0.3 mg/kg), or trained with saline and tested with cocaine, showed altered retention parameters, demonstrating that StD occurred. Therefore, cocaine administered before training produced a chemical state used as an endogenous cue to insure optimal retention. Since sigma(1) receptor activation is an important event during the acquisition of cocaine reward, we tested several sigma(1) ligands and related neurosteroids. The sigma(1) agonist igmesine or antagonist BD1047 failed to produce StD, but modified the cocaine state. Among neuroactive steroids, pregnanolone and allopregnanolone, positive modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor, produced StD. However, steroids also acting as sigma(1) agonists, dehydroepiandrosterone (3beta-hydroxy-5alpha-androsten-17-one (DHEA)), pregnenolone, or antagonist, progesterone, failed to induce StD but modified the cocaine state. Furthermore, optimal retention was observed with mice trained with (igmesine or DHEA)+cocaine and tested with a higher dose of cocaine, or with mice trained with (BD1047 or progesterone)+cocaine and tested with vehicle. This study demonstrated that: (i) low doses of cocaine induce a chemical state/memory trace sustaining StD; (ii) modulation of the sigma(1) receptor activation, although insufficient to provoke StD, modulates the cocaine state; (iii) neuroactive steroids exert a unique role in state-dependent vs state-independent learning, via GABA(A) or sigma(1) receptor modulation, and are able to affect the cocaine-induced mnesic trace at low brain concentrations.

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.

The influence of central administration of dopaminergic and cholinergic agents on morphine-induced amnesia in morphine-sensitized mice

In the present study, effects of intracerebroventricular (i.c.v.) injections of dopaminergic and cholinergic agents on morphine-induced amnesia in morphine-sensitized mice were investigated by using a one-trial passive avoidance task. Amnesia induced by pre-training morphine was significantly reversed in morphine-sensitized mice, which had previously received once daily injections of morphine (20 and 30 mg/kg, s.c.) for 3 days. Three daily injections of SKF 38393 (1, 2 and 4 g/mouse, i.c.v.) or SCH 23390 (0.25, 0.5, 0.75 and 1 g/mouse, i.c.v.) before morphine, and during morphine-sensitization, decreased and increased the amnesia induced by pre-training morphine respectively. Three daily injections of quinpirole (0.3, 1 and 3 g/mouse, i.c.v.) or sulpiride (0.03, 0.1, 0.3 and 1 g/mouse, i.c.v.) before morphine, also decreased and increased the amnesia induced by pre-training morphine respectively. Morphine-sensitized mice received similar injections of cholinergic agents. Three daily injections of physostigmine (1, 3 and 5 g/mouse, i.c.v.) or atropine (1, 4 and 7 g/mouse, i.c.v.) before morphine, and during morphine-sensitization, decreased and increased the amnesia induced by pre-training morphine respectively. Three daily injections of nicotine (0.75, 1 and 2 g/mouse, i.c.v.) or mecamylamine (1, 3 and 6 g/mouse, i.c.v.) before morphine, also decreased and increased the amnesia induced by pre-training morphine respectively. The results suggest that morphine sensitization affects the impairment of memory formation and thus it is postulated that central dopaminergic and cholinergic systems may play an important role in this effect.

Effects of intracerebroventricular administration of ultra low doses of histaminergic drugs on morphine state-dependent memory of passive avoidance in mice

The effects of intracerebroventricular (i.c.v.) administration of ultra low doses (ULDs) of histamine, clobenpropit and pyrilamine are studied on morphine state-dependent (STD) memory in mice. Although pre-test administration of different doses of histamine and clobenpropit showed no effect on impairment of memory induced by pre-training morphine, when the above drugs were co-administered with morphine, they inhibited the restoration of memory by morphine. These effects were opposite to microgram doses of the same drugs.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Discrepancy between effects of milligram and nanogram doses of a COX-2 inhibitor (celecoxib) on morphine state-dependent memory of passive avoidance in mice

This experiment examined and compared the effects of pre-test administration of a selective COX-2 inhibitor (celecoxib), at the doses in the range of mg/kg and ng/kg on morphine state-dependent learning in step-down passive avoidance task in mice. Pre-training administration of 5mg/kg of morphine-impaired memory retrieval tested 24h later, which was restored by pre-test administration of the same dose of the drug. Pre-test administration of celecoxib (12.5, 25 and 50mg/kg), alone or in combination with morphine (1mg/kg) prevents morphine-induced memory impairment. Ultra-low doses (ULDs) of celecoxib (2, 10 and 50 ng/kg) produced no change in morphine-induced memory impairment. However, co-administration of nanogram doses of celecoxib with 5mg/kg of morphine in the test day prevented morphine-induced memory improvement, an action different from mg/kg doses. These findings implicate the involvement of COX-2 in memory retrieval and demonstrate that the effect of celecoxib ULD is different from that of mg/kg doses.

Influence of Intracerebroventricular Administration of Histaminergic Drugs on Morphine State-Dependent Memory in the Step-Down Passive Avoidance Test

The effects of histaminergic drugs on morphine state-dependent memory of a passive avoidance task were examined in mice. Pre-training administration of morphine (5 mg/kg) led to state-dependent learning with impaired memory recall on the test day which was reversed by pre-test administration of the same dose of the opioid. The pre-test intracerebroventricular (i.c.v.) administration of the H(1) blocker (pyrilamine) prevented the restoration of memory by morphine. The H(2) blocker (ranitidine) was ineffective in this regard and the H(3) blocker (clobenpropit) potentiated the effect of morphine on memory recall. The pre-test i.c.v. administration of histamine alone (5, 10, and 20 microg/mouse) not only mimicked the effect of pre-test morphine treatment, but also increased this action of the opioid. The effect of histamine on memory recall was not changed by the pre-test administration of mu-opioid receptor antagonist, naloxone. In conclusion, the improvement of memory recall by morphine treatment, on the test day, seems to be, at least in part, through the release of histamine followed by the stimulation of H(1) receptors. Histamine by itself, when administered on the test day, mimicked morphine-induced memory improvement by a mechanism independent of the mu-opioid receptors.

Effects of ultra-low doses of morphine, naloxone and ethanol on morphine state-dependent memory of passive avoidance in mice

This experiment examined and compared the effects of pre-test administration of morphine, naloxone and ethanol, at doses in the range of milligram/kg to those of nanogram/kg, on morphine state-dependent learning in a step-down passive avoidance task in mice. Morphine (5 mg/kg) administered before training impaired retention tested 24 hours later, but when the same dose of morphine was also administered before the test, the retention was significantly restored. Pre-training administration of 10 or 20 ng/kg (i.p.) of morphine had no effect, but when co-administered with the same drug at 5 mg/kg (s.c.), it prevented significantly the memory recall improvement after the administration of morphine (5 mg/kg, s.c.) alone. In a parallel experiment, naloxone (5 mg/kg) prevented the memory recall improvement by morphine. However, the effects of naloxone at doses in the range of ng/kg were opposite to those of milligram doses of the same drug. Pre-test administration of ethanol (1 mg/kg) improved memory recall and mimicked the effects of pre-test morphine administration. At doses in the nanogram range, the effects of ethanol were opposite those of mg/kg of the drug. A review of the literature indicates that, for several drugs and chemicals, the effects of nanogram doses are the opposite of the effects of milligrams, because different doses have different sites as well as mechanisms of actions. In conclusion, from the above results one may suggest that, in determination of the dose-response of at least some drugs, the study of the effects of doses much lower than two orders of magnitude of the minimum effective dose are warranted.

EFFECT OF ETHANOL ON MORPHINE STATE-DEPENDENT LEARNING IN THE MOUSE: INVOLVEMENT OF GABAERGIC, OPIOIDERGIC AND CHOLINERGIC SYSTEMS

AIMS

We have studied the effect of acute administration of ethanol when it replaced morphine in step-down passive avoidance task on the test day and the effects of antagonists of GABAergic, opioidergic and cholinergic systems on ethanol actions.

METHODS

Morphine (5 mg/kg, s.c.) was administered as pre-training and 24 h later as pre-test drug, and the latencies were measured in mice. Ethanol (0.125, 0.25, 1 and 2 g/kg, i.p.) was administered instead of pre-test morphine. Antagonists of GABAergic (bicuculline 0.5, 1 and 2 mg/kg, i.p.), opioidergic (naloxone 0.06, 0.25 and 1 mg/kg, i.p.) and cholinergic (atropine 0.625 and 1.25 mg/kg, i.p. and mecamylamine 0.5, 1 and 2 mg/kg, i.p.) systems were co-administered with ethanol (0.25 g/kg, i.p.) on the test day. Locomotor activity was measured as well.

RESULTS

Pre-training morphine impaired the memory on the test day which was restored when the same dose of morphine was used as pre-test drug. All four doses of ethanol replaced pre-test morphine and enhanced the memory. This effect was prevented by all of the above antagonists. No significant changes were seen in the locomotor activity of the animals treated with ethanol or antagonists compared to the proper controls.

CONCLUSIONS

GABAergic, endogenous opioidergic and cholinergic systems are involved in the memory recall improvement by ethanol when it replaced morphine on the test day. A review of the literature suggests other possibilities such as the release of intermediate neurotransmitters.