Effects of cholecystokinin-8 on morphine-induced spatial reference memory impairment in mice

Shengmaisan combined with Liuwei Dihuang Decoction alleviates chronic intermittent hypoxia-induced cognitive impairment by activating the EPO/EPOR/JAK2 signaling pathway

Chronic intermittent hypoxia (CIH), a principal pathophysiological aspect of obstructive sleep apnea (OSA), is associated with cognitive deficits. Clinical evidence suggests that a combination of Shengmaisan and Liuwei Dihuang Decoctions (SMS-LD) can enhance cognitive function by nourishing yin and strengthening the kidneys. This study aimed to assess the efficacy and underlying mechanisms of SMS-LD in addressing cognitive impairments induced by CIH. We exposed C57BL/6N mice to CIH for five weeks (20%-5% O2, 5 min/cycle, 8 h/day) and administered SMS-LD intragastrically (15.0 or 30 g·kg-1·day) 30 min before each CIH session. Additionally, AG490, a JJanus kinase 2 (JAK2) inhibitor, was administered via intracerebroventricular injection. Cognitive function was evaluated using the Morris water maze, while synaptic and mitochondrial structures were examined by transmission electron microscopy. Oxidative stress levels were determined using DHE staining, and the activation of the erythropoietin (ER)/ER receptor (EPOR)/JAK2 signaling pathway was analyzed through immunohistochemistry and Western blotting. To further investigate molecular mechanisms, HT22 cells were treated in vitro with either SMS-LD medicated serum alone or in combination with AG490 and then exposed to CIH for 48 h. Our results indicate that SMS-LD significantly mitigated CIH-induced cognitive impairments in mice. Specifically, SMS-LD treatment enhanced dendritic spine density, ameliorated mitochondrial dysfunction, reduced oxidative stress, and activated the EPO/EPOR/JAK2 signaling pathway. Conversely, AG490 negated SMS-LD's neuroprotective and cognitive improvement effects under CIH conditions. These findings suggest that SMS-LD's beneficial impact on cognitive impairment and synaptic and mitochondrial integrity under CIH conditions may predominantly be attributed to the activation of the EPO/EPOR/JAK2 signaling pathway.

The potential role of the cholecystokinin system in declarative memory

As one of the most abundant neuropeptides in the central nervous system, cholecystokinin (CCK) has been suggested to be associated with higher brain functions, including learning and memory. In this review, we examined the potential role of the CCK system in declarative memory. First, we summarized behavioral studies that provide evidence for an important role of CCK in two forms of declarative memory-fear memory and spatial memory. Subsequently, we examined the electrophysiological studies that support the diverse roles of CCK-2 receptor activation in neocortical and hippocampal synaptic plasticity, and discussed the potential mechanisms that may be involved. Last but not least, we discussed whether the reported CCK-mediated synaptic plasticity can explain the strong influence of the CCK signaling system in neocortex and hippocampus dependent declarative memory. The available research supports the role of CCK-mediated synaptic plasticity in neocortex dependent declarative memory acquisition, but further study on the association between CCK-mediated synaptic plasticity and neocortex dependent declarative memory consolidation and retrieval is necessary. Although a direct link between CCK-mediated synaptic plasticity and hippocampus dependent declarative memory is missing, noticeable evidence from morphological, behavioral, and electrophysiological studies encourages further investigation regarding the potential role of CCK-dependent synaptic plasticity in hippocampus dependent declarative memory.

Cholecystokinin (CCK) and its receptors (CCK1R and CCK2R) in chickens: functional analysis and tissue expression

Cholecystokinin (CCK) is widely distributed in the gastrointestinal tract and central nervous system, regulating a range of physiological functions by activating its receptors (CCK1R and CCK2R). Compared to those in mammals, the CCK gene and its receptors have already been cloned in various birds, such as chickens. However, knowledge regarding their functionality and tissue expression is limited. In this study, we examined the expression of CCK and its 2 receptors in chicken tissues. In addition, the functionality of the 2 receptors was investigated. Using 3 cell-based luciferase reporter systems and western blots, we demonstrated that chicken (c-) CCK1R could be potently activated by cCCK-8S but not cCCK-4, whereas cCCK2R could be activated by cCCK-8S and cCCK-4 with similar efficiency. Using RNA-sequencing, we revealed that cCCK is abundantly expressed in the testis, ileum, and several brain regions (cerebrum, midbrain, cerebellum, hindbrain, and hypothalamus). The abundant expression of CCK in the hypothalamus was further supported by immunofluorescence. In addition, cCCK1R is highly expressed in the pancreas and moderately expressed in various intestinal regions (ileum, cecum, and rectum) and the pituitary gland, whereas cCCK2R expression is primarily restricted to the brain. Our data reveal the differential specificities of CCK receptors for various CCK peptides. In combination with the differential tissue distribution of CCK and its receptors, the present study helps to understanding the physiological functions of CCK/CCKRs in birds.

Methamphetamine induced neurotoxic diseases, molecular mechanism, and current treatment strategies

Methamphetamine (MA) is a extremely addictive psychostimulant drug with a significant abuse potential. Long-term MA exposure can induce neurotoxic effects through oxidative stress, mitochondrial functional impairment, endoplasmic reticulum stress, the activation of astrocytes and microglial cells, axonal transport barriers, autophagy, and apoptosis. However, the molecular and cellular mechanisms underlying MA-induced neurotoxicity remain unclear. MA abuse increases the chances of developing neurotoxic conditions such as Parkinson's disease (PD), Alzheimer's disease (AD) and other neurotoxic diseases. MA increases the risk of PD by increasing the expression of alpha-synuclein (ASYN). Furthermore, MA abuse is linked to high chances of developing AD and subsequent neurodegeneration due to biological variations in the brain region or genetic and epigenetic variations. To date, there is no Food and Drug Administration (FDA)-approved therapy for MA-induced neurotoxicity, although many studies are being conducted to develop effective therapeutic strategies. Most current studies are now focused on developing therapies to diminish the neurotoxic effects of MA, based on the underlying mechanism of neurotoxicity. This review article highlights current research on several therapeutic techniques targeting multiple pathways to reduce the neurotoxic effects of MA in the brain, as well as the putative mechanism of MA-induced neurotoxicity.

Combined molecular, structural and memory data unravel the destructive effect of tramadol on hippocampus

Tramadol is a synthetic analogue of codeine and stimulates neurodegeneration in several parts of the brain that leads to various behavioral impairments. Despite the leading role of hippocampus in learning and memory as well as decreased function of them under influence of tramadol, there are few studies analyzing the effect of tramadol administration on gene expression profiling and structural consequences in hippocampus region. Thus, we sought to determine the effect of tramadol on both PC12 cell line and hippocampal tissue, from gene expression changes to structural alterations. In this respect, we investigated genome-wide mRNA expression using high throughput RNA-seq technology and confirmatory quantitative real-time PCR, accompanied by stereological analysis of hippocampus and behavioral assessment following tramadol exposure. At the cellular level, PC12 cells were exposed to 600μM tramadol for 48 hrs, followed by the assessments of ROS amount and gene expression levels of neurotoxicity associated with neurodegenerative pathways such as apoptosis and autophagy. Moreover, the structural and functional alteration of the hippocampus under chronic exposure to tramadol was also evaluated. In this regard, rats were treated with tramadol at doses of 50 mg/kg for three consecutive weeks. In vitro data revealed that tramadol provoked ROS production and caused the increase in the expression of autophagic and apoptotic genes in PC12 cells. Furthermore, in-vivo results demonstrated that tramadol not only did induce hippocampal atrophy, but it also triggered microgliosis and microglial activation, causing upregulation of apoptotic and inflammatory markers as well as over-activation of neurodegeneration. Tramadol also interrupted spatial learning and memory function along with long-term potentiation (LTP). Taken all together, our data disclosed the neurotoxic effects of tramadol on both in vitro and in-vivo. Moreover, we proposed a potential correlation between disrupted biochemical cascades and memory deficit under tramadol administration.

Mitragynine (Kratom)-Induced Cognitive Impairments in Mice Resemble Δ9-THC and Morphine Effects: Reversal by Cannabinoid CB1 Receptor Antagonism

Kratom is a widely abused plant-based drug preparation with a global interest in recent years, well beyond its native grounds in Southeast Asia. Mitragynine, its major psychoactive constituent is known to exhibit opioid-like behavioral effects with resultant neuroplasticity in the brain reward system. Its chronic administration is associated with cognitive impairments in animal studies. However, the underlying molecular mechanism for such a deficit remains elusive. In this study, the involvement of cannabinoid type-1 (CB₁) receptors in cognitive deficits after chronic mitragynine exposures was investigated for 28 days (with incremental dose sensitization from 1 to 25 mg/kg) in adult male Swiss albino mice using the IntelliCage^® system. Chronic high-dose mitragynine exposure (5–25 mg/kg, intraperitoneal [i.p.]), but not low-dose exposure (1–4 mg/kg, i.p.), induced hyperlocomotion, potentiated the preference for sucrose reward, increased resistance to punishment, and impaired place learning and its reversal. Comparable deficits were also observed after chronic treatments with Δ-9-tetrahydrocannabinol (THC, 2 mg/kg, i.p.) or morphine (5 mg/kg, subcutaneous). Mitragynine-, morphine-, and THC-induced learning and memory deficits were reversed by co-treatment with the CB₁ receptor antagonist, NIDA-41020 (10 mg/kg, i.p.). A significant upregulation of CB₁ receptor expression was found in the hippocampal CA1 region and ventral tegmental area after chronic high-dose mitragynine and morphine, whereas a downregulation was observed after chronic THC. In conclusion, the present study suggests a plausible role of the CB₁ receptor in mediating the dose-dependent cognitive deficits after chronic high-dose mitragynine exposure. This also highlights the potential of CB₁ receptor antagonism in ameliorating the cognitive deficits associated with long-term kratom/mitragynine consumption in humans.

Cholecystokinin octapeptide improves hippocampal glutamatergic synaptogenesis and postoperative cognition by inhibiting induction of A1 reactive astrocytes in aged mice

Aims

Delayed neurocognitive recovery (dNCR) is a common postoperative complication in geriatric surgical patients for which there is no efficacious therapy. Cholecystokinin octapeptide (CCK‐8), an immunomodulatory peptide, regulates memory and learning. Here, we explored the effects and mechanism of action of CCK‐8 on dNCR.

Methods

We applied laparotomy to establish a model of dNCR in aged mice. Morris water maze and fear conditioning tests were used to evaluate cognition. Immunofluorescence was used to detect the density of CCK‐8, A1 reactive astrocytes, glutamatergic synapses, and activation of microglia in the hippocampus. Quantitative PCR was performed to determine mRNA levels of synapse‐associated factors. A1 reactive astrocytes, activated microglia, and glutamatergic synapse‐associated protein levels in the hippocampus were assessed by western blotting.

Results

Administration of CCK‐8 suppressed the activation of microglia, the induction of A1 reactive astrocytes, and the expression of tumor necrosis factor alpha, complement 1q, and interleukin 1 alpha in the hippocampus. Furthermore, it promoted glutamatergic synaptogenesis and neurocognitive recovery in aged dNCR model mice.

Conclusion

Our findings indicated that CCK‐8 alleviated cognitive impairment and promoted glutamatergic synaptogenesis by inhibiting the induction of A1 reactive astrocytes and the activation of microglia. CCK‐8 is, therefore, a potential therapeutic target for dNCR.

Cholecystokinin-8 attenuates methamphetamine-induced inflammatory activation of microglial cells through CCK2 receptor

Methamphetamine (METH) exposure reportedly promotes microglial activation and pro-inflammatory cytokines secretion. Sustained inflammation in abusers of psychostimulant drugs further induces neural damage. Cholecystokinin-8 (CCK-8) is a gut-brain peptide which exerts a wide range of biological activities in the gastrointestinal tract and central nervous system. We previously found that pre-treatment with CCK-8 inhibited behavioural and histologic changes typically induced by repeated exposure to METH. Here, we aimed to estimate the effects of CCK-8 on METH-induced neuro-inflammation, which is markedly characterized by microglia activation and increased pro-inflammatory cytokines production in vivo and in vitro. Moreover, we assessed the subtypes of the CCK receptor mediating the regulatory effects of CCK-8, and the changes in the NF-κB signalling pathway. We found that CCK-8 inhibited METH-induced microglial activation and IL-6 and TNF-α generation in vivo and in vitro in a dose-dependent manner. Furthermore, co-treatment of CCK-8 with METH significantly attenuated the activation of the NF-κB signalling pathway by activating the CCK2 receptor subtype in N9 cells. In conclusion, our findings indicated the inhibitory effect of CCK-8 on METH-induced neuro-inflammation in vivo and in vitro, and suggested the underlying mechanism may involve the activation of the CCK2 receptor, which downregulated the NF-κB signalling pathway induced by METH stimulation.

Synergistic improvement effect of nicotine-ghrelin co-injection into the anterior ventral tegmental area on morphine-induced amnesia

In the present study the effect of ghrelin or ghrelin/nicotine injection into the anterior ventral tegmental area (aVTA) on morphine-induced amnesia in passive avoidance learning have been evaluated. Also, the role of the aVTA nicotinic receptors in possible ghrelin-induced effects has been investigated. All animals were bilaterally implanted with chronic cannulas in the aVTA. A step-through type passive avoidance task was used for measurement of memory. We found that post-training subcutaneous (s.c.) injection of morphine (0.5-7.5 mg/kg) dose-dependently reduced the step-through latency, indicating morphine-induced amnesia. Post-training bilateral infusion of ghrelin (0.3, 1.5 and 3 nmol/μl) in a dose-dependent manner reversed amnesia induced by morphine (7.5 mg/kg, s.c.). Furthermore, reversal effect of ghrelin (3 nmol/μl) was blocked by pre-treatment of intra-aVTA administration of mecamylamine (1-3 μg/rat), a nicotinic acetylcholine receptor antagonist. Intra-aVTA administration of the higher dose of mecamylamine (3 μg/rat) into the aVTA by itself decreased the step-through latency and induced amnesia. In addition, post-training intra-aVTA administration of nicotine (0.25, 0.5, 1 μg/rat) which alone cannot affect memory consolidation, decreased significantly the amnesia induced by morphine (7.5 mg/kg, s.c.). Co-treatment of an ineffective dose of ghrelin (0.3 nmol/μl) with an ineffective dose of nicotine (0.25 μg/rat) significantly increased step-through latency of morphine (7.5 mg/kg, s.c.) treated animals, indicating the synergistic effect of the drugs. Taken together, our results suggest that intra-aVTA administration of ghrelin reversed morphine-induced amnesia and that ghrelin interacts synergistically with nicotine to mitigate morphine-induced amnesia.

The effect of epigallocatechin-3-gallate on morphine-induced memory impairments in rat: EGCG effects on morphine neurotoxicity

AIM OF STUDY

This investigation evaluated the capacity of epigallocatechin-3-gallate (EGCG) as the main polyphenolic compound in the green tea extract against memory impairment and neurotoxicity in morphine-treated rats.

METHODS

To measure the EGCG effect (5 and 50 mg/kg, i.p., co-treated with morphine) on spatial learning and memory of morphine-administrated male Wistar rats (45 mg/kg, s.c., 4 weeks), the Morris water maze test was used. Some apoptotic protein levels (Bax, Bcl-2, and cleaved caspase 3) were evaluated in the hippocampus tissue by the Western blot test. Also, oxidative stress status (malondialdehyde level, glutathione peroxidase, and superoxide dismutase activity) was measured in hippocampus tissue.

RESULTS

The data presented that EGCG treatment (50 mg/kg) inhibited the morphine-induced memory deficits in rats. Also, EGCG administration reduced the apoptosis and oxidative stress in the hippocampus of morphine-treated rats.

CONCLUSIONS

Our data indicate that EGCG can improve memory in morphine-treated rats. Molecular mechanisms underlying the detected effects could be related to the prevention of apoptosis and oxidative stress in the hippocampus of morphine-treated rats.

Effects of Molecular Hydrogen on Methamphetamine-Induced Neurotoxicity and Spatial Memory Impairment

Methamphetamine (METH) is a highly addictive stimulant, and METH exposure can induce irreversible neuronal damage and cause neuropsychiatric and cognitive disorders. The ever-increasing levels of METH abuse worldwide have necessitated the identification of effective intervention strategies to protect the brain against METH-induced neurotoxicity. The protective effects of molecular hydrogen on oxidative stress and related neurodegenerative diseases have been recently elucidated. Herein, we investigated whether treatment with molecular hydrogen ameliorated the METH-induced neurotoxicity and spatial learning and memory impairments. Male C57BL/6 mice received four intraperitoneal METH injections (10 mg/kg, 3-h interval), and stereotypic behaviors and hyperthermia were observed. After METH treatment and behavioral observation, the mice were returned to their home cages, where they received water or hydrogen-rich water (HRW) ad libitum for 7 days. We found that the molecular hydrogen delivered by ad libitum HRW consumption significantly inhibited the METH-induced spatial learning impairment and memory loss evidenced in the Barnes maze and Morris water maze tests. Furthermore, molecular hydrogen significantly restrained the neuronal damage in the hippocampus after high-dose METH exposure. Ad libitum HRW consumption also had an inhibitory effect on the METH-induced increase in the expression of Bax/Bcl-2, cleaved caspase-3, glucose-related protein 78 (GRP 78), CCAAT/enhancer-binding protein homologous protein (CHOP), and p-NF-kB p65 expression and elevation of interleukin (IL)-6 and tumor necrosis factor (TNF)-α levels in the hippocampus. These are the first findings to indicate that hydrogen might ameliorate METH-induced neurotoxicity and has a potential application in reducing the risk of neurodegeneration frequently observed in METH abusers.

Effect of oleuropein on morphine-induced hippocampus neurotoxicity and memory impairments in rats

Oleuropein, as an olive leaf extract antioxidant polyphenol, has been reported to be a free radical scavenger. This study was done to investigate the effects of oleuropein, against morphine-induced hippocampus neurotoxicity and memory impairment in rats. The Morris water maze (MWM) test was used to assess the effect of oleuropein (5, 15, and 30 mg/kg, i.p., co-administrated with morphine) on spatial learning and memory of male Wistar rats which were treated with morphine sulfate (45 mg/kg, s.c., 4 weeks). In order to evaluate the cleaved caspase-3, Bax, and Bcl2 protein expression (as biochemical markers of apoptosis) in CA1 area of hippocampus tissue, the western blot test was used. Also, to evaluate the oxidative stress status of hippocampus CA1 area tissue, the malondialdehyde (MDA) level, superoxide dismutase (SOD) activity, and glutathione peroxidase (GPx) activity were assessed. The data showed that oleuropein treatment (15 and 30 mg/kg) improves the spatial learning and memory impairments in morphine-treated animals. Also, oleuropein treatment decreased the apoptosis and oxidative stress levels in the hippocampus CA1 area of morphine-treated rats. Oleuropein can prevent the spatial learning and memory impairments in morphine-treated rats. Molecular mechanisms underlying the observed effects could be at least partially related to the inhibition of neuronal apoptosis and oxidative stress in the hippocampus CA1 area of morphine-treated rats.

The effects of CCK-8S on spatial memory and long-term potentiation at CA1 during induction of stress in rats

Objectives

Cholecystokinin (CCK) has been proposed as a mediator in stress. However, it is still not fully documented what are its effects. We aimed to evaluate the effects of systemic administration of CCK exactly before induction of stress on spatial memory and synaptic plasticity at CA1 in rats.

Materials and Methods

Male Wistar rats were divided into 4 groups: the control, the control-CCK, the stress and the stress-CCK. Restraint stress was induced 6 hr per day, for 24 days. Cholecystokinin sulfated octapeptide (CCK-8S) was injected (1.6 µg/kg, IP) before each session of stress induction. Spatial memory was evaluated by Morris water maze test. Long-term potentiation (LTP) in Schaffer collateral-CA1 synapses was assessed (by 100 Hz tetanization) in order to investigate synaptic plasticity.

Results

Stress impaired spatial memory significantly (P<0.01). CCK in the control rats improved memory (P<0.05), and prevented the impairments in the stress group. With respect to the control group, both fEPSP amplitude and slope were significantly (P<0.05) decreased in the stress group. However, there were no differences between responses of the control-CCK and Stress-CCK groups compared to the control group.

Conclusion

The present results suggest that high levels of CCK-8S during induction of stress can modulate the destructive effects of stress on hippocampal synaptic plasticity and memory. Therefore, the mediatory effects of CCK in stress are likely as compensatory responses.

Mitochondrial impairments contribute to spatial learning and memory dysfunction induced by chronic tramadol administration in rat: Protective effect of physical exercise

Despite the worldwide use of tramadol, few studies have been conducted about its effects on memory and mitochondrial function, and controversial results have been reported. Recently, there has been an increasing interest in physical exercise as a protective approach to neuronal and cognitive impairments. Therefore, the aim of this study was to investigate the effects of physical exercise on spatial learning and memory and brain mitochondrial function in tramadol-treated rats. After completion of 2-week (short-term) and 4-week (long-term) treadmill exercise regimens, male Wistar rats received tramadol (20, 40, 80mg/kg/day) intraperitoneally for 30days. Then spatial learning and memory was assessed by Morris water maze test (MWM). Moreover, brain mitochondrial function was evaluated by determination of mitochondrial reactive oxygen species (ROS) level, mitochondrial membrane potential (MMP), mitochondrial swelling and cytochrome c release from mitochondria. Chronic administration of tramadol impaired spatial learning and memory as well as brain mitochondrial function as indicated by increased ROS level, MMP collapse, increased mitochondrial swelling and cytochrome c release from mitochondria. Conversely, treadmill exercise significantly attenuated the impairments of spatial learning and memory and brain mitochondrial dysfunction induced by tramadol. The results revealed that chronic tramadol treatment caused memory impairments through induction of brain mitochondrial dysfunction. Furthermore, pre-exposure to physical exercise markedly mitigated these impairments through its positive effects on brain mitochondrial function.

Chronic mitragynine (kratom) enhances punishment resistance in natural reward seeking and impairs place learning in mice

Kratom (Mitragyna speciosa) is a widely abused herbal drug preparation in Southeast Asia. It is often consumed as a substitute for heroin, but imposing itself unknown harms and addictive burdens. Mitragynine is the major psychostimulant constituent of kratom that has recently been reported to induce morphine-like behavioural and cognitive effects in rodents. The effects of chronic consumption on non-drug related behaviours are still unclear. In the present study, we investigated the effects of chronic mitragynine treatment on spontaneous activity, reward-related behaviour and cognition in mice in an IntelliCage® system, and compared them with those of morphine and Δ-9-tetrahydrocannabinol (THC). We found that chronic mitragynine treatment significantly potentiated horizontal exploratory activity. It enhanced spontaneous sucrose preference and also its persistence when the preference had aversive consequences. Furthermore, mitragynine impaired place learning and its reversal. Thereby, mitragynine effects closely resembled that of morphine and THC sensitisation. These findings suggest that chronic mitragynine exposure enhances spontaneous locomotor activity and the preference for natural rewards, but impairs learning and memory. These findings confirm pleiotropic effects of mitragynine (kratom) on human lifestyle, but may also support the recognition of the drug's harm potential.

Influences of CCK-8 on expressions of apoptosis-related genes in prefrontal cortex neurons of morphine-relapse rats

In order to elucidate the influences of CCK-8 on expressions of apoptosis-related genes, Bax, Bcl-2 and Caspase-3, of prefrontal cortex neurons in morphine-relapse rats, an effective, successful morphine-relapse-rat model using the conditioned place preference (CPP) under CCK-8 (0.01, 0.1 and 1.0μg, i.c.v) intervention was established. The prefrontal cortexes were made into slices with the cellular plasmas immunohistochemically stained. The expressions of Bax, Bcl-2, Caspase-3 of neurons were evaluated through their scores, and each corresponding ratio of Bax and Bcl-2 (Bax/Bcl-2) was also computed. The results showed that the expression of Bcl-2 was very weak and those of Bax and Caspase-3 were hardly seen in group normal saline; the expressions of Bax and Caspase-3 were strong and that of Bcl-2 was weak in group morphine and compared to group normal saline, there were significant differences (P<0.05); the expressions of Bax, Caspase-3 and the ratios of Bax/Bcl-2 have a gradually-decreased trend in the sequence of group 0.01μg, group 0.1μg and group 1.0μg, but the expression of Bcl-2 has an opposite trend in the same sequence, and compared to group morphine, there were significant differences (P<0.05) excluding group 0.01μg. So we draw a conclusion that CCK-8 (0.1 and 1.0μg, i.c.v) could protect neurons of prefrontal cortex through up-regulating the expression of Bcl-2, down-regulating those of Bax and Caspase-3 and reducing Bax/Bcl-2 ratio in the model of morphine-relapse rats.

Exposure pattern influences the degree of drug-seeking behaviour after withdrawal

OBJECTIVES

The occurrence of a relapse during abstinence is an important issue that must be addressed during treatment for drug addiction. We investigated the influence of drug exposure pattern on morphine-seeking behaviour following withdrawal. We also studied the role of the hippocampus in this process to confirm its involvement in drug relapse.

METHODS

Male Sprague-Dawley rats that were trained to self-administer morphine (1.0 mg/kg) using 2, 4, 6, 8, or 10 h daily sessions underwent withdrawal in their home cages and were re-exposed to the operant chamber to evaluate morphine-seeking behaviour. During the relapse session, rats were intravenously injected with morphine (0.25 mg/kg) or saline before re-exposure to the chamber. In the second experiment, rats were administered a microinjection of saline or cobalt chloride (CoCl2, 1 mM), a synaptic blocker, into the CA1 of the hippocampus prior to the relapse test.

RESULTS

In the first experiment, more morphine-seeking behaviour was observed in the 2 h group (animals trained to self-administer morphine during a 2 h daily session spread over 21 days) during the relapse session, despite all groups being exposed to similar amounts of morphine during the training period before withdrawal. In the second experiment, pretreatment with CoCl2 markedly reduced morphine-seeking behaviour in the 2 h group.

CONCLUSIONS

The present findings suggest that the exposure pattern influences the degree of relapse and that control of memorisation is important for prevention of relapse.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 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 (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 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 (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Recent advances in methamphetamine neurotoxicity mechanisms and its molecular pathophysiology

Methamphetamine (METH) is a sympathomimetic amine that belongs to phenethylamine and amphetamine class of psychoactive drugs, which are widely abused for their stimulant, euphoric, empathogenic, and hallucinogenic properties. Many of these effects result from acute increases in dopamine and serotonin neurotransmission. Subsequent to these acute effects, METH produces persistent damage to dopamine and serotonin release in nerve terminals, gliosis, and apoptosis. This review summarized the numerous interdependent mechanisms including excessive dopamine, ubiquitin-proteasome system dysfunction, protein nitration, endoplasmic reticulum stress, p53 expression, inflammatory molecular, D₃ receptor, microtubule deacetylation, and HIV-1 Tat protein that have been demonstrated to contribute to this damage. In addition, the feasible therapeutic strategies according to recent studies were also summarized ranging from drug and protein to gene level.

Protective effects of cholecystokinin-8 on methamphetamine-induced behavioral changes and dopaminergic neurodegeneration in mice

We investigated whether pretreatment with the neuropeptide cholecystokinin-8 affected methamphetamine (METH)-induced behavioral changes and dopaminergic neurodegeneration in male C57/BL6 mice. CCK-8 pretreatment alone had no effect on locomotion and stereotypic behavior and could not induce behavioral sensitization; however, it attenuated, in a dose-dependent manner, hyperlocomotion and behavioral sensitization induced by a low dose of METH (1mg/kg). CCK-8 attenuated METH-induced stereotypic behavior at a dose of 3mg/kg but not at 10mg/kg. CCK-8 pretreatment attenuated METH (10mg/kg)-induced hyperthermia, the decrease of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum, and TH in the substantia nigra. CCK-8 alone had no effect on rectal temperature, TH and DAT expression in the nigrostriatal region. In conclusion, our study demonstrated that pretreatment with CCK-8 inhibited changes typically induced by repeated exposure to METH, such as hyperlocomotion, behavioral sensitization, stereotypic behavior, and dopaminergic neurotoxicity. These findings make CCK-8 a potential therapeutic agent for the treatment of multiple symptoms associated with METH abuse.

Imbalance of HCN1 and HCN2 expression in hippocampal CA1 area impairs spatial learning and memory in rats with chronic morphine exposure

The hyperpolarization-activated cyclic-nucleotide-gated non-selective cation (HCN) channels play a vital role in the neurological basis underlying nervous system diseases. However, the role of HCN channels in drug addiction is not fully understood. In the present study, we investigated the expression of HCN1 and HCN2 subunits in hippocampal CA1 and the potential molecular mechanisms underlying the modulation of HCN channels in rats with chronic morphine exposure with approaches of electrophysiology, water maze, and Western blotting. We found that chronic morphine exposure (5 mg/kg, sc, for 7 days) caused an inhibition of long-term potentiation (LTP) and impairment of spatial learning and memory, which is associated with a decrease in HCN1, and an increase in HCN2 on cell membrane of hippocampal CA1 area. Additional experiments showed that the imbalance of cell membrane HCN1 and HCN2 expression under chronic morphine exposure was related to an increase in expression of TPR containing Rab8b interacting protein (TRIP8b) (1a-4) and TRIP8b (1b-2), and phosphorylation of protein kinase A (PKA) and adaptor protein 2 μ2 (AP2 μ2). Our results demonstrate the novel information that drug addiction-induced impairment of learning and memory is involved in the imbalance of HCN1 and HCN2 subunits, which is mediated by activation of TRIP8b (1a-4), TRIP8b (1b-2), PKA and AP2 μ2.

Cholecystokinin-octapeptide restored morphine-induced hippocampal long-term potentiation impairment in rats

Cholecystokinin-octapeptide (CCK-8), which is a typical brain-gut peptide, exerts a wide range of biological activities on the central nervous system. We have previously reported that CCK-8 significantly alleviated morphine-induced amnesia and reversed spine density decreases in the CA1 region of the hippocampus in morphine-treated animals. Here, we investigated the effects of CCK-8 on long-term potentiation (LTP) in the lateral perforant path (LPP)-granule cell synapse of rat dentate gyrus (DG) in acute saline or morphine-treated rats. Population spikes (PS), which were evoked by stimulation of the LPP, were recorded in the DG region. Acute morphine (30mg/kg, s.c.) treatment significantly attenuated hippocampal LTP and CCK-8 (1μg, i.c.v.) restored the amplitude of PS that was attenuated by morphine injection. Furthermore, microinjection of CCK-8 (0.1 and 1μg, i.c.v.) also significantly augmented hippocampal LTP in saline-treated (1ml/kg, s.c.) rats. Pre-treatment of the CCK2 receptor antagonist L-365,260 (10μg, i.c.v) reversed the effects of CCK-8, but the CCK1 receptor antagonist L-364,718 (10μg, i.c.v) did not. The present results demonstrate that CCK-8 attenuates the effect of morphine on hippocampal LTP through CCK2 receptors and suggest an ameliorative function of CCK-8 on morphine-induced memory impairment.