Effects of cannabinoid and glutamate receptor antagonists and their interactions on learning and memory in male rats

The role of hippocampal 5-HT1D and 5-HT1F receptors on learning and memory in rats

Serotonin is a neurotransmitter, which is involved in memory via its receptors. The 5-HT_1D and 5-HT_1F receptors mainly exist in the hippocampus, which plays an important role in memory processing. However, few studies have assessed the effect of these serotonin receptors on memory. We evaluated the effect of a 5-HT_1D receptor agonist, PNU142633, 5-HT_1D receptor antagonist, BRL15572 hydrochloride, and 5-HT1F receptor agonist, LY344864, on the recognition and avoidance memory in the hippocampus area. Fifty adult male Wistar rats weighing 200-250 g were divided into the control, sham-operated, PNU, BRL, and LY groups (n=10 per group). Bilateral guide cannulas were implanted into the dentate gyrus area of the hippocampus. The drugs were administered at the dose of 1 μg/μl before the novel object recognition (NOR) and passive avoidance learning (PAL) tests. The results showed that in the NOR test, the administration of PNU and LY had no significant effect on recognition index; however, the recognition index was increased by BRL. In the PAL test, the administration of PNU had no significant effect on recognition index, but the administration of BRL and LY increased the time spent in the dark compartment of the apparatus and decreased the step-through latency into the dark compartment apparatus. It can be concluded that the inhibition of the hippocampal 5-HT_1D receptor improved cognition memory but impaired avoidance memory. Activation of the hippocampal 5-HT_1F receptor had no effect on cognitive memory but impaired avoidance memory.

Targeting mediodorsal thalamic CB1 receptors to inhibit dextromethorphan-induced anxiety/exploratory-related behaviors in rats: The post-weaning effect of exercise and enriched environment on adulthood anxiety

Dextromethorphan (DXM) is an effective over-the-counter antitussive with an alarming increase as an abused drug for recreational purposes. Although reports of the association between DXM administration and anxiety, there are few investigations into the underlying DMX mechanisms of anxiogenic action. Thus, the present study aimed to investigate the role of the mediodorsal thalamus (MD) cannabinoid CB1 receptors (CB1Rs) in DXM-induced anxiety/exploratory-related behaviors in adult male Wistar rats. Animals were bilaterally cannulated in the MD regions. After one week, anxiety and exploratory behaviors were measured using an elevated plus-maze task (EPM) and a hole-board apparatus. Results showed that DXM (3-7 mg/kg, i. p.) dose-dependently increased anxiety-like behaviors. Intra-MD administration of ACPA (2.5-10 ng/rat), a selective CB1 receptor agonist, decreased anxiety-like effects of DXM. The blockade of MD CB1 receptors by AM-251 (40-120 ng/rat) did not affect the EPM task. However, it potentiated the anxiogenic response of an ineffective dose of DXM (3 mg/kg) in the animals. Moreover, the effect of post-weaning treadmill exercise (TEX) and enriched environment (EE) were examined in adulthood anxiety under the drug treatments. Juvenile rats were divided into TEX/EE and control groups. The TEX/EE-juvenile rats were placed on a treadmill and then exposed to EE for five weeks. Interestingly, compared to untreated animals, post-weaning TEX/EE inhibited the anxiety induced by DXM or AM-251/DXM. It can be concluded that the MD endocannabinoid system plays an essential role in the anxiogenic effect of dextromethorphan. Moreover, post-weaning exercise alongside an enriched environment may have an inhibitory effect on adulthood anxiety-like behaviors.

The interactive effects of verapamil and CB1 cannabinoid receptor antagonist/inverse agonist, AM251 on passive avoidance learning and memory in rat

There are reports regarding the effects of intracellular Ca2+ and synthesis and release of endocannabinoids. The secretion of endocannabinoids depends on the L-type calcium channel. The present study evaluated the involvement of the cannabinoid CB1 receptors in the effect of L-type calcium channel blocker verapamil on passive avoidance learning (PAL) in adult male rats. In this study, we examined the effects of an acute administration of the cannabinoid CB1 receptors antagonist/inverse agonist AM251 following a chronic administration of the Ca2+ channel blocker verapamil on PAL. Male Wistar rats were administered verapamil (10, 25 and 50 mg/kg) or saline intraperitoneally (i.p) daily for 13 days (n = 10/group). After this treatment period, a learning test (acquisition) was performed, and a retrieval test was performed the following day. The results indicated that chronic systemic administration of verapamil (in a dose-dependent manner) impaired memory acquisition and retrieval. Pre-training acute administration of a selective CB1 antagonist/inverse agonist, AM251 (5 mg/kg, i.p.) did not change memory acquisition and retrieval. Co-administration of the verapamil and AM251 significantly reversed verapamil-induced amnesia, suggesting a functional interaction between AM251 and verapamil. The results indicated the interactive effects of cannabinoid CB1 receptors and L-type calcium channel in passive avoidance learning and AM251 can counter the effects of verapamil on memory.

Effects of Buprenorphine on the Memory and Learning Deficit Induced by Methamphetamine Administration in Male Rats

Little is known about the effects of methamphetamine (Meth) and buprenorphine (Bup) on memory and learning in rats. The aim of this investigation was to examine the impact of Meth and Bup on memory and learning. Fourteen male Wistar rats weighing 250–300 g were assigned to four groups: Sham, Meth, Bup, and Meth + Bup and were treated for 1 week. Spatial learning and memory, avoidance learning, and locomotion were assessed using the Morris water maze, passive avoidance learning, and open field tests, respectively. Meth and Bup impaired spatial learning and memory in rats. Co-administration of Meth + Bup did not increase the time spent in the target quadrant compared to Meth alone in the MWM. The Bup and Meh + Bup groups were found with an increase in step-through latency (STLr) and a decrease in the time spent in the dark compartment (TDC). Meth and Bup had no effects on locomotor activity in the open field test. Bup showed a beneficial effect on aversive memory. Since Bup demonstrates fewer side effects than other opioid drugs, it may be preferable for the treatment of avoidance memory deficits in patients with Meth addiction.

Low-Frequency Stimulation Prevents Kindling-Induced Impairment through the Activation of the Endocannabinoid System

Background

Cannabinoid system affects memory and has anticonvulsant effects in epileptic models. In the current study, the role of cannabinoid 1 (CB1) receptors was investigated in amelioration of the effects of low-frequency stimulation (LFS) on learning and memory impairments in kindled rats.

Methods

Electrical stimulation of the hippocampal CA1 area was employed to kindle the animals. LFS was applied to the CA1 area in four trials following the last kindling stimulation. One group of animals received intraperitoneal injection of AM251 (0.1 μg/rat), a CB1 receptor antagonist, before the LFS application. Similarly, CB1 agonist WIN55-212-2 (WIN) was administrated to another group prior to LFS. The Morris water maze (MWM) and the novel object recognition (NOR) tests were executed 48 h after the last kindling stimulation to assess learning and memory.

Results

Applying LFS in the kindled+LFS group restored learning and memory impairments in the kindled rats. There was a significant difference between the kindled and the kindled+LFS groups in learning and memory. The application of AM251 reduced the LFS effects significantly. Adversely, WIN acted similarly to LFS and alleviated learning and memory deficits in the kindled+WIN group. In addition, WIN did not counteract the LFS enhancing effects in the KLFS+WIN group.

Conclusions

Improving effects of LFS on learning and memory impairments are mediated through the activation of the endocannabinoid (ECB) system.

Effects of vanillic acid on Aβ1-40-induced oxidative stress and learning and memory deficit in male rats

Alzheimer's disease (AD) is a neurodegenerative disease, in which the accumulation of β-amyloid (Aβ) peptide in the extracellular space causes a progressive reduction in cognitive performance. Aβ stimulates active oxygen species generation leading to oxidative stress and neural cell death. Vanillic Acid (VA) is the oxidant form of vanillin widely found in vanilla beans. VA has many properties, such as suppressing apoptosis and eliminating the harmful effects of oxidative stress in animal models. The VA effects on impaired learning and memory in Aβ rats were assessed. Forty adults male Wistar rats were assigned to the following five groups in random: the control, sham (received saline (vehicle) via intracerebroventricular (ICV) injection), Aβ (received Aβ1-40 via ICV injection), VA (50 mg/kg by oral gavage once a day through four weeks), and Aβ + VA (50 mg/kg) groups. Open field test, novel object recognition (NOR) test, Morris water maze (MWM) test, and passive avoidance learning (PAL) task were performed, and finally, we determined the malondialdehyde (MDA), total antioxidant capacity (TAC) and total oxidant status (TOS) levels. Aβ decreased the cognitive memory in NOR, spatial memory in MWM, and passive avoidance memory in PAL tests. In contrast, VA improved learning and memory in the treated group. Aβ significantly increased MDA and TOS and decreased TAC levels, whereas VA treatment significantly reversed TAC, TOS and MDA levels. In conclusion, VA decreased the Aβ effects on learning and memory by suppressing oxidative stress and can be regarded as a neuroprotective substance in AD.

The Effects of 3,4-methylenedioxymethamphetamine on Neurogenesis in the Hippocampus of Male Rats

Introduction:

The administration of 3,4-methylenedioxymethamphetamine (MDMA) or ecstasy causes memory impairment, whereas neurogenesis improves memory and learning. Hence, this study evaluated the effects of MDMA on neurogenesis in the hippocampus of male rats.

Methods:

Adult male Wistar rats received Intraperitoneal (IP) injections of MDMA (10 mg/ kg). We assessed nestin, sex-determining region Y-box 2 (Sox2), and NeuroD expressions according to the immunohistochemistry analyses.

Results:

MDMA reduced the expressions of nestin, Sox2, and NeuroD compared with the control groups. The reduction in NeuroD expression was age-related.

Conclusion:

MDMA possibly has negative effects on neurogenesis, which specifically results from impaired survival of newborn cells.

Ibuprofen Protection Against Restrained Chronic Stress-induced Depression in Male Rats

Introduction:

Stress predisposes organisms to depression and cognitive impairments, and seems to interact with metabolic homeostasis. The inflammatory response and the upregulation of proinflammatory cytokines are some of the consequences related to chronic stress. In this study, we investigated the preventive effect of chronic administration of ibuprofen, as an inhibitor of cyclooxygenases, on the cognitive and behavioral alterations and the weight gain reduction induced by simultaneous chronic restraint stress in rats.

Materials and Methods:

Male Wistar rats were subjected to chronic restraint stress and injected daily with the variable doses of ibuprofen or vehicle, for 21 consecutive days. Then, all animals were tested with the forced swim test and passive avoidance conditioning. Also, the weight of the animals was recorded before and after the interventions. Ultimately, plasma interleukin 6 (IL-6) levels were measured.

Results:

Chronic stress increased depressive-like behaviors, impaired learning, and disrupted the normal weight gain. However, the animals that received the highest dose of ibuprofen showed less depressive-like behaviors, a better avoidance memory, and a higher weight gain. However, the level of plasma IL-6 did not differ significantly between the study groups.

Conclusion:

The administration of ibuprofen prevents the cognitive and behavioral consequences of chronic stress. During the recovery, the plasma levels of IL-6 were not elevated by stress, and the IL-6 levels did not predict the behavioral performance of the stressed animals. The exact mechanisms of the protective effects of ibuprofen against chronic stress need to be further investigated.

Effects of Regular Exercise on Diabetes-Induced Memory Deficits and Biochemical Parameters in Male Rats

The main objective of current work was to determine the effects of treadmill-running and swimming exercise on passive avoidance learning (PAL) and blood biochemical parameters in rats with streptozotocin (STZ)-induced diabetes. Male Wistar rats were divided into the following 6 groups (N = 6-8 per group): CON, healthy rats without exercise (N = 8); STZ, diabetic rats without exercise (N = 8); CON-SE, healthy rats subjected to swimming exercise (2 months; N = 6); STZ-SE, diabetic rats subjected to swimming exercise (2 months; N = 7); CON-TE, healthy rats subjected to treadmill exercise (2 months; N = 8); STZ-TE, diabetic rats subjected to treadmill exercise (2 months; N = 8). Diabetes was induced by a single intraperitoneal injection of 50 mg/kg STZ. Our results showed that STZ decreased the step-through latency in the retention test (STLr) and increased the time spent in the dark compartment (TDC) when compared with the CON group. However, treadmill-running and swimming exercise in STZ-treated rats increased the STLr and decreased the TDC when compared with STZ-treated rats without exercise in PAL. Blood low-density lipoprotein (LDL) and triglyceride (TG) levels in the STZ group were significantly higher than those in the CON group, whereas plasma total antioxidant capacity (TAC) and levels of catalase (CAT) and glutathione peroxidase (GPx) were lower in the STZ group compared with the CON group. The levels of LDL and TG decreased and the levels of TAC, CAT, and GPx increased in the exercise groups in comparison with the STZ group. The present results indicate that regular exercise enhances learning and memory in diabetic rats and that these effects may occur through activation of the antioxidant system.

Deleterious Effects of Ethanol, Δ(9)-Tetrahydrocannabinol (THC), and Their Combination on the Spatial Memory and Cognitive Flexibility in Adolescent and Adult Male Rats in the Barnes Maze Task

Research demonstrates that adolescents differ from adults in their response to drugs of abuse. The aim of the present study was to examine the influence of ethanol, Δ9-tetrahydrocannabinol hydrochloride (THC), and a combination of these drugs given during adolescence on spatial memory in adolescent and adult rats. Thus, adolescent rats (postnatal day (PND) 30) were subjected to the following groups: 0.9% NaCl; 1.5 g/kg ethanol; 1.0 mg/kg THC; 1.5 g/kg ethanol + 1.0 mg/kg THC. Rats received drug injection four times at three-day intervals. One day after the last injection, half of the treated animals were tested in the Barnes maze task, whereas the remaining animals were tested on PND 70. Results show that there was a significant age effect on spatial memory in the Barnes maze task after these drug administrations. Adolescent animals demonstrated more potent deficits in the spatial learning and memory (probe trial) and in cognitive flexibility (reversal learning) than did adults. However, in adult rats that received these drugs in adolescence, memory decline was observed only after ethanol and ethanol + THC administration. Thus, our results are important in understanding the deleterious impact of THC and/or ethanol abuse during adolescence on memory function across the lifespan (adolescent versus adult).

The effects of aqueous extract of Origanum vulgare on learning and memory in male rats

Introduction: The effectiveness of antioxidants on learning and memory improvement has been shown, previously. Due to the high level of antioxidants, available in Origanum vulgare, the present experiment aimed to examine the effect of aqueous extract of O. vulgare on passive avoidance learning (PAL) in male Wistar rats. Methods: This study was performed on 30 male Wistar rats weighing 250 to 290 g. The rats were randomly assigned into five groups (n=6), as follows: the control, sham (saline), and three groups treated with different doses of O. vulgare extract (150, 250, and 350 mg/kg). The saline or extract was administered via daily oral gavage for 14 days. The groups were then subjected to the passive avoidance task, and their behaviors were recorded. The rats’ locomotor activity was also measured using the open field test. Results: The number of trials to acquisition was significantly lower in the "O. vulgare (350 mg/ kg)" group than the control group. The step-through latency and the time spent in the dark compartment in the retention test, was significantly higher and lower in the "O. vulgare (250 and 350 mg/kg)" groups than the control group, respectively. No significant differences were found in the distances traveled among the experimental groups in the open field test. Conclusion: Aqueous extract of O. vulgare can enhance learning and memory. The high levels of antioxidants in O. vulgare extract may be responsible for its effectiveness in learning and memory.

Influence of Chronic Coenzyme Q10 Supplementation on Cognitive Function, Learning, and Memory in Healthy and Diabetic Middle-Aged Rats

Diabetes mellitus can induce impairment in learning and memory. Cognitive and memory deficits are common in older adults and especially in those with diabetes. This is mainly because of hyperglycemia, oxidative stress, and vascular abnormalities. Coenzyme Q10 (CoQ10) can decrease oxidative stress, hyperglycemia, and inflammatory markers, and improve vascular function. Therefore, the aim of the present study was to investigate the possible effects of CoQ10 on cognitive function, learning, and memory in middle-aged healthy and diabetic rats. Adult middle-aged male Wistar rats (390-460 g, 12-13 months old) were divided into 6 experimental groups. Diabetes was induced by a single i.p. injection of streptozotocin (60 mg/kg). CoQ10 (20 or 120 mg/kg, orally by gavage) was administered for 45 days. The cognitive function and learning memory of rats were evaluated using novel object recognition (NOR) and passive avoidance tests. The discrimination index of the NOR test in the diabetic groups receiving CoQ10 (20 or 120 mg/kg) and the healthy group receiving CoQ10 (120 mg/kg) was significantly higher than that in the control group. In addition, the step through latency was significantly longer and the time spent in the dark compartment was significantly shorter in the diabetic groups receiving CoQ10 than in the control group. CoQ10 supplementation can improve learning and memory deficits induced by diabetes in older subjects. In addition, CoQ10 at higher doses can improve cognitive performance in older healthy subjects.

Effect of a hydro-alcoholic extract of Melissa officinalis on passive avoidance learning and memory

Introduction: Melissa officinalis (MO) or lemon balm is traditionally used as a sedative and anti-spasm herbal medicine. There is also evidence that this plant has effects on learning and memory. This study examined the effect of a hydro-alcoholic extract of MO on passive avoidance learning (PAL) and memory in male rats. Methods: A total of 40 adult male Wistar rats were randomly distributed into four groups (200 to 220 g; n = 10 per group); three dose groups (50, 100, and 200 mg/kg of the hydro-alcoholic extract of MO) and vehicle control (saline) group. Saline or doses of extract were administered daily for 14 days by oral gavage. The rats were trained to enter the shuttle box to record their behavior in the PAL task. A retrieval test was performed 24 hours following training. Results: A significant difference was seen in performance among MO groups and the control. MO administered animals had a decreased number of acquisition trials (P < 0.05). In the retention task, MO administered animals had an increased step-through latency (SLT) (P < 0.01), and a decreased latency in the dark compartment (P < 0.001) compared to the control group. Conclusion: The results of the study show that MO can improve learning and memory in the PAL task. Further investigation is needed to enhance our understanding of the neurobiological mechanisms of the MO extract and its effects on learning and memory.

Cannabinoid Receptor Type 1 Agonist ACEA Improves Cognitive Deficit on STZ-Induced Neurotoxicity Through Apoptosis Pathway and NO Modulation

The cannabinoid system has the ability to modulate cellular and molecular mechanisms, including excitotoxicity, oxidative stress, apoptosis, and inflammation, acting as a neuroprotective agent, by its relationship with signaling pathways associated to the control of cell proliferation, differentiation, and survival. Recent reports have raised new perspectives on the possible role of cannabinoid system in neurodegenerative diseases like Alzheimer disease's (AD). AD is a neurodegenerative disorder characterized by the presence of amyloid plaques, neurofibrillary tangles, neuronal death, and progressive cognitive loss, which could be caused by energy metabolism impairment, changes in insulin signaling, chronic oxidative stress, neuroinflammation, Tau hyperphosphorylation, and Aβ deposition in the brain. Thus, we investigated the presumptive protective effect of the cannabinoid type 1 (CB1)-selective receptor agonist arachidonyl-2'-chloroethylamide (ACEA) against streptozotocin (STZ) exposure stimuli in an in vitro neuronal model (Neuro-2a neuroblastoma cells) and in vivo model (intracerebroventricular STZ injection), experimental models of sporadic AD. Our results demonstrated that ACEA treatment reversed cognitive impairment and increased activity of Akt and ERK triggered by STZ, and increased IR expression and increased the anti-apoptotic proteins levels, Bcl-2. In the in vitro model, ACEA was able to rescue cells from STZ-triggered death and modulated the NO release by STZ. Our study has demonstrated a participation of the cannabinoid system in cellular survival, involving the CB1 receptor, which occurs by positive regulation of the anti-apoptotic proteins, suggesting the participation of this system in neurodegenerative processes. Our data suggest that the cannabinoid system is an interesting therapeutic target for the treatment of neurodegenerative diseases.

Influence of hippocampal GABAB receptor inhibition on memory in rats with acute β-amyloid toxicity

The neurotransmitter γ-aminobutyric acid (GABA) is involved in the process of memory. It has been reported that the inhibition of GABA_B receptors has beneficial effects on cognition. The aim of this study was to investigate the role of CGP35348 (a GABA_B receptor antagonist) on dentate gyrus GABA_B receptor inhibition and its effects on learning and memory impairments that had been induced in adult male rats by microinjection of β-amyloid (Aβ). Seventy Wistar male rats were randomly divided into seven groups: control, sham (receiving the Aβ vehicle only), Aβ, Aβ + CGP35348 (1, 10, and 100 μg/μL), and CGP35348 alone (10 μg/μL). Memory impairment was induced by unilateral interventricular microinjection of Aβ (6 μg/6 μL). Rats were cannulated bilaterally in the dentate gyrus, and then, they were treated for 20 consecutive days. Learning and memory were assessed using the novel object recognition and passive avoidance learning tests. The discrimination index and the step-through latency were significantly increased in the Aβ + CGP35348 group in comparison to the Aβ only group (P < 0.05 and P < 0.01, respectively). Data showed that the discrimination index was decreased in the Aβ + CGP35348 group in comparison with the control group (P < 0.05) and sham group (P < 0.01). Moreover, the step-through latency was significantly decreased in the Aβ + CGP35348 group in comparison to the control and sham groups (P < 0.01). Data from this study indicated that intra-hippocampal microinjection of the GABA_B receptor antagonist counteracts the learning, memory, and cognitive impairments induced by Aβ. It can be concluded that the GABA_B receptor antagonist is a possible therapeutic agent against the progression of acute Aβ toxicity-induced memory impairment.

The effect of NAD-299 and TCB-2 on learning and memory, hippocampal BDNF levels and amyloid plaques in Streptozotocin-induced memory deficits in male rats

RATIONALE

Alzheimer's disease (AD) is the most common form of dementia characterized by a progressive decline in cognitive function. The serotonergic system via the 5-HT1A receptor and 5-HT2A receptor is proposed to affect the cognitive process.

OBJECTIVE

In the present study, the effects of NAD-299 (5-HT1AR antagonist) and TCB-2 (5-HT2AR agonist) on learning and memory processes, hippocampal brain-derived neurotrophic factor (BDNF) levels, neuronal necrosis, and Aβ plaque production have been investigated on the intracerebroventricular (icv) injection of streptozotocin (STZ)-induced memory deficits in rats.

METHODS

Fifty-four adult male Wistar rats (250-300 g) were divided into six groups (n = 9 in each group): control, sham-operated, AD (icv-STZ (3 mg/kg, 10 μl)), AD+NAD-299 (5 μg/1 μl icv for 30 days), AD+TCB-2 (5 μg/1 μl icv for 30 days), and AD+NAD-299 + TCB-2 (NAD-299 (5 μg/0.5 μl icv) and TCB-2 (5 μg/0.5 μl icv) for 30 days). Following the treatment period, rats were subjected to behavioral tests of learning and memory. Then, hippocampal BDNF, amyloid-beta (Aβ) plaque, and neuronal loss were determined by ELISA Kit, Congo red staining, and Nissl staining, respectively.

RESULTS

The results of behavioral tests showed that icv-STZ injection decreased the discrimination index in the novel object recognition (NOR) test. In the passive avoidance learning (PAL) task, icv-STZ injection significantly decreased step-through latency (STLr) and increased time spent in dark compartment (TDC). Treatment with NAD-299, TCB-2, and NAD-299 + TCB-2 attenuated the STZ-induced memory impairment in both NOR and PAL tasks. icv-STZ induced a decrease in hippocampal BDNF levels and increased Aβ plaques production in the brain, whereas treatment with NAD-299, TCB-2, and NAD-299 + TCB-2 reduced Aβ plaques in the brain and increased the hippocampal BDNF level. Results of Nissl staining showed that icv-STZ injection increased neuronal loss in the hippocampus, while treatment with NAD-299, TCB-2, and NAD-299 + TCB-2 reduced hippocampal neurodegeneration.

CONCLUSION

These findings suggest that 5-HT1AR blockade by NAD-299 and 5-HT2AR activation by TCB-2 improve cognitive dysfunction in icv-STZ-treated rats, and these drugs may potentially prevent the progression of AD.

Agmatine attenuates methamphetamine-induced passive avoidance learning and memory and CaMKII-α gene expression deteriorations in hippocampus of rat

Methamphetamine (METH) abuse is one the most worldwide problems with wide-ranging effects on the central nervous system (CNS). Chronic METH abuse can associate with cognitive abnormalities and neurodegenerative changes in the brain. Agmatine, a cationic polyamine, has been proposed as a neuromodulator that modulates many effects of abused drugs. The aim of this study was to determine if agmatine can decrease the impairment effect of METH on memory and hippocampal CaMKII-α gene expression, a gene that plays a major role in memory. Male wistar rats (200-220 g) were allocated into 7 groups, including 5 groups of saline, METH (1, 2 mg/kg), Agmatine (5, 10 mg/kg) and 2 groups of agmatine (5, 10 mg/kg) with higher doses of METH (2 mg/kg) for 5 consecutive days (n = 8 in each group). All injections were done intraperitoneally and agmatine was administrated 10 min before METH treatment. Furthermore, Passive avoidance learning (PAL) test was assessed on the 5th day. Retention test was done 24 h after training and the rats were sacrificed immediately. Hippocampi were removed and stored at -80 °C. Finally, hippocampal CaMKII-α gene expression was measured using Quantitative Real-time PCR. Our data showed that chronic METH dose-dependently impaired PAL retrieval, as it decreased step-through latency (STL) and increased time spent in the dark compartment (TDC). While Agmatine with a higher dose (10 mg/kg) significantly decreased impairment effect of METH (2 mg/kg) on PAL and memory. Also, molecular results revealed that METH (2 mg/kg) markedly decreased hippocampal CaMKII-α gene expression while agmatine (10 mg/kg) co-adminstration prevented it. Taken together, the results propose that agmatine may provide a potential therapy for learning and memory deficits induced by METH.

5-Hydroxytryptamine receptor 6 antagonist, SB258585 exerts neuroprotection in a rat model of Streptozotocin-induced Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory decline. It has been suggested that 5-hydroxytryptamine receptor 6 (5-HT6R) might be involved in AD pathology. The aim of this study was to evaluate the effect of a 5-HT6R antagonist on cognition, learning, memory, and hippocampal apoptosis in an experimental rat model of AD. AD was induced by intracerebroventricular (icv) administration of streptozotocin (STZ; 3 mg/kg, 10 μL, twice). Adult, male rats were divided into the following groups: control, sham, AD (saline treatment, 1 μL icv for 30 days), and AD + SB258585 (5-HT6R antagonist, 1 μg/μL icv for 30 days). Following the treatment period, novel object recognition (NOR) and passive avoidance learning (PAL) tests were conducted to measure cognition, as well as learning and memory, respectively. TUNEL staining was used to evaluate apoptosis in the hippocampus. This study demonstrates that icv STZ injections induce apoptosis in hippocampal cells, decrease the NOR discrimination index, increase the number of trials needed to reach acquisition and the time spent in the dark compartment during PAL, as compared with sham and control groups. Subsequent administration of SB258585 in the STZ treated rats increased the NOR discrimination index, decreased the number of trials till acquisition and the time spent in the dark compartment during PAL, while decreasing neuronal apoptosis, as compared to the untreated AD group. Thus, we conclude that long-term administration of the 5-HT6R antagonist SB258585, ameliorates AD-associated cognitive and behavioral impairments through the suppression of apoptosis in the hippocampus.

The effect of chronic stimulation of serotonin receptor type 7 on recognition, passive avoidance memory, hippocampal long-term potentiation, and neuronal apoptosis in the amyloid β protein treated rat

RATIONALE

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory impairment, neuronal death, and synaptic loss in the hippocampus. Long-term potentiation (LTP), a type of synaptic plasticity, occurs during learning and memory. Serotonin receptor type 7 (5-HTR7) activation is suggested as a possible therapeutic target for AD.

OBJECTIVE

The aim of the present study was to examine the effects of chronic treatment with the 5-HTR7 agonist, AS19, on cognitive function, memory, hippocampal plasticity, amyloid beta (Aβ) plaque accumulation, and apoptosis in an adult rat model of AD.

METHODS

AD was induced in rats using Aβ (single 1 μg/μL intracerebroventricular (icv) injection during surgery). The following experimental groups were included: control, sham-operated, Aβ + saline (1 μL icv for 30 days), and Aβ + AS19 (1 μg/μL icv for 30 days) groups. The animals were tested for cognition and memory performance using the novel object recognition and passive avoidance tests, respectively. Next, anesthetized rats were placed in a stereotaxic apparatus for electrode implantation, and field potentials were recorded in the hippocampal dentate gyrus. Lastly, brains were removed and Aβ plaques and neuronal apoptosis were evaluated using Congo red staining and TUNEL assay, respectively.

RESULTS

Administration of AS19 in the Aβ rats increased the discrimination index of the novel object recognition test. Furthermore, AS19 treatment decreased time spent in the dark compartment during the passive avoidance test. AS19 also enhanced both the population spike (PS) amplitude and the field excitatory postsynaptic potential (fEPSP) slope evoked potentials of the LTP components. Aβ plaques and neuronal apoptosis were decreased in the AS19-treated Aβ rats.

CONCLUSIONS

These results indicate that chronic treatment with a 5-HTR7 agonist can prevent Aβ-related impairments in cognition and memory performance by alleviating Aβ plaque accumulation and neuronal apoptosis, hence improving neuronal plasticity. AS19 may be useful as a therapeutic agent for AD.

CB1 cannabinoid receptor ligands augment the antidepressant-like activity of biometals (magnesium and zinc) in the behavioural tests

OBJECTIVE

During the last few decades, endocannabinoid system has emerged as a novel possible target for antidepressant treatment. Although the medical literature provides information on the mood-changing effects of CB₁ ligands, little is known about the possible interaction between the simultaneous activation or inhibition of the CB₁ receptor and administration of other agents that possess antidepressant potential. The main goal of our study was to evaluate the influence of the CB₁ cannabinoid receptor ligands (oleamide - an endogenous agonist and AM251 - an inverse agonist/antagonist) on the antidepressant-like activity of biometals (i.e. magnesium and zinc).

METHODS

The forced swim test and the tail suspension test in mice were used to determine the antidepressant-like activity.

KEY FINDINGS

Concomitant intraperitoneal administration of per se inactive doses of oleamide (5 mg/kg) or AM251 (0.25 mg/kg) and the tested biometals (i.e. magnesium, 10 mg/kg or zinc, 5 mg/kg) shortened the immobility time of animals in the forced swim test and the tail suspension test. The observed effect was not associated with an increase in spontaneous locomotor activity of mice.

CONCLUSIONS

The simultaneous modulation of the cannabinoid system and supplementation of magnesium or zinc produce at least additive antidepressant-like effect.

Effects of the hydroalcoholic extract of Rosa damascena on learning and memory in male rats consuming a high-fat diet

CONTEXT

High-fat diet (HFD) can cause deficits in learning and memory through oxidative stress and increase Alzheimer disease risk. Rosa damascena Mill. (Rosaceae) extract possesses potent antioxidant properties.

OBJECTIVE

This study investigated the effects of the hydroalcoholic extracts of petals of R. damascena on learning and memory in male rats consuming an HFD.

MATERIALS AND METHODS

Forty male Wistar rats (200-250 g) were randomly assigned to four groups: control, R. damascena extract, HFD and HFD + extract. The extract (1 g/kg bw daily) was administered by oral gavage for 1 month. Animals were allowed free access to high-fat chow for 3 months. The Morris water maze and the passive avoidance learning tests were used to assess learning and memory.

RESULTS

In the passive avoidance learning test, the step-through latencies in the retention test (STLr) of the extract (147.4 ± 23.3) and HFD (150.3 ± 25.2) groups were significantly lower than those of the control group (270.4 ± 10.5) (respectively, p < 0.001 and p < 0.01). STLr was significantly higher in the HFD + extract group (265.3 ± 10.6) than in the HFD group (150.3 ± 25.2) (p < 0.01). Time spent in the dark compartment (TDC) in the HFD + extract group (5.3 ± 2.6) was significantly lower than that in the HFD group (85.8 ± 19.1) (p < 0.05).

DISCUSSION AND CONCLUSION

Our results indicate that, while HFD or R. damascena extract alone leads to memory deficits, R. damascena extract exerted a positive effect on HFD-induced memory deficits. We hypothesize that the observed effects of R. damascena extract are likely due to its strong antioxidant properties.

Resistance training and hawthorn extract ameliorate cognitive deficits in streptozotocin-induced diabetic rats

It has been shown that diabetic rats display cognitive impairment. The aim of this study was to investigate the effects of resistance training and natural antioxidants on learning and memory in type 1 diabetic rats. For this purpose, fifty male Wistar rats were randomly divided into five groups: (i) Control (Con, n=10), (ii) Diabetic (D, n=10), (iii) Diabetic+Resistance training (DRT, n=10), (iv) Diabetic+natural antioxidants (DHE, n=10), and (v) Diabetic+Resistance training+ natural antioxidants (DRH, n=10). Climbing the ladder for a period of 5days/week for 10 consecutive weeks was considered as the resistance training model in our study. Natural antioxidants (100mg/kg per day) were administered to natural antioxidant groups for a period of 10 weeks. Moreover, spatial and passive avoidance learning and memory function were evaluated by Morris Water Maze (MWM) and shuttle box tests. The results showed that, mean of total escape latency decreased 25% (P<0.0001) in the DRH group compared with the D group in MWM. The percentage of time spent in the target quadrant identically decreased (34%) in the D and DHE groups compared with the Con group (p=0.001). In this regard, time spent in the dark Compartment (TDC) respectively rose 86% and 95% in the D and DHE groups compared with the Con group (p<0.05), and decreased 88% in the DRT and DRH groups compared with the D group in the shuttle box test (p<0.05). Furthermore, we noticed that total antioxidant capacity increase and lipid peroxidation decrease in response to the treatments in the diabetic rats as well. Therefore, the current study indicated that exercise training and natural antioxidants synergistically ameliorated learning and memory deficits in type 1 diabetic rats via reducing oxidative stress. Hence, it may propose a potential role of resistance training and natural antioxidants as an adjuvant therapy for the prevention and treatment of diabetic complications.

Effects of Hypericum scabrum extract on learning and memory and oxidant/antioxidant status in rats fed a long-term high-fat diet

A high-fat diet (HFD) causes deficits in learning and memory by increasing oxidative stress. Antioxidants are known to improve learning and memory. Since Hypericum scabrum (H. scabrum) extract is rich in antioxidants, the aim of this study was to investigate the effects of the administration of H. scabrum extract on passive avoidance learning (PAL), novel object recognition (NOR), and locomotor activity in male rats on a HFD. Fifty-four male Wistar rats (weighing 220 ± 10 g) were divided into the following six groups: (1) Control (standard diet), (2) Ext100 (standard diet supplemented with 100 mg/kg extract once/day), (3) Ext300 (standard diet supplemented with 300 mg/kg extract once/day), (4) HFD (high-fat diet), (5) HFD + Ext100, and (6) HFD + Ext300. Rats in these groups were maintained on their respective diets for 3 months. In the PAL test, the step-through latencies in the retention test (STLr) were significantly higher in the HFD + extract group than in the HFD group. The time spent in the dark compartment (TDC) was significantly lesser and the time spent in exploring the novel object was significantly greater in the HFD + extract group than in the HFD group. In the HFD-fed rats, the activity of catalase had significantly decreased, and level of malondialdehyde had significantly increased; H. scabrum extract administration significantly reversed these changes. In conclusion, these results suggested that the administration of H. scabrum extract and its strong antioxidant properties enhanced learning and memory and reversed the memory impairment induced by chronic HFD consumption.

Effects of cannabinoid and vanilloid receptor agonists and their interaction on learning and memory in rats

Despite previous findings on the effects of cannabinoid and vanilloid systems on learning and memory, the effects of the combined stimulation of these 2 systems on learning and memory have not been studied. Therefore, in this study, we tested the interactive effects of cannabinoid and vanilloid systems on learning and memory in rats by using passive avoidance learning (PAL) tests. Forty male Wistar rats were divided into the following 4 groups: (1) control (DMSO+saline), (2) WIN55,212–2, (3) capsaicin, and (4) WIN55,212–2 + capsaicin. On test day, capsaicin, a vanilloid receptor type 1 (TRPV1) agonist, or WIN55,212–2, a cannabinoid receptor (CB1/CB2) agonist, or both substances were injected intraperitoneally. Compared to the control group, the group treated with capsaicin (TRPV1 agonist) had better scores in the PAL acquisition and retention test, whereas treatment with WIN55,212–2 (CB1/CB2 agonist) decreased the test scores. Capsaicin partly reduced the effects of WIN55,212–2 on PAL and memory. We conclude that the acute administration of a TRPV1 agonist improves the rats’ cognitive performance in PAL tasks and that a vanilloid-related mechanism may underlie the agonistic effect of WIN55,212–2 on learning and memory.

The Impact of CB2 Receptor Ligands on the MK-801-Induced Hyperactivity in Mice

It has been known that there is a relationship between cannabis use and schizophrenia-related symptoms; however, it can be a subject of controversy. The involvement of CB1 receptor ligands in the schizophrenia has already been revealed and confirmed. However, there is still lack of information concerning the role of CB2 receptors in the psychosis-like effects in mice and the further studies are needed.The aim of the present research was to study the role of the CB2 receptor ligands in the symptoms typical for schizophrenia. We provoked hyperlocomotion in mice which is analogous to positive psychosis-like effects in humans, by an acute administration of a NMDA receptor antagonist, MK-801 (0.3 and 0.6 mg/kg), a pharmacological model of schizophrenia. An acute administration of MK-801 induced the increase in locomotor activity (hyperactivity) in rodents, measured in actimeters.We revealed that an acute injection of CB2 receptor agonist JWH 133 at the dose range (0.05-1.0 mg/kg) and CB2 receptor antagonist, AM 630 at the dose range (0.1-1.0 mg/kg) decreased locomotion of mice. An acute injection of JWH 133 (2.0 mg/kg) and AM 630 (2.0 mg/kg) had no statistical significant influence on the locomotor activity of mice. However, an acute injection of both CB2 receptor ligands (agonist and antagonist), JWH 133, at the non-effective dose of 2.0 mg/kg and AM 630 at the non-effective dose of 2.0 mg/kg, potentiated the MK-801-induced hyperactivity.The present findings have confirmed that endocannabinoid system, not only via CB1, but also via CB2 receptors, may be involved in the schizophrenia-like responses, including hyperlocomotion in mice.

Endocannabinoid System: the Direct and Indirect Involvement in the Memory and Learning Processes-a Short Review

The endocannabinoid system via cannabinoid (CB: CB1 and CB2) receptors and their endogenous ligands is directly and indirectly involved in many physiological functions, especially in memory and learning processes. Extensive studies reported that this system strictly modulates cognition-related processes evaluated in various animal models. However, the effects of cannabinoids on the cognition have been contradictory. The cannabinoid compounds were able to both impair or improve different phases of memory processes through direct (receptor related) or indirect (non-receptor related) mechanism. The memory-related effects induced by the cannabinoids can be depended on the kind of cannabinoid compound used, dosage, and route of administration as well as on the memory task chosen. Therefore, the objectives of this paper are to review and summarize the results describing the role of endocannabinoid system in cognition, including various stages of memory.

Excess cerebral TNF causing glutamate excitotoxicity rationalizes treatment of neurodegenerative diseases and neurogenic pain by anti-TNF agents

The basic mechanism of the major neurodegenerative diseases, including neurogenic pain, needs to be agreed upon before rational treatments can be determined, but this knowledge is still in a state of flux. Most have agreed for decades that these disease states, both infectious and non-infectious, share arguments incriminating excitotoxicity induced by excessive extracellular cerebral glutamate. Excess cerebral levels of tumor necrosis factor (TNF) are also documented in the same group of disease states. However, no agreement exists on overarching mechanism for the harmful effects of excess TNF, nor, indeed how extracellular cerebral glutamate reaches toxic levels in these conditions. Here, we link the two, collecting and arguing the evidence that, across the range of neurodegenerative diseases, excessive TNF harms the central nervous system largely through causing extracellular glutamate to accumulate to levels high enough to inhibit synaptic activity or kill neurons and therefore their associated synapses as well. TNF can be predicted from the broader literature to cause this glutamate accumulation not only by increasing glutamate production by enhancing glutaminase, but in addition simultaneously reducing glutamate clearance by inhibiting re-uptake proteins. We also discuss the effects of a TNF receptor biological fusion protein (etanercept) and the indirect anti-TNF agents dithio-thalidomides, nilotinab, and cannabinoids on these neurological conditions. The therapeutic effects of 6-diazo-5-oxo-norleucine, ceptriaxone, and riluzole, agents unrelated to TNF but which either inhibit glutaminase or enhance re-uptake proteins, but do not do both, as would anti-TNF agents, are also discussed in this context. By pointing to excess extracellular glutamate as the target, these arguments greatly strengthen the case, put now for many years, to test appropriately delivered ant-TNF agents to treat neurodegenerative diseases in randomly controlled trials.

The Influence of the CB1 Receptor Ligands on the Schizophrenia-Like Effects in Mice Induced by MK-801

A growing body of psychiatric research has emerged, focusing on the role of endocannabinoid system in psychiatric disorders. For example, the endocannabinoid system, via cannabinoid CB (CB1 and CB2) receptors, is able to control the function of many receptors, such as N-methyl-d-aspartate (NMDA) receptors connected strictly with psychosis or other schizophrenia-associated symptoms. The aim of the present research was to investigate the impact of the CB1 receptor ligands on the symptoms typical for schizophrenia. We provoked psychosis-like effects in mice by an acute administration of NMDA receptor antagonist, MK-801 (0.1–0.6 mg/kg). An acute administration of MK-801 induced psychotic symptoms, manifested in the increase in locomotor activity (hyperactivity), measured in actimeters, as well as the memory impairment, assessed in the passive avoidance task. We revealed that an acute injection of CB1 receptor agonist, oleamide (5–20 mg/kg), had no influence on the short- and long-term memory-related disturbances, as well as on the hyperlocomotion in mice, provoking by an acute MK-801. In turn, an amnestic effects or hyperactivity induced by an acute MK-801 was attenuated by an acute administration of AM 251 (0.25–3 mg/kg), a CB1 receptor antagonist. The present findings confirm that endocannabinoid system is able to modify a variety of schizophrenia-like responses, including the cognitive disturbances and hyperlocomotion in mice. Antipsychotic-like effects induced by CB1 receptor antagonist, obtained in our research, confirm the potential effect of CB1 receptor blockade and could have important therapeutic implications on clinical settings, in the future.

Effect of vitamin E on lead exposure-induced learning and memory impairment in rats

Chronic lead (Pb(2+)) exposure has been associated with learning and memory impairments, whereas vitamin E improves cognitive deficits. In this study, using a passive avoidance learning model in rats, we investigated the effects of vitamin E on Pb(2+) exposure-induced learning and memory impairments in rats. In the present study, 56 Wistar male rats (weighting 230-250g) were divided into eight groups (n=7). The Pb(2+) exposure involved gavages of lead acetate solution using three different doses (0.05%, 0.1%, and 0.2%) and the vitamin E consisted of three different doses (10, 25, 50μg/rat) for 30days. After the 30-day period, the rats were tested using a passive avoidance task (acquisition test). In a retrieval test conducted 48h after the training, step through latency (STL) and time in the dark compartment (TDC) were recorded. The statistical analysis of data was performed using ANOVA followed by Tukey's post hoc analysis. In all cases, differences were considered significant if p<0.05. The results of the present study showed that chronic exposure to high doses of Pb(2+) significantly increased both the number of trails required for learning and the TDC, whereas it decreased the STL in the passive avoidance test. Administration of vitamin E ameliorated the effects of Pb(2+) on animal behavior in the passive avoidance learning and memory task. Our results indicate that impairments of learning and memory in Pb(2+)-exposed rats are dose dependent and can be inhibited by antioxidants such as vitamin E.