Low Current Intensity Plus an Ineffective Dose of Morphine Affect Conditioning Place Preference Through Different Pathways in the Lateral Habenula

Background

The involvement of lateral habenula and the ineffective dose of morphine on reward-related learning and memory is less well-known. This study looked into the effects of electrical stimulation, GABAB receptor blockade, and a combination of both with morphine on conditioned place preference.

Materials and Methods

In this experiment, male rats were anesthetized with ketamine/xylazine (six rats in each group). A 5-day biased conditioned place preference paradigm was used for the behavioral test. The effects of electrical stimulation and phaclofen plus a low dose of morphine on the acquisition and expression phases were examined during conditioning sessions and before the test phase, respectively.

Results

The conditioning scores were reduced by antagonist injection during the acquisition phase. Interestingly, different intensities exhibited opposite effects on the acquisition phase. Conditioned place preference scores during the acquisition phase were significantly induced by 25 μA electrical stimulation, while conditioning scores were suppressed by electrical stimulation at 150 μA. Phaclofen (2 μg/rat) combined with high intensity induced aversion during the acquisition phase, while inhibiting expression. In contrast, high intensity with phaclofen (1 μg/rat) inhibited only the acquisition session. However, low intensity during the acquisition phase had an additive effect that was prevented by pretreatment with phaclofen (2 μg/rat), but this response was modified by the antagonist's low dose.

Conclusions

A behavioral technique called conditioned place preference is frequently used to evaluate learning that is related to rewards. Therefore, lateral habenula electrical stimulation and phaclofen plus morphine could affect place preference through the involvement of the reward system.

The effect of medial prefrontal cortex electrical stimulation on passive avoidance memory in healthy and addict rats

BACKGROUND

The medial prefrontal cortex (mPFC) is a part of brain reward system involved in cognitive functions such as learning and memory. The mPFC receives strong dopaminergic innervations from ventral tegmental area (VTA) that comprises a portion of the mesolimbic dopaminergic system (MLDS), and sends glutamatergic projections to both the VTA and nucleus accumbens (NAc).

MATERIALS AND METHODS

In this study, male Wister rats weighing 250-350 g were used. The effect of medial prefrontal cortex (mPFC) electrical stimulation with different current intensities (25, 50,100, and 150 μA) in healthy and addicted rats on passive avoidance memory was studied here.

RESULTS

This study showed that 25 and 150 μA had no effect on improving avoidance memory in rats. Current intensities of 50 and 100 μA differ significantly with 25 and 150 μA. The PL of mPFC contributes to memory processing.

CONCLUSIONS

The electrical stimulations of prelimbic with 50 and 100 μA current intensities were improved avoidance memory in addicted rats while learning impairment is caused in healthy rats while the electrical stimulation with these used current intensities.

Neuroprotective effects of Rosa damascena extract on learning and memory in a rat model of amyloid-β-induced Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disease, which is characterized clinically by serious impairment in memory and cognition. Current medications only slow down the dementia progression and the present treatment one-drug one-target paradigm for anti-AD treatment appears to be clinically unsuccessful. Therefore, alternative therapeutic strategies are urgently needed. With respect to multifunctional and multitargeted characteristics of Rosa damascena via its effective flavonoids, we investigated the effects of R. damascena extract on behavioral functions in a rat model of amyloid-β (A-β)-induced Alzheimer's disease.

MATERIALS AND METHODS

After preparation of the methanolic extract of the R. damascena, HPLC analysis and toxicity studies, median lethal dose (LD50) and dose levels were determined. For evaluation of baseline training behavioral performance, Morris water maze and passive avoidance tests were used. A-β was injected bilaterally into CA1 area of the hippocampus. Twenty-one days after injection of A-β, the first probe trial of the behavioral tests were used to confirm learning and memory impairment. To examine the potential effects of the extract on behavioral tasks, the second probe trials were performed after one month administration of R. damasena extract.

RESULTS

Results showed that the R. damascena extract significantly improved the spatial and long-term memories in the extract- treated groups in a dose-dependent manner, as in the middle and high doses it had significant effect.

CONCLUSION

According to these results, we concluded that R. damascena can reverse behavioral deficits caused by A-β, and may provide a new potential option for prevention and treatment of the cognitive dysfunction in Alzheimer's disease.

The effect of vitamin C on morphine self-administration in rats

BACKGROUND

Recent studies have shown that addiction may be caused by abnormality of neurotransmission in the brain. Two neurotransmitters that involve into morphine addiction are dopamine and glutamate. The glutamatergic and dopaminergic systems are also involved in morphine tolerance and morphine withdrawal syndrome signs. Ascorbic acid (AA), as the antioxidant releases from the glutamatergic neurons, modulates the action of the dopamine and glutamate systems. In this study, the effect of AA on morphine self-administration and morphine withdrawal symptoms has been investigated.

MATERIALS AND METHODS

Male Wistar rats (250 - 300g) were anesthetized with ketamine (11%) and xailazine (15%). The cannula was inserted into the right jugular vein, and it was fixed subcutaneously on the skull. After surgery the animals were placed in individual home cages, and they were allowed to recover from the operation for five days, before the test. The animals were subjected to self-administration morphine for12 consecutive days, two-hour/sessions. The number of infusions and number of active and passive lever pressings were recorded.

RESULTS

An intra peritoneal injection of Ascorbic acid (AA) (400 mg/kg, i.p.), 30 minutes before morphine self-administration, produced a significant decrease in 12 days self-administration of morphine and withdrawal syndrome signs (P < 0.05). The morphine withdrawal signs (MWS) were recorded after naloxone precipitation, which decreased significantly with the injection of AA (400,700mg/kg), (<0.05). The number of self-infusions and the number of active lever pressings had significantly decreased after AA injection (P < 0.05).

CONCLUSION

The chronic administration of AA may prevent the development of tolerance and physical dependence on morphine self-administration via the glutamatergic system.

Effect of Physical Activity on Symptoms of Morphine Addiction in Rats, after and before of Lesion of the mPFC Area

OBJECTIVE(S)

Drug addiction is one of the fastest growing social problems that researchers, for many years, have been trying to find proper strategies for its prevention and treatment. Short-term physical activity is considered as acceptable for the treatment and prevention of addiction. On the other hand, prefrontal cortex is known to be responsible for many of the complex behavioral responses, especially those relevant to addiction and drug abuse. In this study, the effects of short-term physical activity (treadmill running) on withdrawal symptoms in rats, with or without medial Prefrontal Cortex (mPFC) area was evaluated.

MATERIALS AND METHODS

In this experimental study, male Wistar rats, weighing 250-300 g. Were selected and divided into four groups: control, sham, test1 and test 2 groups, with one group having a surgery (test 2). In order to study the effects of short-term physical activity, we employed a treadmill with the adjustable speed of 17 m/min, and a 15% incline. Following the injection of three different doses of morphine (10, 20 and 40 mg/Kg) for 9 days, treadmill running was completed on the tenth day and then the symptoms of addiction were evaluated.

RESULTS

Administration of morphine as aforementioned, and treadmill running on rats with mPFC area, significantly alleviated some of the symptoms and signs, such as, bruxism, cycling, body lift, licking, standing and scratching (P<0.05). Therefore, there are noticeable differences in these symptoms between the exercise and morphine groups (P<0.05). Conclusion : We propose that when using morphine mPFC plays an important role in the reduction of reward symptoms. Running lessens the effects of morphine. Moreover, short-term physical activity might decrease the tendency to use morphine in those with mPFC area, compared to other groups, especially with the one undergoing an mPFC operation.

Effects of microinjection of angiotensin II and captopril to VTA on morphine self-administration in rats

The dopaminergic mesolimbic system is considered to be crucial in rewarding actions of opiates. Recent studies have suggested probable interaction between the renin-angiotensin and mesolimbic dopaminergic systems. The present study was undertaken to investigate the effects of Ang II and captopril injection into VTA on morphine self-administration. Male Wistar rats were initially trained to receive small pellets of food by pressing the active lever in self-administration apparatus. The animals were divided into 4 groups (saline, morphine, captopril and Ang II) and were placed in self-administration apparatus and allowed to self-administer morphine (0.5 mg per infusion all test groups) or saline (saline group) during consecutive days, for 2 h/sessions. Captopril (30 mug) and Ang II (0.25 nmol) were injected into the VTA in the corresponding groups before each session. The numbers of active and passive levers pressed in each group have been recorded. The number of active lever pressing of morphine group was significantly higher than saline group (p < 0.001). In Ang II group, the number of active lever pressing was significantly lower than morphine group (p < 0.01). This study suggests the probable interaction between Ang II and opioid system in the VTA.

Effects of microinjection of angiotensin II and captopril into nucleus accumbens on morphine self-administration in rats

With an aim to investigate the effects of injection of angiotensin II (Ang II) and captopril into the nucleus accumbens (NAC) on morphine self-administration, male Wistar rats were first trained to receive small pellets of food by pressing the active lever in self-administration apparatus. The animals, divided into 4 groups (saline, morphine, captopril and Ang II) were placed in self-administration apparatus and were allowed to self-administer morphine (0.5 mg per infusion all test groups) or saline (saline group) during consecutive days, for 2 h/sessions. Captopril (30 microg) and Ang II (0.25 nM) were injected into NAC in the corresponding groups before each session. In morphine group, the number of active lever pressing was significantly higher than passive during all 5 days and was also significantly higher than saline group. In captopril group, there were no significant differences between the number of active and passive lever pressings. However, the number of active lever pressing was significantly lower than morphine group. The results highlight the interaction between captopril and opioid system in NAC.