Effect of electrical stimulation of nucleus accumbens with low, median and high currents intensities on conditioned place preference induced by morphine in rats

Non-invasive temporal interference brain stimulation reduces preference on morphine-induced conditioned place preference in rats

Long-term use of opioid drugs such as morphine can induce addiction in the central nervous system through dysregulation of the reward system of the brain. Deep brain stimulation (DBS) is a non-pharmacological technique capable of attenuating behavioral responses associated with opioid drug consumption and possesses the capability to selectively activate and target localized brain regions with a high spatial resolution. However, long-term implantation of electrodes in brain tissue may limit the effectiveness of DBS due to changes in impedance, position, and shape of the tip of the stimulation electrode and the risk of infection of nerve tissue around the implanted electrode. The main objective of the current study is to evaluate the effect of temporal interference (TI) brain stimulation on addictive behaviors of morphine-induced conditioned place preference (CPP) in rats. TI stimulation is a non-invasive technique used transcranially to modulate neural activity within targeted brain regions. It involves applying two high-frequency currents with slightly different frequencies, resulting in interference and targeted stimulation of different brain areas with the desired spatial resolution. The results indicated that TI stimulation with the amplitude ofI 1 = I 2 = 0.5 mA, carrier frequency of 2 kHz, frequency difference of 25 Hz, ON-OFF stimulation frequency of 0.25 Hz, and total duration of 10 min in three consecutive days resulted in a significant reduction of morphine preference in the morphine-stimulation group in comparison with the morphine group (p < 0.001). These findings highlight the potential of TI stimulation as a modulatory intervention in mitigating the addictive properties of morphine and provide valuable insights into the therapeutic implications of this stimulation paradigm for treatment of opioid drugs in human subjects.

The electrical stimulation of the central nucleus of the amygdala in combination with dopamine receptor antagonist reduces the acquisition phase of morphine-induced conditioned place preference in male rat

Background and purpose

The central nucleus of the amygdala (CeA) is one of the nuclei involved in the reward system. The aim of the current study was to investigate the electrical stimulation (e-stim) effect of the CeA in combination with dopamine D1 receptor antagonist on morphine-induced conditioned place preference (CPP) in male rats.

Experimental approach

A 5-day procedure of CPP was used in this study. Morphine was administered at an effective dose of 5 mg/kg, and SCH23390 as a selective D1 receptor antagonist was administrated into the CeA. In addition, the CeA was stimulated with an intensity of the current of 150 μA. Finally, the dependence on morphine was evaluated in all experimental groups.

Findings/Results

Morphine significantly increased CPP. While the blockade of the D1 receptor of the CeA reduced the acquisition phase of morphine-induced CPP. Moreover, the combination of D1 receptor antagonist and e-stim suppressed morphine-induced CPP, even it induced an aversion.

Conclusion and implication

The current study suggests that the administration of dopamine D1 receptor antagonist into the CeA in combination with e-stim could play a prominent role in morphine dependence.

Deep brain stimulation of the lateral hypothalamus to block morphine reward: Does the intensity of stimulation matter?

It has been shown that high-frequency deep brain stimulation (DBS) of the lateral hypothalamus (LH) prevents morphine-induced conditioned place preference (CPP) in rats. However, our previous study demonstrated that the application of DBS at 150 µA did not block morphine CPP in all rats. Here, we investigated the possibility to completely block morphine CPP by increasing the intensity of LH DBS. Morphine reward was assessed by the CPP paradigm in male Wistar rats. DBS was applied in the LH during the conditioning trials with morphine (5 mg/kg, S.C.) at 130 Hz pulse frequency, 100 µs pulse duration, and either 150 µA or 200 µA pulse amplitude. Results showed that repeated morphine injections produced a robust CPP that was blocked partially by DBS at 150 µA and completely by DBS at 200 µA. Response rate was 47% with 150-µA and 100% with 200-µA stimulation. DBS treatment was not associated with changes in motor activity. In conclusion, the development of morphine reward was modulated by LH DBS in an intensity-dependent manner.

Effect of electrical stimulation of central nucleus of the amygdala on morphine conditioned place preference in male rats

Objectives

The central nucleus of the amygdala (CeA) is one of the most important areas for the morphine reward system. This study investigated the effect of electrical stimulation of CeA on morphine conditioned place preference (CPP) in male rats.

Materials and Methods

After anesthetizing male Wistar rats, both electrode and cannula were implanted into CeA for stimulating (low intensity: 25 μA, and high intensity: 150 μA) and injecting (lidocaine and dopamine D2 receptor antagonist), respectively. Then, CPP induced by effective (5 mg/kg) and ineffective (0.5 mg/kg) doses of morphine was evaluated for five consecutive days (n = 6 / group).

Results

The low electrical stimulation intensity of 25 μA suppressed both acquisition and expression phases, but the high intensity of 150 µA attenuated only the expression phase. On the other hand, intra-CeA administration of dopamine D2 receptor antagonist, eticlopride (2 µg/rat), with the effective dose of morphine, decreased CPP. In addition, infusion of lidocaine into the CeA inhibited morphine-induced CPP in both acquisition and expression phases with the effective dose of morphine.

Conclusion

Electrical stimulation of the CeA may play an important role in attenuating morphine induced CPP via possible changes in neurotransmitters involved in the reward system such as dopamine (DA) and gamma-aminobutyric acid (GABA).

Extended amygdala, conditioned withdrawal and memory consolidation

Opioid withdrawal can be associated to environmental cues through classical conditioning. Exposure to these cues can precipitate a state of conditioned withdrawal in abstinent subjects, and there are suggestions that conditioned withdrawal can perpetuate the addiction cycle in part by promoting the storage of memories. This review discusses evidence supporting the hypothesis that conditioned withdrawal facilitates memory consolidation by activating a neurocircuitry that involves the extended amygdala. Specifically, the central amygdala, the bed nucleus of the stria terminalis, and the nucleus accumbens shell interact functionally during withdrawal, mediate expression of conditioned responses, and are implicated in memory consolidation. From this perspective, the extended amygdala could be a neural pathway by which drug-seeking behaviour performed during a state of conditioned withdrawal is more likely to become habitual and persistent.

Effect of intracerebroventricular injection of GABA receptors antagonists on morphine-induced changes in GABA and GLU transmission within the mPFC: an in vivo microdialysis study

Objective(s):

Many studies have focused on ventral tegmental area than of other mesocorticolimbic areas, and implicated a key role for the medial prefrontal cortex (mPFC) in the development of addictive behaviors. So far, the role of gamma-aminobutyric acid (GABA) receptors in the discriminative properties of morphine has received little attention and few studies evaluated the role of these receptors in drug dependence. Hence, we investigated the role of this receptor on morphine- induced GABA/ glutamate (GLU) changes in the mPFC following morphine administration using in vivo microdialysis.

Materials and Methods:

In this study, 60 rats weighing 270-300 g were divided into six groups. First, microdialysis probe was inserted into the mPFC and was perfused with artificial cerebrospinal fluid and collected the baseline samples in all groups. In saline and morphine groups, the saline, in phaclophen and (phaclofen+morphine) groups, phaclofen (100 nmol), and in bicuculline and (bicuculline+morphine) groups, bicuculline (20 nmol) was injected intracerebroventricular. In saline, phaclofen and bicuculline groups 20 min later, animals received saline (0.2 ml, IP) and others groups received morphine (20 mg/kg, IP).

Results:

Our results showed that morphine increased the average concentration of GABA and decreased the concentration of GLU within mPFC. Pretreatment with phaclofen and bicuculline 20 min before morphine administration had no effect on GABA and GLU release for 100 min.

Conclusion:

The present study indicated that morphine influence the GABA and GLU transmission in mPFC. Therefore evaluation of neurochemistry changes of this neural circuitry may provide further insight into the mechanisms underlying drug dependence.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.