Acute morphine administration alters the power of local field potentials in mesolimbic pathway of freely moving rats: Involvement of dopamine receptors

Dopaminergic and nitric oxide systems interact to regulate the electrical activity of neurons in the medial septal nucleus in rats

Research characterizing the neuronal substrate of anxiety has implicated different brain areas, including the medial septal nucleus (m-SEPT). Previous reports indicated a role of dopamine and nitric oxide (NO) in anxiety-related behaviors. In this study, the extracellular single-unit recording was performed from the m-SEPT in adult male albino Wistar rats. Baseline activity was recorded for 5 min, and the post-injection recording was performed for another 5 min after the microinjection of each drug. The results showed that (1) both D1- and D2-like receptor agonists (SKF-38393 and quinpirole) enhanced the firing rate of m-SEPT neurons; (2) both D1- and D2-like antagonists (SCH-23390 and sulpiride) attenuated the firing rate of m-SEPT neurons; (3) L-arginine (NO precursor) increased the firing rate of m-SEPT neurons, but a non-specific NOS inhibitor, L-NAME, elicited no significant alterations; (4) the non-specific NOS inhibitor reversed the enhanced firing rate produced by SKF-38393 and quinpirole; (5) neither of the dopaminergic antagonists changed the enhanced activity resulted from the application of the NO precursor. These results contribute to our understanding of the complex neurotransmitter interactions in the m-SEPT and showed that both dopaminergic and NO neurotransmission are involved in the modulation of the firing rate of neurons in the m-SEPT.

Acute morphine administration, morphine dependence, and naloxone-induced withdrawal syndrome affect the resting-state functional connectivity and local field potentials of the rat prefrontal cortex

Opiates are among the widely abused substances worldwide. Also, the clinical use of opioids can cause unwanted and potentially severe consequences such as developing tolerance and dependence. This study simultaneously measured the changes induced after morphine dependence and naloxone-induced withdrawal syndrome on the resting-state functional connectivity (rsFC) and local field potential (LFP) power in the prefrontal cortex of the rat. The obtained results revealed that acute morphine administration significantly increased the LFP power in all frequency bands, as well as the rsFC strength of the prefrontal cortex, and naloxone injection reversed this effect. In contrast, chronic morphine administration reduced neural activity and general correlation values in intrinsic signals, as well as the LFP power in all frequency bands. In morphine-dependent rats, after each morphine administration, the LFP power in all frequency bands and the rsFC strength of the prefrontal cortex were increased, and these effects were further enhanced after naloxone precipitated withdrawal syndrome. The present study concludes that general correlation merely reflects the field activity of the local cortices imaged.

Activation of VTA/CeA/mPFC cannabinoid CB1 receptors induced conditioned drug effects via interacting with hippocampal CAMKII-CREB-BDNF signaling pathway in rats

The present study intended to investigate whether the activation of cannabinoid CB1 receptors of the ventral tegmental area (VTA), the central amygdala (CeA) and the medial prefrontal cortex (mPFC) could induce conditioned place preference or aversion (CPP or CPA) in adult male Wistar rats. The involvement of hippocampal signaling pathway of Ca2+/calmodulin-dependent protein kinase II (CaMKII)/cAMP response element-binding protein (CREB)/brain-derived neurotrophic factor (BDNF) was also examined following a 3-day schedule of conditioning with the injection of arachidonylcyclopropylamide (ACPA; a selective cannabinoid CB1 receptors agonist) into the targeted sites. The results showed that intra-VTA injection of the higher dose of ACPA (5 ng/rat) caused a significant CPP associating with the increased hippocampal level of the phosphorylated (p)-CAMKII/CAMKII. Intra-mPFC injection of ACPA at 3 ng/rat caused a significant CPA associating with the decreased p-CAMKII and p-CREB levels and the increased BDNF level in the hippocampus. Moreover, intra-CeA injection of the ACPA (5 ng/rat) induced a significant CPP which was associated with the increased hippocampal levels of p-CAMKII/total (t) CAMKII, p-CREB/tCREB, and BDNF. Exposing the animals to the CPP apparatus after receiving intra-cerebral vehicle injection increased the hippocampal CAMKII/CREB/BDNF signaling pathway, confirming that CPP is an associative learning task. In all experiments, the conditioning treatment with the different doses of ACPA did not affect locomotor activity in the testing phase. Taken together, it can be concluded that cannabinoid CB1 receptors of the VTA, the CeA, and the mPFC are involved in rewarding/aversion effects through the changes in the hippocampal signaling pathways.

The Antidepressant-Like and Analgesic Effects of Kratom Alkaloids are accompanied by Changes in Low Frequency Oscillations but not ΔFosB Accumulation

Mitragyna speciosa (“kratom”), employed as a traditional medicine to improve mood and relieve pain, has shown increased use in Europe and North America. Here, the dose-dependent effects of a purified alkaloid kratom extract on neuronal oscillatory systems function, analgesia, and antidepressant-like behaviour were evaluated and kratom-induced changes in ΔFosB expression determined. Male rats were administered a low or high dose of kratom (containing 0.5 or 1 mg/kg of mitragynine, respectively) for seven days. Acute or repeated low dose kratom suppressed ventral tegmental area (VTA) theta oscillatory power whereas acute or repeated high dose kratom increased delta power, and reduced theta power, in the nucleus accumbens (NAc), prefrontal cortex (PFC), cingulate cortex (Cg) and VTA. The repeated administration of low dose kratom additionally elevated delta power in PFC, decreased theta power in NAc and PFC, and suppressed beta and low gamma power in Cg. Suppressed high gamma power in NAc and PFC was seen selectively following repeated high dose kratom. Both doses of kratom elevated NAc-PFC, VTA-NAc, and VTA-Cg coherence. Low dose kratom had antidepressant-like properties whereas both doses produced analgesia. No kratom-induced changes in ΔFosB expression were evident. These results support a role for kratom as having both antidepressant and analgesic properties that are accompanied by specific changes in neuronal circuit function. However, the absence of drug-induced changes in ΔFosB expression suggest that the drug may circumvent this cellular signaling pathway, a pathway known for its significant role in addiction.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).

Acute mitragynine administration suppresses cortical oscillatory power and systems theta coherence in rats

BACKGROUND

Mitragynine is the major alkaloid of Mitragyna speciosa (kratom) with potential as a therapeutic in pain management and in depression. There has been debate over the potential side effects of the drug including addiction risk and cognitive decline.

AIMS

To evaluate the effects of mitragynine on neurophysiological systems function in the prefrontal cortex (PFC), cingulate cortex (Cg), orbitofrontal cortex, nucleus accumbens (NAc), hippocampus (HIP), thalamus (THAL), basolateral amygdala (BLA) and ventral tegmental area of rats.

METHODS

Local field potential recordings were taken from animals at baseline and for 45 min following mitragynine administration (10 mg/kg, intraperitoneally). Drug-induced changes in spectral power and coherence between regions at specific frequencies were evaluated. Mitragynine-induced changes in c-fos expression were also analyzed.

RESULTS

Mitragynine increased delta power and reduced theta power in all three cortical regions that were accompanied by increased c-fos expression. A transient suppression of gamma power in PFC and Cg was also evident. There were no effects of mitragynine on spectral power in any of the other regions. Mitragynine induced a widespread reduction in theta coherence (7-9 Hz) that involved disruptions in cortical and NAc connectivity with the BLA, HIP and THAL.

CONCLUSIONS

These findings show that mitragynine induces frequency-specific changes in cortical neural oscillatory activity that could potentially impact cognitive functioning. However, the absence of drug effects within regions of the mesolimbic pathway may suggest either a lack of addiction potential, or an underlying mechanism of addiction that is distinct from other opioid analgesic agents.