Hippocampal D1-like dopamine receptor as a novel target for the effect of cannabidiol on extinction and reinstatement of methamphetamine-induced CPP.

Methamphetamine (METH) is a major health problem without effective pharmacological treatment. Cannabidiol (CBD), a component of the Cannabis sativa plant, is believed to have the potential to inhibit drug-related behavior. However, the neurobiological mechanisms responsible for the effects of CBD remain unclear. Several studies have proposed that the suppressing effects of CBD on drug-seeking behaviors could be through the modulation of the dopamine system. The hippocampus (HIP) D1-like dopamine receptor (D1R) is essential for forming and retrieving drug-associated memory. Therefore, the present study aimed to investigate the role of D1R in the hippocampal CA1 region on the effects of CBD on the extinction and reinstatement of METH-conditioned place preference (CPP). For this purpose, different groups of rats over a 10-day extinction period were administered different doses of intra-CA1 SCH23390 (0.25, 1, or 4 µg/0.5 µl, Saline) as a D1R antagonist before ICV injection of CBD (10 µg/5 µl, DMSO12%). In addition, a different set of animals received intra-CA1 SCH23390 (0.25, 1, or 4 µg/0.5 µl) before CBD injection (50 µg/5 µl) on the reinstatement day. The results revealed that the highest dose of SCH23390 (4 µg) significantly reduced the accelerating effects of CBD on the extinction of METH-CPP (P < 0.01). Furthermore, SCH23390 (1 and 4 µg) in the reinstatement phase notably reversed the preventive effects of CBD on the reinstatement of drug-seeking behavior (P < 0.05 and P < 0.001, respectively). In conclusion, the current study revealed that CBD made a shorter extinction period and suppressed METH reinstatement in part by interacting with D1-like dopamine receptors in the CA1 area of HIP.

The role of orexin receptors within the CA1 area in the acquisition and expression of methamphetamine place preference.

Treatment of Methamphetamine (METH) use disorder has become a crucial public health issue. The orexin system manipulation has provided promising evidence to attenuate addictive-like behaviors. This study explored the role of the orexin 1 receptor and orexin 2 receptor (OX1R and OX2R) in the CA1 area of the hippocampal formation in the acquisition and expression of METH-induced place preference. Animals were subjected to bilateral administration of different dosages (1, 3, 10, and 30 nmol/0.5 µl DMSO per side) of a selective OX1R antagonist, SB334867, or selective OX2R antagonist, TCS OX2 29 into the CA1 area throughout the conditioning phase or once on the post-conditioning phase in separate control and experimental groups. Behavioral data revealed that both OX1R (10 nmol; P < 0.01 and 30 nmol; P < 0.001) and OX2R (10 nmol; P < 0.05 and 30 nmol; P < 0.001) antagonism during the conditioning phase could block the formation of METH place preference dose-dependently. In addition, intra-CA1 microinjection of SB334867 on the post-conditioning phase attenuated the expression of METH place preference in a dose-dependent manner (3 nmol; P < 0.05, 10 nmol; P < 0.01 and 30 nmol; P < 0.001) whereas intra-CA1 administration of TCS OX2 29 only at the highest dosage (30 nmol) declined the expression of METH place preference (P < 0.01). It was also indicated that the suppressive effects of orexin receptor blockade on the METH-seeking behavior in the CA1 area were anatomically specific to this area. These findings support the possibility of targeting the orexin system to develop novel and successful pharmacological options for the treatment of METH dependence.

Blocking the dopaminergic receptors within the hippocampal dentate gyrus reduced analgesic responses induced by restraint stress in the formalin test.

Previous studies have shown that various receptors, including dopamine receptors, are expressed in the hippocampal dentate gyrus (DG). Besides, indicatively, dopamine receptors play an essential role in the modulation of pain perception. On the other hand, stressful experiences can produce analgesia, termed stress-induced analgesia (SIA). The current study examined the probable role of dopamine receptors within the DG in antinociception induced by restraint stress (RS). Ninety-seven male albino Wistar rats were unilaterally implanted with a cannula in the DG. Animals received intra-DG microinjections of SCH23390 or Sulpiride (0.25, 1, and 4 µg/rat) as D1-and D2-like dopamine receptor antagonists, respectively, five minutes before RS. Ten minutes after the end of the induction of RS for three hours, 50 µl 2.5% formalin was injected subcutaneously into the plantar surface of the hind paw to induce persistent inflammatory pain. Pain scores were evaluated at 5-minute intervals for 60 minutes. These findings showed that; exposure to RS for three hours produced SIA in both phases of the formalin test, while this RS-induced analgesia was attenuated in the early and late phases of the formalin test by intra-DG microinjection of SCH23390 and Sulpiride. The results of the present study suggested that both D1- and D2-like dopamine receptors in the DG have a considerable role in the induced analgesia by RS.

The inhibitory effect of cannabidiol on the rewarding properties of methamphetamine in part mediates by interacting with the hippocampal D1-like dopamine receptors.

Cannabidiol (CBD) is a potential treatment to decrease the rewarding properties of psychostimulants. However, the exact mechanism and distinct neuroanatomical areas responsible for the CBD's effects remain unclear. Indicatively, the D1-like dopamine receptors (D1R) in the hippocampus (HIP) are essential for expressing and acquiring drug-associated conditioned place preference (CPP). Therefore, given that involving D1Rs in reward-related behaviors and the encouraging results of CBD in attenuating the psychostimulant's rewarding effects, the present study sought to investigate the role of D1Rs of the hippocampal dentate gyrus (DG) in the inhibitory effects of CBD on the acquisition and expression of METH-induced CPP. To this end, over a 5-day conditioning period by METH (1 mg/kg; sc), different groups of rats were given intra-DG SCH23390 (0.25, 1, or 4 µg/0.5 µl, saline) as a D1Rs antagonist before ICV administration of CBD (10 µg/5 µl, DMSO12%). In addition, a different set of animals, after the conditioning period, received a single dose of SCH23390 (0.25, 1, or 4 µg/0.5 µl) before CBD (50 µg/5 µl) administration on the expression day. The results showed that SCH23390 (1 and 4 µg) significantly reduced the suppressive effects of CBD on the acquisition of METH place preference (P < 0.05 and P < 0.001, respectively). Furthermore, the highest dose of SCH23390 (4 µg) in the expression phase remarkably abolished the preventive effects of CBD on the expression of METH-seeking behavior (P < 0.001). In conclusion, the current study revealed that CBD's inhibitory effect on rewarding properties of METH partially acts through D1Rs in the DG area of the HIP.

Distinct roles for orexin-1 and orexin-2 receptors in the dentate gyrus of the hippocampus in the methamphetamine-seeking behavior in the rats.

Because of the relapsing properties of psychostimulants such as methamphetamine (Meth), there is no established pharmacotherapy for Meth addiction. The orexinergic system is a promising target for treating psychostimulant use disorders and relapse. However, to the best of our knowledge, no investigation regarding the role of orexin receptors in the dentate gyrus (DG) region of the hippocampus has been conducted in the extinction and reinstatement of Meth-seeking behavior. Two stainless-steel guide cannulae were bilaterally implanted into the DG of the rats' brains. The unbiased conditioned place preference (CPP) procedure was conducted to induce Meth conditioning. Following the five days Meth injections (1 mg/kg; sc), animals received intra-DG microinjection of SB334867 or TCS OX2 29, as orexin 1 (OX1) or orexin 2 (OX2) receptor antagonists, respectively (without Meth administration) during extinction phase to elucidate the role of orexin receptors in the latency of the extinction period in the Meth-conditioned rats. To evaluate the role of orexin receptors in the DG region in the reinstatement of Meth-seeking behavior, the extinguished rats received SB334867 or TCS OX2 29 before injecting a priming dose of Meth (0.25 mg/kg; sc). The results indicated two distinct roles for the OX1 and OX2 receptors in the DG region. TCS OX2 29 attenuated the extinction latency, and SB334867 considerably reduced the reinstatement of Meth-seeking behavior in this region. Therefore, the DG region's orexinergic system might be a potential therapeutic target for psychostimulant use disorders.

Compensatory Role of Insulin in the Extinction but Not Reinstatement of Morphine-Induced Conditioned Place Preference in the Streptozotocin-Induced Diabetic Rats.

Insulin receptors are distributed in the whole brain, including different parts of the reward circuit that modulate dopamine as the primary neurotransmitter implicated in addiction. The goal of the current study was to illuminate the role of insulin in the extinction period and reinstatement of morphine-induced conditioned place preference (CPP) in the naïve and diabetic rats. One hundred and twelve male rats were randomly divided into two naïve and diabetic groups. Diabetes was induced by one dose administration of streptozotocin (STZ; 60 mg/kg; IP) ten days before the conditioning procedure. To evaluate the insulin's role in the duration of extinction period of morphine-CPP, naïve and diabetic rats received insulin (10 U/kg; IP) before each morphine injection (5 mg/kg; sc) during the 3-day conditioning phase. All rats that passed the conditioning phase and then underwent the extinction period. Morphine priming-induced reinstatement was determined in both naïve and diabetic rats by injection of different ineffective doses of morphine (0.5 and 1 mg/kg; sc) in extinguished rats. In the following experiments, three groups of diabetic rats received insulin during the conditioning, expression, or reinstatement phase to illustrate insulin's effect on the morphine-induced reinstatement and the duration of the extinction period (insulin was only treated during the acquisition phase). The results showed that the extinction period and reinstatement of morphine were potentiated in the STZ-induced diabetic rats. The obtained findings also revealed that insulin replacement shortened the extinction period of morphine-induced CPP in STZ-diabetic rats. However, insulin replacements in conditioning, expression, and reinstatement phases did not affect morphine priming-induced reinstatement in diabetic animals.

Elastic resistance training is more effective than vitamin D3 supplementation in reducing oxidative stress and strengthen antioxidant enzymes in healthy men.

OBJECTIVE: Today, reducing oxidative stress and improving the antioxidant system with antioxidant supplements along with exercise training has received a lot of attention. Vitamin D plays a very important role in general health and reducing oxidative stress. The aim of this study was to examine the effect of vitamin D3 supplements during elastic-band resistance training (EBT) on oxidative stress and antioxidant indices in healthy men. METHODS: Forty healthy men (Serum: 20 ≤ 25 (OH) D ≤ 25 ng/mL) voluntarily participated in the current study and randomly were assigned to EBT-vitamin D3 (ED, n = 10), EBT-placebo (EP, n = 10), vitamin D3 (VD, n = 10), and control (Con, n = 10). EBT was performed three times per week on non-consecutive days for eight weeks, in seven exercises. The subjects in the ED, VD, and EP consumed 50,000 IU vitamin D3 or placebo once every 2 weeks. Ten ccs blood samples were collected before and after exercise training and the total antioxidant capacity (TAC), superoxide dismutase (SOD), glutathione peroxidase (GPX), and creatine kinase (CK) activities were measured in the plasma. Malondialdehyde (MDA), as the lipid peroxidation index, and 25(OH) D were measured in the plasma. RESULTS: We found that there was a significant difference between ED with VD (p = 0.011) and Con (p = 0.022) for MDA. A significant difference was also seen for SOD in ED with VD (p = 0.024) and Con (p = 0.038) and TAC in ED with VD (p = 0.020) and Con (p = 0.030), and GPX in ED with VD (p = 0.040) and Con (p = 0.010). While there were no significant differences between ED and EP in all mentioned variables (p > 0.05). CONCLUSION: Finally, it can be said that elastic resistance training improved antioxidant defence. However, vitamin D3 supplementation during resistance elastic training has no synergistic effect on attenuating oxidative stress indices.

Insulin replacement prevents the acquisition but not the expression of morphine-induced conditioned place preference in streptozotocin-induced diabetic rats

Abstract Insulin receptors have distributed in all brain regions, including the nucleus Accumbens (NAc), and where is implicated in the reward properties of drugs. It is well known that insulin signaling can regulate dopamine release. Therefore, in the present study, we tried to examine the effect of insulin replacement on the acquisition and expression of morphine-induced conditioned place preference (CPP) in diabetic rats. Forty-eight male Wistar rats were divided into two non-diabetic (Naïve) and diabetic groups rendered by a single injection of streptozotocin (STZ). These groups separately received insulin (10U/kg) or saline (1 ml/kg) one hour prior to morphine administration (5mg/kg;s.c.) during conditioning days (acquisition phase) or post-conditioning day (expression phase) in the CPP paradigm. In this paradigm, conditioning score (CS) and locomotion activity were recorded by Ethovision. The STZ-induced diabetic rats displayed higher CS compared to naïve rats (P<0.05). This effect was abolished in all diabetic rats that received insulin during conditioning days but not the expression phase. This study has provided evidence that insulin plays a modulatory role in morphine-induced CPP, and insulin replacement during the acquisition phase could reduce the rewarding properties of morphine in diabetes conditions through a possible modulating effect on dopamine release in the NAc region

Effects of dopamine D1- and D2-like receptors in the CA1 region of the hippocampus on expression and extinction of morphine-induced conditioned place preference in rats.

Considering the extent of drug use and its relapse rate worldwide, in the present study, we explored the role of intra-CA1 administration of D1-like and D2-like receptor antagonists on the expression and extinction of morphine-induced CPP. To induce morphine CPP, adult male Wistar rats received a daily subcutaneous injection of morphine (5 mg/kg) during a 3-day conditioning phase. Different doses of SCH23390 (0.25, 1 or 4 µg/0.5 µl saline), as a selective D1-like receptor antagonist, and sulpiride (0.25, 1, or 4 µg/0.5 µl DMSO), as a selective D2-like receptor antagonist, were bilaterally microinjected into the CA1 region in the expression and extinction phases 1 h before CPP evaluation. Conditioning scores and locomotor activities were recorded during the tests. Results indicated that the injection of the antagonists into the CA1 region dose-dependently attenuated the expression of the morphine-induced CPP and sulpiride revealed prominent behavioral results compared to SCH23390 in the expression phases. Furthermore, microinjections of SCH23390 and sulpiride shortened the extinction phase of the morphine-induced CPP without changing the locomotor activity. The results indicated the involvement of D1- and D2-like receptors within the CA1 region in the expression and extinction of rewarding properties of morphine.

Role of Orexin-1 Receptor Within the Ventral Tegmental Area in Mediating Stress- and Morphine Priming-induced Reinstatement of Conditioned Place Preference in Rats.

INTRODUCTION: Orexin-containing neurons exist in the lateral hypothalamic region, sending their projections toward mesolimbic regions such as the Ventral Tegmental Area (VTA). METHODS: In the current study, a Reinstatement model is used to examine the effects of intra-VTA administration of SB334867 as an Orexin-1 Receptor (OX1R) antagonist on drug priming- and Forced Swim Stress (FSS)-induced reinstatement of morphine. Eighty-eight male adult albino Wistar rats, weighing 200-280 g, were bilaterally implanted by cannulas into the VTA. We induced the Conditioned Place Preference (CPP) by Subcutaneous (SC) injection of morphine (5 mg/kg) daily in three days. Then, the CPP score was calculated. After a 24-h "off" period following achievement of extinction criterion, the rats were tested for drug priming-induced reinstatement by a priming dose of morphine (1 mg/kg, SC) and for FSS-induced reinstatement 10 min after FSS. In the next experiments, the animals received different doses of intra-VTA administration of SB334867 (0.3, 3, and 1 nM/0.3 µL 12% DMSO per side) and bilaterally were subsequently tested for FSS- and morphine priming-induced reinstatement. RESULTS: Our findings indicated that the FSS could induce the reinstatement of seeking behaviors. Furthermore, intra-VTA administration of OX1R antagonists suppressed FSS- and drug priming-induced reinstatement dose-dependently. CONCLUSION: It is concluded that FSS and drug priming-induced reinstatement might be mediated, at least in part, by stimulation of orexin receptors in the VTA.

Involvement of orexinergic receptors in the nucleus accumbens, in the effect of forced swim stress on the reinstatement of morphine seeking behaviors.

Orexinergic system is involved in primary rewards; the neural circuit of the ventral tegmental area (VTA), nucleus accumbens (NAc), prefrontal cortex and amygdala represents overlapping elements mediating the rewarding effects of drugs and stressful experiences. The NAc integrates reward-related information from the VTA. Also, it has been indicated that orexinergic system activates the mesolimbic dopamine projecting neurons to the NAc and promotes the development of reward in rodents. Therefore, in the present study, the conditioned place preference (CPP) paradigm was used to determine the role of the two types of orexin receptors (OXR) in the NAc in forced swim stress (FSS), as physical stress, and/or priming-induced reinstatement of morphine. The CPP was induced by injecting morphine (5 mg/kg, SC for 3 days) and lasted for eight free-morphine days; the reinstatement was induced by administration of effective priming dose of morphine (1 mg/kg; sc). The extinguished rats received intra-NAc injection of SB334867 as OX1R antagonist or TCSOX229 as OX2R antagonist before effective priming dose injection of morphine (1 mg/kg; sc). In others, the extinguished rats were given intra-NAc injection of SB334867 or TCSOX229 and then, they underwent FSS before injection of ineffective priming dose of morphine (0.5 mg/kg; sc). Our results showed that intra-accumbal administration of SB334867 or TCSOX229 could inhibit morphine priming- and FSS-induced reinstatement of extinguished morphine-seeking in the rats. It seems that OXR in the NAc may be involved in reward and could play an important role in the effect of stress on reinstatement of morphine-seeking behaviors in this area.

Involvement of orexin-2 receptor in the ventral tegmental area in stress- and drug priming-induced reinstatement of conditioned place preference in rats.

Orexin neurons originate from the lateral hypothalamus and send their projections broadly throughout the central nervous system including to the ventral tegmental area (VTA). In the current study, the reinstatement model has been used to examine the effects of intra-VTA administration of TCS-OX2-29, an orexin-2 receptor (OX2R) antagonist, on drug priming- and forced swim stress (FSS)-induced reinstatement of morphine-induced conditioned place preference (CPP). A total of 73 adult male Wistar rats weighing 200-280 g were bilaterally implanted with cannulas into the VTA. For induction of CPP, subcutaneous (sc) injection of morphine (5 mg/kg) was done daily during a 3-day conditioning phase. After a 24-h "off" period following achievement of extinction criterion, the rats were tested for drug priming-induced reinstatement with a priming dose of morphine (1 mg/kg;sc) or after application of FSS on the reinstatement day. The animals then received different doses of the OX2R antagonist, TCS-OX2-29 (0.3,3,1 and 10 nM) bilaterally in the VTA (0.3 µl/side) and were tested for FSS- and morphine priming-induced reinstatement of CPP. Our findings indicate that intra-VTA administration of OX2R antagonist suppresses FSS and morphine priming-induced reinstatement in a dose-dependent manner. The role of the orexinergic system in morphine-induced reinstatement through activation of OX2R in the VTA provides evidence that the OX2R antagonist could be a useful therapeutic target for prevention of reinstatement of morphine-induced CPP.

N-methyl-D-aspartate receptors involved in morphine-induced hyperalgesia in sensitized mice.

The aim of this study was to investigate role of the N-Methyl-D-Aspartate (NMDA) receptors in the decrease of morphine analgesia in mice after nociceptive sensitization. We used a hot plate test to assess effects of morphine on pain behavior in male NMRI mice. All drugs were administered through an intraperitoneal route. Sensitization schedule composed of 3-days pre-treatment of morphine (20mg/kg) followed by 5-days washout. The results showed that morphine (5, 7.5, 10 and 15mg/kg) induced a significant analgesia in normal mice. However, the analgesic effects of morphine significantly decreased at higher dose (15mg/kg) in sensitized mice. Injections of either a competitive NMDA receptor antagonist, D-AP5 (0, 0.25, 0.5 and 1mg/kg) or an NMDA receptor channel blocker (30, 60 and 120mg/kg) alone had no effect on pain behavior. However, injections of D-AP5 (1mg/kg), along with morphine over 3-days of the sensitization schedule, significantly prevented the decrease in the analgesic effect of the opioid at doses of 7.5 and 10mg/kg on the hot plate test. Similarly, injections of MgSO4 (120mg/kg), along with morphine over 3-days of the sensitization schedule, significantly prevented the decrease in analgesic effect of morphine at doses of 10 and 15mg/kg. It can be concluded that NMDA receptors are influenced by morphine during the sensitization schedule, which in turn may affect morphine analgesia after the schedule. This may further support the potential effectiveness of NMDA blockade during repeated use of morphine for control of chronic pain.

Interaction between gamma-aminobutyric acid type A (GABAA) receptor agents and scopolamine in the nucleus accumbens on impairment of inhibitory avoidance memory performance in rat.

We designed this study to investigate effects of intra-nucleus accumbens (intra-NAc) infusions of GABA(A) receptors agonist (muscimol) and antagonist (bicuculline) by themselves and their interaction with scopolamine on inhibitory avoidance (IA) memory performance. This study used a step-through IA task to assess memory in male Wistar rats. The results showed that post-training intra-NAc infusions of muscimol at doses of 0.01 and 0.02 µg/rat significantly impaired IA memory performance, while bicuculline (0.1, 0.2 and 0.4 µg/rat) had no effect. Post-training intra-NAc infusions of scopolamine at dose of 0.5 µg/rat impaired IA memory performance by itself, and in combination with an ineffective dose of muscimol increased impairment of IA memory performance. The results also showed that post-training intra-NAc infusions of bicuculline prevented the impairing effect of higher doses of scopolamine on IA memory performance. Pre-test intra-NAc infusions of muscimol (0.01 and 0.02 µg/rat) and bicuculline (0.001, 0.01 and 0.1 µg/rat) impaired IA memory performance. The results also revealed that pre-test intra-NAc infusions of scopolamine (0.25 and 0.5 µg/rat) impaired IA memory performance, and its co-infusions with an ineffective dose of muscimol (0.005 µg/rat) increased impairment of IA memory performance. Interestingly, pre-test intra-NAc infusions of bicuculline impaired performance by itself, but did not prevent the impairing effect of scopolamine. It can be concluded that GABA(A) and muscarinic receptors of the NAc may have an interaction in modulation of IA memory performance, which may result from affecting output neurons in the NAc directly or indirectly via cholinergic and GABAergic interneurons.

Nicotine restores morphine-induced memory deficit through the D1 and D2 dopamine receptor mechanisms in the nucleus accumbens.

Involvement of the dopamine D1 and D2 receptors in the nucleus accumbens (NAc) with interaction between morphine and nicotine on inhibitory avoidance (IA) memory was investigated. A step-through type of inhibitory avoidance tasks was used to assess memory in male Wistar rats. The results showed that subcutaneous (s.c.) administration of morphine (7.5 mg/kg) after training decreased retrieval of IA memory in the animals when tested 24 h later. Pre-test administration of the same dose of morphine significantly reversed the deficiency in retrieval. The results also showed that pre-test administration of nicotine (0.2 and 0.4 mg/kg, s.c.) by itself mimicked the effect of pre-test morphine, and lower doses of nicotine (0.1 and 0.2 mg/kg) also improved the effect of a low dose of morphine (2.5 mg/kg) on retrieval of IA memory. Pre-test intra-NAc administration of the dopamine D1 receptor antagonist, SCH 23390 (0.001 and 0.01 µg/rat), and the dopamine D2 receptor antagonist, sulpiride (0.5 and 1 µg/rat) caused no significant effects on IA memory by themselves, but both prevented reinstatement of the retrieval of IA memory by the effective dose of nicotine (0.4 mg/kg). It can be concluded that the dopaminergic mechanism(s) in the NAc is a crosslink for the effect of morphine and nicotine on reinstatement of retrieval of IA memory impaired by post-training administration of morphine.