Effects of cholinergic system of dorsal hippocampus of rats on MK-801 induced anxiolytic-like behavior

Targeting NMDA Receptors in Emotional Disorders: Their Role in Neuroprotection

Excitatory glutamatergic neurotransmission mediated through N-methyl-D-Aspartate (NMDA) receptors (NMDARs) is essential for synaptic plasticity and neuronal survival. While under pathological states, abnormal NMDAR activation is involved in the occurrence and development of psychiatric disorders, which suggests a directional modulation of NMDAR activity that contributes to the remission and treatment of psychiatric disorders. This review thus focuses on the involvement of NMDARs in the pathophysiological processes of psychiatric mood disorders and analyzes the neuroprotective mechanisms of NMDARs. Firstly, we introduce NMDAR-mediated neural signaling pathways in brain function and mood regulation as well as the pathophysiological mechanisms of NMDARs in emotion-related mental disorders such as anxiety and depression. Then, we provide an in-depth summary of current NMDAR modulators that have the potential to be developed into clinical drugs and their pharmacological research achievements in the treatment of anxiety and depression. Based on these findings, drug-targeting for NMDARs might open up novel territory for the development of therapeutic agents for refractory anxiety and depression.

Nanonaringenin and Vitamin E Ameliorate Some Behavioral, Biochemical, and Brain Tissue Alterations Induced by Nicotine in Rats

Nicotine is the major alkaloid present in cigarettes that induces various biochemical and behavioral changes. Nanonaringenin (NNG) and vitamin E are antioxidants that are reported to mitigate serious impairments caused by some toxins and oxidants. Thus, we aimed to investigate the efficacy of NNG, vitamin E, and their combinations to ameliorate behavioral, biochemical, and histological alterations induced by nicotine in rats. Adult male albino rats were randomly grouped into six equal groups (10 rats/group): control, N (nicotine 1 mg/kg b.w./day S/C from 15^th to 45^th day, 5 days a week), NNG (25 mg/kg b.w./day orally for 45 days), N + NNG, N + E (nicotine + vitamin E 200 mg/kg b.w./day orally), and N + NNG + E (nicotine + NNG + vitamin E at the aforementioned doses). Behavioral tests were conducted on day 15 and 30 postnicotine injection, while memory tests, brain neurotransmitters, antioxidants, and histopathological examination were examined at day 30 only. As a result, nicotine impaired rats' activity (hypoactivity and hyperactivity) and memory, induced anxiolytic and anxiogenic effects on rats, and altered neurotransmitters (acetylcholinesterase, serotonin, and dopamine), and redox markers (MDA, H₂O₂, GSH, and catalase) levels in brain homogenates. Thickening and congestion of the meninges and degeneration of the cerebral neurons and glia cells were observed. Cosupplementation with NNG, vitamin E, and their combination with nicotine was beneficial in the alleviation of activity impairments and improved short memory and cognition defects and exploratory behaviors. Our results indicate the antioxidant potential of NNG and vitamin E by modulating redox markers and neurotransmitters in the brain. Thus, data suggest that the prophylactic use of NNG, vitamin E, and/or their combination for (45 days) may have a successful amelioration of the disrupted behavior and cognition and biochemical and histopathological alterations induced by nicotine.

Additive interaction between scopolamine and nitric oxide agents on immobility in the forced swim test but not exploratory activity in the hole-board

RATIONALE

The muscarinic cholinergic antagonist scopolamine has received an attention due to its unique antidepressant effects. However, the considerable adverse effects on nervous system limit the use of scopolamine as a psychiatric drug.

OBJECTIVE

In order to overcome the limitations and increase the therapeutic effects of scopolamine, we decided to examine the effects of joint administration of sub-effective dose of scopolamine and the sub-effective dose of a nitric oxide (NO) precursor L-Arginine or a non-selective nitric oxide synthase (NOS) inhibitor L-NAME on depression- and anxiety-related behaviors in male NMRI mice.

METHODS

To this aim, animal behavior was assessed in the forced swim test (FST) and hole-board apparatus.

RESULTS

Scopolamine (0.05 mg/kg) significantly decreased immobility time in the FST, suggesting an antidepressant-like effect. Moreover, L-Arginine (50 mg/kg) produced an antidepressant-like response in the FST and decreased head-dip counts in the hole-board apparatus, indicating an anxiety-like effect. The same doses of scopolamine and L-Arginine decreased the locomotor activity in mice. Joint administration of sub-effective dose of scopolamine (0.01 mg/kg) with a low dose of L-Arginine (25 mg/kg) or L-NAME (1 mg/kg) induced a profound antidepressant-like effect in the FST. These drug combinations did not influence on anxiety-related behaviors. Meanwhile, L-NAME alone did not alter the performance of mice in the FST and hole-board. Isobolographic analysis revealed an additive effect for scopolamine and L-Arginine or L-NAME.

CONCLUSION

Data suggests that NO agents could positively impact the therapeutic profile of scopolamine, because they might be useful for inducing antidepressant-like effect associated to scopolamine.

The role of calcium-calmodulin-dependent protein kinase II in modulation of spatial memory in morphine sensitized rats

It has been shown that drug addiction and memory system are related but the signaling cascades underlying this interaction is not completely revealed yet. It has been demonstrated that binding of Calcium-calmodulin-dependent protein kinase II (CaMKII) to NMDA receptor is important in the memory process. The main objective of the study was to evaluate the role of CaMKII on the spatial memory of rats which previously were sensitized by morphine. The effect of CaMKII inhibitor (KN-93) on memory changes was investigated by hippocampal microinjection of KN-93 on the morphine-sensitized rats. Also, the role of the NMDA receptor in memory retention by KN-93 on the morphine sensitized rat was investigated with NMDA agonist and antagonist. Sensitization was induced by morphine injection (once daily for 3 days) followed by 5 days free of the drug before the trial phase. For the evaluation of spatial memory, the Morris Water Maze test (MWM) was used. Results showed that pre-trial administration of morphine, induced amnesia in MWM (p < 0.05). Also, three days pretreatment with morphine (20 mg/kg) followed by five days washout period, caused to enhance memory retrieval in confront with a pre-trial challenging dose of morphine (5 mg/kg). In addition, KN-93 administration during induction phase in morphine sensitization phenomena facilitated morphine-induced memory retention. In addition, inhibition of the NMDA receptor and KN-93 during the induction phase did not improve memory. However; intra-CA1 co-administration of KN-93 and NMDA during the induction phase of morphine sensitization resulted in improving spatial memory. It can be concluded that the effect of CaMKII on memory retention in morphine-sensitized rats depends on NMDA receptor.

Involvement of M1 and CB₁ receptors in the anxiogenic-like effects induced by neostigmine injected into the rat prelimbic medial prefrontal cortex

The prelimbic (PL) medial prefrontal cortex is a brain region highly involved in the control of emotional responses, being modulated by several neurotransmitter systems, including the cholinergic and endocannabinoid. Activation of muscarinic type 1 (M1) receptors in the brain induces retrograde suppression of inhibition through the induction of endocannabinoid release, which, in turn, activates cannabinoid type 1 (CB1) receptors. No study so far, however, has been conducted to investigate if the cholinergic and endocannabinoid systems interact in the PL to modulate anxiety-related behaviors. Thus, the present work aimed at verifying if intra-PL administration of neostigmine, an acetylcholinesterase inhibitor, would produce changes in anxiety-like behavior and if these effects are mediated by M1 and CB1 receptor activation. Independent groups of animals received bilateral injections of vehicle, the M1 receptor antagonist pirenzepine (0.06, 0.6, and 6 nmol), the CB1 receptor antagonist AM251 (0.1 nmol), or the fatty acid amide hydrolase (FAAH) enzyme inhibitor URB597 (1, 3, and 10 pmol), followed by vehicle or neostigmine (0.01, 0.1, and 1 nmol), and were submitted to the elevated plus-maze (EPM) test. Neostigmine (1 nmol) decreased open arm exploration of the maze. This anxiogenic-like effect was reproduced in another anxiety-related animal model, the light-dark box. Previous injection of pirenzepine or AM251 abolished this response in the EPM, whereas URB597 had no effect. These results suggest that CB1 and M1 receptors interact in the PL to control anxiety-like behaviors.

The effect of BLA GABA(A) receptors in anxiolytic-like effect and aversive memory deficit induced by ACPA

The roles of GABAergic receptors of the Basolateral amygdala (BLA) in the cannabinoid CB1 receptor agonist (arachydonilcyclopropylamide; ACPA)-induced anxiolytic-like effect and aversive memory deficit in adult male mice were examined in elevated plus-maze task. Results showed that pre-test intra-peritoneal injection of ACPA induced anxiolytic-like effect (at dose of 0.05 mg/kg) and aversive memory deficit (at doses of 0.025 and 0.05 mg/kg). The results revealed that Pre-test intra-BLA infusion of muscimol (GABA_A receptor agonist; at doses of 0.1 and 0.2 µg/mouse) or bicuculline (GABA_A receptor antagonist; at all doses) impaired and did not alter aversive memory, respectively. All previous GABA agents did not have any effects on anxiety-like behaviors. Interestingly, pretreatment with a sub-threshold dose of muscimol (0.025 µg/mouse) and bicuculline (0.025 µg/mouse) did not alter anxiolytic-like behaviors induced by ACPA, while both drugs restored ACPA-induced amnesia. Moreover, muscimol or bicuculline increased and decreased ACPA-induced locomotor activity, respectively. Finally the data may indicate that BLA GABA_A receptors have critical and different roles in anxiolytic-like effect, aversive memory deficit and locomotor activity induced by ACPA.

The expression of contextual fear conditioning involves activation of a NMDA receptor-nitric oxide-cGMP pathway in the dorsal hippocampus of rats

The dorsal portion of the hippocampus is a limbic structure that is involved in fear conditioning modulation in rats. Moreover, evidence shows that the local dorsal hippocampus glutamatergic system, nitric oxide (NO) and cGMP modulate behavioral responses during aversive situations. Therefore, the present study investigated the involvement of dorsal hippocampus NMDA receptors and the NO/cGMP pathway in contextual fear conditioning expression. Male Wistar rats were submitted to an aversive contextual conditioning session and 48 h later they were re-exposed to the aversive context in which freezing, cardiovascular responses (increase of both arterial pressure and heart rate) and decrease of tail temperature were recorded. The intra-dorsal hippocampus administration of the NMDA receptor antagonist AP7, prior to the re-exposure to the aversive context, attenuated fear-conditioned responses. The re-exposure to the context evoked an increase in NO concentration in the dorsal hippocampus of conditioned animals. Similar to AP7 administration, we observed a reduction of contextual fear conditioning after dorsal hippocampus administration of either the neuronal NO synthase inhibitor N-propyl-L-arginine, the NO scavenger c-PTIO or the guanylate cyclase inhibitor ODQ. Therefore, the present findings suggest the possible existence of a dorsal hippocampus NMDA/NO/cGMP pathway modulating the expression of contextual fear conditioning in rats.

Effects of rhynchophylline on GluN1 and GluN2B expressions in primary cultured hippocampal neurons

N-methyl-d-aspartate (NMDA) receptor subunits GluN1 and GluN2B in hippocampal neurons play key roles in anxiety. Our previous studies show that rhynchophylline, an active component of the Uncaria species, down-regulates GluN2B expression in the hippocampal CA1 area of amphetamine-induced rat. The effects of rhynchophylline on expressions of GluN1 and GluN2B in primary hippocampal neurons in neonatal rats in vitro were investigated. Neonatal hippocampal neurons were cultured with neurobasal-A medium. After incubation for 6h or 48 h with rhynchophylline (non-competitive NMDAR antagonist) and MK-801 (non-competitive NMDAR antagonist with anxiolytic effect, as the control drug) from day 6, neuron toxicity, mRNA and protein expressions of GluN1 and GluN2B were analyzed. GluN1 is mainly distributed on neuronal axons and dendritic trunks, cytoplasm and cell membrane near axons and dendrites. GluN2B is mainly distributed on the membrane, dendrites, and axon membranes. GluN1 and GluN2B are codistributed on dendritic trunks and dendritic spines. After 48 h incubation, a lower concentration of rhynchophylline (lower than 400 μmol/L) and MK-801 (lower than 200 μmol/L) have no toxicity on neonatal hippocampal neurons. Rhynchophylline up-regulated GluN1 mRNA expression at 6h and mRNA and protein expressions at 48h, but down-regulated GluN2B mRNA and protein expressions at 48 h. However, GluN1 and GluN2B mRNA expressions were down-regulated at 6h, and mRNA and protein expressions were both up-regulated by MK-801 at 48h. These findings show that rhynchophylline reciprocally regulates GluN1 and GluN2B expressions in hippocampal neurons, indicating a potential anxiolytic property for rhynchophylline.

Animal models of serotonergic psychedelics

The serotonin 5-HT(2A) receptor is the major target of psychedelic drugs such as lysergic acid diethylamide (LSD), mescaline, and psilocybin. Serotonergic psychedelics induce profound effects on cognition, emotion, and sensory processing that often seem uniquely human. This raises questions about the validity of animal models of psychedelic drug action. Nonetheless, recent findings suggest behavioral abnormalities elicited by psychedelics in rodents that predict such effects in humans. Here we review the behavioral effects induced by psychedelic drugs in rodent models, discuss the translational potential of these findings, and define areas where further research is needed to better understand the molecular mechanisms and neuronal circuits underlying their neuropsychological effects.