Anxiolytic-like effect of pyridoxine in mice by elevated plus maze and light and dark box: Evidence for the involvement of GABAergic and NO-sGC-cGMP pathway

GABAergic implications in anxiety and related disorders

Evidence indicates that anxiety disorders arise from an imbalance in the functioning of brain circuits that govern the modulation of emotional responses to possibly threatening stimuli. The circuits under consideration in this context include the amygdala's bottom-up activity, which signifies the existence of stimuli that may be seen as dangerous. Moreover, these circuits encompass top-down regulatory processes that originate in the prefrontal cortex, facilitating the communication of the emotional significance associated with the inputs. Diverse databases (e.g., Pubmed, ScienceDirect, Web of Science, Google Scholar) were searched for literature using a combination of different terms e.g., "anxiety", "stress", "neuroanatomy", and "neural circuits", etc. A decrease in GABAergic activity is present in both anxiety disorders and severe depression. Research on cerebral functional imaging in depressive individuals has shown reduced levels of GABA within the cortical regions. Additionally, animal studies demonstrated that a reduction in the expression of GABAA/B receptors results in a behavioral pattern resembling anxiety. The amygdala consists of inhibitory networks composed of GABAergic interneurons, responsible for modulating anxiety responses in both normal and pathological conditions. The GABAA receptor has allosteric sites (e.g., α/γ, γ/β, and α/β) which enable regulation of neuronal inhibition in the amygdala. These sites serve as molecular targets for anxiolytic medications such as benzodiazepine and barbiturates. Alterations in the levels of naturally occurring regulators of these allosteric sites, along with alterations to the composition of the GABAA receptor subunits, could potentially act as mechanisms via which the extent of neuronal inhibition is diminished in pathological anxiety disorders.

Nose-to-brain delivery of perampanel formulated in a self-microemulsifying drug delivery system improves anticonvulsant and anxiolytic activity in mice

Perampanel (PER) is a potent third-generation antiepileptic drug only available for oral administration. Additionally, PER has shown potential in managing epilepsy comorbidities such as anxiety. Previously, we demonstrated that the intranasal (IN) administration of PER, loaded in a self-microemulsifying drug delivery system (SMEDDS), improved brain-targeting and exposure in mice. Herein, we investigated PER brain biodistribution, its anticonvulsant and anxiolytic effects, and its potential olfactory and neuromotor toxicity after IN administration to mice (1 mg/kg). PER showed a rostral-caudal brain biodistribution pattern when administered intranasally. At short times post-nasal dosing, high PER concentrations were found in olfactory bulbs (olfactory bulbs/plasma ratios of 1.266 ± 0.183 and 0.181 ± 0.027 after IN and intravenous administrations, respectively), suggesting that a fraction of the drug directly reaches brain through the olfactory pathway. In maximal electroshock seizure test, IN PER protected 60% of mice against seizure development, a substantially higher value than the 20% protected after receiving oral PER. . PER also demonstrated anxiolytic effects in open field and elevated plus maze tests. Buried food-seeking test showed no signs of olfactory toxicity. Neuromotor impairment was found in rotarod and open field tests at the times of PER maximum concentrations after IN and oral administrations. Nevertheless, neuromotor performance was improved after repeated administrations. Compared with IN vehicle, PER IN administration decreased brain levels of L-glutamate (0.91 ± 0.13 mg/mL vs 0.64 ± 0.12 mg/mL) and nitric oxide (100 ± 15.62% vs 56.62 ± 4.95%), without interfering in GABA levels. Altogether, these results suggest that the IN PER delivery through the developed SMEDDS can be a safe and promising alternative to oral treatment, which support the design of clinical studies to evaluate the IN PER delivery to treat epilepsy and neurological-related conditions as anxiety.

K. J, H. R. R, Shivamurthy VKN, Patil SM, Shirahatti PS, Ramu R. New insights on the phytochemical intervention for the treatment of neuropsychiatric disorders using the leaves of Michelia champaca: an in vivo and in silico approach

CONTEXT

Michelia champaca L. (Magnoliaceae) has been known since ancient times for its rich medicinal properties.

OBJECTIVE

The ethanol extract of Michelia champaca leaves (EEMC) was evaluated on depression and anxiety using in vivo and in silico studies.

MATERIALS AND METHODS

Swiss albino mice were divided into control, standard, 100 and 200 mg/kg b.w. EEMC groups and for drug administration using oral gavage. The antidepressant activity was evaluated using forced swim test (FST) and tail suspension test (TST) whereas the anxiolytic activity through elevated plus maze and light and dark tests. The in silico studies included molecular docking against human potassium channel KCSA-FAB and human serotonin transporter, and ADME/T analysis.

RESULTS

Open arm duration and entries were comparable between 200 mg/kg b.w. group (184.45 ± 1.00 s and 6.25 ± 1.11, respectively) and that of diazepam treated group (180.02 s ± 0.40 and 6.10 ± 0.05, respectively). Time spent in the light cubicle was higher (46.86 ± 0.03%), similar to that of diazepam (44.33 ± 0.64%), suggesting its potent anxiolytic activity. A delayed onset of immobility and lowered immobility time was seen at both the treatment doses (FST: 93.7 ± 1.70 and 89.1 ± 0.40 s; TST: 35.05 ± 2.75 and 38.50 ± 4.10 s) and the standard drug imipramine (FST: 72.7 ± 3.72 and TST: 30.01 ± 2.99 s), indicative of its antidepressant ability. In silico studies predicted doripenem to induce anxiolytic and antidepressant activity by inhibiting human potassium channel KCSA-FAB and human serotonin transporter proteins, respectively.

CONCLUSIONS

EEMC is a rich source of bioactive compounds with strong antidepressant and anxiolytic properties.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

Possible involvement of NO-sGC-cGMP signaling in the antidepressant like effect of pyridoxine in mice

The present study was designed to determine the antidepressant like effect of pyridoxine in mice. Pyridoxine (12.5, 25 and 50 mg/kg, i.p.) was administered to the mice and depression related behavioral and neurochemical alterations were determined. It was observed that pyridoxine (50 mg/kg, i.p.) treatment decreased the immobility period in tail suspension test (TST) and forced swim test (FST) significantly as compared to control. Pyridoxine (50 mg/kg, i.p.) treatment increased the level of serotonin (5-HT) and decreased the level of nitrite in the brain of mice significantly as compared to control. Pyridoxine thus confer antidepressant like effect by increasing the level of 5-HT and by decreasing the level of nitrite in the brain of mice. Further the influence of nitric oxide (NO)/ soluble guanylate cyclase (sGC)/ cyclic guanosine monophosphate (cGMP) in antidepressant-like effect of pyridoxine was studied. It was observed that the pretreatment of NO donor (i.e. L-Arginine) and cGMP modulator (i.e. sildenafil) counteracted while the pretreatment of NO/sGC inhibitor (i.e. methylene blue) potentiated the effect of pyridoxine in TST and FST. Pretreatment of NO donor did not influence, pretreatment of NO/sGC inhibitor decreased while the pretreatment of cGMP modulator increased the level of brain nitrite in pyridoxine treated mice. Further the pretreatment of NO donor and cGMP modulator decreased while the pretreatment of NO/sGC inhibitor increased the level of brain serotonin in pyridoxine treated mice. Pyridoxine thus exerted antidepressant like effect and NO-sGC-cGMP signaling modulated the antidepressant like effect of pyridoxine in mice.

Neonatal pyridoxine administration long lastingly accelerates cortical spreading depression in male rats, without affecting anxiety-like behavior

Objectives: Pyridoxine plays a key role in the development of the human nervous system. Several reports suggest that administration of high doses of pyridoxine can be helpful in improving disturbances such as anxiety and pyridoxine-dependent epilepsy, although it has also been associated with a proconvulsive action. In this study, we investigated in developing rats the effects of repeated administration of various doses of pyridoxine on anxiety-like behavior and the brain excitability-related phenomenon known as cortical spreading depression (CSD).Methods: From postnatal day (P) 7 to P27, Wistar rat pups received per gavage pyridoxine hydrochloride (1 mg/kg/day, or 5 mg/kg/day, or 10 mg/kg/day). On P60-70, the animals were tested in the elevated plus maze (EPM) to evaluate anxiety-like behavior. On P71-80, we recorded the CSD (4-hour recording session).Results: Compared with naïve (gavage-free) and saline-treated controls, pyridoxine-treated groups displayed a significant (p < 0.001) increase in CSD propagation velocity and amplitude of the CSD negative direct-current (DC)-shift, and a decrease in the CSD DC-shift duration. These effects were long-lasting and dose-dependent. In the EPM, no significant pyridoxine-associated effect was observed.Discussion: Our data demonstrate a novel action of pyridoxine on an electrical activity-related phenomenon (CSD) in the developing brain, confirming the hypothesis that the chronic treatment with pyridoxine early in life modulates CSD. Data on CSD propagation suggest that pyridoxine at a high dose might act as a prooxidant agent in the developing brain, a hypothesis that deserves further testing.

Anxiolytic like effect of L-Carnitine in mice: Evidences for the involvement of NO-sGC-cGMP signaling pathway

L-Carnitine (LC) is an endogenous compound synthesized from the essential amino acids lysine and methionine. LC act as an antioxidant and modulates the levels of neurochemicals such as glutamate, GABA, NO etc. implicated in the regulation of anxiety and related behavior. However its exact role in the anxiety is not known. The present study was designed to investigate the anxiolytic like effect of LC in mice. LC (2.5, 5.0 and 10 mg/kg, i.p.) was administered to the mice and the anxiety related behavior was determined using light and dark box (LDB) and elevated plus maze (EPM) tests. The whole brain nitrite level was also determined. The results obtained demonstrated that LC (10 mg/kg, i.p.) exerted anxiolytic like effect in mice, accompanied by the reduction of whole brain nitrite level significantly as compared to control. Further, the influence of NO and GABA modulators pretreatments on the effect of subtherapeutic dose of LC was also determined. The results obtained demonstrated that NO donor/cGMP modulator counteracted while NO inhibitor potentiated the effect confers by the subtherapeutic dose of LC mice. Pretreatment of diazepam (1 mg/kg, i.p.) further potentiated the effect of subtherapeutic dose of LC (5 mg/kg, i.p.) in EPM and LDB tests and further reduced the brain nitrite level significantly as compared to LC (5 mg/kg, i.p.) alone treatment. Thus, LC exerted anxiolytic like effect in mice and NO-sGC-cGMP signaling pathway influences the anxiolytic like effect of LC in mice.

Amantadine exerts anxiolytic like effect in mice: Evidences for the involvement of nitrergic and GABAergic signaling pathways

Amantadine is a glutamatergic antagonist that works by inhibiting the NMDA receptor. Besides the inhibition of NMDA receptors amantadine also stabilizes the glutamatergic system and protects the neurons against the NMDA toxicity. Amantadine treatment also reduces the production of NO and metabolism of GABA. Therefore amantadine modulates glutamate, GABA and NO which are known to be implicated in the pathogenesis of anxiety and related behavior. The present study was designed to investigate the anxiolytic like effect of amantadine in mice. Nitrergic and GABAergic signaling influence in the anxiolytic like effect of amantadine was also studied. Amantadine (25, 50 and 75 mg/kg, i.p.) was administered and the anxiety related behavior was determined using light and dark box (LDB) and elevated plus maze (EPM) methods. Further, the effect of various treatments on the whole brain glutamate, nitrite and GABA levels were also determined. The results obtained demonstrated that the amantadine (50 mg/kg, i.p.) exerted anxiolytic like effect in mice and reduced the levels of glutamate, nitrite and GABA in the brain of mice as compared to control. Further, the influence of NO and GABA in the anxiolytic like effect of the amantadine was also determined. The results obtained demonstrated that NO donor counteracted while NO inhibitor potentiated the anxiolytic like effect of amantadine in mice. Also the combined treatment of amantadine (25 mg/kg, i.p.) and diazepam (1 mg/kg, i.p.) did not affect the anxiety related behavior, brain GABA and nitrite level of mice but reduced the levels the brain glutamate levels significantly as compared to amantadine (25 mg/kg, i.p.) and diazepam (1 mg/kg, i.p.) treated mice. Thus, amantadine exerted anxiolytic like effect in mice and the anxiolytic like effect of amantadine was modulated by nitrergic and GABAergic signaling pathway.

Home-cage monitoring ascertains signatures of ictal and interictal behavior in mouse models of generalized seizures

Epilepsy is a significant contributor to worldwide disability. In epilepsy, disability can be broadly divided into two components: ictal (pertaining to the burden of unpredictable seizures and associated medical complications including death) and interictal (pertaining to more pervasive debilitating changes in cognitive and emotional behavior). In this study, we objectively and noninvasively appraise aspects of ictal and interictal behavior in mice using instrumented home-cage chambers designed to assay kinematic and appetitive behavioral measures. Through daily intraperitoneal injections of the chemoconvulsant pentylenetetrazole (PTZ) applied to C57BL/6J mice, we coordinately measure how “behavioral severity” (complex dynamic changes in movement and sheltering behavior) and convulsive severity (latency and occurrence of convulsive seizures) evolve or kindle with repeated injections. By closely studying long epochs between PTZ injections, we identify an interictal syndrome of nocturnal hypoactivity and increased sheltering behavior which remits with the cessation of seizure induction. We observe elements of this interictal behavioral syndrome in seizure-prone DBA/2J mice and in mice with a pathogenic Scn1a mutation (modeling Dravet syndrome). Through analyzing their responses to PTZ, we illustrate how convulsive severity and “behavioral” severity are distinct and independent aspects of the overall severity of a PTZ-induced seizure. Our results illustrate the utility of an ethologically centered automated approach to quantitatively appraise murine expressions of disability in mouse models of seizures and epilepsy. In doing so, this study highlights the very unique psychopharmacological profile of PTZ.

Role of pyridoxine in GABA synthesis and degradation in the hippocampus

Pyridoxal-5'-phosphate, the active form of vitamin B₆, is associated with activities of several enzymes and the treatment of various neurological disorders. Here, we investigated the effects of pyridoxine on the immunoreactivity and protein levels of γ-aminobutyric acid (GABA)-synthesizing and degradation enzymes such as glutamic acid decarboxylase (GAD), GABA transaminase (GABA-T), and succinic semialdehyde dehydrogenase (SSADH), in the hippocampus of mice. The mice intraperitonially received physiological saline and 350 mg/kg pyridoxine, twice a day for 21 days, and were euthanized 2 h after the final dose. In the vehicle-treated group, we observed GAD67 immunoreactivity in the stratum pyramidale of the CA1 and CA3 region, Schaffer collateral, polymorphic layer, and outer granule cell layer of the dentate gyrus. Pyridoxine administration significantly increased GAD67 immunoreactivity, while significantly decreasing GABA-T immunoreactivity in pyridoxine-treated mouse hippocampi (CA1 region and dentate gyrus). In the stratum lacunosum-moleculare of CA1 region, GABA-T immunoreactivity was significantly increased in the pyridoxine-treated group compared to that in the vehicle-treated group, although GAD67 immunoreactivity was similarly observed in these groups. Alternatively, there were no significant differences in SSADH immunoreactivity in any regions of the hippocampus between the vehicle- and pyridoxine-treated groups. Western blot analysis showed significant increases in GAD67 and GABA-T protein levels in the pyridoxine-treated group compared with those in the vehicle-treated group. Therefore, pyridoxine administration facilitates GABA turnover in mouse hippocampus by modulating the GABA-synthesizing and degradation enzymes.

Lithium potentiated, pyridoxine abolished and fluoxetine attenuated the anxiolytic effect of diazepam in mice

In the present study, the anxiolytic effect of diazepam (1 and 2 mg/kg, i.p.) was determined alone and in combination with lithium (50 mg/kg, i.p.), pyridoxine (90 mg/kg, i.p.) and fluoxetine (10 mg/kg, i.p.) using elevated plus maze (EPM) and light/dark box (LDB) tests in experimental mice. The effect of various treatments on the brain GABA levels and glutamic acid decarboxylase (GAD) expression were also determined. The results obtained suggested that the diazepam (2 mg/kg, i.p.) exerted anxiolytic effect and significantly increased the brain GABA levels and GAD expression as compared to control group. Fluoxetine (10 mg/kg, i.p.) exerted anxiogenic effects, but did not affect the brain GABA levels and GAD activity significantly as compared to control. Pretreatments of pyridoxine (90 mg/kg, i.p.) abolished; lithium (50 mg/kg, i.p.) potentiated while fluoxetine (10 mg/kg, i.p.) attenuated the anxiolytic and neurochemical effects of diazepam (1 and 2 mg/kg, i.p.) treatment in mice. Therefore, the combined treatment of lithium and diazepam might be a promising treatment for anxiety.