Role of adenosine signaling on pentylenetetrazole-induced seizures in zebrafish

Neuropharmacological potential of Mimosa tenuiflora in adult zebrafish: An integrated approach to GABAergic and serotonergic neuromodulation

Mimosa tenuiflora ("jurema-preta") is traditionally used in folk medicine for various diseases. The study investigated the neuropharmacological potential of Mimosa tenuiflora bark fraction (FATEM) in adult zebrafish. This included the acute toxicity (LC50) of FATEM (0.01; 0.05; 0.1; 0.5; 1.0 and 5.0 mg/mL; i.p.) and the effects on behavioral tests, such as open field, light & dark and zebrafish tail immobilization test (ZTI). The anxiolytic response induced by alcohol withdrawal and the seizure induced by pentylenetetrazole were also tested. The possible mechanisms of anxiolytic and antidepressant actions of FATEM were evaluated through the administration of specific antagonists (Flumazenil, Cyproheptadine, Pizotifen or Granisetron). Furthermore, the study investigated the ADME profile and molecular docking simulations of the major FATEM compound, Benzyloxyamine, with GABAergic and serotonergic receptors. FATEM did not present acute toxicity and caused a reduction in locomotor activity (p < 0.0001 vs. Control) similar (p< 0.0001) to Diazepam, indicating a sedative/anxiolytic effect. The anxiolytic activity in the light & dark test was similar to Diazepam (p < 0.0001), prevented by GABA and serotonergic antagonists. FATEM also prevented anxious behaviors induced by alcohol withdrawal and exhibited an antidepressant effect in the ZTI (p < 0.0001 vs. Control) similar (p < 0.0001) to the effect of Fluoxetine, which was reversed by serotonergic antagonists. In silico evaluations indicated favorable pharmacokinetic properties and affinity of FATEM with GABAergic and serotonergic receptors. The study reveals that FATEM has adequate physicochemical characteristics to act on the CNS with specific affinity for GABAA and serotonergic receptors, indicating its potential as a treatment for anxiety and depression.

Anxiolytic and Anticonvulsant Effects of Fisetin Isolated from Bauhinia pentandra on Adult Zebrafish (Danio rerio)

Anxiety and epilepsy are common worldwide and represent a primary global health concern. Fisetin, a flavonoid isolated from Bauhinia pentandra, has a wide range of biological activities may be a promising alternative to combat diseases related to the central nervous system (CNS). The present study aimed to investigate the anxiolytic and anticonvulsant effects of fisetin on adult zebrafish. Furthermore, molecular docking simulations were performed to improve the results. Fisetin did not present toxicity and caused anxiolytic behavior and delayed seizures in animals. This effect may occur through serotonin neurotransmission at 5-HT3A and/or 5-HT3B receptors. Molecular docking simulations showed that fisetin interacts with the orthosteric site of the 5-HT3A receptor with strong H-bond interactions with the Trp156 residue, with a strong contribution from the catechol ring, a behavior similar to that of the antagonist co-crystallized inhibitor granisetron (CWB). Fisetin may be a promising alternative to combat diseases related to the central nervous system.

Anticonvulsant and anxiolytic-like potential of the essential oil from the Ocimum basilicum Linn leaves and its major constituent estragole on adult zebrafish (Danio rerio)

The Ocimum species present active compounds with the potential to develop drugs for treating chronic disease conditions, such as anxiety and seizures. The present study aims to investigate the anticonvulsant and anxiolytic-like effect of the essential oil from O. basilicum Linn (OEFOb) leaves and its major constituent estragole (ES) in vivo on adult zebrafish (aZF) and in silico. The aZF were treated with OEFOb or ES or vehicle and submitted to the tests of toxicity, open-field, anxiety, and convulsion and validated the interactions of the estragole on the involvement of GABAergic and serotonergic receptors by molecular docking assay. The results showed that the oral administration of OEFOb and ES did not have a toxic effect on the aZF and showed anxiolytic-like effects with the involvement of GABAA, 5-HT1, 5-HT2A/2C and 5-HT3A/3B as well on anxiety induced by alcohol withdrawal. The OEFOb and ES showed anticonvulsant potential attenuating the seizures induced by pentylenetetrazole (PTZ) by modulation of the GABAA system. Both anxiolytic and anticonvulsant effects were corroborated by the potential of the interaction of ES by in silico assay. These study samples demonstrate the pharmacological evidence and potential for using these compounds to develop new anxiolytic and anticonvulsant drugs.

Berberine and hesperidin prevent the memory consolidation impairment induced by pentylenetetrazole in zebrafish

This study verified the effects of the natural compounds berberine and hesperidin on seizure development and cognitive impairment triggered by pentylenetetrazole (PTZ) in zebrafish. Adult animals were submitted to a training session in the inhibitory avoidance test and, after 10 minutes, they received an intraperitoneal injection of 25, 50, or 100 mg/kg berberine or 100 or 200 mg/kg hesperidin. After 30 minutes, the animals were exposed to 7.5 mM PTZ for 10 minutes. Animals were submitted to the test session 24 h after the training session to verify their cognitive performance. Zebrafish larvae were exposed to 100 µM or 500 µM berberine or 10 µM or 50 µM hesperidin for 30 minutes. After, larvae were exposed to PTZ and had the seizure development evaluated by latency to reach the seizure stages I, II, and III. Adult zebrafish pretreated with 50 mg/kg berberine showed a longer latency to reach stage III. Zebrafish larvae pretreated with 500 µM berberine showed a longer latency to reach stages II and III. Hesperidin did not show any effect on seizure development both in larvae and adult zebrafish. Berberine and hesperidin pretreatments prevented the memory consolidation impairment provoked by PTZ-induced seizures. There were no changes in the distance traveled in adult zebrafish pretreated with berberine or hesperidin. In larval stage, berberine caused no changes in the distance traveled; however, hesperidin increased the locomotion. Our results reinforce the need for investigating new therapeutic alternatives for epilepsy and its comorbidities.

Chemically-induced epileptic seizures in zebrafish: A systematic review

The use of zebrafish as a model organism is gaining evidence in the field of epilepsy as it may help to understand the mechanisms underlying epileptic seizures. As zebrafish assays became popular, the heterogeneity between protocols increased, making it hard to choose a standard protocol to conduct research while also impairing the comparison of results between studies. We conducted a systematic review to comprehensively profile the chemically-induced seizure models in zebrafish. Literature searches were performed in PubMed, Scopus, and Web of Science, followed by a two-step screening process based on inclusion/exclusion criteria. Qualitative data were extracted, and a sample of 100 studies was randomly selected for risk of bias assessment. Out of the 1058 studies identified after removing duplicates, 201 met the inclusion criteria. We found that the most common chemoconvulsants used in the reviewed studies were pentylenetetrazole (n = 180), kainic acid (n = 11), and pilocarpine (n = 10), which increase seizure severity in a dose-dependent manner. The main outcomes assessed were seizure scores and locomotion. Significant variability between the protocols was observed for administration route, duration of exposure, and dose/concentration. Of the studies subjected to risk of bias assessment, most were rated as low risk of bias for selective reporting (94%), baseline characteristics of the animals (67%), and blinded outcome assessment (54%). Randomization procedures and incomplete data were rated unclear in 81% and 68% of the studies, respectively. None of the studies reported the sample size calculation. Overall, these findings underscore the need for improved methodological and reporting practices to enhance the reproducibility and reliability of zebrafish models for studying epilepsy. Our study offers a comprehensive overview of the current state of chemically-induced seizure models in zebrafish, highlighting the common chemoconvulsants used and the variability in protocol parameters. This may be particularly valuable to researchers interested in understanding the underlying mechanisms of epileptic seizures and screening potential drug candidates in zebrafish models.

Functioning and Gene Expression of Adenosine A1 Receptor During Zebrafish (Danio rerio) Development

The A1 adenosine receptor is the most widely expressed P1 receptor in vertebrates, performing inhibitory tone of the nervous system. Increased levels of adenosine are crucial to promote tissue protection in threatening situations, such as convulsion and hypoxia. Zebrafish is an established model organism for studies on health and disease. In this study, we evaluated the functionality of A1 adenosine receptor through development of zebrafish (6-7-day-, 3-, 8-, and 24-month-old), assessing: (I) the effects of the agonist N6-cyclopenthyladenosine (CPA) over locomotor parameters, (II) the anticonvulsant properties of CPA and adenosine per se in the pentylenetetrazol-induced seizure, and (III) the gene expression of adora1b through development. CPA promoted decreased distance traveled in the highest concentrations/doses tested (larvae: 75 to 500 μM; adults: 20 mg.kg-1), altered mean velocity (larvae: 50-500 μM; adults: 20 mg.kg-1) and time in the bottom zone of apparatus (adults: decrease in 20 mg.kg-1). Adenosine increased the latency of the larvae to reach stage II at 5 and 10 μM. CPA anticonvulsant effect against convulsive stage II was reached at 75 μM, although it decreased basal locomotor activity in larvae. For adults, CPA 10 mg.kg-1 was effective as anticonvulsant without locomotory effects. Adenosine had minor anticonvulsant effects in the concentration tested (larvae: 5 and 10 μM). The level of gene expression of adora1b was stable in brain from adult animals (8- and 24-month-old animals). These results suggest that zebrafish has similar responses to CPA as mammals. To avoid confounding factors, such as locomotor effects, during any brain function investigation using A1 adenosine receptor as a target, the concentration below 75 μM or below the dose of 20 mg.kg-1 of CPA is ideal for zebrafish at larval and adult stages, respectively.

The Effect of Adenosine Signaling on Memory Impairment Induced by Pentylenetetrazole in Zebrafish

Epilepsy is characterized by the manifestation of spontaneous and recurrent seizures. The high prevalence of comorbidities associated with epilepsy, such as cognitive dysfunction, affects the patients quality of life. Adenosine signaling modulation might be an effective alternative to control seizures and epilepsy-associated comorbidities. This study aimed to verify the role of adenosine modulation on the seizure development and cognitive impairment induced by pentylenetetrazole (PTZ) in zebrafish. At first, animals were submitted to a training session in the inhibitory avoidance test and, after 10 min, they received an intraperitoneal injection of valproate, adenosine A₁ receptor agonist cyclopentyladenosine (CPA), adenosine A₁ receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), adenosine A_2A receptor antagonist ZM 241385, adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nony1)-adenine hydrochloride (EHNA) or the nucleoside transporter inhibitor dipyridamole. Thirty min after the intraperitoneal injection, the animals were exposed to 7.5 mM PTZ for 10 min, where they were evaluated for latency to reach the seizure stages (I, II, and III). Finally, 24 h after the training session, the animals were submitted to the inhibitory avoidance test to verify their cognitive performance during the test session. Valproate, CPA, and EHNA showed antiseizure effects and prevented the memory impairment induced by PTZ exposure. DPCPX, ZM 241385, and dipyridamole pretreatments caused no changes in seizure development; however, these drugs prevented memory impairment without altering locomotion. Our results reinforce the antiseizure effects of adenosine signaling and support the idea that the involvement of adenosine in memory processes may be a target for preventive strategies against cognitive impairment associated with epilepsy.

Anxiolytic and anticonvulsant effect of Ibuprofen derivative through GABAergic neuromodulation in adult Zebrafish

Anxiety and epilepsy affect millions of people worldwide, and the treatment of these pathologies involves the use of Benzodiazepines, drugs that have serious adverse effects such as dependence and sedation, so the discovery of new anxiolytic and antiepileptic drugs are necessary. Many routes for synthesizing ibuprofen derivatives have been developed, and these derivatives have shown promising pharmacological effects. Therefore, this study aims to evaluate its anxiolytic and anticonvulsant effect against the adult Zebrafish animal model of Ibuprofen (IBUACT) and its interaction with the GABAergic receptor through in silico studies. The light/dark preference test (Scototaxis test) was used to evaluate the anxiolytic behavior of adult Zebrafish acutely treated with IBUACT and Diazepam, and their anticonvulsant effects were investigated through the pentylenetetrazol (PTZ)-induced seizure model. Animals treated with IBUACT showed anxiolytic behavior similar to Diazepam, and pretreatment with flumazenil reversed this behavior. PTZ-induced seizures were delayed by IBUACT in all three stages and were shown to bind strongly in the Diazepam region of GABAA. In addition, this work presents evidence of new pharmacological applications of ibuprofen derivative in pathologies of the central nervous system (CNS), opening the horizon for new studies.Communicated by Ramaswamy H. Sarma.

Diterpene Sonderianin isolated from Croton blanchetianus exhibits acetylcholinesterase inhibitory action and anxiolytic effect in adult zebrafish (Danio rerio) by 5-HT system

Croton blanchetianus is known as 'marmeleiro preto', a very widespread shrub in Northeast Brazil. Terpenoids, steroids and phenolic compounds are among the reported secondary metabolites of the Croton genus that are a potential source of bioactive compounds. This study evaluated the anxiolytic potential of clerodine-type diterpene, sonderianin (CBWS) isolated from the stem bark of C. blanchetianus and its mechanism of action in adult zebrafish (Danio rerio) (ZFa). The anticonvulsant and anti-acetylcholinesterase effects have also been explored. ZFa (n = 6/group) were treated intraperitoneally (ip; 20 µL) with CBWS (4, 12 and 40 mg/kg) and vehicle (3% DMSO; 20 µL) and subjected to locomotor activity tests, as well as toxicity acute 96 h. CBWS was also administered for analysis in the light/dark test. The involvement of the serotonergic system (5-HT) was investigated using 5-HTR₁, 5-HTR_2A/2C and 5-HTR_3A/3B receptor antagonists. Anxiolytic doses were tested for pentylenetetrazol-induced seizure in ZFa. The inhibitory activity of the enzyme acetylcholinesterase (AChE) was measured. CBWS was not considered toxic and reduced locomotor activity. The results of the present study identified for the first time the interaction of the diterpene sonderianina in the CNS. This study provides evidence that CBWS has an anxiolytic effect mediated by serotonergic (5-HT) involvement and anti-acetylcholinesterase action. The 5-HTR₁ and 5-HTR_2A/2C receptors may be implicated in the low anticonvulsant effect in CBWS.Communicated by Ramaswamy H. Sarma.

Modulation of adenosine signaling reverses 3-nitropropionic acid-induced bradykinesia and memory impairment in adult zebrafish

Huntington's disease (HD) is a neurodegenerative disorder, characterized by motor dysfunction, psychiatric disturbance, and cognitive decline. In the early stage of HD, occurs a decrease in dopamine D₂ receptors and adenosine A_2A receptors (A_2AR), while in the late stage also occurs a decrease in dopamine D₁ receptors and adenosine A₁ receptors (A₁R). Adenosine exhibits neuromodulatory and neuroprotective effects in the brain and is involved in motor control and memory function. 3-Nitropropionic acid (3-NPA), a toxin derived from plants and fungi, may reproduce HD behavioral phenotypes and biochemical characteristics. This study investigated the effects of acute exposure to CPA (A₁R agonist), CGS 21680 (A_2AR agonist), caffeine (non-selective of A₁R and A_2AR antagonist), ZM 241385 (A_2AR antagonist), DPCPX (A₁R antagonist), dipyridamole (inhibitor of nucleoside transporters) and EHNA (inhibitor of adenosine deaminase) in an HD pharmacological model induced by 3-NPA in adult zebrafish. CPA, CGS 21680, caffeine, ZM 241385, DPCPX, dipyridamole, and EHNA were acutely administered via i.p. in zebrafish after 3-NPA (at dose 60 mg/kg) chronic treatment. Caffeine and ZM 241385 reversed the bradykinesia induced by 3-NPA, while CGS 21680 potentiated the bradykinesia caused by 3-NPA. Moreover, CPA, caffeine, ZM 241385, DPCPX, dipyridamole, and EHNA reversed the 3-NPA-induced memory impairment. Together, these data support the hypothesis that A_2AR antagonists have an essential role in modulating locomotor function, whereas the activation of A₁R and blockade of A_2AR and A₁R and modulation of adenosine levels may reduce the memory impairment, which could be a potential pharmacological strategy against late-stage symptoms HD.

Combretum lanceolatum extract reverses anxiety and seizure behavior in adult zebrafish through GABAergic neurotransmission: an in vivo and in silico study

Combretaceae are reported in the literature for presenting neuroprotective and anxiolytic effects in animal models. Combretum lanceolatum Pohl. has few scientific reports on its pharmacological effects. The aim of this study was to evaluate the anxiolytic and anticonvulsant effects of the ethanol extract from the leaves of C. lanceolatum Pohl. (EtFoCl) and its possible mechanism of GABAergic action in adult zebrafish. EtFoCl was subjected to determination of the total phenol concentration, identification of phytochemical flavonoids by HPLC and in vitro antioxidant activity test, open field test and 96-hour acute toxicity in zebrafish. Anxiolytic doses were tested for pentylenetetrazole-induced seizures in adult zebrafish. To study the mechanisms of action, molecular docking simulations were performed between the main phytochemicals and the GABAA receptor (anxiolytic activity) and carbonic anhydrase II (anticonvulsant). The non-toxic doses that caused motor impairment were assessed in acute and chronic anxiety using the light and dark test. EtFoCl had altered the animals' locomotion, presenting an effect similar to the anxiolytic and anticonvulsant. These effects were prevented with flumazenil (GABAA antagonist). The phytochemicals homoorientin and quercetin-3-O-galactoside coupling in a region close to that of the inhibitor diazepam (GABAA receptor). Regarding the anticonvulsant mechanism, Homoorientina and Isovitexina were identified as the most favorable for the complex form with the carbonic anhydrase enzyme. C. lanceolatum has pharmacological potential for the treatment of acute and chronic anxiety and seizures, which can be partially explained by an interaction with the GABAA receptor.Communicated by Ramaswamy H. Sarma.

CD73-Mediated Formation of Extracellular Adenosine Is Responsible for Adenosine A2A Receptor-Mediated Control of Fear Memory and Amygdala Plasticity

Adenosine A2A receptors (A2AR) control fear memory and the underlying processes of synaptic plasticity in the amygdala. In other brain regions, A2AR activation is ensured by ATP-derived extracellular adenosine formed by ecto-5'-nucleotidase or CD73. We now tested whether CD73 is also responsible to provide for the activation of A2AR in controlling fear memory and amygdala long-term potentiation (LTP). The bilateral intracerebroventricular injection of the CD73 inhibitor αβ-methylene ADP (AOPCP, 1 nmol/ventricle/day) phenocopied the effect of the A2AR blockade by decreasing the expression of fear memory, an effect disappearing in CD73-knockout (KO) mice and in forebrain neuronal A2AR-KO mice. In the presence of PPADS (20 μM) to eliminate any modification of ATP/ADP-mediated P2 receptor effects, both AOPCP (100 μM) and the A2AR antagonist, SCH58261 (50 nM), decreased LTP magnitude in synapses of projection from the external capsula into the lateral amygdala, an effect eliminated in slices from both forebrain neuronal A2AR-KO mice and CD73-KO mice. These data indicate a key role of CD73 in the process of A2AR-mediated control of fear memory and underlying synaptic plasticity processes in the amygdala, paving the way to envisage CD73 as a new therapeutic target to interfere with abnormal fear-like emotional processing.

Role of the nucleoside-metabolizing enzymes on pain responses in zebrafish larvae

Purinergic signaling is a pathway related to pain underlying mechanisms. Adenosine is a neuromodulator responsible for the regulation of multiple physiological and pathological conditions. Extensive advances have been made to understand the role of adenosine in pain regulation. Here we investigated the effects of purinergic compounds able to modulate adenosine production or catabolism on pain responses induced by Acetic Acid (AA) in zebrafish larvae. We investigated the preventive role of the ecto-5'-nucleotidase inhibitor adenosine 5'-(α,β-methylene)diphosphate (AMPCP) and adenosine deaminase inhibitor erythro-9-(2-Hydroxy-3-nonyl)-adenine (EHNA) on the AA-pain induced model. The pain responses were evaluated through exploratory and aversive behaviors in zebrafish larvae. The exploratory behavior showed a reduction in the distance covered by animals exposed to 0.0025% and 0.050% AA. The movement and acceleration were reduced when compared to control. The treatment with AMPCP or EHNA followed by AA exposure did not prevent behavioral changes induced by AA for any parameter tested. There were no changes in aversive behavior after the AA-induced pain model. After AA-induced pain, the AMP hydrolysis increased on zebrafish larvae. However, the AMPCP or EHNA exposure did not prevent changes in AMP hydrolysis induced by the AA-induced pain model in zebrafish larvae. Although AMPCP or EHNA did not show differences in the AA-induced pain model, our results revealed changes in AMP hydrolysis, suggesting the involvement of the purinergic system in zebrafish larvae pain responses.

Evaluation of Resveratrol and Piceatannol Anticonvulsant Potential in Adult Zebrafish (Danio rerio)

Epilepsy is a common neurological disorder which affects 50 million people worldwide. Patients with epilepsy may present cognitive deficits and psychological impairment. Currently, 30% of patients fail to respond to any available antiseizure drug, and a significant number of patients do not well tolerate the offered treatments. Then, it is necessary to find out alternatives for controlling epileptic seizures. Studies have shown that despite its neuroprotective effects, resveratrol shows poor anticonvulsant properties. Resveratrol analog, piceatannol, possesses higher biological activity than resveratrol and could be an alternative to control seizure. Thus, the present study investigated the effects of resveratrol and piceatannol in pentylenetetrazole-induced seizures in adult zebrafish (Danio rerio). Only the experimental positive control (diazepam) showed anticonvulsant effect in this study. In addition, no behavioral changes were observed 24 h after seizure occurrence. Finally, the expression of genes related to neuronal activity (c-fos), neurogenesis (p70S6Ka and p70S6Kb), inflammatory response (interleukin 1β), and cell apoptosis (caspase-3) did not change by pentylenetetrazole-induced seizures. Therefore, we failed to observe any anticonvulsant and neuroprotective potential of resveratrol and piceatannol in adult zebrafish. However, resveratrol and piceatannol benefits in epilepsy are not discharged, and more studies are necessary.

Pentylenetetrazole-induced seizures cause impairment of memory acquisition and consolidation in zebrafish (Danio rerio)

Epilepsy is characterized by the occurrence seizures, and the high prevalence of epilepsy-associated comorbidities affects the quality of patients' life. We investigated the effects of pentylenetetrazole (PTZ) exposure in zebrafish cognitive performance on inhibitory avoidance test. The animals were exposed to the 7.5mM PTZ for 10minutes, in the acquisition (before training) and in the consolidation memory phases (after training). In the acquisition phase, the animals were submitted to PTZ-induced seizures and trained in periods of 1, 24, or 48hours after exposure, and 24hours after training were tested. In the consolidation phase, animals were trained and exposed to PTZ 10minutes after training and were tested 24hours later. Control groups in periods of 1, 24, or 48hours before or 10minutes after training showed a significantly increased latency to enter the dark compartment. The latencies between training and test sessions did not differ in PTZ groups of animals exposed and trained 1 and 24hours or exposed to PTZ 10minutes after training. At 48hours, animals exposed to PTZ showed an increased latency to enter the dark compartment. Animals exposed to PTZ and trained 1h after increased the traveled distance, when compared to the control group. Traveled distance did not differ in animals that were exposed to PTZ and trained 24 and 48hours, or 10minutes after training. Our findings indicate that PTZ causes a cognitive deficit in the pre-and post-training phase, allowing us to explore the influence of seizures at different memory phases.

Anxiolytic-like effect of natural product 2-hydroxy-3,4,6-trimethoxyacetophenone isolated from Croton anisodontus in adult zebrafish via serotonergic neuromodulation involvement of the 5-HT system

Benzodiazepines are highly effective in combating anxiety; however, they have considerable adverse effects, so it is important to discover new safe anxiolytic agents. This study was designed to investigate the effect of the natural product 2-hydroxy-3,4,6-trimethoxyacetophenone (HTMCX) on anxiety and seizure behavior in adult zebrafish and its possible mechanisms of action. The acute toxicity of 96 h of HTMCX was analyzed, and the open and light/dark field tests (n = 6 animals/group) were used to assess the anxiety behavior of animals treated with HTMCX. In addition, the mechanisms of action were investigated with antagonists of the GABA_A, 5-HT receptors, and molecular anchorage study. Pentylenetetrazole (PTZ) was used to induce seizure by immersion. As a result, acetophenone HTMCX (1, 3 and 10 mg/kg; v.o.) was non-toxic and affected locomotor activity. The higher doses (3 and 10 mg/kg; v.o.) produced signs of anxiolytic action in the light/dark test, and this effect was reversed by the pizotifen (antagonist 5HTR₁ and 5HTR_2A/2C), having the potential to form a complex with 5HTR1B. However, the anxiolytic effect of HTMCX has not been abolished by flumazenil (antagonist GABA_A), cyproheptadine (antagonist 5HTR_2A), and granisetron (antagonist 5HTR_3A/3B). Therefore, HTMCX demonstrated an anxiolytic effect, suggesting that the 5HTR₁ and 5HTR_2C receptors may be involved in the pharmacological performance of this acetophenone in the central nervous system.

Chalcones reverse the anxiety and convulsive behavior of adult zebrafish

In the treatment of anxiety and seizures, drugs of the benzodiazepine (BZD) class are used, which act on the Central Nervous System (CNS) through the neurotransmitter gamma-aminobutyric acid (GABA). Flavonoids modulate GABAA receptors. The aim of this study was to evaluate the anxiolytic and anticonvulsant effects of synthetic chalcones and their mechanisms of action via the GABAergic system, using adult zebrafish (ZFa). The animals were treated with chalcones (4.0 or 20 or 40 mg/kg; 20 µL; i.p) and submitted to the open field and 96 h toxicity test. Chalcones that cause locomotor alteration were evaluated in the light and dark anxiolytic test. The same doses of chalcones were evaluated in the anticonvulsant test. The lowest effective dose was chosen to assess the possible involvement in the GABAA receptor by blocking the flumazenil (fmz) antagonist. No chalcone was toxic and altered ZFa's locomotion. All chalcones had anxiolytic and anticonvulsant effects, mainly chalcones 1, where all doses showed effects in both tests. These effects were blocked by Fmz (antagonist GABAA), where it shows evidence of the performance of these activities of the GABA system. Therefore, this study demonstrated in relation to structure-activity, that the position of the substituents is important in the intensity of activities and that the absence of toxicity and the action of these compounds in the CNS, shows the pharmacological potential of these molecules, and, therefore, the insights are designed for the development of new drugs.

Equilibrative Nucleoside Transporters-1 Inhibitors Act as Anti-epileptic Agents by Inhibiting Glutamatergic Transmission

Background and Purpose: Adenosine dysregulation is associated with the occurrence of the epilepsy and equilibrative nucleoside transporters-1 (ENT-1) functions as an important regulator of extracellular adenosine in the brain. This study was aimed to prove the anti-epileptic effect of BBB permeable ENT-1 inhibitors, JMF1907 and J4, on animal models of various epilepsy, and the mechanisms that are involved. Experimental Approach: Maximal electroshock seizure (MES), pentylenetetrazol (PTZ)-induced seizure and kindling models were used as mouse models of generalized tonic-clonic epilepsy, generalized myoclonic epilepsy, and partial epilepsy, respectively. The epilepsy frequency, duration, and Racine score were evaluated. Whole-cell recordings were made from the hippocampal dentate granule cells by using a patch-clamp technique in the brain slice of the mice. Key Results: In MES, JMF1907 at a dose of 5 mg kg^-1 was efficacious in decreasing hindlimb extension, while J4 did not decrease hindlimb extension until a higher dose (10 mg kg^-1). Both JMF1907 and J4 were more potent in lengthening onset latency than ethosuximide (ETH) in PTZ-induced myoclonic epilepsy model, whereas ETH had better effects on the Racine score. In kindling model, JMF1907 and J4 at a dose of 1 mg kg^-1 had effects on seizure frequency and duration, and the effects of JMF1907 were comparable with those of carbamazepine. Both JMF1907 and J4 can reduce the glutamatergic spontaneous excitatory post-synaptic currents (sEPSCs) frequency. The maximal inhibition was about 50% for JMF1907 at a concentration of 1 μg L^-1, whereas J4 only inhibited 40% of sEPSCs frequency at a dose of 10 μg L^-1. Conclusion and Implications: ENT-1 inhibitors, JMF1907 and J4, showed anti-epileptic effects in different epilepsy models and the effects involved pre-synaptic neuronal modulation.

Micronized Resveratrol Shows Anticonvulsant Properties in Pentylenetetrazole-Induced Seizure Model in Adult Zebrafish

Epilepsy affects 50 million people around the world, and the patients experience cognitive, psychological and social consequences. Despite the considerable quantity of antiepileptic drugs available, 30% of patients still suffer in seizure. Therefore, the advance in therapeutic alternatives is mandatory. Resveratrol has been attracting the attention of many researchers because of its pharmacological potential. However, despite its neuroprotective and anti-epileptic effects, clinical resveratrol use is impaired by its low bioavailability. Here, we applied the supercritical fluid micronization technology (SEDS) to overcome this deficit, and investigated the anticonvulsant potential of micronized resveratrol in a PTZ-induced seizure model in adult zebrafish (Danio rerio). SEDS permits obtaining significantly reduced particle size with a fine size distribution in comparison with the starting material. It can improve the pharmacotherapeutic efficacy. Our data showed that micronized resveratrol decreased the occurrence of the tonic-clonic seizure stage and slowed the development of the seizures in a similar manner of diazepam. Non-processed resveratrol was not able to protect the animals. Furthermore, diazepam decreased the locomotion and exploratory behavior. Differently from diazepam, the micronized resveratrol did not induce behavioral adverse events. In addition, our data showed that the PTZ-induced seizures increased the c-fos transcript levels following the neural excitability. However, the increase in c-fos levels was prevented by micronized resveratrol. In conclusion, our results demonstrate that the micronized resveratrol shows anticonvulsant effect, like the classical antiepileptic drug diazepam in a PTZ-induced seizure model. Excitingly, different from diazepam, micronized resveratrol did not provoke behavioral adverse events.

Inhibition of ecto-5'-nucleotidase and adenosine deaminase is able to reverse long-term behavioural effects of early ethanol exposure in zebrafish (Danio rerio)

The behavioural impacts of prenatal exposure to ethanol include a lower IQ, learning problems, anxiety and conduct disorders. Several components of the neurochemical network could contribute to the long-lasting effects of ethanol embryonic exposure. Adenosine is an important neuromodulator, that has been indicated to be affected by acute and chronic exposure to ethanol. Here, embryos of zebrafish exposed to 1% ethanol during the developmental stages of gastrula/segmentation or pharyngula exhibited anxiolytic effect, increased aggressiveness, and decreased social interaction. The exposure during pharyngula stage was able to affect all behavioural parameters analysed at 3 months-post fertilization (mpf), while the treatment during gastrula stage affected the anxiety and social interaction parameters. The aggressiveness was the only behavioural effect of early ethanol exposure that lasted to 12 mpf. The use of a specific inhibitor of adenosine production, the inhibitor of ecto-5′-nucleotidase (AMPCP/150 mg/kg), and the specific inhibitor of adenosine degradation, the inhibitor of adenosine deaminase, EHNA (100 mg/kg) did not affect the effects over anxiety. However, AMPCP at 3 mpf, but not EHNA, reversed aggressive parameters. AMPCP also recovered the social interaction parameter at 3 mpf in animals treated in both stages, while EHNA recovered this parameter just in those animals treated with ethanol during the gastrula stage. These results suggest that long-lasting behavioural effects of ethanol can be modulated by intervention on ecto-5′-nucleotidase and adenosine deaminase activities.

Aberrant energy metabolism and redox balance in seizure onset zones of epileptic patients

Epilepsy is a disorder that affects around 1% of the population. Approximately one third of patients do not respond to anti-convulsant drugs treatment. To understand the underlying biological processes involved in drug resistant epilepsy (DRE), a combination of proteomics strategies was used to compare molecular differences and enzymatic activities in tissue implicated in seizure onset to tissue with no abnormal activity within patients. Label free quantitation identified 17 proteins with altered abundance in the seizure onset zone as compared to tissue with normal activity. Assessment of oxidative protein damage by protein carbonylation identified additional 11 proteins with potentially altered function in the seizure onset zone. Pathway analysis revealed that most of the affected proteins are involved in energy metabolism and redox balance. Further, enzymatic assays showed significantly decreased activity of transketolase indicating a disruption of the Pentose Phosphate Pathway and diversion of intermediates into purine metabolic pathway, resulting in the generation of the potentially pro-convulsant metabolites. Altogether, these findings suggest that imbalance in energy metabolism and redox balance, pathways critical to proper neuronal function, play important roles in neuronal network hyperexcitability and can be used as a primary target for potential therapeutic strategies to combat DRE. SIGNIFICANCE: Epileptic seizures are some of the most difficult to treat neurological disorders. Up to 40% of patients with epilepsy are resistant to first- and second-line anticonvulsant therapy, a condition that has been classified as refractory epilepsy. One potential therapy for this patient population is the ketogenic diet (KD), which has been proven effective against multiple refractory seizure types However, compliance with the KD is extremely difficult, and carries severe risks, including ketoacidosis, renal failure, and dangerous electrolyte imbalances. Therefore, identification of pathways disruptions or shortages can potentially uncover cellular targets for anticonvulsants, leading to a personalized treatment approach depending on a patient's individual metabolic signature.

Seizing the moment: Zebrafish epilepsy models

Zebrafish are now widely accepted as a valuable animal model for a number of different central nervous system (CNS) diseases. They are suitable both for elucidating the origin of these disorders and the sequence of events culminating in their onset, and for use as a high-throughput in vivo drug screening platform. The availability of powerful and effective techniques for genome manipulation allows the rapid modelling of different genetic epilepsies and of conditions with seizures as a core symptom. With this review, we seek to summarize the current knowledge about existing epilepsy/seizures models in zebrafish (both pharmacological and genetic) and compare them with equivalent rodent and human studies. New findings obtained from the zebrafish models are highlighted. We believe that this comprehensive review will highlight the value of zebrafish as a model for investigating different aspects of epilepsy and will help researchers to use these models to their full extent.

Low-frequency Stimulation Decreases Hyperexcitability Through Adenosine A1 Receptors in the Hippocampus of Kindled Rats

INTRODUCTION

In this study, the role of A1 adenosine receptors in improving the effect of Low-Frequency Electrical Stimulation (LFS) on seizure-induced hyperexcitability of hippocampal CA1 pyramidal neurons was investigated.

METHODS

A semi-rapid hippocampal kindling model was used to induce seizures in male Wistar rats. Examination of the electrophysiological properties of CA1 pyramidal neurons of the hippocampus using whole-cell patch-clamp recording 48 h after the last kindling stimulation revealed that the application of LFS as two packages of stimulations at a time interval of 6 h for two consecutive days could significantly restore the excitability CA1 pyramidal neurons evidenced by a decreased in the of the number of evoked action potentials and enhancement of amplitude, maximum rise slope and decay slope of the first evoked action potential, rheobase, utilization time, adaptation index, first-spike latency, and post-AHP amplitude. Selective locked of A1 receptors by the administration of 8-Cyclopentyl-1,3-dimethylxanthine (1 μM, 1 μl, i.c.v.) before applying each LFS package, significantly reduced LFS effectiveness in recovering these parameters.

RESULTS

On the other hand, selective activation of A1 receptors by an injection of N6-cyclohexyladenosine (10 μM, 1 μl, i.c.v.), instead of LFS application, could imitate LFS function in improving these parameters.

CONCLUSION

It is suggested that LFS exerts its efficacy on reducing the neuronal excitability, partially by activating the adenosine system and activating its A1 receptors.

Zebrafish models: Gaining insight into purinergic signaling and neurological disorders

Zebrafish (Danio rerio) has been considered a complementary model for biomedical studies, especially due to advantages such as external and rapid development, and genetic manipulation. There is growing interest in this model in neuroscience research since the species has morphological and physiological similarities to mammals and a complex behavioral repertoire. The purinergic signaling has been described in zebrafish, and purinoceptors and nucleotide- and nucleoside-metabolizing enzymes have already been identified in the central nervous system (CNS) of this species. The involvement of the purinergic system in several models of neurological disorders, such as Alzheimers disease, Parkinson's disease, epilepsy, schizophrenia, and autism has been investigated in zebrafish. This mini review presents several studies describing purinergic signaling in the zebrafish CNS and the action of this neurotransmitter system in models of neurological disorders using this species as a biological model. The use of pharmacological approaches at different stages of development may be a useful tool for preclinical assays and the testing of purinergic compounds as new alternatives for the treatment of neurological disorders.

Persistent increase in ecto‑5'‑nucleotidase activity from encephala of adult zebrafish exposed to ethanol during early development

Prenatal alcohol exposure causes alterations to the brain and can lead to numerous cognitive and behavioral outcomes. Long-lasting effects of early ethanol exposure have been registered in glutamatergic and dopaminergic systems. The purinergic system has been registered as an additional target of ethanol exposure. The objective of this research was to evaluate if the ecto‑5'‑nucleotidase and adenosine deaminase activities and gene expression of adult zebrafish exposed to 1% ethanol during early development could be part of the long-lasting targets of ethanol. Zebrafish embryos were exposed to 1% ethanol in two distinct developmental phases: gastrula/segmentation (5-24 h post-fertilization) or pharyngula (24-48 h post-fertilization). At the end of three months, after checking for morphological outcomes, the evaluation of enzymatic activity and gene expression was performed. Exposure to ethanol did not promote gross morphological defects; however, a significant decrease in the body length was observed (17% in the gastrula and 22% in the pharyngula stage, p < 0.0001). Ethanol exposure during the gastrula/segmentation stage promoted an increase in ecto‑5'‑nucleotidase activity (39.5%) when compared to the control/saline group (p < 0.0001). The ecto‑5'‑nucleotidase gene expression and the deamination of adenosine exerted by ecto and cytosolic adenosine deaminase were not affected by exposure to ethanol in both developmental stages. HPLC experiments did not identify differences in adenosine concentration on the whole encephala of adult animals exposed to ethanol during the gastrula stage or on control animals (p > 0.05). Although the mechanism underlying these findings requires further investigation, these results indicate that ethanol exposure during restricted periods of brain development can have long-term consequences on ecto‑5'‑nucleotidase activity, which could have an impact on subtle sequels of ethanol early exposure.

Early exposure to ethanol is able to affect the memory of adult zebrafish: Possible role of adenosine

Ethanol is one of the most widely consumed drugs in the world, and the effects of ethanol during early development include morphological and cognitive problems. The regulation of adenosine levels is essential for the proper function of major neurotransmitter systems in the brain, particularly glutamate and dopamine; thus, the investigation of the relation of adenosine and memory after early ethanol exposure becomes relevant. Embryos of zebrafish were exposed to 1% ethanol during two distinct developmental stages: gastrula/segmentation or pharyngula. The evaluation of memory, morphology, and locomotor parameters was performed when fish were 3 months old. The effect of ecto-5'-nucleotidase and adenosine deaminase inhibition on the consequences of ethanol exposure with regard to memory formation was observed. Morphological evaluation showed decreases in body length and the relative telencephalic and cerebellar areas in ethanol exposed animals. The locomotor parameters evaluated were not affected by ethanol. In the inhibitory avoidance paradigm, ethanol exposure during the gastrula/segmentation and pharyngula stages decreased zebrafish memory retention. When ethanol was given in the pharyngula stage, the inhibition of ecto-5'-nucleotidase in the acquisition phase of memory tests was able to revert the effects of ethanol on the memory of adults. These findings suggest that the increased adenosine levels caused by ethanol could alter the neuromodulation of important components of memory formation, such as neurotransmitters. The adjustment of adenosine levels through ecto-5'-nucleotidase inhibition appears to be effective at restoring normal adenosine levels and the acquisition of memory in animals exposed to ethanol during the pharyngula stage.

Nitrobenzylthioinosine mimics adenosine to attenuate the epileptiform discharge of hippocampal neurons from epileptic rats

Nitrobenzylthioinosine (NBTI), a specific inhibitor of type 1 equilibrative nucleoside transporter, could regulate the extracellular adenosine concentration and have protective roles in seizures. However, the protection mechanism of NBTI in seizures remains poorly understood. Here, the expression pattern and subcellular distribution of adenosine A1 receptor were detected by Western blot analysis and double-labeling immunofluorescence staining in Lithium Chloride-Pilocarpine induced epileptic rat model. At 24 h after pilocarpine induced rat seizures, hippocampal slices were prepared and the evoked excitatory postsynaptic currents (eEPSCs) amplitude of pyramidal neurons in hippocampus CA1 region was recorded using whole-cell patch clamp. In vivo, compared to control group, Western blotting analysis showed that the expression of adenosine A1 receptor protein was increased at 24 h and 72 h after seizure, didn't change at 0 min and 1 w, and decreased at 2 w. Double-label immunofluorescence revealed that adenosine A1 receptor was mainly expressed in the membrane and cytoplasm of neurons. In Vitro, adenosine decreased the eEPSCs amplitude of pyramidal neurons in hippocampus CA1 region, NBTI also had the same effect. Meantime, NBTI could further inhibit eEPSCs amplitude on the basis of lower concentration adenosine (50μM), and adenosine A1 receptor inhibitor DPCPX partially reversed this effect. Taken together, we confirmed that the expression of adenosine A1 receptor protein was increased in the early seizures and decreased in the late seizures. At the same time, NBTI mimics adenosine to attenuate the epileptiform discharge through adenosine A1 receptor, which might provide a novel therapeutic approach toward the control of epilepsy.

Zebrafish Models of Human Disease: Gaining Insight into Human Disease at ZFIN

The Zebrafish Model Organism Database (ZFIN; https://zfin.org) is the central resource for genetic, genomic, and phenotypic data for zebrafish (Danio rerio) research. ZFIN continuously assesses trends in zebrafish research, adding new data types and providing data repositories and tools that members of the research community can use to navigate data. The many research advantages and flexibility of manipulation of zebrafish have made them an increasingly attractive animal to model and study human disease.To facilitate disease-related research, ZFIN developed support to provide human disease information as well as annotation of zebrafish models of human disease. Human disease term pages at ZFIN provide information about disease names, synonyms, and references to other databases as well as a list of publications reporting studies of human diseases in which zebrafish were used. Zebrafish orthologs of human genes that are implicated in human disease etiology are routinely studied to provide an understanding of the molecular basis of disease. Therefore, a list of human genes involved in the disease with their corresponding zebrafish ortholog is displayed on the disease page, with links to additional information regarding the genes and existing mutations. Studying human disease often requires the use of models that recapitulate some or all of the pathologies observed in human diseases. Access to information regarding existing and published models can be critical, because they provide a tractable way to gain insight into the phenotypic outcomes of the disease. ZFIN annotates zebrafish models of human disease and supports retrieval of these published models by listing zebrafish models on the disease term page as well as by providing search interfaces and data download files to access the data. The improvements ZFIN has made to annotate, display, and search data related to human disease, especially zebrafish models for disease and disease-associated gene information, should be helpful to researchers and clinicians considering the use of zebrafish to study human disease.

Non-mammalian models in behavioral neuroscience: consequences for biological psychiatry

Current models in biological psychiatry focus on a handful of model species, and the majority of work relies on data generated in rodents. However, in the same sense that a comparative approach to neuroanatomy allows for the identification of patterns of brain organization, the inclusion of other species and an adoption of comparative viewpoints in behavioral neuroscience could also lead to increases in knowledge relevant to biological psychiatry. Specifically, this approach could help to identify conserved features of brain structure and behavior, as well as to understand how variation in gene expression or developmental trajectories relates to variation in brain and behavior pertinent to psychiatric disorders. To achieve this goal, the current focus on mammalian species must be expanded to include other species, including non-mammalian taxa. In this article, we review behavioral neuroscientific experiments in non-mammalian species, including traditional "model organisms" (zebrafish and Drosophila) as well as in other species which can be used as "reference." The application of these domains in biological psychiatry and their translational relevance is considered.