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Cannabidiol (CBD) is a phytocannabinoid devoid of psychostimulant properties and is currently under investigation as a potential antidepressant drug. However, the mechanisms underlying CBD's antidepressant effects are not yet well understood. CBD targets include a variety of receptors, enzymes, and transporters, with different binding-affinities. Neurochemical and pharmacological evidence indicates that both serotonin and BDNF-TrkB signalling in the prefrontal cortex are necessary for the antidepressant effects induced by CBD in animal models. Herein, we reviewed the current literature to dissect if these are independent mechanisms or if CBD-induced modulation of the serotonergic neurotransmission could mediate its neuroplastic effects through subsequent regulation of BDNF-TrkB signalling, thus culminating in rapid neuroplastic changes. It is hypothesized that: a) CBD interaction with serotonin receptors on neurons of the dorsal raphe nuclei and the resulting disinhibition of serotonergic neurons would promote rapid serotonin release in the PFC and hence its neuroplastic and antidepressant effects; b) CBD facilitates BDNF-TRKB signalling, especially in the PFC, which rapidly triggers neurochemical and neuroplastic effects. These hypotheses are discussed with perspectives for new drug development and clinical applications., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest., (Copyright © 2024. Published by Elsevier Inc.)

Studies investigated how stressful experiences modulate physiological and behavioral responses and the consequences of stress-induced corticosterone release in anxiety-like behavior. Adolescence is crucial to brain maturation, and several neurobiological changes in this period lead individuals to increased susceptibility or resilience to aversive situations. Despite the effects of stress in adults, information about adolescents' responses to acute stress is lacking. We aimed to understand how adolescence affects acute stress responses. Male adolescent rats (30 days old) were 2 h restrained, and anxiety-like behaviors were measured immediately or 10 days after stress in the elevated plus-maze (EPM) and the light-dark box (LDB) tests. To verify the importance of CORT modulation in stress-induced anxiety, another group of rats was treated, 30 min before restraint, with metyrapone to blunt the stress-induced CORT peak and tested immediately after stress. To show that stress effects on behavior were age-dependent, another set of rats was tested in two different periods - early adolescence (30 days old) and mid-adolescence (40 days old) and were treated or not with metyrapone before the stress session and tested immediately or ten days later in the LDB test. Only early adolescent male rats were resilient to delayed anxiety-like behavior in EPM and LDB tests. Metyrapone treatment increased the rats' exploration immediately and ten days after stress. These data suggest a specific age at which adolescent rats are resilient to the delayed effects of acute restraint stress and that the metyrapone treatment has long-term behavioral consequences., (Copyright © 2022. Published by Elsevier Ltd.)

This study examined the psychometric properties of a Brazilian adapted version of the Coronavirus Anxiety Scale (CAS-BR) in a sample of adults in Brazil. Confirmatory factor analyses demonstrated that the CAS-BR produces a reliable (α = .84), unidimensional construct whose structure was shown to be invariant across gender, race, and age. However, some items of the CAS-BR were stronger indicators of the coronavirus anxiety construct for women and younger adults. Although the CAS-BR demonstrated evidence of discrimination ability for functional impairment (AUC = .77), Youden indexes were low to identify a clinical cut-score. Construct validity was demonstrated with correlations between CAS-BR scores and measures of functional impairment, generalized anxiety, and depression. Exploratory analyses revealed that CAS-BR total scores were higher among women and participants with a history of anxiety disorder. These findings are consistent with previous investigations and support the validity of CAS-BR for measuring coronavirus anxiety with Brazilian adults.

Background: Knowledge on the neurobiological systems underlying psychiatric disorders has considerably evolved due to findings on basic research using animal models. Anxiety-like behaviors in rodents are widely explored in neuroethological apparatuses, such as the light-dark box (LDB) test through different protocols, which have been shown to influence the behavioral outcomes and probably the activation of the hypothalamic-pituitary-adrenal (HPA) axis., New Method: Adult male Wistar rats were submitted to LDB in different room illumination conditions (25/0, 65/0 and/or 330/0 lux), initial positioning in the LDB compartments and previous stressful experience in the Elevated Plus Maze (EPM) or restraint stress (RS). Rats' behavior (exploratory and risk assessment) was registered during a 15 min period, divided into blocks of 5 min RESULTS: Exploration of the lit compartment decreased in higher luminosity condition, as after positioning rats in the dark compartment or previous exposure to the EPM, while low luminosity increased exploration of the LDB. No differences were observed on serum corticosterone in all groups and experimental conditions., Comparison With Existing Methods: Light intensity and test duration influenced exploration of the LDB jeopardizing the anxiolytic/anxiogenic effects. Low light intensity increased exploration, while high intensity decreased it. These results suggest that 65/0 lux is a neutral condition to investigate possible anxiolytic/anxiogenic effects of drugs and/or exposure to previous aversive stimuli as the EPM., Conclusions: Different factors impact on exploratory and risk assessment behaviors which may be related to safety maximization behavior. Unraveling how different factors affect behavior may be a crucial step towards understanding its expression and the contributions on advances in the physiopathology 1 and treatment of psychiatric disorders., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The facilitation of corticostriatal transmission is modulated by the pharmacological inhibition of striatal phosphodiesterase 10A (PDE10A). Since L-DOPA-induced dyskinesia is associated with abnormal corticostriatal transmission, we hypothesized that inhibition of PDE10A would modulate L-DOPA-induced dyskinesia (LID) by regulating corticostriatal activity. 6-OHDA-lesioned rats were chronically treated with L-DOPA for one week. After that, for two additional weeks, animals were treated with the PDE10A inhibitor PDM-042 (1 and 3 mg/kg) one hour before L-DOPA. Behavioral analyses were performed to quantify abnormal involuntary movements (AIMs) and to assess the antiparkinsonian effects of L-DOPA. Single-unit extracellular electrophysiological recordings were performed in vivo to characterize the responsiveness of MSNs to cortical stimulation. The low dose of PDM-042 had an antidyskinetic effect (i.e., attenuated peak-dose dyskinesia) and did not interfere with cortically evoked spike activity. Conversely, the high dose of PDM-042 did not affect peak-dose dyskinesia, prolonged AIMs, and increased cortically evoked spike activity. These data suggest that the facilitation of corticostriatal transmission is likely to contribute to the expression of AIMs. Therefore, cyclic nucleotide manipulation is an essential target in controlling LID.

Parvalbumin is a calcium-binding protein present in inhibitory interneurons that play an essential role in regulating many physiological processes, such as intracellular signaling and synaptic transmission. Changes in parvalbumin expression are deeply related to epilepsy, which is considered one of the most disabling neuropathologies. Epilepsy is a complex multi-factor group of disorders characterized by periods of hypersynchronous activity and hyperexcitability within brain networks. In this scenario, inhibitory neurotransmission dysfunction in modulating excitatory transmission related to the loss of subsets of parvalbumin-expressing inhibitory interneuron may have a prominent role in disrupted excitability. Some studies also reported that parvalbumin-positive interneurons altered function might contribute to psychiatric comorbidities associated with epilepsy, such as depression, anxiety, and psychosis. Understanding the epileptogenic process and comorbidities associated with epilepsy have significantly advanced through preclinical and clinical investigation. In this review, evidence from parvalbumin altered function in epilepsy and associated psychiatric comorbidities were explored with a translational perspective. Some advances in potential therapeutic interventions are highlighted, from current antiepileptic and neuroprotective drugs to cutting edge modulation of parvalbumin subpopulations using optogenetics, designer receptors exclusively activated by designer drugs (DREADD) techniques, transcranial magnetic stimulation, genome engineering, and cell grafting. Creating new perspectives on mechanisms and therapeutic strategies is valuable for understanding the pathophysiology of epilepsy and its psychiatric comorbidities and improving efficiency in clinical intervention., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Godoy, Prizon, Rossignoli, Leite and Liberato.)

Motor symptoms of Parkinson's disease (PD)-bradykinesia, akinesia, and tremor at rest-are consequences of the neurodegeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) and dopaminergic striatal deficit. Animal models have been widely used to simulate human pathology in the laboratory. Rodents are the most used animal models for PD due to their ease of handling and maintenance. Moreover, the anatomy and molecular, cellular, and pharmacological mechanisms of PD are similar in rodents and humans. The infusion of the neurotoxin, 6-hydroxydopamine (6-OHDA), into a medial forebrain bundle (MFB) of rats reproduces the severe destruction of dopaminergic neurons and simulates PD symptoms. This protocol demonstrates how to perform the unilateral microinjection of 6-OHDA in the MFB in a rat model of PD and shows the motor deficits induced by 6-OHDA and predicted dopaminergic lesions through the stepping test. The 6-OHDA causes significant impairment in the number of steps performed with the contralateral forelimb.

Epileptogenesis is a multistage process and seizure susceptibility can be influenced by stress early in life. Wistar Audiogenic Rat (WAR) strain is an interesting model to study the association between stress and epilepsy, since it is naturally susceptible to seizures and present changes in the hypothalamus-pituitary-adrenal (HPA) axis activity. All these features are related to the pathogenic mechanisms usually associated with psychiatric comorbidities present in epilepsy. Therefore, the current study aimed to evaluate the neonate HPA axis function and maternal care under control and stress conditions in the WAR strain. Maternal behavior and neonate HPA axis were evaluated in Wistar and WAR strains under rest and after the presence of stressors. We observed that WAR pups present higher plasmatic corticosterone concentration as compared to Wistar pups. Although WAR dams do not show significant altered maternal behavior at rest, there is a higher latency to recover the litter in the pup retrieval test, while some did not recover all the litter. Wistar Audiogenic Rat dams presented similar behaviors to Wistar dams to a female intruder and maternal care with the pups in the maternal defense test. Taken together, these findings indicate that the WAR strain could show HPA axis disruption early in life and dams present altered maternal behavior under stressful events. Those alterations make the WAR strain an interesting model to evaluate vulnerability to epilepsy and its associated neuropsychiatric comorbidities., Competing Interests: Declaration of Competing Interests The authors declare that there is not conflict of interest., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Early life adversity (ELA) is associated with altered neural development and increased risk for the development of psychopathology across the lifespan. Rodent models of ELA are an important tool for investigating the possible mechanistic underpinnings of pathology development. We used a limited bedding and nesting model (LBN) to induce stress in the dam and alter dam-pup interactions during a sensitive period in early postnatal development. The primary characteristics previously identified in this model include fragmented and unpredictable maternal care and possibly neglect. However, previous studies have not considered the effects of this manipulation over the full circadian cycle and the evolution of changes of maternal behavior throughout the duration of the manipulation. In the current study, we leverage a novel continuous video monitoring setup to unobtrusively observe and subsequently analyze maternal behaviors. Through this more in-depth analysis, we discovered that LBN dams spent more time than control dams on their nest, returned to their nest more frequently than control dams, and showed intact maternal care. Importantly, a subset of LBN dams (~40%) engaged in abusive-like kicking, a behavioral pattern not previously identified in this paradigm. Exposure to ELA and abusive-like kicking were associated with differences in risk-taking behavior in adulthood. The LBN model of ELA may drive a more complex constellation of effects on maternal behavior driving a pattern of increased dam-pup interactions and increased abuse-like kicking behavior, with unique consequences for pup outcomes.

Background: Studies on toad poison are relevant since they are considered a good source of toxins that act on different biological systems. Among the molecules found in the toad poison, it can be highlighted the cardiotonic heterosides, which have a known mechanism that inhibit Na + /K + -ATPase enzyme. However, these poisons have many other molecules that may have important biological actions. Therefore, this work evaluated the action of the low molecular weight components from Rhinella schneideri toad poison on Na + /K + -ATPase and their anticonvulsive and / or neurotoxic effects, in order to detect molecules with actions of biotechnological interest., Methods: Rhinella schneideri toad (male and female) poison was collected by pressuring their parotoid glands and immediately dried and stored at -20 °C. The poison was dialysed and the water containing the low molecular mass molecules (< 8 kDa) that permeate the dialysis membrane was collected, frozen and lyophilized, resulting in the sample used in the assays, named low molecular weight fraction (LMWF). Na + /K + ATPase was isolated from rabbit kidneys and enzyme activity assays performed by the quantification of phosphate released due to enzyme activity in the presence of LMWF (1.0; 10; 50 and 100 µg/mL) from Rhinella schneideri poison. Evaluation of the L-Glutamate (L-Glu) excitatory amino acid uptake in brain-cortical synaptosomes of Wistar rats was performed using [3H]L-glutamate and different concentration of LMWF (10 -5 to 10 µg/µL). Anticonvulsant assays were performed using pentylenetetrazole (PTZ) and N-methyl-D-aspartate (NMDA) to induce seizures in Wistar rats (n= 6), which were cannulated in the lateral ventricle and treated with different concentration of LMWF (0.25; 0.5; 1.0; 2.0; 3.0 and 4.0 µg/µL) 15 min prior to the injection of the seizure agent., Results: LMWF induced a concentration-dependent inhibition of Na + /K + -ATPase (IC 50% = 107.5 μg/mL). The poison induces an increased uptake of the amino acid L-glutamate in brain-cortical synaptosomes of Wistar rats. This increase in the L-glutamate uptake was observed mainly at the lowest concentrations tested (10 -5 to 10 -2 µg/µL). In addition, this fraction showed a very relevant central neuroprotection on seizures induced by PTZ and NMDA., Conclusions: LMWF from Rhinella schneideri poison has low molecular weight compounds, which were able to inhibit Na + /K + -ATPase activity, increase the L-glutamate uptake and reduced seizures induced by PTZ and NMDA . These results showed that LMWF is a rich source of components with biological functions of high medical and scientific interest., Competing Interests: Competing interests: The authors declare that there are no competing interests.

Epilepsy is considered as one of the major disabling neuropathologies. Almost one third of adult patients with temporal lobe epilepsy (TLE) do not respond to current antiepileptic drugs (AEDs). Additionally, most AEDs do not have neuroprotective effects against the inherent neurodegenerative process underlying the hippocampal sclerosis on TLE. Dysfunctions in the GABAergic neurotransmission may contribute not only to the onset of epileptic activity but also constitute an important system for therapeutic approaches. Therefore, molecules that enhance GABA inhibitory effects could open novel avenues for the understanding of epileptic plasticity and for drug development. Parawixin2, a compound isolated from Parawixia bistriata spider venom, inhibits both GABA and glycine uptake and has an anticonvulsant effect against a wide range of chemoconvulsants. The neuroprotective potential of Parawixin2 was analyzed in a model of TLE induced by a long-lasting Status Epilepticus (SE), and its efficiency was compared to well-known neuroprotective drugs, such as riluzole and nipecotic acid. Neuroprotection was assessed through histological markers for cell density (Nissl), astrocytic reactivity (GFAP) and cell death labeling (TUNEL), which were performed 24 h and 72 h after SE. Parawixin2 treatment resulted in neuroprotective effects in a dose dependent manner at 24 h and 72 h after SE, as well as reduced reactive astrocytes and apoptotic cell death. Based on these findings, Parawixin2 has a great potential to be used as a tool for neuroscience research and as a probe to the development of novel GABAergic neuroprotective agents.

Stress is recognized as an important issue in basic and clinical neuroscience research, based upon the founding historical studies by Walter Canon and Hans Selye in the past century, when the concept of stress emerged in a biological and adaptive perspective. A lot of research after that period has expanded the knowledge in the stress field. Since then, it was discovered that the response to stressful stimuli is elaborated and triggered by the, now known, stress system , which integrates a wide diversity of brain structures that, collectively, are able to detect events and interpret them as real or potential threats. However, different types of stressors engage different brain networks, requiring a fine-tuned functional neuroanatomical processing. This integration of information from the stressor itself may result in a rapid activation of the Sympathetic-Adreno-Medullar (SAM) axis and the Hypothalamus-Pituitary-Adrenal (HPA) axis, the two major components involved in the stress response. The complexity of the stress response is not restricted to neuroanatomy or to SAM and HPA axes mediators, but also diverge according to timing and duration of stressor exposure, as well as its short- and/or long-term consequences. The identification of neuronal circuits of stress, as well as their interaction with mediator molecules over time is critical, not only for understanding the physiological stress responses, but also to understand their implications on mental health.

Evidences suggest the contributive role of early-life stress (ELS) to affective and anxiety disorders. Chronic exposure to the same stressor may generate habituation, while the exposure to different and repeated stressors gradually promotes maladaptive plasticity. Therefore, to further understand the effects of heterotypic stressors during early life period, male Wistar rat pups (P1-P21) were exposed to Multimodal ELS paradigm. Results indicate pups did not habituate to multimodal ELS and neonates respond to both physical and psychogenic stressors. Adult rats that underwent ELS protocol showed significant lower sucrose intake, decreased latency to immobility in the forced swim test and increased latency to light compartment in the light-dark test when compared to control group. Although it has been shown that ELS-induced changes in hippocampus can be used as biomarkers, multimodal ELS did not significantly alter BDNF, Tyrosine Kinase B (TrkB) receptor expression or neurogenesis in the hippocampus. Taken together, these findings indicate that multimodal ELS protocol can be an interesting experimental model for understanding long-term psychiatric disorders associated with stress. Indeed, our data with neurogenesis, BDNF and TrkB, and conflicting data from the literature, suggest that additional studies on synaptic plasticity/intracellular cascades would help to detect the underlying mechanisms., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The Wistar Audiogenic Rat (WAR) is a well-characterized seizure-prone, inbred rodent strain that, when acutely stimulated with high-intensity sounds, develops brainstem-dependent tonic-clonic seizures that can evolve to limbic-like, myoclonic (forebrain) seizures when the acoustic stimuli are presented chronically (audiogenic kindling). In order to investigate possible mechanisms underlying WAR susceptibility to seizures, we evaluated Na,K-ATPase activity, Ca-ATPase activity, Mg-ATPase activity, lipid membrane composition and oxidative stress markers in whole forebrain and whole brainstem samples of naïve WAR, as compared to samples from control Wistar rats. We also evaluated the expression levels of α1 and α3 isoforms of Na,K-ATPase in forebrain samples. We observed increased Na,K-ATPase activity in forebrain samples and increased oxidative stress markers (lipid peroxidation, glutathione peroxidase and superoxide dismutase) in brainstem samples of WAR. The Ca-ATPase activity, Mg-ATPase activity, lipid membrane composition and expression levels of α1 and α3 isoforms of Na,K-ATPase were unaltered. In view of previous data showing that the membrane potentials from naïve WAR's neurons are less negative than that from neurons from Wistar rats, we suggest that Na,K-ATPase increased activity might be involved in a compensatory mechanism necessary to maintain WAR's brains normal activity. Additionally, ongoing oxidative stress in the brainstem could bring Na,K-ATPase activity back to normal levels, which may explain why WAR's present increased susceptibility to seizures triggered by high-intensity sound stimulation., (Copyright © 2017 Elsevier B.V. All rights reserved.)

(1) Background: Temporal lobe epilepsy (TLE) is the most common type of epilepsy in adults. It is also the one with the highest percentage of drug-resistance to the current available anti-epileptic drugs (AED). Additionaly, most antiepileptic drugs are only able to control seizures in epileptogenesis, but do not decrease the hippocampal neurodegenerative process. TLE patients have a reduced population of interneuronal cells, which express Parvalbumin (PV) proteins. This reduction is directly linked to seizure frequency and severity in the chronic period of epilepsy. There is therefore a need to seek new therapies with a disease-modifying profile, and with efficient antiepileptic and neuroprotective properties. Parawixin2, a compound isolated from the venom of the spider Parawixia bistriata , has been shown to inhibit GABA transporters (GAT) and to have acute anticonvulsant effects in rats. (2) Methods: In this work, we studied the effects of Parawixin2 and Tiagabine (an FDA- approved GAT inhibitor), and compared these effects in a TLE model. Rats were subjected to lithium-pilocarpine TLE model and the main features were evaluated over a chronic period including: (a) spontaneous recurrent seizures (SRS), (b) neuronal loss, and (c) PV cell density in different regions of the hippocampus (CA1, CA3, DG and Hilus). (3) Results: Parawixin2 treatment reduced SRS frequency whereas Tiagabine did not. We also found a significant reduction in neuronal loss in CA3 and in the hilus regions of the hippocampus, in animals treated with Parawixin2. Noteworthy, Parawixin2 significantly reversed PV cell loss observed particularly in DG layers. (4) Conclusions: Parawixin2 exerts a promising neuroprotective and anti-epileptic effect and has potential as a novel agent in drug design., Competing Interests: The authors declare no conflict of interest.

Scope: Nutrigenomics is a rapidly expanding field that elucidates the link between diet-genome interactions. Recent evidence demonstrates that regulation of the epigenome, and in particular inhibition of histone deacetylases (HDACs), impact pathogenetic mechanisms involved in chronic disease. Few studies, to date, have screened libraries of bioactive compounds that act as epigenetic modifiers. This study screened a library of 131 natural compounds to determine bioactive compounds that inhibit Zn-dependent HDAC activity., Methods and Results: Using class-specific HDAC substrates, we screened 131 natural compounds for HDAC activity in bovine cardiac tissue. From this screen, we identified 18 bioactive compound HDAC inhibitors. Using our class-specific HDAC substrates, we next screened these 18 bioactive compounds against recombinant HDAC proteins. Consistent with inhibition of HDAC activity, these compounds were capable of inhibiting activity of individual HDAC isoforms. Lastly, we report that treatment of H9c2 cardiac myoblasts with bioactive HDAC inhibitors was sufficient to increase lysine acetylation as assessed via immunoblot., Conclusion: This study provided the first step in identifying multiple bioactive compound HDAC inhibitors. Taken together, this report sets the stage for future exploration of these bioactive compounds as epigenetic regulators to potentially ameliorate chronic disease., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Polyamines are compounds that interact with ionotropic receptors, mainly modulating the NMDA receptor, which is strictly related to many neurologic diseases such as epilepsy. Consequently, polyamines rise as potential neuropharmacological tools in the prospection of new therapeutic drugs. In this paper, we report on the biological activity of synthetic polyamine Mygalin, which was tested as an anticonvulsant in model of chemically induced seizures. Male Wistar rats were injected with vehicle, diazepam, MK-801 or Mygalin at different doses followed by Pentylenetetrazole or N-Methyl-D-Aspartate administration. Mygalin presented protection against seizures induced by both NMDA injections and PTZ administration by 83.3% and 16.6%, respectively. Moreover, it prolonged the onset of tonic-clonic seizures induced by PTZ. Furthermore, it was tested in neuroethological schedule evaluating possible side-effects and it presented mild changes in Open Field, Rotarod and Morris Water Maze tests when compared to available anticonvulsant drugs. The mechanism underlying the anticonvulsant effect of Mygalin is noteworthy of further investigation, nevertheless, based on these findings, we hypothesize that it may be wholly or in part due to a possible NMDA receptor antagonism. Altogether, the results demonstrate that Mygalin has an anticonvulsant activity that may be an important tool in the study of prospection of therapeutics in epilepsy neuropharmacology.

The regulation of cardiac delayed rectifier potassium (Kv) currents by cAMP-dependent protein kinase (PKA) contributes to the control of blood pressure and heart rate. We investigated the modulation by PKA and protein phosphatases of cloned Kv1.5 channels expressed in Xenopus laevis oocytes. Exposure of oocytes to activators of PKA (100 nM forskolin, 1 mM 8-bromo-cAMP, or 1 mM 3-isobutyl-1-methylxanthine) had no effect on the amplitude of Kv1.5 currents. Inhibition of PKA by injection of protein kinase A inhibitor peptide or exposure to myristoylated protein kinase A inhibitor peptide (M-PKI; 100 nM) reduced currents mediated by Kv1.5. M-PKI also reduced the amplitude of currents mediated by mutated Kv1.5 channels in which the COOH terminal PKA phosphorylation sites and PSD-95, Disc-large, and ZO-1-binding domain were removed. The reduction of Kv1.5 currents by M-PKI was attenuated by inhibition of actin polymerization by 1 microM cytochalasins B and D, but was not affected by 10 microM phalloidin (stabilizes actin filaments) or 50 microM colchicine (disrupts microtubules). Treatment of oocytes with antisense oligonucleotides against alpha-actinin-2 abolished the reduction in Kv1.5 current by M-PKI. These observations suggest that Kv1.5 currents are activated by endogenous PKA in "resting" oocytes and that inhibition of PKA activity reveals the action of endogenous phosphatases. Indeed, injection of alkaline phosphatase reduced currents mediated by Kv1.5. Further preincubation of oocytes with 1 mM sodium orthovanadate (a protein tyrosine phosphatase inhibitor) abolished the reduction in Kv1.5 currents by M-PKI. We conclude that currents encoded by Kv1.5 are regulated by PKA and protein tyrosine phosphatase and that this regulation requires an intact actin cytoskeleton and alpha-actinin-2.