Proconvulsive effects of oxytocin in the generalized pentylenetetrazol mouse model are mediated by vasopressin 1a receptors

Protective Effects of Intranasally Administrated Oxytocin-Loaded Nanoparticles on Pentylenetetrazole-Kindling Epilepsy in Terms of Seizure Severity, Memory, Neurogenesis, and Neuronal Damage

Pentylenetetrazole (PTZ)-induced kindling is an animal model for studying human temporal lobe epilepsy (TLE), which is characterized by alterations of hippocampal neurons and memory. Although the intranasal (IN) administration of oxytocin (OT) has limited efficiency, nanoparticles (NPs) are a promising candidate to deliver OT to the brain. However, there are very limited data on epilepsy research about oxytocin-loaded nanoparticles (NP-OTs). The aim of this study is to investigate the effects of IN administration of chronic NP-OTs on the hippocampus of PTZ-induced male epileptic rats in terms of seizure severity, memory, neurogenesis, and neuronal damage. Saline/OT/NP-OTs were administrated to both control (Ctrl) and PTZ groups intranasally. Consequently, saline and PTZ were injected, respectively, 25 times every 48 h. Then, seizure severity (score and latency) was calculated for the PTZ groups. A spatial working memory evaluation test (SWMET) was performed after the last injection. Hippocampus histopathology, neurogenesis, and apoptosis were demonstrated. Serum total antioxidant status (TAS) and total oxidant status (TOS) levels and the oxidative stress index (OSI) were measured. We showed that OTs and NP-OTs prevented the kindling development and had positive effects on seizure severity. SWMET-related behaviors were also recovered in the PTZ + NP-OT group. A significant increase of neurogenesis and decrease of apoptosis in the hippocampus of the PTZ + NP-OT group were observed, while OTs and NP-OTs had protective effects against PTZ-induced damage to hippocampal neurons. Our results indicate that the chronic administration of NP-OTs may have positive effects on hippocampal damage via increasing neurogenesis and decreasing apoptosis and seizure severity.

Neuroendocrine changes in the hypothalamic-neurohypophysial system in the Wistar audiogenic rat (WAR) strain submitted to audiogenic kindling

The Wistar audiogenic rat (WAR) strain is used as an animal model of epilepsy, which when submitted to acute acoustic stimulus presents tonic-clonic seizures, mainly dependent on brainstem (mesencephalic) structures. However, when WARs are exposed to chronic acoustic stimuli (audiogenic kindling-AK), they usually present tonic-clonic seizures, followed by limbic seizures, after recruitment of forebrain structures such as the cortex, hippocampus and amygdala. Although some studies have reported that hypothalamic-hypophysis function is also altered in WAR through modulating vasopressin (AVP) and oxytocin (OXT) secretion, the role of these neuropeptides in epilepsy still is controversial. We analyzed the impact of AK and consequent activation of mesencephalic neurocircuits and the recruitment of forebrain limbic (LiR) sites on the hypothalamic-neurohypophysial system and expression of Avpr1a and Oxtr in these structures. At the end of the AK protocol, nine out of 18 WARs presented LiR. Increases in both plasma vasopressin and oxytocin levels were observed in WAR when compared to Wistar rats. These results were correlated with an increase in the expressions of heteronuclear (hn) and messenger (m) RNA for Oxt in the paraventricular nucleus (PVN) in WARs submitted to AK that presented LiR. In the paraventricular nucleus, the hnAvp and mAvp expressions increased in WARs with and without LiR, respectively. There were no significant differences in Avp and Oxt expression in supraoptic nuclei (SON). Also, there was a reduction in the Avpr1a expression in the central nucleus of the amygdala and frontal lobe in the WAR strain. In the inferior colliculus, Avpr1a expression was lower in WARs after AK, especially those without LiR. Our results indicate that both AK and LiR in WARs lead to changes in the hypothalamic-neurohypophysial system and its receptors, providing a new molecular basis to better understaind epilepsy.

Nanoparticle encapsulated oxytocin increases resistance to induced seizures and restores social behavior in Scn1a-derived epilepsy

Oxytocin (OT) has broad effects in the brain and plays an important role in cognitive, social, and neuroendocrine function. OT has also been identified as potentially therapeutic in neuropsychiatric disorders such as autism and depression, which are often comorbid with epilepsy, raising the possibility that it might confer protection against the behavioral and seizure phenotypes in epilepsy. Dravet syndrome (DS) is an early-life encephalopathy associated with prolonged and recurrent early-life febrile seizures (FSs), treatment-resistant afebrile epilepsy, and cognitive and behavioral deficits. De novo loss-of-function mutations in the voltage-gated sodium channel SCN1A are the main cause of DS, while genetic epilepsy with febrile seizures plus (GEFS+), also characterized by early-life FSs and afebrile epilepsy, is typically caused by inherited mutations that alter the biophysical properties of SCN1A. Despite the wide range of available antiepileptic drugs, many patients with SCN1A mutations do not achieve adequate seizure control or the amelioration of associated behavioral comorbidities. In the current study, we demonstrate that nanoparticle encapsulation of OT conferred robust and sustained protection against induced seizures and restored more normal social behavior in a mouse model of Scn1a-derived epilepsy. These results demonstrate the ability of a nanotechnology formulation to significantly enhance the efficacy of OT. This approach will provide a general strategy to enhance the therapeutic potential of additional neuropeptides in epilepsy and other neurological disorders.

Social Interaction Improved by Oxytocin in the Subclass of Autism with Comorbid Intellectual Disabilities

Approximately half of all autism spectrum disorder (ASD) individuals suffer from comorbid intellectual disabilities. Furthermore, the prevalence of epilepsy has been estimated to be 46% of patients with low intelligence quotient. It is important to investigate the therapeutic benefits and adverse effects of any recently developed drugs for this proportion of individuals with the so-called Kanner type of ASD. Therefore, we investigated the therapeutic and/or adverse effects of intranasal oxytocin (OT) administration, especially in adolescents and adults with ASD and comorbid intellectual disability and epilepsy, with regard to core symptoms of social deficits. We have already reported three randomized placebo-controlled trials (RCTs). However, we revisit results in our pilot studies from the view of comorbidity. Most of the intellectually disabled participants were found to be feasible participants of the RCT. We observed significantly more events regarded as reciprocal social interaction in the OT group compared with the placebo group. In the trial, no or little differences in adverse events were found between the OT and placebo arms, as found in some other reports. However, seizures were induced in three participants with medical history of epilepsy during or after OT treatment. In conclusion, we stress that behavioral changes in ASD patients with intellectual disabilities could be recognized not by the conventional measurements of ASD symptoms but by detailed evaluation of social interactions arising in daily-life situations.

Acute and long-lasting effects of oxytocin in cortico-limbic circuits: consequences for fear recall and extinction

The extinction of conditioned fear responses entrains the formation of safe new memories to decrease those behavioral responses. The knowledge in neuronal mechanisms of extinction is fundamental in the treatment of anxiety and fear disorders. Interestingly, the use of pharmacological compounds that reduce anxiety and fear has been shown as a potent co-adjuvant in extinction therapy. However, the efficiency and mechanisms by which pharmacological compounds promote extinction of fear memories remains still largely unknown and would benefit from a validation based on functional neuronal circuits, and the neurotransmitters that modulate them. From this perspective, oxytocin receptor signaling, which has been shown in cortical and limbic areas to modulate numerous functions (Eliava et al. Neuron 89(6):1291-1304, 2016), among them fear and anxiety circuits, and to enhance the salience of social stimuli (Stoop Neuron 76(1):142-59, 2012), may offer an interesting perspective. Experiments in animals and humans suggest that oxytocin could be a promising pharmacological agent at adjusting memory consolidation to boost fear extinction. Additionally, it is possible that long-term changes in endogenous oxytocin signaling can also play a role in reducing expression of fear at different brain targets. In this review, we summarize the effects reported for oxytocin in cortico-limbic circuits and on fear behavior that are of relevance for the modulation and potential extinction of fear memories.

Cross-talk among oxytocin and arginine-vasopressin receptors: Relevance for basic and clinical studies of the brain and periphery

Oxytocin (OT) and arginine-vasopressin (AVP) act in the brain to regulate social cognition/social behavior and in the periphery to influence a variety of physiological processes. Although the chemical structures of OT and AVP as well as their receptors are quite similar, OT and AVP can have distinct or even opposing actions. Here, we review the increasing body of evidence that exogenously administered and endogenously released OT and AVP can activate each other's canonical receptors (i.e., cross-talk) and examine the possibility that receptor cross-talk following the synaptic and non-synaptic release of OT and AVP contributes to their distinct roles in the brain and periphery. Understanding the consequences of cross-talk between OT and AVP receptors will be important in identifying how these peptides control social cognition and behavior and for the development of drugs to treat a variety of psychiatric disorders.

Cerebral Cortical Circuitry Formation Requires Functional Glycine Receptors

The development of the cerebral cortex is a complex process that requires the generation, migration, and differentiation of neurons. Interfering with any of these steps can impair the establishment of connectivity and, hence, function of the adult brain. Neurotransmitter receptors have emerged as critical players to regulate these biological steps during brain maturation. Among them, α2 subunit-containing glycine receptors (GlyRs) regulate cortical neurogenesis and the present work demonstrates the long-term consequences of their genetic disruption on neuronal connectivity in the postnatal cerebral cortex. Our data indicate that somatosensory cortical neurons of Glra2 knockout mice (Glra2KO) have more dendritic branches with an overall increase in total spine number. These morphological defects correlate with a disruption of the excitation/inhibition balance, thereby increasing network excitability and enhancing susceptibility to epileptic seizures after pentylenetetrazol tail infusion. Taken together, our findings show that the loss of embryonic GlyRα2 ultimately impairs the formation of cortical circuits in the mature brain.

Regional c-Fos expression induced by peripheral oxytocin administration is prevented by the vasopressin 1A receptor antagonist SR49059

Peripherally administered oxytocin induces a wide range of behavioural and physiological effects that are thought to be mediated by the oxytocin receptor (OTR). However, oxytocin also has considerable affinity for the vasopressin 1A receptor (V_1AR), such that various oxytocinergic effects may in fact be mediated by the V_1AR rather than the OTR. Here we used c-Fos immunohistochemistry to determine the extent to which the regional pattern of neuronal activation produced by peripheral oxytocin involves the V_1AR. Male Wistar rats were administered oxytocin (1mg/kg, IP) alone, or following pre-treatment with the V_1AR antagonist SR49059 (1mg/kg, IP), and were assessed for locomotor activity changes and for c-Fos expression across a number of brain regions. Oxytocin reduced the distance travelled by rats during a 70min test session, and this inhibitory behavioural effect was prevented by SR49059. Consistent with previous reports, oxytocin increased c-Fos expression in a number of brain regions. In several of these regions-the supraoptic and paraventricular (PVN) nuclei of the hypothalamus, locus coeruleus and nucleus of the solitary tract-the c-Fos response was prevented by SR49059 pre-treatment. Notably, SR49059 inhibited the c-Fos activation in oxytocin-synthesising magnocellular neurons in the PVN. However, c-Fos expression in the central amygdala to oxytocin was unaffected by SR49059. The current findings add to an increasing body of research suggesting that many of the functional effects of oxytocin may be V_1AR mediated.

The modulatory effect of nitric oxide in pro- and anti-convulsive effects of vasopressin in PTZ-induced seizures threshold in mice

Vasopressin neuropeptides play an important role in the several cognitive, social, and neuroendocrine functions. Also, several studies report the involvement of nitrergic system in the vasopressin functions in central nervous system. This study investigates the effect of Arginine-Vasopressin (AVP) in pentylenetetrazol (PTZ)-induced seizures threshold and the probable role of nitric oxide (NO). AVP is administered intraperitoneally (0.01-20μg/kg, i.p.) 30min before induction of seizures. Administration of AVP (0.1μg/kg) significantly lowered the PTZ-induced seizures threshold. But, administration of AVP (10 and 20μg/kg) increased the seizures threshold, significantly. Pretreatment of SR 49059 (V1a receptor antagonist, 2mg/kg, i.p.) just reversed the pro-convulsant effect of AVP. Meanwhile, SSR 149415 (V1b receptor antagonist, 10mg/kg, i.p.) pretreatment reversed both pro-and anti-convulsant effects of AVP. The nitric oxide precursor, L-arginine (60mg/kg, i.p.) increased pro-convulsant effect of AVP, but did not change anticonvulsant activity. The nitric oxide synthase (NOS) inhibitor L-NAME (10mg/kg, i.p.) reversed both pro- and anti-convulsant effect of AVP. Selective inducible NOS inhibitor, aminoguanidine (100mg/kg, i.p.) just reversed the anti-convulsant effects of AVP. The results of the present study showed nitric oxide system may contribute to the biphasic effects of AVP on PTZ-induced seizures. V1a receptor may modulate only the proconvulsive effect. While, V1b receptors can mediate both the pro- and anti-convulsive effect of AVP.

Neuropeptide diversity and the regulation of social behavior in New World primates

Oxytocin (OT) and vasopressin (AVP) are important hypothalamic neuropeptides that regulate peripheral physiology, and have emerged as important modulators of brain function, particularly in the social realm. OT structure and the genes that ultimately determine structure are highly conserved among diverse eutherian mammals, but recent discoveries have identified surprising variability in OT and peptide structure in New World monkeys (NWM), with five new OT variants identified to date. This review explores these new findings in light of comparative OT/AVP ligand evolution, documents coevolutionary changes in the oxytocin and vasopressin receptors (OTR and V1aR), and highlights the distribution of neuropeptidergic neurons and receptors in the primate brain. Finally, the behavioral consequences of OT and AVP in regulating NWM sociality are summarized, demonstrating important neuromodulatory effects of these compounds and OT ligand-specific influences in certain social domains.

Effects of intranasal oxytocin on steroid hormones in men and women

BACKGROUND

Recent interest in the social and cognitive effects of intranasal oxytocin prompts a need for understanding its physiological effects in humans. Few studies have examined the effects of intranasal oxytocin on steroid hormones. Filling this gap is especially important given the evidence that steroid hormones participate in some of the same behavioral functions as oxytocin, e.g. in stress, processing of emotional stimuli, aggression, trust, empathy, and parental care.

METHODS

In randomized, double-blind experiments, we administered oxytocin (24 IU) or saline placebo to 97 healthy participants. Saliva samples were collected before and at several time points after the oxytocin/placebo administration to assess the levels of cortisol, progesterone, and testosterone.

RESULTS

Oxytocin had no effects on testosterone, progesterone, or cortisol in women or men.

CONCLUSION

Acute intranasal oxytocin does not affect the levels of cortisol, testosterone or progesterone in humans, at least in the absence of a stressful context. These data suggest that acute oxytocin does not have a direct impact on the human hypothalamic-pituitary-adrenal or hypothalamic-pituitary-gonadal axes under nonstressful circumstances. This knowledge helps rule out potential mechanisms for some of the effects of oxytocin in humans and adds to the generally limited body of knowledge on the basic physiological or psychological effects of intranasal oxytocin in human beings.

Body temperature and cardiac changes induced by peripherally administered oxytocin, vasopressin and the non-peptide oxytocin receptor agonist WAY 267,464: a biotelemetry study in rats

BACKGROUND AND PURPOSE

There is current interest in oxytocin (OT) as a possible therapeutic in psychiatric disorders. However, the usefulness of OT may be constrained by peripheral autonomic effects, which may involve an action at both OT and vasopressin V1A receptors. Here, we characterized the cardiovascular and thermoregulatory effects of OT, vasopressin (AVP) and the non-peptide OT receptor agonist WAY 267,464 in rats, and assessed the relative involvement of the OT and V1A receptors in these effects.

EXPERIMENTAL APPROACH

Biotelemetry in freely moving male Wistar rats was used to examine body temperature and heart rate after OT (0.01 - 1 mg kg(-1); i.p.), AVP (0.001 - 0.1 mg kg(-1); i.p.) or WAY 267,464 (10 and 100 mg kg(-1); i.p.). The actions of the OT receptor antagonist Compound 25 (C25, 5 and 10 mg kg(-1)) and V1A receptor antagonist SR49059 (1 and 10 mg kg(-1)) were studied, as well as possible V1A receptor antagonist effects of WAY 267,464.

KEY RESULTS

OT and AVP dose-dependently reduced body temperature and heart rate. WAY 267,464 had similar, but more modest, effects. SR49059, but not C25, prevented the hypothermia and bradycardia induced by OT and AVP. WAY 267,464 (100 mg·kg(-1)) prevented the effects of OT, and to some extent AVP.

CONCLUSIONS AND IMPLICATIONS

Peripherally administered OT and AVP have profound cardiovascular and thermoregulatory effects that appear to principally involve the V1A receptor rather than the OT receptor. Additionally, WAY 267,464 is not a simple OT receptor agonist, as it has functionally relevant V1A antagonist actions.

Neuropeptides as targets for the development of anticonvulsant drugs

Epilepsy is a common neurological disorder characterized by recurrent seizures. These seizures are due to abnormal excessive and synchronous neuronal activity in the brain caused by a disruption of the delicate balance between excitation and inhibition. Neuropeptides can contribute to such misbalance by modulating the effect of classical excitatory and inhibitory neurotransmitters. In this review, we discuss 21 different neuropeptides that have been linked to seizure disorders. These neuropeptides show an aberrant expression and/or release in animal seizure models and/or epilepsy patients. Many of these endogenous peptides, like adrenocorticotropic hormone, angiotensin, cholecystokinin, cortistatin, dynorphin, galanin, ghrelin, neuropeptide Y, neurotensin, somatostatin, and thyrotropin-releasing hormone, are able to suppress seizures in the brain. Other neuropeptides, such as arginine-vasopressine peptide, corticotropin-releasing hormone, enkephalin, β-endorphin, pituitary adenylate cyclase-activating polypeptide, and tachykinins have proconvulsive properties. For oxytocin and melanin-concentrating hormone both pro- and anticonvulsive effects have been reported, and this seems to be dose or time dependent. All these neuropeptides and their receptors are interesting targets for the development of new antiepileptic drugs. Other neuropeptides such as nesfatin-1 and vasoactive intestinal peptide have been less studied in this field; however, as nesfatin-1 levels change over the course of epilepsy, this can be considered as an interesting marker to diagnose patients who have suffered a recent epileptic seizure.

Acute prosocial effects of oxytocin and vasopressin when given alone or in combination with 3,4-methylenedioxymethamphetamine in rats: involvement of the V1A receptor

The neuropeptides oxytocin (OT) and vasopressin (AVP) are recognized for their modulation of social processes in humans when delivered peripherally. However, there is surprisingly little evidence for acute social effects of peripherally administered OT or AVP in animal models. On the other hand, the party drug 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') has powerful prosocial effects in rats that appear to occur through stimulation of central OT release. Here, we directly compared the social effects of peripherally administered OT and AVP with those of MDMA, and examined a possible role for the vasopressin 1A receptor (V1AR) in the observed prosocial effects. Adult male Long-Evans rats were tested in a social interaction paradigm after OT (0.1, 0.25, 0.5, and 1 mg/kg, intraperitoneal (IP)), AVP (0.001, 0.0025, 0.005, 0.01, and 0.1 mg/kg, IP), and MDMA (2.5, 5 mg/kg, IP), or combined low doses of OT and MDMA, or AVP and MDMA. The effects of pretreatment with the non-peptide OT receptor antagonist compound 25 (C25; 5 mg/kg, IP) and the V1AR antagonist SR49059 (1 mg/kg, IP) were also examined. OT (0.5 mg/kg), AVP (0.01 mg/kg), and MDMA (5 mg/kg) potently increased 'adjacent lying', where rats meeting for the first time lie passively next to each other. C25 did not inhibit adjacent lying induced by OT, whereas SR49059 inhibited adjacent lying induced by MDMA (5 mg/kg), OT (0.5 mg/kg), and AVP (0.01 mg/kg). Interestingly, when ineffective doses of OT and MDMA, or AVP and MDMA, were combined, a robust increase in adjacent lying was observed. These results show for the first time acute prosocial effects of peripherally injected OT and AVP in laboratory rats, and suggest a commonality of action of OT, AVP, and MDMA in stimulating social behavior that involves V1ARs.

Antidepressant-like effects of oxytocin in mice are dependent on the presence of insulin-regulated aminopeptidase

Oxytocin is a neuromodulator with antidepressant-like effects. In vitro, oxytocin is rapidly cleaved by insulin-regulated aminopeptidase (IRAP). Oxytocin metabolites are known to exert strong central activities that are different from the effects of the parent molecule. Our goal is to investigate in vivo whether IRAP deletion modifies the antidepressant-like effects of oxytocin. Male and female C57Bl/6 mice, IRAP wild-type (IRAP(+/+)) and knock-out (IRAP(-/-)) mice were injected subcutaneously with saline, oxytocin or oxytocin combined with angiotensin IV. One hour after injection, immobility was timed during a 5 min forced swim that was preceded by an open field to study locomotor behaviour. Oxytocin induced antidepressant-like effects in male (0.25 mg/kg oxytocin) and female (0.15 mg/kg oxytocin) C57Bl/6 mice subjected to the forced swim test. Oxytocin did not influence locomotor behaviour in mice, as shown with the open field. These findings were reproduced in transgenic male (aged 3-6 months) and female (aged 12-18 months) IRAP(+/+) mice. However, the major findings of our study were that the antidepressant-like effect was reversed in angiotensin IV treated IRAP(+/+) mice and was completely absent in age- and gender-matched IRAP(-/-) mice. The lack of an antidepressant-like effect of oxytocin in young male and middle-aged female IRAP(-/-) mice attributes an important role to IRAP in mediating this effect.

Oxytocin inhibits pentylentetrazol-induced seizures in the rat

We aimed to reveal the anti-convulsant effects of oxytocin (OT) in pentylenetetrazol (PTZ)-induced seizures in rats. Thirty rats were randomly divided into 5 equal groups. Using stereotaxy, we implanted electroencephologram (EEG) electrodes in the left nucleus of the posterior thalamus. After 2 days, the first and second groups were used as the control and PTZ (35 mg/kg) groups, respectively. We administered 40, 80 and 160 nmol/kg OT+35 mg/kg PTZ to the rats, constituting the third, fourth, and fifth groups, respectively, for 5 days. At the end of 5 days, we recorded EEGs via bipolar EEG electrodes. After 12h, all groups except the first received 70 mg/kg PTZ and we determined the dose-response ratio. Racine's Convulsion Scale was used to evaluate seizures. The spike-wave complex percentage in the EEG was determined as 0% for the first group, 38.6%±7.2 for the second group, 36.4%±5.6 for the third group, 4.3%±1.8 for the fifth group and 4.1%±1.1 for the fifth group. The fourth and fifth groups had significantly decreased spike-wave complex percentages compared to the second group (p<0.0001). OT may prevent PTZ-induced epilepsy on an EEG. OT may also be considered for use in the treatment of epilepsy in the future.

Neurohypophyseal hormones protect against pentylenetetrazole-induced seizures in zebrafish: role of oxytocin-like and V1a-like receptor

Oxytocin (OT) and arginine-vasopressin (AVP) are involved in the physiological response to different stressors like the occurrence of seizures which is regarded as a severe stress factor. Zebrafish (Danio rerio) is recently featured as a model of epilepsy but the role of neurohypophyseal hormones on this teleost is still unknown. We attempted to determine whether non-mammalian homologues like isotocin (IT) and vasotocin (AVT) affected pentylenetetrazole (PTZ)-induced seizures in adult zebrafish in comparison with OT/AVP. The mechanism was studied using the most selective OT and AVP receptor antagonists. Zebrafish were injected i.m. with increasing doses (0.1-40 ng/kg) of the neuropeptides 10 min before PTZ exposure. DesGly-NH2-d(CH2)5-[D-Tyr2,Thr4]OVT (desglyDTyrOVT) for OT receptor and SR49059 for V1a subtype receptor, were injected together with each agonist 20 min before PTZ exposure. All the peptides significantly decreased the number of seizures, increased the mean latency time to the first seizure and decreased lethality. This protective effect led to a dose-response curve following a U-shaped form. IT was approximately 40 times more active than OT while AVT was 20 times more potent than AVP in reducing the number of seizures. DesglyDTyrOVT was more effective in antagonizing OT/IT, while SR49059 mainly blocked AVP/AVT-induced protection against PTZ-induced seizures. The present findings provide direct evidence of an important involvement of IT/OT and AVP/AVT as anticonvulsant agents against PTZ-induced seizures with a receptor-mediated mechanism in zebrafish. These data reinforce zebrafish as an emerging experimental model to study and identify new antiepileptic drugs.