Differential suppression of seizures via Y2 and Y5 neuropeptide Y receptors

Collagen VI: Role in synaptic transmission and seizure-related excitability

Collagen VI (Col-VI) is an extracellular matrix protein primarily known for its bridging role in connective tissues that has been suggested to play a neuroprotective role. In the present study we report increased mRNA and protein expression of Col-VI in the hippocampus and cortex at a late stage of epileptogenesis in a post-status epilepticus (SE) model of epilepsy and in brain tissue from patients with epilepsy. We further present a novel finding that exposure of mouse hippocampal slices to Col-VI augments paired-pulse facilitation in Schaffer collateral-CA1 excitatory synapses indicating decreased release probability of glutamate. In line with this finding, lack of Col-VI expression in the knock-out mice show paired-pulse depression in these synapses, suggesting increased release probability of glutamate. In addition, we observed dynamic changes in Col-VI blood plasma levels in rats after Kainate-induced SE, and increased levels of Col-VI mRNA and protein in autopsy or postmortem brain of humans suffering from epilepsy. Thus, our data indicate that elevated levels of ColVI following seizures leads to attenuated glutamatergic transmission, ultimately resulting in less overall network excitability. Presumably, increased Col-VI may act as part of endogenous compensatory mechanism against enhanced excitability during epileptogenic processes in the hippocampus, and could be further investigated as a potential functional biomarker of epileptogenesis, and/or a novel target for therapeutic intervention.

Gene therapy for epilepsy targeting neuropeptide Y and its Y2 receptor to dentate gyrus granule cells

Gene therapy is emerging as an alternative option for individuals with drug-resistant focal epilepsy. Here, we explore the potential of a novel gene therapy based on Neuropeptide Y (NPY), a well-known endogenous anticonvulsant. We develop a lentiviral vector co-expressing NPY with its inhibitory receptor Y2 in which, for the first time, both transgenes are placed under the control of the minimal CamKIIa(0.4) promoter, biasing expression toward excitatory neurons and allowing autoregulation of neuronal excitability by Y2 receptor-mediated inhibition. Vector-induced NPY and Y2 expression and safety are first assessed in cultures of hippocampal neurons. In vivo experiments demonstrate efficient and nearly selective overexpression of both genes in granule cell mossy fiber terminals following vector administration in the dentate gyrus. Telemetry video-EEG monitoring reveals a reduction in the frequency and duration of seizures in the synapsin triple KO model. This study shows that targeting a small subset of neurons (hippocampal granule cells) with a combined overexpression of NPY and Y2 receptor is sufficient to reduce the occurrence of spontaneous seizures.

Neuroglobin deficiency increases seizure susceptibility but does not affect basal behavior in mice

Neuroglobin (Ngb) is found in the neurones of several different brain areas and is known to bind oxygen and other gaseous molecules and reactive oxygen species (ROS) in vitro, but it does not seem to act as a respiratory molecule for neurones. Using male and female Ngb‐knockout (KO) mice, we addressed the role of Ngb in neuronal brain activity using behavioral tests but found no differences in general behaviors, memory processes, and anxiety−/depression‐like behaviors. Oxidative stress and ROS play key roles in epileptogenesis, and oxidative injury produced by an excessive production of free radicals is involved in the initiation and progression of epilepsy. The ROS binding properties led us to hypothesize that lack of Ngb could affect central coping with excitatory stimuli. We consequently explored whether exposure to the excitatory molecule kainate (KA) would increase severity of seizures in mice lacking Ngb. We found that the duration and severity of seizures were increased, while the latency time to develop seizures was shortened in Ngb‐KO compared to wildtype adult female mice. Consistently, c‐fos expression after KA was significantly increased in Ngb‐KO mice in the amygdala and piriform cortex, regions rich in Ngb and known to be centrally involved in seizure generation. Moreover, the measured c‐fos expression levels were correlated with seizure susceptibility. With these new findings combined with previous studies we propose that Ngb could constitute an intrinsic defense mechanism against neuronal hyperexcitability and oxidative stress by buffering of ROS in amygdala and other Ngb‐containing brain regions.

Pathological Targets for Treating Temporal Lobe Epilepsy: Discoveries From Microscale to Macroscale

Temporal lobe epilepsy (TLE) is one of the most common and severe types of epilepsy, characterized by intractable, recurrent, and pharmacoresistant seizures. Histopathology of TLE is mostly investigated through observing hippocampal sclerosis (HS) in adults, which provides a robust means to analyze the related histopathological lesions. However, most pathological processes underlying the formation of these lesions remain elusive, as they are difficult to detect and observe. In recent years, significant efforts have been put in elucidating the pathophysiological pathways contributing to TLE epileptogenesis. In this review, we aimed to address the new and unrecognized neuropathological discoveries within the last 5 years, focusing on gene expression (miRNA and DNA methylation), neuronal peptides (neuropeptide Y), cellular metabolism (mitochondria and ion transport), cellular structure (microtubule and extracellular matrix), and tissue-level abnormalities (enlarged amygdala). Herein, we describe a range of biochemical mechanisms and their implication for epileptogenesis. Furthermore, we discuss their potential role as a target for TLE prevention and treatment. This review article summarizes the latest neuropathological discoveries at the molecular, cellular, and tissue levels involving both animal and patient studies, aiming to explore epileptogenesis and highlight new potential targets in the diagnosis and treatment of TLE.

From Physiology to Pathology of Cortico-Thalamo-Cortical Oscillations: Astroglia as a Target for Further Research

The electrographic hallmark of childhood absence epilepsy (CAE) and other idiopathic forms of epilepsy are 2.5-4 Hz spike and wave discharges (SWDs) originating from abnormal electrical oscillations of the cortico-thalamo-cortical network. SWDs are generally associated with sudden and brief non-convulsive epileptic events mostly generating impairment of consciousness and correlating with attention and learning as well as cognitive deficits. To date, SWDs are known to arise from locally restricted imbalances of excitation and inhibition in the deep layers of the primary somatosensory cortex. SWDs propagate to the mostly GABAergic nucleus reticularis thalami (NRT) and the somatosensory thalamic nuclei that project back to the cortex, leading to the typical generalized spike and wave oscillations. Given their shared anatomical basis, SWDs have been originally considered the pathological transition of 11-16 Hz bursts of neural oscillatory activity (the so-called sleep spindles) occurring during Non-Rapid Eye Movement (NREM) sleep, but more recent research revealed fundamental functional differences between sleep spindles and SWDs, suggesting the latter could be more closely related to the slow (<1 Hz) oscillations alternating active (Up) and silent (Down) cortical activity and concomitantly occurring during NREM. Indeed, several lines of evidence support the fact that SWDs impair sleep architecture as well as sleep/wake cycles and sleep pressure, which, in turn, affect seizure circadian frequency and distribution. Given the accumulating evidence on the role of astroglia in the field of epilepsy in the modulation of excitation and inhibition in the brain as well as on the development of aberrant synchronous network activity, we aim at pointing at putative contributions of astrocytes to the physiology of slow-wave sleep and to the pathology of SWDs. Particularly, we will address the astroglial functions known to be involved in the control of network excitability and synchronicity and so far mainly addressed in the context of convulsive seizures, namely (i) interstitial fluid homeostasis, (ii) K⁺ clearance and neurotransmitter uptake from the extracellular space and the synaptic cleft, (iii) gap junction mechanical and functional coupling as well as hemichannel function, (iv) gliotransmission, (v) astroglial Ca²⁺ signaling and downstream effectors, (vi) reactive astrogliosis and cytokine release.

Hypothalamic hormone-sensitive lipase regulates appetite and energy homeostasis

Objective

The goal of this study was to investigate the importance of central hormone-sensitive lipase (HSL) expression in the regulation of food intake and body weight in mice to clarify whether intracellular lipolysis in the mammalian hypothalamus plays a role in regulating appetite.

Methods

Using pharmacological and genetic approaches, we investigated the role of HSL in the rodent brain in the regulation of feeding and energy homeostasis under basal conditions during acute stress and high-fat diet feeding.

Results

We found that HSL, a key enzyme in the catabolism of cellular lipid stores, is expressed in the appetite-regulating centers in the hypothalamus and is activated by acute stress through a mechanism similar to that observed in adipose tissue and skeletal muscle. Inhibition of HSL in rodent models by a synthetic ligand, global knockout, or brain-specific deletion of HSL prevents a decrease in food intake normally seen in response to acute stress and is associated with the increased expression of orexigenic peptides neuropeptide Y (NPY) and agouti-related peptide (AgRP). Increased food intake can be reversed by adeno-associated virus-mediated reintroduction of HSL in neurons of the mediobasal hypothalamus. Importantly, metabolic stress induced by a high-fat diet also enhances the hyperphagic phenotype of HSL-deficient mice. Specific deletion of HSL in the ventromedial hypothalamic nucleus (VMH) or AgRP neurons reveals that HSL in the VMH plays a role in both acute stress-induced food intake and high-fat diet-induced obesity.

Conclusions

Our results indicate that HSL activity in the mediobasal hypothalamus is involved in the acute reduction in food intake during the acute stress response and sensing of a high-fat diet.

•

HSL is expressed in appetite-regulating nuclei of the mouse hypothalamus.

•

HSL in the hypothalamus is activated via β-adrenergic receptor signaling.

•

The anorexic response to acute stress is blunted in mice without hypothalamic HSL.

•

Central HSL deficiency results in obesity in mice on a high-fat diet.

•

HSL in SF1-positive neurons contributes to the anorexigenic stress response.

NPY and Gene Therapy for Epilepsy: How, When,... and Y

Neuropeptide Y (NPY) is a neuropeptide abundantly expressed in the mammalian central and peripheral nervous system. NPY is a pleiotropic molecule, which influences cell proliferation, cardiovascular and metabolic function, pain and neuronal excitability. In the central nervous system, NPY acts as a neuromodulator, affecting pathways that range from cellular (excitability, neurogenesis) to circuit level (food intake, stress response, pain perception). NPY has a broad repertoire of receptor subtypes, each activating specific signaling pathways in different tissues and cellular sub-regions. In the context of epilepsy, NPY is thought to act as an endogenous anticonvulsant that performs its action through Y2 and Y5 receptors. In fact, its overexpression in the brain with the aid of viral vectors can suppress seizures in animal models of epilepsy. Therefore, NPY-based gene therapy may represent a novel approach for the treatment of epilepsy patients, particularly for pharmaco-resistant and genetic forms of the disease. Nonetheless, considering all the aforementioned aspects of NPY signaling, the study of possible NPY applications as a therapeutic molecule is not devoid of critical aspects. The present review will summarize data related to NPY biology, focusing on its anti-epileptic effects, with a critical appraisal of key elements that could be exploited to improve the already existing NPY-based gene therapy approaches for epilepsy.

Gene Therapy Vector Encoding Neuropeptide Y and Its Receptor Y2 for Future Treatment of Epilepsy: Preclinical Data in Rats

Gene therapy to treat pharmacoresistant temporal lobe epilepsy in humans is now being developed using an AAV vector (CG01) that encodes the combination of neuropeptide Y and its antiepileptic receptor Y2. With this in mind, the present study aimed to provide important preclinical data on the effects of CG01 on the duration of transgene expression, cellular tropism, and potential side effects on body weight and cognitive function. The CG01 vector was administered unilaterally into the dorsal and ventral hippocampus of adult male rats and expression of both transgenes was found to remain elevated without a sign of decline at 6 months post-injection. CG01 appeared to mediate expression selectively in hippocampal neurons, without expression in astrocytes or oligodendrocytes. No effects were seen on body weight as well as on short- or long-term memory as revealed by testing in the Y-maze or Morris water maze tests. Thus these data show that unilateral CG01 vector treatment as future gene therapy in pharmacoresistant temporal lobe epilepsy patients should result in stable and long-term expression predominantly in neurons and be well tolerated without side effects on body weight and cognitive function.

Neuropeptide Y system mRNA expression changes in the hippocampus of a type I diabetes rat model

BACKGROUND

Neuropeptide Y (NPY) plays a crucial role in many neurobiological functions, such as cognition and memory. Cognitive and memory impairment have been described in diabetic patients. The metabolism of NPY is determined by the activity of proteases, primarily dipeptidyl-peptidase-IV (DPP-IV). Therefore, DPP-IV inhibitors, such as sitagliptin, may modulate the function of NPY. In this study, we investigated the effect of type 1 diabetes and sitagliptin treatment on the regulation of the mRNA encoding for NPY and its receptors (Y1, Y2, and Y5 receptors) in the hippocampus.

METHODS

Type 1 diabetes was induced in male Wistar rats by i.p. injection of streptozotocin. Starting two weeks after diabetes onset, animals were treated orally with sitagliptin (5mg/kg, daily) for two weeks. The mRNA expression of Npy and its receptors (Npy1r, Npy2r, and Npy5r) in the hippocampus was evaluated using in situ hybridization with ³³P-labeled oligonucleotides.

RESULTS

The mRNA expression of Npy, Npy1r and Npy5r was higher in the dentate gyrus, whereas Npy2r highest level was observed in the CA3 subregion. The mRNA expression of Npy, Npy1r and Npy5r in dentate gyrus, CA1 and CA3 was not affected by diabetes and/or by sitagliptin treatment. Type 1 diabetes increased the mRNA expression of Npy2r in the CA3 subregion, which was prevented by sitagliptin treatment.

CONCLUSIONS

Our results show that type 1 diabetes, at early stages, induces mild changes in the NPY system in the hippocampus that were counteracted by sitagliptin treatment.

Disease Modification by Combinatorial Single Vector Gene Therapy: A Preclinical Translational Study in Epilepsy

Gene therapy has been suggested as a plausible novel approach to achieve seizure control in patients with focal epilepsy that do not adequately respond to pharmacological treatment. We investigated the seizure-suppressant potential of combinatorial neuropeptide Y and Y2 receptor single vector gene therapy based on adeno-associated virus serotype 1 (AAV1) in rats. First, a dose-response study in the systemic kainate-induced acute seizure model was performed, whereby the 10¹² genomic particles (gp)/mL titer of the vector was selected as an optimal concentration. Second, an efficacy study was performed in the intrahippocampal kainate chronic model of spontaneous recurrent seizures (SRSs), designed to reflect a likely clinical scenario, with magnetic resonance image (MRI)-guided focal unilateral administration of the vector in the hippocampus during the chronic stage of the disease. The efficacy study demonstrated a favorable outcome of the gene therapy, with a 31% responder rate (more than 50% reduction in SRS frequency) and 13% seizure-freedom rate, whereas no such effects were observed in the control animals. The inter-SRS and SRS cluster intervals were also significantly prolonged in the treated group compared to controls. In addition, the SRS duration was significantly reduced in the treated group but not in the controls. This study establishes the SRS-suppressant ability of the single vector combinatorial neuropeptide Y/Y2 receptor gene therapy in a clinically relevant chronic model of epilepsy.

Differential plastic changes in synthesis and binding in the mouse somatostatin system after electroconvulsive stimulation

OBJECTIVE

Electroconvulsive therapy (ECT) is regularly used to treat patients with severe major depression, but the mechanisms underlying the beneficial effects remain uncertain. Electroconvulsive stimulation (ECS) regulates diverse neurotransmitter systems and induces anticonvulsant effects, properties implicated in mediating therapeutic effects of ECT. Somatostatin (SST) is a candidate for mediating these effects because it is upregulated by ECS and exerts seizure-suppressant effects. However, little is known about how ECS might affect the SST receptor system. The present study examined effects of single and repeated ECS on the synthesis of SST receptors (SSTR1-4) and SST, and SST receptor binding ([125I]LTT-SST28) in mouse hippocampal regions and piriform/parietal cortices.

RESULTS

A complex pattern of plastic changes was observed. In the dentate gyrus, SST and SSTR1 expression and the number of hilar SST immunoreactive cells were significantly increased at 1 week after repeated ECS while SSTR2 expression was downregulated by single ECS, and SSTR3 mRNA and SST binding were elevated 24 h after repeated ECS. In hippocampal CA1 and parietal/piriform cortices, we found elevated SST mRNA levels 1 week after repeated ECS and elevated SST binding after single ECS and 24 h after repeated ECS. In hippocampal CA3, repeated ECS increased SST expression 1 week after and SST binding 24 h after. In the parietal cortex, SSTR2 mRNA expression was downregulated after single ECS while SSTR4 mRNA expression was upregulated 24 h after repeated ECS.

CONCLUSION

Considering the known anticonvulsant effects of SST, it is likely that these ECS-induced neuroplastic changes in the SST system could participate in modulating neuronal excitability and potentially contribute to therapeutic effects of ECT.

Altered expression of neuropeptide Y receptors caused by focal cortical dysplasia in human intractable epilepsy

Focal cortical dysplasia (FCD) is a common cause of pharmacologically-intractable epilepsy, however, the precise mechanisms underlying the epileptogenicity of FCD remains to be determined. Neuropeptide Y (NPY), an endogenous anticonvulsant in the central nervous system, plays an important role in the regulation of neuronal excitability. Increased expression of NPY and its receptors has been identified in the hippocampus of patients with mesial temporal lobe epilepsy, presumed to act as an endogenous anticonvulsant mechanism. Therefore, we investigated whether expression changes in NPY receptors occurs in patients with FCD. We specifically investigated the expression of seizure-related NPY receptor subtypes Y1, Y2, and Y5 in patients with FCD versus autopsy controls. We found that Y1R and Y2R were up-regulated at the mRNA and protein levels in the temporal and frontal lobes in FCD lesions. By contrast, there was no significant change in either receptor detected in parietal lesions. Notably, overexpression of Y5R was consistently observed in all FCD lesions. Our results demonstrate the altered expression of Y1R, Y2R and Y5R occurs in FCD lesions within the temporal, frontal and parietal lobe. Abnormal NPY receptor subtype expression may be associated with the onset and progression of epileptic activity and may act as a therapeutic candidate for the treatment of refractory epilepsy caused by FCD.

Anxiolytic-Like Effects of Increased Ghrelin Receptor Signaling in the Amygdala

BACKGROUND

Besides the well-known effects of ghrelin on adiposity and food intake regulation, the ghrelin system has been shown to regulate aspects of behavior including anxiety and stress. However, the effect of virus-mediated overexpression of the ghrelin receptor in the amygdala has not previously been addressed directly.

METHODS

First, we examined the acute effect of peripheral ghrelin administration on anxiety- and depression-like behavior using the open field, elevated plus maze, forced swim, and tail suspension tests. Next, we examined the effect of peripheral ghrelin administration and ghrelin receptor deficiency on stress in a familiar and social environment using the Intellicage system. Importantly, we also used a novel approach to study ghrelin receptor signaling in the brain by overexpressing the ghrelin receptor in the amygdala. We examined the effect of ghrelin receptor overexpression on anxiety-related behavior before and after acute stress and measured the modulation of serotonin receptor expression.

RESULTS

We found that ghrelin caused an anxiolytic-like effect in both the open field and elevated plus maze tests. Additionally, it attenuated air-puff-induced stress in the social environment, while the opposite was shown in ghrelin receptor deficient mice. Finally, we found that overexpression of the ghrelin receptor in the basolateral division of the amygdala caused an anxiolytic-like effect and decreased the 5HT1a receptor expression.

CONCLUSIONS

Ghrelin administration and overexpression of the ghrelin receptor in the amygdala induces anxiolytic-like behavior. Since the ghrelin receptor has high constitutive activity, ligand-independent signaling in vivo may be important for the observed anxiolytic-like effects. The anxiolytic effects seem to be mediated independently from the HPA axis, potentially engaging the central serotonin system.

Neuropeptide Y-stimulated [(35) S]GTPγs functional binding is reduced in the hippocampus after kainate-induced seizures in mice

Kainate-induced seizures constitute a model of temporal lobe epilepsy where prominent changes are observed in the hippocampal neuropeptide Y (NPY) system. However, little is known about the functional state and signal transduction of the NPY receptor population resulting from kainate exposure. Thus, in this study, we explored functional NPY receptor activity in the mouse hippocampus and neocortex after kainate-induced seizures using NPY-stimulated [(35) S]GTPγS binding. Moreover, we also studied levels of [(125) I]-peptide YY (PYY) binding and NPY, Y1, Y2, and Y5 receptor mRNA in these kainate-treated mice. Functional NPY binding was unchanged up to 12 h post-kainate, but decreased significantly in all hippocampal regions after 24 h and 1 week. Similarly, a decrease in [(125) I]-PYY binding was found in the dentate gyrus (DG) 1 week post-kainate. However, at 2 h, 6 h, and 12 h, [(125) I]-PYY binding was increased in all regions, and in the CA1 also at 24 h post-kainate. NPY mRNA levels were prominently increased in hippocampal regions, reaching maximum at 12 and 24 h. Y1 and Y5 mRNA levels were lowered in the DG at 24 and 2 h, respectively, while Y2 mRNA levels were elevated at 24 h in the DG and CA3. This study confirms rat kainate studies by showing pronounced adaptive changes in the mouse hippocampus both with regard to NPY synthesis and NPY receptor synthesis and binding, which may contribute to regulating neuronal seizure susceptibility after kainate. However, the potential seizure-suppressant effects of increased NPY gene expression at late time points post-kainate could be attenuated by the novel finding of reduced NPY-receptor G-protein activation.

Altered expression of neuropeptide Y, Y1 and Y2 receptors, but not Y5 receptor, within hippocampus and temporal lobe cortex of tremor rats

As an endogenous inhibitor of glutamate-mediated synaptic transmission in mammalian central nervous system, neuropeptide Y (NPY) plays a crucial role in regulating homeostasis of neuron excitability. Loss of balance between excitatory and inhibitory neurotransmission is thought to be a chief mechanism of epileptogenesis. The abnormal expression of NPY and its receptors observed following seizures have been demonstrated to be related to the production of epilepsy. The tremor rat (TRM) is a hereditary epileptic animal model. So far, there is no report concerning whether NPY and its receptors may be involved in TRM pathogenesis. In this study, we focused on the expression of NPY and its three receptor subtypes: Y1R, Y2R and Y5R in the TRM brain. We first found the expression of NPY in TRM hippocampus and temporal lobe cortex was increased compared with control (Wistar) rats. The mRNA and protein expression of Y1R was down-regulated in hippocampus but up-regulated in temporal lobe cortex, whereas Y2R expression was significantly increased in both areas. There was no significant change of Y5R expression in either area. The immunohistochemistry data showed that Y1R, Y2R, Y5R were present throughout CA1, CA3, dentate gyrus (DG) and the entorhinal cortex which is included in the temporal lobe cortex of TRM. In conclusion, our results showed the altered expression of NPY, Y1R and Y2R but not Y5R in hippocampus and temporal lobe cortex of TRM brain. This abnormal expression may be associated with the generation of epileptiform activity and provide a candidate target for treatment of genetic epilepsy.

Long-term valproate treatment increases brain neuropeptide Y expression and decreases seizure expression in a genetic rat model of absence epilepsy

The mechanisms by which valproate, one of the most widely prescribed anti-epileptic drugs, suppresses seizures have not been fully elucidated but may involve up-regulation of neuropeptide Y (NPY). We investigated the effects of valproate treatment in Genetic Absence Epilepsy Rats from Strasbourg (GAERS) on brain NPY mRNA expression and seizure control. GAERS were administered either valproate (42 mg.kg⁻¹ hr⁻¹) or saline continuously for 5 days. Electroencephalograms were recorded for 24 hrs on treatment days 1, 3 and 5 and the percentage of time spent in seizure activity was analysed. NPY mRNA expression was measured in different brain regions using qPCR. Valproate treatment suppressed seizures by 80% in GAERS (p<0.05) and increased NPY mRNA expression in the thalamus (p<0.05) compared to saline treatment. These results demonstrate that long-term valproate treatment results in an upregulation of thalamic expression of NPY implicating this as a potential contributor to the mechanism by which valproate suppresses absence seizures.

NPY Receptors Blockade Prevents Anticonvulsant Action of Ghrelin in the Hippocampus of Rat

PURPOSE

Ghrelin has been shown to have antiepileptic function. However, the underlying mechanisms by which, ghrelin exerts its antiepileptic effects are still unclear. In the present study, we investigated whether neuropeptide Y (NPY) mediates ghrelin anticonvulsant effect in the brain through its Y1, Y2 or Y5 receptors.

METHODS

Male Wistar rats were bilaterally microinjected with ghrelin 0.3 nmol/μl/side and NPY antagonists; GR231118 (Y1 receptor antagonist), BIIE0246 (Y2 receptor antagonist), CGP71683 (Y5 receptor antagonist) or solvents (Saline, DMSO) into the dorsal hippocampus 20 minutes before ghrelin administration. Thirty minutes after ghrelin microinjection, a single convulsive dose of pentylenetetrazole (PTZ) (50 mg/kg) was injected intraperitoneally (ip). Afterwards, duration of seizure and total seizure score (TSS) were assessed for 30 minutes in all animals.

RESULTS

Intrahippocampal injection of 0.3 nmol/μl/side ghrelin decreased duration of seizure and TSS induced by PTZ. The suppression of both duration (p<0.001) and TSS (p<0.001) induced by ghrelin in hippocampus were significantly blocked by GR231118 (10 μg/μl/side), BIIE0246 (400 pmol/μl/side) and CGP 71683A (5 nmol/μl/side).

CONCLUSION

Our findings suggest that NPY Y1, Y2 and Y5 receptors in the hippocampus may somehow mediate the anticonvulsive action of ghrelin. Therefore, it is possible to speculate that ghrelin acts in the hippocampus to modulate seizures via NPY.

Neuropeptide Y Y5 receptor antagonism causes faster extinction and attenuates reinstatement in cocaine-induced place preference

Several studies have suggested a role for neuropeptide Y (NPY) in addiction to drugs of abuse, including cocaine. Recently, our group showed a role for the NPY Y5 receptor in the modulation of acute reinforcing effects of cocaine using self-administration and hyperlocomotion paradigms. In the present study, we further explored potential anti-addiction-related effects of Y5 antagonism in another murine model of cocaine addiction-related behavior: conditioned place-preference (CPP). Using this model, it was tested whether blockade or deficiency of the NPY Y5 receptor could influence the induction, extinction or reinstatement of a conditioned cocaine response. We found that the Y5 antagonist L-152,804 causes faster extinction and reduced reinstatement of cocaine-induced CPP but did not reduce the ability of cocaine to induce CPP. Similarly, Y5-KO mice displayed faster extinction, and reinstatement of cocaine-induced CPP was absent. The development of CPP for cocaine was similar between Y5-KO and WT mice. Taken together, the present data show that Y5 antagonism attenuates relapse to cocaine addiction-related behavior. Prevention of relapse is considered to be of pivotal importance for the development of an effective treatment against cocaine addiction and therefore Y5 receptors could be a potential future therapeutic target in cocaine addiction.

Methamphetamine-induced changes in the mice hippocampal neuropeptide Y system: implications for memory impairment

Methamphetamine (METH) is a psychostimulant drug that causes irreversible brain damage leading to several neurological and psychiatric abnormalities, including cognitive deficits. Neuropeptide Y (NPY) is abundant in the mammalian central nervous system (CNS) and has several important functions, being involved in learning and memory processing. It has been demonstrated that METH induces significant alteration in mice striatal NPY, Y(1) and Y(2) receptor mRNA levels. However, the impact of this drug on the hippocampal NPY system and its consequences remain unknown. Thus, in this study, we investigated the effect of METH intoxication on mouse hippocampal NPY levels, NPY receptors function, and memory performance. Results show that METH increased NPY, Y(2) and Y(5) receptor mRNA levels, as well as total NPY binding accounted by opposite up- and down-regulation of Y(2) and Y(1) functional binding, respectively. Moreover, METH-induced impairment in memory performance and AKT/mammalian target of rapamycin pathway were both prevented by the Y(2) receptor antagonist, BIIE0246. These findings demonstrate that METH interferes with the hippocampal NPY system, which seems to be associated with memory failure. Overall, we concluded that Y(2) receptors are involved in memory deficits induced by METH intoxication.

Neuropeptide Y Y5 receptor antagonism attenuates cocaine-induced effects in mice

RATIONALE

Several studies suggest a role for neuropeptide Y (NPY) in addiction to drugs of abuse, including cocaine. However, the NPY receptors mediating addiction-related effects remain to be determined.

OBJECTIVES

To explore the potential role of Y5 NPY receptors in cocaine-induced behavioural effects.

METHODS

The Y5 antagonist L-152,804 and Y5-knockout (Y5-KO) mice were tested in two models of cocaine addiction-related behaviour: acute self-administration and cocaine-induced hyperactivity. We also studied effects of Y5 receptor antagonism on cocaine-induced c-fos expression and extracellular dopamine with microdialysis as well as dopamine transporter-mediated uptake of dopamine in vitro. Immunocytochemistry was used to determine whether dopamine neurons express Y5-like immunoreactivity.

RESULTS

In self-administration, L-152,804 prominently decreased nose-poking for the peak dose of cocaine and shifted the dose-response curve for cocaine downward. Y5-KO mice also showed modestly attenuated self-administration. Cocaine-induced hyperactivity was attenuated by L-152,804 and in Y5-KO mice. Cocaine failed to increase c-fos expression in the nucleus accumbens and striatum of L-152,804-treated mice, indicating that the Y5 antagonist could act by influencing neural activity in these regions. Accordingly, the cocaine-induced increase in accumbal extracellular dopamine was attenuated by L-152,804 and in Y5-KO mice, suggesting that Y5 antagonism influences cocaine-induced behaviour by regulating dopamine. Consistent with this concept, dopamine neurons in the ventral tegmental area appeared to contain Y5 receptors. In contrast, neither L-152,804 nor NPY influenced dopamine transporter-mediated dopamine uptake.

CONCLUSIONS

The present data indicate that Y5 antagonism may attenuate cocaine-induced behavioural effects, suggesting that Y5 receptors could be a potential therapeutic target in cocaine addiction.

Y5 neuropeptide Y receptor overexpression in mice neither affects anxiety- and depression-like behaviours nor seizures but confers moderate hyperactivity

Neuropeptide Y (NPY) has been implicated in anxiolytic- and antidepressant-like behaviour as well as seizure-suppressant effects in rodents. Although these effects appear to be predominantly mediated via other NPY receptors (Y1 and/or Y2), several studies have also indicated a role for Y5 receptors. Gene therapy using recombinant viral vectors to induce overexpression of NPY, Y1 or Y2 receptors in the hippocampus or amygdala has previously been shown to modulate emotional behaviour and seizures in rodents. The present study explored the potential effects of gene therapy with the Y5 receptor, by testing effects of recombinant adeno-associated viral vector (rAAV) encoding Y5 (rAAV-Y5) in anxiety- and depression-like behaviour as well as in kainate-induced seizures in adult mice. The rAAV-Y5 vector injected into the hippocampus and amygdala induced a pronounced and sustained increase in Y5 receptor mRNA expression and functional Y5 receptor binding, but no significant effects were found with regard to anxiety- and depression-like behaviours or seizure susceptibility. Instead, rAAV-mediated Y5 receptor transgene overexpression resulted in moderate hyperactivity in the open field test. These results do not support a potential role for single transgene overexpression of Y5 receptors for modulating anxiety-/depression-like behaviours or seizures in adult mice. Whether the induction of hyperactivity by rAAV-Y5 could be relevant for other conditions remains to be studied.

Activation of NPY type 5 receptors induces a long-lasting increase in spontaneous GABA release from cerebellar inhibitory interneurons

Neuropeptide Y (NPY), a widely distributed neuropeptide in the central nervous system, can transiently suppress inhibitory synaptic transmission and alter membrane excitability via Y2 and Y1 receptors (Y2rs and Y1rs), respectively. Although many GABAergic neurons express Y5rs, the functional role of these receptors in inhibitory neurons is not known. Here, we investigated whether activation of Y5rs can modulate inhibitory transmission in cerebellar slices. Unexpectedly, application of NPY triggered a long-lasting increase in the frequency of miniature inhibitory postsynaptic currents in stellate cells. NPY also induced a sustained increase in spontaneous GABA release in cultured cerebellar neurons. When cerebellar cultures were examined for Y5r immunoreactivity, the staining colocalized with that of VGAT, a presynaptic marker for GABAergic cells, suggesting that Y5rs are located in the presynaptic terminals of inhibitory neurons. RT-PCR experiments confirmed the presence of Y5r mRNA in the cerebellum. The NPY-induced potentiation of GABA release was blocked by Y5r antagonists and mimicked by application of a selective peptide agonist for Y5r. Thus Y5r activation is necessary and sufficient to trigger an increase in GABA release. Finally, the potentiation of inhibitory transmission could not be reversed by a Y5r antagonist once it was initiated, consistent with the development of a long-term potentiation. These results indicate that activation of presynaptic Y5rs induces a sustained increase in spontaneous GABA release from inhibitory neurons in contrast to the transient suppression of inhibitory transmission that is characteristic of Y1r and Y2r activation. Our findings thus reveal a novel role of presynaptic Y5rs in inhibitory interneurons in regulating GABA release and suggest that these receptors could play a role in shaping neuronal network activity in the cerebellum.

Neuropeptide Y Y1 receptor hippocampal overexpression via viral vectors is associated with modest anxiolytic-like and proconvulsant effects in mice

Neuropeptide Y (NPY) exerts anxiolytic- and antidepressant-like effects in rodents that appear to be mediated via Y1 receptors. Gene therapy using recombinant viral vectors to induce overexpression of NPY in the hippocampus or amygdala has previously been shown to confer anxiolytic-like effect in rodents. The present study explored an alternative and more specific approach: overexpression of Y1 receptors. Using a recombinant adeno-associated viral vector (rAAV) encoding the Y1 gene (rAAV-Y1), we, for the first time, induced overexpression of functional transgene Y1 receptors in the hippocampus of adult mice and tested the animals in anxiety- and depression-like behavior. Hippocampal Y1 receptors have been suggested to mediate seizure-promoting effect, so the effects of rAAV-induced Y1 receptor overexpression were also tested in kainate-induced seizures. Y1 receptor transgene overexpression was found to be associated with modest anxiolytic-like effect in the open field and elevated plus maze tests, but no effect was seen on depression-like behavior using the tail suspension and forced swim tests. However, the rAAV-Y1 vector modestly aggravated kainate-induced seizures. These data indicate that rAAV-induced overexpression of Y1 receptors in the hippocampus could confer anxiolytic-like effect accompanied by a moderate proconvulsant adverse effect. Further studies are clearly needed to determine whether Y1 gene therapy might have a future role in the treatment of anxiety disorders.

Anticonvulsant neuropeptides as drug leads for neurological diseases

Anticonvulsant neuropeptides are best known for their ability to suppress seizures and modulate pain pathways. Galanin, neuropeptide Y, somatostatin, neurotensin, dynorphin, among others, have been validated as potential first-in-class anti-epileptic or/and analgesic compounds in animal models of epilepsy and pain, but their therapeutic potential extends to other neurological indications, including neurodegenerative and psychatric disorders. Disease-modifying properties of neuropeptides make them even more attractive templates for developing new-generation neurotherapeutics. Arguably, efforts to transform this class of neuropeptides into drugs have been limited compared to those for other bioactive peptides. Key challenges in developing neuropeptide-based anticonvulsants are: to engineer optimal receptor-subtype selectivity, to improve metabolic stability and to enhance their bioavailability, including penetration across the blood–brain barrier (BBB). Here, we summarize advances toward developing systemically active and CNS-penetrant neuropeptide analogs. Two main objectives of this review are: (1) to provide an overview of structural and pharmacological properties for selected anticonvulsant neuropeptides and their analogs and (2) to encourage broader efforts to convert these endogenous natural products into drug leads for pain, epilepsy and other neurological diseases.

Neuropeptide Y has a protective role during murine retrovirus-induced neurological disease

Viral infections in the central nervous system (CNS) can lead to neurological disease either directly by infection of neurons or indirectly through activation of glial cells and production of neurotoxic molecules. Understanding the effects of virus-mediated insults on neuronal responses and neurotrophic support is important in elucidating the underlying mechanisms of viral diseases of the CNS. In the current study, we examined the expression of neurotrophin- and neurotransmitter-related genes during infection of mice with neurovirulent polytropic retrovirus. In this model, virus-induced neuropathogenesis is indirect, as the virus predominantly infects macrophages and microglia and does not productively infect neurons or astrocytes. Virus infection is associated with glial cell activation and the production of proinflammatory cytokines in the CNS. In the current study, we identified increased expression of neuropeptide Y (NPY), a pleiotropic growth factor which can regulate both immune cells and neuronal cells, as a correlate with neurovirulent virus infection. Increased levels of Npy mRNA were consistently associated with neurological disease in multiple strains of mice and were induced only by neurovirulent, not avirulent, virus infection. NPY protein expression was primarily detected in neurons near areas of virus-infected cells. Interestingly, mice deficient in NPY developed neurological disease at a faster rate than wild-type mice, indicating a protective role for NPY. Analysis of NPY-deficient mice indicated that NPY may have multiple mechanisms by which it influences virus-induced neurological disease, including regulating the entry of virus-infected cells into the CNS.

Adeno-associated viral vector-induced overexpression of neuropeptide Y Y2 receptors in the hippocampus suppresses seizures

Gene therapy using recombinant adeno-associated viral vectors overexpressing neuropeptide Y in the hippocampus exerts seizure-suppressant effects in rodent epilepsy models and is currently considered for clinical application in patients with intractable mesial temporal lobe epilepsy. Seizure suppression by neuropeptide Y in the hippocampus is predominantly mediated by Y2 receptors, which, together with neuropeptide Y, are upregulated after seizures as a compensatory mechanism. To explore whether such upregulation could prevent seizures, we overexpressed Y2 receptors in the hippocampus using recombinant adeno-associated viral vectors. In two temporal lobe epilepsy models, electrical kindling and kainate-induced seizures, vector-based transduction of Y2 receptor complementary DNA in the hippocampus of adult rats exerted seizure-suppressant effects. Simultaneous overexpression of Y2 and neuropeptide Y had a more pronounced seizure-suppressant effect. These results demonstrate that overexpression of Y2 receptors (alone or in combination with neuropeptide Y) could be an alternative strategy for epilepsy treatment.

Cell and gene therapies for refractory epilepsy

Despite recent advances in the development of antiepileptic drugs, refractory epilepsy remains a major clinical problem affecting up to 35% of patients with partial epilepsy. Currently, there are few therapies that affect the underlying disease process. Therefore, novel therapeutic concepts are urgently needed. The recent development of experimental cell and gene therapies may offer several advantages compared to conventional systemic pharmacotherapy: (i) Specificity to underlying pathogenetic mechanisms by rational design; (ii) specificity to epileptogenic networks by focal delivery; and (iii) avoidance of side effects. A number of naturally occurring brain substances, such as GABA, adenosine, and the neuropeptides galanin and neuropeptide Y, may function as endogenous anticonvulsants and, in addition, may interact with the process of epileptogenesis. Unfortunately, the systemic application of these compounds is compromised by limited bioavailability, poor penetration of the blood-brain barrier, or the widespread systemic distribution of their respective receptors. Therefore, in recent years a new field of cell and gene-based neuropharmacology has emerged, aimed at either delivering endogenous anticonvulsant compounds by focal intracerebral transplantation of bioengineered cells (ex vivo gene therapy), or by inducing epileptogenic brain areas to produce these compounds in situ (in vivo gene therapy). In this review, recent efforts to develop GABA-, adenosine-, galanin-, and neuropeptide Y- based cell and gene therapies are discussed. The neurochemical rationales for using these compounds are discussed, the advantages of focal applications are highlighted and preclinical cell transplantation and gene therapy studies are critically evaluated. Although many promising data have been generated recently, potential problems, such as long-term therapeutic efficacy, long-term safety, and efficacy in clinically relevant animal models, need to be addressed before clinical applications can be contemplated.

Gene expression in the neuropeptide Y system during ethanol withdrawal kindling in rats

BACKGROUND

Multiple episodes of ethanol intoxication and withdrawal result in progressive, irreversible intensification of the withdrawal reaction, a process termed "ethanol withdrawal kindling." Previous studies show that a single episode of chronic ethanol intoxication and withdrawal causes prominent changes in neuropeptide Y (NPY) and its receptors that have been implicated in regulating withdrawal hyperexcitability. This study for the first time examined the NPY system during ethanol withdrawal kindling.

METHODS

Ethanol withdrawal kindling was studied in rats receiving 16 episodes of 2 days of chronic ethanol intoxication by intragastric intubations followed by 5 days withdrawal. The study included 6 groups: 4 multiple withdrawal episode (MW) groups [peak withdrawal plus (MW+)/minus (MW-) seizures, 3-day (MW3d), and 1-month (MW1mth) withdrawal], a single withdrawal episode group (SW), and an isocalorically fed control group. Gene expression of NPY and its receptors Y1, Y2, and Y5 was studied in the hippocampal dentate gyrus (DG) and CA3/CA1, as well as piriform cortex (PirCx), and neocortex (NeoCx).

RESULTS

MW+/- as well as SW groups showed decreased NPY gene expression in all hippocampal areas compared with controls, but, in the DG and CA3, decreases were significantly smaller in the MW- group compared with the SW group. In the MW+/- and SW groups, Y1, Y2, and Y5 mRNA levels were decreased in most brain areas compared with controls; however, decreases in Y1 and Y5 mRNA were augmented in the MW+/- groups compared with the SW group. The MW+ group differed from the MW- group in the PirCx, where Y2 gene expression was significantly higher.

CONCLUSION

Multiple withdrawal episodes reversibly decreased NPY and NPY receptor mRNA levels at peak withdrawal, with smaller decreases in NPY mRNA levels and augmented decreases in Y1/Y5 mRNA levels compared with a SW episode. Multiple withdrawal-induced seizures increased the Y2 mRNA levels in PirCx. These complex changes in NPY system gene expression could play a role in the ethanol withdrawal kindling process.

Interactions of peptide amidation and copper: novel biomarkers and mechanisms of neural dysfunction

Mammalian genomes encode only a small number of cuproenzymes. The many genes involved in coordinating copper uptake, distribution, storage and efflux make gene/nutrient interactions especially important for these cuproenzymes. Copper deficiency and copper excess both disrupt neural function. Using mice heterozygous for peptidylglycine alpha-amidating monooxygenase (PAM), a cuproenzyme essential for the synthesis of many neuropeptides, we identified alterations in anxiety-like behavior, thermoregulation and seizure sensitivity. Dietary copper supplementation reversed a subset of these deficits. Wildtype mice maintained on a marginally copper-deficient diet exhibited some of the same deficits observed in PAM(+/-) mice and displayed alterations in PAM metabolism. Altered copper homeostasis in PAM(+/-) mice suggested a role for PAM in the cell type specific regulation of copper metabolism. Physiological functions sensitive to genetic limitations of PAM that are reversed by supplemental copper and mimicked by copper deficiency may serve as indicators of marginal copper deficiency.

Positive correlation between the density of neuropeptide y positive neurons in the amygdala and parameters of self-reported anxiety and depression in mesiotemporal lobe epilepsy patients

BACKGROUND

Neuropeptide Y (NPY) has been implicated in depression, anxiety, and memory. Expression of human NPY and the number of NPY-positive neurons in the rodent amygdala correlate with anxiety and stress-related behavior. Increased NPY expression in the epileptic brain is supposed to represent an adaptive mechanism counteracting epilepsy-related hyperexcitability. We attempted to investigate whether NPY-positive neurons in the human amygdala are involved in these processes.

METHODS

In 34 adult epileptic patients undergoing temporal lobe surgery for seizure control, the density of NPY-positive neurons was assessed in the basal, lateral, and accessory-basal amygdala nuclei. Cell counts were related to self-reported depression, anxiety, quality of life, clinical parameters (onset and duration of epilepsy, seizure frequency), antiepileptic medication, and amygdala and hippocampal magnetic resonance imaging volumetric measures.

RESULTS

Densities of NPY-positive basolateral amygdala neurons showed significant positive correlations with depression and anxiety scores, and they were negatively correlated with lamotrigine dosage. In contrast, NPY cell counts showed no relation to clinical factors or amygdalar and hippocampal volumes.

CONCLUSIONS

The results point to a role of amygdalar NPY in negative emotion and might reflect state processes at least in patients with temporal lobe epilepsy. Correlations with common clinical parameters of epilepsy were not found. The question of a disease-related reduction of the density of NPY-positive amygdalar neurons in temporal lobe epilepsy requires further investigation.

Complex plastic changes in the neuropeptide Y system during ethanol intoxication and withdrawal in the rat brain

Previous studies show that chronic ethanol treatment induces prominent changes in brain neuropeptide Y (NPY). The purpose of the present study was to explore ethanol effects at a deeper NPY-system level, measuring expression of NPY and its receptors (Y1, Y2, Y5) as well as NPY receptor binding and NPY-stimulated [(35)S]GTPgammaS functional binding. Rats received intragastric ethanol repeatedly for 4 days, and the NPY system was studied in the hippocampal dentate gyrus (DG), CA3, CA1, and piriform cortex (PirCx) and neocortex (NeoCx) during intoxication, peak withdrawal (16 hr), late withdrawal (3 days), and 1 week after last ethanol administration. NPY mRNA levels decreased during intoxication and at 16 hr in hippocampal regions but increased in the PirCx and NeoCx at 16 hr. NPY mRNA levels were increased at 3 days and returned to control levels in most regions at 1 week. Substantial changes also occurred at the receptor level. Thus Y1, Y2, and Y5 mRNA labelling decreased at 16 hr in most regions, returning to control levels at 3 days, except for PirCx Y2 mRNA, which increased at 3 days and 1 week. Conversely, increases in NPY receptor binding occurred in hippocampal regions during intoxication and in functional binding in the DG and NeoCx during intoxication and at 16 hr and in PirCx during intoxication and at 1 week. Thus this study shows that ethanol intoxication and withdrawal induce complex plastic changes in the NPY system, with decreased/increased gene expression or binding occurring in a time- and region-specific manner. These changes may play an important role in mediating ethanol-induced changes in neuronal excitability.

Neuropeptide Y Y2 receptor in health and disease

We briefly survey the current knowledge and concepts regarding structure and function of the neuropeptide Y Y2 receptor and its agonists, especially as related to pharmacology of the receptor and its roles in pathological processes. Specific structural features are considered that could be responsible for the known compartmentalization and participation of the receptor in cell and tissue organization. This is further discussed in relation to changes of levels of the Y2 receptor in pathological conditions (especially in epilepsy and drug abuse), to endocytosis and recycling, and to participation in wound healing, retinopathy and angiogenesis. Properties of the receptor and of Y2 agonists are considered and reviewed in connection to the negative regulation of transmitter release, feeding, mood and social behavior. The possible involvement of the Y2 receptor in diabetes, carcinogenesis and bone formation is also reviewed.

Decreased gene expression of neuropeptide Y and its receptors in hippocampal regions during ethanol withdrawal in rats

Ethanol withdrawal is associated with neuronal hyperexcitability and increased hippocampal glutamate release. Neuropeptide Y (NPY) appears to play an important role in regulation of hippocampal neuronal excitability by inhibiting glutamate release. Expression of NPY and its receptors Y1, Y2, and Y5 was studied in hippocampal areas of rats during ethanol withdrawal after repeated intragastric ethanol administration for 2 or 4 days using in situ hybridization. Withdrawal was associated with decreased hippocampal expression of NPY and each of its receptors, particularly Y2, after 2 and/or 4 days of ethanol compared to control rats. These data suggest that the hippocampal NPY system is downregulated during ethanol withdrawal and these neuroadaptational changes could play a role in mediating withdrawal hyperexcitability.

Expression patterns of promoters for NPY Y1 and Y5 receptors in Y5RitTA and Y1RVenus BAC-transgenic mice

In the rat brain, neuropeptide Y (NPY) Y(1) and Y(5) receptors are coexpressed in various forebrain regions where they mediate several NPY-activated functions, including feeding behaviour, anxiety, neuronal excitability and hormone secretion. We studied the distribution pattern and cellular colocalization of the Y(1) and the Y(5) receptor gene expression in the mouse brain by using transgenic mice with genomically integrated BAC clones, where the coding regions of the Y(1) and Y(5) receptor genes were replaced by Venus and the synthetic transcription factor itTA reporter genes, respectively (Tg(Y5RitTA/Y1RVenus) mice). Analysis of Venus fluorescence and itTA-mediated activation of Cre recombinase revealed copy number-dependent expression levels, between the lines, but similar expression patterns. In three transgenic lines the BAC encoded Y(5) receptor promoter induced strong Cre expression in the olfactory system, cerebral cortex, hippocampus and basal ganglia. Weaker expression was found in most of the hypothalamic nuclei of line 25, the highest-expressing transgenic line. Activation of Cre was itTA-dependent and could be regulated by doxycycline. The Y(1) receptor promoter-induced Venus fluorescence was intense, widely present through the brain and colocalized with Cre immunostaining in neurons of distinct brain regions, including the cerebral cortex, basolateral amygdala, dentate gyrus and paraventricular nucleus. These data provide a detailed and comparative mapping of Y(1) and Y(5) receptor promoter activity within cells of the mouse brain. The Tg(Y5RitTA/Y1RVenus)-transgenic mice generated here also represent a genetic tool for conditional mutagenesis via the Cre lox system, particularly of genes involved in feeding behaviour, neuronal excitability and hormone secretion.

Beta-estradiol increases dentate gyrus inhibition in female rats via augmentation of hilar neuropeptide Y

The dentate gyrus filters incoming activity into the hippocampus proper. It plays a role in learning and memory and in pathological states such as epilepsy. Some of hilar interneurons of the dentate gyrus express neuropeptide Y (NPY), which modulates granule cell activity. A subpopulation of the NPY-expressing inhibitory interneurons is sensitive to seizure-induced damage. Pretreatment with beta-estradiol in ovariectomized rats protects hilar interneurons against seizure-induced injury, including the NPY-containing damage-sensitive subpopulation. Here, we demonstrate that beta-estradiol enhances NPY expression within the hilar interneurons. In vitro paired-pulse stimulation of the mixed perforant path revealed beta-estradiol-induced augmentation of granule cell network inhibition, which at interstimulus intervals between 200 and 300 ms (corresponding to approximately 3-5 Hz) was NPY sensitive and involved Y1 receptors, whereas it was insensitive to GABA(B) or metabotropic glutamate receptor antagonists. Additionally, beta-estradiol pretreatment attenuated propagation of low-frequency (3.3 or 5 Hz) burst activity through the dentate gyrus. Scavenging endogenous NPY by intracerebroventricular administration of anti-NPY antibody accelerated kainic acid-induced seizure onset and increased seizure-induced neuronal damage in the hilus compared with rats treated with beta-estradiol alone. Together, we show that beta-estradiol upregulates hilar NPY and that this leads to enhancement in dentate gyrus inhibition of incoming frequencies between 3 and 5 Hz. Such frequencies are similar to the discharge frequencies recorded during seizure initiation in some patients with epilepsy. Thus, beta-estradiol-induced NPY-sensitive filtering of 3-5 Hz frequencies may be an important regulator of incoming seizure activity, but it could also serve a physiological purpose in modulating information flow into the hippocampus proper.

Gene therapy in epilepsy: the focus on NPY

Gene therapy represents an innovative and promising alternative for the treatment of epileptic patients who are resistant to conventional antiepileptic drugs. Among the various approaches for the application of gene therapy in the treatment of CNS disorders, recombinant viral vectors have been most widely used so far. Several gene targets could be used to correct the compromized balance between inhibitory and excitatory transmission in epilepsy. Transduction of neuropeptide genes such as galanin and neuropeptide Y (NPY) in specific brain areas in experimental models of seizures resulted in significant anticonvulsant effects. In particular, the long-lasting NPY over-expression obtained in the rat hippocampus using intracerebral application of recombinant adeno-associated viral (AAV) vectors reduced the generalization of seizures from their site of onset, delayed acquisition of fully kindled seizures and afforded neuroprotection. These results establish a proof-of-principle for the applicability of AAV-NPY vectors for the inhibition of seizures in epilepsy. Additional investigations are required to demonstrate a therapeutic role of gene therapy in chronic models of seizures and to address in more detail safety concerns and possible side-effects.

Unaltered neuropeptide Y (NPY)-stimulated [35S]GTPgammaS binding suggests a net increase in NPY signalling after repeated electroconvulsive seizures in mice

Although electroconvulsive seizures (ECS) are widely used as a treatment for severe depression, the working mechanism of ECS remains unclear. Repeated ECS causes anticonvulsant effects that have been proposed to underlie the therapeutic effect of ECS, and neuropeptide Y (NPY) is a potential candidate for mediating this anticonvulsant effect. Repeated ECS results in prominent increases in NPY synthesis. In contrast, NPY-sensitive receptor binding is decreased, so it is unclear whether ECS causes a net increase in NPY signalling. Agonist-stimulated [35S]GTPgammaS binding is a method for detecting functional activation of G-protein-coupled receptors. The present study in mice examined the effects of daily ECS for 14 days on NPY-stimulated [35S]GTPgammaS functional binding and compared this with gene expression of NPY and NPY receptors as well as [125I]peptide YY (PYY) binding in hippocampus of the same animals. Significant increases in NPY mRNA and concomitant reductions in NPY-sensitive binding were found in the dentate gyrus, hippocampal CA1, and neocortex of ECS treated mice, which is consistent with previous rat data. These changes remained significant 1 week after repeated ECS. Significant increases in NPY Y1, Y2, and Y5 mRNA were found in the dentate gyrus after ECS. Surprisingly, unaltered levels of functional NPY receptor binding accompanied the decreased NPY-sensitive binding. This suggests that mechanisms coupling NPY receptor stimulation to G-protein activation could be augmented after repeated ECS. Thus increased synthesis of NPY after repeated ECS should result in a net increase in NPY signalling in spite of reduced levels of NPY-sensitive binding.

Protein kinase C activity blocks neuropeptide Y-mediated inhibition of glutamate release and contributes to excitability of the hippocampus in status epilepticus

The unbalanced excitatory/inhibitory neurotransmitter function in the neuronal network afflicted by seizures is the main biochemical and biophysical hallmark of epilepsy. The aim of this work was to identify changes in the signaling mechanisms associated with neuropeptide Y (NPY)-mediated inhibition of glutamate release that may contribute to hyperexcitability. Using isolated rat hippocampal nerve terminals, we showed that the KCl-evoked glutamate release is inhibited by NPY Y2 receptor activation and is potentiated by the stimulation of protein kinase C (PKC). Moreover, we observed that immediately after status epilepticus (6 h postinjection with kainate, 10 mg/kg), the functional inhibition of glutamate release by NPY Y2 receptors was transiently blocked concomitantly with PKC hyperactivation. The pharmacological blockade of seizure-activated PKC revealed again the Y2 receptor-mediated inhibition of glutamate release. The functional activity of PKC immediately after status epilepticus was assessed by evaluating phosphorylation of the AMPA receptor subunit GluR1 (Ser-831), a substrate for PKC. Moreover, NPY-stimulated [35S]GTPgammaS autoradiographic binding studies indicated that the common target for Y2 receptor and PKC on the inhibition/potentiation of glutamate release was located downstream of the Y2 receptor, or its interacting G-protein, and involves voltage-gated calcium channels.

Neuropeptide gene therapy for epilepsy: viral vectors, stem cells and neurogenesis

Gene therapy for epilepsy is a relatively novel concept compared with previous approaches, which have relied on primary embryonic cells to deliver gene products of interest into localized brain regions. In vivo and ex vivo gene transfer offer promising, but yet insufficiently explored, possibilities to inhibit seizures, either by genetically modifying postmitotic neurons of the brain using viral vectors, or by transplanting genetically modified and in vitro tested cell lines, particularly stem cell lines, to produce and release gene products of interest. In this regard, neuropeptides are discussed as emerging candidates for such gene therapy approaches. Selective modification of newly generated neurons in the dentate gyrus by retroviral vector-based gene delivery opens novel possibilities in gene therapy for epilepsy. However, the limited number of new neurons targeted remains a main obstacle. Despite its early stage, gene therapy for epilepsy might not be a remote prospect for clinical trials, particularly in patients with intractable temporal lobe epilepsy. Ex vivo gene transfer using encapsulated genetically modified cells could be of particular value for such initial trials.