Galanin: an endogenous anticonvulsant?

Galanin diminishes cortical spreading depolarization across rodents - A candidate for treatment?

Galanin (Gal) is a neuropeptide with the potential to ameliorate cortical spreading depolarization (CSD), an electrophysiological phenomenon occurring after brain injury or in migraine aura. Gal is expressed in all cortical neurons both in rat and in mouse cortices. Here we investigated whether the effect of Gal on CSD previously described in the rat is conserved in the mouse cortex. In rats, the topical application of Gal to the cortex for 1 h did not induce any change in CSD amplitudes, propagation velocity, or threshold of elicitation. Rather, topical application of Gal for 3 h was necessary to obtain a significant decrease in these CSD parameters and to develop a remarkable increase in the KCl threshold to elicit a CSD in rat cortex. In contrast, the topical application of Gal on cortical surface for 1 h in mice was sufficient to significantly attenuate CSD amplitudes and increase threshold. A thinner cortex, a faster diffusion or different affinity/expression of receptors for Gal are possible reasons to explain this difference in the time course between rats and mice. Our data are relevant to postulate Gal as a potential target for inhibition of CSD under pathological situations such as stroke or ischemia. SIGNIFICANCE STATEMENT: The neuropeptide Galanin (Gal) is expressed in all neurons throughout the cerebral cortex, both in rats and mice, and is able to reduce or even inhibit Cortical Spreading Depolarization, thus, Gal has the potential to control neuronal excitability that may identify Gal as a target in drug development against CSD.

Cortical spreading depolarization is a potential target for rat brain excitability modulation by Galanin

The inhibitory neuropeptide Galanin (Gal) has been shown to mediate anticonvulsion and neuroprotection. Here we investigated whether Gal affects cortical spreading depolarization (CSD). CSD is considered the pathophysiological neuronal mechanism of migraine aura, and a neuronal mechanism aggravating brain damage upon afflictions of the brain. Immunohistochemistry localized Gal and the Gal receptors 1-3 (GalR1-3) in native rat cortex and evaluated microglial morphology after exposure to Gal. In anesthetized rats, Gal was applied alone and together with the GalR antagonists M40, M871, or SNAP 37889 locally to the exposed cortex. The spontaneous electrocorticogram and CSDs evoked by remote KCl pressure microinjection were measured. In rat cortex, Gal was present in all neurons of all cortical layers, but not in astrocytes, microglia and vessels. GalR2 and GalR3 were expressed throughout all neurons, whereas GalR1 was preponderantly located at neurons in layers IV and V, but only in about half of the neurons. In susceptible rats, topical application of Gal on cortex decreased CSD amplitude, slowed CSD propagation velocity, and increased the threshold for KCl to ignite CSD. In some rats, washout of previously applied Gal induced periods of epileptiform patterns in the electrocorticogram. Blockade of GalR2 by M871 robustly prevented all Gal effects on CSD, whereas blockade of GalR1 or GalR3 was less effective. Although microglia did not express GalRs, topical application of Gal changed microglial morphology indicating microglial activation. This effect of Gal on microglia was prevented by blocking neuronal GalR2. In conclusion, Gal has the potential to ameliorate CSD thus reducing pathophysiological neuronal events caused by or associated with CSD.

What Makes GPCRs from Different Families Bind to the Same Ligand?

G protein-coupled receptors (GPCRs) are the largest class of cell-surface receptor proteins with important functions in signal transduction and often serve as therapeutic drug targets. With the rapidly growing public data on three dimensional (3D) structures of GPCRs and GPCR-ligand interactions, computational prediction of GPCR ligand binding becomes a convincing option to high throughput screening and other experimental approaches during the beginning phases of ligand discovery. In this work, we set out to computationally uncover and understand the binding of a single ligand to GPCRs from several different families. Three-dimensional structural comparisons of the GPCRs that bind to the same ligand revealed local 3D structural similarities and often these regions overlap with locations of binding pockets. These pockets were found to be similar (based on backbone geometry and side-chain orientation using APoc), and they correlate positively with electrostatic properties of the pockets. Moreover, the more similar the pockets, the more likely a ligand binding to the pockets will interact with similar residues, have similar conformations, and produce similar binding affinities across the pockets. These findings can be exploited to improve protein function inference, drug repurposing and drug toxicity prediction, and accelerate the development of new drugs.

Insights into Potential Targets for Therapeutic Intervention in Epilepsy

Epilepsy is a chronic brain disease that affects approximately 65 million people worldwide. However, despite the continuous development of antiepileptic drugs, over 30% patients with epilepsy progress to drug-resistant epilepsy. For this reason, it is a high priority objective in preclinical research to find novel therapeutic targets and to develop effective drugs that prevent or reverse the molecular mechanisms underlying epilepsy progression. Among these potential therapeutic targets, we highlight currently available information involving signaling pathways (Wnt/β-catenin, Mammalian Target of Rapamycin (mTOR) signaling and zinc signaling), enzymes (carbonic anhydrase), proteins (erythropoietin, copine 6 and complement system), channels (Transient Receptor Potential Vanilloid Type 1 (TRPV1) channel) and receptors (galanin and melatonin receptors). All of them have demonstrated a certain degree of efficacy not only in controlling seizures but also in displaying neuroprotective activity and in modifying the progression of epilepsy. Although some research with these specific targets has been done in relation with epilepsy, they have not been fully explored as potential therapeutic targets that could help address the unsolved issue of drug-resistant epilepsy and develop new antiseizure therapies for the treatment of epilepsy.

Clinical value of a set of neuropeptides in term and preterm neonates with seizures: Brain derived neurotrophic factor, galanin and neuropeptide Y

The aim of our study to investigate clinical value of a set of neuropeptides (brain derived neurotrophic factor-BDNF, galanin and neuropeptide Y-NPY) in critically ill neonates. A total of 53 neonates (preterm: 26, term: 27) evaluated with lumbar pucture for etiologic evaluation were consequtively included into the study. Serum and CSF levels of the neuropeptides were measured in the first 48 h of life. All infants were prospectively followed for prognostic outcome (survival and neurodevelopmental) at the first year of life. The study cohort was categorized into four groups with respect to seizure development; preterm neonates with or without seizure and term neonates with or without seizure. Mean CSF levels of NPY (pg/ml) were significantly higher in term neonates with than those without seizures (389.76 vs. 122.66) and galanin (3.31 vs. 1.55) respectively. Term neonates with seizures had significantly higher serum levels of NPY (ng/mL) as compared with neonates without seizures (54.00 vs. 9.10). No significant difference was noted in serum and CSF levels for the set of neuropeptides in neonates with respect to prognostic outcome. Serum NPY and CSF NPY and galanin levels have a potential role for detection of clinical seizures in term neonates.

Fronto-temporal galanin modulates impulse control

RATIONALE

The neuropeptide galanin has been implicated in a wide range of pathological conditions in which frontal and temporal structures are compromised. It works through three subtypes of G-protein-coupled receptors. One of these, the galanin receptor 1 (Gal-R1) subtype, is densely expressed in the ventral hippocampus (vHC) and ventral prefrontal cortex (vPFC); two brain structures that have similar actions on behavioral control. We hypothesize that Gal-R1 contributes to cognitive-control mechanisms that require hippocampal-prefrontal cortical circuitry.

OBJECTIVE

To examine the effect of local vHC and vPFC infusions of M617, a Gal-R1 agonist, on inhibitory mechanisms of response control.

METHODS

Different cohorts of rats were implanted with bilateral guide cannulae targeting the vPFC or the vHC. Following infusion of the Gal-R1 agonist, we examined the animals' behavior using a touchscreen version of the 5-choice reaction time task (5-choice task).

RESULTS

The Gal-R1 agonist produced opposing behaviors in the vPFC and vHC, leading to disruption of impulse control when infused in the vPFC but high impulse control when infused into the vHC. This contrast between areas was accentuated when we added variability to the timing of the stimulus, which led to long decision times and reduced accuracy in the vPFC group but a general improvement in performance accuracy in the vHC group.

CONCLUSIONS

These results provide the first evidence of a selective mechanism of Gal-R1-mediated modulation of impulse control in prefrontal-hippocampal circuitry.

Neuroanatomical Localization of Galanin in Zebrafish Telencephalon and Anticonvulsant Effect of Galanin Overexpression

Galanin is a neuropeptide widely expressed in the nervous system, but it is also present in non-neuronal locations. In the brain, galanin may function as an inhibitory neurotransmitter. Several studies have shown that galanin is involved in seizure regulation and can modulate epileptic activity in the brain. The overall goal of the study was to establish zebrafish as a model to study the antiepileptic effect of galanin. The goal of this study was achieved by (1) determining neuroanatomical localization of galanin in zebrafish lateral pallium, which is considered to be the zebrafish homologue of the mammalian hippocampus, the brain region essential for initiation of seizures, and (2) testing the anticonvulsant effect of galanin overexpression. Whole mount immunofluorescence staining and pentylenotetrazole (PTZ)-seizure model in larval zebrafish using automated analysis of motor function and qPCR were used in the study. Immunohistochemical staining of zebrafish larvae revealed numerous galanin-IR fibers innervating the subpallium, but only scarce fibers reaching the dorsal parts of telencephalon, including lateral pallium. In three-month old zebrafish, galanin-IR innervation of the telencephalon was similar; however, many more galanin-IR fibers reached the dorsal telencephalon, but in the lateral pallium only scarce galanin-IR fibers were visible. qRT-PCR revealed, as expected, a strong increase in the expression of galanin in the Tg(hsp70l:galn) line after heat shock; however, also without heat shock, the galanin expression was several-fold higher than in the control animals. Galanin overexpression resulted in downregulation of c-fos after PTZ treatment. Behavioral analysis showed that galanin overexpression inhibited locomotor activity in PTZ-treated and control larvae. The obtained results show that galanin overexpression reduced the incidence of seizure-like behavior episodes and their intensity but had no significant effect on their duration. The findings indicate that in addition to antiepileptic action, galanin modulates arousal behavior and demonstrates a sedative effect. The current study showed that galanin overexpression correlated with a potent anticonvulsant effect in the zebrafish PTZ-seizure model.

Uncovering new disease indications for G-protein coupled receptors and their endogenous ligands

Background

The Open Targets Platform integrates different data sources in order to facilitate identification of potential therapeutic drug targets to treat human diseases. It currently provides evidence for nearly 2.6 million potential target-disease pairs. G-protein coupled receptors are a drug target class of high interest because of the number of successful drugs being developed against them over many years. Here we describe a systematic approach utilizing the Open Targets Platform data to uncover and prioritize potential new disease indications for the G-protein coupled receptors and their ligands.

Results

Utilizing the data available in the Open Targets platform, potential G-protein coupled receptor and endogenous ligand disease association pairs were systematically identified. Intriguing examples such as GPR35 for inflammatory bowel disease and CXCR4 for viral infection are used as illustrations of how a systematic approach can aid in the prioritization of interesting drug discovery hypotheses. Combining evidences for G-protein coupled receptors and their corresponding endogenous peptidergic ligands increases confidence and provides supportive evidence for potential new target-disease hypotheses. Comparing such hypotheses to the global pharma drug discovery pipeline to validate the approach showed that more than 93% of G-protein coupled receptor-disease pairs with a high overall Open Targets score involved receptors with an existing drug discovery program.

Conclusions

The Open Targets gene-disease score can be used to prioritize potential G-protein coupled receptors-indication hypotheses. In addition, availability of multiple different evidence types markedly increases confidence as does combining evidence from known receptor-ligand pairs. Comparing the top-ranked hypotheses to the current global pharma pipeline serves validation of our approach and identifies and prioritizes new therapeutic opportunities.

Electronic supplementary material

The online version of this article (10.1186/s12859-018-2392-y) contains supplementary material, which is available to authorized users.

The novel anticonvulsant neuropeptide and galanin analogue, NAX-5055, does not alter energy and amino acid metabolism in cultured brain cells

A large body of evidence suggests that the neuropeptide galanin plays an important role in seizure control. In line with this, it was demonstrated that the galanin analogue, NAX-5055, exerts a potent anticonvulsant activity in animal seizure models. We recently found that the NAX-5055-mediated anticonvulsant action involves modulation of both excitatory and inhibitory neurotransmission. Since homeostasis of neurotransmitters and cerebral energy metabolism are intimately linked, it was investigated whether the effects of NAX-5055 on neurotransmission involve changes in energy metabolism and in particular glucose- and amino acid metabolism. With this aim, cultured neurons from mouse brain were incubated with [U-¹³ C]glucose in absence or presence of NAX-5055. Since effects of NAX-5055 on neurotransmission were detected during repetitive stimulation, we tested potential metabolic effects while mimicking repetitive bursts of neurotransmitter release as occurring in the intact brain. The metabolic pathways were mapped using gas-chromatography coupled to mass-spectrometry. We found that NAX-5055 does not modify glucose metabolism in glutamatergic and GABAergic neurons. Furthermore, the effect of NAX-5055 on astrocyte-neuron metabolic interactions was investigated by incubating co-cultures of astrocytes and either glutamatergic or GABAergic neurons with [U-¹³ C]glucose or the glial-selective substrate [1,2-¹³ C]acetate, with or without NAX-5055. In the presence of NAX-5055, no changes in the metabolic landscape were traced. The findings suggest that the anticonvulsant action of NAX-5055 and the accompanying changes in neurotransmission do not involve alterations in energy and amino acid metabolism. Hence, NAX-5055 appears to be an anti-seizure drug candidate displaying no unwanted side effects concerning brain energy and amino acid homeostasis. © 2017 Wiley Periodicals, Inc.

The effect of leptin, ghrelin, and neuropeptide-Y on serum Tnf-Α, Il-1β, Il-6, Fgf-2, galanin levels and oxidative stress in an experimental generalized convulsive seizure model

The objective of this study is to examine the effects of the endogenous ligands leptin, ghrelin, and neuropeptide Y (NPY) on seizure generation, the oxidant/antioxidant balance, and cytokine levels, which are a result of immune response in a convulsive seizure model. With this goal, Wistar rats were divided into 5 groups-Group 1: Saline, Group 2: Saline+PTZ (65mg/kg), Group 3: leptin (4mg/kg)+PTZ, Group 4: ghrelin (80μg/kg)+PTZ, and Group 5: NPY (60μg/kg)+PTZ. All injections were delivered intraperitoneally, and simultaneous electroencephalography (EEG) records were obtained. Seizure activity was scored by observing seizure behavior, and the onset time, latency, and seizure duration were determined according to the EEG records. At the end of the experiments, blood samples were obtained in all groups to assess the serum TNF-α, IL-1β, IL-6, FGF-2, galanin, nitric oxide (NOֹ), malondialdehyde (MDA), and glutathione (GSH) levels. The electrophysiological and biochemical findings (p<0.05) of this study show that all three peptides have anticonvulsant effects in the pentylenetetrazol (PTZ)-induced generalized tonic-clonic convulsive seizure model. The reduction of the levels of the pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 caused by leptin, ghrelin, and NPY shows that these peptides may have anti-inflammatory effects in epileptic seizures. Also, leptin significantly increases the serum levels of the endogenous anticonvulsive agent galanin. The fact that each one of these endogenous peptides reduces the levels of MDA and increases the serum levels of GSH leads to the belief that they may have protective effects against oxidative damage that is thought to play a role in the pathogenesis of epilepsy. Our study contributes to the clarification of the role of these peptides in the brain in seizure-induced oxidative stress and immune system physiology and also presents new approaches to the etiology and treatment of tendency to epileptic seizures.

Differential Effect of Neuropeptides on Excitatory Synaptic Transmission in Human Epileptic Hippocampus

Development of novel disease-modifying treatment strategies for neurological disorders, which at present have no cure, represents a major challenge for today's neurology. Translation of findings from animal models to humans represents an unresolved gap in most of the preclinical studies. Gene therapy is an evolving innovative approach that may prove useful for clinical applications. In animal models of temporal lobe epilepsy (TLE), gene therapy treatments based on viral vectors encoding NPY or galanin have been shown to effectively suppress seizures. However, how this translates to human TLE remains unknown. A unique possibility to validate these animal studies is provided by a surgical therapeutic approach, whereby resected epileptic tissue from temporal lobes of pharmacoresistant patients are available for neurophysiological studies in vitro. To test whether NPY and galanin have antiepileptic actions in human epileptic tissue as well, we applied these neuropeptides directly to human hippocampal slices in vitro. NPY strongly decreased stimulation-induced EPSPs in dentate gyrus and CA1 (up to 30 and 55%, respectively) via Y2 receptors, while galanin had no significant effect. Receptor autoradiographic binding revealed the presence of both NPY and galanin receptors, while functional receptor binding was only detected for NPY, suggesting that galanin receptor signaling may be impaired. These results underline the importance of validating findings from animal studies in human brain tissue, and advocate for NPY as a more appropriate candidate than galanin for future gene therapy trials in pharmacoresistant TLE patients.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Trophic Mechanisms for Exercise-Induced Stress Resilience: Potential Role of Interactions between BDNF and Galanin

Current concepts of the neurobiology of stress-related disorders, such as anxiety and depression emphasize disruptions in neural plasticity and neurotrophins. The potent trophic actions of exercise, therefore, represent not only an effective means for prevention and treatment of these disorders, they also afford the opportunity to employ exercise paradigms as a basic research tool to uncover the neurobiological mechanisms underlying these disorders. Novel approaches to studying stress-related disorders focus increasingly on trophic factor signaling in corticolimbic circuits that both mediate and regulate cognitive, behavioral, and physiological responses to deleterious stress. Recent evidence demonstrates that the neural plasticity supported by these trophic mechanisms is vital for establishing and maintaining resilience to stress. Therapeutic interventions that promote these mechanisms, be they pharmacological, behavioral, or environmental, may therefore prevent or reverse stress-related mental illness by enhancing resilience. The present paper will provide an overview of trophic mechanisms responsible for the enhancement of resilience by voluntary exercise with an emphasis on brain-derived neurotrophic factor, galanin, and interactions between these two trophic factors.

Efficacy and tolerability of the galanin analog NAX 5055 in the multiple-hit rat model of symptomatic infantile spasms

Infantile spasms are seizures manifesting in infantile epileptic encephalopathies that are associated with poor epilepsy and cognitive outcomes. The current therapies are not always effective or are associated with serious side effects. Early cessation of spasms has been proposed to improve long-term outcomes. To identify new therapies for infantile spasms with rapid suppression of spasms, we are using the multiple-hit rat model of infantile spasms, which is a model of refractory infantile spasms. Here, we are testing the efficacy and tolerability of a single dose of the galanin receptor 1 preferring analog, NAX 5055, in the multiple-hit model of spasms. To induce the model, postnatal day 3 (PN3) male Sprague-Dawley rats underwent right intracerebral infusions of doxorubicin and lipopolysaccharide; p-chlorophenylalanine was then injected intraperitoneally (i.p.) at PN5. After the onset of spasms at PN4, 11-14 rats/group were injected i.p. with either NAX 5055 (0.5, 1, 2, or 4mg/kg) or vehicle. Video monitoring for spasms included a 1h pre-injection period, followed by 5h of recording post-injection, and two 2h sessions on PN5. The study was conducted in a randomized, blinded manner. Neurodevelopmental reflexes were assessed daily as well as at 2h after injection. Respiratory function, heart rate, pulse distension, oximetry and blood glucose were measured 4h after injection. The relative expression of GalR1 and GalR2 mRNA over β-actin in the cerebral cortex and hippocampus was determined with real time reverse transcription polymerase chain reaction. There was no acute effect of NAX 5055 on spasm frequency after the single dose of NAX 5055 (n=11-13 rats/group, following exclusions). Neurodevelopmental reflexes, vital signs, blood glucose measured 4h post-injection, and survival were not affected. A reduction in pulse and breath distention of unclear clinical significance was observed with the 7mg/kg NAX 5055 dose. GalR1 mRNA was present in the cerebral cortex and hippocampus of PN4 and adult rats. The hippocampal - but not the cortical - GalR1 mRNA expression was significantly lower in PN4 pups than in adults. GalR1 mRNA was also at least 20 times less abundant in the PN4 cortex than GalR2 mRNA. In conclusion, a single dose of NAX 5055 has no acute efficacy on spasms or toxicity in the multiple hit rat model of medically refractory infantile spasms. Our findings cannot exclude the possibility that repetitive NAX 5055 administration may show efficacy on spasms. The higher expression of GalR2 in the PN4 cortex suggests that GalR2-preferring analogs may be of interest to test for efficacy on spasms.

Galnon facilitates extinction of morphine-conditioned place preference but also potentiates the consolidation process

Learning and memory systems are intimately involved in drug addiction. Previous studies suggest that galanin, a neuropeptide that binds G-protein coupled receptors, plays essential roles in the encoding of memory. In the present study, we tested the function of galnon, a galanin receptor 1 and 2 agonist, in reward-associated memory, using conditioned place preference (CPP), a widely used paradigm in drug-associated memory. Either before or following CPP-inducing morphine administration, galnon was injected at four different time points to test the effects of galanin activation on different reward-associated memory processes: 15 min before CPP training (acquisition), immediately after CPP training (consolidation), 15 min before the post-conditioning test (retrieval), and multiple injection after post-tests (reconsolidation and extinction). Galnon enhanced consolidation and extinction processes of morphine-induced CPP memory, but the compound had no effect on acquisition, retrieval, or reconsolidation processes. Our findings demonstrate that a galanin receptor 1 and 2 agonist, galnon, may be used as a viable compound to treat drug addiction by facilitating memory extinction process.

Infusion of galanin into the mid-caudal portion of the dorsal raphe nucleus has an anxiolytic effect on rats in the elevated T-maze

Galanin and 5-HT coexist in dorsal raphe nucleus (DRN) neurons. Microinjection of galanin into the DRN reduces the firing rate of serotonin neurons. Serotonergic neurons projecting from the DRN to the amygdala facilitate learned anxiety producing an anxiogenic effect, while those projecting from the periaqueductal grey affect innate anxiety producing a panicolytic effect. We tested the hypothesis that injection of galanin into rat DRN would induce anxiolytic/panicogenic effects in the elevated T-maze (ETM), a model that allows for the evaluation of both of these effects. Galanin infusion into the mid-caudal DRN, but not into the rostral DRN, impaired inhibitory avoidance, suggesting an anxiolytic effect. The effective dose of galanin (0.3 nmol) did not modify locomotor activity in the open field. Contrary to expectations, microinjection of galanin into the DRN did not facilitate the latency of one-way escape in the ETM. Pretreatment with a galanin antagonist, M40, attenuated galanin-induced impairment of inhibitory avoidance. The results show that microinjection of a low dose of galanin only into the mid-caudal DRN has an anxiolytic effect. This effect seems to be mediated, at least in part, by galanin receptors. Further investigation is necessary to identify the receptor subtypes and the DRN subregion involved in the anxiolytic effect of galanin.

Cyclic analogs of galanin and neuropeptide Y by hydrocarbon stapling

Hydrocarbon stapling is an effective strategy to stabilize the helical conformation of bioactive peptides. Here we describe application of stapling to anticonvulsant neuropeptides, galanin (GAL) and neuropeptide Y (NPY), that are implicated in modulating seizures in the brain. Dicarba bridges were rationally introduced into minimized analogs of GAL and NPY resulting in increased α-helical content, in vitro metabolic stability and n-octanol/water partitioning coefficient (logD). The stapled analogs retained agonist activities towards their respective receptors and suppressed seizures in a mouse model of epilepsy.

Adeno associated viral vector-mediated expression of somatostatin in rat hippocampus suppresses seizure development

Somatostatin (SST) has been suggested to play an important role in maintaining hippocampal homeostasis by modulating excitatory neurotransmission. The putative anticonvulsant role for SST was tested in an electrical amygdala kindling model. SST was cloned into serotype 5 of the adeno-associated viral (AAV) vector and delivered bilaterally into the hippocampus of adult male Sprague Dawley rats that were subsequently electrically kindled. Behavioral severity and duration of kindled seizures was compared to uninjected and GFP-injected control rats. Results demonstrated that 70% of SST treated animals did not experience class IV or V seizures without affecting the threshold for individual stimulation-evoked seizures. This result was significantly different from control groups where 100% of animals reached class V seizures. No difference in the number of stimulations required to reach the first class I-III seizures was observed in the experimental cohort relative to age-matched controls. These preclinical results suggest a putative role for SST as an anticonvulsant therapeutic modality for epilepsy.

Regulation of the galanin system by repeated electroconvulsive seizures in mice

Even though induction of seizures by electroconvulsive stimulation (ECS) is a treatment widely used for major depression in humans, the working mechanism of ECS remains uncertain. The antiepileptic effect of ECS has been suggested to be involved in mediating the therapeutic effect of ECS. The neuropeptide galanin exerts antiepileptic and antidepressant-like effects and has also been implicated in the pathophysiology of depression. To explore a potential role of galanin in working mechanisms of ECS, the present study examined effects of repeated ECS on the galanin system using QRT-PCR, in situ hybridization, and [(125) I]galanin receptor binding. ECS was administered to adult mice daily for 14 days, and this paradigm was confirmed to exert antidepressant-like effect in the tail suspension test. Prominent increases in galanin gene expression were found in several brain regions involved in regulation of epileptic activity and depression, including the piriform cortex, hippocampal dentate gyrus, and amygdala. Likewise, GalR2 gene expression was up-regulated in both the central and the medial amygdala, whereas GalR1 gene expression showed a modest down-regulation in the medial amygdala. [(125) I]galanin receptor binding in the piriform cortex, hippocampus, and amygdala was found to be significantly down-regulated. These data show that the galanin system is regulated by repeated ECS in a number of brain regions implicated in seizure regulation and depression. These changes may play a role in the therapeutic effect of ECS.

New and investigational antiepileptic drugs

In the last fifteen years, new antiepileptic medications have been offered for the treatment of patients with epilepsy. Nevertheless, despite optimal medical treatment, up to 30% of patients still experience recurrent seizures and the challenge for new, more efficacious and better-tolerated drugs continues. New antiepileptic drugs include the evolution of pre-existing drugs and new compounds identified through the investigation of additional molecular targets, such as SV2A synaptic vesicle protein, voltage-gated potassium channels, ionotropic and metabotropic glutamate receptors, and gap junctions. This paper reviews the available information on various classes of molecules that are in the pipeline as well as on the innovative approaches to the treatment of epilepsy.

Galanin impairs cognitive abilities in rodents: relevance to Alzheimer's disease

The neuropeptide galanin and its receptors are localized in brain pathways that mediate learning and memory. Central microinjection of galanin impairs performance of a variety of cognitive tasks in rats. Transgenic mice overexpressing galanin display deficits in some learning and memory tests. The inhibitory role of galanin in cognitive processes, taken together with the fact that overexpression of galanin occurs in Alzheimer's disease, suggests that galanin antagonists may offer a novel therapeutic approach to treat memory loss in patients suffering from Alzheimer's.

Progress report on new antiepileptic drugs: a summary of the Ninth Eilat Conference (EILAT IX)

The Ninth Eilat Conference on New Antiepileptic Drugs (AEDs)-EILAT IX, took place in Sitges, Barcelona from the 15th to 19th of June 2008. Over 300 basic scientists, clinical pharmacologists and neurologists from 25 countries attended the conference, whose main themes included old and new AEDs in generalized epilepsies, novel formulations and routes of administration of AEDs, common targets and mechanisms of action of drugs for treating epilepsy and other central nervous system (CNS) disorders, and opportunities and perspectives in new AED discovery. Consistent with previous formats of this conference, a large part of the programme was devoted to a review of AEDs in development, as well as updates on AEDs introduced since 1989. Unlike previous EILAT manuscripts, the current (EILAT IX) manuscript focuses only on the preclinical and clinical pharmacology of AEDs that are currently in development. These include brivaracetam, carisbamate (RWJ-333369), 2-deoxy-d-glucose, eslicarbazepine acetate (BIA-2-093), ganaxolone, huperzine, JZP-4, lacosamide, NAX-5055, propylisopropylacetamide (PID), retigabine, T-2000, tonabersat, valrocemide and YKP-3089. The CNS efficacy of these compounds in anticonvulsant animal models as well as other disease model systems are presented in first and second tables and their proposed mechanisms of action are summarized in the third table.

Galanin impairs cognitive abilities in rodents: relevance to Alzheimer's disease

The neuropeptide galanin and its receptors are localized in brain pathways mediating learning and memory. Central microinjection of galanin impairs performance of a variety of cognitive tasks in rats. Transgenic mice overexpressing galanin display deficits in some learning and memory tests. The inhibitory role of galanin in cognitive processes, taken together with the overexpression of galanin in Alzheimer's disease, suggests that galanin antagonists may offer a novel therapeutic approach to treat memory loss in Alzheimer's patients.

Structural consequences of Kcna1 gene deletion and transfer in the mouse hippocampus

PURPOSE

Mice lacking the Kv1.1 potassium channel alpha subunit encoded by the Kcna1 gene develop recurrent behavioral seizures early in life. We examined the neuropathological consequences of seizure activity in the Kv1.1(-/-) (knock-out) mouse, and explored the effects of injecting a viral vector carrying the deleted Kcna1 gene into hippocampal neurons.

METHODS

Morphological techniques were used to assess neuropathological patterns in hippocampus of Kv1.1(-/-) animals. Immunohistochemical and biochemical techniques were used to monitor ion channel expression in Kv1.1(-/-) brain. Both wild-type and knockout mice were injected (bilaterally into hippocampus) with an HSV1 amplicon vector that contained the rat Kcna1 subunit gene and/or the E. coli lacZ reporter gene. Vector-injected mice were examined to determine the extent of neuronal infection.

RESULTS

Video/EEG monitoring confirmed interictal abnormalities and seizure occurrence in Kv1.1(-/-) mice. Neuropathological assessment suggested that hippocampal damage (silver stain) and reorganization (Timm stain) occurred only after animals had exhibited severe prolonged seizures (status epilepticus). Ablation of Kcna1 did not result in compensatory changes in expression levels of other related ion channel subunits. Vector injection resulted in infection primarily of granule cells in hippocampus, but the number of infected neurons was quite variable across subjects. Kcna1 immunocytochemistry showed "ectopic" Kv1.1 alpha channel subunit expression.

CONCLUSIONS

Kcna1 deletion in mice results in a seizure disorder that resembles--electrographically and neuropathologically--the patterns seen in rodent models of temporal lobe epilepsy. HSV1 vector-mediated gene transfer into hippocampus yielded variable neuronal infection.

Locus Coeruleus and Neuronal Plasticity in a Model of Focal Limbic Epilepsy

PURPOSE

A lesion of the noradrenergic nucleus Locus Coeruleus (LC) converts sporadic seizures evoked by microinfusion of bicuculline into the anterior piriform cortex (APC) of rats into limbic status epilepticus (SE). The purpose of this study was to evaluate the chronic effects of this new model of SE on the onset of secondary epileptogenesis. We further related the loss of noradrenaline (NE) with hippocampal mossy fiber sprouting.

METHODS

Male Sprague Dawley rats were treated with systemic saline or DSP-4 (a neurotoxin selective for noradrenergic terminals originating from the LC), microinfused with bicuculline into the APC three days later, and sacrificed after 45 days. Naïve and DSP-4 pretreated sham-operated rats served as respective controls. The following evaluations were performed: (a) monitoring of acute seizures and delayed occurrence of spontaneous recurrent seizures (SRS); (b) NE levels in the hippocampus, frontal and olfactory cortex; (c) occurrence of mossy fiber sprouting into the inner molecular layer of the dentate gyrus of the dorsal hippocampus.

RESULTS

In 30% of rats lacking noradrenergic terminals, SE evoked from the APC was followed by SRS. Conversely, seizures evoked in intact rats did not result in chronic epileptogenesis. Seizures/SE did not modify NE levels as compared with baseline levels both in naïve and DSP-4-pretreated rats. Rats undergoing SE following DSP-4 + bicuculline developed SRS which were accompanied by hippocampal mossy fiber sprouting.

CONCLUSIONS

Noradrenergic loss converts focally induced sporadic seizures into an epileptogenic SE, which is accompanied by mossy fiber sprouting within the dentate gyrus.

Potential new antiepileptogenic targets indicated by microarray analysis in a rat model for temporal lobe epilepsy

To get insight into the mechanisms that may lead to progression of temporal lobe epilepsy, we investigated gene expression during epileptogenesis in the rat. RNA was obtained from three different brain regions [CA3, entorhinal cortex (EC), and cerebellum (CB)] at three different time points after electrically induced status epilepticus (SE): acute phase [group D (1 d)], latent period [group W (1 week)], and chronic epileptic period [group M (3-4 months)]. A group that was stimulated but that had not experienced SE and later epilepsy was also included (group nS). Gene expression analysis was performed using the Affymetrix Gene Chip System (RAE230A). We used GENMAPP and Gene Ontology to identify global biological trends in gene expression data. The immune response was the most prominent process changed during all three phases of epileptogenesis. Synaptic transmission was a downregulated process during the acute and latent phases. GABA receptor subunits involved in tonic inhibition were persistently downregulated. These changes were observed mostly in both CA3 and EC but not in CB. Rats that were stimulated but that did not develop spontaneous seizures later on had also some changes in gene expression, but this was not reflected in a significant change of a biological process. These data suggest that the targeting of specific genes that are involved in these biological processes may be a promising strategy to slow down or prevent the progression of epilepsy. Especially genes related to the immune response, such as complement factors, interleukins, and genes related to prostaglandin synthesis and coagulation pathway may be interesting targets.

A molecular study of hippocampus in dogs with convulsion during canine distemper virus encephalitis

In this study, we have investigated the expression of the nuclear transcription factor (c-Fos, NFkB), growth factors (nerve growth factor--NGF, brain-derived neurotrophic factor--BDNF), peptides (enkephalin, galanin) and glutamate transporter (AA 504-523 rat EAAC1) in 6 dogs sacrificed immediately after seizure attack during encephalomyelitis due to canine distemper virus (CDV) (as assessed by clinical examination, RT-PCR and viral RNA detection either in blood or brain tissue and CDV immunohistochemistry in brain slices). In all these CDV affected dogs, the observed neurological signs included untreatable seizures, leading to cluster seizure activity and status epilepticus. In the inter-ictal phase abnormal mentation, postural and gait deficits and sometimes involuntary movements such as myoclonus were recorded. The same investigation was carried out in 5 control dogs affected by different disorders, all characterized by the absence of seizures. Brains were dissected out immediately after euthanasia and fixed; sections collected from the dorsal hippocampus were processed for immunohistochemistry. By comparing hippocampus sections obtained from dog with and without seizure, the following regulations were observed. A strong up-regulation of glutamate transporter throughout the cell layers was found together with the onset of nuclear Fos and NFkB-IR in the pyramidal cell layer X. Among the investigated peptides, we observed a slight increase in enkephalinergic fibers and a strong up-regulation of mu-opioid receptors, whereas galanin-IR seemed to be weaker. Finally, both NGF and BDNF expression was strongly up-regulated. BDNF-IR was mainly localized in the apical dendrite in pyramidal neurons. To our knowledge, these data offer the first indication that molecular events described in experimental kindling also occur during spontaneous pathology in animal species sharing close similarities to human neuropathology.

Galanin as a modulator of anxiety and depression and a therapeutic target for affective disease

Galanin is a 29 amino-acid (30 in humans) neuropeptide with a close functional relationship with neurotransmitter systems implicated in the pathophysiology and treatment of depression and anxiety disorders. In rodent models of depression-related behavior, treatment with galanin or compounds with agonist actions at galanin receptors has been shown to affect depression-related behaviors and the behavioral and neurochemical effects of antidepressants. Treatment with clinically efficacious antidepressants alters galanin and galanin receptor gene expression in rodents. Rodent anxiety-like behaviors appear to be modulated by galanin in a complex manner, with studies showing either increases, decreases and no effects of galanin treatments and galanin mutations on anxiety-like behavior in various tasks. One concept to emerge from this literature is that galanin recruitment during extreme behavioral and physiological provocations such as stress and opiate withdrawal may serve to attenuate negative emotional states caused by noradrenergic hyperactivation. The specific galanin receptor subtypes mediating the anxiety- and depression-related effects of galanin remains to be determined, with evidence supporting a possible contribution of GalR1, GalR2 and GalR3. While our understanding of the role of galanin as a modulator of emotion remains at an early stage, recent progress in this rapidly evolving field raise possibility of that galanin may represent a target for the development of novel antidepressant and anxiolytic drug treatments.

Leukemia inhibitory factor is a key regulator of astrocytic, microglial and neuronal responses in a low-dose pilocarpine injury model

Insult to the central nervous system (CNS) induces many changes, including altered neurotransmitter expression, activation of astrocytes and microglia, neurogenesis and cell death. Cytokines and growth factors are candidates to be involved in astrocyte and microglial activation, and the up-regulation of glial fibrillary acidic protein (GFAP) is associated with brain damage. One of these candidates is leukemia inhibitory factor (LIF), a pro-inflammatory cytokine that is induced in astrocytes by brain damage or seizure. LIF also regulates expression of both neuropeptide Y (NPY) and galanin following peripheral nerve injury. To test the hypothesis that LIF regulates astrocyte, microglial and neuropeptide responses to a mild insult, we used a low-dose pilocarpine model to induce a brief seizure in LIF knock-out (KO) mice. Compared to wild type mice, the LIF KO mouse displays reduced astrocyte and microglial activation in the hippocampus. In addition, LIF KO mice display dramatically altered NPY, but not galanin, expression in response to injury. Thus, LIF is required for normal glial responses to brain damage, and, as in the periphery, LIF regulates NPY expression in the CNS.

Somatostatin receptor type 2 undergoes plastic changes in the human epileptic dentate gyrus

Temporal lobe epilepsy (TLE) is characterized by hippocampal sclerosis together with profound losses and phenotypic changes of different classes of interneurons, including those expressing somatostatin (SRIF). To understand the functional significance of the plasticity of SRIF transmission in TLE, unraveling the status of SRIF receptors is, however, a prerequisite. To address this issue, we characterized expression and distribution of the major SRIF receptor, the sst2 subtype, in hippocampal tissue resected in patients with TLE using complementary neuroanatomic approaches. In patients with hippocampal sclerosis, the number of cells expressing sst2 receptor mRNA as well as sst2 receptor-binding sites and immunoreactivity decreased significantly in the CA1-3, reflecting neuronal loss. By contrast, in the dentate gyrus, sst2 receptor mRNA expression was strongly increased in the granule cell layer, and sst2 receptor-binding sites and immunoreactivity was preserved in the inner but decreased significantly in the outer molecular layer. In this latter region, pronounced changes in SRIF terminal fields were observed. Decreased receptor density in the distal dendrites of granule cells is likely to reflect downregulation of sst2 receptors in response to physiopathologic release of SRIF. Because sst2 receptors have anticonvulsant and antiepileptogenic properties, this phenomenon may contribute to the etiology of TLE seizures.

Gene therapy in epilepsy

The generation of viral vectors, such as adeno-associated virus (AAV) and lentivirus, which are capable of stable transduction of neurons, offers an attractive strategy for introducing novel genes into the brain, resulting in a long-lasting production of specific proteins. An alternative approach to achieving transgene expression in brain is to graft cells that are genetically engineered to produce neuroactive substances. Neuroactive peptides, adenosine, and gamma-aminobutyric acid, are agents that can be delivered by gene and cell therapy with potential utility in epilepsy therapy.

The galanin-R2 agonist AR-M1896 reduces glutamate toxicity in primary neural hippocampal cells

Galanin is a neuropeptide involved in a variety of biological functions, including having a strong anticonvulsant activity. To assess a possible role of galanin in modulation of glutamatergic synapses and excitotoxicity, we studied effects of a galanin receptor 2(3) agonist (AR-M1896) on several molecular events induced by glutamate administration in primary neural hippocampal cells. Exposure of cells, after 5 days in vitro, to glutamate 0.5 mM for 10 min caused morphological alterations, including disaggregation of beta-tubulin and MAP-2 cytoskeletal protein assembly, loss of neurites and cell shrinkage. When present in culture medium together with glutamate, 1 and 10 nM of AR-M1896 reduced these alterations. Moreover, AR-M1896 counteracted glutamate-induced c-fos mRNA and c-Fos protein up-regulation after 30-150 min, and 24 h, respectively. Massive nuclear alterations (Hoechst 33258 staining), observed 24 h after glutamate exposure, were also antagonized by AR-M1896 (0.1-100 nM) in a dose-dependent manner. These findings indicate that galanin, probably mainly through its type 2 receptor, interferes with events associated with glutamate toxicity.

The ketogenic diet does not alter brain expression of orexigenic neuropeptides

Neuropeptide Y (NPY) and galanin are neuropeptides that are regulated by energy states and are also anticonvulsant. We tested the hypothesis that the anticonvulsant efficacy of the ketogenic diet (KD) is mediated by increased expression of NPY and galanin via alterations in food intake and energy metabolism. In situ hybridization revealed no effect of the KD on NPY or galanin mRNA expression, suggesting that increased expression of NPY and galanin do not contribute to the anticonvulsant effect of the KD.

Intraganglionic laminar endings and their relationships with neuronal and glial structures of myenteric ganglia in the esophagus of rat and mouse

Intraganglionic laminar endings (IGLEs) represent the only vagal mechanosensory terminals in the tunica muscularis of the esophagus and may be involved in local reflex control. We recently detected extensive though not complete colocalization of the vesicular glutamate transporter 2 (VGLUT2) with markers for IGLEs. To elucidate this colocalization mismatch, this study aimed at identifying markers for nitrergic, cholinergic, peptidergic, and adrenergic neurons and glial cells, which may colocalize with VGLUT2 outside of IGLEs. Confocal imaging revealed, besides substantial colocalization of VGLUT2 and substance P (SP), no other significant colocalizations of VGLUT2 and immunoreactivity for any of these markers within the same varicosities. However, we found close contacts of VGLUT2-positive structures to vesicular acetylcholine transporter, choline acetyltransferase, neuronal nitric oxide synthase, galanin, neuropeptide Y, and vasoactive intestinal peptide immunoreactive cell bodies and varicosities, as well as to glial cells. Neuronal perikarya were never positive for VGLUT2. Thus, VGLUT2 was almost exclusively found in IGLEs and may serve as a specific marker for them. In addition, many IGLEs also contained SP. The close contacts established by IGLEs to myenteric cell bodies, dendrites, and varicose fibers suggest that IGLEs modulate various types of enteric neurons and vice versa.

Galmic, a nonpeptide galanin receptor agonist, affects behaviors in seizure, pain, and forced-swim tests

The pharmacological exploitation of the galanin receptors as drug targets for treatment of epilepsy, depression, and pain has been hampered by the lack of workable compounds for medicinal chemists from random screening of large chemical libraries. The present work uses the tripeptidomimetic galnon and displays its presumed pharmacophores on a rigid molecular scaffold. The scaffold is related to marine natural products and presents three functional groups near one another in space, in a manner reminiscent of a protein surface. An active compound, Galmic, was identified from a small synthetic library and tested in vitro and in vivo for its affinity and efficacy at galanin receptors. Galmic has micromolar affinity for GalR1 receptors (Ki = 34.2 microM) and virtually no affinity for GalR2 receptors. In vitro, Galmic, like galanin, suppresses long-term potentiation in the dentate gyrus; it blocks status epilepticus when injected intrahippocampally or administered i.p. Galmic applied i.p. shows antidepressant-like effects in the forced-swim test, and it is a potent inhibitor of flinching behavior in the inflammatory pain model induced by formalin injection. These data further implicate brain and spinal cord galanin receptors as drug targets and provide an example of a systemically active compound based on a scaffold that mimics protein surfaces.

Plasticity of somatostatin and somatostatin sst2A receptors in the rat dentate gyrus during kindling epileptogenesis

Increasing evidence suggests that somatostatin may control neuronal excitability during epileptogenesis. In the hippocampus, sst2A receptors are likely to mediate somatostatin inhibitory actions but little is known about their status in kindled tissues. In the present study, sst2A receptor and somatostatin immunoreactivity were examined by confocal microscopy in the hippocampus during and after kindling acquisition. In control rats, somatostatin-positive axon terminals were mainly found in the stratum lacunosum moleculare of CA1 area and in the outer molecular layer of the dentate gyrus. sst2A receptor immunoreactivity was diffusely distributed in the strata radiatum and oriens of CA1 and in the stratum moleculare of the dentate gyrus. Immunogold electron microscopy revealed that sst2A receptors were predominantly localized postsynaptically, at the plasma membrane of dendritic shafts and spines of principal neurons. During kindling epileptogenesis, qualitative and semiquantitative analysis revealed a progressive decrease of sst2A immunoreactivity in the outer molecular layer, which was spatially associated with an increase in somatostatin immunoreactivity. No obvious changes in sst2A receptor immunoreactivity were observed in other hippocampal subfields. These results suggest that the decrease of sst2A receptor immunoreactivity in the outer molecular layer reflects receptor down-regulation in distal dendrites of granule cells in response to chronic somatostatin release. Because the sst2A receptor appears to mediate anticonvulsant and antiepileptogenic effects of somatostatin, this may represent a pivotal mechanism contributing to epileptogenesis.

Galanin GAL-R1 receptor null mutant mice display increased anxiety-like behavior specific to the elevated plus-maze

The neuropeptide galanin coexists with norepinephrine and serotonin in neural systems mediating emotion. Previous findings suggested that galanin modulates anxiety-related behaviors in rodents. Three galanin receptor subtypes have been cloned; however, understanding their functions has been limited by the lack of galanin receptor subtype-selective ligands. To study the role of the galanin GAL-R1 receptor subtype in mediating anxiety-related behavior, we generated mice with a null mutation in the Galr1 gene. GAL-R1 -/- are viable and show no abnormalities in health, neurological reflexes, motoric functions, or sensory abilities. On a battery of tests for anxiety-like behavior, GAL-R1 -/- showed increased anxiety-like behavior on the elevated plus-maze test. Anxiety-related behaviors on the light/dark exploration, emergence, and open field tests were normal in GAL-R1 -/-. This test-specific anxiety-like phenotype was confirmed in a second, independent cohort of GAL-R1 null mutant mice and +/+ controls. Principal components factor analysis of behavioral scores from 279 mice suggested that anxiety-like behavior on the elevated plus-maze was qualitatively distinct from behavior on other tests in the battery. In addition, exposure to the elevated plus-maze produced a significantly greater neuroendocrine response than exposure to the light/dark exploration test, as analyzed in normal C57BL/6J mice. These behavioral findings in the first galanin receptor null mutant mouse are consistent with the hypothesis that galanin exerts anxiolytic actions via the GAL-R1 receptor under conditions of relatively high stress.

Differential galanin receptor-1 and galanin expression by 5-HT neurons in dorsal raphé nucleus of rat and mouse: evidence for species-dependent modulation of serotonin transmission

Galanin and galanin receptors are widely expressed by neurons in rat brain that either synthesize/release and/or are responsive to, classical transmitters such as gamma-aminobutyric acid, acetylcholine, noradrenaline, histamine, dopamine and serotonin (5-hydroxytryptamine, 5-HT). The dorsal raphé nucleus (DRN) contains approximately 50% of the 5-HT neurons in the rat brain and a high percentage of these cells coexpress galanin and are responsive to exogenous galanin in vitro. However, the precise identity of the galanin receptor(s) present on these 5-HT neurons has not been previously established. Thus, the current study used a polyclonal antibody for the galanin receptor-1 (GalR1) to examine the possible expression of this receptor within the DRN of the rat and for comparative purposes also in the mouse. In the rat, intense GalR1-immunoreactivity (IR) was detected in a substantial population of 5-HT-immunoreactive neurons in the DRN, with prominent receptor immunostaining associated with soma and proximal dendrites. GalR1-IR was also observed in many cells within the adjacent median raphé nucleus. In mouse DRN, neurons exhibited similar levels and distribution of 5-HT-IR to that in the rat, but GalR1-IR was undetectable. Consistent with this, galanin and GalR1 mRNA were also undetectable in mouse DRN by in situ hybridization histochemistry, despite the detection of GalR1 mRNA (and GalR1-IR) in adjacent cells in the periaqueductal grey and other midbrain areas. 5-HT neuron activity in the DRN is primarily regulated via 5-HT1A autoreceptors, via inhibition of adenylate cyclase and activation of inward-rectifying K+ channels. Notably, the GalR1 receptor subtype signals via identical mechanisms and our findings establish that galanin modulates 5-HT neuron activity in the DRN of the rat via GalR1 (auto)receptors. However, these studies also identify important species differences in the relationship between midbrain galanin and 5-HT systems, which should prompt further investigations in relation to comparative human neurochemistry and which have implications for studies of animal models of relevant neurological conditions such as stress, anxiety and depression.

Anticonvulsant effects of four neuropeptides in the rat hippocampus during self-sustaining status epilepticus

We compared the anticonvulsant actions of dynorphin A (1-13), galanin, neuropeptide Y and somatostatin in a model of self-sustaining status epilepticus (SSSE). SSSE was induced in adult Wistar rats by 30 min intermittent perforant path stimulation. Peptides or saline were injected into the hilus of the dentate gyrus 10 min after the end of perforant path stimulation. EEG was analyzed using Harmonie software (Stellate systems). While all neuropeptides showed significant seizure protecting effects, their anticonvulsant profiles followed different patterns: somatostatin and NPY induced strong, but transient suppression of spikes and seizures, while seizure suppression by dynorphin and galanin was more profound and irreversible.

Short-term plasticity of hippocampal neuropeptides and neuronal circuitry in experimental status epilepticus

PURPOSE

We used a model of self-staining status epilepticus (SSSE), induced by brief intermittent stimulation of the perforant path in unanesthetized rats, to study the mechanism of initiation and of maintenance of SSSE and the role of neuropeptides in those processes.

METHODS

The perforant path was stimulated intermittently for 7 min (ineffective stimulation) or 30 min (generating SSSE). Peptides and their agonists and antagonists were delivered either intraperitoneally, or directly into the hippocampus through a implanted cannula. Behavior and electroencephalogram (EEG) were recorded through a videotape-telemetry system with automatic spike and seizures detection programs, which were supplemented by manual review of the records to confirm the diagnosis. Immunocytochemistry and enzyme-linked immunosorbent assay followed published methods.

RESULTS

Initiation of SSSE was blocked by many agonists of inhibitory neurotransmitters or neuromodulators, and by many antagonists of excitatory synapses, and was facilitated by agents with the opposite action, suggesting the activation of a complex circuit with multiple potential entry points. Once SSSE was established, however, only N-methyl-d-aspartate (NMDA)-receptor ligands and a few neuropeptides had major effects on its maintenance. Galanin and dynorphin had powerful anticonvulsant roles in the maintenance phase of SSSE, whereas somatostatin and neuropeptide Y suppressed seizures only transiently. SSSE seemed to induce maladaptive changes in neuropeptides: it depleted the hippocampus of the galanin- and dynorphin-immunoreactive (IR) fibers, which normally function as endogenous anticonvulsants; whereas it induced overexpression of the proconvulsant neuropeptides substance P and neurokinin B; however, late in the course of SSSE, galanin-IR interneurons appeared in the dentate hilus.

CONCLUSIONS

Initiation of SSSE seems to involve a circuit with many points of entry, and blockage of any point along this circuit inhibits the development of SSSE. Far fewer agents alter the maintenance phase of SSSE. Galanin, dynorphin, somatostatin, and neuropeptide Y have anticonvulsant roles, matching the previous described convulsant role of substance P and neurokinin B. Galanin and dynorphin seem to undergo maladaptive changes, which appear to play an important role of the maintenance phase of SSSE. Later, the de novo expression of inhibitory neuropeptides in novel cells in hippocampus coincides with the waning of seizures and may play a role in their termination.

Anticonvulsant activity of a nonpeptide galanin receptor agonist

Galanin is a neuropeptide with a wide variety of biological functions, including that of a strong endogenous anticonvulsant. No nonpeptide ligands, capable of activating galanin receptors, are available today. Based on known pharmacophores of galanin, a combinatorial library was designed, synthesized, and screened at the rat hippocampal galanin receptor. A low molecular weight galanin receptor agonist, 7-((9-fluorenylmethoxycarbonyl)cyclohexylalanyllysyl)amino-4-methylcoumarin (galnon) was found to displace (125)I-galanin with micromolar affinity at Bowes cellular and rat hippocampal membranes. Autoradiographic binding assay on rat spinal cord sections confirmed the ability of galnon to displace (125)I-galanin from its binding sites. Galnon inhibited adenylate cyclase activity, suggesting an agonist action at galanin receptors. When injected i.p. galnon reduced the severity and increased the latency of pentylenetetrazole-induced seizures in mice and reversed the proconvulsant effects of the galanin receptor antagonist M35, injected into a lateral ventricle. Intrahippocampal injection of galnon also shortened the duration of self-sustaining status epilepticus in rats, confirming its agonist properties in vivo. Pretreatment of rats with antisense peptide nucleic acid targeted to galanin receptor type 1 mRNA abolished the effect of galnon, suggesting mediation of its anticonvulsant properties through this receptor subtype. These findings introduce a systemically active nonpeptide galanin agonist anticonvulsant.

Galanin overexpressing transgenic mice

Galanin overexpressing transgenic mice (GAL-tg) were generated on two different promoters. Both lines of GAL-tg displayed high levels of galanin in the hippocampus and reduced sensitivity to seizures, as compared to their respective wildtype littermate controls (WT). Performance deficits on learning and memory tasks, impaired long-term potentiation, reduced hippocampal excitability, lower evoked glutamate release, and reduced numbers of choline acetyltransferase immunoreactive neurons in the horizontal limb of the diagonal band were detected in GAL-tg as compared to WT. Changes in sensitivity to nociceptive stimuli were demonstrated in one line. GAL-tg represent a new model for investigating the biological actions of endogenous galanin, and for testing novel therapeutics based on galanin receptor ligands.