Regulation of the galanin system by repeated electroconvulsive seizures in mice

Galanin analogs prevent mortality from seizure-induced respiratory arrest in mice

Objective

Sudden Unexpected Death in Epilepsy (SUDEP) accounts for 20% of mortality in those with recurrent seizures. While risk factors, monitoring systems, and standard practices are in place, the pathophysiology of SUDEP is still not well understood. Better knowledge of SUDEP and its potential mechanisms of action is crucial to reducing risk in this patient population and developing potential treatment options. Clinical studies and animal models of SUDEP suggest that diminished post-ictal respiratory control may be the dominant mechanism contributing to mortality. Recently, it was demonstrated that the depletion of the neuropeptide galanin in the amygdala occurs in human SUDEP. The amygdala plays a key role in the central integration of respiratory signaling; the depletion of galanin may represent a critical change that predisposes individuals to SUDEP.

Materials and methods

To evaluate the impact of enhancing galaninergic signaling to potentially protect against SUDEP, we studied seizure-induced respiratory arrest (S-IRA) following central (intracerebroventricular, intra-amygdala) and systemic (intraperitoneal, subcutaneous) administration of galanin analogs. Seizure naïve and seizure experienced (fully kindled) mice were tested.

Results

Central and systemically administered galanin analogs protect against S-IRA in naïve C57Bl/6J mice. Differential efficacy between receptor subtype-selective analogs varied based on the route of administration. Sub-chronic systemic administration at doses that reduced 6 Hz seizures also protected against S-IRA. Acute treatment benefits also extended to fully kindled mice experiencing tonic extension.

Significance

These data demonstrate that galanin analogs may be protective against post-ictal respiratory collapse.

α-Synuclein Overexpression Increases Dopamine D2/3 Receptor Binding and Immune Activation in a Model of Early Parkinson’s Disease

Progressive degeneration of dopaminergic neurons, immune activation, and α-synuclein pathology characterize Parkinson’s disease (PD). We previously reported that unilateral intranigral injection of recombinant adeno-associated viral (rAAV) vectors encoding wild-type human α-synuclein produced a rat model of early PD with dopamine terminal dysfunction. Here we tested the hypothesis that decreases in dopamine result in increased postsynaptic dopamine D2/D3 receptor expression, neuroinflammation, and reduced synaptic vesicle glycoprotein 2A (SV2A) density. Rats were injected with rAAV encoding α-synuclein or green fluorescent protein and subjected to non-pharmacological motor tests, before euthanization at 12 weeks post-injection. We performed: (1) in situ hybridization of nigral tyrosine hydroxylase mRNA, (2) HPLC of striatal dopamine content, and (3) autoradiography with [³H]raclopride, [³H]DTBZ, [³H]GBR12935, [³H]PK11195, and [³H]UCB-J to measure binding at D2/3 receptors, vesicular monoamine transporter 2, dopamine transporters, mitochondrial translocator protein, and SV2A, respectively. rAAV-α-synuclein induced motor asymmetry and reduced tyrosine hydroxylase mRNA and dopamine content in ipsilateral brain regions. This was paralleled by elevated ipsilateral postsynaptic dopamine D2/3 receptor expression and immune activation, with no changes to synaptic SV2A density. In conclusion, α-synuclein overexpression results in dopaminergic degeneration that induced compensatory increases in D2/3 binding and immune activation, recapitulating many of the pathological characteristics of PD.

Neuropeptide depletion in the amygdala in sudden unexpected death in epilepsy: A postmortem study

OBJECTIVE

Sudden unexpected death in epilepsy (SUDEP) is typically unwitnessed but can be preceded by seizures in the period prior to death. Peri-ictal respiratory dysfunction is a likely mechanism for some SUDEP, and central apnea has been shown following amygdala stimulation. The amygdala is enriched in neuropeptides that modulate neuronal activity and can be transiently depleted following seizures. In a postmortem SUDEP series, we sought to investigate alterations of neuropeptidergic networks in the amygdala, including cases with recent poor seizure control.

METHODS

In 15 SUDEP cases, 12 epilepsy controls, and 10 nonepilepsy controls, we quantified the labeling index (LI) for galanin, neuropeptide Y (NPY), and somatostatin (SST) in the lateral, basal, and accessory basal nuclei and periamygdala cortex with whole slide scanning image analysis. Within the SUDEP group, seven had recent generalized seizures with recovery 24 hours prior to death (SUDEP-R).

RESULTS

Galanin, NPY, and SST LIs were significantly lower in all amygdala regions in SUDEP cases compared to epilepsy controls (P < .05 to P < .0005), and galanin LI was lower in the lateral nucleus compared to nonepilepsy controls (P < .05). There was no difference in the LI in the SUDEP-R group compared to other SUDEP. Higher LI was noted in epilepsy controls than nonepilepsy controls; this was significant for NPY in lateral and basal nuclei (P < .005 and P < .05).

SIGNIFICANCE

A reduction in galanin in the lateral nucleus in SUDEP could represent acute depletion, relevant to postictal amygdala dysfunction. In addition, increased amygdala neuropeptides in epilepsy controls support their seizure-induced modulation, which is relatively deficient in SUDEP; this could represent a vulnerability factor for amygdala dysfunction in the postictal period.

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.

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.

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.

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.

Anxiolytic-like effects after vector-mediated overexpression of neuropeptide Y in the amygdala and hippocampus of mice

Neuropeptide Y (NPY) causes anxiolytic- and antidepressant-like effects after central administration in rodents. These effects could theoretically be utilized in future gene therapy for anxiety and depression using viral vectors for induction of overexpression of NPY in specific brain regions. Using a recombinant adeno-associated viral (rAAV) vector, we addressed this idea by testing effects on anxiolytic- and depression-like behaviours in adult mice after overexpression of NPY transgene in the amygdala and/or hippocampus, two brain regions implicated in emotional behaviours. In the amygdala, injections of rAAV-NPY caused significant anxiolytic-like effect in the open field, elevated plus maze, and light-dark transition tests. In the hippocampus, rAAV-NPY treatment was associated with anxiolytic-like effect only in the elevated plus maze. No additive effect was observed after combined rAAV-NPY injection into both the amygdala and hippocampus where anxiolytic-like effect was found in the elevated plus maze and light-dark transition tests. Antidepressant-like effects were not detected in any of the rAAV-NPY injected groups. Immobility was even increased in the tail suspension and forced swim tests after intra-amygdaloid rAAV-NPY. Taken together, the present data show that rAAV-NPY treatment may confer non-additive anxiolytic-like effect after injection into the amygdala or hippocampus, being most pronounced in the amygdala.

Neuropeptides function in a homeostatic manner to modulate excitation-inhibition imbalance in C. elegans

Neuropeptides play crucial roles in modulating neuronal networks, including changing intrinsic properties of neurons and synaptic efficacy. We previously reported a Caenorhabditis elegans mutant, acr-2(gf), that displays spontaneous convulsions as the result of a gain-of-function mutation in a neuronal nicotinic acetylcholine receptor subunit. The ACR-2 channel is expressed in the cholinergic motor neurons, and acr-2(gf) causes cholinergic overexcitation accompanied by reduced GABAergic inhibition in the locomotor circuit. Here we show that neuropeptides play a homeostatic role that compensates for this excitation-inhibition imbalance in the locomotor circuit. Loss of function in genes required for neuropeptide processing or release of dense core vesicles specifically modulate the convulsion frequency of acr-2(gf). The proprotein convertase EGL-3 is required in the cholinergic motor neurons to restrain convulsions. Electrophysiological recordings of neuromuscular junctions show that loss of egl-3 in acr-2(gf) causes a further reduction of GABAergic inhibition. We identify two neuropeptide encoding genes, flp-1 and flp-18, that together counteract the excitation-inhibition imbalance in acr-2(gf) mutants. We further find that acr-2(gf) causes an increased expression of flp-18 in the ventral cord cholinergic motor neurons and that overexpression of flp-18 reduces the convulsion of acr-2(gf) mutants. The effects of these peptides are in part mediated by two G-protein coupled receptors, NPR-1 and NPR-5. Our data suggest that the chronic overexcitation of the cholinergic motor neurons imposed by acr-2(gf) leads to an increased production of FMRFamide neuropeptides, which act to decrease the activity level of the locomotor circuit, thereby homeostatically modulating the excitation and inhibition imbalance.

Imbalanced neuronal circuit activity is considered a major underlying cause in many neurological disorders, such as epilepsy and autism. Neuropeptides are small polypeptides that are released from neurons. They are widely known to provide neuromodulatory functions and have diverse roles in the nervous system. By investigating a C. elegans mutant that exhibits convulsions as the result of an imbalanced excitation and inhibition in the locomotor circuit, we have identified a homeostatic mechanism involving two distinct neuropeptide genes. We find that the expression of the neuropeptides is up-regulated in response to over-excitation and that, in turn, they act to increase inhibitory transmission. While current treatment strategies for epilepsy have focused on targeting fast synaptic transmission, this work supports the general notion that manipulating slow neuropeptide neurotransmission can strongly influence neural excitation and inhibition imbalance.

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.

Exploration of new molecular mechanisms for antidepressant actions of electroconvulsive seizure

Electroconvulsive seizure (ECS) therapy is a clinically proven treatment for depression and is often effective even in patients resistant to chemical antidepressants. However, the molecular mechanisms underlying the therapeutic efficacy of ECS are not fully understood. Here, I review studies that show molecular, cellular, and behavioral changes by ECS treatment, and discuss the functions of ECS to underlie the action of antidepressant effects. In hippocampus, these changes cover gene induction, increased adult neurogenesis, and electrophysiological reactivity. Especially, the role of vascular endothelial growth factor (VEGF) in neurogenesis is discussed. Among other gene expression changes in hippocampus, a role of cyclooxygenase (COX)-2, an inducible type of the rate-limiting enzyme of prostanoid synthesis, is focused. ECS-induced changes in other brain regions such as prefrontal cortex and hypothalamus, and ECS-induced behavioral changes are also reviewed. Understanding the molecular, cellular, and behavioral changes by ECS will provide a new view to find potential targets for novel antidepressant design that are highlighted by these findings.

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.

Regulation of the galanin system in the brainstem and hypothalamus by electroconvulsive stimulation in mice

Induction of seizures by electroconvulsive stimulation (ECS) is amongst the most efficacious treatments for major depression. However, the working mechanism by which ECS exerts its antidepressant effects remains elusive. The galanin system is regulated by ECS in seizure-prone brain regions and has been shown to modulate depression-like behaviour. To further explore its potential role in the antidepressant effects of ECS the galanin system was investigated by in situ hybridisation and [(125)I]-galanin receptor binding during repeated ECS in the locus coeruleus, dorsal raphe and discrete nuclei of the hypothalamus. Adult mice were treated with ECS once daily for 14 consecutive days, a paradigm previously shown to exert antidepressant-like effects. Significant increases in galanin transcription were found in the locus coeruleus and dorsomedial nuclei of the hypothalamus. In addition, GalR2 mRNA levels in the ventro- and dorsomedial nuclei of the hypothalamus were upregulated whereas no GalR1 mRNA upregulation was observed. [(125)I]-galanin receptor binding was downregulated in the ventromedial nuclei of the hypothalamus and dorsal raphe. These data show that the galanin system is regulated by repeated ECS in brain regions involved in monoaminergic neurotransmission and stress modulation thus indicating a possible role of the galanin system in the therapeutic effects of ECS.