No abstract

Stress and anxiety-related behaviors controlled by the basolateral amygdala (BLA) are regulated in vivo by neuropeptide Y (NPY) and corticotrophin-releasing factor (CRF): NPY produces anxiolytic effects, whereas CRF produces anxiogenic effects. These opposing actions are likely mediated via regulation of excitatory output from the BLA to afferent targets. In these studies, we examined mechanisms underlying the effects of NPY and CRF in the BLA using whole-cell patch-clamp electrophysiology in rat brain slices. NPY, even with tetrodotoxin present, caused a dose-dependent membrane hyperpolarization in BLA pyramidal neurons. The hyperpolarization resulted in the inhibition of pyramidal cells, despite arising from a reduction in a voltage-dependent membrane conductance. The Y1 receptor agonist, F 7P 34 NPY, produced a similar membrane hyperpolarization, whereas the Y1 antagonist, BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N 2-(diphenylacetyl)-argininamide trifluoroacetate], blocked the effect of NPY. The NPY-inhibited current was identified as Ih, which is active at and hyperpolarized to rest. Responses to NPY were occluded by either Cs+ or ZD7288 (4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride), but unaffected by the GIRK-preferring blockers Ba 2+ and SCH23390 [(R)-(+)-7-chloro-8-hydroxy-3-methyl-l-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride]. Application of CRF, with or without TTX present, depolarized NPY-sensitive BLA pyramidal neurons, resulting from an increase in Ih. Electrophysiological and immunocytochemical data were consistent with a major role for the HCN1 subunit. Our results indicate that NPY, via Y1 receptors, directly inhibits BLA pyramidal neurons by suppressing a postsynaptic Ih, whereas CRF enhances resting Ih, causing an increased excitability of BLA pyramidal neurons. The opposing actions of these two peptides on the excitability of BLA output cells are consistent with the observed behavioral actions of NPY and CRF in the BLA.

BACKGROUND AND PURPOSEWith a prevalence of 1-2%, epilepsies belong to the most frequent neurological diseases worldwide. Although antiepileptic drugs are available since several decades, the incidence of patients that are refractory to medication is still over 30%. Antiepileptic effects of κ opioid receptor (κ receptor) agonists have been proposed since the 1980s. However, their clinical use was hampered by dysphoric side effects. Recently, G-protein biased κ receptor agonists were developed, suggesting reduced aversive effects. EXPERIMENTAL APPROACHWe investigated the effects of the κ receptor agonist U-50488H and the G-protein biased partial κ receptor agonist 6′-GNTI in models of acute seizures and drug-resistant temporal lobe epilepsy and in the conditioned place avoidance (CPA) test. Moreover, we performed slice electrophysiology to understand the functional mechanisms of 6′-GNTI. KEY RESULTSAs previously shown for U-50488H, 6′-GNTI markedly increased the threshold for pentylenetetrazole-induced seizures. All treated mice displayed reduced paroxysmal activity in response to U-50488H (20 mg·kg À1 ) or 6′-GNTI (10-30 nmoles) treatment in the mouse model of intra-hippocampal injection of kainic acid. Single cell recordings on hippocampal pyramidal cells revealed enhanced inhibitory signalling as potential mechanisms causing the reduction of paroxysmal activity. Effects of 6′-GNTI were blocked in both seizure models by the κ receptor antagonist 5′-GNTI. Moreover, 6′-GNTI did not induce CPA, a measure of aversive effects, while U-50488H did. CONCLUSIONS AND IMPLICATIONSOur data provide the proof of principle that anticonvulsant/antiseizure and aversive effects of κ receptor activation can be pharmacologically separated in vivo.

Neuropeptide Y (NPY) expression is tightly linked with the development of stress resilience in rodents and humans. Local NPY injections targeting the basolateral amygdala (BLA) produce long-term behavioral stress resilience in male rats via an unknown mechanism. Previously, we showed that activation of NPY Y receptors hyperpolarizes BLA principal neurons (PNs) through inhibition of the hyperpolarization-activated, depolarizing H-current, The present studies tested whether NPY treatment induces stress resilience by modulating NPY (10 pmol) was delivered daily for 5 d bilaterally into the BLA to induce resilience; thereafter, the electrophysiological properties of PNs and the expression of in the BLA were characterized. As reported previously, increases in social interaction (SI) times persisted weeks after completion of NPY administration. intracellular recordings showed that repeated intra-BLA NPY injections resulted in hyperpolarization of BLA PNs at 2 weeks (2W) and 4 weeks (4W) after NPY treatment. At 2W, spontaneous IPSC frequencies were increased, whereas at 4W, resting was markedly reduced and accompanied by decreased levels of HCN1 mRNA and protein expression in BLA. Knock-down of HCN1 channels in the BLA with targeted delivery of lentivirus containing HCN1-shRNA increased SI beginning 2W after injection and induced stress resilience. NPY treatment induced sequential, complementary changes in the inputs to BLA PNs and their postsynaptic properties that reduce excitability, a mechanism that contributes to less anxious behavior. Furthermore, HCN1 knock-down mimicked the increases in SI and stress resilience observed with NPY, indicating the importance of in stress-related behavior. Resilience improves mental health outcomes in response to adverse situations. Neuropeptide Y (NPY) is associated with decreased stress responses and the expression of resilience in rodents and humans. Single or repeated injections of NPY into the basolateral amygdala (BLA) buffer negative behavioral effects of stress and induce resilience in rats, respectively. Here, we demonstrate that repeated administration of NPY into the BLA unfolds several cellular mechanisms that decrease the activity of pyramidal output neurons. One key mechanism is a reduction in levels of the excitatory ion channel HCN1. Moreover, shRNA knock-down of HCN1 expression in BLA recapitulates some of the actions of NPY and causes potent resilience to stress, indicating that this channel may be a possible target for therapy.

Huntington's disease (HD) is a hereditary neurodegenerative disorder of typically middle-aged onset for which there is no disease-modifying treatment. Caudate and putamen medium-sized spiny projection neurons (SPNs) most severely degenerate in HD. However, it is unclear why mutant huntingtin protein (mHTT) is preferentially toxic to these neurons or why symptoms manifest only relatively late in life. mHTT interacts with numerous neuronal proteins. Likewise, multiple SPN cellular processes have been described as altered in various HD models. Among these, altered neuronal Ca influx and intracellular Ca handling feature prominently and are addressed here. Specifically, we focus on extrasynaptic NMDA-type glutamate receptors, endoplasmic reticulum IP3 receptors, and mitochondria. As mHTT is expressed throughout development, compensatory processes will likely be mounted to mitigate any deleterious effects. Although some compensations can lessen mHTT's disruptive effects, others-such as upregulation of the ER-refilling store-operated Ca channel response-contribute to pathogenesis. A causation-based approach is therefore necessary to decipher the complex sequence of events linking mHTT to neurodegeneration, and to design rational therapeutic interventions. With this in mind, we highlight evidence, or lack thereof, that the above alterations in Ca handling occur early in the disease process, clearly interact with mHTT, and show disease-modifying potential when reversed in animals.