Acute and chronic alcohol modulation of extended amygdala calcium dynamics

The central amygdala (CeA) and bed nucleus of the stria terminalis (BNST) are reciprocally connected nodes of the extended amygdala thought to play an important role in alcohol consumption. Studies of immediate-early genes indicate that BNST and CeA are acutely activated following alcohol drinking and may signal alcohol reward in nondependent drinkers, while stress signaling in the extended amygdala following chronic alcohol exposure drives increased drinking via negative reinforcement. However, the temporal dynamics of neuronal activation in these regions during drinking behavior are poorly understood. In this study, we used fiber photometry and the genetically encoded calcium sensor GCaMP6s to assess acute changes in neuronal activity during alcohol consumption in BNST and CeA before and after a chronic drinking paradigm. Activity was examined in the pan-neuronal population and separately in dynorphinergic neurons. BNST and CeA showed increased pan-neuronal activity during acute consumption of alcohol and other fluid tastants of positive and negative valence, as well as highly palatable chow. Responses were greatest during initial consummatory bouts and decreased in amplitude with repeated consumption of the same tastant, suggesting modulation by stimulus novelty. Dynorphin neurons showed similar consumption-associated calcium increases in both regions. Following three weeks of continuous alcohol access (CA), calcium increases in dynorphin neurons during drinking were maintained, but pan-neuronal activity and BNST-CeA coherence were altered in a sex-specific manner. These results indicate that BNST and CeA, and dynorphin neurons specifically, are engaged during drinking behavior, and activity dynamics are influenced by stimulus novelty and chronic alcohol.

Prefrontal cortical dynorphin peptidergic transmission constrains threat-driven behavioral and network states

Prefrontal cortical (PFC) circuits provide top-down control of threat reactivity. This includes ventromedial PFC (vmPFC) circuitry, which plays a role in suppressing fear-related behavioral states. Dynorphin (Dyn) has been implicated in mediating negative affect and maladaptive behaviors induced by severe threats and is expressed in limbic circuits, including the vmPFC. However, there is a critical knowledge gap in our understanding of how vmPFC Dyn-expressing neurons and Dyn transmission detect threats and regulate expression of defensive behaviors. Here, we demonstrate that Dyn cells are broadly activated by threats and release Dyn locally in the vmPFC to limit passive defensive behaviors. We further demonstrate that vmPFC Dyn-mediated signaling promotes a switch of vmPFC networks to a fear-related state. In conclusion, we reveal a previously unknown role of vmPFC Dyn neurons and Dyn neuropeptidergic transmission in suppressing defensive behaviors in response to threats via state-driven changes in vmPFC networks.

Opioids, microglia, and temporal lobe epilepsy

A lack of treatment options for temporal lobe epilepsy (TLE) demands an urgent quest for new therapies to recover neuronal damage and reduce seizures, potentially interrupting the neurotoxic cascades that fuel hyper-excitability. Endogenous opioids, along with their respective receptors, particularly dynorphin and kappa-opioid-receptor, present as attractive candidates for controlling neuronal excitability and therapeutics in epilepsy. We perform a critical review of the literature to evaluate the role of opioids in modulating microglial function and morphology in epilepsy. We find that, in accordance with anticonvulsant effects, acute opioid receptor activation has unique abilities to modulate microglial activation through toll-like 4 receptors, regulating downstream secretion of cytokines. Abnormal activation of microglia is a dominant feature of neuroinflammation, and inflammatory cytokines are found to aggravate TLE, inspiring the challenge to alter microglial activation by opioids to suppress seizures. We further evaluate how opioids can modulate microglial activation in epilepsy to enhance neuroprotection and reduce seizures. With controlled application, opioids may interrupt inflammatory cycles in epilepsy, to protect neuronal function and reduce seizures. Research on opioid-microglia interactions has important implications for epilepsy and healthcare approaches. However, preclinical research on opioid modulation of microglia supports a new therapeutic pathway for TLE.

KNDy Neurons of the Hypothalamus and Their Role in GnRH Pulse Generation: an Update

There is considerable evidence that synchronized activity within a reciprocally connected population of cells in the arcuate nucleus (ARC) coexpressing kisspeptin, neurokinin B (NKB), and dynorphin (KNDy cells) is crucial for the generation of gonadotrophin-releasing hormone (GnRH) pulses in mammals. The initial "KNDy hypothesis" proposed that pulsatile GnRH secretion is elicited by episodic kisspeptin release from KNDy cells following synchronized activation and termination of the population by NKB and dynorphin, respectively. Since then, the role of KNDy cells as a critical component of the pulse generator has been further supported by studies at the single-cell level, demonstrating that the population is both necessary and sufficient for pulsatility. In addition, there have been considerable modifications and expansion of the original hypothesis, including work demonstrating the critical role of glutamate in synchronization of the KNDy cell network, functional interactions with other ARC subpopulations, and the existence of species differences in the role of dynorphin in pulse generation. Here we review these recent changes and discuss how the translation of these findings has led to the development of new therapies for disorders related to pulse generation. We also outline critical gaps in knowledge that are currently limiting the application of KNDy research in the clinic, particularly regarding the role of dynorphin in pulse generation in primates.

A female-specific role for trigeminal dynorphin in orofacial pain comorbidity

ABSTRACT

Migraine is commonly reported in patients with temporomandibular disorders (TMDs), but little is known about the mechanisms underlying the comorbid condition. Here, we prepared a mouse model to investigate this comorbidity, in which masseter muscle tendon ligation (MMTL) was performed to induce a myogenic TMD, and the pre-existing TMD enabled a subthreshold dose of nitroglycerin (NTG) to produce migraine-like pain in mice. RNA sequencing followed by real-time quantitative polymerase chain reaction confirmation showed that MMTL plus NTG treatment increased prodynorphin ( Pdyn ) mRNA expression in the spinal trigeminal nucleus caudalis (Sp5C) of female mice but not in male mice. Chemogenetic inhibition of Pdyn -expressing neurons or microinjection of antidynorphin antiserum in the Sp5C alleviated MMTL-induced masseter hypersensitivity and diminished the MMTL-enabled migraine-like pain in female mice but not in male mice. Moreover, chemogenetic activation of Pdyn -expressing neurons or microinjection of dynorphin A (1-17) peptide in the Sp5C enabled a subthreshold dose of NTG to induce migraine-like pain in female mice but not in male mice. Taken together, our results suggest that trigeminal dynorphin has a female-specific role in the modulation of comorbid TMDs and migraine.

Mechanism of Arcuate Kisspeptin Neuron Synchronization in Acute Brain Slices From Female Mice

The mechanism by which arcuate kisspeptin (ARNKISS) neurons co-expressing glutamate, neurokinin B, and dynorphin intermittently synchronize their activity to drive pulsatile hormone secretion remains unclear in females. In order to study spontaneous synchronization within the ARNKISS neuron network, acute brain slices were prepared from adult female Kiss1-GCaMP6 mice. Analysis of both spontaneous synchronizations and those driven by high frequency stimulation of individual ARNKISS neurons revealed that the network exhibits semi-random emergent excitation dependent upon glutamate signaling through AMPA receptors. No role for NMDA receptors was identified. In contrast to male mice, ongoing tachykinin receptor tone within the slice operated to promote spontaneous synchronizations in females. As previously observed in males, we found that ongoing dynorphin transmission in the slice did not contribute to synchronization events. These observations indicate that a very similar AMPA receptor-dependent mechanism underlies ARNKISS neuron synchronizations in the female mouse supporting the "glutamate two-transition" model for kisspeptin neuron synchronization. However, a potentially important sex difference appears to exist with a more prominent facilitatory role for tachykinin transmission in the female.

Prelimbic cortex dynorphin/κ opioid receptor system modulates methamphetamine-induced cognitive impairment

Chronic exposure to methamphetamine (METH) causes severe and persistent cognitive impairment. The present study aimed to investigate the role of dynorphin/κ opioid receptor (KOR) system in the development of METH-induced cognitive impairment. We found that mice showed significant cognitive impairment in the novel object recognition test (NOR) following daily injections of METH (10 mg/kg) for seven consecutive days. Systemic blockade of KOR prevented METH-induced cognitive impairment by pretreatment of the selective KOR antagonist norBNI (10 mg/kg, i.p.) or KOR deletion. Then, significant increased dynorphin and KOR mRNA were observed exclusively in prelimbic cortex (PL) other than infralimbic cortex. Finally, microinjection with norBNI into PL also improved cognitive memory in METH-treated mice using NOR and spontaneous alternation behaviour test. Our results demonstrated that dynorphin/KOR system activation in PL may be a possible mechanism for METH-induced cognitive impairment and shed light on KOR antagonists as a potential neuroprotective agent against the cognitive deficits induced by drug abuse.

Endogenous Opioids in Crohn's Disease

Caring for patients with Crohn's disease (CD) is a serious challenge in modern medicine. The increasing incidence of CD among adolescents and the severe course of the disease create the need for new methods of diagnosis and therapy. Endogenous opioids are a group of low molecular weight chemical compounds with analgesic and anti-inflammatory properties. Endorphins, enkephalins, and dynorphins may have potentially beneficial effects on the course of CD. Previous research data on this topic are inconsistent. Some authors have reported an increase in the concentration of leukocytes during the course of inflammatory bowel disease (IBD) while others have described a downward trend, explained by DPP-IV enzyme activity. Even fewer data are available on plasma endo-opioid level. There is also a lack of comprehensive studies that have assessed the endo-opioid system in patients with IBD. Therefore, the objective of this study was to measure the serum concentrations of human β-endorphin, human proenkephalin (A), and human big dynorphin in CD patients in the acute phase of the disease, during hospital treatment, and in the remission state. All determinations were performed using ELISA kits. The results of our study showed that the concentrations of all the tested endo-opioids, especially β-endorphin and proenkephalin (A), were reduced in adolescents with CD compared to those in the healthy control group, during the acute phase of the disease, and in the remission state. Modulation of the endogenous opioid system and the use of selective nonnarcotic agonists of opioid receptors seems to be promising goals in the future treatment of CD.

Involvement of the Opioid Peptide Family in Cancer Progression

Peptides mediate cancer progression favoring the mitogenesis, migration, and invasion of tumor cells, promoting metastasis and anti-apoptotic mechanisms, and facilitating angiogenesis/lymphangiogenesis. Tumor cells overexpress peptide receptors, crucial targets for developing specific treatments against cancer cells using peptide receptor antagonists and promoting apoptosis in tumor cells. Opioids exert an antitumoral effect, whereas others promote tumor growth and metastasis. This review updates the findings regarding the involvement of opioid peptides (enkephalins, endorphins, and dynorphins) in cancer development. Anticancer therapeutic strategies targeting the opioid peptidergic system and the main research lines to be developed regarding the topic reviewed are suggested. There is much to investigate about opioid peptides and cancer: basic information is scarce, incomplete, or absent in many tumors. This knowledge is crucial since promising anticancer strategies could be developed alone or in combination therapies with chemotherapy/radiotherapy.

Insula Dynorphin and Kappa Opioid Receptor Systems Regulate Alcohol Drinking in a Sex-Specific Manner in Mice

Alcohol use disorder is complex and multifaceted, involving the coordination of multiple signaling systems across numerous brain regions. Previous work has indicated that both the insular cortex and dynorphin (DYN)/kappa opioid receptor (KOR) systems contribute to excessive alcohol use. More recently, we identified a microcircuit in the medial aspect of the insular cortex that signals through DYN/KOR. Here, we explored the role of insula DYN/KOR circuit components on alcohol intake in a long-term intermittent access (IA) procedure. Using a combination of conditional knock-out strategies and site-directed pharmacology, we discovered distinct and sex-specific roles for insula DYN and KOR in alcohol drinking and related behavior. Our findings show that insula DYN deletion blocked escalated consumption and decreased the overall intake of and preference for alcohol in male and female mice. This effect was specific to alcohol in male mice, as DYN deletion did not impact sucrose intake. Further, insula KOR antagonism reduced alcohol intake and preference during the early phase of IA in male mice only. Alcohol consumption was not affected by insula KOR knockout in either sex. In addition, we found that long-term IA decreased the intrinsic excitability of DYN and deep layer pyramidal neurons (DLPNs) in the insula of male mice. Excitatory synaptic transmission was also impacted by IA, as it drove an increase in excitatory synaptic drive in both DYN neurons and DLPNs. Combined, our findings suggest there is a dynamic interplay between excessive alcohol consumption and insula DYN/KOR microcircuitry.SIGNIFICANCE STATEMENT The insular cortex is a complex region that serves as an integratory hub for sensory inputs. In our previous work, we identified a microcircuit in the insula that signals through the kappa opioid receptor (KOR) and its endogenous ligand dynorphin (DYN). Both the insula and DYN/KOR systems have been implicated in excessive alcohol use and alcohol use disorder (AUD). Here, we use converging approaches to determine how insula DYN/KOR microcircuit components contribute to escalated alcohol consumption. Our findings show that insula DYN/KOR systems regulate distinct phases of alcohol consumption in a sex-specific manner, which may contribute to the progression to AUD.

Pain-related Behavioral and Electrophysiological Actions of Dynorphin A (1-17)

Dynorphin A (1-17) (DynA17) has been identified as a key regulator of both sensory and affective dimensions of chronic pain. Following nerve injury, increases in DynA17 have been reported in the spinal and supraspinal areas involved in chronic pain. Blocking these increases provides therapeutic benefits in preclinical chronic pain models. Although heavily characterized at the behavioral level, how DynA17 mediates its effects at the cellular physiological level has not been investigated. In this report, we begin to decipher how DynA17 mediates its direct effects on mouse dorsal root ganglion (DRG) cells and how intrathecal administration modifies a key node in the pain axis, the periaqueductal gray (PAG). These findings build on the plethora of literature defining DynA17 as a critical neuropeptide in the pathophysiology of chronic pain syndromes.

Avian opioid peptides: evolutionary considerations, functional roles and a challenge to address critical questions

The present review considers the putative hormonal opioid peptides in birds. In birds and all other vertebrates, there are four opioid related genes encoding a series of peptides. These genes are, respectively, proenkephalin (PENK), prodynorphin (PDYN), pronociceptin (PNOC) and proopiomelanocortin (POMC). Proenkephalin (PENK) encodes Met- and Leu-enkephalin together with peptides containing met enkephalin motifs in birds, mammals and reptiles. Proopiomelanocortin (POMC) encodes β endorphin together with adrenocorticotropic hormone (ACTH), and melanocyte stimulating hormone (MSH). Prodynorphin (PDYN) encoding dynorphins A and B with α- and β-neoendorphins together intermediate polypeptides across the vertebrates. Pronociceptin (PNOC) encodes nociceptin together with possibly putative avian nocistatin and a non-opioid peptide derived from the C terminal of pronociceptin. There is a high degree of identity in the sequences of enkephalin peptides, dynorphin-A and B and nociceptin in birds and, to a less extent, across vertebrates. The opioid peptides exert effects related to pain together with other biological actions such as growth/development acting via a series of opioid receptors. What is unclear, particularly in birds, is the biological roles and interactions (additivity, antagonistic and synergistic) for the individual opioid peptides, the processing of the prohormones in different tissues and the physiological relevance of the different peptides and, particularly, of the circulating forms.

Stress-related neuropeptide systems as targets for treatment of alcohol addiction: A clinical perspective

Alcohol use is a major cause of disability and death globally. These negative consequences disproportionately affect people who develop alcohol addiction, a chronic relapsing condition characterized by increased motivation to use alcohol, choice of alcohol over healthy, natural rewards, and continued use despite negative consequences. Available pharmacotherapies for alcohol addiction are few, have effect sizes in need of improvement, and remain infrequently prescribed. Research aimed at developing novel therapeutics has in large part focused on attenuating pleasurable or "rewarding" properties of alcohol, but this targets processes that primarily play a role as initiation factors. As clinical alcohol addiction develops, long-term changes in brain function result in a shift of affective homeostasis, and rewarding alcohol effects become progressively reduced. Instead, increased stress sensitivity and negative affective states emerge in the absence of alcohol and create powerful incentives for relapse and continued use through negative reinforcement, or "relief." Based on research in animal models, several neuropeptide systems have been proposed to play an important role in this shift, suggesting that these systems could be targeted by novel medications. Two mechanisms in this category, antagonism at corticotropin-releasing factor type 1, and neurokinin 1/substance P receptors, have been subject to initial evaluation in humans. A third, kappa-opioid receptor antagonism, has been evaluated in nicotine addiction and could soon be tested for alcohol. This paper discusses findings with these mechanisms to date, and their prospects as future targets for novel medications.

κ-Opioid Receptor Plasma Levels Are Associated With Sex and Diagnosis of Major Depressive Disorder But Not Response to Ketamine

BACKGROUND

Preclinical evidence indicates that the κ-opioid receptor (KOR)/dynorphin pathway is implicated in depressive-like behaviors. Ketamine is believed to partly exert its antidepressant effects by modulating the opioid system. This post hoc study examined the following research questions: (1) at baseline, were there differences in KOR or dynorphin plasma levels between individuals with major depressive disorder (MDD) and healthy volunteers (HVs) or between men and women? (2) in individuals with MDD, did KOR or dynorphin baseline plasma levels moderate ketamine's therapeutic effects or adverse effects? and (3) in individuals with MDD, were KOR or dynorphin plasma levels affected after treatment with ketamine compared with placebo?

METHODS

Thirty-nine unmedicated individuals with MDD (23 women) and 25 HVs (16 women) received intravenous ketamine (0.5 mg/kg) and placebo in a randomized, crossover, double-blind trial. Blood was obtained from all participants at baseline and at 3 postinfusion time points (230 minutes, day 1, day 3). Linear mixed model regressions were used.

RESULTS

At baseline, participants with MDD had lower KOR plasma levels than HVs ( F1,60 = 13.16, P < 0.001), and women (MDD and HVs) had higher KOR plasma levels than men ( F1,60 = 4.98, P = 0.03). Diagnosis and sex had no significant effects on baseline dynorphin levels. Baseline KOR and dynorphin levels did not moderate ketamine's therapeutic or adverse effects. Compared with placebo, ketamine was not associated with postinfusion changes in KOR or dynorphin levels.

CONCLUSIONS

In humans, diagnosis of MDD and biological sex are involved with changes in components of the KOR/dynorphin pathway. Neither KOR nor dynorphin levels consistently moderated ketamine's therapeutic effects or adverse effects, nor were levels altered after ketamine infusion.

TRIAL REGISTRATION

NCT00088699 ( ClinicalTrials.gov ).

Mechanism of kisspeptin neuron synchronization for pulsatile hormone secretion in male mice

The mechanism by which arcuate nucleus kisspeptin (ARN^KISS) neurons co-expressing glutamate, neurokinin B, and dynorphin intermittently synchronize their activity to generate pulsatile hormone secretion remains unknown. An acute brain slice preparation maintaining synchronized ARN^KISS neuron burst firing was used alongside in vivo GCaMP GRIN lens microendoscope and fiber photometry imaging coupled with intra-ARN microinfusion. Studies in intact and gonadectomized male mice revealed that ARN^KISS neuron synchronizations result from near-random emergent network activity within the population and that this was critically dependent on local glutamate-AMPA signaling. Whereas neurokinin B operated to potentiate glutamate-generated synchronizations, dynorphin-kappa opioid tone within the network served as a gate for synchronization initiation. These observations force a departure from the existing "KNDy hypothesis" for ARN^KISS neuron synchronization. A "glutamate two-transition" mechanism is proposed to underlie synchronizations in this key hypothalamic central pattern generator driving mammalian fertility.

Structures of the entire human opioid receptor family

Opioids are effective analgesics, but their use is beset by serious side effects, including addiction and respiratory depression, which contribute to the ongoing opioid crisis. The human opioid system contains four opioid receptors (μOR, δOR, κOR, and NOPR) and a set of related endogenous opioid peptides (EOPs), which show distinct selectivity toward their respective opioid receptors (ORs). Despite being key to the development of safer analgesics, the mechanisms of molecular recognition and selectivity of EOPs to ORs remain unclear. Here, we systematically characterize the binding of EOPs to ORs and present five structures of EOP-OR-Gi complexes, including β-endorphin- and endomorphin-bound μOR, deltorphin-bound δOR, dynorphin-bound κOR, and nociceptin-bound NOPR. These structures, supported by biochemical results, uncover the specific recognition and selectivity of opioid peptides and the conserved mechanism of opioid receptor activation. These results provide a structural framework to facilitate rational design of safer opioid drugs for pain relief.

Design and development of novel, short, stable dynorphin-based opioid agonists for safer analgesic therapy

Kappa opioid receptors have exceptional potential as an analgesic target, seemingly devoid of many problematic Mu receptor side-effects. Kappa-selective, small molecule pharmaceutical agents have been developed, but centrally mediated side-effects limit clinical translation. We modify endogenous dynorphin peptides to improve drug-likeness and develop safer KOP receptor agonists for clinical use. Using rational, iterative design, we developed a series of potent, selective, and metabolically stable peptides from dynorphin 1-7. Peptides were assessed for in vitro cAMP-modulation against three opioid receptors, metabolic stability, KOP receptor selectivity, desensitisation and pERK-signalling capability. Lead peptides were evaluated for in vivo efficacy in a rat model of inflammatory nociception. A library of peptides was synthesised and assessed for pharmacological and metabolic stability. Promising peptide candidates showed low nanomolar KOP receptor selectivity in cAMP assay, and improved plasma and trypsin stability. Selected peptides showed bias towards cAMP signalling over pERK activity, also demonstrating reduced desensitisation. In vivo, two peptides showed significant opioid-like antinociception comparable to morphine and U50844H. These highly potent and metabolically stable peptides are promising opioid analgesic leads for clinical translation. Since they are somewhat biased peptide Kappa agonists they may lack many significant side-effects, such as tolerance, addiction, sedation, and euphoria/dysphoria, common to opioid analgesics.

Molecular examination of the endogenous opioid system in rhesus macaque monkeys with self-injurious behavior

Self-injurious behavior (SIB) can lead to serious injury and occurs in approximately 1%-4% of the adult population, with higher incidences in adolescent and institutionalized populations, as well as in children with developmental disorders such as Autism. SIB also spontaneously occurs in a low percentage of captive monkeys. Rhesus macaque (Macaca mulatta) monkeys are evolutionarily and physiologically similar to humans, share 93% genetic sequence similarity to humans, and have long been used as testing subjects for vaccine and clinical trials. Previous studies hypothesized that altered endogenous opioid expression occurs in the brains of individuals and animals that self-injure. We examined the regional mRNA expression of opioid signaling genes in sixteen rhesus macaques that exhibited SIB and eight sex- and age- matched controls. The brain regions examined are linked to reward reinforcement and stress adaptation including the hypothalamus, orbital frontal cortex, nucleus accumbens, hippocampus, caudate, and the amygdala. We found decreased μ-opioid receptor (OPRM1) in the amygdala of monkeys with SIB, and reduced prodynorphin (PDYN) in the hypothalamus. Our data suggest dysfunction in the regulation of opioid peptide precursors and calls for further investigation of the endogenous opioid system in SIB.

Acute Wheel-Running Increases Markers of Stress and Aversion-Related Signaling in the Basolateral Amygdala of Male Rats

Physical activity (PA) is a non-invasive, cost-effective means of reducing chronic disease. Most US citizens fail to meet PA guidelines, and individuals experiencing chronic stress are less likely to be physically active. To better understand the barriers to maintaining active lifestyles, we sought to determine the extent to which short- versus long-term PA increases stress- and aversion-related markers in wild-type (WT) and low voluntary running (LVR) rats, a unique genetic model of low physical activity motivation. Here, we tested the effects of 1 and 4 weeks of voluntary wheel-running on physiological, behavioral, and molecular measures of stress and Hypothalamic Pituitary Adrenal (HPA)-axis responsiveness (corticosterone levels, adrenal wet weights, and fecal boli counts). We further determined measures of aversion-related signaling (kappa opioid receptor, dynorphin, and corticotropin releasing hormone mRNA expression) in the basolateral amygdala (BLA), a brain region well characterized for its role in anxiety and aversion. Compared to sedentary values, 1, but not 4 weeks of voluntary wheel-running increased adrenal wet weights and plasma corticosterone levels, suggesting that HPA responsiveness normalizes following long-term PA. BLA mRNA expression of prodynorphin (Pdyn) was significantly elevated in WT and LVR rats following 1 week of wheel-running compared to sedentary levels, suggesting that aversion-related signaling is elevated following short- but not long-term wheel-running. In all, it appears that the stress effects of acute PA may increase molecular markers associated with aversion in the BLA, and that LVR rats may be more sensitive to these effects, providing a potential neural mechanism for their low PA motivation.

Modulation of 5-HT release by dynorphin mediates social deficits during opioid withdrawal

Social isolation during opioid withdrawal is a major contributor to the current opioid addiction crisis. We find that sociability deficits during protracted opioid withdrawal in mice require activation of kappa opioid receptors (KORs) in the nucleus accumbens (NAc) medial shell. Blockade of release from dynorphin (Pdyn)-expressing dorsal raphe neurons (DRPdyn), but not from NAcPdyn neurons, prevents these deficits in prosocial behaviors. Conversely, optogenetic activation of DRPdyn neurons reproduced NAc KOR-dependent decreases in sociability. Deletion of KORs from serotonin (5-HT) neurons, but not from NAc neurons or dopamine (DA) neurons, prevented sociability deficits during withdrawal. Finally, measurements with the genetically encoded GRAB5-HT sensor revealed that during withdrawal KORs block the NAc 5-HT release that normally occurs during social interactions. These results define a neuromodulatory mechanism that is engaged during protracted opioid withdrawal to induce maladaptive deficits in prosocial behaviors, which in humans contribute to relapse.

The κ-opioid receptor-induced autophagy is implicated in stress-driven synaptic alterations

Recent evidence has shown that G protein-coupled receptors (GPCRs) are direct sensors of the autophagic machinery and opioid receptors regulate neuronal plasticity and neurotransmission with an as yet unclarified mechanism. Using in vitro and in vivo experimental approaches, this study aims to clarify the potential role of autophagy and κ-opioid receptor (κ-OR) signaling in synaptic alterations. We hereby demonstrate that the selective κ-OR agonist U50,488H, induces autophagy in a time-and dose-dependent manner in Neuro-2A cells stably expressing the human κ-OR by upregulating microtubule-associated protein Light Chain 3-II (LC3-II), Beclin 1 and Autophagy Related Gene 5 (ATG5). Pretreatment of neuronal cells with pertussis toxin blocked the above κ-OR-mediated cellular responses. Our molecular analysis also revealed a κ-OR-driven upregulation of becn1 gene through ERK1,2-dependent activation of the transcription factor CREB in Neuro-2A cells. Moreover, our studies demonstrated that sub-chronic U50,488H administration in mice causes profound increases of specific autophagic markers in the hippocampus with a concomitant decrease of several pre-and post-synaptic proteins, such as spinophilin, postsynaptic density protein 95 (PSD-95) and synaptosomal associated protein 25 (SNAP25). Finally, using acute stress, a stimulus known to increase the levels of the endogenous κ-OR ligand dynorphin, we are demonstrating that administration of the κ-ΟR selective antagonist, nor-binaltorphimine (norBNI), blocks the induction of autophagy and the stress-evoked reduction of synaptic proteins in the hippocampus. These findings provide novel insights about the essential role of autophagic machinery into the mechanisms through which κ-OR signaling regulates brain plasticity.

Dynorphin promotes stress-induced depressive behaviors by inhibiting ventral pallidal neurons in rats

AIM

Endogenous dynorphin signaling via kappa opioid receptors (KORs) plays a key role in producing the depressive and aversive consequences of stress. We investigated the behavioral effects of the dynorphin/KOR system in the ventral pallidum (VP) and studied the underlying mechanisms.

METHODS

To investigate the effects of dynorphin on the VP, we conducted behavioral experiments after microinjection of drugs or shRNA and brain-slice electrophysiological recordings. Histological tracing and molecular biological experiments were used to identify the distribution of KORs and the possible sources of dynorphin projections to the VP.

RESULTS

An elevated dynorphin concentration and increased KOR activity were observed in the VP after acute stress. Infusion of dynorphin-A into the VP produced depressive-like phenotypes including anhedonia and despair and anxiety behaviors, but did not alter locomotor behavior. Mechanistically, dynorphin had an inhibitory effect on VP neurons-reducing their firing rate and inhibiting excitatory transmission-through direct activation of KORs and modulation of downstream G-protein-gated inwardly rectifying potassium (GIRK) channels and high-voltage gated calcium channels (VGCCs). Tracing revealed direct innervation of VP neurons by dynorphin-positive projections; potential sources of these dynorphinergic projections include the nucleus accumbens, amygdala, and hypothalamus. Blockade of dynorphin/KOR signaling in the VP by drugs or viral knock-down of KORs significantly reduced despair behavior in rats.

CONCLUSIONS

Endogenous dynorphinergic modulation of the VP plays a critical role in mediating depressive reactions to stress.

Conditional Deletion of KOR (Oprk1) in Kisspeptin Cells Does Not Alter LH Pulses, Puberty, or Fertility in Mice

Classic pharmacological studies suggested that endogenous dynorphin-KOR signaling is important for reproductive neuroendocrine regulation. With the seminal discovery of an interconnected network of hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B, and dynorphin (KNDy neurons), the KNDy hypothesis was developed to explain how gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) pulses are generated. Key to this hypothesis is dynorphin released from KNDy neurons acting in a paracrine manner on other KNDy neurons via kappa opioid receptor (KOR) signaling to terminate neural "pulse" events. While in vitro evidence supports this aspect of the KNDy hypothesis, a direct in vivo test of the necessity of KOR signaling in kisspeptin neurons for proper LH secretion has been lacking. We therefore conditionally knocked out KOR selectively from kisspeptin neurons of male and female mice and tested numerous reproductive measures, including in vivo LH pulse secretion. Surprisingly, despite validating successful knockout of KOR in kisspeptin neurons, we found no significant effect of kisspeptin cell-specific deletion of KOR on any measure of puberty, LH pulse parameters, LH surges, follicle-stimulating hormone (FSH) levels, estrous cycles, or fertility. These outcomes suggest that the KNDy hypothesis, while sufficient normally, may not be the only neural mechanism for sculpting GnRH and LH pulses, supported by recent findings in humans and mice. Thus, besides normally acting via KOR in KNDy neurons, endogenous dynorphin and other opioids may, under some conditions, regulate LH and FSH secretion via KOR in non-kisspeptin cells or perhaps via non-KOR pathways. The current models for GnRH and LH pulse generation should be expanded to consider such alternate mechanisms.

Dynorphin/KOR inhibits neuronal autophagy by activating mTOR signaling pathway to prevent acute seizure epilepsy

In previous studies, we found that dynorphin exerts antiepileptic effect by activating the kappa opioid receptor (KOR). However, the role of neuronal autophagy in dynorphin/KOR-mediated antiepileptic is still unclear. This study aimed to investigate the molecular mechanism of dynorphin's antiepileptic effect by inhibiting autophagy and reducing neuronal apoptosis. Here, a pilocarpine-induced rat model of epilepsy was established and hippocampal neurons were treated with Mg²⁺ -free exposed for epileptiform activity induction. The real-time polymerase chain reaction and Western blot analysis were used to evaluate messenger RNA and protein expression. The TdT-mediated dUTP-biotin nick end labeling staining and flow cytometry were used to analyze cell apoptosis in vivo and in vitro. Neuron cells viability was detected by Cell Counting Kit-8 assay. Immunofluorescent staining and green fluorescent protein-light chain 3 immunofluorescence were used to measure autophagy in vivo and in vitro. Results showed that overexpression of prodynorphin alleviated neuronal apoptosis, activated the mammalian target of rapamycin (mTOR) signaling pathway, and inhibited neuronal autophagy in epileptic rats. Dynorphin inhibited Mg²⁺ -free-induced seizure-like neuron apoptosis, partially reversing the effect of Mg²⁺ -free on the mTOR signaling pathway and seizure-like neuron autophagy. Further, using rapamycin, we found that dynorphin inhibited Mg²⁺ -free-induced seizure-like neuron autophagy and apoptosis by activating the mTOR signaling pathway. In conclusion, dynorphin inhibits autophagy by activating the mTOR signaling pathway and has a protective effect on epilepsy acute seizure and epilepsy-induced brain injury.

The impact of undernutrition on KNDy (kisspeptin/neurokinin B/dynorphin) neurons in female lambs

Undernutrition limits reproduction through inhibition of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) secretion. Because KNDy neurons coexpress neuropeptides that play stimulatory (kisspeptin and neurokinin B [NKB]) and inhibitory (dynorphin) roles in pulsatile GnRH/LH release, we hypothesized that undernutrition would inhibit kisspeptin and NKB expression at the same time as increasing dynorphin expression. Fifteen ovariectomized lambs were either fed to maintain pre-study body weight (controls) or feed-restricted to lose 20% of pre-study body weight (FR) over 13 weeks. Blood samples were collected and plasma from weeks 0 and 13 were assessed for LH by radioimmunoassay. At week 13, animals were killed, and brain tissue was processed for assessment of KNDy peptide mRNA or protein expression. Mean LH and LH pulse amplitude were lower in FR lambs compared to controls. We observed lower mRNA abundance for kisspeptin within KNDy neurons of FR lambs compared to controls with no significant change in mRNA for NKB or dynorphin. We also observed that FR lambs had fewer numbers of arcuate nucleus kisspeptin and NKB perikarya compared to controls. These findings support the idea that KNDy neurons are important for regulating reproduction during undernutrition in female sheep.

Traumatic Stress-Induced Vulnerability to Addiction: Critical Role of the Dynorphin/Kappa Opioid Receptor System

Substance use disorders (SUD) may emerge from an individual’s attempt to limit negative affective states and symptoms linked to stress. Indeed, SUD is highly comorbid with chronic stress, traumatic stress, or post-traumatic stress disorder (PTSD), and treatments approved for each pathology individually often failed to have a therapeutic efficiency in such comorbid patients. The kappa-opioid receptor (KOR) and its endogenous ligand dynorphin (DYN), seem to play a key role in the occurrence of this comorbidity. The DYN/KOR function is increased either in traumatic stress or during drug use, dependence acquisition and DYN is released during stress. The behavioural effects of stress related to the DYN/KOR system include anxiety, dissociative and depressive symptoms, as well as increased conditioned fear response. Furthermore, the DYN/KOR system is implicated in negative reinforcement after the euphoric effects of a drug of abuse ends. During chronic drug consumption DYN/KOR functions increase and facilitate tolerance and dependence. The drug-seeking behaviour induced by KOR activation can be retrieved either during the development of an addictive behaviour, or during relapse after withdrawal. DYN is known to be one of the most powerful negative modulators of dopamine signalling, notably in brain structures implicated in both reward and fear circuitries. KOR are also acting as inhibitory heteroreceptors on serotonin neurons. Moreover, the DYN/KOR system cross-regulate with corticotropin-releasing factor in the brain. The sexual dimorphism of the DYN/KOR system could be the cause of the gender differences observed in patients with SUD or/and traumatic stress-related pathologies. This review underlies experimental and clinical results emphasizing the DYN/KOR system as common mechanisms shared by SUD or/and traumatic stress-related pathologies, and suggests KOR antagonist as a new pharmacological strategy to treat this comorbidity.

Brain site-specific regulation of hedonic intake by orexin and DYN peptides: role of the PVN and obesity

The orexin peptides promote hedonic intake and other reward behaviors through different brain sites. The opioid dynorphin peptides are co-released with orexin peptides but block their effects on reward in the ventral tegmental area (VTA). We previously showed that in the paraventricular hypothalamic nucleus (PVN), dynorphin and not orexin peptides enhance hedonic intake, suggesting they have brain-site-specific effects. Obesity alters the expression of orexin and dynorphin receptors, but whether their expression across different brain sites is important to hedonic intake is unclear. We hypothesized that hedonic intake is regulated by orexin and dynorphin peptides in PVN and that hedonic intake in obesity correlates with expression of their receptors. Here we show that in mice, injection of DYN-A_1-13 (an opioid dynorphin peptide) in the PVN enhanced hedonic intake, whereas in the VTA, injection of OXA (orexin-A, an orexin peptide) enhanced hedonic intake. In PVN, OXA blunted the increase in hedonic intake caused by DYN-A_1-13. In PVN, injection of norBNI (opioid receptor antagonist) reduced hedonic intake but a subsequent OXA injection failed to increase hedonic intake, suggesting that OXA activity in PVN is not influenced by endogenous opioid activity. In the PVN, DYN-A_1-13 increased the intake of the less-preferred food in a two-food choice task. In obese mice fed a cafeteria diet, orexin 1 receptor mRNA across brain sites involved in hedonic intake correlated with fat preference but not caloric intake. Together, these data support that orexin and dynorphin peptides regulate hedonic intake in an opposing manner with brain-site-specific effects.

Amygdala dynorphin/κ opioid receptor system modulates depressive-like behavior in mice following chronic social defeat stress

Major depression disorder is a severe and recurrent neuropsychological disorder characterized by lowered mood and social activity and cognitive impairment. Owing to unclear molecular mechanisms of depression, limited interventions are available in clinic. In this study we investigated the role of dynorphin/κ opioid receptor system in the development of depression. Mice were subjected to chronic social defeat stress for 14 days. Chronic social defeat stress induced significant social avoidance in mice characterized by decreased time duration in the interaction zone and increased time duration in the corner zone. Pre-administration of a κ opioid receptor antagonist norBNI (10 mg/kg, i.p.) could prevent the development of social avoidance induced by chronic social defeat stress. Social avoidance was not observed in κ opioid receptor knockout mice subjected to chronic social defeat stress. We further revealed that social defeat stress activated c-fos and ERK signaling in the amygdala without affecting the NAc, hippocampus and hypothalamus, and ERK activation was blocked by systemic injection of norBNI. Finally, the expression of dynorphin A, the endogenous ligand of κ opioid receptor, was significantly increased in the amygdala following social defeat stress; microinjection of norBNI into the amygdala prevented the development of depressive-like behaviors caused by social defeat stress. The present study demonstrates that upregulated dynorphin/κ opioid receptor system in the amygdala leads to the emergence of depression following chronic social defeat stress, and sheds light on κ opioid receptor antagonists as potential therapeutic agents for the prevention and treatment of depression following chronic stress.

Cabergoline, a long-acting dopamine agonist, attenuates L-dopa-induced dyskinesia without L-dopa sparing in a rat model of Parkinson's disease

Intermittent administration of L-dopa in Parkinson's disease is associated with L-dopa-induced dyskinesia (LID). Long-acting dopamine agonists may reduce the risk of LID by continuous dopaminergic stimulation. We examined the LID-like behavior, preprodynorphin messenger ribonucleic acid (mRNA) expression in the striatum (a neurochemical LID hallmark), and the volume of the entopeduncular nucleus (a pathological LID hallmark) in Parkinson's disease rat models that were treated with L-dopa and cabergoline. Cabergoline co-treatment with L-dopa reduced LID, striatal preprodynorphin mRNA expression, and hypertrophy of the entopeduncular nucleus, indicating that cabergoline has an anti-LID effect independent of the L-dopa-sparing effect.

Hypothalamic Kisspeptin Neurons and the Control of Homeostasis

Hypothalamic kisspeptin (Kiss1) neurons provide indispensable excitatory transmission to gonadotropin-releasing hormone (GnRH) neurons for the coordinated release of gonadotropins, estrous cyclicity, and ovulation. But maintaining reproductive functions is metabolically demanding so there must be a coordination with multiple homeostatic functions, and it is apparent that Kiss1 neurons play that role. There are 2 distinct populations of hypothalamic Kiss1 neurons, namely arcuate nucleus (Kiss1ARH) neurons and anteroventral periventricular and periventricular nucleus (Kiss1AVPV/PeN) neurons in rodents, both of which excite GnRH neurons via kisspeptin release but are differentially regulated by ovarian steroids. Estradiol (E2) increases the expression of kisspeptin in Kiss1AVPV/PeN neurons but decreases its expression in Kiss1ARH neurons. Also, Kiss1ARH neurons coexpress glutamate and Kiss1AVPV/PeN neurons coexpress gamma aminobutyric acid (GABA), both of which are upregulated by E2 in females. Also, Kiss1ARH neurons express critical metabolic hormone receptors, and these neurons are excited by insulin and leptin during the fed state. Moreover, Kiss1ARH neurons project to and excite the anorexigenic proopiomelanocortin neurons but inhibit the orexigenic neuropeptide Y/Agouti-related peptide neurons, highlighting their role in regulating feeding behavior. Kiss1ARH and Kiss1AVPV/PeN neurons also project to the preautonomic paraventricular nucleus (satiety) neurons and the dorsomedial nucleus (energy expenditure) neurons to differentially regulate their function via glutamate and GABA release, respectively. Therefore, this review will address not only how Kiss1 neurons govern GnRH release, but how they control other homeostatic functions through their peptidergic, glutamatergic and GABAergic synaptic connections, providing further evidence that Kiss1 neurons are the key neurons coordinating energy states with reproduction.

Repeated Ethanol Exposure Alters DNA Methylation Status and Dynorphin/Kappa-Opioid Receptor Expression in Nucleus Accumbens of Alcohol-Preferring AA Rats

Growing evidence suggests that epigenetic mechanisms, such as DNA methylation and demethylation, and histone modifications, are involved in the development of alcohol and drug addiction. However, studies of alcohol use disorder (AUD) that are focused on epigenetic DNA modifications and gene expression changes remain conflicting. Our aim was to study the effect of repeated ethanol consumption on epigenetic regulatory enzymes such as DNA methyltransferase and demethylase enzymes and whether those changes affected dynorphin/kappa-opioid receptor system in the Nucleus Accumbens (NAc). Two groups of male alcohol-preferring Alko Alcohol (AA) rats, rats which are selectively bred for high voluntary alcohol consumption and one group of male Wistar rats were used. The first group of AA rats had access to alcohol (10% ethanol solution) for 90 min on Mondays, Wednesdays and Fridays over a period of 3 weeks to establish a stable baseline of ethanol intake (AA-ethanol). The second group of AA rats (AA-water) and the Wistar rats (Wistar-water) were provided with water. Using qPCR, we found that voluntary alcohol drinking increased Dnmt1, -3a, and -3b mRNA levels and did not affect Tet family transcripts in the AA-ethanol group when compared with AA- and Wistar-water rats. DNMT and TET enzymatic activity measurements showed similar results to qPCR, where DNMT activity was increased in AA-ethanol group compared with AA-water and Wistar-water groups, with no statistically significant difference between groups in TET enzyme activity. In line with previous data, we found an increased percentage of global DNA methylation and hydroxymethylation in the AA-ethanol group compared with control rats. Finally, we investigated changes of selected candidate genes from dynorphin/kappa-opioid receptor system (Pdyn, Kor) and Dnmt3a genes that might be important in AUD-related behaviour. Our gene expression and promoter methylation analysis revealed a significant increase in the mRNA levels of Pdyn, Kor, and Dnmt3a in the AA-ethanol group, however, these changes can only be partially associate with the aberrant DNA methylation in promoter areas of the selected candidate genes. Thus, our findings suggest that the aberrant DNA methylation is rather one of the several mechanisms involved in gene expression regulation in AA rat model.

Functional Characterization of Spinocerebellar Ataxia Associated Dynorphin A Mutant Peptides

Mutations in the prodynorphin gene (PDYN) are associated with the development of spinocerebellar ataxia type 23 (SCA23). Pathogenic missense mutations are localized predominantly in the PDYN region coding for the dynorphin A (DynA) neuropeptide and lead to persistently elevated mutant peptide levels with neurotoxic properties. The main DynA target in the central nervous system is the kappa opioid receptor (KOR), a member of the G-protein coupled receptor family, which can elicit signaling cascades mediated by G-protein dissociation as well as β-arrestin recruitment. To date, a thorough analysis of the functional profile for the pathogenic SCA23 DynA mutants at KOR is still missing. To elucidate the role of DynA mutants, we used a combination of assays to investigate the differential activation of G-protein subunits and β-arrestin. In addition, we applied molecular modelling techniques to provide a rationale for the underlying mechanism. Our results demonstrate that DynA mutations, associated with a severe ataxic phenotype, decrease potency of KOR activation, both for G-protein dissociation as well as β-arrestin recruitment. Molecular modelling suggests that this loss of function is due to disruption of critical interactions between DynA and the receptor. In conclusion, this study advances our understanding of KOR signal transduction upon DynA wild type or mutant peptide binding.

Rapid-Onset Anti-Stress Effects of a Kappa-Opioid Receptor Antagonist, LY2795050, Against Immobility in an Open Space Swim Paradigm in Male and Female Mice

The kappa-opioid receptor (KOR) / dynorphin system is implicated with behavioral and neurobiological effects of stress exposure (including heavy exposure to drugs of abuse) in translational animal models. Thus some KOR-antagonists can decrease the aversive, depressant-like and anxiety-like effects caused by stress exposure. The first generation of selective KOR-antagonists have slow onsets (hours) and extremely long durations of action (days-weeks), in vivo. A new generation of KOR antagonists with rapid onset and shorter duration of action can potentially decrease the effects of stress exposure in translational models, and may be of interest for medication development. This study examined the rapid onset anti-stress effects of one of the shorter acting novel KOR-antagonists (LY2795050, (3-chloro-4-(4-(((2S)-2-pyridin-3-ylpyrrolidin-1-yl)methyl) phenoxy)benzamide)) in a single-session open space swim (OSS) stress paradigm (15 min duration), in adult male and female C57BL/6 J mice. LY2795050 (0.32 mg/kg, i.p.) had rapid onset (within 15 min) and short duration (<3 h) of KOR-antagonist effects, based on its blockade of the locomotor depressant effects of the KOR-agonist U50,488 (10 mg/kg). LY2795050 (0.32 mg/kg), when administered only 1 min prior to the OSS stress paradigm, decreased immobility in males, but not females. With a slightly longer pretreatment time (15 min), this dose of LY2795050 decreased immobility in both males and females. A 10-fold smaller dose of LY2795050 (0.032 mg/kg) was inactive in the OSS, showing dose-dependence of this anti-stress effect. Overall, these studies show that a novel KOR-antagonist can produce very rapid onset anti-immobility effects in this model of acute stress exposure.

Experience-dependent myelination following stress is mediated by the neuropeptide dynorphin

Emerging evidence implicates experience-dependent myelination in learning and memory. However, the specific signals underlying this process remain unresolved. We demonstrate that the neuropeptide dynorphin, which is released from neurons upon high levels of activity, promotes experience-dependent myelination. Following forced swim stress, an experience that induces striatal dynorphin release, we observe increased striatal oligodendrocyte precursor cell (OPC) differentiation and myelination, which is abolished by deleting dynorphin or blocking its endogenous receptor, kappa opioid receptor (KOR). We find that dynorphin also promotes developmental OPC differentiation and myelination and demonstrate that this effect requires KOR expression specifically in OPCs. We characterize dynorphin-expressing neurons and use genetic sparse labeling to trace their axonal projections. Surprisingly, we find that they are unmyelinated normally and following forced swim stress. We propose a new model whereby experience-dependent and developmental myelination is mediated by unmyelinated, neuropeptide-expressing neurons that promote OPC differentiation for the myelination of neighboring axons.

Evidence that pubertal status impacts KNDy neurons in the gilt

Puberty onset is a complex physiological process which enables the capacity for reproduction through increased gonadotropin-releasing hormone (GnRH), and subsequently luteinizing hormone (LH), secretion. While cells that coexpress kisspeptin, neurokinin B (NKB), and dynorphin in the hypothalamic arcuate nucleus (ARC) are believed to govern the timing of puberty, the degree to which KNDy neurons exist and are regulated by pubertal status remains to be determined in the gilt. Hypothalamic tissue from prepubertal and postpubertal, early follicular phase gilts was used to determine the expression of kisspeptin, NKB, and dynorphin within the ARC. Fluorescent in situ hybridization revealed that the majority (> 74%) of ARC neurons that express mRNA for kisspeptin coexpressed mRNA for NKB and dynorphin. There were fewer ARC cells that expressed mRNA for dynorphin in postpubertal gilts compared to prepubertal gilts (P < 0.05), but the number of ARC cells expressing mRNA for kisspeptin or NKB was not different between groups. Within KNDy neurons, mRNA abundance for kisspeptin, NKB, and dynorphin of postpubertal gilts was the same as, less than, and greater than, respectively, prepubertal gilts. Immunostaining for kisspeptin did not differ between prepubertal and postpubertal gilts, but there were fewer NKB immunoreactive fibers in postpubertal gilts compared to prepubertal gilts (P < 0.05). Together, these data reveal novel information about KNDy neurons in gilts and supports the idea that NKB and dynorphin play a role in puberty onset in the female pig.

A midbrain dynorphin circuit promotes threat generalization

Discrimination between predictive and non-predictive threat stimuli decreases as threat intensity increases. The central mechanisms that mediate the transition from discriminatory to generalized threat responding remain poorly resolved. Here, we identify the stress- and dysphoria-associated kappa opioid receptor (KOR) and its ligand dynorphin (Dyn), acting in the ventral tegmental area (VTA), as a key substrate for regulating threat generalization. We identify several dynorphinergic inputs to the VTA and demonstrate that projections from the bed nucleus of the stria terminalis (BNST) and dorsal raphe nucleus (DRN) both contribute to anxiety-like behavior but differentially affect threat generalization. These data demonstrate that conditioned threat discrimination has an inverted "U" relationship with threat intensity and establish a role for KOR/Dyn signaling in the midbrain for promoting threat generalization.

Kisspeptin, Neurokinin B, and Dynorphin Expression during Pubertal Development in Female Sheep

The neural mechanisms underlying increases in gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion that drive puberty onset are unknown. Neurons coexpressing kisspeptin, neurokinin B (NKB), and dynorphin, i.e., KNDy neurons, are important as kisspeptin and NKB are stimulatory, and dynorphin inhibitory, to GnRH secretion. Given this, we hypothesized that kisspeptin and NKB expression would increase, but that dynorphin expression would decrease, with puberty. We collected blood and hypothalamic tissue from ovariectomized lambs implanted with estradiol at five, six, seven, eight (puberty), and ten months of age. Mean LH values and LH pulse frequency were the lowest at five to seven months, intermediate at eight months, and highest at ten months. Kisspeptin and NKB immunopositive cell numbers did not change with age. Numbers of cells expressing mRNA for kisspeptin, NKB, or dynorphin were similar at five, eight, and ten months of age. Age did not affect mRNA expression per cell for kisspeptin or NKB, but dynorphin mRNA expression per cell was elevated at ten months versus five months. Thus, neither KNDy protein nor mRNA expression changed in a predictable manner during pubertal development. These data raise the possibility that KNDy neurons, while critical, may await other inputs for the initiation of puberty.

Estrogen Regulation of the Molecular Phenotype and Active Translatome of AVPV Kisspeptin Neurons

In females, ovarian estradiol (E2) exerts both negative and positive feedback regulation on the neural circuits governing reproductive hormone secretion, but the cellular and molecular mechanisms underlying this remain poorly understood. In rodents, estrogen receptor α-expressing kisspeptin neurons in the hypothalamic anteroventral periventricular region (AVPV) are prime candidates to mediate E2 positive feedback induction of preovulatory gonadotropin-releasing hormone and luteinizing hormone (LH) surges. E2 stimulates AVPV Kiss1 expression, but the full extent of estrogen effects in these neurons is unknown; whether E2 stimulates or inhibits other genes in AVPV Kiss1 cells has not been determined. Indeed, understanding of the function(s) of AVPV kisspeptin cells is limited, in part, by minimal knowledge of their overall molecular phenotype, as only a few genes are currently known to be co-expressed in AVPV Kiss1 cells. To provide a more detailed profiling of co-expressed genes in AVPV Kiss1 cells, including receptors and other signaling factors, and test how these genes respond to E2, we selectively isolated actively translated mRNAs from AVPV Kiss1 cells of female mice and performed RNA sequencing (RNA-seq). This identified >13 000 mRNAs co-expressed in AVPV Kiss1 cells, including multiple receptor and ligand transcripts positively or negatively regulated by E2. We also performed RNAscope to validate co-expression of several transcripts identified by RNA-seq, including Pdyn (prodynorphin), Penk (proenkephalin), Vgf (VGF), and Cartpt (CART), in female AVPV Kiss1 cells. Given the important role of AVPV kisspeptin cells in positive feedback, E2 effects on identified genes may relate to the LH surge mechanism and/or other physiological processes involving these cells.

Central injection of neuropeptide Y modulates sexual behavior in male rats: interaction with GnRH and kisspeptin/neurokinin B/dynorphin

AIMS

A number of studies have shown that neuropeptide Y (NPY) is considered to be one of the key regulators of hypothalamic-pituitary-gonadal (HPG) axis in the mammals. In addition, kisspeptin (encode by Kiss1 gene), neurokinin B (encode by Tac3 gene) and dynorphin (encode by Pdyn gene) (commonly known as KNDy secreting neurons) are a powerful upstream regulators of GnRH neuron in hypothalamus.

MATERIALS AND METHODS

The present study aims to investigate the effects of the intracerebroventricular (icv) injection of NPY and BIBP3226 (NPY receptor antagonist (NPYRA)) on the male sexual behavioral. Additionally, in order to see whether NPY signals can be relayed through the pathway of kisspeptin/neurokinin B/dynorphin, the gene expression of these peptides along with Gnrh1 gene in the hypothalamus were measured.

RESULTS

The icv injection of NPY decreased the latencies and increase the frequencies of sexual parameters of the male rats in a significant way. In this line, NPYRA antagonized the stimulative effects of NPY. Moreover, data from real-time quantitative PCR indicated that injection of NPY significantly increased the gene expression of Gnrh1, Kiss1 and Tac3 and decrease the Pdyn while treatment with NPYRA controlled the modulative effects of NPY on these gene expression.

CONCLUSIONS

In conclusion based on the results of this study, NPY can exert its impacts on the sexual behavior of male rats via modulation of the KNDy secreting neurons as an interneural pathway to GnRH neurons.

Effects of Aging on Levo-Dihydroxyphenylalanine- Induced Dyskinesia in a Rat Model of Parkinson's Disease

Background

It remains unclear why patients with young-onset Parkinson's disease more often develop levo-dihydroxyphenylalanine (L-dopa)-induced dyskinesia (LID) and have a more severe form than patients with old-onset Parkinson's disease. Previous studies using animal models have failed to show young-onset Parkinson's disease enhances LID.

Objectives

To evaluate the association of age at dopaminergic denervation (onset age) and initiation of L-dopa treatment (treatment age) with LID development in model rats.

Methods

We established rat models of young- and old-lesioned Parkinson's disease (6-hydroxydopamine lesions at 10 and 88 weeks of age, respectively). Dopaminergic denervation was confirmed by the rotational behavior test using apomorphine. Rats in the young-lesioned group were allocated to either L-dopa treatment at a young or old age, or saline treatment. Rats in the old-lesioned group were allocated to either L-dopa treatment or saline group. We evaluated L-dopa-induced abnormal involuntary movements during the 14-day treatment period. We also examined preprodynorphin mRNA expression in the striatum (a neurochemical hallmark of LID) and the volume of the medial globus pallidus (a pathological hallmark of LID).

Results

LID-like behavior was enhanced in L-dopa-treated young-lesioned rats compared with L-dopa-treated old-lesioned rats. Preprodynorphin mRNA expression was higher in L-dopa-treated young-lesioned rats than in in L-dopa-treated old-lesioned rats. The volume of the medial globus pallidus was greater in L-dopa-treated young-lesioned rats than in L-dopa-treated old-lesioned rats. Treatment age did not affect LID-like behavior or the degree of medial globus pallidus hypertrophy in the young-lesioned model.

Conclusion

Both dopaminergic denervation and L-dopa initiation at a young age contributed to the development of LID; however, the former may be a more important factor.

Endogenous Opioid Levels Do Not Correlate With Itch Intensity and Therapeutic Interventions in Hepatic Pruritus

Background: Chronic pruritus affects up to 70% of patients with immune-mediated hepatobiliary disorders. Antagonists of the μ-opioid receptor (MOR) and agonists of the κ-opioid receptor (KOR) are used to treat hepatic itch, albeit with limited success. An imbalance between ligands of MOR and KOR receptors has recently been suggested as a potential mechanism of hepatic pruritus. In this study, we therefore investigated systemic levels of important endogenous opioids such as β-endorphin, dynorphin A, Leu- and Met-enkephalin in plasma of a large cohort of well-characterized patients with immune-mediated cholestatic disorders, including patients with liver cirrhosis, and during effective anti-pruritic therapy.

Methods: Plasma samples and clinical data were prospectively collected from well-characterized patients with primary/secondary sclerosing cholangitis (PSC/SSC), primary biliary cholangitis (PBC) and overlap syndromes suffering from pruritus (n = 29) and age-, gender- and disease-matched controls without pruritus (n = 27) as well as healthy controls (n = 20). General laboratory testing for hepatobiliary and renal function was performed. Levels of β-endorphin, dynorphin A, Leu- and Met-enkephalin were quantified in plasma by ELISA. Intensity of pruritus over the last week was evaluated using a visual analog scale (VAS, 0–10).

Results: PBC and PSC patients with or without pruritus did neither differ in disease entity, disease stage, nor in the presence of cirrhosis. While both dynorphin A and β-endorphin concentrations were lower in pruritic patients compared to those without pruritus and healthy controls, the MOR/KOR ligand ratio was unaltered. No significant differences were observed for Leu- and Met-enkephalin concentrations. Opioid levels correlated with neither itch intensity nor stage of disease. Cirrhotic patients displayed higher concentrations of MOR agonist Leu-enkephalin and KOR agonist dynorphin A. Endogenous opioid levels remained largely unchanged after successful treatment with the potent anti-pruritic drugs rifampicin and bezafibrate.

Conclusions: Endogenous opioid levels and the MOR/KOR ligand ratio neither correlate with itch intensity nor differentiate pruritic from non-pruritic patients with immune-mediated liver diseases. Thus, endogenous opioids may modulate signaling pathways involved in hepatic pruritus, but are unlikely to represent the major pruritogens in liver disease.

Cocaine Reduces the Neuronal Population While Upregulating Dopamine D2-Receptor-Expressing Neurons in Brain Reward Regions: Sex-Effects

Addiction to cocaine is associated with dysfunction of the dopamine mesocortical system including impaired dopamine-2 receptor (D2r) signaling. However, the effects of chronic cocaine on neuronal adaptations in this system have not been systematically examined and data available is mostly from males. Here, we investigated changes in the total neuronal density and relative concentration of D2r-expressing neurons in the medial prefrontal cortex (mPFC), dorsal striatum (Dstr), nucleus accumbens (NAc), and ventral tegmental area (VTA) in both male and female mice passively exposed to cocaine for two weeks. In parallel experiments, we measured mRNA levels for Drd2 and for opioid peptides (mPenk and mPdyn). Through a combination of large field of view fluorescent imaging with BAC transgenic D2r-eGFP mice and immunostaining, we observed that cocaine exposed mice had a higher density of D2r-positive cells that was most prominent in mPFC and VTA and larger for females than for males. This occurred amidst an overall significant decrease in neuronal density (measured with NeuN) in both sexes. However, increases in Drd2 mRNA levels with cocaine were only observed in mPFC and Dstr in females, which might reflect the limited sensitivity of the method. Our findings, which contrast with previous findings of cocaine-induced downregulation of D2r binding availability, could reflect a phenotypic shift in neurons that did not previously express Drd2 and merits further investigation. Additionally, the neuronal loss particularly in mPFC with chronic cocaine might contribute to the cognitive impairments observed with cocaine use disorder.

Efferent projections of CGRP/Calca-expressing parabrachial neurons in mice

The parabrachial nucleus (PB) is composed of glutamatergic neurons at the midbrain-hindbrain junction. These neurons form many subpopulations, one of which expresses Calca, which encodes the neuropeptide calcitonin gene-related peptide (CGRP). This Calca-expressing subpopulation has been implicated in a variety of homeostatic functions, but the overall distribution of Calca-expressing neurons in this region remains unclear. Also, while previous studies in rats and mice have identified output projections from CGRP-immunoreactive or Calca-expressing neurons, we lack a comprehensive understanding of their efferent projections. We began by identifying neurons with Calca mRNA and CGRP immunoreactivity in and around the PB, including populations in the locus coeruleus and motor trigeminal nucleus. Calca-expressing neurons in the PB prominently express the mu opioid receptor (Oprm1) and are distinct from neighboring neurons that express Foxp2 and Pdyn. Next, we used Cre-dependent anterograde tracing with synaptophysin-mCherry to map the efferent projections of these neurons. Calca-expressing PB neurons heavily target subregions of the amygdala, bed nucleus of the stria terminalis, basal forebrain, thalamic intralaminar and ventral posterior parvicellular nuclei, and hindbrain, in different patterns depending on the injection site location within the PB region. Retrograde axonal tracing revealed that the previously unreported hindbrain projections arise from a rostral-ventral subset of CGRP/Calca neurons. Finally, we show that these efferent projections of Calca-expressing neurons are distinct from those of neighboring PB neurons that express Pdyn. This information provides a detailed neuroanatomical framework for interpreting experimental work involving CGRP/Calca-expressing neurons and opioid action in the PB region.

Dysregulation of Nociceptin/Orphanin FQ and Dynorphin Systems in the Extended Amygdala of Alcohol Preferring Marchigian Sardinian (msP) Rats

Previous studies have shown that genetically selected Marchigian Sardinian alcohol-preferring (msP) rats consume excessive amounts of ethanol to self-medicate from negative moods and to relieve innate hypersensitivity to stress. This phenotype resembling a subset of alcohol use disorder (AUD) patients, appears to be linked to a dysregulation of the equilibrium between stress and antistress mechanisms in the extended amygdala. Here, comparing water and alcohol exposed msP and Wistar rats we evaluate the transcript expression of the anti-stress opioid-like peptide nociceptin/orphanin FQ (N/OFQ) and its receptor NOP as well as of dynorphin (DYN) and its cognate κ-opioid receptor (KOP). In addition, we measured the transcript levels of corticotropin-releasing factor (CRF), CRF receptor 1 (CRF1R), brain-derived neurotrophic factor (BDNF) and of the tropomyosin receptor kinase B receptor (Trk-B). Results showed an innately up-regulation of the CRFergic system, mediating negative mood and stress responses, as well as an inherent up-regulation of the anti-stress N/OFQ system, both in the amygdala (AMY) and bed nucleus of the stria terminalis (BNST) of msP rats. The up-regulation of this latter system may reflect an attempt to buffer the negative condition elicited by the hyperactivity of pro-stress mechanisms since results showed that voluntary alcohol consumption dampened N/OFQ. Alcohol exposure also reduced the expression of dynorphin and CRF transmissions in the AMY of msP rats. In the BNST, alcohol intake led to a more complex reorganization of these systems increasing receptor transcripts in msP rats, along with an increase of CRF and a decrease of N/OFQ transcripts, respectively. Moreover, mimicking the effects of alcohol in the AMY we observed that the activation of NOP receptor by intracerebroventricular administration of N/OFQ in msP rats caused an increase of BDNF and a decrease of CRF transcripts. Our study indicates that both stress and anti-stress mechanisms are dysregulated in the extended AMY of msP rats. The voluntary alcohol drinking, as well as NOP agonism, have a significant impact on neuropeptidergic systems arrangement, bringing the systems back to normalization.

κ Opioid Receptor-Dynorphin Signaling in the Central Amygdala Regulates Conditioned Threat Discrimination and Anxiety

Neuropeptides within the central nucleus of the amygdala (CeA) potently modulate neuronal excitability and have been shown to regulate conditioned threat discrimination and anxiety. Here, we investigated the role of κ opioid receptor (KOR) and its endogenous ligand dynorphin in the CeA for regulation of conditioned threat discrimination and anxiety-like behavior in mice. We demonstrate that reduced KOR expression through genetic inactivation of the KOR encoding gene, Oprk1, in the CeA results in increased anxiety-like behavior and impaired conditioned threat discrimination. In contrast, reduction of dynorphin through genetic inactivation of the dynorphin encoding gene, Pdyn, in the CeA has no effect on anxiety or conditioned threat discrimination. However, inactivation of Pdyn from multiple sources, intrinsic and extrinsic to the CeA phenocopies Oprk1 inactivation. These findings suggest that dynorphin inputs to the CeA signal through KOR to promote threat discrimination and dampen anxiety.

Novel inhibitory brainstem neurons with selective projections to spinal lamina I reduce both pain and itch

Sensory information is transmitted from peripheral nerves, through the spinal cord, and up to the brain (“bottom up” pathway). Some of this information may be modulated by “top‐down” projections from the brain to the spinal cord. Discovering endogenous mechanisms for reducing pain and itch holds enormous potential for developing new treatments. However, neurons mediating the top‐down inhibition of pain are not well understood, nor has any such pathway been identified for itch sensation. Here, we identify a novel population of GABAergic neurons in the ventral brainstem, distinguished by prodynorphin expression, which we named LJA5. LJA5 neurons provide the only known inhibitory projection specifically to lamina I of the spinal cord, which contains sensory neurons that transmit pain and itch information up to the brain. Chemogenetically activating LJA5 neurons in male mice reduces capsaicin‐induced pain and histamine‐induced itch. Identifying this new pathway opens new treatment opportunities for chronic, refractory pain, and pruritis.

Spinal and Peripheral Mechanisms Individually Lead to the Development of Remifentanil-induced Hyperalgesia

The present study was performed to determine neuronal loci and individual molecular mechanisms responsible for remifentanil-induced hyperalgesia. The effect of methylnaltrexone (MNX) on remifentanil-induced behavioral hyperalgesia was assessed to distinguish contributions of the peripheral and/or central nervous system to remifentanil-induced hyperalgesia. Phosphorylation of p38 mitogen-activated protein kinase (p38MAPK) in the dorsal root ganglion (DRG) neurons after remifentanil infusion, and the effect of a p38MAPK inhibitor on remifentanil-induced hyperalgesia were analyzed to investigate involvement of p38MAPK in the peripheral mechanisms of remifentanil-induced hyperalgesia. Spinal levels of prodynorphin mRNA after remifentanil infusion, and the effect of the BK2 bradykinin receptor antagonist on remifentanil-induced hyperalgesia were investigated to assess potential spinal mechanisms. The effects of MNX and BK2 antagonists on remifentanil-induced exacerbation of post-incisional hyperalgesia were also investigated using behavioral analysis. Remifentanil infusion induced hyperalgesia in the early (4 h to 2 days) and late (8-14 days) post-infusion periods. MNX inhibited hyperalgesia only during the early post-infusion period. p38MAPK phosphorylation was observed in the DRG neuron, and the p38MAPK inhibitor inhibited hyperalgesia during the early post-infusion period. Prodynorphin expression increased in the spinal cord, and a BK2 antagonist inhibited hyperalgesia during the late post-infusion period. Remifentanil-induced exacerbation of incisional hyperalgesia was inhibited by MNX and the BK2 antagonist. The present study demonstrated that remifentanil activates peripheral and spinal neurons to promote chronologically distinctive hyperalgesia. p38MAPK phosphorylation in the DRG neuron leads to peripherally-driven hyperalgesia during the early post-infusion period, while spinal dynorphin-bradykinin signaling promotes hyperalgesia during the late post-infusion period.

Efferent projections of Vglut2, Foxp2, and Pdyn parabrachial neurons in mice

The parabrachial nucleus (PB) is a complex structure located at the junction of the midbrain and hindbrain. Its neurons have diverse genetic profiles and influence a variety of homeostatic functions. While its cytoarchitecture and overall efferent projections are known, we lack comprehensive information on the projection patterns of specific neuronal subtypes in the PB. In this study, we compared the projection patterns of glutamatergic neurons here with a subpopulation expressing the transcription factor Foxp2 and a further subpopulation expressing the neuropeptide Pdyn. To do this, we injected an AAV into the PB region to deliver a Cre-dependent anterograde tracer (synaptophysin-mCherry) in three different strains of Cre-driver mice. We then analyzed 147 neuroanatomical regions for labeled boutons in every brain (n = 11). Overall, glutamatergic neurons in the PB region project to a wide variety of sites in the cerebral cortex, basal forebrain, bed nucleus of the stria terminalis, amygdala, diencephalon, and brainstem. Foxp2 and Pdyn subpopulations project heavily to the hypothalamus, but not to the cortex, basal forebrain, or amygdala. Among the few differences between Foxp2 and Pdyn cases was a notable lack of Pdyn projections to the ventromedial hypothalamic nucleus. Our results indicate that genetic identity determines connectivity (and therefore, function), providing a framework for mapping all PB output projections based on the genetic identity of its neurons. Using genetic markers to systematically classify PB neurons and their efferent projections will enhance the translation of research findings from experimental animals to humans.

Dissecting the Roles of GABA and Neuropeptides from Rat Central Amygdala CRF Neurons in Anxiety and Fear Learning

Central amygdala (CeA) neurons that produce corticotropin-releasing factor (CRF) regulate anxiety and fear learning. These CeA^CRF neurons release GABA and several neuropeptides predicted to play important yet opposing roles in these behaviors. We dissected the relative roles of GABA, CRF, dynorphin, and neurotensin in CeA^CRF neurons in anxiety and fear learning by disrupting their expression using RNAi in male rats. GABA, but not CRF, dynorphin, or neurotensin, regulates baseline anxiety-like behavior. In contrast, chemogenetic stimulation of CeA^CRF neurons evokes anxiety-like behavior dependent on CRF and dynorphin, but not neurotensin. Finally, knockdown of CRF and dynorphin impairs fear learning, whereas knockdown of neurotensin enhances it. Our results demonstrate distinct behavioral roles for GABA, CRF, dynorphin, and neurotensin in a subpopulation of CeA neurons. These results highlight the importance of considering the repertoire of signaling molecules released from a given neuronal population when studying the circuit basis of behavior.

Pomrenze et al. demonstrate that CRF neurons of the central amygdala differentially regulate fear and anxiety through the release of GABA and different neuropeptides.

Intravenous Administration of Pyroglutamyl Apelin-13 Alleviates Murine Inflammatory Pain via the Kappa Opioid Receptor

Apelin is an endogenous neuropeptide, which has wide distribution in central nervous system and peripheral tissues. Pyroglutamyl apelin-13 [(pyr)apelin-13] is the major apelin isoform in human plasma. However, the role of peripheral (pyr)apelin-13 in pain regulation is unknown. The aim of this study was to investigate the effect of the peripheral injection of (pyr)apelin-13 on inflammatory pain using the formalin test as well as to evaluate the mechanistic basis for the effect. Results showed intravenous (i.v.) injection of (pyr)apelin-13 (10, 20 mg/kg) to significantly decrease licking/biting time during the second phase of the mouse formalin test. In contrast, i.v. injection of apelin-13 had no influence on such effect. Intramuscular injection of (pyr)apelin-13 reduced licking/biting time during the second phase only at a dose of 20 mg/kg. The antinociception of i.v. (pyr)apelin-13 was antagonized by the apelin receptor (APJ, angiotensin II receptor-like 1) antagonist, apelin-13(F13A). (pyr)apelin-13 (i.v. 20 mg/kg) markedly upregulated Aplnr and Adcy2 gene expression in the prefrontal cortex, whereas Fos gene expression was downregulated. The antinociception of i.v. (pyr)apelin-13 was blocked by the opioid receptor antagonist naloxone and the specific kappa opioid receptor (KOR) antagonist nor-binaltorphimine (nor-BNI). (pyr)Apelin-13 upregulated the dynorphin and KOR gene expression and protein levels in the mouse prefrontal cortex, not in striatum. (pyr)Apelin-13 did not influence the motor behavior. Our results demonstrate that i.v. injection of (pyr)apelin-13 induces antinociception via the KOR in the inflammatory pain mouse model.