Stress-induced expression of co-localized neuropeptides in hypothalamic and amygdaloid neurons

Neurobiological Mechanisms Underlying Psychological Dysfunction After Brain Injuries

Despite the presentation of similar psychological symptoms, psychological dysfunction secondary to brain injury exhibits markedly lower treatment efficacy compared to injury-independent psychological dysfunction. This gap remains evident, despite extensive research efforts. This review integrates clinical and preclinical evidence to provide a comprehensive overview of the neurobiological mechanisms underlying neuropsychological disorders, focusing on the role of key brain regions in emotional regulation across various forms of brain injuries. It examines therapeutic interventions and mechanistic targets, with the primary goal of identifying pathways for targeted treatments. The review highlights promising therapeutic avenues for addressing injury-associated psychological dysfunction, emphasizing Nrf2, neuropeptides, and nonpharmacological therapies as multi-mechanistic interventions capable of modulating upstream mediators to address the complex interplay of factors underlying psychological dysfunction in brain injury. Additionally, it identifies sexually dimorphic factors as potential areas for further exploration and advocates for detailed investigations into sex-specific patterns to uncover additional contributors to these disorders. Furthermore, it underscores significant gaps, particularly the inadequate consideration of interactions among causal factors, environmental influences, and individual susceptibilities. By addressing these gaps, this review provides new insights and calls for a paradigm shift toward a more context-specific and integrative approach to developing targeted therapies for psychological dysfunction following brain injuries.

Interaction between corticotropin-releasing factor, orexin, and dynorphin in the infralimbic cortex may mediate exacerbated alcohol-seeking behavior

A major challenge for the treatment of alcohol use disorder (AUD) is relapse to alcohol use, even after protracted periods of self-imposed abstinence. Stress significantly contributes to the chronic relapsing nature of AUD, given its long-lasting ability to elicit intense craving and precipitate relapse. As individuals transition to alcohol dependence, compensatory allostatic mechanisms result in insults to hypothalamic-pituitary-adrenal axis function, mediated by corticotropin-releasing factor (CRF), which is subsequently hypothesized to alter brain reward pathways, influence affect, elicit craving, and ultimately perpetuate problematic drinking and relapse vulnerability. Orexin (OX; also called hypocretin) plays a well-established role in regulating diverse physiological processes, including stress, and has been shown to interact with CRF. Interestingly, most hypothalamic cells that express Ox mRNA also express Pdyn mRNA. Both dynorphin and OX are located in the same synaptic vesicles, and they are co-released. The infralimbic cortex (IL) of the medial prefrontal cortex (mPFC) has emerged as being directly involved in the compulsive nature of alcohol consumption during dependence. The IL is a CRF-rich region that receives OX projections from the hypothalamus and where OX receptor mRNA has been detected. Although not thoroughly understood, anatomical and behavioral pharmacology data suggest that CRF, OX, and dynorphin may interact, particularly in the IL, and that functional interactions between these three systems in the IL may be critical for the etiology and pervasiveness of compulsive alcohol seeking in dependent subjects that may render them vulnerable to relapse. The present review presents evidence of the role of the IL in AUD and discusses functional interactions between CRF, OX, and dynorphin in this structure and how they are related to exacerbated alcohol drinking and seeking.

Translational aspects of deep brain stimulation for chronic pain

The use of deep brain stimulation (DBS) for the treatment of chronic pain was one of the first applications of this technique in functional neurosurgery. Established brain targets in the clinic include the periaqueductal (PAG)/periventricular gray matter (PVG) and sensory thalamic nuclei. More recently, the anterior cingulum (ACC) and the ventral striatum/anterior limb of the internal capsule (VS/ALIC) have been investigated for the treatment of emotional components of pain. In the clinic, most studies showed a response in 20%-70% of patients. In various applications of DBS, animal models either provided the rationale for the development of clinical trials or were utilized as a tool to study potential mechanisms of stimulation responses. Despite the complex nature of pain and the fact that animal models cannot reliably reflect the subjective nature of this condition, multiple preparations have emerged over the years. Overall, DBS was shown to produce an antinociceptive effect in rodents when delivered to targets known to induce analgesic effects in humans, suggesting a good predictive validity. Compared to the relatively high number of clinical trials in the field, however, the number of animal studies has been somewhat limited. Additional investigation using modern neuroscience techniques could unravel the mechanisms and neurocircuitry involved in the analgesic effects of DBS and help to optimize this therapy.

Opioidergic pathways and kisspeptin in the regulation of female reproduction in mammals

Endogenous opioid peptides have attracted attention as critical neuropeptides in the central mechanism regulating female reproduction ever since the discovery that arcuate dynorphin neurons that coexpress kisspeptin and neurokinin B (NKB), which are also known as kisspeptin/neurokinin B/dynorphin (KNDy) neurons, play a role as a master regulator of pulsatile gonadotropin-releasing hormone (GnRH) release in mammals. In this study, we first focus on the role of dynorphin released by KNDy neurons in the GnRH pulse generation. Second, we provide a historical overview of studies on endogenous opioid peptides. Third, we discuss how endogenous opioid peptides modulate tonic GnRH/gonadotropin release in female mammals as a mediator of inhibitory internal and external cues, such as ovarian steroids, nutritional status, or stress, on reproduction. Then, we discuss the role of endogenous opioid peptides in GnRH surge generation in female mammals.

Central and peripheral neuropeptide RFRP-3: A bridge linking reproduction, nutrition, and stress response

This article is an amalgamation of the current status of RFRP-3 (GnIH) in reproduction and its association with the nutrition and stress-mediated changes in the reproductive activities. GnIH has been demonstrated in the hypothalamus of all the vertebrates studied so far and is a well-known inhibitor of GnRH mediated reproduction. The RFRP-3 neurons interact with the other hypothalamic neurons and the hormonal signals from peripheral organs for coordinating the nutritional, stress, and environmental associated changes to regulate reproduction. RFRP-3 has also been shown to regulate puberty, reproductive cyclicity and senescence depending upon the nutritional status. A favourable nutritional status and the environmental cues which are permissive for the successful breeding and pregnancy outcome keep RFRP-3 level low, whereas unfavourable nutritional status and stressful conditions increase the expression of RFRP-3 which impairs the reproduction. Still our knowledge about RFRP-3 is incomplete regarding its therapeutic application for nutritional or stress-related reproductive disorders.

Rescue of Vasopressin Synthesis in Magnocellular Neurons of the Supraoptic Nucleus Normalises Acute Stress-Induced Adrenocorticotropin Secretion and Unmasks an Effect on Social Behaviour in Male Vasopressin-Deficient Brattleboro Rats

The relevance of vasopressin (AVP) of magnocellular origin to the regulation of the endocrine stress axis and related behaviour is still under discussion. We aimed to obtain deeper insight into this process. To rescue magnocellular AVP synthesis, a vasopressin-containing adeno-associated virus vector (AVP-AAV) was injected into the supraoptic nucleus (SON) of AVP-deficient Brattleboro rats (di/di). We compared +/+, di/di, and AVP-AAV treated di/di male rats. The AVP-AAV treatment rescued the AVP synthesis in the SON both morphologically and functionally. It also rescued the peak of adrenocorticotropin release triggered by immune and metabolic challenges without affecting corticosterone levels. The elevated corticotropin-releasing hormone receptor 1 mRNA levels in the anterior pituitary of di/di-rats were diminished by the AVP-AAV-treatment. The altered c-Fos synthesis in di/di-rats in response to a metabolic stressor was normalised by AVP-AAV in both the SON and medial amygdala (MeA), but not in the central and basolateral amygdala or lateral hypothalamus. In vitro electrophysiological recordings showed an AVP-induced inhibition of MeA neurons that was prevented by picrotoxin administration, supporting the possible regulatory role of AVP originating in the SON. A memory deficit in the novel object recognition test seen in di/di animals remained unaffected by AVP-AAV treatment. Interestingly, although di/di rats show intact social investigation and aggression, the SON AVP-AAV treatment resulted in an alteration of these social behaviours. AVP released from the magnocellular SON neurons may stimulate adrenocorticotropin secretion in response to defined stressors and might participate in the fine-tuning of social behaviour with a possible contribution from the MeA.

Spexin and Galanin in Metabolic Functions and Social Behaviors With a Focus on Non-Mammalian Vertebrates

Spexin (SPX) and galanin (GAL) are two neuropeptides that are phylogenetically related and have descended from a common ancestral gene. Considerable attention has been given to these two multifunctional neuropeptides because they share GAL receptors 1,2, and 3. Since GAL and SPX-synthesizing neurons have been detected in several brain areas, therefore, it can be speculated that SPX and GAL are involved in various neurophysiological functions. Several studies have shown the functions of these two neuropeptides in energy regulation, reproduction, and response to stress. SPX acts as a satiety factor to suppress food intake, while GAL has the opposite effect as an orexigenic factor. There is evidence that SPX acts as an inhibitor of reproductive functions by suppressing gonadotropin release, while GAL modulates the activity of gonadotropin-releasing hormone (GnRH) neurons in the brain and gonadotropic cells in the pituitary. SPX and GAL are responsive to stress. Furthermore, SPX can act as an anxiolytic factor, while GAL exerts anti-depressant and pro-depressive effects depending on the receptor it binds. This review describes evidence supporting the central roles of SPX and GAL neuropeptides in energy balance, reproduction, stress, and social behaviors, with a particular focus on non-mammalian vertebrate systems.

Electroacupuncture Alleviates Pain-Related Emotion by Upregulating the Expression of NPS and Its Receptor NPSR in the Anterior Cingulate Cortex and Hypothalamus

Objective

Electroacupuncture (EA) is reported effective in alleviating pain-related emotion; however, the underlying mechanism of its effects still needs to be elucidated. The NPS-NPSR system has been validated for the involvement in the modulation of analgesia and emotional behavior. Here, we aimed to investigate the role of the NPS-NPSR system in the anterior cingulate cortex (ACC), hypothalamus, and central amygdala (CeA) in the use of EA to relieve affective pain modeled by complete Freund's adjuvant- (CFA-) evoked conditioned place aversion (C-CPA). Materials and Methods. CFA injection combined with a CPA paradigm was introduced to establish the C-CPA model, and the elevated O-maze (EOM) was used to test the behavioral changes after model establishment. We further explored the expression of NPS and NPSR at the protein and gene levels in the brain regions of interest by immunofluorescence staining and quantitative real-time PCR.

Results

We observed that EA stimulation delivered to the bilateral Zusanli (ST36) and Kunlun (BL60) acupoints remarkably inhibited sensory pain, pain-evoked place aversion, and anxiety-like behavior. The current study showed that EA significantly enhanced the protein expression of this peptide system in the ACC and hypothalamus, while the elevated expression of NPSR protein alone was just confined to the affected side in the CeA. Moreover, EA remarkably upregulated the mRNA expression of NPS in CeA, ACC, and hypothalamus and NPSR mRNA in the hypothalamus and CeA.

Conclusions

These data suggest the effectiveness of EA in alleviating affective pain, and these benefits may at least partially be attributable to the upregulation of the NPS-NPSR system in the ACC and hypothalamus.

Neurobiology and consequences of social isolation stress in animal model-A comprehensive review

The brain is a vital organ, susceptible to alterations under genetic influences and environmental experiences. Social isolation (SI) acts as a stressor which results in alterations in reactivity to stress, social behavior, function of neurochemical and neuroendocrine system, physiological, anatomical and behavioral changes in both animal and humans. During early stages of life, acute or chronic SIS has been proposed to show signs and symptoms of psychiatric and neurological disorders such as anxiety, depression, schizophrenia, epilepsy and memory loss. Exposure to social isolation stress induces a variety of endocrinological changes including the activation of hypothalamic-pituitary-adrenal (HPA) axis, culminating in the release of glucocorticoids (GCs), release of catecholamines, activation of the sympatho-adrenomedullary system, release of Oxytocin and vasopressin. In several regions of the central nervous system (CNS), SIS alters the level of neurotransmitter such as dopamine, serotonin, gamma aminobutyric acid (GABA), glutamate, nitrergic system and adrenaline as well as leads to alteration in receptor sensitivity of N-methyl-D-aspartate (NMDA) and opioid system. A change in the function of oxidative and nitrosative stress (O&NS) mediated mitochondrial dysfunction, inflammatory factors, neurotrophins and neurotrophicfactors (NTFs), early growth response transcription factor genes (Egr) and C-Fos expression are also involved as a pathophysiological consequences of SIS which induce neurological and psychiatric disorders.

Kappa opioid receptor antagonists: A possible new class of therapeutics for migraine prevention

Background Stress is the most commonly reported migraine trigger. Dynorphin, an endogenous opioid peptide acting preferentially at kappa opioid receptors (KORs), is a key mediator of stress responses. The aim of this study was to use an injury-free rat model of functional cephalic pain with features of migraine and medication overuse headache (MOH) to test the possible preventive benefit of KOR blockade on stress-induced cephalic pain. Methods Following sumatriptan priming to model MOH, rats were hyper-responsive to environmental stress, demonstrating delayed cephalic and extracephalic allodynia and increased levels of CGRP in the jugular blood, consistent with commonly observed clinical outcomes during migraine. Nor-binaltorphimine (nor-BNI), a long-acting KOR antagonist or CYM51317, a novel short-acting KOR antagonist, were given systemically either during sumatriptan priming or immediately before environmental stress challenge. The effects of KOR blockade in the amygdala on stress-induced allodynia was determined by administration of nor-BNI into the right or left central nucleus of the amygdala (CeA). Results KOR blockade prevented both stress-induced allodynia and increased plasma CGRP. Stress increased dynorphin content and phosphorylated KOR in both the left and right CeA in sumatriptan-primed rats. However, KOR blockade only in the right CeA prevented stress-induced cephalic allodynia as well as extracephalic allodynia, measured in either the right or left hindpaws. U69,593, a KOR agonist, given into the right, but not the left, CeA, produced allodynia selectively in sumatriptan-primed rats. Both stress and U69,593-induced allodynia were prevented by right CeA U0126, a mitogen-activated protein kinase inhibitor, presumably acting downstream of KOR. Conclusions Our data reveal a novel lateralized KOR circuit that mediated stress-induced cutaneous allodynia and increased plasma CGRP in an injury-free model of functional cephalic pain with features of migraine and medication overuse headache. Selective, small molecule, orally available, and reversible KOR antagonists are currently in development and may represent a novel class of preventive therapeutics for migraine.

Molecular diversity of corticotropin-releasing hormone mRNA-containing neurons in the hypothalamus

Hormonal responses to acute stress rely on the rapid induction of corticotropin-releasing hormone (CRH) production in the mammalian hypothalamus, with subsequent instructive steps culminating in corticosterone release at the periphery. Hypothalamic CRH neurons in the paraventricular nucleus of the hypothalamus are therefore considered as 'stress neurons'. However, significant morphological and functional diversity among neurons that can transiently produce CRH in other hypothalamic nuclei has been proposed, particularly as histochemical and molecular biology evidence associates CRH to both GABA and glutamate neurotransmission. Here, we review recent advances through single-cell RNA sequencing and circuit mapping to suggest that CRH production reflects a state switch in hypothalamic neurons and thus confers functional competence rather than being an identity mark of phenotypically segregated neurons. We show that CRH mRNA transcripts can therefore be seen in GABAergic, glutamatergic and dopaminergic neuronal contingents in the hypothalamus. We then distinguish 'stress neurons' of the paraventricular nucleus that constitutively express secretagogin, a Ca²⁺ sensor critical for the stimulus-driven assembly of the molecular machinery underpinning the fast regulated exocytosis of CRH at the median eminence. Cumulatively, we infer that CRH neurons are functionally and molecularly more diverse than previously thought.

Effects of chronic restraint stress on social behaviors and the number of hypothalamic oxytocin neurons in male rats

Oxytocin (OXT) and vasopressin (AVP) are considered to be related to mammalian social behavior and the regulation of stress responses. The present study investigated the effects of chronic homotypic restraint stress (CHRS) on social behaviors and anxiety, as well as its repercussions on OXT- and AVP-positive neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) nuclei in rat. Male Sprague-Dawley rats receiving CHRS were exposed to repeated restraint stress of 30min per day for 10days. Changes in social approach behaviors were evaluated with the three-chambered social approach task. Changes in anxiety-like behaviors were evaluated in the light-dark box test. The number of neurons expressing oxytocin and/or vasopressin in PVN and SON were examined by immunohistochemistry techniques. The results demonstrated that social approach was increased and anxiety was decreased following 10-day exposure to CHRS. Furthermore, the number of OXT-immunoreactive cells in PVN was increased significantly, whereas no change in SON was seen. The number of AVP immunoreactive cells either in PVN or SON was unaffected. The results of this study suggest that certain types of stress could be effective in the treatment of social dysfunction in persons with mental disorders such as autism, social anxiety disorder. The therapeutic effects may be mediated by changes in the function of OXT neurons in PVN.

Changes in Galanin Systems in a Rat Model of Post-Traumatic Stress Disorder (PTSD)

Post-traumatic stress disorder (PTSD) is a chronic syndrome triggered by exposure to trauma and a failure to recover from a normal negative emotional reaction to traumatic stress. The neurobiology of PTSD and the participation of neuropeptides in the neural systems and circuits that control fear and anxiety are not fully understood. The long-term dysregulation of neuropeptide systems contributes to the development of anxiety disorders, including PTSD. The neuropeptide galanin (Gal) and its receptors participate in anxiety-like and depression-related behaviors via the modulation of neuroendocrine and monoaminergic systems. The objective of this research was to investigate how Gal expression changes in the brain of rats 2 weeks after exposure to footshock. Rats exposed to footshocks were subdivided into high responders (HR; immobility>60%) and low responders (LR; immobility<40%) based on immobility elicited by a novel tone one day after exposure. On day 14, rats were anesthetized, and the amygdala, hypothalamus, pituitary and adrenal glands were removed for analysis using real-time polymerase chain reaction (RT-PCR). Gal mRNA levels were increased in the amygdala and hypothalamus of HR compared with the control and LR. In contrast, Gal mRNA levels were decreased in the adrenal and pituitary glands of HR compared with the control and LR. Thus, the differential regulation (dysregulation) of the neuropeptide Gal in these tissues may contribute to anxiety and PTSD development.

Hypothalamic Astrocytes Respond to Gastric Mucosal Damage Induced by Restraint Water-Immersion Stress in Rat

Restraint water-immersion stress (RWIS), a compound stress model, includes both psychological and physical stimulation. Studies have shown that neurons in the hypothalamus are involved in RWIS, but the role of astrocytes and the interactions between astrocytes and neurons in RWIS are not clear. Here, we tested our hypothesis that hypothalamus astrocytes are involved in RWIS and interact with neurons to regulate gastric mucosal damage induced by RWIS. The expression of Glial fibrillary acidic protein (GFAP) and c-Fos in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) significantly increased following the RWIS. GFAP and c-Fos expression are similar in the temporal pattern, peaked at 1 h after the RWIS, then reduced gradually, and reached a maximal level again at 5 h which show “double-peak” characteristics. Intracerebroventricular administration of astroglial toxin L-a-aminoadipate (L-AA) and c-Fos antisense oligodeoxy nucleotides (ASO) both decreased RWIS-induced gastric mucosal damage. Results of immunohistochemistry assay revealed that both L-AA and ASO decreased the activation of astrocytes and neurons in the hypothalamus by RWIS. These results showed that hypothalamus neuron-astrocyte “network” involved in gastric mucosal damage induced by RWIS. This study may offer theoretical basis for some novel therapeutic strategies for RWIS-induced gastric ulcers.

Fluoxetine reverses the behavioral despair induced by neurogenic stress in mice: role of N-methyl-d-aspartate and opioid receptors

Opioid and N-methyl-d-aspartate (NMDA) receptors mediate different effects of fluoxetine. We investigated whether opioid and NMDA receptors are involved in the protective effect of fluoxetine against the behavioral despair induced by acute physical stress in male mice. We used the forced swimming test (FST), tail suspension test (TST), and open-field test (OFT) for behavioral evaluation. We used fluoxetine, naltrexone (opioid receptor antagonist), MK-801 (NMDA receptor antagonist), morphine (opioid receptor agonist), and NMDA (NMDA receptor agonist). Acute foot-shock stress (FSS) significantly induced behavioral despair (depressive-like) and anxiety-like behaviors in tests. Fluoxetine (5 mg/kg) reversed the depressant-like effect of FSS, but it did not alter the locomotion and anxiety-like behavior in animals. Acute administration of subeffective doses of naltrexone (0.3 mg/kg) or MK-801 (0.01 mg/kg) potentiated the antidepressant-like effect of fluoxetine, while subeffective doses of morphine (1 mg/kg) and NMDA (75 mg/kg) abolished this effect of fluoxetine. Also, co-administration of subeffective doses of naltrexone (0.05 mg/kg) and MK-801 (0.003 mg/kg) with fluoxetine (1 mg/kg) induced a significant decrease in the immobility time in FST and TST. Our results showed that opioid and NMDA receptors (alone or in combination) are involved in the antidepressant-like effect of fluoxetine against physical stress.

Galanin and Cognition

Since the neuropeptide galanin’s discovery in 1983, information has accumulated that implicates it in a wide range of functions, including pain sensation, stress responses, appetite regulation, and learning and memory. This article reviews the evidence for specific functions of galanin in cognitive processes. Consistencies as well as gaps in the literature are organized around basic questions of methodology and theory. This review shows that although regularities are evident in the observed behavioral effects of galanin across several methods for measuring learning and memory, generalization from these findings is tempered with concerns about confounds and a restricted range of testing conditions. Furthermore, it is revealed that many noncognitive behavioral constructs that are relevant for assessing potential roles for galanin in cognition have not been thoroughly examined. The review concludes by laying out how future theory and experimental work can overcome these concerns and confidently define the nature of the association of galanin with particular cognitive constructs.

Brain Systems Underlying Susceptibility to Helplessness and Depression

There has been a relative lack of research into the neurobiological predispositions that confer vulnerability to depression. This article reviews functional brain mappings from a genetic animal model, the congenitally helpless rat, which is predisposed to develop learned helplessness. Neurometabolic findings from this model are integrated with the neuroscientific literature from other animal models of depression as well as depressed humans. Changes in four major brain systems are suggested to underlie susceptibility to helplessness and possibly depression: (a) an unbalanced prefrontal-cingulate cortical system, (b) a dissociated hypothalamic-pituitary-adrenal axis, (c) a dissociated septal-hippocampal system, and (d) a hypoactive brain reward system, as exemplified by a hypermetabolic habenula-interpeduncular nucleus pathway and a hypometabolic ventral tegmental area-striatum pathway. Functional interconnections and causal relationships among these systems are considered and further experiments are suggested, with theoretical attention to how an abnormality in any one system could affect the others.

Activity of muscarinic, galanin and cannabinoid receptors in the prodromal and advanced stages in the triple transgenic mice model of Alzheimer's disease

Neurochemical alterations in Alzheimer's disease (AD) include cholinergic neuronal loss in the nucleus basalis of Meynert (nbM) and a decrease in densities of the M2 muscarinic receptor subtype in areas related to learning and memory. Neuromodulators present in the cholinergic pathways, such as neuropeptides and neurolipids, control these cognitive processes and have become targets of research in order to understand and treat the pathophysiological and clinical stages of the disease. This is the case of the endocannabinoid and galaninergic systems, which have been found to be up-regulated in AD, and could therefore have a neuroprotective role. In the present study, the functional coupling of Gi/o protein-coupled receptors to GalR1, and the CB1 receptor subtype for endocannabinoids were analyzed in the 3xTg-AD mice model of AD. In addition, the activity mediated by Gi/o protein-coupled M2/4 muscarinic receptor subtypes was also analyzed in brain areas involved in anxiety and cognition. Thus, male mice were studied at 4 and 15months of age (prodromal and advanced stages, respectively) and compared to age-matched non-transgenic (NTg) mice (adult and old, respectively). In 4-month-old 3xTg-AD mice, the [(35)S]GTPγS binding stimulated by galanin was significantly increased in the hypothalamus, but a decrease of functional M2/4 receptors was observed in the posterior amygdala. The CB1 cannabinoid receptor activity was up-regulated in the anterior thalamus at that age. In 15-month-old 3xTg-AD mice, muscarinic receptor activity was found to be increased in motor cortex, while CB1 activity was decreased in nbM. No changes were found in GalR1-mediated activity at this age. Our results provide further evidence of the relevance of limbic areas in the prodromal stage of AD, the profile of which is characterized by anxiety. The up-regulation of galaninergic and endocannabinoid systems support the hypothesis of their neuroprotective roles, and these are established prior to the onset of clear clinical cognitive symptoms of the disease.

Modification of Anxious Behavior after Psychogenic Trauma and Treatment with Galanin Receptor Antagonist

Effects of blockage of central galanin receptors on anxiety manifestations were studied in rats with psychogenic trauma. Psychogenic trauma was modeled by exposure of a group of rats to the situation when the partner was killed by a predator. Antagonist of galanin receptors was intranasally administered before stress exposure. Animal behavior was evaluated using the elevated-plus maze test, free exploratory paradigm, and open-field test. Psychogenic trauma was followed by an increase in anxiety level and appearance of agitated behavior. Blockage of galanin receptors aggravated behavioral impairment, which manifested in the pathological anxious reactions - manifestations of hypervigilance and hyperawareness. The results suggest that endogenous pool of galanin is involved into prevention of excessive CNS response to stressful stimuli typical of posttraumatic stress disorder.

Enkephalin knockout male mice are resistant to chronic mild stress

Enhanced stress reactivity or sensitivity to chronic stress increases the susceptibility to mood pathologies such as major depression. The opioid peptide enkephalin is an important modulator of the stress response. Previous studies using preproenkephalin knockout (PENK KO) mice showed that these animals exhibit abnormal stress reactivity and show increased anxiety behavior in acute stress situations. However, the consequence of enkephalin deficiency in the reactivity to chronic stress conditions is not known. In this study, we therefore submitted wild-type (WT) and PENK KO male mice to chronic stress conditions, using the chronic mild stress (CMS) protocol. Subsequently, we studied the CMS effects on the behavioral and hormonal level and also performed gene expression analyses. In WT animals, CMS increased the expression of the enkephalin gene in the paraventricular nucleus (PVN) of the hypothalamus and elevated the corticosterone levels. In addition, WT mice exhibited enhanced anxiety in the zero-maze test and depression-related behaviors in the sucrose preference and forced swim tests. Surprisingly, in PENK KO mice, we did not detect anxiety and depression-related behavioral changes after the CMS procedure, and even measured a decreased hormonal stress response. These results indicate that PENK KO mice are resistant to the CMS effects, suggesting that enkephalin enhances the reactivity to chronic stress.

Dynorphins regulate fear memory: from mice to men

Reexposure to trauma reminders is an integral element of trauma-focused cognitive behavioral therapy (Roberts et al., 2009), but little is known about the physiological processes underlying the therapeutic progress. While it is well established that amygdala, prefrontal cortex and hippocampus are key brain structures in fear memory processing (McGaugh, 2004; Herry et al., 2008; Likhtik et al., 2008), it is not well known which neurotransmitters or neuromodulators are involved. Here with a translational approach we investigated the role of dynorphins in the formation and extinction of fear memories in mice and in humans. Mice lacking dynorphin showed an enhanced cue-dependent fear conditioning, as well as delayed extinction in contextual conditioning/extinction paradigms. The pharmacological blockade of κ-opioid receptors before the extinction trials but not before or after the conditioning produced a similar effect. Analysis of neuronal activity, using the immediate early gene c-fos, demonstrated a reduced neuronal activity in key limbic structures during extinction in the absence of dynorphin. Translating these findings into the human domain, fear conditioning and extinction, coupled with functional MRI was then performed in volunteers preselected for a functionally relevant polymorphism in the dynorphin gene. Human volunteers bearing the (T) allele of PDYN (prodynorphin) at rs1997794 showed reduced fear extinction and a significantly diminished functional connectivity between amygdala and ventromedial prefrontal cortex. Our findings establish a role of dynorphin κ-opioid receptor signaling in fear extinction.

The delta opioid receptor antagonist, SoRI-9409, decreases yohimbine stress-induced reinstatement of ethanol-seeking

A major problem in treating alcohol use disorders (AUDs) is the high rate of relapse due to stress and re-exposure to cues or an environment previously associated with alcohol use. Stressors can induce relapse to alcohol-seeking in humans or reinstatement in rodents. Delta opioid peptide receptors (DOP-Rs) play a role in cue-induced reinstatement of ethanol-seeking; however, their role in stress-induced reinstatement of ethanol-seeking is not known. The objective of this study was to determine the role of DOP-Rs in yohimbine-stress-induced reinstatement of ethanol-seeking. Male, Long-Evans rats were trained to self-administer 10% ethanol in daily 30-minute operant self-administration sessions using a FR3 schedule of reinforcement, followed by extinction training. Once extinction criteria were met, we examined the effects of the DOP-R antagonist, SoRI-9409 (0-5 mg/kg, i.p.) on yohimbine (2 mg/kg, i.p.) stress-induced reinstatement. Additionally, DOP-R-stimulated [(35) S]GTPγS binding was measured in brain membranes and plasma levels of corticosterone (CORT) were determined. Pre-treatment with SoRI-9409 decreased yohimbine stress-induced reinstatement of ethanol-seeking but did not affect yohimbine-induced increases in plasma CORT levels. Additionally, yohimbine increased DOP-R-stimulated (35) [S]GTPγS binding in brain membranes of ethanol-trained rats, an effect that was inhibited by SoRI-9409. This suggests that the DOP-R plays an important role in yohimbine-stress-induced reinstatement of ethanol-seeking behavior, and DOP-R antagonists may be promising candidates for further development as a treatment for AUDs.

Neuropeptide modulation of central amygdala neuroplasticity is a key mediator of alcohol dependence

Alcohol use disorders are characterized by compulsive drug-seeking and drug-taking, loss of control in limiting intake, and withdrawal syndrome in the absence of drug. The central amygdala (CeA) and neighboring regions (extended amygdala) mediate alcohol-related behaviors and chronic alcohol-induced plasticity. Acute alcohol suppresses excitatory (glutamatergic) transmission whereas chronic alcohol enhances glutamatergic transmission in CeA. Acute alcohol facilitates inhibitory (GABAergic) transmission in CeA, and chronic alcohol increases GABAergic transmission. Electrophysiology techniques are used to explore the effects of neuropeptides/neuromodulators (CRF, NPY, nociceptin, dynorphin, endocannabinoids, galanin) on inhibitory transmission in CeA. In general, pro-anxiety peptides increase, and anti-anxiety peptides decrease CeA GABAergic transmission. These neuropeptides facilitate or block the action of acute alcohol in CeA, and chronic alcohol produces plasticity in neuropeptide systems, possibly reflecting recruitment of negative reinforcement mechanisms during the transition to alcohol dependence. A disinhibition model of CeA output is discussed in the context of alcohol dependence- and anxiety-related behaviors.

Oxytocin and vasopressin involved in restraint water-immersion stress mediated by oxytocin receptor and vasopressin 1b receptor in rat brain

Aims

Vasopressin (AVP) and oxytocin (OT) are considered to be related to gastric functions and the regulation of stress response. The present study was to study the role of vasopressinergic and oxytocinergic neurons during the restraint water-immersion stress.

Methods

Ten male Wistar rats were divided into two groups, control and RWIS for 1h. The brain sections were treated with a dual immunohistochemistry of Fos and oxytocin (OT) or vasopressin (AVP) or OT receptor or AVP 1b receptor (V_1bR).

Results

(1) Fos-immunoreactive (Fos-IR) neurons dramatically increased in the hypothalamic paraventricular nucleus (PVN), the supraoptic nucleus (SON), the neucleus of solitary tract (NTS) and motor nucleus of the vagus (DMV) in the RWIS rats; (2) OT-immunoreactive (OT-IR) neurons were mainly observed in the medial magnocellular part of the PVN and the dorsal portion of the SON, while AVP-immunoreactive (AVP-IR) neurons mainly distributed in the magnocellular part of the PVN and the ventral portion of the SON. In the RWIS rats, Fos-IR neurons were indentified in 31% of OT-IR neurons and 40% of AVP-IR neurons in the PVN, while in the SON it represented 28%, 53% respectively; (3) V_1bR-IR and OTR-IR neurons occupied all portions of the NTS and DMV. In the RWIS rats, more than 10% of OTR-IR and V_1bR-IR neurons were activated in the DMV, while lower ratio in the NTS.

Conclusion

RWIS activates both oxytocinergic and vasopressinergic neurons in the PVN and SON, which may project to the NTS or DMV mediating the activity of the neurons by OTR and V_1bR.

The effects of single and repeated exposure to 2.45 GHz radiofrequency fields on c-Fos protein expression in the paraventricular nucleus of rat hypothalamus

This study investigated the effects of microwave radiation on the PVN of the hypothalamus, extracted from rat brains. Expression of c-Fos was used to study the pattern of cellular activation in rats exposed once or repeatedly (ten times in 2 weeks) to 2.45 GHz radiation in a GTEM cell. The power intensities used were 3 and 12 W and the Finite Difference Time Domain calculation was used to determine the specific absorption rate (SAR). High SAR triggered an increase of the c-Fos marker 90 min or 24 h after radiation, and low SAR resulted in c-Fos counts higher than in control rats after 24 h. Repeated irradiation at 3 W increased cellular activation of PVN by more than 100% compared to animals subjected to acute irradiation and to repeated non-radiated repeated session control animals. The results suggest that PVN is sensitive to 2.45 GHz microwave radiation at non-thermal SAR levels.

Regulatory interactions of stress and reward on rat forebrain opioidergic and GABAergic circuitry

Palatable food intake reduces stress responses, suggesting that individuals may consume such ?comfort? food as self-medication for stress relief. The mechanism by which palatable foods provide stress relief is not known, but likely lies at the intersection of forebrain reward and stress regulatory circuits. Forebrain opioidergic and gamma-aminobutyric acid ergic signaling is critical for both reward and stress regulation, suggesting that these systems are prime candidates for mediating stress relief by palatable foods. Thus, the present study (1) determines how palatable ?comfort? food alters stress-induced changes in the mRNA expression of inhibitory neurotransmitters in reward and stress neurocircuitry and (2) identifies candidate brain regions that may underlie comfort food-mediated stress reduction. We used a model of palatable ?snacking? in combination with a model of chronic variable stress followed by in situ hybridization to determine forebrain levels of pro-opioid and glutamic acid decarboxylase (GAD) mRNA. The data identify regions within the extended amygdala, striatum, and hypothalamus as potential regions for mediating hypothalamic-pituitary-adrenal axis buffering following palatable snacking. Specifically, palatable snacking alone decreased pro-enkephalin-A (ENK) mRNA expression in the anterior bed nucleus of the stria terminalis (BST) and the nucleus accumbens, and decreased GAD65 mRNA in the posterior BST. Chronic stress alone increased ENK mRNA in the hypothalamus, nucleus accumbens, amygdala, and hippocampus; increased dynorphin mRNA in the nucleus accumbens; increased GAD65 mRNA in the anterior hypothalamus and BST; and decreased GAD65 mRNA in the dorsal hypothalamus. Importantly, palatable food intake prevented stress-induced gene expression changes in subregions of the hypothalamus, BST, and nucleus accumbens. Overall, these data suggest that complex interactions exist between brain reward and stress pathways and that palatable snacking can mitigate many of the neurochemical alterations induced by chronic stress.

The neurobiology of anxiety disorders: brain imaging, genetics, and psychoneuroendocrinology

Anxiety disorders are highly comorbid with each other and with major depressive disorder. As syndromes, anxiety and mood disorders share many symptoms, and several treatments are effective for both. Despite this overlap, there exist many distinguishing features that support the continued classification of individual anxiety disorders that are distinct from each other and from major depression. The goal of this article is to describe the key biological similarities and differences between anxiety disorders.

A role for the androgen metabolite, 5alpha androstane 3beta, 17beta diol (3β-diol) in the regulation of the hypothalamo-pituitary-adrenal axis

Activation of the hypothalamo-pituitary-adrenal (HPA) axis is a basic reaction of animals to environmental perturbations that threaten homeostasis. These responses are ultimately regulated by neurons residing within the paraventricular nucleus (PVN) of the hypothalamus. Within the PVN, corticotrophin-releasing hormone (CRH), vasopressin (AVP), and oxytocin (OT) expressing neurons are critical as they can regulate both neuroendocrine and autonomic responses. Estradiol (E2) and testosterone (T) are well known reproductive hormones; however, they have also been shown to modulate stress reactivity. In rodent models, evidence shows that under some conditions E2 enhances stress activated adrenocorticotropic hormone (ACTH) and corticosterone secretion. In contrast, T decreases the gain of the HPA axis. The modulatory role of testosterone was originally thought to be via 5 alpha reduction to the potent androgen dihydrotestosterone (DHT) and its subsequent binding to the androgen receptor, whereas E2 effects were thought to be mediated by estrogen receptors alpha (ERalpha) and beta (ERbeta). However, DHT has been shown to be metabolized to the ERbeta agonist, 5α- androstane 3β, 17β Diol (3β-Diol). The actions of 3β-Diol on the HPA axis are mediated by ERbeta which inhibits the PVN response to stressors. In gonadectomized rats, ERbeta agonists reduce CORT and ACTH responses to restraint stress, an effect that is also present in wild-type but not ERbeta-knockout mice. The neurobiological mechanisms underlying the ability of ERbeta to alter HPA reactivity are not currently known. CRH, AVP, and OT have all been shown to be regulated by estradiol and recent studies indicate an important role of ERbeta in these regulatory processes. Moreover, activation of the CRH and AVP promoters has been shown to occur by 3β-Diol binding to ERbeta and this is thought to occur through alternate pathways of gene regulation. Based on available data, a novel and important role of 3β-Diol in the regulation of the HPA axis is suggested.

A novel transgenic mouse for gene-targeting within cells that express corticotropin-releasing factor

Corticotropin-releasing factor (CRF) orchestrates the mammalian endocrine, autonomic, and behavioral stress response and has been implicated in the pathophysiology of illnesses ranging from irritable bowel syndrome to mood and anxiety disorders. CRF is produced and released from a variety of cell types, making it difficult to distinguish the specific role of CRF from other neurotransmitters with which it colocalizes. To clarify the basic biology of the CRF neuron, we must be able to manipulate selectively CRFergic cells. Here we describe a novel transgenic mouse using 3.0 kb of the CRF promoter to drive expression of Cre-recombinase (CRFp3.0Cre). Crossing CRFp3.0Cre with a fluorescent reporter strain results in Cre-dependent green fluorescent protein expression within CRF-producing cells. Thus, CRF cells can be identified for single-cell polymerase chain reaction and electrophysiological procedures. Furthermore, the CRFp3.0Cre transgenic can be combined with other available mouse strains containing a "floxed" gene of interest to allow unparalleled detailed analysis of the CRF system.

Galanin and consummatory behavior: special relationship with dietary fat, alcohol and circulating lipids

Galanin (GAL) plays an integral role in consummatory behavior. In particular, hypothalamic GAL has a positive, reciprocal relationship with dietary fat and alcohol. In this relationship, GAL increases the consumption of fat or alcohol which, in turn, stimulates the expression of GAL, ultimately leading to overconsumption. Through actions in the amygdala, this relationship may become especially important in stress-induced food or drug intake. These effects of GAL in promoting overconsumption may involve various neurotransmitters, with GAL facilitating intake by stimulating norepinephrine and dopamine and reducing satiety by decreasing serotonin and acetylcholine. In addition, GAL in the hypothalamus stimulates the opioid, enkephalin, throughout the brain, which also promotes overconsumption. The relationship between GAL, fat, and alcohol may involve triglycerides, circulating lipids that are released by fat or alcohol and that correlate positively with hypothalamic GAL expression. In females, levels of endogenous GAL also fluctuate across the reproductive cycle, driven by a rise in the ovarian steroids, estrogen, and progesterone. They peak during the proestrous phase and also at puberty, simultaneous to a sharp increase in preference for fat to meet energy demands. Prenatal exposure to a high-fat diet also enhances hypothalamic expression of GAL into adulthood because of an increase in neurogenesis and proliferation of GAL-expressing neurons in this region. This organizational change may reflect the role of GAL in neuronal development, including neurite growth in adulthood, cell survival in aging, and cell stability in the disease state. By responding positively to fat and alcohol and guiding further neuronal development, GAL potentiates a long-term propensity to overconsume fat and alcohol.

Comparison of the spatial distribution of seven types of neuroendocrine neurons in the rat paraventricular nucleus: toward a global 3D model

The paraventricular nucleus of the hypothalamus (PVH) coordinates neuroendocrine, autonomic, and behavioral responses to help maintain energy and body water balance. The rat paraventricular nucleus has three major divisions: descending with axonal projections to somatomotor-behavioral and autonomic circuitry, magnocellular neuroendocrine with projections directly to the posterior pituitary, and parvicellular neuroendocrine with projections to the median eminence for controlling anterior pituitary hormone secretion. The present work was undertaken to provide high-resolution mapping of spatial relationships among the two magnocellular neuroendocrine and five parvicellular neuroendocrine neuron types throughout the nucleus. Double immunohistochemical labeling for two neuron types combined with retrograde labeling to identify neuroendocrine neurons positively was used in individual sections spaced 45 mum apart, along with a grid transfer method for reducing plane of section artifacts when comparing staining pattern data between animals. The results indicate that whereas each neuroendocrine neuron phenotype displays a unique distribution pattern, there is extensive partial overlap in a complex pattern between small "hot spots" with a relatively high density of a particular neuron type and few if any other phenotypes. In addition, the distribution of non-neuroendocrine neurons staining with each of the markers (but not retrogradely labeled) was mapped and compared with each other and with the neuroendocrine neuron populations. This spatial organization raises important questions about the differential functional regulation of individual-and perhaps sets of-neuroendocrine motor neuron populations in the PVH by synaptic mechanisms and by less traditional mechanisms like dendritic neurotransmitter release and gap junctions within and between neuron types.

The neurobiology of anxiety disorders: brain imaging, genetics, and psychoneuroendocrinology

Anxiety disorders are highly comorbid with each other and with major depressive disorder. As syndromes, anxiety and mood disorders share many symptoms, and several treatments are effective for both. Despite this overlap, there exist many distinguishing features that support the continued classification of individual anxiety disorders that are distinct from each other and from major depression. The goal of this article is to describe the key biological similarities and differences between anxiety disorders.

Effects of neonatal stress and morphine on kappa opioid receptor signaling

BACKGROUND

Critically ill neonates experience multiple stressors during hospitalization. Opioids are commonly prescribed to ameliorate their pain and stress. However, the enduring effects of stress and opioids are not understood. The kappa opioid system is important in the mediation of stress in adults, but little is known about its function in neonates.

OBJECTIVES

To characterize kappa opioid receptor (KOR) distribution in the neonatal mouse brain and test whether neonatal exposure to morphine, stress, or both, change KOR signaling.

METHODS

Five groups of wild-type C57BL/6 or prodynorphin (Pdyn) knockout mice were tested: (1) untreated control (dam-reared, no handling), (2) saline-injected control, (3) morphine-injected control, (4) stressed with saline injections and (5) stressed with morphine injections. Mice were treated from postnatal day 5 to postnatal day 9, after which their brains were immunolabeled with a phospho-specific KOR antibody (KOR-P), glial fibrillary acidic protein or glutamic acid decarboxylase.

RESULTS

There were no effects of saline or morphine injection on KOR-P immunoreactivity. Neonatal stress increased KOR-P labeling in wild-type brains (p < 0.05), but not in Pdyn(-/-) animals. Mice exposed to stress and morphine showed region-specific increases in KOR-P immunoreactivity from 38 to 500% (p < 0.05 to p < 0.001), with marked gliosis. In stressed morphine-treated Pdyn(-/-) animals, KOR-P immunoreactivity was absent, but gliosis increased compared to wild-type animals.

CONCLUSIONS

Neonatal stress increases KOR activation via the dynorphin system. Neonatal stress plus morphine treatment further increased this response and also resulted in hippocampal gliosis. Enhanced gliosis noted in Pdyn(-/-) animals suggests that the endogenous dynorphin may play a role in downregulating this inflammatory response.

Nandrolone decanoate administration dose-dependently affects the density of kappa opioid peptide receptors in the rat brain determined by autoradiography

The kappa opioid receptor ligand [(3)H]CI-977 was used to autoradiographically determine the density of kappa opioid receptors in the male rat brain following chronic treatment with the anabolic androgenic steroid nandrolone decanoate at two different doses. As compared to controls, significantly lower densities of the kappa opioid receptor were encountered after two weeks of high dose nandrolone decanoate (15 mg/kg) in the nucleus accumbens shell (16%), lateral hypothalamic area (36%), ventromedial hypothalamic nucleus (37%), dorsomedial hypothalamic nucleus (49%), central amygdaloid nucleus, capsular part (28%), lateral globus pallidus (35%) and in the stria terminalis (24%). Furthermore, an up-regulation of the receptor level was observed in the caudate putamen (18%) and in the dorsal endopiriform nucleus (23%). These alterations in the kappa opioid receptor expression are possibly attributed to a previously observed pronounced impact of nandrolone decanoate on the dynorphinergic system and could also include involvement of the dopaminergic reward system.

The role of the galaninergic system in modulating stress-related responses in an animal model of posttraumatic stress disorder

BACKGROUND

Converging evidence implicates the regulatory neuropeptide galanin in anxiety- and depression-related behaviors, through modulation of neuroendocrine, serotonergic, and noradrenergic systems. This study examined the relationship between stress-induced posttraumatic stress disorder (PTSD)-like behavioral response patterns in rats and galanin mRNA levels in key brain areas and the effects of acute phase pharmacologic manipulation using an agonist (galnon) on behavioral, physiologic, and response patterns of brain-derived neurotrophic factor (BDNF) and 5-hydroxytryptamine-1A (5HT-1A).

METHOD

Galanin mRNA expression was assessed in the frontal cortex and hippocampus in the short- and long-term (30 min and 7 days) after exposure to predator scent stress. The effects of intraperitoneal galnon .5 mg/kg versus saline 1 hour postexposure on behavioral tests (elevated plus maze and acoustic startle response) were evaluated 7 days later. Trauma-cue response, circulating corticosterone, and localized brain expression of 5HT-1A receptors and BDNF were subsequently assessed. All data were analyzed in relation to individual behavior patterns.

RESULTS

Whereas animals with minimal behavioral disruption displayed a lasting upregulation of galanin mRNA in the hippocampal CA1 area, those with extreme behavioral responses displayed downregulation in both CA1 and frontal cortex. Immediate postexposure treatment with galnon significantly reduced prevalence rates of extreme responders, reduced trauma-cue freezing responses, corrected the corticosterone response, and increased CA1 expression of 5HT-1A and BDNF mRNA compared with saline controls.

CONCLUSIONS

Galanin is actively involved in the neurobiological response to predator scent stress with resilience/recovery after stress exposure and thus warrants further study as a potential therapeutic avenue for the treatment of anxiety-related disorders.

Control of hormonal stress reactivity by the endogenous opioid system

Regulations of hormonal stress responses entail the initiation, amplitude and termination of the reaction, as well as its integration with other stress response systems. This study investigates the role of endogenous opioids in the regulation and integration of behavioral, thermal and hormonal stress responses, as these neuromodulators and their receptors are expressed in limbic structures responsible for stress responses. For this purpose, we subjected mice with selective deletion of beta-endorphin, enkephalin or dynorphin to the zero-maze test, a mildly stressful situation, and registered behaviors and stress hormone levels. Behavioral stress reactivity was assessed using zero-maze, light-dark and startle-reactivity paradigms. Animals lacking enkephalin displayed increased anxiety-related behavioral responses in each three, dynorphin knockouts in two models, whereas the responses of beta-endorphin knockouts indicated lower anxiety level in the zero-maze test. All knockout strains showed marked changes in hormonal stress reactivity. Increase in ACTH level after zero-maze test situation, unlike in wild type animals, failed to reach the level of significance in Penk1(-/-) and Pdyn(-/-) mice. Corticosterone plasma levels rapidly increased in all strains, with a lower peak response in knockouts. In wild-type and beta-endorphin-deficient mice, corticosterone levels returned to baseline within 60min after stress exposure. In contrast, mice lacking dynorphin and enkephalin showed longer-lasting elevated corticosterone levels, indicating a delayed termination of the stress reaction. Importantly, the behavioral and hormonal responses correlated in wild-type but not in knockout mice. Hyperthermia elicited by stress was reduced in animals lacking dynorphin and absent in Penk1(-/-) mice, despite of the heightened behavioral anxiety level of these strains. These results demonstrate an important role on the endogenous opioid system in the integration of behavioral and hormonal stress responses.

The impact of postnatal environment on opioid peptides in young and adult male Wistar rats

Early environmental influences can change the neuronal development and thereby affect behavior in adult life. The aim in the present study was to thoroughly examine the impact of early environmental factors on endogenous opioids by using a rodent maternal separation (MS) model. The endogenous opioid peptide system is not fully developed at birth, and short- and/or long-term alterations may occur in these neural networks in animals exposed to manipulation of the postnatal environment. Rat pups were subjected to one of five rearing conditions; 15 min (MS15) litter (l) or individual (i), 360 min (MS360) l or i daily MS, or housed under normal animal facility rearing (AFR) conditions during postnatal days 1-21. Measurements of immunoreactive (ir) Met-enkephalin-Arg6Phe7 (MEAP) and dynorphin B (DYNB) peptide levels in the pituitary gland and in a number of brain areas, were performed at three and 10 weeks of age, respectively. MS-induced changes were more pronounced in ir MEAP levels, especially in individually separated rats at three weeks of age and in litter-separated rats at 10 weeks of age. The enkephalin and dynorphin systems have different developmental patterns, dynorphin appearing earlier, which may point at a more sensitive enkephalin system during the early postnatal weeks. The results provide evidence that opioid peptides are sensitive for early environmental factors and show that the separation conditions are critical and also result in changes manifesting at different time points. MS-induced effects were observed in areas related to stress, drug reward and dependence mechanisms. By describing effects on opioid peptides, the study addresses the possible role of a deranged endogenous opioid system in the previously described behavioral consequences of MS.

Changes in vasoactive intestinal peptide and arginine vasopressin expression in the suprachiasmatic nucleus of the rat brain following footshock stress

The neuropeptides, arginine vasopressin (AVP) and vasoactive intestinal polypeptide (VIP) are synthesized by neurons of the suprachiasmatic nucleus (SCN) of the hypothalamus and are important regulators of SCN function. Previous studies have demonstrated that acute exposure to stressors can disrupt circadian activity rhythms, suggesting the possibility of stress-related alterations in the expression of these neuropeptides within SCN neurons. In this study, we examined the effect of intermittent footshock stress on AVP mRNA and heterogeneous nuclear RNA (hnRNA) and VIP mRNA expression in neurons of the SCN. Young adult male Sprague/Dawley rats were subjected to 15 s of scrambled intermittent footshock (0.50 mA pulses, 1 pulse/s, 300 ms duration) every 5 min for 30 min. Animals were sacrificed 75 or 135 min after the onset of stress and brains examined for AVP mRNA and hnRNA, and VIP mRNA using in situ hybridization. Footshock stress increased AVP hnRNA levels at the 75 min time point whereas AVP mRNA was elevated at both the 75 and 135 min time points. In contrast, footshock stress decreased the number of cells expressing VIP mRNA in the SCN without changing hybridization level per cell. These data indicate that the disruptive effect of stress on activity rhythms correlate with alterations in the expression of regulatory peptides within the SCN.

Interleukin-1 signaling modulates stress-induced analgesia

Exposure to stressful stimuli is often accompanied by reduced pain sensitivity, termed "stress-induced analgesia" (SIA). In the present study, the hypothesis that interleukin-1 (IL-1) may play a modulatory role in SIA was examined. Two genetic mouse models impaired in IL-1-signaling and their wild-type (WT) controls were employed. Another group of C57 mice was acutely administered with IL-1 receptor antagonist (IL-1ra). Mice were exposed to 2min swim stress at one of three water temperatures: 32 degrees C (mild stress), 20-23 degrees C (moderate stress), or 15 degrees C (severe stress); and then tested for pain sensitivity using the hot-plate test. Corticosterone levels were assessed in separate groups of WT and mutant mice following exposure to the three types of stress. Mild stress induced significant analgesia in the two WT strains and saline-treated mice, but not in the mutant strains or the IL-1ra-treated mice. Similarly, mild stress induced significantly elevated corticosterone levels in WT mice, and blunted corticosterone response in mutant mice. In contrast, both WT and mutant strains, as well as IL-1ra-treated mice, displayed analgesic and corticosterone responses following moderate and severe stress. Interestingly, the analgesic response to moderate stress was markedly potentiated in the mutant strains, as compared with their WT controls. The present results support our previous findings that in the absence of IL-1, stress response to mild stress is noticeably diminished. However, the analgesic response to moderate stress is markedly potentiated in mice with impaired IL-1 signaling, corroborating the anti-analgesic role of IL-1 in several pain modulatory conditions, including SIA.

Experimental Neuropathy in Mice Is Associated with Delayed Behavioral Changes Related to Anxiety and Depression

BACKGROUND

Patients with chronic pain frequently suffer affective disorders, particularly anxiety and depression. Although clinical research on the relationship between pain and depressive symptoms has been done, it is not clear whether pain causes depression or depression exaggerates pain. To investigate the relation between pain and affect, we measured anxiety and depression-related behaviors in mice after spinal nerve ligation using classical behavioral tests.

METHODS

After unilateral ligation of the left fifth lumbar nerve, we measured pain behaviors using von Frey and radiant heat tests. Activity level, anxiety-related behaviors, and depression-related behaviors were tested with open field, light-dark exploration, elevated plus-maze, and forced swim tests.

RESULTS

Sensory hypersensitivity was observed within a few days after ligation. Anxiety and depression-related behaviors were not seen 2 and 7 days after ligation. However, 15 and 30 days after ligation we found clear evidence of anxiety and depression-related behaviors, without loss of mobility.

CONCLUSIONS

Nerve injury can trigger affective disturbances in mice that appear much later than sensory hypersensitivity.

Up-regulation of galanin and corticotropin-releasing hormone mRNAs in the key hypothalamic and amygdaloid nuclei in a mouse model of visceral pain

Cyclophosphamide (CP)-induced cystitis is often used as an animal model of visceral pain. Various neuropeptides in the hypothalamic and amygdaloid nuclei are implicated in pain-induced responses. However, little information is available regarding the regulation of the neuropeptides in response to visceral pain. In the present study, we examined the effects of CP-induced cystitis on the levels of mRNAs encoding galanin, corticotropin-releasing hormone (CRH), substance P, and enkephalins in the hypothalamic and limbic nuclei using in situ hybridization histochemistry in mouse. Galanin mRNA levels in CP-treated group increased significantly in the arcuate nucleus and the paraventricular nucleus (PVN) but not in the medial preoptic area after the intraperitoneal administration of CP (200 mg/kg body weight) in comparison to those in saline-treated group. CRH mRNA levels in CP-treated group also increased significantly in the central amygdala as well as the PVN after the CP administration. In contrast, CP-induced cystitis failed to upregulate the preprotachykinin-A and preproenkephalin genes which encode substance P and enkephalins, respectively in the hypothalamic and limbic nuclei at any of the time points examined. These results suggest that visceral nociception may upregulate both galanin and CRH gene expression in the hypothalamic and limbic nuclei.

Glucocorticoids, chronic stress, and obesity

Glucocorticoids either inhibit or sensitize stress-induced activity in the hypothalamo-pituitary-adrenal (HPA) axis, depending on time after their administration, the concentration of the steroids, and whether there is a concurrent stressor input. When there are high glucocorticoids together with a chronic stressor, the steroids act in brain in a feed-forward fashion to recruit a stress-response network that biases ongoing autonomic, neuroendocrine, and behavioral outflow as well as responses to novel stressors. We review evidence for the role of glucocorticoids in activating the central stress-response network, and for mediation of this network by corticotropin-releasing factor (CRF). We briefly review the effects of CRF and its receptor antagonists on motor outflows in rodents, and examine the effects of glucocorticoids and CRF on monoaminergic neurons in brain. Corticosteroids stimulate behaviors that are mediated by dopaminergic mesolimbic "reward" pathways, and increase palatable feeding in rats. Moreover, in the absence of corticosteroids, the typical deficits in adrenalectomized rats are normalized by providing sucrose solutions to drink, suggesting that there is, in addition to the feed-forward action of glucocorticoids on brain, also a feedback action that is based on metabolic well being. Finally, we briefly discuss the problems with this network that normally serves to aid in responses to chronic stress, in our current overindulged, and underexercised society.

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

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

Distribution of prodynorphin mRNA and its interaction with the NPY system in the mouse brain

Using radioactive in situ hybridisation, the distribution of prodynorphin mRNA in the brains of C57Bl/6 mice was systemically investigated, and double-labelling in situ hybridisation was used to determine the extent to which neuropeptide Y (NPY) and prodynorphin mRNAs were co-expressed. Our results demonstrate that prodynorphin mRNA expression in the mouse brain is localised at specific subregions of the olfactory bulb, cortex, hippocampus, amygdala, basal ganglia, thalamus, hypothalamus, mesencephalon and myelencephalon. Among the regions displaying the most intense labelling were the olfactory tubercle, lateral septum (LS), caudate putamen (Cpu), central amygdaloid nucleus (Ce), paraventricular hypothalamic nucleus (PVN), supraoptic nucleus (SO), lateral hypothalamic area (LHA), ventromedial hypothalamic nucleus (VMH), lateral reticular nucleus (LRt) and solitary tract nucleus (NTS). In the arcuate nucleus of the hypothalamus (Arc), double-labelling in situ hybridisation revealed that prodynorphin expressing neurons also contained NPY mRNA, with a co-localisation rate of approximately 88% in the lateral part of the Arc, and 79% in the dorsal part of the Arc, respectively, suggesting potential overlapping functions of these two neurotransmitters in feeding type behaviour.

Clorazepate affects cell surface regulation of delta and kappa opioid receptors, thereby altering buprenorphine-induced adaptation in the rat brain

Concomitant abuse of buprenorphine (BPN) and benzodiazepines (BZD) may relate to a pharmacodynamic interaction between the two. The objective of the present work was to investigate the acute and chronic effects of clorazepate (CRZ) alone or in combination with BPN on selective kappa opiate tritiated ligand [3H]-U69 593 and delta opiate radioligand [3H]-deltorphine II binding in the rat brain. Bmax (maximal receptor density) and Kd (the dissociation constant) were directly determined at different brain regions of interest (ROI) selected for high densities of kappa and/or delta receptors in rats treated with BPN and/or CRZ. The agents were administered either once or for 21 consecutive days. Differences in Bmax and Kd (for both specific ligands) were related to drug treatment and receptor location. Globally, single BPN administration induced no changes in kappa or delta opiate receptor binding, whereas repeated BPN administration up-regulated kappa receptor density and decreased delta affinity. At the kappa receptor level, repeated administration of CRZ acted only on Kd, whereas the delta receptor was up-regulated. Repeated addition of CRZ to BPN had no effect on kappa receptor Bmax versus chronic controls. By significantly decreasing Bmax, CRZ nullified the effect of chronic BPN on the kappa receptor. The modifications were strongest in the nucleus accumbens, where both types of receptor occur. Treatments had region-selective effects in some brain areas, such as the amygdala, periaqueductal gray matter, hypothalamus and caudate putamen. Increased mu and delta receptor densities would be expected to provide reinforcement by enhancing reward, and impairment of kappa receptor availability would be expected to decrease aversion. The effects described are likely to influence addictive behavior among people abusing BZD and BPN.

Electroacupuncture reduces stress-induced expression of c-fos in the brain of the rat

We have previously shown that electroacupuncture (EA) at Shaohai and Neiguan (HT3-PC6) points significantly attenuated stress-induced peripheral responses, including increases in blood pressure, heart rate and plasma catecholamines. In this study, we examined the central effect of EA on the expression of c-fos, one of the immediate-early genes in the brain of rats subjected to immobilization stress. Immobilization stress (180 minutes) preferentially produced a significant increase in Fos-like immunoreactivity (FLI) in stress-relevant regions including the paraventricular hypothalamic nucleus (PVN), arcuate nucleus (ARN), supraoptic nucleus (SON), suprachiasmatic nucleus (SCN), medial amygdaloid nucleus (AMe), bed nucleus of the stria terminalis (BST), hippocampus, lateral septum (LS), nucleus accumbens, and the locus coeruleus (LC). EA (3 Hz, 0.2 ms rectangular pulses, 20 mA) at HT3-PC6 on the heart and pericardium channels for 30 minutes during stress, significantly attenuated stress-induced FLI in the parvocellular PVN, SON, SCN, AMe, LS and the LC. However, EA stimulations at HT3-PC6 had no effect on FLI in the magnocelluar PVN, ARN, BST or the hippocampus. EA stimulation at HT3-PC6 had a greater inhibitory effect on stress-induced FLI than that at TE5-LI11, the triple energizer and large intestine meridian, or non-acupoints. These results demonstrated that EA attenuated stress-induced c-fos expression in brain areas. These results suggest that decreased c-fos expression in hypothalamic and LC neurons, among stress-related areas, may reflect the integrative action of acupuncture in stress response.