Chronic Environmental or Genetic Elevation of Galanin in Noradrenergic Neurons Confers Stress Resilience in Mice.

The neuropeptide galanin has been implicated in stress-related neuropsychiatric disorders in humans and rodent models. While pharmacological treatments for these disorders are ineffective for many individuals, physical activity is beneficial for stress-related symptoms. Galanin is highly expressed in the noradrenergic system, particularly the locus coeruleus (LC), which is dysregulated in stress-related disorders and activated by exercise. Galanin expression is elevated in the LC by chronic exercise, and blockade of galanin transmission attenuates exercise-induced stress resilience. However, most research on this topic has been done in rats, so it is unclear whether the relationship between exercise and galanin is species specific. Moreover, use of intracerebroventricular (ICV) galanin receptor antagonists in prior studies precluded defining a causal role for LC-derived galanin specifically. Therefore, the goals of this study were twofold. First, we investigated whether physical activity (chronic wheel running) increases stress resilience and galanin expression in the LC of male and female mice. Next, we used transgenic mice that overexpress galanin in noradrenergic neurons (Gal OX) to determine how chronically elevated noradrenergic-derived galanin, alone, alters anxiogenic-like responses to stress. We found that three weeks of ad libitum access to a running wheel in their home cage increased galanin mRNA in the LC of mice, which was correlated with and conferred resilience to stress. The effects of exercise were phenocopied by galanin overexpression in noradrenergic neurons, and Gal OX mice were resistant to the anxiogenic effect of optogenetic LC activation. These findings support a role for chronically increased noradrenergic galanin in mediating resilience to stress.SIGNIFICANCE STATEMENT Understanding the neurobiological mechanisms underlying behavioral responses to stress is necessary to improve treatments for stress-related neuropsychiatric disorders. Increased physical activity is associated with stress resilience in humans, but the neurobiological mechanisms underlying this effect are not clear. Here, we investigate a potential causal mechanism of this effect driven by the neuropeptide galanin from the main noradrenergic nucleus, the locus coeruleus (LC). We show that chronic voluntary wheel running in mice increases stress resilience and increases galanin expression in the LC. Furthermore, we show that genetic overexpression of galanin in noradrenergic neurons causes resilience to a stressor and the anxiogenic effects of optogenetic LC activation. These findings support a role for chronically increased noradrenergic galanin in mediating resilience to stress.

Supplementation with macular carotenoids reduces psychological stress, serum cortisol, and sub-optimal symptoms of physical and emotional health in young adults.

PURPOSE: Oxidative stress and systemic inflammation are the root cause of several deleterious effects of chronic psychological stress. We hypothesize that the antioxidant and anti-inflammatory capabilities of the macular carotenoids (MCs) lutein, zeaxanthin, and meso-zeaxanthin could, via daily supplementation, provide a dietary means of benefit. METHODS: A total of 59 young healthy subjects participated in a 12-month, double-blind, placebo-controlled trial to evaluate the effects of MC supplementation on blood cortisol, psychological stress ratings, behavioural measures of mood, and symptoms of sub-optimal health. Subjects were randomly assigned to one of three groups: placebo, 13 mg, or 27 mg / day total MCs. All parameters were assessed at baseline, 6 months, and 12 months. Serum MCs were determined via HPLC, serum cortisol via ELISA, and macular pigment optical density (MPOD) via customized heterochromatic flicker photometry. Behavioural data were obtained via questionnaire. RESULTS: Significant baseline correlations were found between MPOD and Beck anxiety scores (r = -0.28; P = 0.032), MPOD and Brief Symptom Inventory scores (r = 0.27; P = 0.037), and serum cortisol and psychological stress scores (r = 0.46; P < 0.001). Supplementation for 6 months improved psychological stress, serum cortisol, and measures of emotional and physical health (P < 0.05 for all), versus placebo. These outcomes were either maintained or improved further at 12 months. CONCLUSIONS: Supplementation with the MCs significantly reduces stress, cortisol, and symptoms of sub-optimal emotional and physical health. Determining the basis for these effects, whether systemic or a more central (i.e. brain) is a question that warrants further study.

The galanin receptor agonist, galnon, attenuates cocaine-induced reinstatement and dopamine overflow in the frontal cortex.

Relapse represents one of the most significant problems in the long-term treatment of drug addiction. Cocaine blocks plasma membrane monoamine transporters and increases dopamine (DA) overflow in the brain, and DA is critical for the motivational and primary reinforcing effects of the drug as well as cocaine-primed reinstatement of cocaine seeking in rats, a model of relapse. Thus, modulators of the DA system may be effective for the treatment of cocaine dependence. The endogenous neuropeptide galanin inhibits DA transmission, and both galanin and the synthetic galanin receptor agonist, galnon, interfere with some rewarding properties of cocaine. The purpose of this study was to further assess the effects of galnon on cocaine-induced behaviors and neurochemistry in rats. We found that galnon attenuated cocaine-induced motor activity, reinstatement and DA overflow in the frontal cortex at a dose that did not reduce baseline motor activity, stable self-administration of cocaine, baseline extracellular DA levels or cocaine-induced DA overflow in the nucleus accumbens (NAc). Similar to cocaine, galnon had no effect on stable food self-administration but reduced food-primed reinstatement. These results indicate that galnon can diminish cocaine-induced hyperactivity and relapse-like behavior, possibly in part by modulating DA transmission in the frontal cortex.

Antidepressant and anticonvulsant effects of exercise in a rat model of epilepsy and depression comorbidity.

The bidirectional comorbidity between epilepsy and depression is associated with severe challenges for treatment efficacy and safety, often resulting in poor prognosis and outcome for the patient. We showed previously that rats selectively bred for depression-like behaviors (SwLo rats) also have increased limbic seizure susceptibility compared with their depression-resistant counterparts (SwHi rats). In this study, we examined the therapeutic efficacy of voluntary exercise in our animal model of epilepsy and depression comorbidity. We found that chronic wheel running significantly increased both struggling duration in the forced swim test and latency to pilocarpine-induced limbic motor seizure in SwLo rats but not in SwHi rats. The antidepressant and anticonvulsant effects of exercise were associated with an increase in galanin mRNA specifically in the locus coeruleus of SwLo rats. These results demonstrate the beneficial effects of exercise in a rodent model of epilepsy and depression comorbidity and suggest a potential role for galanin.

Prenatal exposure to bisphenol A and/or diethylhexyl phthalate alters stress responses in rat offspring in a sex- and dose-dependent manner.

Background: Prenatal exposures to endocrine disrupting chemicals (EDCs) are correlated with adverse behavioral outcomes, but the effects of combinations of these chemicals are unclear. The aim of this study was to determine the dose-dependent effects of prenatal exposure to EDCs on male and female behavior. Methods: Pregnant Sprague-Dawley rats were orally dosed with vehicle, bisphenol A (BPA) (5 µg/kg body weight (BW)/day), low-dose (LD) diethylhexyl phthalate (DEHP) (5 µg/kg BW/day), high-dose (HD) DEHP (7.5 mg/kg BW/day), a combination of BPA and LD-DEHP (B + D (LD)), or a combination of BPA and HD-DEHP (B + D (HD)) on gestational days 6-21. Adult offspring were subjected to the Open Field Test (OFT), Elevated Plus Maze (EPM), and Shock Probe Defensive Burying test (SPDB) in adulthood. Body, adrenal gland, and pituitary gland weights were collected at sacrifice. Corticosterone (CORT) was measured in the serum. Results: Female EDC-exposed offspring showed anxiolytic effects in the OFT, while male offspring were unaffected. DEHP (HD) male offspring demonstrated a feminization of behavior in the EPM. Most EDC-exposed male offspring buried less in the SPDB, while their female counterparts showed reduced shock reactivity, indicating sex-specific maladaptive alterations in defensive behaviors. Additionally, DEHP (LD) males and females and B + D (LD) females displayed increased immobility in this test. DEHP (LD) alone and in combination with BPA led to lower adrenal gland weights, but only in male offspring. Finally, females treated with a mixture of B + D (HD) had elevated CORT levels. Conclusion: Prenatal exposure to BPA, DEHP, or a mixture of the two, affects behavior, CORT levels, and adrenal gland weights in a sex- and dose-dependent manner.

The gut-brain axis mediates bacterial driven modulation of reward signaling.

OBJECTIVE: Our goal is to investigate if microbiota composition modulates reward signaling and assess the role of the vagus in mediating microbiota to brain communication. METHODS: Male germ-free Fisher rats were colonized with gastrointestinal contents from chow (low fat (LF) ConvLF) or HF (ConvHF) fed rats. RESULTS: Following colonization, ConvHF rats consumed significantly more food than ConvLF animals. ConvHF rats displayed lower feeding-induced extracellular DOPAC levels (a metabolite of dopamine) in the Nucleus Accumbens (NAc) as well as reduced motivation for HF foods compared to ConvLF rats. Dopamine receptor 2 (DDR2) expression levels in the NAc were also significantly lower in ConvHF animals. Similar deficits were observed in conventionally raised HF fed rats, showing that diet-driven alteration in reward can be initiated via microbiota. Selective gut to brain deafferentation restored DOPAC levels, DRD2 expression, and motivational drive in ConvHF rats. CONCLUSIONS: We concluded from these data that a HF-type microbiota is sufficient to alter appetitive feeding behavior and that bacteria to reward communication is mediated by the vagus nerve.

An endocannabinoid mechanism for stress-induced analgesia.

Acute stress suppresses pain by activating brain pathways that engage opioid or non-opioid mechanisms. Here we show that an opioid-independent form of this phenomenon, termed stress-induced analgesia, is mediated by the release of endogenous marijuana-like (cannabinoid) compounds in the brain. Blockade of cannabinoid CB(1) receptors in the periaqueductal grey matter of the midbrain prevents non-opioid stress-induced analgesia. In this region, stress elicits the rapid formation of two endogenous cannabinoids, the lipids 2-arachidonoylglycerol (2-AG) and anandamide. A newly developed inhibitor of the 2-AG-deactivating enzyme, monoacylglycerol lipase, selectively increases 2-AG concentrations and, when injected into the periaqueductal grey matter, enhances stress-induced analgesia in a CB1-dependent manner. Inhibitors of the anandamide-deactivating enzyme fatty-acid amide hydrolase, which selectively elevate anandamide concentrations, exert similar effects. Our results indicate that the coordinated release of 2-AG and anandamide in the periaqueductal grey matter might mediate opioid-independent stress-induced analgesia. These studies also identify monoacylglycerol lipase as a previously unrecognized therapeutic target.

Engineered glycomaterial implants orchestrate large-scale functional repair of brain tissue chronically after severe traumatic brain injury.

Severe traumatic brain injury (sTBI) survivors experience permanent functional disabilities due to significant volume loss and the brain's poor capacity to regenerate. Chondroitin sulfate glycosaminoglycans (CS-GAGs) are key regulators of growth factor signaling and neural stem cell homeostasis in the brain. However, the efficacy of engineered CS (eCS) matrices in mediating structural and functional recovery chronically after sTBI has not been investigated. We report that neurotrophic factor functionalized acellular eCS matrices implanted into the rat M1 region acutely after sTBI significantly enhanced cellular repair and gross motor function recovery when compared to controls 20 weeks after sTBI. Animals subjected to M2 region injuries followed by eCS matrix implantations demonstrated the significant recovery of "reach-to-grasp" function. This was attributed to enhanced volumetric vascularization, activity-regulated cytoskeleton (Arc) protein expression, and perilesional sensorimotor connectivity. These findings indicate that eCS matrices implanted acutely after sTBI can support complex cellular, vascular, and neuronal circuit repair chronically after sTBI.

A role for 2-arachidonoylglycerol and endocannabinoid signaling in the locomotor response to novelty induced by olfactory bulbectomy.

Bilateral olfactory bulbectomy (OBX) in rodents produces behavioral and neurochemical changes associated clinically with depression and schizophrenia. Most notably, OBX induces hyperlocomotion in response to the stress of exposure to a novel environment. We examined the role of the endocannabinoid system in regulating this locomotor response in OBX and sham-operated rats. In our study, OBX-induced hyperactivity was restricted to the first 3 min of the open field test, demonstrating the presence of novelty (0-3 min) and habituation (3-30 min) phases of the open field locomotor response. Levels of the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide were decreased in the ventral striatum, a brain region deafferented by OBX, whereas cannabinoid receptor densities were unaltered. In sham-operated rats, 2-AG levels in the ventral striatum were negatively correlated with distance traveled during the novelty phase. Thus, low levels of 2-AG are reflected in a hyperactive open field response. This correlation was not observed in OBX rats. Conversely, 2-AG levels in endocannabinoid-compromised OBX rats correlated with distance traveled during the habituation phase. In OBX rats, pharmacological blockade of cannabinoid CB(1) receptors with either AM251 (1 mg kg(-1) i.p.) or rimonabant (1 mg kg(-1) i.p.) increased distance traveled during the habituation phase. Thus, blockade of endocannabinoid signaling impairs habituation of the hyperlocomotor response in OBX, but not sham-operated, rats. By contrast, in sham-operated rats, effects of CB(1) antagonism were restricted to the novelty phase. These findings suggest that dysregulation in the endocannabinoid system, and 2-AG in particular, is implicated in the hyperactive locomotor response induced by OBX. Our studies suggest that drugs that enhance 2-AG signaling, such as 2-AG degradation inhibitors, might be useful in human brain disorders modeled by OBX.

Extracellular Vesicles Mediate Neuroprotection and Functional Recovery after Traumatic Brain Injury.

The lack of effective therapies for moderate-to-severe traumatic brain injuries (TBIs) leaves patients with lifelong disabilities. Neural stem cells (NSCs) have demonstrated great promise for neural repair and regeneration. However, direct evidence to support their use as a cell replacement therapy for neural injuries is currently lacking. We hypothesized that NSC-derived extracellular vesicles (NSC EVs) mediate repair indirectly after TBI by enhancing neuroprotection and therapeutic efficacy of endogenous NSCs. We evaluated the short-term effects of acute intravenous injections of NSC EVs immediately following a rat TBI. Male NSC EV-treated rats demonstrated significantly reduced lesion sizes, enhanced presence of endogenous NSCs, and attenuated motor function impairments 4 weeks post-TBI, when compared with vehicle- and TBI-only male controls. Although statistically not significant, we observed a therapeutic effect of NSC EVs on brain lesion volume, nestin expression, and behavioral recovery in female subjects. Our study demonstrates the neuroprotective and functional benefits of NSC EVs for treating TBI and points to gender-dependent effects on treatment outcomes, which requires further investigation.

Endocannabinoid modulation of amphetamine sensitization is disrupted in a rodent model of lesion-induced dopamine dysregulation.

We tested the hypothesis that increased dopaminergic sensitivity induced by olfactory bulbectomy is mediated by dysregulation of endocannabinoid signaling. Bilateral olfactory bulbectomy induces behavioral and neurobiological symptomatology related to increased dopaminergic sensitivity. Rats underwent olfactory bulbectomy or sham operations and were assessed 2 weeks later in two tests of hyperdopaminergic responsivity: locomotor response to novelty and locomotor sensitization to amphetamine. Amphetamine (1 mg/kg i.p.) was administered to rats once daily for 8 consecutive days to induce locomotor sensitization. URB597, an inhibitor of the anandamide hydrolyzing enzyme fatty-acid amide hydrolase (FAAH), was administered daily (0.3 mg/kg i.p.) to sham and olfactory bulbectomized (OBX) rats to investigate the impact of FAAH inhibition on locomotor sensitization to amphetamine. Pharmacological specificity was evaluated with the CB(1) antagonist/inverse agonist rimonabant (1 mg/kg i.p). OBX rats exhibited heightened locomotor activity in response to exposure either to a novel open field or to amphetamine administration relative to sham-operated rats. URB597 produced a CB(1)-mediated attenuation of amphetamine-induced locomotor sensitization in sham-operated rats. By contrast, URB597 failed to inhibit amphetamine sensitization in OBX rats. The present results demonstrate that enhanced endocannabinoid transmission attenuates development of amphetamine sensitization in intact animals but not in animals with OBX-induced dopaminergic dysfunction. Our data collectively suggest that the endocannabinoid system is compromised in olfactory bulbectomized rats.

Galanin administration into the prelimbic cortex impairs consolidation and expression of contextual fear conditioning.

The neuropeptide galanin is a potential therapeutic target for treating stress-related disorders, such as post-traumatic stress disorder (PTSD); however, its effects on contextual fear conditioning (CFC), an accepted animal model of PTSD, are not well understood. Dysregulation of the medial prefrontal cortex (mPFC) is implicated in PTSD. We investigated the effects of galanin (1 ug) administrated bilaterally into the prelimbic cortex, a division of the mPFC, on the consolidation, expression, and extinction of CFC of male Sprague-Dawley rats. Galanin administration significantly reduced consolidation and expression of CFC, but had no effect on retention or retrieval of extinction learning. These data further implicate galanin as a potential therapeutic target for treating stress-related disorders, particularly those characterized by aberrant emotional memory.

Effects of macular xanthophyll supplementation on brain-derived neurotrophic factor, pro-inflammatory cytokines, and cognitive performance.

PURPOSE: Oxidative and inflammatory processes play a major role in stress-induced neural atrophy. There is a wide body of literature linking oxidative and inflammatory stress with reductions in neurotrophic factors, stress resilience, and cognitive function. Based on their antioxidant and anti-inflammatory capacity, we investigated the effect of the dietary carotenoids lutein and zeaxanthin, along with the zeaxanthin isomer meso-zeaxanthin (collectively the "macular xanthophylls" [MXans]) on systemic brain-derived neurotrophic factor (BDNF) and anti-oxidant capacity (AOC), and the pro-inflammatory cytokines TNF-α, IL-6, and IL-1ß. To investigate higher-order effects, we assessed cognitive performance. METHODS: 59 young (18-25 yrs.), healthy subjects participated in a 6-month, double-blind, placebo-controlled trial to evaluate the effects of MXan supplementation on the aforementioned serum parameters and cognitive performance. Subjects were randomly assigned to one of three groups: placebo, 13 mg, or 27 mg/day total MXans; all measures were taken at baseline and 6 months. Blood was obtained via fasting blood draw, and MXan concentration in the retina (termed macular pigment optical density [MPOD]) was measured via customized heterochromatic flicker photometry. Serum BDNF and cytokines were assessed via ELISA. Serum antioxidant capacity (AOC) and serum MXan concentrations were quantified via colorimetric microplate assay, and high-performance liquid chromatography, respectively. Cognitive performance was measured via a computer-based assessment tool (CNS Vital Signs). RESULTS: BDNF, MPOD, serum MXans, and AOC all increased significantly versus placebo in both treatment groups over the 6-month study period (p < .05 for all). IL-1ß decreased significantly versus placebo in both treatment groups (p = .0036 and p = .006, respectively). For cognitive measures, scores for composite memory, verbal memory, sustained attention, psychomotor speed, and processing speed all improved significantly in treatment groups (p < .05 for all) and remained unchanged in the placebo group. Several measures were found to be significantly associated in terms of relational changes over the course of the study. Notably, change in BDNF was related to change in IL-1ß (r = -0.47; p < .001) and MPOD (r = 0.44; p = .0086). Additionally, changes in serum MXans were strongly related to AOC (r = 0.79 & 0.61 for lutein and zeaxanthin isomers respectively; p < .001). For cognitive scores, change in BDNF was correlated to change in composite memory (r = 0.32; p = .014) and verbal memory (r = 0.35; p = .007), whereas change in MPOD was correlated with change in both psychomotor speed (r = 0.38; p = .003), and processing speed (r = 0.35; p = .007). Change in serum lutein was found to be significantly correlated to change in verbal memory (r = 0.41; p < .001), composite memory (r = 0.31; p = .009), and sustained attention (r = 0.28; p = .036). Change in serum zeaxanthin isomers was significantly correlated with change in verbal memory (r = 0.33; p = .017). Lastly, change in AOC was significantly associated with verbal memory (r = 0.34; p = .021), composite memory (r = 0.29; p = .03), and sustained attention (r = 0.35; p = .016). No significant relational changes in any cognitive parameter were found for the placebo group. CONCLUSIONS: Six months of daily supplementation with at least 13 mg of MXans significantly reduces serum IL-1ß, significantly increases serum MXans, BDNF, MPOD, and AOC, and improves several parameters of cognitive performance. Findings suggest that increased systemic antioxidant/anti-inflammatory capacity (and not necessarily deposition of the carotenoids in neural tissues), may explain many of the effects determined in this study. The significant relationship between change in BDNF and IL-1ß over the course of the study suggests that regular consumption of MXans interrupts the inflammatory cascade that can lead to reduction of BDNF. Changes in MPOD and BDNF appear to account for enhancement in cognitive parameters that involve speed of processing and complex processing, respectively. ISRCTN Clinical Trial Registration: ISRCTN16156382.

Intracerebroventricular administration of galanin or galanin receptor subtype 1 agonist M617 induces c-Fos activation in central amygdala and dorsomedial hypothalamus.

The neuropeptide galanin and galanin receptors are widespread throughout cortical, limbic and midbrain areas implicated in reward, learning/memory, pain, drinking and feeding. While many studies have shown that galanin produces a variety of presynaptic and post-synaptic responses, work studying the effects of galanin on neural activation is limited. The present study examined patterns of c-Fos immunoreactivity resulting from intracerebroventricular administration of galanin versus saline injection in awake rats. An initial comprehensive qualitative survey was conducted to identify regions of high c-Fos expression followed up with quantitative analysis. Galanin induced a significant increase in c-Fos levels relative to saline-treated controls in dorsomedial hypothalamus and in the central nucleus of the amygdala. This pattern of activation was also produced by galanin receptor type 1 agonist M617. The present findings confirm that galanin upregulates c-Fos activation in hypothalamic nuclei, and supports roles for galanin in central amygdala-mediated regulation of stress-responses, food intake, and Pavlovian conditioning.

Chronic and voluntary exercise enhances learning of conditioned place preference to morphine in rats.

Previous research has shown that brief and intermittent activity wheel running attenuates conditioned place preference (CPP) to morphine in rats, which suggests that exercise may produce a cross-tolerance to opiates. On the other hand, a different exercise paradigm, chronic and voluntary wheel running, enhances learning in contextual conditioning tasks. The present experiments tested CPP to 2.5, 5, and 7.5 mg/kg morphine in sedentary rats and rats provided free access to running wheels for three weeks. Sucrose preference was also tested to determine exercise's influence on appetitive processes. Levels of mRNA encoding brain-derived neurotrophic factor and preprogalanin mRNA were quantified using in situ hybridization. In rats that exhibited CPP to morphine, exercising rats spent significantly more time per entry in the morphine-paired chamber during the CPP test. CPP to morphine was dose-dependent. The expression of hippocampal brain-derived neurotrophic factor (BDNF) was greater in exercising rats compared to the sedentary group. Preprogalanin (GAL) mRNA expression in the locus coeruleus (LC) was positively correlated with mean distance run. These results suggest that while chronic exercise may produce cross-tolerance to opioids, exercise-induced enhancement of associative learning caused by exercise may override this effect in the conditioned place preference procedure.

Voluntary exercise and clomipramine treatment elevate prepro-galanin mRNA levels in the locus coeruleus in rats.

Exercise exerts antidepressant effects in humans and rodent models of affective disorders. These effects may be mediated by the upregulation of endogenous factors that exert antidepressant actions. The physiological functions and behavioral actions of the neuropeptide galanin (GAL) suggest antidepressant activity. Previous studies have shown that various modes of exercise elevate GAL gene expression in the locus coeruleus (LC) in rats. The present experiments examined the interaction between voluntary exercise and antidepressant pharmacotherapy. Male Sprague-Dawley rats were provided access to activity wheels (exercise condition) or inoperative wheels (sedentary condition) for 28 days. Rats in each group were injected with clomipramine (10mg/kg/day) or vehicle throughout this period (for 3 weeks). Prepro-GAL mRNA in the LC was measured by in situ hybridization histochemistry. Exercise and clomipramine treatment significantly elevated GAL gene expression, though prepro-GAL mRNA levels in rats receiving both interventions did not differ from sedentary controls that received vehicle. Prepro-GAL mRNA levels were significantly correlated with running distance. The results further implicate a role for GAL in the antidepressant effects of exercise and pharmacotherapy, though the mechanisms through which these treatments influence GAL gene expression appear to differ significantly.

Regulation of neurological and neuropsychiatric phenotypes by locus coeruleus-derived galanin.

Decades of research confirm that noradrenergic locus coeruleus (LC) neurons are essential for arousal, attention, motivation, and stress responses. While most studies on LC transmission focused unsurprisingly on norepinephrine (NE), adrenergic signaling cannot account for all the consequences of LC activation. Galanin coexists with NE in the vast majority of LC neurons, yet the precise function of this neuropeptide has proved to be surprisingly elusive given our solid understanding of the LC system. To elucidate the contribution of galanin to LC physiology, here we briefly summarize the nature of stimuli that drive LC activity from a neuroanatomical perspective. We go on to describe the LC pathways in which galanin most likely exerts its effects on behavior, with a focus on addiction, depression, epilepsy, stress, and Alzheimer׳s disease. We propose a model in which LC-derived galanin has two distinct functions: as a neuromodulator, primarily acting via the galanin 1 receptor (GAL1), and as a trophic factor, primarily acting via galanin receptor 2 (GAL2). Finally, we discuss how the recent advances in neuropeptide detection, optogenetics and chemical genetics, and galanin receptor pharmacology can be harnessed to identify the roles of LC-derived galanin definitively. This article is part of a Special Issue entitled SI: Noradrenergic System.

Pharmacological stimulation of GAL1R but not GAL2R attenuates kainic acid-induced neuronal cell death in the rat hippocampus.

The neuropeptide galanin is widely distributed in the central and peripheral nervous systems and part of a bigger family of bioactive peptides. Galanin exerts its biological activity through three G-protein coupled receptor subtypes, GAL1-3R. Throughout the last 20years, data has accumulated that galanin can have a neuroprotective effect presumably mediated through the activation of GAL1R and GAL2R. In order to test the pharmaceutical potential of galanin receptor subtype selective ligands to inhibit excitotoxic cell death, the GAL1R selective ligand M617 and the GAL2R selective ligand M1145 were compared to the novel GAL1/2R ligand M1154, in their ability to reduce the excitotoxic effects of intracerebroventricular injected kainate acid in rats. The peptide ligands were evaluated in vitro for their binding preference in a competitive (125)I-galanin receptor subtype binding assay, and G-protein signaling was evaluated using both classical signaling and a label-free real-time technique. Even though there was no significant difference in the time course or severity of the kainic acid induced epileptic behavior in vivo, administration of either M617 or M1154 before kainic acid administration significantly attenuated the neuronal cell death in the hippocampus. Our results indicate the potential therapeutic value of agonists selective for GAL1R in the prevention of neuronal cell death.

Area postrema-lesions increase operant responding to sucrose in rats.

Rats with lesions of the area postrema (APX) are known to exhibit an enhanced intake of highly palatable foods such as sweetened condensed milk and cookies. These observations suggest the possibility that APX rats find these foods more rewarding and will work harder to obtain these foods. Sham and APX rats were tested on fixed ratio (FR) and progressive ratio (PR) schedules. APX rats consistently pressed more times to receive sucrose solution and attained both FR 3 and FR 5 criteria significantly faster than sham-lesioned control rats. Furthermore, rats with APX had significantly higher break points than sham-lesioned control rats on a progressive ratio schedule. These results support the hypothesis that rats with lesions of the area postrema will consistently work harder to obtain a highly palatable food reward.

The effects of post-extinction exercise on cocaine-primed and stress-induced reinstatement of cocaine seeking in rats.

RATIONALE: Voluntary aerobic exercise has shown promise as a treatment for substance abuse, reducing relapse in cocaine-dependent people. Wheel running also attenuates drug-primed and cue-induced reinstatement of cocaine seeking in rats, an animal model of relapse. However, in most of these studies, wheel access was provided throughout cocaine self-administration and/or extinction and had effects on several parameters of drug seeking. Moreover, the effects of exercise on footshock stress-induced reinstatement have not been investigated. OBJECTIVES: The purposes of this study were to isolate and specifically examine the protective effect of exercise on relapse-like behavior elicited by a drug prime or stress. METHODS: Rats were trained to self-administer cocaine at a stable level, followed by extinction training. Once extinction criteria were met, rats were split into exercise (24 h, continuous access to running wheel) and sedentary groups for 3 weeks, after which, drug-seeking behavior was assessed following a cocaine prime or footshock. We also measured galanin messenger RNA (mRNA) in the locus coeruleus and A2 noradrenergic nucleus. RESULTS: Exercising rats ran ∼4-6 km/day, comparable to levels previously reported for rats without a history of cocaine self-administration. Post-extinction exercise significantly attenuated cocaine-primed, but not footshock stress-induced, reinstatement of cocaine seeking, and increased galanin mRNA expression in the LC but not A2. CONCLUSION: These results indicate that chronic wheel running can attenuate some forms of reinstatement, even when initiated after the cessation of cocaine self-administration, supporting the idea that voluntary exercise programs may help maintain abstinence in clinical populations.