Neuropeptides

Editorial Board

2010-08-01

Effects of centrally-injected glucagon-like peptide-1 on pilocarpine-induced seizures, anxiety and locomotor and exploratory activity in rat

Guldal Gulec, Naciye Isbil-Buyukcoskun, Nevzat Kahveci — 2010-03-15

Abstract: Glucagon-like peptide-1 (7-36)-amide (GLP-1) is a gut peptide, which exerts significant effects on glucose homeostasis. GLP-1 and GLP-1 receptors are also widely distributed in the central nervous system. In the present study, we aimed to investigate the effects of intracerebroventricularly (i.c.v.)-injected GLP-1 on pilocarpine-induced seizures, anxiety and locomotor and exploratory activity in rat. Rats were pretreated with GLP-1 (1–1000ng/5μl; i.c.v.) or saline (5μl; i.c.v.) 30min before seizure induction by pilocarpine (2.4mg/5μl; i.c.v.) and with GLP-1 (1, 10, 100ng/5μl; i.c.v.) or saline (5μl; i.c.v.) 30min before the open field test or the elevated plus maze test. GLP-1 did not produce any protective effect against pilocarpine-induced seizures and did not also produce statistically significant differences in the number of squares visited (measure of locomotor activity) or number of rearings (measure of exploratory behaviour), compared to the saline-treated rats in the open field test. On the other hand, GLP-1 (1ng and 10ng; i.c.v.) induced an anxiogenic effect, indicated by a decrease in the time spent in open arms, an increase in the time spent in closed arms, and a decrease in the anxiety scores in the elevated plus maze test. Pretreatment with an arginine vasopressin (AVP) V1 receptor antagonist (125ng/5μl; i.c.v.) and L-NAME (100μg/5μl and 200μg/5μl) significantly abolished the anxiogenic effect of GLP-1 (1ng/5μl; i.c.v.). These results suggest that, centrally-injected GLP-1 produces anxiogenic effects via NO pathway and AVP V1 receptors, but does not have any effects on pilocarpine-induced seizures or locomotor and exploratory activity in the open field test.

Effect of genetic deletion of the vanilloid receptor TRPV1 on the expression of Substance P in sensory neurons of mice with adjuvant-induced arthritis

Helen H. Willcockson, Yong Chen, Ji Eun Han, Juli G. Valtschanoff — 2010-03-22

Abstract: The neuropeptide Substance P (SP), expressed by nociceptive sensory afferents in joints, plays an important role in the pathogenesis of arthritis. Capsaicin causes neurons in the dorsal root ganglia (DRG) to release SP from their central and peripheral axons, suggesting a functional link between SP and the capsaicin receptor, the transient receptor potential vanilloid 1 (TRPV1). The expression of both TRPV1 and SP have been reported to increase in several models of arthritis but the specific involvement of TRPV1-expressing articular afferents that can release SP is not completely understood. We here wanted to ascertain whether the increase in the number of SP-positive primary afferents in arthritis may be affected by genetic deletion of TRPV1. For this, we used immunohistochemistry to quantify the expression of SP in primary afferent neurons in wild-type mice (WT) vs. TRPV1-knockout (KO) mice with adjuvant-induced arthritis (AIA). We found that the expression of SP in DRG (1) increased significantly over naïve level in both WT and KO mice 3weeks after AIA, (2) was significantly higher in KO mice than in WT mice in naïve mice and 2–3weeks after AIA, (3) was significantly higher on the side of AIA than on the contralateral, vehicle-injected side at all time points in WT mice, but not in KO mice, and (4) increased predominantly in small-size neurons in KO mice and in small- and medium-size neurons in WT mice. Since the size distribution of SP-positive DRG neurons in arthritic TRPV1-KO mice was not significantly different from that in naïve mice, we speculate that the increased expression of SP is unlikely to reflect recruitment of A-fiber primary afferents and that the higher expression of SP in KO mice may represent a plastic change to compensate for the missing receptor in a major sensory circuit.

Changes in the gene expression of specific G-protein subunits correlate with morphine insensitivity in streptozotocin-induced diabetic rats

2010-03-24

Abstract: Several animal and human studies have shown a decreased analgesic potency of morphine in diabetic subjects. Since G-protein subunits have an important role in morphine effects at the cellular level and the exact mechanism(s) of diabetes-induced morphine insensitivity has not been fully clarified yet, the present study was designed to determine the changes in the levels of Gαi, Gαs, Gβ mRNAs and proteins involved in this phenomenon. All experiments were carried out on male Wistar rats. The tail-flick test was used to assess the nociceptive threshold. Diabetes was induced by injection of 50mg/kg (i.p.) streptozotocin. Four weeks after diabetes induction, the dorsal half of the lumbar spinal cord was assayed for the expression of G-protein subunits using semiquantitative RT-PCR and immunoblotting.The antinociceptive effect of intrathecal morphine (5, 10 and 15μg i.t.) was significantly reduced in diabetic rats and these effects were reversed with insulin replacement. In diabetic animals, a significant increase in the mRNA levels of Gαi (23.5%) was observed in the dorsal portion of the lumbar spinal cord. The mRNA level of Gαs and Gβ did not change. Following diabetes a significant decrease in the protein levels of Gαi was induced. In contrast, no significant changes were observed in the protein level of Gαs and Gβ. In diabetic animals that received insulin, levels of Gαi mRNA and protein were close to those in control rats.In conclusion, our results demonstrate that the expression pattern of the cellular components involved in morphine analgesia changes in diabetic animals. This may be, at least partly, responsible for diabetes-induced morphine insensitivity.

Aβ20–29 peptide blocking apoE/Aβ interaction reduces full-length Aβ42/40 fibril formation and cytotoxicity in vitro

2010-04-05

Abstract: A key event in the pathogenesis of Alzheimer’s disease (AD) is the conversion of the peptide beta-amyloid (Aβ) from its soluble monomeric form into various aggregated morphologies in the brain. Apolipoprotein E (apoE) is known to act as a pathological chaperone of Aβ in this process, promoting its fibril formation from soluble Aβ by binding interaction between carboxy-terminal domain of apoE and residues 12–28 of full-length Aβ. Therefore, blocking apoE/Aβ interaction is being actively pursued as a primary therapeutic strategy for AD. Aβ20–29, a short peptide, contains the residues to competitively bind to apoE and may potentially block the interaction between apoE and full-length Aβ. However, little is known whether Aβ20–29 could block apoE/Aβ interaction to play an effective role in reducing full-length Aβ fibrillization and cytotoxicity. Utilizing fluorescence spectroscopic analysis with thioflavin T and electron microscopic study, we show here that Aβ20–29 alone was non-fibrillogenic, and had no direct effects on Aβ1–42 or Aβ1–40 aggregation. Moreover, apoE can directly promote both Aβ1–42 and Aβ1–40 aggregation and fibril formation, while this promoting effect was inhibited when adding Aβ20–29, with a dose-dependent manner. In the series of cell culture experiments, Aβ20–29 alone shows no cytotoxicity to PC12 cells as demonstrated by MTT assay, while co-incubation apoE isoforms and Aβ1–42 or Aβ1–40 shows stronger cytotoxicity as compared to Aβ1–42 or Aβ1–40 alone. When incubated with Aβ20–29, whereas such strong cytotoxic effect was concentration-dependently reduced. Taken together, we demonstrate for the first time that Aβ20–29 has no direct effect on full-length Aβ aggregation, and may competitively block the binding of full-length Aβ to apoE, resulting in an inhibitory effect on apoE’s promoting full-length Aβ fibrillogenesis and Aβ-induced cytotoxicity. Our results raise the possibility that Aβ20–29 peptide blocking the interaction between full-length Aβ and apoE isoforms may be effective as a therapeutic agent for AD.

Age-dependence of alpha-MSH-induced anorexia

E. Pétervári, A. Garami, S. Soós, M. Székely, M. Balaskó — 2010-04-12

Abstract: Long-term regulation of energy balance involves two major trends: first age-related obesity develops in the middle-aged, later it is followed by anorexia of aging (sarcopenia and/or cachexia). A dynamic balance between orexigenic and anorexigenic neuropeptides is essential for the regulation of energy homeostasis. Special imbalances of neuropeptide effects may be assumed corresponding to different age-periods. Anorexia induced by acute alpha-MSH (alpha-melanocyte stimulating hormone; endogenous melanocortin agonist) injections was analyzed in male Wistar rats aged 6–9 weeks (juvenile), 3–4 months (young adult), 6 or 12 months (two middle-aged groups), 18 months (aging) and 24–26 months (old). Alpha-MSH injected through a preimplanted intracerebroventricular (ICV) cannula (compared with saline injection) dose-dependently suppressed spontaneous food intake and also re-feeding following 24-h fasting, but the rate of suppression varied between age-groups. An ICV injection of 5μg alpha-MSH attenuated the 2-h re-feeding by 21.9±3.2% in juvenile rats, strongly (68.7±2.5%) suppressed it in young adults, the suppression became progressively weaker in the two middle-aged groups (55.7±4.9%, vs. 26.4±4.9%, respectively), but it turned extreme in aging (94.7±4.2%) and old (74.3±4.5%) rats. Body composition also changed with age: unlike the tibialis anterior muscle, the epididymal and retroperitoneal fat pads increased until middle-age and remained large even in old animals, while the measured indicator of muscle mass decreased in the oldest group. The food intake suppressing and body weight decreasing effects of a 7-day-long ICV infusion of 1μg/h alpha-MSH were weakest in the 12-month-old and most pronounced in the 24month-old rats. In conclusion, responsiveness to the anorexic effect of alpha-MSH varies with age, with a nadir of the curve in the middle-aged, and a peak in the aging and old animals. This age-related nadir of melanocortin-responsiveness may promote obesity in middle-aged rats, while the tendency for anorexia and incipient sarcopenia of old (still obese) rats may result from age-related melanocortin-hypersensitivity rather than from adiposity.

Multiple neurotrophic effects of VEGF on cultured neurons

Alma Sanchez, Suchin Wadhwani, Paula Grammas — 2010-04-30

Abstract: A large literature demonstrates the multifunctional nature of vascular endothelial growth factor (VEGF). Though initially characterized as an endothelial cell-specific factor, recent studies reveal that VEGF has numerous effects on diverse cell types in the brain including neurons. The objective of this study is to examine the effects of VEGF in cultured cortical neurons on survival, p38 mitogen-activated protein kinase (p38 MAP kinase) activity, pro- and anti-apoptotic protein expression and on release of neurotrophic and neurotoxic factors. The results show that VEGF dose-dependently enhances the survival of neurons in culture. VEGF decreases active caspase 3 levels and increases expression of the anti-apoptotic protein Bcl-2. VEGF decreases phosphorylated p38 MAP kinase level and activity in cortical neurons. In addition to modulating survival/death pathways in cortical neurons, VEGF also regulates release of proteins that affect neuronal viability. VEGF causes a dose-dependent release of the neurotrophic protein pigment epithelial-derived factor (PEDF), while significantly decreasing release of the neurotoxic protein amyloid beta. The VEGF-mediated decrease in amyloid beta is dependent on a functional Flt-1 receptor and is inhibited by dicoumarol, a multifunctional inhibitor of stress-activated protein kinase (SAPK)/JNK and NFkappaB pathways. Taken together, these data demonstrate that the neurotrophic effects of VEGF are likely mediated directly by increasing survival and decreasing apoptotic proteins and signals as well as indirectly by modulating release of proteins that affect neuronal viability.

Alarin stimulates food intake in male rats and LH secretion in castrated male rats

2010-05-03

Abstract: Alarin is a newly identified member of the galanin family of neuropeptides that includes galanin-like peptide (GALP) and galanin. Alarin was discovered as an alternate transcript of the GALP gene in neuroblastoma cells, and subsequently alarin mRNA was detected in the brain of rodents. GALP and galanin are important central regulators of both feeding and reproductive behavior. We hypothesized, that, as a member of the galanin family of peptides, alarin would also have central effects on feeding and reproduction. To test this hypothesis, we treated male rats with alarin intracerebroventricularly (i.c.v.) and measured its effects on food intake and energy homeostasis as well as sexual behavior and luteinizing hormone (LH) secretion. We observed that i.c.v. injection of 1.0nmol alarin significantly increased food intake (p<0.01) and body weight (p<0.05). Alarin did not affect sexual behavior in male rats; however, alarin did significantly (p<0.01) increase LH levels in castrated, but not intact, male rats. Alarin immunoreactive cell bodies were detected within the locus coeruleus and locus subcoeruleus of the midbrain, which is a brainstem nucleus involved in coordinating many physiological activities, including food intake and reproduction. Lastly, alarin stimulated Fos induction in hypothalamic nuclei, such as the paraventricular nucleus and the nucleus of the tractus solitarious. Our studies demonstrate that alarin, like other members of the galanin family, is a neuromediator of food intake and body weight.

Galanin influences on vasopressin and oxytocin release: In vitro studies

K. Izdebska, J. Ciosek — 2010-05-13

Abstract: Galanin (Gal) acts in the central nervous system as the neuromodulator of the hypothalamo-neurohypophysial system function. Present investigations in vitro were undertaken to study the influence of Gal, added to the incubative media at the concentrations of 10−10, 10−9, 10−8 or 10−7M, on AVP and OT release from isolated rat hypothalamus (Hth), neurohypophysis (NH) and hypothalamo–neurohypophysial system (Hth–NH).The present results showed that Gal at the concentrations of 10−10, 10−9 and 10−8M inhibited basal AVP secretion from the all incubated tissues as well as OT release from the NH and Hth–NH explant. On the contrary, 10−10M Gal was the reason of intensified basal hypothalamic OT secretion.The presence of Gal at the concentrations of 10−10 and 10−8M in the incubative media enriched in potassium ions excess was the cause of diminished AVP release from the NH and from the Hth–NH explant, respectively. Any effect of Gal on AVP release from the Hth has been observed. All the concentrations of Gal did not exert any effect on OT release from the NH as well as Hth–NH explants. However, the K+-evoked OT release from the Hth was distinctly intensified under influence of 10−10M as well as 10−8M Gal.It may be concluded that:

CRF2 null mutation increases sensitivity to isolation rearing effects on locomotor activity in mice

2010-05-13

Abstract: Background: Developmental stressors are consistently reported to increase risk for certain neuropsychiatric disorders including schizophrenia, depression, and post-traumatic stress disorder. Recent clinical evidence supports a “double-hit” hypothesis of genetic vulnerability interacting with developmental challenges to modulate this risk. Early life stressor effects on behavior may be modulated in part by alterations in corticotropin releasing factor (CRF) signaling via two known receptors, CRF1 and CRF2. One extant hypothesis is that CRF2 activation may modulate long-term adaptive responses after homeostatic challenge. As such, loss of CRF2 activity via genetic variance may increase sensitivity to the long-term effects of developmental stress.Methods: We tested the hypothesis that CRF2 function may mitigate the behavioral effects of isolation rearing, predicting that loss of CRF2 function increases sensitivity to this developmental challenge. Using the behavioral pattern monitor (BPM), we examined exploratory behavior and locomotor patterns in adult CRF2 wild-type (WT) and gene knockout (KO) mice reared socially or in isolation.Results: Isolation housing produced robust increases in the amount of locomotor activity and investigatory holepoking, and altered the temporal distribution of activity in CRF2 KO but not CRF2 WT mice. Isolation housing significantly increased rearing behavior and altered spatial patterns of locomotor activity regardless of genotype.Conclusions: Loss of CRF2 function increased sensitivity to the effects of chronic social isolation on exploratory locomotor behavior. Thus, CRF2 activation appears to mitigate isolation rearing effects on exploratory behavior. Further research assessing the interaction between CRF2 function and developmental challenges is warranted.

Meetings Calendar

2010-08-01