Effects of alpha-MSH on kainic acid induced changes in core temperature in rats

Laurdan spectrum decomposition as a tool for the analysis of surface bilayer structure and polarity: a study with DMPG, peptides and cholesterol

The highly hydrophobic fluorophore Laurdan (6-dodecanoyl-2-(dimethylaminonaphthalene)) has been widely used as a fluorescent probe to monitor lipid membranes. Actually, it monitors the structure and polarity of the bilayer surface, where its fluorescent moiety is supposed to reside. The present paper discusses the high sensitivity of Laurdan fluorescence through the decomposition of its emission spectrum into two Gaussian bands, which correspond to emissions from two different excited states, one more solvent relaxed than the other. It will be shown that the analysis of the area fraction of each band is more sensitive to bilayer structural changes than the largely used parameter called Generalized Polarization, possibly because the latter does not completely separate the fluorescence emission from the two different excited states of Laurdan. Moreover, it will be shown that this decomposition should be done with the spectrum as a function of energy, and not wavelength. Due to the presence of the two emission bands in Laurdan spectrum, fluorescence anisotropy should be measured around 480 nm, to be able to monitor the fluorescence emission from one excited state only, the solvent relaxed state. Laurdan will be used to monitor the complex structure of the anionic phospholipid DMPG (dimyristoyl phosphatidylglycerol) at different ionic strengths, and the alterations caused on gel and fluid membranes due to the interaction of cationic peptides and cholesterol. Analyzing both the emission spectrum decomposition and anisotropy it was possible to distinguish between effects on the packing and on the hydration of the lipid membrane surface. It could be clearly detected that a more potent analog of the melanotropic hormone alpha-MSH (Ac-Ser(1)-Tyr(2)-Ser(3)-Met(4)-Glu(5)-His(6)-Phe(7)-Arg(8)-Trp(9)-Gly(10)-Lys(11)-Pro(12)-Val(13)-NH(2)) was more effective in rigidifying the bilayer surface of fluid membranes than the hormone, though the hormone significantly decreases the bilayer surface hydration.

Inflammation in the nervous system--physiological and pathophysiological aspects

There is ample evidence for the occurrence of inflammatory processes in most major neurodegenerative disorders, both in acute conditions such as traumatic brain injury and stroke, and in chronic disorders such as Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis and Parkinson's disease. Studies on inflammatory factors such as pro- and antiinflammatory cytokines in experimental models of neurodegenerative disorders suggest that they are not merely bystanders, but may be involved in the neurodegenerative process. In addition, there are findings indicating that inflammatory factors may have beneficial effects on the nervous system, particularly during development of the nervous system. The challenge is to understand when, where and during which circumstances inflammation and inflammatory factors are positive or negative for neuronal survival and functioning. Some of our studies on cytokines, particularly the interleukin-1 system, are summarised and discussed in relation to neurodegeneration, cognition, and temperature changes.

The influence of kainic acid on core temperature and cytokine levels in the brain

Excitotoxic brain injury is associated with hyperthermia, and there are data showing beneficial effects of hypothermia on neurodegeneration and that hyperthermia facilitates the neurodegeneration. Cytokines are inflammatory proteins that seem to be involved in the neuroinflammation associated with epilepsy. Core temperature changes caused by the epileptogenic glutamate analogue kainic acid (KA) were investigated in relation to changes in levels of the pro-inflammatory cytokines interleukin-1beta (IL-1beta) and interleukin-6 (IL-6), and the endogenous interleukin-1 receptor antagonist (IL-1ra). The temperature was measured every 10 min during the first hour, and at 90 and 120 min, and hourly until 8 h after KA-injection (10 mg/kg). The cytokines were measured in the hypothalamus, a site of temperature regulation, and in hippocampus, cerebellum, and frontal cortex. KA induced a brief hypothermia followed by hyperthermia. IL-1beta levels were increased after KA-administration in all brain regions examined and, excepting hippocampus, returned to baseline levels at 24 h. The hippocampal IL-1ra levels were significantly increased at 24 h, whereas no changes in IL-6 levels were observed. The changes in IL-1beta levels and in ratios between the levels of the three cytokines, may account for some of the temperature changes and the behavioural manifestations induced by KA.

alpha-Melanocyte-stimulating hormone is neuroprotective in rat global cerebral ischemia

The aim of the study was to investigate the effects of alpha-melanocyte-stimulating hormone (alpha-MSH), a tridecapeptide derived from proopiomelanocortin (POMC), on the neurodegeneration following global cerebral ischemia and reperfusion in the rat. The biological activities of alpha-MSH include inhibition of inflammatory responses and anti-pyretic effects. Male Sprague-Dawley rats were subjected to four-vessel occlusion (4-VO) global cerebral ischemia followed by reperfusion, and treated with alpha-MSH (intraperitoneally, i.p.) at 30 min, and 24, 48, 72 and 96 h post-ischemia. Stereological quantification of the pyramidal cells in the CA1 area of the hippocampus showed that the number of viable neurons in ischemic rats was 96,945+/-18,610 (means+/-SD) as compared to 183,156+/-49,935 in sham-operated rats (P<0.05). The number of viable neurons after treatment of ischemic rats with alpha-MSH was 162,829+/-34,757, i.e. significantly different from the number of viable neurons in ischemic rats injected with saline (P<0.01). Astrocyte proliferation due to the ischemic insult was markedly reduced by the treatment with alpha-MSH, and the loss in body weight was reduced by alpha-MSH. In conclusion, post-ischemic administration of alpha-MSH was found to provide neuroprotection in the CA1 pyramidal cell layer in the hippocampus, concomitant with a reduction in glial activation, indicating that alpha-MSH or mimetics thereof may have a potential in the treatment of stroke or other neurodegenerative diseases. Further studies will be required to define the post-ischemic time window for administration of alpha-MSH.

??-MSH decreases core and brain temperature during global cerebral ischemia in rats

A key pathological event during cerebral ischemia is the excitotoxic release of glutamate. We have shown previously that alpha-melanocyte-stimulating hormone (alpha-MSH) enhances the hypothermia induced by kainic acid. We have investigated the effects of systemic administration of alpha-MSH on four-vessel occlusion forebrain ischemia on core temperature (CT) and brain temperature (BT), respectively. After 10 min cerebral ischemia, BT was lower in alpha-MSH- than in saline-injected animals. After 10 min reperfusion, both CT and BT were lower than the corresponding pre-ischemic levels after injection of alpha-MSH. alpha-MSH did not influence CT or BT in sham-operated rats. The alpha-MSH-induced hypothermia and its potentiation of reduction in BT during global cerebral ischemia, may contribute to neuroprotective effects of alpha-MSH.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

Inflammatory mechanisms associated with brain damage induced by kainic acid with special reference to the interleukin-1 system

The evidence of inflammatory processes in the clinical manifestations and neuropathological sequelae of epilepsy have accumulated in the last decade. Administration of kainic acid, an analogue of the excitatory amino acid glutamate, induces a characteristic behavioural syndrome and a reproducible pattern of neurodegeneration in several brain areas, closely resembling human temporal lobe epilepsy. Results from studies using the kainic acid model indicate that manipulation of pro- and anti-inflammatory cytokines can modify the outcome with regard to the behavioural syndrome as well as the neuropathological consequences. Interleukin-1 is one of the most important cytokines and has several actions in the brain that are critical for the host defense against injury and infection, and it is involved in the initiation of early stages of inflammation. It is believed that interleukin-1 plays a pivotal role in the neuroinflammation associated with certain forms of neurodegeneration, including cerebral ischemia, trauma and excitotoxic brain injury. In this review, we have summarized the experimental data available with regard to the involvement of the interleukin-1 system in kainic acid-induced changes in the brain and emphasized the modulatory role of interleukin-1beta in this model of epilepsy

Dantrolene protects neurons against kainic acid induced apoptosis in vitro and in vivo

Apoptotic cell death induced by kainic acid (KA) in cultures of rat cerebellar granule cells (CGC) and in different brain regions of Wistar rat pups on postnatal day 21 (P21) was studied. In vitro, KA (100-500 microM) induced a concentration-dependent loss of cell viability in MTT assay and cell death had apoptotic morphology as studied by chromatin staining with propidium iodide (PI). In vivo, twenty-four hours after induction of status epilepticus (SE) by an intraperitoneal KA injection (5 mg/kg) we quantified apoptotic cells in hippocampus (CA1 and CA3), parietal cortex and cerebellum using PI staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique. We report that dantrolene, a specific ryanodine receptor antagonist, was able to significantly reduce the apoptotic cell death in CGC cultures and in hyppocampal CA1 and parietal cortex regions. Our finding can be valuable for neuroprotective therapy strategies in patients with repeated generalized seizures or status epilepticus.

Effects of kainic acid on rat body temperature: unmasking by dizocilpine

The effects of intraperitoneal (i.p.) administration of kainic acid (KA) and dizocilpine, alone or in combination, on body temperature of freely moving rats were examined. Injection of saline or dizocilpine (3.0 or 5.0 mg/kg) was followed after an hour by injection of saline or KA (10 mg/kg) and the body temperature was measured at different time points during the first 5 h. KA alone produced an initial short-lasting hypothermia followed by a longer-lasting hyperthermic effect. Administration of dizocilpine alone produced an early increase in core temperature. Pretreatment of KA-injected rats with dizocilpine potentiated the KA-induced hypothermic effect at 30 min and dose-dependently reduced the temperature measured at 1 h after KA-injection without influencing the ensuing hyperthermia.These data suggest that the KA-induced changes in body temperature do not necessarily involve the activation of NMDA-receptors as opposed to KA-induced behavioural changes that are blocked by dizocilpine in a dose-dependent manner. It is unlikely, therefore, that the KA-induced hyperthermia is a result of the KA-induced seizure motor activity. Furthermore, our findings indicate that KA-induced changes in core temperature may be used as a criterion of drug-responsiveness when the behavioural changes are blocked, e.g. with dizocilpine.