M.G. De Simoni

Neuroprotection by complement (C1) inhibitor in mouse transient brain ischemia.

The authors investigated the effect of the C1 inhibitor (C1-INH), the only known inhibitor of complement C1, in a murine model of transient focal ischemia. Ischemia was induced by intraluminal occlusion of the middle cerebral artery. After 2 hours, reperfusion was produced by removing the nylon monofilament occluding the artery. The effect of 15 U C1-INH (intravenously) was evaluated in terms of general and focal neurologic deficits, ischemic volume, neutral red staining (to identify the brain areas subject to ischemic damage), and glial fibrillary acidic protein immunoreactivity (to show astrocytic response). Forty-eight hours after ischemia, C1-INH significantly improved general and focal deficits by 36% and 54%, respectively, and significantly reduced infarct volume (CI-INH, 6.69% ± 2.93%; saline, 24.24% ± 8.24%) of total brain. Neutral red staining further showed the strong protective effect of C1-INH in cortex, hippocampus, and striatum. Astrocyte activation induced by ischemia was not affected by C1-INH. These findings show that C1-INH displayed a potent neuroprotective action by effectively reducing ischemia—reperfusion injury.

Glutamate release in the nucleus tractus solitarius induced by peripheral lipopolysaccharide and interleukin-1β

The involvement of vagal afferents in the communication pathway from the immune system to the brain was studied. Glutamate was measured in the nucleus tractus solitarius, the brain area receiving glutamatergic vagal afferents, after peripheral injection of lipopolysaccharide or interleukin-1 beta. Intraperitoneal or intravenous saline or intraperitoneal heat-inactivated interleukin-1 beta increased glutamate release, measured by brain microdialysis in freely-moving rats at 20 min (137 +/- 19%, 126 +/- 10% and 133 +/- 6%, respectively), without inducing any other change up to 3 h after injection. Intraperitoneal lipopolysaccharide (10 micrograms/rat) increased glutamate at 20 min (132 +/- 10%) and at 60 min (208 +/- 26%). To compare lipopolysaccharide effectiveness by the two routes, serum levels of interleukin-1 beta, interleukin-6 and tumour necrosis factor-alpha were measured. Intravenous lipopolysaccharide induced each cytokine more rapidly and efficiently than intraperitoneal lipopolysaccharide. Perfusion with tetrodotoxin (1 microM) in the dialysis probe decreased glutamate basal levels by approximately 20% and completely prevented lipopolysaccharide effects, showing the neuronal component of the glutamate measured. Except for the 20-min increase, intravenous lipopolysaccharide (10 micrograms/rat) did not affect glutamate release. Intraperitoneal interleukin-1 beta (4 micrograms/rat) increased glutamate release at 20 min (126 +/- 6%) and at 40 min (150 +/- 18%). These data indicate that vagal glutamatergic system in the nucleus tractus solitarius is activated by intraperitoneal injections of immunoactive compounds.

Changes in the serotonergic system during the sleep-wake cycle: Simultaneous polygraphic and voltammetric recordings in hypothalamus using a telemetry system

Changes in the serotonergic system in the posterior hypothalamus of freely moving rats were related to sleep and wakefulness using in vivo voltammetry (with carbon fiber microelectrodes) and polygraphic recordings. By using an optoelectronic telemetry system for the voltammetric signals, electrical cross-talk between the two settings was avoided and simultaneous neurochemical and electro-physiological recordings could be made so that a detailed time course of events could be obtained. Extracellular levels of the serotonin metabolite, 5-hydroxy-indoleacetic acid, measured every 2 min, increased with wakefulness and decreased with sleep: levels were significantly lower during desynchronized sleep than slow wave sleep. In vivo voltammetry associated with the optoelectronic telemetry system appears to be a useful tool for studying the relationship between neurochemical changes and electrophysiological events.

Peripheral Inflammatory Response in Alzheimer's Disease and Multiinfarct Dementia

Whether peripheral inflammatory molecules can be considered markers of dementia is still an open issue. We have investigated the presence of circulating cytokines and the ability of blood cells to release them in response to an inflammatory stimulus in patients with different types of dementia and in age-matched controls. A significant increase in circulating interleukin-1beta in moderate Alzheimer and in multiinfarct (145 and 224 times control concentration, respectively) dementia and in circulating tumor necrosis factor-alpha concentration in multiinfarct dementia patient group (156%) were found. Tumor necrosis factor-alpha and interleukin-6 released from blood cells after exposure to lipopolysaccharide were significantly reduced in moderate Alzheimer (60%, both cytokines) and multiinfarct patients (71 and 50%, respectively), while interleukin-10 was decreased only in multiinfarct patients (61%). The results show that patients with Alzheimer disease or multiinfarct dementia have an upregulation of circulating cytokines and a downregulation of cytokines released by blood cells.

The sympathetic nervous system tonically inhibits peripheral interleukin-1β and interleukin-6 induction by central lipopolysaccharide

To study the role of the sympathetic nervous system in the induction of inflammatory cytokines elicited by central lipopolysaccharide, sympathetic chemical denervation was performed by intraperitoneal injection of 6-hydroxydopamine. Rats received the neurotoxin according to the following schedule: 50 mg/kg on days 1 and 2, 100 mg/kg on days 3, 4 and 7. On day 8, lipopolysaccharide (2.5 microg/6 microl/rat) was injected intracerebroventricularly and rats were killed 2 h later. 6-Hydroxydopamine reduced noradrenaline and dopamine content in the spleen by 88.7% and 88.8% respectively, without affecting striatal contents indicating that the chemical sympathectomy had been effective and selective. In sympathectomized rats, lipopolysaccharide raised interleukin-1beta and interleukin-6 serum levels more than in control rats given the vehicle. Tumour necrosis factor-alpha serum levels in sympathectomized rats were no different from those in vehicle-treated rats. Interleukin-1beta and interleukin-6 messenger RNA expression, measured by northern blot analysis, was clearly detectable in adrenals and spleen of rats given lipopolysaccharide. Sympathectomy increased lipopolysaccharide-induced interleukin-1beta and interleukin-6 messenger RNA in adrenals and spleen. Corticosterone basal levels were raised by central lipopolysaccharide and not further changed by sympathectomy. The present study shows that sympathetic nervous system denervation enhances the synthesis and production of peripheral interleukin-1beta and interleukin-6 in rats given central lipopolysaccharide and suggests a tonic inhibitory control of the sympathetic nervous system on these inflammatory cytokines.

Permissive role of glucocorticoids on interleukin-1 activation of the hypothalamic serotonergic system.

The present study analyses the effect of IL-1 beta (10 ng i.c.v.) on the hypothalamic serotonergic system and the modulatory role of glucocorticoids. Changes in the serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA) were recorded in freely moving rats by in vivo voltammetry using chronically implanted carbon fiber electrodes (8 microns) in the medial preoptic area. IL-1 beta induced a dual increase in 5HIAA levels: a rapid, short-term rise was followed by a lasting increase possibly due to newly synthesized IL-1. The synthetic glucocorticoid dexamethasone (DEX, 3 mg/kg i.p., 30 min before IL-1 beta), prevented the effect of IL-1 beta starting from 150 min, suggesting that it only inhibited the second increase. In adrenalectomized rats IL-1 beta had no effect but when these rats were given DEX (40 micrograms/kg a day for 3 days) the short-term increase was restored. The glucocorticoid receptor antagonist RU38486 (25 mg/kg s.c., 60 min before IL-1 beta) completely prevented IL-1 beta activation of the serotonergic system. The results indicate that the glucocorticoids are effective inhibitors of IL-1 synthesis but that they play a permissive role on IL-1 beta induced activation of the serotonergic system.

Multiple and complex effects of buspirone on central dopaminergic system.

The effects of the anxiolytic drug buspirone and its metabolite 1-PP on the dopaminergic system were investigated. A single buspirone administration was found to decrease DA levels and increase its metabolite DOPAC in striatal samples. The levels of the other DA metabolite, 3MT, were unaffected; however its formation rate after inhibition of its metabolism, was found to be increased by buspirone. 1-PP did not affect either DOPAC or 3MT levels and formation. Striatal microdialysis showed that buspirone enhances DA release. In vivo voltammetry indicates that the increase of DA metabolism is identical in the two sampled dopaminergic areas, striatum and nucleus accumbens. On the basis of the results obtained ex vivo and in vivo the multiple effect of buspirone on dopaminergic system is discussed.

Miniaturized optoelectronic system for telemetry of in vivo voltammetric signals.

In vivo voltammetry is an electrochemical technique that uses carbon fiber microelectrodes stereotaxically implanted in brain areas to monitor monoamine metabolism and release continuously, in freely moving animals. Electric wires connect the polarograph to the animal. A wire-less transmission system (optoelectronic transmission, OPT) of voltammetric signals is described here. It uses infrared diffused light, exploiting the diffusion of the transmitted light over walls and ceiling towards a receiver. The transmission system consists of a main unit and a satellite unit (40 x 30 x 5 mm) positioned on the animals back. Voltammetric recordings obtained by the classical system (with wires) and by OPT are well defined and almost identical in shape. The power supply is provided by two thin lithium batteries (+/- 3V) that can record for up to 20 h. OPT permits detailed behavioral observations since the animal can be left free to move in a spacious environment. Voltammetry using OPT allows simultaneous recording of neuronal firing activity as well as electroencephalographic recordings (EEG) since there is no cross-talk between the circuits used. The results illustrate the reliability and usefulness of this wire-less transmission system for studying relationships between neurochemical, behavioral and electrophysiological activities.

Hypothalamic serotonergic activity correlates better with brain temperature than with sleep-wake cycle and muscle tone in rats

The activity of the serotonergic system varies in phase with the sleep-wake cycle, which is associated with changes in several physiological functions, including electroencephalographic activity, brain temperature, and locomotion. The aim of the present study was to clarify which of these parameters correlates better with serotonergic activity in spontaneous conditions. Voltammetric recordings by telemetry of serotonergic metabolism in the medial preoptic area and polygraphic recordings of sleep-wake activity (by means of electroencephalographic delta band, brain cortical temperature and neck electromyographic activity recordings) were simultaneously performed in freely moving rats. Univariate analyses of variance revealed that each variable under investigation was statistically correlated with serotonergic metabolism. When the variables were entered into the model simultaneously, both partial correlation and step-wise multiple regression analyses indicated that the highest correlation exists between serotonergic metabolism and brain cortical temperature. The present data show that serotonergic activity in the medial preoptic area is closely linked to physiological changes in brain temperature.

Impaired central stress-induced release of noradrenaline in rats with heart failure: A microdialysis study

Sympathetic hyperactivity in rats with heart failure is associated with increased extracellular noradrenaline in the hypothalamic paraventricular nucleus at rest. However, it is unknown how this nucleus responds to stressful stimuli. In the present study we therefore examined the basal and stress-induced release of noradrenaline in the paraventricular nucleus of conscious Sprague-Dawley rats with heart failure measured by in vivo microdialysis. Basal noradrenaline concentration in the paraventricular nucleus of rats with heart failure was more than double that in sham-operated controls. Immobilization stress decreases noradrenaline levels in the paraventricular nucleus of rats with heart failure to 57% of baseline, while it increased in sham-operated controls to 228%. However, serum corticosterone was similarly elevated at 30 and 90 min post-stress in both experimental groups. We have shown that heart failure causes an impairment of the central noradrenergic systems response to acute sympatho-excitation but does not affect the hypothalamo-pituitary-adrenocortical response.