Sub-chronic celecoxib prevents soluble beta amyloid-induced depressive-like behaviour in rats.

BACKGROUND: Depression and Alzheimer's disease (AD) are co-morbid conditions. Neuropsychiatric symptoms have been reported as prodromal symptoms of AD-like dementia and soluble forms of beta amyloid peptide (Aß), the main constituent of insoluble plaques typical of AD brains, have been implicated in such an effect. We have previously shown that intracerebral injection of Aß can evoke a depressive-like state in rats, accompanied by neurochemical and neuroendocrine alterations reminiscent of depressive symptoms in humans. AD and depression are crucially linked by neuroinflammation and cyclooxygenase II (COX-2) enzyme involvement is an intriguing field of research. Indeed, its pharmacological inhibition has shown both antidepressant and Aß modulating effects. METHODS: Male rats were exposed to sub-chronic celecoxib (15 mg/kg/day sc for 8 days), a selective COX-2 inhibitor or vehicle (saline), starting from the day before central intracerebroventricular injection of Aß peptide (5µL of 4 µM solution or vehicle for sham). Animals were tested for depressive-like behaviour by using the forced swimming test paradigm and prefrontal serotonin (5-HT) content and plasma Aß levels were further evaluated. RESULTS: We found that celecoxib treatment prevented the pro-depressive effects induced by Aß. Moreover, it also prevented the reduction in 5-HT content in prefrontal cortex of Aß-treated rats and decreased their plasma Aß levels. CONCLUSIONS: Taken together, our data indicate that celecoxib could be a suitable pharmaceutical tool for the treatment of depressive state related to increased Aß levels.

N-3 PUFA diet enrichment prevents amyloid beta-induced depressive-like phenotype.

Among neuropsychiatric diseases, depression is one of the most prevalent. Many pathologies have been indicated as comorbid with depression and in particular, neurodegenerative disorders such as Alzheimer's diseases (AD). In this regard, several evidences endorse a strong relationship between depression and AD, so much that this mental illness has been proposed either as a risk factor for AD or as a prodromic AD phase. Furthermore, amyloid beta (Aß) peptide, the main constituent of amyloid plaques commonly considered the principal hallmark of AD brains, has been shown to be increased, in its soluble form, in depressed patients. Accordingly, we have previously found that Aß, intracerebroventricularly (i.c.v.) injected, is able to evoke a depressive-like profile in rats accompanied by low cortical serotonin and reduced neurotrophin content. Taking into account the great increase in AD and depression prevalence, many environmental factors have been under study, particularly dietary factors, and the role of polyunsaturated fatty acids (PUFA) is becoming central in this field of research. Thus, aim of the present study was to evaluate the neurobehavioral effects of lifelong exposure to either n-3 PUFA rich or n-3 PUFA poor diet after Aß central administration. Results showed that n-3 PUFA enriched diet prevented the Aß- induced depressive-like behaviors, as reveled by the reduction in the immobility time in the FST test. Furthermore, n-3 PUFA rich diet exposure reverted also serotonin and neurotrophin level reduction in prefrontal cortex of Aß treated rats. Taken together, our data support the concept that supplementation of diet with n-3 PUFA represents a valid approach to reduce the risk of developing depressive symptoms, as well as reducing the risk of Aß-related pathologies, such as AD.

The NADPH oxidase NOX2 as a novel biomarker for suicidality: evidence from human post mortem brain samples.

Recent evidence points towards a role of oxidative stress in suicidality. However, few studies were carried out on the sources of reactive oxygen species (ROS) in subjects with suicidal behaviour. We have previously demonstrated that the NADPH oxidase NOX2-derived oxidative stress has a major role in the development of neuropathological alterations observed in an animal model of psychosis. Here, we investigated the possible increase in NOX2 in post mortem brain samples of subjects who died by asphyctic suicide (AS) compared with controls (CTRL) and subjects who died by non-suicidal asphyxia (NSA). We found that NOX2 expression was significantly higher in the cortex of AS subjects than in the other two experimental groups. NOX2 immunostaining was mainly detected in GABAergic neurons, with a minor presence of NOX2-positive-stained cells in glutamatergic and dopaminergic neurons, as well as astrocytes and microglia. A sustained increase in the expression of 8-hydroxy-2'-deoxyguanosine, an indirect marker of oxidative stress, was also detected in the cortex of AS subjects, compared with CTRL and NSA subjects. A significant elevation in cortical interleukin-6 immunoreactivity in AS subjects suggested an involvement of cytokine-associated molecular pathways in NOX2 elevations. Our results suggest that the increase in NOX2-derived oxidative stress in the brain might be involved in the neuropathological pathways leading to suicidal behaviour. These results may open innovative insights in the identification of new pathogenetic and necroscopic biomarkers, predictive for suicidality and potentially useful for suicide prevention.

Endocannabinoid signaling in Alzheimer’s disease: current knowledge and future directions.

The importance of the endocannabinoid system (ECS) in the modulation functions of the central nervous system has been extensively investigated during the last few years. In particular, accumulated evidence has implicated ECS in the pathophysiology of Alzheimer’s disease (AD), that is a progressive, degenerative, and irreversible disorder characterized by the accumulation in the brain of beta-amyloid fragments forming insoluble plaques, and of intracellular neurofibrillary tangles (NTFs) associated with synaptic and neuronal loss. In all the processes involved in the formation of both plaques and NFTs, the key-role played by the ECS has been documented. Here, we review current knowledge and future directions of ECS modulation both in animal models of AD and in human tissues, underlying the role of endocannabinoid signaling in the development of AD hallmarks. Overall, the available data suggest that next generation therapeutics might target distinct ECS elements, for instance CB2 receptor or fatty acid amide hydrolase, as a promising approach to halt or at least to slow down disease progression.

Nimodipine inhibits IL-1ß release stimulated by amyloid ß from microglia.

BACKGROUND AND PURPOSE: There is growing evidence that inflammation plays a major role in the pathogenesis of neural damage caused by deposition of amyloid ß (Aß) in the brain. Nimodipine has received attention as a drug that might improve learning and reduce cognitive deficits in Alzheimer's disease, but the mechanism of action is poorly known. In this study, we tested the hypothesis that nimodipine inhibited Aß-stimulated IL-1ß release from microglia. EXPERIMENTAL APPROACH: Cultures of N13 microglia cells or primary mouse microglia were treated with nimodipine, and intracellular accumulation and release of IL-1ß in response to Aß or to the P2 receptor agonists ATP and benzoyl ATP (BzATP) were measured. Accumulation of IL-1ß was measured in vivo after intrahippocampal inoculation of Aß in the absence or presence of nimodipine. The effect of nimodipine on Aß-triggered cytotoxicity was also investigated. KEY RESULTS: We show here that nimodipine dose-dependently inhibited Aß-stimulated IL-1ß synthesis and release from primary microglia and microglia cell lines. Furthermore, nimodipine also inhibited Aß-induced IL-1ßin vivo accumulation at concentrations known to be reached in the CNS. Finally, nimodipine protected microglia from Aß-dependent cytotoxicity. CONCLUSION AND IMPLICATIONS: These data suggest that alleviation of symptoms of Alzheimer's disease following nimodipine administration might be due to an anti-inflammatory effect and point to a novel role for nimodipine as a centrally acting anti-inflammatory drug.

NADPH oxidase elevations in pyramidal neurons drive psychosocial stress-induced neuropathology.

Oxidative stress is thought to be involved in the development of behavioral and histopathological alterations in animal models of psychosis. Here we investigate the causal contribution of reactive oxygen species generation by the phagocyte NADPH oxidase NOX2 to neuropathological alterations in a rat model of chronic psychosocial stress. In rats exposed to social isolation, the earliest neuropathological alterations were signs of oxidative stress and appearance of NOX2. Alterations in behavior, increase in glutamate levels and loss of parvalbumin were detectable after 4 weeks of social isolation. The expression of the NOX2 subunit p47(phox) was markedly increased in pyramidal neurons of isolated rats, but below detection threshold in GABAergic neurons, astrocytes and microglia. Rats with a loss of function mutation in the NOX2 subunit p47(phox) were protected from behavioral and neuropathological alterations induced by social isolation. To test reversibility, we applied the antioxidant/NOX inhibitor apocynin after initiation of social isolation for a time period of 3 weeks. Apocynin reversed behavioral alterations fully when applied after 4 weeks of social isolation, but only partially after 7 weeks. Our results demonstrate that social isolation induces rapid elevations of the NOX2 complex in the brain. Expression of the enzyme complex was strongest in pyramidal neurons and a loss of function mutation prevented neuropathology induced by social isolation. Finally, at least at early stages, pharmacological targeting of NOX2 activity might reverse behavioral alterations.

Extraction, characterization and in vivo neuromodulatory activity of phytosterols from microalga Dunaliella tertiolecta.

In recent years, a great deal of research has been devoted to identify new natural sources of phytosterols and to improve methods for their recovery and purification. In this regard, unexplored natural sources of bioactive ingredients are gaining much attention since they can lead to the isolation of new compounds or bioactivities. The field of available natural sources has been further increased by including algae and, even more interestingly, microalgae. In the present study, a multidisciplinary approach has been used considering, in an integrated view, extraction, chemical composition and bioactivity of phytosterols from the microalga Dunaliella tertiolecta. A novel methodology to extract, separate and characterize microalgal-derived phytosterols has been developed. In addition, recoverable and reusable eluents have been selected in order to reduce the quantities of employed organic solvents. Finally, we addressed the question whether orally administered phytosterols reach the brain and if those interfere with the major neurotransmitter systems, such as the dopaminergic, serotoninergic and noradrenergic ones, in several brain areas of rats. Flash Liquid Chromatography has been used to separate the Total Sterol (TS) fraction, composed of twelve sterols, with a purity of 97.87% and a recovery percentage of 98%, while the "flash version" of Silver Ion Liquid Chromatography has been used to purify the most abundant phytosterols in TS, (22E,24R)- methylcholesta-5,7,22-trien-3ß-ol (ergosterol) and (22E,24R)-ethylcholesta-5,7,22-trien-3ß-ol (7-dehydroporiferasterol), with a purity of 97.4%. These two combined methods did not need sophisticated technologies but only cheap laboratory supplies. Moreover, the possibility of recovering and recycling the solvents used as eluents made it a cleaner process. Finally, for the first time, a neuromodulatory action of Dunaliella tertiolecta-derived phytosterols has been found in selective brain areas of rats.

Estrous cycle affects the neurochemical and neurobehavioral profile of carvacrol-treated female rats.

Carvacrol is the major constituent of essential oils from aromatic plants. It showed antimicrobial, anticancer and antioxidant properties. Although it was approved for food use and included in the chemical flavorings list, no indication on its safety has been estimated. Since the use of plant extracts is relatively high among women, aim of this study was to evaluate carvacrol effects on female physiology and endocrine profiles by using female rats in proestrus and diestrus phases. Serotonin and metabolite tissue content in prefrontal cortex and nucleus accumbens, after carvacrol administration (0.15 and 0.45g/kg p.o.), was measured. Drug effects in behavioral tests for alterations in motor activity, depression, anxiety-related behaviors and endocrine alterations were also investigated. While in proestrus carvacrol reduced serotonin and metabolite levels in both brain areas, no effects were observed in diestrus phase. Only in proestrus phase, carvacrol induced a depressive-like behavior in forced swimming test, without accompanying changes in ambulation. The improvement of performance in FST after subchronic treatment with fluoxetine (20mg/kg) suggested a specific involvement of serotonergic system. No differences were found across the groups with regard to self-grooming behavior. Moreover, in proestrus phase, carvacrol reduced only estradiol levels without binding hypothalamic estradiol receptors. Our study showed an estrous-stage specific effect of carvacrol on depressive behaviors and endocrine parameters, involving serotonergic system. Given the wide carvacrol use not only as feed additive, but also as cosmetic essence and herbal remedy, our results suggest that an accurate investigation on the effects of its chronic exposure is warranted.

Soluble beta amyloid(1-42): a critical player in producing behavioural and biochemical changes evoking depressive-related state?

BACKGROUND AND PURPOSE: Depression is common in early phases of Alzheimer's disease (AD) and may represent prodromal symptoms of dementia. Recent reports suggest that early memory deficits and neuropsychiatric symptoms are caused by soluble rather than aggregated betaamyloid (Abeta). Thus, we investigated the effects of soluble Abeta(1-42) on working memory and depressive/anxiety-related behaviour in rats and on 5-hydroxytryptaminergic neurotransmission and neurotrophin content in various brain regions. EXPERIMENTAL APPROACH: Behavioural reactivity to novel object recognition, open field, elevated plus maze and forced swimming test were assessed 7 days after i.c.v. injection of Abeta(1-42) or its vehicle. BDNF (brain-derived neurotrophic factor) and NGF (nerve growth factor) mRNA and protein levels and 5-hydroxytriptamine (5-HT) content were measured in the prefrontal cortex (PFC), striatum (STR) and nucleus accumbens (NAc). KEY RESULTS: Abeta(1-42) did not affect the ability to distinguish between familiar and novel objects, but Abeta-treated rats exhibited an increase in forced swimming immobility. No differences were revealed between experimental groups in the elevated plus maze test or in self-grooming (evaluated in the open field). In the PFC, but not STR or NAc, Abeta-injected rats exhibited a selective reduction in 5-HT content, BDNF and NGF expression. CONCLUSIONS AND IMPLICATIONS: Our data suggest that soluble Abeta-treated rats have a depressive, but not anxiogenic-like, profile, accompanied by brain region-dependent alterations in the expression of neurotrophins and 5-hydroxytryptaminergic neurotransmission. Hence, these alterations induced by soluble Abeta might be sensitive indicators of early phases of AD and possible risk factors for the expression of neuropsychiatric symptoms in AD.

Soluble amyloid beta1-42 reduces dopamine levels in rat prefrontal cortex: relationship to nitric oxide.

Several studies suggest a pivotal role of amyloid beta (Abeta)(1-42) and nitric oxide (NO) in the pathogenesis of Alzheimer's disease. NO also possess central neuromodulatory properties. To study the soluble Abeta(1-42) effects on dopamine concentrations in rat prefrontal cortex, microdialysis technique was used. We showed that i.c.v. injection or retrodialysis Abeta(1-42) administration reduced basal and K(+)-stimulated dopamine levels, measured 2 and 48 h after peptide administration. Immunofluorescent experiments revealed that after 48 h from i.c.v. injection Abeta(1-42) was no longer detectable in the ventricular space. We then evaluated the role of NO on Abeta(1-42)-induced reduction in dopamine concentrations. Subchronic L-arginine administration decreased basal dopamine levels, measured either 2 h after i.c.v. Abeta(1-42) or on day 2 post-injection, whereas subchronic 7-nitroindazole administration increased basal dopamine concentrations, measured 2 h after i.c.v. Abeta(1-42) injection, and decreased them when measured on day 2 post-Abeta(1-42)-injection. No dopaminergic response activity was observed after K(+) stimulation in all groups. These results suggest that the dopaminergic system seems to be acutely vulnerable to soluble Abeta(1-42) effects. Finally, the opposite role of NO occurring at different phases might be regarded as a possible link between Abeta(1-42)-induced effects and dopaminergic dysfunction.

Prenatal exposure to the cannabinoid receptor agonist WIN 55,212-2 and carbon monoxide reduces extracellular glutamate levels in primary rat cerebral cortex cell cultures.

The effects of prenatal exposure to the cannabinoid receptor agonist WIN 55,212-2 (0.5 mg/kg s.c.), alone or in combination with carbon monoxide, on extracellular glutamate levels in primary rat cerebral cortical neuronal cultures, were investigated. Dam weight gain, pregnancy length and litter size at birth were not affected by prenatal treatment with WIN 55,212-2 and carbon monoxide alone or in combination. Basal and K(+)-evoked extracellular glutamate levels were reduced in cortical cultures from pups born to mothers exposed to WIN 55,212-2 and carbon monoxide alone or in combination compared to cultures from rats born to vehicle-treated mothers. In cultures obtained from rats exposed to vehicle or carbon monoxide alone during gestation, WIN 55,212-2 (0.01-100 nM) increased extracellular glutamate levels, displaying a bell-shaped concentration-response curve. In cultures from rats born to mothers exposed to WIN 55,212-2 alone or in combination with carbon monoxide the WIN 55,212-2 ( 1 nM)-induced increase in extracellular glutamate levels was lower than that observed in cultures from rats born to vehicle-treated mothers and similar at those observed at 10 and 100 nM concentrations. The selective CB1 receptor antagonist SR141716A (10 nM) counteracted the WIN 55,212-2-induced increase in extracellular glutamate levels in cultures exposed to vehicle or carbon monoxide during gestation, but failed to antagonise it in cultures from rats born to mothers exposed to WIN 55,212-2 alone or in combination with carbon monoxide. These findings provide evidence that prenatal exposure to the cannabinoid receptor agonist WIN 55,212-2 and carbon monoxide, alone or in combination, is associated with an impairment in cortical glutamatergic transmission. It could be speculated that such detrimental effects might be involved in the reported deficit in learning and memory associated with prenatal marijuana exposure.

Combined chronic treatment with citalopram and lithium does not modify the regional neurochemistry of nitric oxide in rat brain.

A substantial number of patients do not respond sufficiently to antidepressant drugs and are therefore often co-medicated with lithium as an augmentation strategy. Also inhibitors of nitric oxide synthase (NOS) have been used as an augmentation strategy, while inhibitors of NOS exhibit antidepressant-like properties in various animal models. Therefore, we hypothesized that modulation of NOS may be involved in the long-term effects of antidepressants and lithium, and studied the influence of acute and chronic administration of citalopram, alone or in combination with lithium, on NOS activity in hippocampus, cerebellum, and frontal cortex, by determination of L-citrulline being formed. We found that administration of acute or chronic citalopram (5 mg/kg and 20 mg/kg/24h, respectively) alone or in combination with subchronic lithium (60 mmol/kg chow pellet) did not influence the activity of NOS ex vivo in all regions compared to control. In contrast, high doses of lithium caused a significant decrease in NOS activity in vitro. We conclude that basal conditions are unsuitable for the study of antidepressant effects on NOS, and that the neurochemistry of nitric oxide remains unaltered following chronic citalopram or subchronic lithium under normal physiological conditions.

Long-term effects on cortical glutamate release induced by prenatal exposure to the cannabinoid receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinyl-methyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone: an in vivo microdialysis study in the awake rat.

The aim of the present in vivo microdialysis study was to investigate whether prenatal exposure to the CB(1) receptor agonist WIN55,212-2 mesylate (WIN; (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinyl-methyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone), at a dose of 0.5 mg/kg (s.c. from the fifth to the 20th day of gestation), that causes neither malformations nor overt signs of toxicity, influences cortical glutamate extracellular levels in adult (90-day old) rats. Dam weight gain, pregnancy length and litter size at birth were not significantly affected by prenatal treatment with WIN. Basal and K(+)-evoked dialysate glutamate levels were lower in the cerebral cortex of adult rats exposed to WIN during gestation than in those born from vehicle-treated mothers. In both group of animals WIN (0.1 mg/kg, i.p.) increased dialysate glutamate levels. However, while the blockade of the CB1 receptors with the selective receptor antagonist SR141716A completely counteracted the WIN-induced increase in those rats exposed to vehicle during gestation, it failed to antagonise the increase in those born from WIN-treated dams. These findings suggest that prenatal exposure to the CB1 receptor agonist WIN, at a concentration which is not associated with gross malformations and/or overt signs of toxicity, induces permanent alterations in cortical glutamatergic function. The possibility that these effects might underlie, at least in part, some of the cognitive deficits affecting the offspring of marijuana users is discussed.

Prenatal low-level exposure to CO alters postnatal development of hippocampal nitric oxide synthase and haem-oxygenase activities in rats.

The effects of prenatal CO exposure (150 ppm from days 0 to 20 of pregnancy) on the postnatal development of hippocampal neuronal NO synthase (nNOS) and haem-oxygenase (HO-2) isoform activities in 15-, 30- and 90-d-old rats were investigated. Unlike HO-2, hippocampal nNOS activity increased from postnatal days 15-90 in controls. Prenatal CO produced a long-lasting decrease in either nNOS or HO-2. The results suggest that the altered developmental profile of hippocampal nNOS and HO-2 activities could be involved in cognitive deficits and long-term potentiation dysfunction exhibited by rats prenatally exposed to CO levels resulting in carboxyhaemoglobin (HbCO) levels equivalent to those observed in human cigarette smokers.

Effects of ENA713 and CHF2819, two anti-Alzheimer's disease drugs, on rat amino acid levels.

The effects of oral ENA713 and CHF2819 (0.5, 1.5 and 4.5 mg/kg), two novel acetylcholinesterase inhibitors, on extracellular concentrations of amino acids in rat hippocampus, were evaluated using in vivo microdialysis. ENA713, at 4.5 mg/kg, but not CHF2819, significantly decreased glutamate, taurine, arginine and citrulline levels, without affecting aspartate concentrations. These results suggest that the modulation of amino acidergic transmission could represent an additional mechanism of action in Alzheimer's disease for some acetylcholinesterase inhibitors.

Neurofunctional effects of developmental alcohol exposure in alcohol-preferring and alcohol-nonpreferring rats.

The neurofunctional effects of developmental alcohol exposure (3% v/v solution from day 15 of gestation to day 7 after parturition) have been investigated in Sardinian alcohol-preferring (sP) and alcohol-nonpreferring (sNP) rat lines, selectively bred for opposite alcohol preference and consumption. Alcohol exposure significantly decreased the rate of ultrasonic emission in sP male pups; whereas, it did not affect this indicator of emotional reactivity in sNP animals. Perinatal alcohol intake did not influence either learning of an active avoidance task or hippocampal long-term potentiation in both offspring lines. Significant differences in time spent exploring novel objects were observed between control sP and sNP rats subjected to the novel exploration object test. Alcohol exposed sP rats, but not alcohol exposed sNP rats, apparently lost the capacity to discriminate between the novel and the familiar object, even though this difference is difficult to interpret because of the large differences in the respective responses to the novel objects. Neurochemical experiments have shown that basal levels of dopamine (DA) and homovanillic acid (HVA) were significantly higher in the nucleus accumbens (NAC) of sP rats with respect to sNP animals. Perinatal alcohol did not affect basal DA and HVA concentrations or amphetamine-induced DA increase and HVA decrease in the NAC of either sP or sNP offspring. These results suggest that subtle behavioral alterations induced by developmental exposure to low doses of alcohol, which do not cause malformations and/or overt neurotoxicity, may be associated with genetic factors, although not necessarily those responsible for differences in alcohol preference.

Prenatal exposure to low levels of carbon monoxide alters sciatic nerve myelination in rat offspring.

Prenatal exposure to low concentrations of carbon monoxide (CO, 75 and 150 ppm from day 0 to day 20 of gestation), resulting in maternal blood HbCO concentrations equivalent to those maintained by human cigarette smokers, leads to subtle myelin alterations in the sciatic nerve of male rat offspring. The rapid growth spurt in pup body weight was related to the period of maximal increase in myelin sheath thickness in both control and CO-exposed animals. A significant reduction in myelin sheath thickness of sciatic nerve fibers, paralleled by changes in the frequency distribution, occurred in both 40- and 90-day-old rats exposed in utero to CO (75 and 150 ppm). Myelin deficit observed in 75 and 150 ppm CO-exposed animals showed up only after the major spurt in myelination but not early during development. The subtle myelin alterations observed in CO-exposed offspring were not accompanied by changes in developmental pattern of axon diameters and did not result in a gross impairment of motor activity. These results suggest that the myelination process is selectively targeted by a prenatal exposure model simulating the CO exposure observed in human cigarette smokers.

Prenatal exposure model simulating CO inhalation in human cigarette smokers: sphingomyelin alterations in the rat sciatic nerve.

Prenatal exposure to low concentrations of carbon monoxide (CO, 150 ppm) causes long-term alterations in sphingomyelin (SM) homeostasis in peripheral nervous system, but not brain of male rat offspring. In particular, unlike sphinganine (intermediate of complex sphingolipid biosynthesis de novo), the concentrations of sphingosine (intermediate of complex sphingolipid turnover) were increased by 2.35-fold in the sciatic nerve of CO-exposed offspring with respect to controls (P<0.05, overall one-way ANOVA). These subtle alterations were not accompanied by changes in motor activity (F=0.25, df=1/10, n.s., overall one-way-ANOVA). The results suggest that the SM homeostasis in the sciatic nerve is particularly susceptible to prenatal CO exposure resulting in maternal carboxyhaemoglobin (HbCO) levels equivalent to those found in human cigarette smokers.

Serotonergic modulation of rat pineal gland activity: in vivo evidence for a 5-Hydroxytryptamine(2C) receptor involvement.

There are some suggestions that, in the pineal gland, serotonin acts not only as a precursor of melatonin but also plays a role in the modulation of the pineal biosynthetic activity. To corroborate this possible neuromodulatory role of 5-hydroxytryptamine (serotonin) (5-HT) on the pineal gland, the effects of two 5-HT(2) receptor agonists meta-chlorophenylpiperazine (m-CPP) and 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane were assessed in vivo on pineal N-acetyltransferase (NAT) activity and melatonin content in rats. m-CPP potentiated the enhancement of NAT activity and pineal melatonin content induced by isoproterenol administration during daytime, whereas it did not affect the diurnal basal biosynthetic activity of the gland. At night, m-CPP and 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane enhanced significantly the physiological increases in both pineal NAT activity and melatonin content. This enhancement was prevented by pretreatment with N-(1-methyl-5-indolyl)-N'-(3-pyridyl) urea hydrochloride, an antagonist with higher affinity for 5-HT(2B/C) than for 5-HT(2A) receptor, as well as by pretreatment with 8-[5-(2, 4-dimethoxy-5-(4-trifluoromethyl-phenylsulphonamido)-phenyl-5-o xopent hyl]-1,3,8-triazospiro[4,5]decane-2,4-dione, the most specific 5-HT(2C) receptor now available, but not by pretreatment with ketanserin, an antagonist with higher affinity for 5-HT(2A) than for 5-HT(2C) receptor. These results suggest that 5-HT(2C) receptors are likely involved in the mediation of the serotonergic modulation of pineal biosynthetic activity in rats.

Nitric oxide can differentially modulate striatal neurotransmitter concentrations via soluble guanylate cyclase and peroxynitrite formation.

In vivo microdialysis was used to investigate whether nitric oxide (NO) modulates striatal neurotransmitter release in the rat through inducing cyclic GMP formation via soluble guanylate cyclase or formation of peroxynitrite (ONOO(-)). When NO donors, S-nitroso-N-acetyl-DL-penicillamine (SNAP; 1 mM) or (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1, 2-diolate (NOC-18; 1 mM), were retrodialysed for 15 min, acetylcholine (ACh), serotonin (5-HT), glutamate (Glu), gamma-aminobutyric acid (GABA), and taurine levels were significantly increased, whereas those of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) were decreased. Only effects on ACh, 5-HT, and GABA showed calcium dependency. Inhibition of soluble guanylate cyclase by 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ; 100 and 200 microM) dose-dependently reduced NO donor-evoked increases in ACh, 5-HT, Glu, and GABA levels. Coperfusion of SNAP or NOC-18 with an ONOO(-) scavenger, L-cysteine (10 mM) resulted in enhanced concentrations of Glu and GABA. On the other hand, DA concentrations increased rather than decreased, and no reductions in DOPAC and 5-HIAA occurred. This increase in DA and the potentiation of Glu and GABA were calcium-dependent and prevented by ODQ. Similar to NO, infusions of ONOO(-) (10 or 100 microM) decreased DA, DOPAC, and 5-HIAA. Overall, these results demonstrate that NO increases ACh, 5-HT, Glu, and GABA levels primarily through a cyclic GMP-dependent mechanism. For DA, DOPAC, and 5-HIAA, effects are determined by levels of ONOO(-) stimulated by NO donors. When these are high, they effectively reduce extracellular concentrations through oxidation. When they are low, DA concentrations are increased in a cyclic GMP-dependent manner and may act to facilitate Glu and GABA release further. Thus, changes in brain levels of antioxidants, and the altered ability of NO to stimulate cyclic GMP formation during ageing, or neurodegenerative pathologies, may particularly impact on the functional consequences of NO on striatal dopaminergic and glutamatergic function.