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Biomedical subjects

A Philippu

Publications and source records attributed to A Philippu.

At least 19 recordsLinked to original sources
PubMed2004

7-nitroindazole, nNOS inhibitor, attenuates amphetamine-induced amino acid release and nitric oxide generation but not lipid peroxidation in the rat brain.

The aim of the present study was to elucidate whether amphetamine modulates the output of the neurotransmitters glutamate, aspartate, GABA and acetylcholine (ACh) in nucleus accumbens (NAc) as well as the formation of lipid peroxidation (LPO) and nitric oxide (NO). D,L-amphetamine (AMPH, 5 mg/kg, i.p., 4 times every 2 h) was injected into anaesthetized rats and the release of neurotransmitters in the NAc, tissue content of NO and LPO products were determined. While AMPH increased the release of aspartate, GABA and ACh in the NAc, the glutamate release was not affected. Levels of NO and LPO products were elevated in striatum and cortex. Pretreatment with the neuronal NO synthase inhibitor 7-nitroindazole (50 mg/kg, i.p.) was highly effective in abating the rise of the neurotransmitter release and NO generation but failed to influence the intensity of LPO elicited by the AMPH administration. These findings suggest that activation of NO synthesis is a potent factor in the AMPH-induced neurotransmitter release and that activation of NO synthesis and LPO by AMPH are not parallel processes.

Amino Acids↗
PubMed2004

Differential amino acid transmission in the locus coeruleus of Wistar Kyoto and spontaneously hypertensive rats.

In addition to differences in their blood pressure, Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) are known to differ in their emotional behaviour. The neurochemistry underlying these differences is not well understood. In the present study the release rates of the two main regulatory amino acids in the locus coeruleus, glutamate and gamma-aminobutyric acid (GABA), were monitored in WKY rats and SHR to investigate whether basal and/or challenged neurotransmission differs between these strains. The strains differed in their basal blood pressure (WKY 102+/-2 mmHg, SHR 140+/-4 mmHg), as well as in their emotional behaviour, since WKY rats displayed enhanced anxiety-related behaviour in the open field test (time in centre: WKY 197+/-40 s/30 min, SHR 741+/-93 s/30 min). Basal glutamate and GABA release rates did not differ between WKY rats and SHR. A rise in blood pressure induced by intravenous infusion of noradrenaline for 10 min enhanced GABA release in WKY rats by 60%, while no effect was observed in SHR. Glutamate release did not respond to experimental hypertension in both strains. Intravenous infusion of sodium nitroprusside led to a fall in blood pressure, which was less pronounced and was of shorter duration in WKY rats than in SHR. The depressor response had no effect on amino acid release in the locus coeruleus of both strains. Mild stress induced by noise or tail pinch led to slight rises in arterial blood pressure (10 mmHg and 20 mmHg respectively), which were similar in WKY rats and SHR. Tail pinch enhanced the release rates of glutamate and GABA in the locus coeruleus of WKY rats and SHR; however, no strain differences were noted. Noise stress did not significantly influence amino acid release. These findings demonstrate that SHR and WKY rats differ in GABAergic neurotransmission, which is revealed in response to specific cardiovascular challenges, but not to mild stressors. The observed lack of GABA response to blood pressure elevation in SHR may reflect a disturbed mechanism counteracting high blood pressure, possibly contributing to hypertension in this strain.

Amino Acids↗
PubMed2001

Importance of histamine in modulatory processes, locomotion and memory.

Acetylcholine modulates histaminergic transmission via M(1) receptors. On the other hand, cholinergic transmission is modulated by neighbouring histaminergic neurons via H(1), H(2) and H(3) receptors. Dopaminergic and GABAergic neurons are also involved in these modulatory mechanisms. Furthermore, the release of histamine is modulated by glutamatergic neurons and nitric oxide of neuronal origin. The release of histamine in the brain oscillates according to circadian, slow ultradian and fast ultradian rhythms. Ultradian fluctuations have also been observed in the theta- and delta-frequency bands of the EEG spectral power. Simultaneous recordings of histamine outflow and EEG in the hypothalamus revealed that the ultradian histamine release rhythm coincides temporally with ultradian fluctuations in the EEG spectral power. Histamine receptor ligands used in pharmacotherapy, like H(1) and H(2) antagonists, modify the frequency of the EEG fluctuations. Brain histamine seems to be involved in memory processes, since inhibition of histamine synthesis deteriorates, while H(3) antagonists, histamine and histidine improve short-term memory. The latter finding may open new horizons in pharmacological treatment of memory disorders.

Activity Cycles↗
PubMed2001

Role of nitric oxide in the stress-induced release of serotonin in the locus coeruleus.

Serotonergic mechanisms within the locus coeruleus (LC) are thought to be important in various functions including the stress response. In this study we investigated a possible role of nitric oxide (NO) as an intermediary messenger in the regulation of the serotonin (5-HT) neurotransmission within the LC. Using the push-pull superfusion technique coupled with HPLC and electrochemical detection, the in vivo release of 5-HT was determined in time periods of 10 min in the LC of freely moving rats. Superfusion with three different NO donors, SIN-1 (linsidomine), S-nitroso-N-penicillamine (SNAP) or 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPANO) increased 5-HT release in the LC. Superfusion with the precursor of NO, L-arginine, for 1 h led to a sustained increase in 5-HT release. On the other hand, the NOS inhibitor N-methyl-L-arginine methyl ester (L-NAME) did not significantly change the release of 5-HT. Infusion of N-methyl-D-aspartate (NMDA) or kainic acid, as well as exposure of rats to noise stress or tail pinch increased the release of 5-HT in the LC. Superfusion with L-NAME prevented the increase in 5-HT outflow by all these procedures, while the inactive isomer D-NAME had no effect. Taken together, the results of this study suggest that the release of 5-HT in the LC is facilitated by NO. Under resting conditions inhibition of NOS does not appear to substantially influence the release of 5-HT in the LC. However, there seems to be a facilitatory nitrergic influence on serotonergic responses evoked by excitatory amino acid receptor stimulation or various stress stimuli.

Animals↗
PubMed2001

Nitric oxide as modulator of neuronal function.

The gas NO is a messenger that modulates neuronal function. The use of NO donors and NO synthase inhibitors as pharmacological tools revealed that this free radical is probably implicated in the regulation of excitability and firing, in long-term potentiation and long-term depression, as well as in memory processes. Moreover, NO modulates neurotransmitter release. In vivo and in vitro studies have shown that, in all brain structures investigated, endogenous NO modulates the release of several neurotransmitters, such as acetylcholine, catecholamines, excitatory and inhibitory amino acids, serotonin, histamine, and adenosine. In most cases, enhanced NO level in the tissue increases the release of neurotransmitters, although decreasing effects have also been observed. Cyclic 3'-5' guanosine monophosphate and glutamate mediate the modulation of transmitter release by NO. Recent observations suggest that the release of some transmitters is dually influenced by NO. Thus, besides modulation by presynaptically located auto- and heteroreceptors, NO released from nitrergic neurons seems to play a universal role in modulating the release of transmitters in the brain.

Animals↗
PubMed2001

In vivo neurotransmitter release in the locus coeruleus--effects of hyperforin, inescapable shock and fear.

Hyperforin, the main antidepressant constituent of Hypericum perforatum, influences the extracellular concentrations of transmitters in vitro and in vivo. In vivo experiments have shown that hyperforin enhances the extracellular concentrations of dopamine, norepinephrine, serotonin and glutamate in the locus coeruleus. Hyperforin-free Hypericum extract also elevates the extracellular concentrations of dopamine and norepinephrine in the locus coeruleus, but, in contrast to hyperforin, the extracellular concentration of serotonin is diminished. The differing profiles of hyperforin and hyperforin-free Hypericum extract on the extracellular transmitter concentrations point to the presence of an additional biologically active compound in Hypericum perforatum. Inescapable shock increases the release of monoamines and several amino acids, as well as motility, blood pressure and heart rate. Conditioned fear, similar to hyperforin-free Hypericum extract, decreases the release of serotonin in the locus coeruleus. Conditioned fear also leads to tachycardia. The latter finding shows that telemetric heart rate recording is a good index for conditioned fear. In vivo findings confirm the idea that the anti-depressive properties of Hypericum extract and hyperforin result from increases in extracellular neurotransmitter concentrations. Since hyperforin-free extract, like conditioned fear, reduces the extracellular concentration of serotonin, hyperforin may be more beneficial than Hypericum extract in the treatment of depressive disorders.

Animals↗
PubMed2001

Role of histaminergic and cholinergic transmission in cognitive processes.

Mutual modulatory and functional interactions exist between the histaminergic and cholinergic systems in the brain. The activity of histaminergic neurons is permanently modulated by neighboring cholinergic neurons via muscarinic M(1) receptors, cholinergic transmission by histaminergic neurons through H(1), H(2), H(3A) and H(3B) receptors. In the nucleus accumbens, glutamatergic neurons originating from the hippocampus modulate cholinergic transmission in a direct way via stimulation of NMDA receptors located on cholinergic neurons. Additionally, glutamatergic neurons of the hippocampus modulate the activity of cholinergic neurons in an indirect way by stimulating histaminergic neurons within the nucleus accumbens. Reciprocal regulatory influences and neurotransmission are subjected to the global modulatory influence of nitric oxide. Both histaminergic and cholinergic systems in the nucleus accumbens are implicated in the response to aversive stimuli. Memory acquisition is associated with activation of cholinergic transmission in the nucleus accumbens, while stimulation of histaminergic neurons facilitates memory in a way that is independent of the cholinergic system. Hence, both histaminergic and cholinergic transmission within the nucleus accumbens and interactions between the two systems seem to play a predominant role in cognition.

Journal Article↗
PubMed2000

Peripheral chemoreceptor activation enhances 5-hydroxytryptamine release in the locus coeruleus of conscious rats.

Intravenous bolus injection of KCN (40 microg) elicited brief but pronounced tachypnea, bradycardia and pressor response, and led to a 37% increase in 5-hydroxytryptamine (serotonin) (5-HT) release in the locus coeruleus (LC) of freely moving rats. Slow infusion of KCN (15 microg/min) for 10 min induced only a slight pressor response, but increased the respiration rate (+39 breaths/min), as well as 5-HT release in the LC (+60%) throughout the infusion. In rats with transected chemoreceptor afferents, neither injection or infusion of KCN changed 5-HT release, suggesting that in intact animals, the effect on extracellular 5-HT was due to activation of peripheral chemoreceptors. In summary, we report that peripheral chemoreceptor activation enhances 5-HT release in the LC, indicating that 5-HT might be involved in the modulation of LC activity by ascending chemosensory information.

Animals↗
PubMed2000

Release of glutamate and GABA in the amygdala of conscious rats by acute stress and baroreceptor activation: differences between SHR and WKY rats.

To reveal the functional importance of amino acid neurotransmission in the amygdala (AMY) of conscious spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats, the in vivo release of glutamate (GLU) and GABA in this brain structure was studied using the push-pull superfusion technique. Basal GLU and GABA release rates in the AMY were comparable in SHR and WKY rats, although arterial blood pressure (BP) in SHR (152+/-6 mmHg) was higher than in WKY rats (102+/-4 mmHg). Neuronal depolarization by superfusion with veratridine enhanced the release of GLU and GABA to a similar extent in both rat strains. On the other hand, exposure to noise stress (95 dB) for 3 min led to a tetrodotoxin-sensitive increase in GLU release in the AMY of SHR, but not WKY rats. The concurrent pressor response to noise was enhanced in SHR as compared to WKY rats. A rise in BP induced by intravenous infusion of phenylephrine for 9 min had no effect on amino acid release in the AMY of both strains. The data suggest an exaggerated stress response of glutamatergic neurons in the AMY of SHR as compared with WKY rats, which might be of significance for the strain differences in the cardiovascular and behavioural responses to stress. The results also show that, in both rat strains, glutamatergic and GABAergic neurons in the AMY are not modulated by baroreceptor activation. Moreover, hypertension in adult SHR does not seem to be linked to a disturbed synaptic regulation of glutamatergic or GABAergic transmission in the AMY.

Amygdala↗
PubMed2000

Conditioned fear and inescapable shock modify the release of serotonin in the locus coeruleus.

The aim of the present study was to investigate the importance of the serotonergic transmission in the locus coeruleus (LC) to conditioned fear. Rats were conditioned to fear by exposing them to noise signal (N), light signal (L) and electric foot shock (S) for 4 days. Control rats were exposed to the same events without receiving S. The LC was superfused with artificial cerebrospinal fluid (aCSF) through a push-pull cannula, and the release of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) was determined in the superfusate. Motility, blood pressure (BP) and heart rate (HR) were telemetrically recorded. (1) The process of moving animals from their home cage into the grid-floor chamber transiently increased the release rate of 5-HT and the outflow of 5-HIAA in control and naive rats. In conditioned rats, 5-HT release was similarly increased during transfer but was permanently decreased in the grid-floor chamber. Control rats showed phases of enhanced motility in the chamber, while conditioned animals displayed continuous immobility. In naive rats, enhanced motility persisted in the novel environment. (2) Exposure of rats to N+L+S increased the release of 5-HT and the outflow of 5-HIAA to the same extent in conditioned and naive rats. These changes were associated with elevated motility, rise in BP and tachycardia. (3) In conditioned subjects, exposure to N+L in the fifth day led to a pronounced and sustained decrease in the release rate of 5-HT and to tachycardia, while no effects were observed in control rats or naive rats. The findings suggest that conditioned fear attenuates serotonergic neurotransmission within the LC. Telemetric recording of HR proves to be a valuable index for fear and stress processes.

Animals↗
PubMed2000

Effects of inescapable shock and conditioned fear on the release of excitatory and inhibitory amino acids in the locus coeruleus.

We investigated the importance of endogenous amino acids in the locus coeruleus in inescapable electric shock and conditioned fear. In naive rats and in rats exposed to noise (N), light (L) and electric shock (S) or to N + L only, the locus coeruleus was superfused with artificial cerebrospinal fluid through a push-pull cannula and the release of GABA, taurine, glutamate, aspartate, serine and glutamine was determined in the superfusate by HPLC after derivatization with o-phthaldialdehyde. Locomotor activity, arterial blood pressure and heart rate were telemetrically monitored. The placement of naive rats or conditioned rats from their home cage to a chamber provided with a grid-floor for shock virtually did not change the release rates of the amino acids in the locus coeruleus. Motility was enhanced in naive and conditioned rats to a similar extent. Blood pressure and heart rate were enhanced in conditioned rats only. Exposure to N + L + S for 5 min greatly enhanced the release rates of all determined amino acids in the locus coeruleus. In conditioned rats the increase in release of most amino acids lasted longer than in naive rats. Electric shock also enhanced motility, blood pressure and heart rate. In conditioned rats, motility and cardiovascular changes were more pronounced and/or lasted longer than in naive rats. Exposure of conditioned rats to the conditioned stimuli N + L for 5 min led to an increased release of taurine and aspartate. The enhanced release of taurine lasted 30 min. Exposure to N + L did not affect the release rates of amino acids in naive rats. N + L did not influence motility but arterial blood pressure and heart rate were elevated in conditioned rats. The findings show that inescapable electric shock enhances the release of several amino acids in the locus coeruleus, while conditioned fear selectively increases the outflow of taurine and aspartate. Moreover, conditioned fear prolongs the response of excitatory and inhibitory amino acids to electric shock. The results suggest that an excitatory amino acid (aspartate) and an inhibitory amino acid (taurine) of the locus coeruleus are implicated in conditioned fear.

Amino Acids↗
PubMed2000

Release of catecholamines in the locus coeruleus of freely moving and anaesthetized normotensive and spontaneously hypertensive rats: effects of cardiovascular changes and tail pinch.

Noradrenaline turnover has been found to be increased in the locus coeruleus of young spontaneously hypertensive rats (SHR). There is also evidence that the noradrenergic projection from the locus coeruleus to the posterior hypothalamus contributes to the development of genetic hypertension. To investigate whether the release of noradrenaline and dopamine in the locus coeruleus is modified in genetic hypertension, this brain region of adult SHR and normotensive Wistar-Kyoto (WKY) rats was superfused with artificial cerebrospinal fluid through a push-pull cannula. Dopamine and noradrenaline released in the superfusate were determined radioenzymatically. There was no difference in the basal release of noradrenaline and dopamine in the locus coeruleus of conscious, anaesthetized or diazepam-treated adult WKY rats and SHR. In conscious animals, a rise in blood pressure elicited by intravenous infusion of phenylephrine enhanced the release of noradrenaline and dopamine in both strains to the same extent. Intravenous infusion of sodium nitroprusside elicited a fall in blood pressure and also increased to the same degree the release of noradrenaline and dopamine in the locus coeruleus of normotensive and hypertensive conscious rats. In anaesthetized rats, baroreceptor activation by phenylephrine decreased the release of noradrenaline and dopamine, while sodium nitroprusside lowered blood pressure and enhanced the release rates of the two catecholamines. Treatment of conscious rats with diazepam (10 mg/kg, i.p., 120 min prior to starting collection of the superfusate) abolished the phenylephrine-evoked release of catecholamines observed in conscious animals. The sensory stimulus tail pinch led to a slight increase in blood pressure. In conscious animals, this aversive stimulus led to enhanced release of noradrenaline and dopamine that lasted longer in SHR than in WKY rats. The release of catecholamines evoked by tail pinch was abolished in rats treated with diazepam, as well as in anaesthetized animals. Our findings show that in adult rats, genetic hypertension does not modify the release of noradrenaline and dopamine in the locus coeruleus. Since in anaesthetized rats increases in blood pressure diminish, while decreases in blood pressure enhance, the release of noradrenaline and dopamine, it seems that both amines possess a counteracting, hypertensive function in the rat locus coeruleus. When baroreceptor activation by phenylephrine is carried out on conscious animals, stress predominates and the release of catecholamines is enhanced. This study demonstrates the importance of the noradrenergic system of the locus coeruleus in central cardiovascular control and in emotional, stress and pain-regulating processes.

Anesthesia↗
PubMed2000

Acute transcranial magnetic stimulation of frontal brain regions selectively modulates the release of vasopressin, biogenic amines and amino acids in the rat brain.

Using intracerebral microdialysis in urethane-anaesthetized adult male Wistar rats, we monitored the effects of acute repetitive transcranial magnetic stimulation (rTMS; 20 trains of 20 Hz, 2.5 s) on the intrahypothalamic release of arginine vasopressin (AVP) and selected amino acids (glutamate, glutamine, aspartate, serine, arginine, taurine, gamma-aminobutyric acid) and the intrahippocampal release of monoamines (dopamine, noradrenaline, serotonin) and their metabolites (homovanillic acid, 3,4-dihydroxyphenylacetic acid, 5-hydroxyindoleacetic acid). The stimulation parameters were adjusted according to the results of accurate computer reconstructions of the current density distributions induced by rTMS in the rat and human brains, ensuring similar stimulation patterns in both cases. There was a continuous reduction in AVP release of up to 50% within the hypothalamic paraventricular nucleus in response to rTMS. In contrast, the release of taurine, aspartate and serine was selectively stimulated within this nucleus by rTMS. Furthermore, in the dorsal hippocampus the extracellular concentration of dopamine was elevated in response to rTMS. Taken together, these data provide the first in vivo evidence that acute rTMS of frontal brain regions has a differentiated modulatory effect on selected neurotransmitter/neuromodulator systems in distinct brain areas.

Amino Acids↗
PubMed1999

Influence of NOS inhibitors on changes in ACH release and NO level in the brain elicited by amphetamine neurotoxicity.

We studied the possible role of neurotoxicity in the d,l-amphetamine (AMPH)-induced release of acetylcholine (ACH) in the nucleus accumbens (Nac) and the involvement of endogenous NO in this process. For determination of ACH release the Nac was superfused using the push-pull-technique. NO was directly measured using the electron paramagnetic resonance technique. Repeated administration of AMPH increased ACH release by about 400%. N-nitro-L-arginine (L-NNA) and 7-nitroindazole (7-NI) nearly abolished the AMPH-induced increase in ACH release. AMPH increased NO as well as lipid peroxidation (LPO) products in the cortex. L-NNA and 7-NI substantially diminished NO increase. AMPH-evoked LPO was only slightly reduced by these compounds. It is concluded that AMPH enhances ACH release through increased NO synthesis and induces neurotoxicity via NO and by LPO independent NO generation.

Acetylcholine↗
PubMed1999

Nitric oxide modulates the release of serotonin in the rat hypothalamus.

To investigate the effect of nitric oxide (NO) on the release of serotonin and its main metabolite, 5-hydroxyindoleacetic acid (5-HIAA), the posterior hypothalamus of the conscious rat was superfused through a push-pull cannula with drugs which either liberate NO, or inhibit NO synthase (NOS). The NO donors, linsidomine, diethylamine/nitric oxide (DEA/NO), S-nitroso-N-acetylpenicillamine (SNAP), S-nitroso-glutathione (SNOG) and sodium nitroprusside influenced the release of serotonin in a biphasic way. Low concentrations of drugs diminished, while higher concentrations of these compounds enhanced the outflow of serotonin. The NOS inhibitors N(G)-methyl-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NINA) enhanced the serotonin release. A high concentration of L-NAME slightly diminished the outflow of serotonin. Inhibition of the guanylyl cyclase by oxodiazolo[4, 3]quinoxaline-one (ODQ) abolished the changes in serotonin outflow induced by both low and high concentrations of linsidomine. The extracellular concentration of the 5-HIAA was not influenced by the compounds used. These data suggest that endogenous NO modulates the release of serotonin in a biphasic and cGMP-dependent way.

Animals↗
PubMed1999

Noradrenaline release in the locus coeruleus of conscious rats is triggered by drugs, stress and blood pressure changes.

The in vivo release of noradrenaline (NA) in the locus coeruleus (LC) of conscious rats was enhanced by local superfusion of pargyline, idazoxan, bicuculline, AMPA as well as by experimentally induced hypotension. Noise stress considerably enhanced NA release in the LC and this response was promoted after local alpha2-adrenoceptor blockade by idazoxan. Air jet stress and noise stress elicited comparable increases in NA release in the LC and the simultaneously superfused amygdala. The NA responses in both areas did not change during a second exposure to each of the stressors. It is concluded that NA release at the somatodendritic level of LC neurons is triggered by high LC activity and most likely serves to limit LC activation to excitatory stimuli by feedback inhibition via alpha2-adrenoceptors.

Adrenergic alpha-Antagonists↗
PubMed1999

Hyperforin enhances the extracellular concentrations of catecholamines, serotonin and glutamate in the rat locus coeruleus.

Hyperforin is the main antidepressant component of hypericum perforatum (St. John's Wort). Using the push-pull superfusion technique we tested whether hyperforin influences extracellular concentrations of neurotransmitters in the rat locus coeruleus. Hyperforin (10 mg/kg, i.p.) not only enhanced the extracellular levels of the monoamines dopamine, noradrenaline and serotonin, but also that of the excitatory amino acid glutamate. The levels of the main serotonin metabolite 5-hydroxyindolacetic acid, as well as those of the amino acids GABA, taurine, aspartate, serine and arginine, were not influenced. Together with in vitro studies, our findings suggest that the antidepressant property of hyperforin is due to enhanced concentrations of monoamines and glutamate in the synaptic cleft, probably as a consequence of uptake inhibition.

Amino Acids↗