Acute exposure of rats to air ions: effects on the regional concentration and utilization of serotonin in brain

Exposure to electrically charged gas molecules (air ions) has been reported to influence physiological and behavioral functions in animals and humans although there is controversy as to whether these findings are valid. A popular hypothesis concerning the reported effects of air ions is that alterations in serotonin (5HT) metabolism, particularly in the brain, are involved. We measured the concentration and turnover of 5HT in rats exposed to 5.0 X 10(5) ions/cm3 for up to 66 hours. Contrary to previous reports of other investigators, we were unable to demonstrate any effect of exposure to air ions or associated DC electric fields on the concentration or turnover of 5HT in rats under carefully controlled and characterized exposure conditions.     

Dynamics of endogenous Hsp70 synthesis in the brain of olfactory bulbectomized mice

Numerous epidemiological studies have established acute brain injury as one of the major risk factors for the Alzheimer''s disease (AD). However, the lack of animal models of AD-like degeneration triggered by a defined injury hampered the development of adequate therapies. Here we report that the surgical damage of the olfactory bulbs triggers the development of several pathologies, including amyloid-β accumulation and strong decrease of neuron density in the cortex and hippocampus as well as significant disturbance of spatial memory. Characteristically, these harmful consequences of the olfactory bulbectomy (OBX) have a peculiar dynamics in time with maximal manifestation in periods of 1–1.5 months and 8 months after the surgery and, hence, exhibit biphasic pattern with almost complete recovery period taking place at 5–6 months after the operation. The quantitative determination of endogenous inducible form of Hsp70 in different brain areas of OBX mice demonstrated characteristic fluctuations of Hsp70 levels depending on the time after the operation and age of mice. Interestingly, maximal induction of Hsp70 synthesis in the hippocampus exhibits clear-cut coincidence with the recovery period in OBX animals. The observed correlation enables to suggest curing effect of Hsp70 synthesis at an earlier period of pathology development and establishes it as a possible therapeutic agent for secondary grave consequences of brain injury, such as AD-like degeneration, for which neuroprotective therapy is urgently needed.     

Biochemical and behavioral effects of long-term citalopram administration and discontinuation in rats: role of serotonin synthesis

We have investigated effects of continuous SSRI administration and abrupt discontinuation on biochemical and behavioral indices of rat brain serotonin function, and attempted to identify underlying mechanisms. Biochemistry of serotonin was assessed with brain tissue assays and microdialysis; behavior was assessed as the acoustic startle reflex. Long-term SSRI administration to rats reduced the content of 5-HT and its main metabolite shortly after inhibition of 5-HT synthesis in many brain areas with more than 50%. Turnover was not appreciably decreased, but significantly increased within 48h of drug discontinuation. The microdialysis experiments indicate that neuronal release of 5-HT depends strongly on new synthesis and emphasize the role of 5-HT(1B) receptors in the regulation of these processes. Discontinuation of the SSRI rapidly increased behavioral reactivity to the external stimulus. Additional startle experiments suggest that the increased reactivity is more likely related to the reduced extracellular 5-HT levels than to impaired synthesis. The combination of the marked reduction of serotonin content and limited synthesis may destabilize brain serotonin transmission during long-term SSRI treatment. These combined effects may compromise the efficacy of an SSRI therapy and facilitate behavioral changes following non-compliance.     

Acute effects of 3,4-methylenedioxymethamphetamine on brain serotonin synthesis in the dog studied by positron emission tomography

The influence of an acute dose (2 mg/kg; i.v.; infused over 10 min) of 3,4-methylenedioxymethamphetamine (MDMA; Ecstasy) on the brain serotonin synthesis in the dog was assessed using alpha [11C]methyl-L-tryptophan and positron emission tomography. The rate of serotonin synthesis measured 1 h after injection of MDMA was six times greater than the base line (before MDMA) synthesis. Five hours after the MDMA injection, serotonin synthesis was about one half that at the base line, and about one thirteenth of the synthesis at 1 h after MDMA. A large increase seen 1 h after MDMA probably relates to the large release of serotonin by MDMA and reflects an attempt of the serotonergic system to replenish released serotonin. This probably correlates with the mood changes reported by humans after MDMA intake. Decrease observed 5 h after MDMA, in part, probably relates to the inhibitory effects of the released serotonin, which could act on the activity of tryptophan hydroxylase directly or indirectly via other monoaminergic systems (e.g. dopaminergic).     

Acute administration of fluoxetine normalizes rapid eye movement sleep abnormality, but not depressive behaviors in olfactory bulbectomized rats

In humans, depression is associated with altered rapid eye movement (REM) sleep. However, the exact nature of the relationship between depressive behaviors and sleep abnormalities is debated. In this study, bilateral olfactory bulbectomy (OBX) was carried out to create a model of depression in rats. The sleep-wake profiles were assayed using a cutting-edge sleep bioassay system, and depressive behaviors were evaluated by open field and forced swimming tests. The monoamine content and monoamine metabolite levels in the brain were determined by a HPLC-electrochemical detection system. OBX rats exhibited a significant increase in REM sleep, especially between 15:00 and 18:00 hours during the light period. Acute treatment with fluoxetine (10 mg/kg, i.p.) immediately abolished the OBX-induced increase in REM sleep, but hyperactivity in the open field test and the time spent immobile in the forced swimming test remained unchanged. Neurochemistry studies revealed that acute administration of fluoxetine increased serotonin (5-HT) levels in the hippocampus, thalamus, and midbrain and decreased levels of the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA). The ratio of 5-HIAA to 5-HT decreased in almost all regions of the brain. These results indicate that acute administration of fluoxetine can reduce the increase in REM sleep but does not change the depressive behaviors in OBX rats, suggesting that there was no causality between REM sleep abnormalities and depressive behaviors in OBX rats.     

Acute effects of heroin and morphine on newly synthesized serotonin in rat brain.

Heroin and morphine, in acute intraperitoneal doses of 2 and 10 mg/kg respectively, produced significant increments in the formation of newly formed brain serotonin from tritiated (³H)-L-tryptophan to ³H-serotonin. Opiate analgesia, Straub tail sign and catatonia, were observed during the increase in the synthesis of serotonin. The transport of radio-labelled tryptophan into the rat brain was not increased by the acute injection of the opiates, but brain levels of ³H-serotonin and of its main metabolite, 5-hydroxyindoleacetic acid, were significantly elevated. These opiates do not interfere with the accumulation of serotonin or with the transport of its metabolite in serotonergic neurons after inhibition of monoamine oxidases with Pargyline. An increase in the activity of tryptophan hydroxylases was more pronounced in the forebrain than in the brain stem. Stimulation of newly synthesized serotonin is probably mediated by an increase in tryptophan hydroxylase activity and not by an increase in the transport of tryptophan into the brain.     

Effects of desipramine on regional serotonin synthesis in the rat brain: acute and chronic autoradiographic studies

Various studies have implicated the involvement of noradrenaline (NA) and/or serotonin (5-hydroxytryptamine (5-HT)) in the pathogenesis and treatment of depression. The aim of the present study was to investigate the effects of acute and 7 days of administration of desipramine, a NA re-uptake inhibitor, on the rate of 5-HT synthesis in the rat brain. The study was done by an autoradiographic method using alpha-[14C]-methyl-L-tryptophan as a tracer. The acute (10mg/kg, i.p., 2h before i.v. infusion of the tracer) or 7 days of desipramine (10mg/kg per day, i.p.) did not affect plasma tryptophan (Trp) concentrations, as compared to control (saline treated) rats. Acute treatment with desipramine decreased the rate of 5-HT synthesis in the brain regions that contain 5-HT cell bodies between 19 and 28%, and increased the rate of 5-HT synthesis in the majority of areas containing 5-HT terminals between 21 and 65%. In contrast to the acute treatment, a 7-day administration increased 5-HT synthesis rates in the dorsal raphe (24%), but decreased it in raphe magnus (35%), superior olive (45%), caudate (31%), superior (38%) and inferior (53%) colliculus, and in the auditory cortex (35%). This suggests that the effect of desipramine on 5-HT synthesis rate is time-dependent and differs in the cell bodies and structures containing 5-HT nerve terminals.     

Effects of pentadecapeptide BPC157 on regional serotonin synthesis in the rat brain: alpha-methyl-L-tryptophan autoradiographic measurements

A novel pentadecapeptide, BPC157, was recently reported to have a large spectrum of in vivo activities, from anti-ulcer to central action on the brain dopaminergic system. The mechanisms of these actions are not well understood. In this study, the evaluation of the effects of acute and repeated administration of BPC157 on serotonin (5-HT) synthesis in the rat brain is reported. The alpha-[14C]methyl-L-tryptophan (alpha-MTrp) autoradiographic method was used to measure regional 5-HT synthesis rates. In the first series of experiments, a single dose treatment of BPC157 (10 microg/kg) administered intraperitoneally 40 min before the alpha-MTrp tracer injection significantly reduced the regional rate of 5-HT synthesis in the dorsal thalamus, hippocampus, lateral geniculate body and hypothalamus. 5-HT synthesis rates in the substantia nigra reticulate and medial anterior olfactory nucleus in BPC157 treated rats were significantly higher than in the control rats. No significant change in the synthesis rate was observed in the raphe nuclei. In the second series of experiments, following a 7-day treatment with BPC157 (10 microg/kg; s.c.), a significant reduction in the 5-HT synthesis rate was observed in the dorsal raphe nucleus, and significant increases were observed in the substantia nigra, lateral caudate, accumbens nucleus and superior olive. This data suggests that BPC157, a gut peptide, influences brain 5-HT synthesis in rats, but we cannot determine, from this data, the mechanism of this action.     

Differential effects of DSP-4 administration on regional brain norepinephrine turnover in rats

The effects of DSP-4 on brain NE levels and turnover in rats were investigated in six brain regions: cortex, hippocampus, cerebellum, brainstem, hypothalamus and locus coeruleus. Administration of 50 mg/kg of DSP-4 significantly decreased NE levels in all brain regions; greatest reductions occurred in the cortex (86% decrease) and in the hippocampus (91% decrease). Doses of DSP-4 less than 50 mg/kg did not significantly lower NE levels in other brain regions, except within the cerebellum. Levels of the NE metabolite 3-methoxy, 4-hydroxyphenylethylene glycol sulfate (MHPG-S04) declined in parallel with those of NE, except within the brainstem and the locus coeruleus. NE turnover, expressed as the ratio of the MHPG-S04 concentration to that of NE, was higher in the cortex and hippocampus than other regions in control animals, and NE turnover significantly increased only in these two areas after the administration of 50 mg/kg of DSP-4 (p less than 0.01). There were no significant changes in the levels of dopamine and a significant decrease of serotonin only in the striatum. These results indicate that DSP-4 is a neurotoxin with a strong predilection for noradrenergic neurons, that its effects vary according to brain region and that its administration increases NE turnover in those brain regions showing the greatest depletion of NE.     

Regionally specific effects of diazepam on brain serotonin metabolism in rats: Sustained effects following repeated administration

The effects of single (1mg/kg) and repeated (1mg/kg 2¹ daily for 4 days) diazepam administration are investigated on brain regional 5-hydroxytryptamine (5-HT; serotonin) and 5-hydroxy indoleacetic acid (5-HIAA) concentration in rats. Daily treatment decreased food intakes but body weights did not decrease. Administration of diazepam (1mg/kg) to 4 day sahne injected rats on the 5th day decreased 5-HT levels in the hippocampus and increased it in the hypothalamus. 5-HIAA levels were increased in the striatum and decreased in the hypothalamus. 4 day diazepam injected rats injected with sahne on the 5th day also exhibited silmilar changes of 5-HT and 5-HIAA. Cortical levels of 5-HIAA were also smaller in these rats. Administration of diazepam to 4 day diazepam injected rats again decreased 5-HT in the hippocampus and 5-HIAA in the hypothalamus. 5-HT and 5-HIAA were both decreased in the striatum. Regionally specific effects of diazepam on brain serotonin metabolism are discussed in relation to their possible functions.     

Regional brain serotonin synthesis is increased in the olfactory bulbectomy rat model of depression: an autoradiographic study

Serotonin synthesis rates were evaluated using alpha-[14C]methyl-l-tryptophan (alpha-MTrp) autoradiographic methods in olfactory bulbectomized (OBX) rats. They were significantly (p < 0.05) increased in the frontal (50%) and parietal (40%) cortices, superior olive (over 30%), and the substantia nigra (30%) in the OBX rats as compared to the sham operated animals. There were also increases in 5-hydroxytryptamine (5-HT) synthesis in some limbic areas: the cingulate (32%), the medial forebrain bundle (58%), the hippocampus (13-25%) and the thalamus (22-40%). The largest increase in 5-HT synthesis after OBX was observed in the sensory-motor cortex (67%). 5-HT synthesis rates were significantly decreased in the dorsal and medial raphe nuclei, but there was no significant change the ventral tegmental area and the locus coeruleus following OBX. These results indicate that olfactory bulbectomy causes an imbalance in 5-HT synthesis in some projection areas by disproportionally increasing 5-HT synthesis rates in specific brain regions and making more 5-HT available for neurotransmission. This imbalance in 5-HT synthesis and the subsequent elevation of tissue 5-HT may be responsible for the creation of non-physiological circuitry which may, in part, be reflected in the symptoms resembling human depression.     

Effects of propranolol and pindolol on platelet aggregation and serotonin release

The aggregation of human platelets by adrenaline and adenosine di-phosphate (ADP) and its inhibition by β-blockers was studied by measuring the light transmission of plateletrich plasma (PRP) and suspensions of washed platelets exposed to these agents. Inhibition of aggregation of PRP and washed platelets was dose related in the two β-blockers tested: propranolol and pindolol. The potent β-blockers pindolol was less inhibitory than propranolol when adrenaline and ADP were used to induce platelet aggregation. The aggregation of platelets by adrenaline has two phases. With low doses of the blockers only the second phase was inhibited whereas higher doses blocked both phases. Preincubation of human platelets (PRP and washed platelets) with both blockers per se resulted in release of ¹⁴C-labelled serotonin. Propranolol released more serotonin than pindolol. There was no concomitant release of lactic dehydrogenase. It is concluded that the effects of propranolol and pindolol on platelets do not correlate with the β-blocking activity of these agents. Rather, the more lypophilic agent, propranolol, is more active both in inhibition of aggregation and in releasing platelet serotonin. It is suggested that these actions of the drugs are related to their non-specific membrane effects.     

Acute effects of corticosterone on tissue protein synthesis and insulin-sensitivity in rats in vivo.

The effect of corticosterone treatment on the sensitivity of muscle protein synthesis to insulin infusion was assessed in post-absorptive young rats. To select the optimal time period for corticosterone treatment, protein synthesis was measured by injection of L-[2,6-3H]phenylalanine (1.5 mmol/kg body weight) 1, 4, 12 or 24 h after injection of corticosterone (5 mg/kg body wt.). Muscle protein synthesis was significantly decreased at 4 h and the effect was maximal by 12 h; liver protein synthesis was elevated at 12 h and 24 h. The dose-response of muscle protein synthesis to a 30 min infusion with 0-150 munits of insulin/h was then compared in rats pretreated with corticosterone (10 mg/100 g body wt.) or vehicle alone. When no insulin was infused, corticosterone inhibited protein synthesis in gastrocnemius muscle. High doses of insulin stimulated protein synthesis, but the inhibition by corticosterone was similar to that in the absence of insulin. At intermediate doses of insulin there was an increased requirement for insulin to elicit an equivalent response in muscle protein synthesis. Plantaris muscle responded in a manner similar to that of gastrocnemius, but neither soleus muscle nor liver responded significantly to insulin. These data suggest that corticosterone has two modes of action; one which is independent from and opposite to that of insulin, and a second which causes insulin-resistance through a decrease in sensitivity rather than a change in responsiveness.     

Acute effects of caffeine injection on neutral amino acids and brain monoamine levels in rats

The injection of caffeine (100 mg/kg, i.p.) into male rats acutely increased brain levels of trytophan, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA). Blood levels of glucose, nonesterified fatty acids (NEFA) and insulin also increased, while those of the aromatic and branched-chain amino acids fell. Serum tryptophan levels either did not fall, or increased. Consequently, the serum ratio of trypthopahn to the sum of other large neutral amino acids (LNAA) increased. Less consistently noted were increases in serum free tryptophan levels. Brain tyrosine levels were not appreciably altered by caffeine, nor was the serum tyrosine ratio. In dose-response studies, 25 mg/kg of caffeine was the minimal effective dose needed to raise brain tryptophan, but only the 100 mg/kg dose elevated all three indoles in brain. In no experiments did caffeine, at any time or dose, alter brain levels of dopamine or norepinephrine. Caffeine thus probably raises brain tryptophan levels by causing insulin secretion, and thereby changing plasma amino acid levels to favor increased tryptophan uptake into brain. The rises in brain 5-HT and 5-HIAA may follow from the increase in brain tryptophan, although further data are required clearly to establish such a mechanism.     

Pharmacological effects of GABA on serotonin metabolism in the rat brain

The pharmacological effects of GABA-related drugs were studied on the serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA) contents of various regions of the rat brain. These effects were examined in the nuclei raphe dorsalis, magnus and centralis and in structures receiving a dense serotonin innervation such as the habenula complex and subcommissural organ. The GABA agonist, muscimol, increased the 5-HT contents and reduced 5-HIAA levels in structures containing serotoninergic terminals suggesting an inhibitory effect of GABA on the firing of serotoninergic neurons with concomitant reduction of 5-HT utilisation. In contrast, the GABA antagonist, bicuculline, probably stimulated 5-HT turnover since its intraperitoneally administration produced significant increase of 5-HT and/or 5-HIAA levels in the same brain regions. These data are in agreement with a transsynaptic inhibitory control of GABA on serotoninergic neurons. Drugs which inhibit the GABA catabolism such as amino-oxyacetic acid or gamma-vinyl-GABA and which should elevate GABA levels in the synaptic gap were capable of increasing or decreasing the 5-HT and the 5-HIAA levels depending on the experimental conditions. These results suggest that several processes are probably involved in the control of serotoninergic neurons by GABA in the rat brain. Among them, an intracellular effect of GABA on 5-HT metabolism might well occur in cells containing both GABA and 5-HT.