Effects of chronic variate stress on feeding behavior and on monoamine levels in different rat brain structures

Chronic variate stress was seen to decrease the ingestion of sweet food when compared to control rats. Brain monoamines are known to be involved in the control of food intake, serotonin appears to be involved in the mechanisms of satiety, and dopamine in mediating appetite or approach behaviors triggered by incentive stimuli associated with rewards. The effect of chronic variate stress on cerebral levels of monoamines was also studied in rats. Increased levels of DOPAC were observed in the frontal cortex and in the hippocampus and an increased 5-HIAA/5-HT ratio was also observed in this latter structure. In the hypothalamus, levels of HVA and DOPAC were decreased, as well as the DOPAC/DA ratio, while no difference was found in amygdala. During the treatment, there were no differences in the consumption of water and regular food between stressed and control animals. An increase in the adrenal weight was observed at the end of the treatment. The results suggest that emotional changes, such as exposure to stress situations can influence feeding behavior, chronic variate stress causes decreased ingestion of sweet food and decreased dopaminergic neurotransmission in hypothalamus. Increased dopamine metabolite levels in the cortex and hippocampus were also observed and some of these modifications may be related to alterations in feeding behavior.     

Regional brain monoamine levels and utilization in middle-aged rats.

Significant changes in monoamine levels and utilization were noted in certain brain regions of middle-aged Fisher 344 rats when compared with young adult controls. In the prefrontal cortex and septum, 3,4 dihydroxyphenylglycol (MHPG) and the MHPG/norepinephrine (NE) ratio were decreased. The septum also showed increases in dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) but there was a decrease in the DOPAC/DA ratio. The striatum showed an increase in the MPHG/NE ratio and an increase in DOPAC. The hippocampus and thalamus showed an increase in 5-hydroxyindoleacetic acid (5HIAA). This demonstrates that selected neurotransmitter systems in the brain are altered at an early stage of senescence. This could lead to ensuing neurological deficits.     

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.     

n-3 polyunsaturated fatty acid supplementation reverses stress-induced modifications on brain monoamine levels in mice

The aim of this study was to examine the effects of supplementation with n-3 polyunsaturated fatty acids (PUFAs) on stress responses in mice subjected to an unpredictable chronic mild stress (UCMS) procedure. Stress-induced modifications in coat and aggressiveness were evaluated, and phospholipid PUFA profiles and monoamine levels were analyzed in the frontal cortex, hippocampus, and striatum. The results showed that repeated exposure to mild stressors induced degradation in the physical state of the coat, lowered body weight gain, and increased aggressiveness, without any effect of n-3 PUFA supplementation. The UCMS induced a significant decrease in the levels of norepinephrine in the frontal cortex and striatum, and a nonsignificant decrease in the hippocampus. The tissue levels of serotonin (5-HT) were 40% to 65% decreased in the three brain regions studied. Interestingly, the n-3 PUFA supplementation reversed this stress-induced reduction in 5-HT levels. These findings showed that supplementation in n-3 long-chain PUFAs might reverse certain effects of UCMS in cerebral structures involved in stress-related behaviors.     

Central nervous system actions of growth hormone on brain monoamine levels and behavior of juvenile rainbow trout

Growth hormone (GH) has been demonstrated to alter the behavior of juvenile salmonids. However, the mechanisms behind this action are not yet understood. In mammals and birds, peripheral GH treatment has been shown to affect monoaminergic activity in the central nervous system, which may be a mechanism whereby GH alters behavior. To investigate if GH may influence behavior directly at the central nervous system, juvenile rainbow trout were injected with GH into the third ventricle of the brain, whereupon physical activity and food intake were observed during 2 h. Thereafter, brains were sampled and the content of serotonin, dopamine, and noradrenaline and their metabolites were measured in hypothalamus, telencephalon, optic tectum, and brainstem. The GH-treated fish increased their swimming activity relative to sham-injected controls, while appetite remained unchanged, compared with sham-injected controls. Analysis of brain content of monoamines revealed that the GH treatment caused a decrease in the dopamine metabolite homovanillic acid in the hypothalamus, indicating a lowered dopaminergic activity. It is concluded that GH may alter behavior by acting directly on the central nervous system in juvenile rainbow trout. Furthermore, GH seems to alter the dopaminergic activity in the hypothalamus. Whether this is a mechanism whereby GH affects swimming activity remains to be clarified.     

Effects of DSP-4 on monoamine and monoamine metabolite levels and on beta adrenoceptor binding kinetics in rat brain at different times after administration

Effects of DSP-4 on noradrenaline (NA), 3-methoxy-4-hydroxyphenyl glycol (MHPG), serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels and on beta adrenoceptor binding kinetics (Bmax and K_D) in rat hippocampus, cortex and hypothalamus were studied between 24 hours and 14 days after systemic administration. Beta adrenoceptor numbers in hippocampus and cortex, but not in hypothalamus, were significantly increased after DSP-4. No significant changes in K_D values were observed in hypothalamus, but significant increases in this parameter were measured in hippocampus and cortex. NA and MHPG levels were significantly decreased in all three brain regions, but MHPG/NA ratios were increased in hippocampus, decreased in cortex and unchanged in hypothalamus. Very prominent increases in 5-HIAA levels were observed in all three brain regions, but only at one day after DSP-4. The greatest increases in 5-HIAA levels occurred in the hippocampus, but this effect of DPS-4 appeared to be slightly diminished by pre-treatment with fluoxetine. In cortex and hippocampus 5-HT levels were slightly, but significantly decreased after DSP-4.     

Effects of ethanol on brain monoamine content of spontaneously hypertensive rats (SHR)

Spontaneously hypertensive rats (SHR) were administered either 2.4 g/kg ethanol or an isocaloric glucose daily for 4 weeks and the levels of norepinephrine (NE), epinephrine (EP), dopamine (DA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in different brain regions were determined. Results indicated a 3-fold increase in NE level in brain stem and hypothalamus and more than 2-fold increase in DA in corpus striatum in alcohol-treated rats as compared to controls. There was a significant increase in the level of DA in the corpus striatum but the levels in cerebral cortex, brain stem and hippocampus were decreased instead. Decreases in 5-HT levels were found in hypothalamus, brain stem, cortex and cerebellum of alcohol-treated brain as compared to untreated controls. These results indicate alterations of the biogenic amine contents in different regions of the SHR brain after chronic ethanol ingestion. Since stimulated release of biogenic amines in the SHR brain has been implicated in the regulation of blood pressure, changes due to ethanol ingestion may be a risk factor in hypertensive patients.     

Effects of eicosapentaenoic acid and docosahexaenoic acid on anxiety-like behavior in socially isolated rats

Abstract

The effects of fish oil for improving mental health have been reported. The present study was undertaken to compare the effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on anxiety-like behavior using a rat model. Experimental diets enriched in EPA or DHA as glycerides were prepared. Rats were exposed to social isolation stress and fed the experimental diet for 14 days. The results of behavioral tests revealed that rats fed the EPA-enriched diet exhibited less anxiety-like behavior than rats fed the control or DHA-enriched diets. Furthermore, EPA suppressed anxiety-like behavior only in socially isolated rats. The increase in EPA contents in the brain phospholipid fraction by feeding EPA-enriched diet was more significant than that of DHA by feeding DHA-enriched diet. These results suggest that dietary EPA is more anxiolytic than DHA in rats exposed to social isolation stress and is effective in increasing EPA content in brain membranes.     

Effects of fluoxetine on growth and behavior in the crayfish Orconectes rusticus

This laboratory study examined the effects of the specific serotonin reuptake inhibitor fluoxetine on growth following molting and on a range of behaviors in the crayfish Orconectes rusticus. For growth experiments, male Form I and Form II crayfish were weighed and measured and placed individually in water containing 0–500 μg/L of fluoxetine. They were held in fluoxetine or control water until they molted and were reweighed two weeks post-molt. In behavior experiments, juvenile and adult animals were held individually in 0, 2, 200, or 500 μg/L of fluoxetine for 10 days and tested in an open field arena to assess locomotion, thigmotaxis, sheltering, and habituation to a novel environment. Under our laboratory conditions, crayfish exposed to fluoxetine at 500 μg/L showed significantly enhanced growth: post-molt Form I animals had greater body weight and post-molt Form II animals had greater carapace length, relative to controls. In open field tests, juvenile crayfish exposed to 2 and 500 μg/L fluoxetine displayed significantly reduced locomotion compared to controls. The results indicate that crayfish growth and locomotion can be manipulated by short-term exposure to ambient fluoxetine, suggesting that this means of exposure may offer a useful and noninvasive way to examine drug effects in freely moving animals. However, effects were only observed at concentrations well above fluoxetine levels currently reported in the environment. This suggests that O. rusticus may be relatively resistant to this form of pharmaceutical pollution but whether effects would occur following long-term exposure to lower concentrations is unknown.     

Effects of treadmill running and swimming on plasma and brain vasopressin levels in rats

The influence of treadmill or swimming exercise on resting values of plasma and brain arginine vasopressin (AVP), and plasma sodium, potassium, osmolality and proteins was studied after 5 weeks of training using female Wistar rats. The duration of daily training sessions was progressively increased to reach 6 h/day for swim training (S) and 3 h/day for treadmill running (T). Compared to their untrained controls, treadmill and swim training were respectively associated with: a significant lower body weight; a decreased plasma AVP (36.4% for T and 47.4% for S) and hypothalamic AVP (20% for T and 16% for S); a higher hypophyseal AVP (145% for T and 36.3 for S); a decreased plasma osmolality (6.7% for T and 6.1% for S), sodium (1.2% for both) and potassium (15% for T and 22.4% for S); and no change in protein concentration. For T, rectal temperature increased (38.5 +/- 0.20 to 39.7 +/- 0.5) and for S rectal temperature decreased from 38.6 +/- 0.12 to 37.74 +/- 0.10). The differences observed in AVP contents of the pineal and Harderian glands (enhanced only in the treadmill groups) could be explained by the supposed role of these glands in thermoregulation. Two conclusions could be drawn from this study: there are no parallel changes in the hypothalamo-hypophyseal system (where AVP plays its endocrine role) and the brain (where AVP is a neurotransmitter); plasma changes could be explained by an extracellular fluid expansion with Na and K loss leading to a decrease in AVP secretion.     

Effect of cadmium and zinc ethanolamine complexes on rat brain monoamine oxidase-B activity in vitro

Monoamine oxidase-B (MAO-B) from rat brain was inhibited strongly by the prepared cadmium and zinc ethanolamine complexes obtained from their sulphate and chloride salts. The inhibition of MAO-B by these complexes was time-dependent and fully reversible after dilution and sedimentation. In vitro, the cadmium ethanolamine complexes were more potent at inhibiting MAO-B than the zinc complexes. The inhibitory effect of these complexes follow the order: TEA>DEA>MEA, due to the alkyl residues and steric effect properties. The inhibition of MAO-B by cadmium and zinc ethanolamine complexes was a noncompetitive type. The K(i) values were calculated. The influence of the complexes on the activity of MAO-B was rather evaluated. It decreased the MAO-B activity. The IC(50) values of the two potent cadmium and zinc triethanolamine complexes on MAO-B were evaluated indicating that the complexes were tightly binding, but reversible inhibitors for MAO-B. In general, these systems may be used for preventing some neurodegenerative diseases.     

Anticataleptic effect of delta sleep-inducing peptide and its action on brain monoamine oxidase in rats genetically predisposed to catalepsy

Rats with genetic susceptibility to catalepsy (GC strain) were compared with Wistar rats (W). After an intraperitoneal administration of 120 micrograms/100 g delta sleep-inducing peptide (DSIP) in GC rats the duration of cataleptic freezing was shortened (13.8 +/- 9.5 sec against 27.2 +/- 7.5 sec in control). MAO-B activity decreased due to DSIP administration both in GC and W rats. It is hypothesized that the DSIP effect MAO-B in GC rats may correct the lost MAO-A function in deamination of dopamine, a common MAO-A and MAO-B substrate, and the dopaminergic neurotransmission in catalepsy.     

Effects of dopaminergic agents on monoamine levels and motor behaviour in planaria

1. Dopamine, serotonin and, in lesser amounts, norepinephrine were detected in Dugesia gonocephala using electrochemical detection coupled with liquid chromatography (LCED). 2. Treatment with L-dopa induced hyperkinesias, and a rise in dopamine, serotonin and norepinephrine content, whereas reserpine reduced motor activity and the concentrations of all three monoamines. 3. Haloperidol reduced motor activity and dopamine and norepinephrine levels. 4. Apomorphine induced hyperkinesias without altering monoamine levels.