M. Aldegunde

Energy metabolism of fish brain.

This review focuses on recent research on the metabolic function of fish brain. Fish brain is isolated from the systemic circulation by a blood-brain barrier that allows the transport of glucose, monocarboxylates and amino acids. The limited information available in fishes suggests that oxidation of exogenous glucose and oxidative phosphorylation provide most of the ATP required for brain function in teleosts, whereas oxidation of ketones and amino acids occurs preferentially in elasmobranchs. In several agnathans and benthic teleosts brain glycogen levels rather than exogenous glucose may be the proximate glucose source for oxidation. In situations when glucose is in limited supply, teleost brains utilize other fuels such as lactate or ketones. Information on use of lipids and amino acids as fuels in fish brain is scarce. The main pathways of brain energy metabolism are changed by several effectors. Thus, several parameters of brain energy metabolism have been demonstrated to change post-prandially in teleostean fishes. The absence of food in teleosts elicits profound changes in brain energy metabolism (increased glycogenolysis and use of ketones) in a way similar to that demonstrated in mammals though delayed in time. Environmental factors induce changes in brain energy parameters in teleosts such as the enhancement of glycogenolysis elicited by pollutants, increased capacity for anaerobic glycolysis under hypoxia/anoxia or changes in substrate utilization elicited by adaptation to cold. Furthermore, several studies demonstrate effects of melatonin, insulin, glucagon, GLP-1, cortisol or catecholamines on energy parameters of teleost brain, although in most cases the results are quite preliminary being difficult to relate the effects of those hormones to physiological situations. The few studies performed with the different cell types available in the nervous system of fish allow us to hypothesize few functional relationships among those cells. Future research perspectives are also outlined.

Selective changes in the contents of noradrenaline, dopamine and serotonin in rat brain areas during aging.

Summary. This study examines the age-associated changes in noradrenaline (NA), dopamine (DA), 3,4-dihydroxyphenyl-acetic acid (DOPAC), serotonin (5-HT) and 5-hydroxy-3-indoleacetic acid (5-HIAA) in different brain areas of rats. DA and DOPAC concentrations in striatum increased at third month of age, remaining without significant variations until 12th month of age, and decreasing in 24-month-old rats. DA concentration dropped in hippocampus, amygdala and brainstem of 24-month-old-rats, whereas DOPAC levels decreased only in hippocampus. These changes suggest an age-dependent deficit of the dopaminergic system, presumably related to a reduced number/activity of DA nigrostriatal and mesolimbic neurons. An age-induced decline in NA content was found in the pons-medulla, the area containing NA neuronal bodies. Concentrations of 5-HT were reduced with aging in frontal cortex, showing a tendency to decrease in all brain areas examined. The increased 5-HIAA/5-HT ratio found in frontal cortex, amygdala and striatum suggests an age-related decreased synthesis and an accelerated 5-HT metabolism. The 5-HIAA content decreased in brainstem of the oldest rats. These findings point to a selective impairment of nigrostriatal and mesolimbic DA in aging rats, whereas reductions in NA were restricted to cell bodies region and 5-HT showed changes of different extent in areas of terminals and neuronal cell bodies.

Pineal and plasma melatonin as determined by high-performance liquid chromatography with electrochemical detection

A rapid and sensitive method for the routine quantitative determination of melatonin in pineal and plasma is described. The assay used reversed-phase high-performance liquid chromatography (RP-HPLC) separation combined with either amperometric (system A) or coulometric (system B) detection. The method gave satisfactory reproducibility and accuracy, and detection limits for melatonin were as low as 8.5 pg (system A) and 1 pg (system B). This high sensitivity, together with the short analysis time (less than 10 min), and the simplicity of sample procedure make the present RP-HPLC method suitable for a wide range of studies concerning melatonin measurements. Melatonin values obtained in this study from both rat pineal and human plasma agree with those reported previously, and clearly determined a circadian pattern.

Acute effects of L-tryptophan on tryptophan hydroxylation rate in brain regions (hypothalamus and medulla) of rainbow trout (Oncorhynchus mykiss).

Levels of 5-hydroxytryptophan (5-HTP) in brain regions (hypopthalamus and medulla) of rainbow trout were analysed by HPLC-EC 0, 10, 30, and 40 min after intraperitoneal administration of different doses of L-tryptophan (Trp) (0, 12.5, and 25 mg. kg(-1) body weight) in fish treated with 3-hydroxybenzylhydrazine (NSD1015; 75 mg. kg(-1)). The results show that, in control fish, 5-HTP levels in hypothalamus (58.03 +/- 6.36 pg. mg(-1) brain tissue) were significantly higher than those observed in medulla (28.04 +/- 4.32 pg. mg(-1) brain tissue). Basal tryptophan hydroxylation rates (after 0 mg. kg(-1) Trp administration) were 0.42 +/- 0.07 pg 5-HTP. mg(-1). min(-1), and 0.63 +/- 0.24 pg 5HTP. mg(-1). min(-1), for hypothalamus and medulla respectively. On the other hand, the results demonstrate that L-tryptophan administration induced significant increases in the rate of tryptophan hydroxylation, both in hypothalamus and medulla. These findings indicate that, in a way similar to that observed in mammals, brain tryptophan hydroxylase is unsaturated by its substrate (tryptophan) under normal physiological conditions. J. Exp. Zool. 286:131-135, 2000.

Effects of single doses and daily melatonin treatments on serotonin metabolism in rat brain regions

Miguez, JM, Martin F. J, Aldegunde M. Effects of single doses and daily melatonin treatments on serotonin metabolism in rat brain regions. J. Pineal Res. 1994; 17:170–176.

Changes with age in daytime and nighttime contents of melatonin, indoleamines, and catecholamines in the pineal gland: A comparative study in rat and Syrian hamster

Abstract: Previous studies in rodents showed a severe deterioration of pineal physiology with aging. The present study investigated the age‐related changes in the content of monoamines and metabolites in rat and Syrian hamster pineal gland. In addition to melatonin, the levels of 5‐hydroxytryptophan (5HTP), serotonin (5HT), 5‐hydroxyindoleacetic acid (5HIAA), N‐acetylserotonin (N‐Ac‐5HT), dopamine (DA), 3,4‐dihydroxyphenylacetic acid (DOPAC), and noradrenaline (NA) were measured by HPLC. Pronounced reductions were found in 5HT and 5HIAA contents during daytime in rats of 24 months, which had not been observed in animals of 12 months. In addition, nighttime pineal 5HIAA, N‐Ac‐5HT, and melatonin contents were decreased in the old rats, although a significant day: night variation persisted. Also a diurnal fluctuation in NA, DA, and DOPAC contents was present in young and middle‐aged rats but not for NA and DOPAC in the oldest rats due to a decrease in the nighttime levels. Pineal DA levels were also reduced in 24‐month‐old rats during the night, although a marked day: night change was still found. In the Syrian hamster pineal, significant reductions in daytime 5HT and 5HIAA were found respectively at 12 and 18 months, while nighttime levels of these compounds were decreased from 18 months. The nocturnal content of N‐Ac‐5HT dropped gradually from 12 months, and melatonin was reduced by 74% and 86% in hamsters of 18 and 24 months, respectively. In all these compounds, a significant day: night variation was observed irrespective of age. However, neither a day: night variation nor an effect of aging was found in terms of pineal NA content. In contrast, pineal DA and DOPAC levels displayed a diurnal variation in hamsters of 1.5 and 6 months, but not in animals of 12 and 18 months due a reduced nighttime content. These data suggest that the decline of pineal melatonin with age is a consequence of a deficit in the pathway of serotonin utilization. This probably is explained by a reduced N‐acetyltransferase activity, which may be linked to impaired pineal catecholaminergic neurotransmission.

High-performance liquid chromatographic separation with electrochemical detection of amino acids focusing on neurochemical application

Abstract Twenty-three amino acids and dipeptides, including compounds of neurochemical interest, are measured by high-performance liquid chromatography using electrochemical detection after precolumn derivatization with o -phthalaldehyde/β-mercaptoethanol. The method uses a multistep polarity gradient system and the entire separation is performed in less than 23 min of analysis. The minimum detectable quantity was 0.66 pmol injected, corresponding to 50 n m concentration in the sample; the response was linear in the tested range of 1.33–1333 pmol (0.1–100 μ m ). Relative standard deviations ranged from 0.75 to 6.089% for area measurements (mean, 2.33) and from 0.209 to 0.779% for retention times (mean, 0.546). Examples of application of the method to analysis of biological samples such as rat brain homogenate and human cerebrospinal fluid are shown.

Effect of streptozotocin-induced diabetes mellitus on serotonin measures of peripheral tissues in rats

The present study was conducted to examine whether experimental diabetes (streptozotocin-induced) promotes changes in serotonin (5HT) measures of peripheral tissue. Platelet-free plasma 5HT, tryptophan and 5-hydroxyindolacetic acid (5HIAA), whole blood 5HT and renal, liver, intestinal and lung 5HT and 5HIAA levels were measured in rats of four experimental groups: control, diabetic, diabetic+insulin and non-diabetic+insulin. Several serotonin measures were unaltered in all four experimental groups, i.e. plasma, liver and lung 5HT and 5HIAA levels. Whole blood 5HT levels descended about 50% in diabetic rats, then recovered their proper levels after 1 week of insulin therapy. Diabetic animals had a significantly greater intestinal 5HT concentration (+50% versus control), while intestinal 5HIAA levels did not achieve statistical significance despite a -26% decrement in their value. Both renal 5HT and 5HIAA levels were decreased in diabetic animals and recovered with insulin therapy. Peripheral tissue 5HT measures were not varied by insulin administration to non-diabetic animals. The results are consistent with a 5HT release, which is diminished in enterochromaffin cells and enhanced in platelet concomitantly to a minor platelet 5HT uptake, for explaining alterations of plasma/blood 5HT measures in experimental diabetes, and with a diminished synthesis of 5HT for explaining renal changes.

Melatonin Effects on Serotonin Synthesis and Metabolism in the Striatum, Nucleus Accumbens, and Dorsal and Median Raphe Nuclei of Rats

This work examined the influence of the pineal gland and its hormone melatonin on the metabolism of serotonin (5-HT) in discrete areas of the forebrain, such as the Striatum and the nucleus accumbens, and the midbrain raphe. The content of 5-HT and its major oxidative metabolite, the 5-hydroxyindoleacetic acid (5-HIAA), as well as the in-vivo tryptophan hydroxylation rate were examined after long-term pinealectomy (one month) and daily melatonin treatment (500 μg/kg; twice daily for ten days) in pinealectomized rats. Pinealectomy did not alter 5-HT content in any of these brain areas, but it significantly increased the content of 5-HIAA in Striatum and the 5-HIAA/5-HT ratio in nucleus accumbens. The normal values of these parameters were recuperated after administration of exogenous melatonin, but it also increased the rate of tryptophan hydroxylation in both areas. In addition, melatonin treatment decreased the levels of 5-HIAA in dorsal raphe nucleus. These data suggest that the pineal gland, through the secretion of melatonin, modulates the local metabolism of 5-HT in forebrain areas by acting on the oxidative deamination. Moreover, melatonin injected in pinealectomized rats derives in a more extended effect than pinealectomy and induces a stimulation of 5-HT synthesis in the striatum, probably due to a pharmacological effect. These results point to the striatum as a target area for the interaction between pineal melatonin and the serotonergic function, and suggest a differential effect of the melatonin injected on areas containing serotonergic terminals and cell bodies, which may relevant for the mode of action of melatonin and its behavioral effects.

Effects of cortisol and thyroid hormone treatment on the glycogen metabolism of selected tissues of domesticated rainbow trout, Oncorhynchus mykiss

Abstract Glycogen, glucose, protein and glycogen phosphorylase and glycogen synthetase activity in liver, white muscle and kidney were determined in domesticated rainbow trout (Oncorhynchus mykiss) treated with 3,5,3′-triiodo-L-thyronine (T3), thyroxine (T4) and cortisol and combinations of all these hormones for 10 days. Plasma protein and glucose levels were also determined. Declines in liver glycogen and glucose were observed after cortisol treatment as compared to values obtained in controls (controls: 27.54 ± 1.73 mg glycogen/g and 16.81 ± 1.50 mg glucose/g) such as 15.94 ± 2.64 mg glycogen/g and 8.63 ± 1.22 mg glucose/g. T4 treatment did not produce any effects on the measured parameters. T3 plus T4 treatment caused a fall in hepatic glycogen and glucose levels ( 11.97 ± 1.27 mg glycogen/g and 8.98 ± 2.06 mg/g, respectively). All cortisol and thyroid hormone combinations produced a fall in liver glycogen levels (range between 6.07 ± 1.19 and 16.38 ± 1.56 mg glycogen/g) as well as an increase (from 37 to 44%) in glycogen phosphorylase activity. No changes were observed in any of the measured parameters for the different hormone treatments assessed in white muscle and kidney. Under our experimental conditions, cortisol and probably T3 are involved in liver glycogen mobilization and apparently do not elicit a response in white muscle and kidney.