Rubén V. Rial

Effect of orally administered l-tryptophan on serotonin, melatonin, and the innate immune response in the rat

To assess the effects of external administration of L-tryptophan on the synthesis of serotonin and melatonin as well as on the immune function of Wistar rats, 300 mg of the amino acid were administered through an oral cannula either during daylight (08:00) or at night (20:00) for 5 days. Brain, plasma, and peritoneal macrophage samples were collected 4 h after the administration. The accumulation of 5-hydroxytryptophan (5-HTP) after decarboxylase inhibition was used to measure the rate of tryptophan hydroxylation in vivo. Circulating melatonin levels were determined by radioimmunoassay, and the phagocytic activity of macrophages was measured by counting, under oil-immersion phase-contrast microscopy, the number of particles ingested. The results showed a diurnal increase (p < 0.05) in the brain 5-HTP, serotonin (5-hydroxytryptamine, 5-HT), and 5-hydroxyindolacetic acid (5-HIAA) of the animals which had received tryptophan at 08:00 and were killed 4 h later. In the animals which received tryptophan during the dark period, the 5-HT declined but the 5-HT/5-HIAA ratio remained unchanged. There was also a significant increase (p < 0.05) in nocturnal circulating melatonin levels and in the innate immune response of the peritoneal macrophages in the animals which had received tryptophan at 20:00. The results indicated that the synthesis of serotonin and melatonin, as well as the innate immune response, can be modulated by oral ingestion of tryptophan. (Mol Cell Biochem 267: 39–46, 2004)

Chronic melatonin treatment and its precursor L-tryptophan improve the monoaminergic neurotransmission and related behavior in the aged rat brain

Abstract:  Melatonin has an important role in the aging process as a potential drug to relieve oxidative damage, a likely cause of age‐associated brain dysfunction. As age advances, the nocturnal production of melatonin decreases potentially causing physiological alterations. The present experiments were performed to study in vivo the effects of exogenously administered melatonin chronically on monoaminergic central neurotransmitters serotonin (5‐HT), dopamine (DA) and norepinephrine (NE) and behavioral tests in old rats. The accumulation of 5‐hydroxy‐tryptophan (5‐HTP) and L‐3,4‐dihydroxyphenylalanine (DOPA) after decarboxylase inhibition was used as a measure of the rate of tryptophan and tyrosine hydroxylation in rat brain. Also neurotransmitters 5‐HT, DA and NE and some metabolites were quantified by HPLC. In control rats, an age‐related decline was observed in neurochemical parameters. However, chronic administration of melatonin (1 mg/kg/day, diluted in drinking water, 4 wk) significantly reversed the age‐induced deficits in all the monoaminergic neurotransmitters studied. Also, neurochemical parameters were analyzed after administration of melatonin biosynthesis precursor L‐tryptophan (240 mg/kg/day, i.p., at night for 4 wk) revealing similar improvement effects to those induced by melatonin. Behavioral data corresponded well with the neurochemical findings since spatial memory test in radial‐maze and motor coordination in rota‐rod were significantly improved after chronic melatonin treatment. In conclusion, these in vivo findings suggest that melatonin and L‐tryptophan treatments exert a long‐term effect on the 5‐HT, DA and NE neurotransmission by enhancing monoamine synthesis in aged rats, which might improve the age‐dependent deficits in cognition and motor coordination.

Melatonin and Tryptophan Affect the Activity–Rest Rhythm, Core and Peripheral Temperatures, and Interleukin Levels in the Ringdove: Changes With Age

Aging is known to alter the circadian rhythms of melatonin, serotonin, thermoregulatory responses, cytokine production, and sleep/wakefulness which affect sleep quality. We tested the possible palliative effects of a 3-day administration of melatonin (0.25 or 2.5 mg/kg of body weight [b.w.] to young and old ringdoves, respectively) or tryptophan (300 mg/kg of b.w. to old ringdoves) on these rhythms. Doves are a monophasic, diurnal species; these characteristics are similar in humans. Old animals presented lower melatonin and serotonin levels; higher interleukin (IL)-1beta, IL-6, and tumor necrosis factor alpha values; and reductions in the Midline-Estimating Statistic of Rhythm and amplitude of activity-rest rhythm and in the amplitude of the core temperature rhythm. Melatonin raised serum melatonin levels; tryptophan increased both melatonin and serotonin levels. Melatonin and tryptophan lowered nocturnal activity, core temperature, and cytokine levels and increased peripheral temperature in both groups. Melatonin or tryptophan may limit or reverse some of the changes that occur in sleep-wake rhythms and temperature due to age.

A role played by the vitelline diverticulum in the yolk sac resorption in young post-hatched chickens

SummaryYolk sac resorption, with special reference to the role of the vitelline stalk, was studied in young post-hatched chickens (0, 1, and 2 days old) using a radioactive (14C-PEG-4000) and coloured (Evans Blue) marker injected into the yolk sac lumen of conscious birds. When the animals were newly-hatched and 1 day old, the radioactive material was recovered from the lumen of the gastrointestinal tract, but not when the vitelline diverticulum was tied. These results suggest a role played by the vitelline diverticulum in the removal of vitelline contents during the first post-hatching 48 h of chick life.

Evolution of wakefulness, sleep and hibernation: From reptiles to mammals

Thus far, most hypotheses on the evolutionary origin of sleep only addressed the probable origin of its main states, REM and NREM. Our article presents the origin of the whole continuum of mammalian vigilance states including waking, sleep and hibernation and the causes of the alternation NREM-REM in a sleeping episode. We propose: (1) the active state of reptiles is a form of subcortical waking, without homology with the cortical waking of mammals; (2) reptilian waking gave origin to mammalian sleep; (3) reptilian basking behaviour evolved into NREM; (4) post-basking risk assessment behaviour, with motor suspension, head dipping movements, eye scanning and stretch attending postures, evolved into phasic REM; (5) post-basking, goal directed behaviour evolved into tonic REM and (6) nocturnal rest evolved to shallow torpor. A small number of changes from previous reptilian stages explain these transformations.

Cognitive recovery and restoration of cell proliferation in the dentate gyrus in the 5XFAD transgenic mice model of Alzheimer's disease following 2-hydroxy-DHA treatment

Alzheimer’s disease (AD) is the most common neurodegenerative disorder in the elderly. In the last years, abnormalities of lipid metabolism and in particular of docosahexaenoic acid (DHA) have been recently linked with the development of the disease. According to the recent studies showing how hydroxylation of fatty acids enhances their biological activity, here we show that chronic treatment with a hydroxylated derivative of DHA, the 2-hydroxy-DHA (2OHDHA) in the 5XFAD transgenic mice model of AD improves performance in the radial arm maze test and restores cell proliferation in the dentate gyrus, with no changes in the presence of beta amyloid (Aβ) plaques. These results suggest that 2OHDHA induced restoration of cell proliferation can be regarded as a major component in memory recovery that is independent of Aβ load thus, setting the starting point for the development of a new drug for the treatment of AD.

Age-related changes in circadian rhythm of serotonin synthesis in ring doves: Effects of increased tryptophan ingestion

Alterations in the function of the hypothalamic suprachiasmatic nucleus (SCN) with age have been reported. As serotonin is an important regulator of the circadian clock located in SCN, this work studied the changes produced in the synthesis of serotonin with age using the accumulation of 5-HTP after decarboxylase inhibition as a measure of serotonin synthesis in the brain in vivo, in young and old ring doves at the onset of lights-on and lights-off. A diurnal cycle in tryptophan hydroxylation was observed in young animals, with an increased daylight synthesis and metabolism of 5-HT in hippocampus, neostriatum and hypothalamus. A single dose of melatonin (1 mg/kg, i.p., 1 h) at lighttime produced an inhibitory effect on the synthesis of 5-HT. In contrast, differences in 5-HT synthesis and metabolism between day and night disappeared in old animals indicating an absence of a circadian rhythm in 5-HT synthesis and metabolism. The administration of L-tryptophan (240 mg/kg, i.p.) strongly increased the 5-HT synthesis in young animals only during lights-off time while it increased in old ones irrespective of the administration time. These results suggest that the supplemental administration of tryptophan might aid to improve the descent in 5-HT that normally occurs, as animals get old.

Chrononutrition: Use of dissociated day/night infant milk formulas to improve the development of the wake–sleep rhythms. Effects of tryptophan

Abstract Three different lactation experiments have been tested in a double blind procedure for 3 weeks, to improve sleep–wake patterns in infants. In a control experiment, standard infant commercial milk (1.5% tryptophan) was administered without changes during the day. In a second control (inverse), enriched milk (3.4% tryptophan) was given during light-time (06.00–18.00 h), and standard commercial milk during night-time (18.00–06.00 h). During the experimental week, the infants received standard milk during light-time and tryptophan enriched milk during night-time. The infants receiving the enriched formula during dark time showed improvements in the sleep parameters studied, and no statistical differences were found between the two control lactations. The urinary metabolites of serotonin suggest that the observed improvements were due to an increased use of serotonin to melatonin synthesis. In conclusion, the chronobiological changes in the normal components of the diet can improve infantile development of sleep/wake rhythms.

Age related changes in the activity-rest circadian rhythms and c-fos expression of ring doves with aging. Effects of tryptophan intake

Age related changes in the circadian rhythms and sleep quality has been linked with impairment in the function of the suprachiasmatic nucleus (SCN) and melatonin secretion. The precursor of melatonin, serotonin (5-HT) is a neurotransmitter involved in the synchronisation of the circadian clock located in SCN, which shows decreased levels with age. The present work studied the effects of L-tryptophan, the precursor of 5-HT, on the circadian activity-rest rhythm and c-fos expression in the SCN of young and old ring doves, animals diurnal and monocyclic as humans. Two hours before the onset of dark phase, animals housed in cages equipped for activity recording and maintained under 12/12 L/D conditions, received orally L-tryptophan (100 and 240 mg/kg) and, for comparative purposes, melatonin (2.5 and 5 mg/kg). The administration of both L-tryptophan and melatonin reduced the nocturnal activity of all ring doves although only the highest doses were effective in old ones. A reduced amplitude in the activity-rest rhythm was observed in old animals in comparison to youngest, but it was increased after the treatments. Sleep parameters, calculated from the activity data, indicated a worsened sleep quality in old animals but it was improved with the treatments. In addition, the expression of c-fos in the SCN was reduced after both mentioned treatments. The results point to the SCN as a target for the observed nocturnal effects of L-tryptophan and melatonin, and support the supplemental administration of the essential amino acid L-tryptophan to reverse the disturbances of the circadian activity-rest cycle related with ageing.

ELECTROENCEPHALOGRAM FUNCTIONAL CONNECTIVITY BETWEEN RAT HIPPOCAMPUS AND CORTEX AFTER PILOCARPINE TREATMENT

The muscarinic agonist pilocarpine has been shown to increase the duration and total number of episodes presenting theta rhythm-simultaneously in hippocampus and cortex-in rats during the waking states. Theta waves are suggested to be involved in the flow of information between hippocampus and cortex during memory processes. This work investigates this functional interdependence using the spectral and phase synchronization analysis of the electroencephalogram (EEG) theta band recorded in these brain structures of rats after pilocarpine treatment. Pilocarpine was used at doses devoid of epilepticus-like seizures effects in conscious freely moving rats. The results showed that pilocarpine administration significantly increased the relative theta power during the waking states in the cortex, but not in the hippocampus of rats. Additionally, the EEG coherence between the hippocampal EEG theta band and that arising at the frontal cortex increased after pilocarpine treatment but only during the waking states. This result reveals an increase of the linear correlation between the theta waves of these two brain structures after pilocarpine treatment during the waking states. Moreover, phase synchronization results showed an effective phase locking with non-zero phase difference between hippocampus and frontal cortex theta waves that remained after pilocarpine treatment. Therefore, pilocarpine seems to reinforce the neural transmission waves from the hippocampus toward the cortex during waking. In conclusion, the present EEG study could suggest an effect of the muscarinic cholinergic agonist pilocarpine on the hippocampal-cortical functional connectivity.