Acute melatonin and para-chloroamphetamine interactions on pineal, brain and serum serotonin levels as well as stress hormone levels

Effect of diet on serotonergic neurotransmission in depression

Depression is characterized by sadness, purposelessness, irritability, and impaired body functions. Depression causes severe symptoms for several weeks, and dysthymia, which may cause chronic, low-grade symptoms. Treatment of depression involves psychotherapy, medications, or phototherapy. Clinical and experimental evidence indicates that an appropriate diet can reduce symptoms of depression. The neurotransmitter, serotonin (5-HT), synthesized in the brain, plays an important role in mood alleviation, satiety, and sleep regulation. Although certain fruits and vegetables are rich in 5-HT, it is not easily accessible to the CNS due to blood brain barrier. However the serotonin precursor, tryptophan, can readily pass through the blood brain barrier. Tryptophan is converted to 5-HT by tryptophan hydroxylase and 5-HTP decarboxylase, respectively, in the presence of pyridoxal phosphate, derived from vitamin B(6). Hence diets poor in tryptophan may induce depression as this essential amino acid is not naturally abundant even in protein-rich foods. Tryptophan-rich diet is important in patients susceptible to depression such as certain females during pre and postmenstrual phase, post-traumatic stress disorder, chronic pain, cancer, epilepsy, Parkinson's disease, Alzheimer's disease, schizophrenia, and drug addiction. Carbohydrate-rich diet triggers insulin response to enhance the bioavailability of tryptophan in the CNS which is responsible for increased craving of carbohydrate diets. Although serotonin reuptake inhibitors (SSRIs) are prescribed to obese patients with depressive symptoms, these agents are incapable of precisely regulating the CNS serotonin and may cause life-threatening adverse effects in the presence of monoamine oxidase inhibitors. However, CNS serotonin synthesis can be controlled by proper intake of tryptophan-rich diet. This report highlights the clinical significance of tryptophan-rich diet and vitamin B(6) to boost serotonergic neurotransmission in depression observed in various neurodegenerative diseases. However pharmacological interventions to modulate serotonergic neurotransmission in depression, remains clinically significant. Depression may involve several other molecular mechanisms as discussed briefly in this report.

Short-term effects of melatonin and pinealectomy on serotonergic neuronal activity across the light-dark cycle

Melatonin (MLT) and serotonin (5-HT) are two biosynthetically related compounds implicated in several common physiological functions and the etiology of mood disorders. How they interact, though, is not yet fully understood. In this study, single-unit extracellular recordings were used to monitor dorsal raphe nucleus (DR) 5-HT neuronal activity in anesthetized rats, under basal conditions (CTRL), in response to MLT administration, and after pinealectomy (PX) across the light-dark cycle. Under basal conditions, the number of spontaneously active 5-HT neurons and their firing rate were both significantly lower in the dark phase. In the light phase, administration of MLT at low doses (0.5-1 mg/kg, i.v.) decreased 5-HT firing activity. This inhibitory effect of MLT was completely blocked by the MT₁/MT₂ receptor antagonist luzindole, but not by the selective MT(2) receptor antagonist 4P-PDOT, the selective 5-HT(1A) receptor antagonist WAY100635, or by the α₂ adrenoceptor antagonist idazoxan. In the opposite experiment, PX increased 5-HT firing activity in the dark phase, and this was reversed by MLT administration (1 mg/kg, i.v.). Finally, in a forced swim test, MLT (1 mg/kg, i.p.) increased immobility time and decreased swimming behavior. Together, these results suggest that nocturnal MLT secretion imposes tonic inhibitory control over a sub-population of DR 5-HT neurons. This MLT-induced decrease in 5-HT neurotransmission may represent a biological mechanism underlying mood disorders characterized by increased MLT secretion, such as seasonal affective disorder.

Melatonin reduces the expression of alpha-synuclein in the dopamine containing neuronal regions of amphetamine-treated postnatal rats

Alpha-synuclein (α-syn) is a neuronal protein that is involved in various degenerative disorders such as Parkinson's disease. It is found in the presynaptic terminals and perinuclear zones of many brain regions. Amphetamine (AMPH), a psychostimulant drug abused progressively more commonly in recent years, has been known to induce neurotoxicity in the central dopaminergic pathway, which is associated with increased oxidative stress. Recently, AMPH has been shown to significantly increase the level of α-syn in dopaminergic neuroblastoma cell cultures. Melatonin is recognized as an antioxidant for the nervous system. This study tested whether melatonin can attenuate the effect of AMPH on the expression of α-syn in the dopaminergic pathway of the neonatal rat. Four-day old postnatal rats (P4) were injected subcutaneously with either AMPH (increasing dose, 5-10 mg/kg daily) alone or AMPH with melatonin (2 mg/kg) daily at 10:00 AM for 7 consecutive days. As determined using Western blot, the level of α-syn was significantly increased in the substantia nigra, dorsal striatum, nucleus accumbens, and prefrontal cortex of the AMPH-treated group, while melatonin treatment either prior to AMPH or alone decreased the accumulation of the protein to 77%, 96%, 78%, and 77% of the control value, respectively. Furthermore, an immunofluorescent study showed that the α-syn-immunoreactivity increased noticeably in the nuclei of cell bodies and nerve terminals of the AMPH-treated group. Again, melatonin lowered this immunoreactivity. These results indicate that melatonin has a direct or indirect effect in reducing the expression of α-syn in the postnatal rat. The exact mechanism of this mitigation should be further investigated.

Hematological, immunological and neurochemical effects of chronic amphetamine treatment in male rats

In the present study, we have analyzed the effect of chronic amphetamine sulfate (AMPH) treatment on haematological, immunological and neurochemical parameters in the male rat. AMPH increased the total peripheral leukocyte count, and altered its differential counts, decreasing lymphocytes and increasing neutrophils. Flow cytometry study showed that the decline in circulating lymphocytes was caused by the loss of a particular lymphocyte subset, B-cell, which reduced both in percentage and in absolute number by 50%. T-cell population increased by 15% but not in absolute number, however there was no difference in either CD4+ or CD8+ T lymphocyte subsets between experimental groups. Neurochemically, AMPH reduced norepinephrine (NE) and serotonin (5-HT) contents in the hypothalamus and increased dopamine (DA) content in the striatum. Chronic AMPH increased in a dose-dependent manner serum corticosterone levels, had no effect on circulating catecholamines, reduced adrenal weights, and did not affect spleen weights although reduced their cellularities. These results show that chronic AMPH have important effects on immune function, particularly on humoral immune response because it reduced the circulating B cell population by half. In addition, AMPH plays an important role in the redistribution and trafficking of leukocytes, and both effects seem to be mediated by sympathetic innervation of the lymphoid organs.

Central serotonin depletion affects rat brain areas differently: a qualitative and quantitative comparison between different treatment schemes

Depletion of rat brain serotonin (5-hydroxytryptamin, 5-HT) has been widely used to study effects of serotonin and its interaction with other transmitter systems. Various treatment regimes for serotonin depletion have been applied, but the efficacy of these seems to vary considerably. So far, no studies have systematically examined and compared different approaches. The present work combines quantitative and qualitative measurements and compares six different treatment schemes for 5-HT depletion. Treatment outcome was evaluated by HPLC measurements of 5-HT and 5-HIAA concentrations, and by 5-HT and tyrosine hydroxylase immunocytochemistry. The schemes included repeated administration of fenfluramine (FEN) and/or p-chlorophenylalanine (pCPA). The most efficient treatment for rat brain 5-HT depletion was the combined treatment with one daily pCPA (200 mg/kg) injection for 3 days followed by one injection of d,l-FEN (20 mg/kg) on the fourth day, causing a 94.9% brain 5-HT depletion. Immunostaining revealed a distinct brain distribution of the remaining 5-HT, with an almost complete depletion of 5-HT in the cerebral cortex, hippocampus and thalamus, while a substantial amount of 5-HT still was left in the raphe nuclei, the medial forebrain bundle, and the medial eminence. FEN or pCPA treatment alone caused from 68.2 to 94.0% decrease in 5-HT levels. While the pattern of 5-HT depletion using pCPA alone was comparable to the one seen with the combined treatment, the 5-HT depletion using FEN alone showed a different pattern with 5-HT distributed in several brain regions.