Pansiri Phansuwan-Pujito

Pineal opioid receptors and analgesic action of melatonin

Abstract: Physicians have noted since antiquity that their patients complained of less pain and required fewer analgesics at night times. In most species, including the humans, the circulating levels of melatonin, a substance with analgesic and hypnotic properties, exhibit a pronounced circadian rhythm with serum levels being high at night and very low during day times. Moreover, melatonin exhibits maximal analgesic effects at night, pinealectomy abolishes the analgesic effects of melatonin, and mu opioid receptor antagonists disrupt the day‐night rhythm of nociception. It is believed that melatonin, with its sedative and analgesic effects, is capable of providing a pain free sleep so that the body may recuperate and restore itself to function again at its peak capacity. Moreover, in conditions when pain is associated with extensive tissue injury, melatonins ability to scavenge free radicals and abort oxidative stress is yet another beneficial effect to be realized. Since melatonin may behave as a mixed opioid receptor agonist‐antagonist, it is doubtful that a physician simply could potentiate the analgesic efficacy of narcotics such as morphine by coadministering melatonin. Therefore, future research may synthesize highly efficacious melatonin analogues capable of providing maximum analgesia and hopefully being devoid of addiction liability now associated with currently available narcotics.

Melatonin protects against hydrogen peroxide-induced cell death signaling in SH-SY5Y cultured cells: involvement of nuclear factor kappa B, Bax and Bcl-2

Abstract:  Oxidative stress is defined as a disturbance in the prooxidant–antioxidant balance, leading to potential cell damage. Reactive oxygen species such as superoxide radicals, hydroxyl radicals and hydrogen peroxide may act also as secondary intermediaries in intracellular signaling leading to cell death. The neuroprotective effect of melatonin has been observed both in vivo and in vitro. The objective of this research, therefore, was to better understand the cellular mechanisms of neuronal cell degeneration induced via oxidative stress and the protective roles of melatonin on this cell death. In the present study, the effects of melatonin on H2O2‐induced neuronal cell degeneration in human dopaminergic neuroblastoma SH‐SY5Y cultured cells were investigated. The results showed that H2O2 significantly decreased cell viability and melatonin reversed the toxic effects of H2O2. An inhibition of caspase enzyme activity by Ac‐DEVD‐CHO, a caspase‐3 inhibitor, significantly increased cell viability in H2O2‐treated cells. The phosphorylation of transcription factors, nuclear factor kappa B (NF‐κB) was increased in H2O2‐treated cells and this effect was abolished by melatonin. Translocation of phosphorylated NF‐κB to perinuclear and nuclear sites, estimated using immunofluorescence, occurred to a greater extent in H2O2‐treated cells than in untreated control cells and again this effect was abolished by melatonin. In addition, induction of Bcl‐2 and Bax proteins was demonstrated in SH‐SY5Y cultured cells treated with H2O2, whereas the induction of Bax but not Bcl‐2 was diminished by melatonin. In light of these finding, it is possible that the antioxidative stress effect of melatonin associated with inhibition of Bax expression, may offer a means of treating neuronal degeneration and disease.

Melatonin increases proliferation of cultured neural stem cells obtained from adult mouse subventricular zone

Abstract:  Melatonin, a circadian rhythm–promoting molecule secreted mainly by the pineal gland, has a variety of biological functions and neuroprotective effects including control of sleep–wake cycle, seasonal reproduction, and body temperature as well as preventing neuronal cell death induced by neurotoxic substances. Melatonin also modulates neural stem cell (NSC) function including proliferation and differentiation in embryonic brain tissue. However, the involvement of melatonin in adult neurogenesis is still not clear. Here, we report that precursor cells from adult mouse subventricular zone (SVZ) of the lateral ventricle, the main neurogenic area of the adult brain, express melatonin receptors. In addition, precursor cells derived from this area treated with melatonin exhibited increased proliferative activity. However, when cells were treated with luzindole, a competitive inhibitor of melatonin receptors, or pertussis toxin, an uncoupler of Gi from adenylate cyclase, melatonin‐induced proliferation was reduced. Under these conditions, melatonin induced the differentiation of precursor cells to neuronal cells without an upregulation of the number of glia cells. Because stem cell replacement is thought to play an important therapeutic role in neurodegenerative diseases, melatonin might be beneficial for stimulating endogenous neural stem cells.

5‐HT2A Receptor Activation and Nitric Oxide Synthesis: A Possible Mechanism Determining Migraine Attacks

Objective.—To determine the effect of the 5‐HT2A receptor in control of spinal nociception, cerebral circulation, and nitric oxide synthase (nNOS) expression in trigeminovascular neurons.

Light Touch Cue Through a Cane Improves Pelvic Stability During Walking in Stroke

OBJECTIVE To examine the effect of a light touch cue provided through a cane on mediolateral (ML) pelvic stability during walking in subjects poststroke. DESIGN Crossover trial examining ML pelvic stability during walking using a cane with the force contact and touch contact methods. SETTING Physical therapy clinic, tertiary care center. PARTICIPANTS Subacute patients (N=40) with stroke with a mean age of 59.6 years and mean stroke duration of 46.8 days. The average gait speed with a cane was .13 m/s (.05-.29 m/s). INTERVENTION Using a cane with the force contact and touch contact methods during walking. MAIN OUTCOME MEASURES ML pelvic stability as measured by averaged peak-to-peak pelvic acceleration, muscle activation of bilateral tensor fascia latae (TFL), semitendinosus (ST), and vastus medialis (VM) using an electromyography system, and vertical cane force. RESULTS The average amount of cane force during touch contact and force contact cane use conditions was 2.3N and 49.3N, respectively. A light touch cue through a cane was required only when the paretic leg accepted the body weight, and this cue can provide ML pelvic stability (.16 g of average pelvic acceleration) during walking to the same degree as the force contact method of cane use. However, significant increases in single-limb support duration with higher activations of TFL, VM, and ST muscles on the paretic leg were found during the paretic stance phase when using a cane in the touch contact fashion (P<.05). CONCLUSIONS A light touch cue can be provided during walking through the use of a cane. This augmented somatosensory information provides lateral stability during walking for subjects with stroke by facilitating the activations of weight-bearing muscles on the paretic leg during the stance phase.

Melatonin protects SK‐N‐SH neuroblastoma cells from amphetamine‐induced neurotoxicity

Abstract:  Several hypotheses regarding the mechanism underlying amphetamine‐induced neurotoxicity have been proposed. One of them is based on the observation of free radical formation and oxidative stress produced by auto‐oxidation of dopamine (DA). The formation of DA‐related reactive oxygen species (ROS) such as superoxide and hydroxyl radicals appears to play an important role in amphetamine‐induced neurotoxicity. Melatonin, the main secretory product of pineal gland, is well known for its protective effects that are currently attributed mainly to its radical scavenging and antioxidant properties. The present study was conducted to investigate the protective effects of melatonin on d‐amphetamine (AMPH)‐induced neurotoxicity in cultured human dopaminergic neuroblastoma SK‐N‐SH cells. Our data indicate that AMPH significantly reduces cell viability, induces oxidative stress (enhances ROS production and malondialdehyde levels), up‐regulates α‐synuclein expression and decreases intracellular ATP levels. However, pretreatment of SK‐N‐SH cells with melatonin prevents AMPH‐induced loss of cell viability and induction of oxidative stress, while reducing α‐synuclein expression and increasing ATP production. These results suggest that the antioxidant properties of melatonin may provide a protective mechanism against AMPH‐induced neuronal degeneration.

Localization and diurnal expression of mRNA encoding the β1-adrenoceptor in the rat pineal gland: an in situ hybridization study

Abstract.The rat pinealocyte is stimulated by norepinephrine, which is released from sympathetic nerve fibers innervating the gland. Norepinephrine binds to β1-adrenoceptors situated on the pinealocyte cell membrane. Ligand binding to these receptors exhibits a diurnal rhythm, with the largest number occurring in the late part of the light phase when the release of norepinephrine is minimal. By using in situ hybridization with a cDNA antisense oligonucleotide probe recognizing mRNA encoding the rat β1-adrenoceptor, we have demonstrated a stronger hybridization signal in the rat pineal gland than in other brain regions. Cells containing β1-mRNA are located in the superficial pineal gland, the deep pineal gland, and the pineal stalk. However, the number of receptors varies considerably between the individual pinealocytes. The β1-mRNA in situ hybridization signal for mRNA encoding the β1-adrenoceptor of the rat pineal has been quantified over a 24-h period; the strongest signal is found at mid-dark and the weakest signal at mid-light, indicating that the transcriptional regulation of β1-mRNA synthesis in the rat pineal is diurnal. In addition, maximal receptor protein expression occurs late in the light phase in the rat pineal and is thus considerably delayed compared with its peak mRNA synthesis. This lag time indicates that the β1-receptor is regulated at the translational or post-translational level. Removal of the sympathetic input to the pineal gland by superior cervical ganglionectomy decreases the β1-mRNA signal in the gland.

Melatonin attenuates methamphetamine-induced reduction of tyrosine hydroxylase, synaptophysin and growth-associated protein-43 levels in the neonatal rat brain.

Methamphetamine (METH) is a most commonly abused drug which damages nerve terminals by causing formation of reactive oxygen species (ROS), apoptosis, and finally neuronal damage. Fetal exposure to neurotoxic METH causes significant behavioral effects. The developing fetus is substantially deficient in most antioxidative enzymes, and may therefore be at high risk from both endogenous and drug-enhanced oxidative stress. Little is known about the effects of METH on vesicular proteins such as synaptophysin and growth-associated protein 43 (GAP-43) in the immature brain. The present study attempted to investigate the effects of METH-induced neurotoxicity in the dopaminergic system of the neonatal rat brain. Neonatal rats were subcutaneously exposed to 5-10mg/kg METH daily from postnatal day 4-10 for 7 consecutive days. The results showed that tyrosine hydroxylase enzyme levels were significantly decreased in the dorsal striatum, prefrontal cortex, nucleus accumbens and substantia nigra, synaptophysin levels decreased in the striatum and prefrontal cortex and growth-associated protein-43 (GAP-43) levels significantly decreased in the nucleus accumbens of neonatal rats. Pretreatment with 2mg/kg melatonin 30 min prior to METH administration prevented METH-induced reduction in tyrosine hydroxylase, synaptophysin and growth-associated protein-43 protein levels in different brain regions. These results suggest that melatonin provides a protective effect against METH-induced nerve terminal degeneration in the immature rat brain probably via its antioxidant properties.

A cholinergic innervation of the bovine pineal gland visualized by immunohistochemical detection of choline acetyltransferase-immunoreactive nerve fibers

An immunohistochemical investigation of the bovine pineal gland was performed using both a rabbit polyclonal antibody and a rat monoclonal antibody against choline acetyltransferase (ChAT). A network of ChAT-immunoreactive (IR) nerve fibers was located throughout the pineal gland, both in the perivascular spaces and between the pinealocytes. Most of the intrapineal ChAT-IR nerve fibers were endowed with varicosities. In addition, some ChAT-IR intrapineal neurons were found, often located at the base of the gland near the pineal recess. Within the habenular nucleus and pineal stalk, ChAT-IR perikarya and nerve fibers were also present. Some of these fibers projected towards the pineal gland. A number of ChAT-IR nerves were also located in the posterior commissure and could be followed into the gland. At the caudal tip of the pineal gland, a bundle of ChAT-IR nerve fibers was observed to penetrate into the gland together with blood vessels. The presence of a cholinergic innervation of the bovine pineal gland, together with previous demonstration of the presence of choline acetyltransferase and muscarinic receptor binding sites in the bovine pineal gland, indicates a functional influence of a cholinergic nervous system on the pinealocyte.

Melatonin inhibits amphetamine-induced increase in α-synuclein and decrease in phosphorylated tyrosine hydroxylase in SK–N–SH cells

alpha-Synuclein is an abundant presynaptic protein implicated in neuronal plasticity and neurodegeneration disorders. Understanding alpha-synuclein function in dopaminergic cells could add to our knowledge of this key protein which is implicated in Parkinsons disease. Chronic or intermittent amphetamine (AMPH) abuse may create temporary or permanent disturbances in the dopaminergic system of the brain that may predispose individuals to Parkinsonism. Our previous studies showed that neurotoxicity induced by AMPH was mediated by enhanced oxidative stress and these effects were abolished by melatonin, a main secretory product of pineal gland. The present study was conducted to investigate the effect of AMPH on alpha-synuclein in regulating tyrosine hydroxylase (TH), a rate limiting enzyme for dopamine synthesis, in cultured human dopaminergic SK-N-SH cells. Of these, phosphorylation of Ser40 (pSer40) contributes significantly to TH activation and dopamine synthesis. Our data indicated that AMPH significantly increased the level of alpha-synuclein to 183% of the control value while reducing the levels of phosphorylated TH (TH-pSer40) enzyme and mitochondrial complex I to 78 and 52.9% of the control values, respectively and these effects were attenuated by melatonin. Further studies are needed to explore the mechanism by which alpha-synuclein contributes to TH-pSer40 dephosphorylation and the mechanism by which melatonin contributes to this interaction.