Regulation of neurotransmitter reuptake by nitric oxide

Regulation of Glutamate, GABA and Dopamine Transporter Uptake, Surface Mobility and Expression

Neurotransmitter transporters limit spillover between synapses and maintain the extracellular neurotransmitter concentration at low yet physiologically meaningful levels. They also exert a key role in providing precursors for neurotransmitter biosynthesis. In many cases, neurons and astrocytes contain a large intracellular pool of transporters that can be redistributed and stabilized in the plasma membrane following activation of different signaling pathways. This means that the uptake capacity of the brain neuropil for different neurotransmitters can be dynamically regulated over the course of minutes, as an indirect consequence of changes in neuronal activity, blood flow, cell-to-cell interactions, etc. Here we discuss recent advances in the mechanisms that control the cell membrane trafficking and biophysical properties of transporters for the excitatory, inhibitory and modulatory neurotransmitters glutamate, GABA, and dopamine.

Neuronal nitric oxide synthase (NOS1) polymorphisms interact with financial hardship to affect depression risk

There is increasing evidence that genetic factors have a role in differential susceptibility to depression in response to severe or chronic adversity. Studies in animals suggest that nitric oxide (NO) signalling has a key role in depression-like behavioural responses to stress. This study investigated whether genetic variation in the brain-expressed nitric oxide synthase gene NOS1 modifies the relationship between psychosocial stress and current depression score. We recruited a population sample of 1222 individuals who provided DNA and questionnaire data on symptoms and stress. Scores on the List of Life-Threatening Experiences (LTE) questionnaire for the last year and self-rated current financial hardship were used as measures of recent/ongoing psychosocial stress. Twenty SNPs were genotyped. Significant associations between eight NOS1 SNPs, comprising two regional haplotypes, and current depression score were identified that survived correction for multiple testing when current financial hardship was used as the interaction term. A smaller three-SNP haplotypes (rs10507279, rs1004356 and rs3782218) located in a regulatory region of NOS1 showed one of the strongest effects, with the A-C-T haplotype associating with higher depression scores at low adversity levels but lower depression scores at higher adversity levels (p=2.3E-05). These results suggest that NOS1 SNPs interact with exposure to economic and psychosocial stressors to alter individual's susceptibility to depression.

Neonatal handling impairs spatial memory and leads to altered nitric oxide production and DNA breaks in a sex specific manner

Early life events lead to behavioral and neurochemical changes in adulthood. The aim of this study is to verify the effects of neonatal handling on spatial memory, nitric oxide (NO) production, antioxidant enzymatic activities and DNA breaks in the hippocampus of male and female adult rats. Litters of rats were non-handled or handled (10 min/day, days 1-10 after birth). In adulthood they were subjected to a Morris water maze or used for biochemical evaluations. Female handled rats showed impairment in spatial learning. They also showed decreased NO production, while no effects were observed in these parameters in male rats. No effects were observed on the number of hippocampal NADPH diaphorase positive cells. In the Comet Assay, male handled rats showed increased DNA breaks index when compared to non-handled ones. We conclude that neonatal handling impairs learning performance in a sex-specific manner, what may be related to NO decreased levels.

Nitric Oxide Synthase Inhibitors as Antidepressants

Affective and anxiety disorders are widely distributed disorders with severe social and economic effects. Evidence is emphatic that effective treatment helps to restore function and quality of life. Due to the action of most modern antidepressant drugs, serotonergic mechanisms have traditionally been suggested to play major roles in the pathophysiology of mood and stress-related disorders. However, a few clinical and several pre-clinical studies, strongly suggest involvement of the nitric oxide (NO) signaling pathway in these disorders. Moreover, several of the conventional neurotransmitters, including serotonin, glutamate and GABA, are intimately regulated by NO, and distinct classes of antidepressants have been found to modulate the hippocampal NO level in vivo. The NO system is therefore a potential target for antidepressant and anxiolytic drug action in acute therapy as well as in prophylaxis. This paper reviews the effect of drugs modulating NO synthesis in anxiety and depression.

Treatment of ADHD with French maritime pine bark extract, Pycnogenol

Attention Deficit/Hyperactivity Disorder (ADHD) is the most common psychiatric disorder in children. Pycnogenol, an extract from the bark of the French maritime pine, consisting of phenolic acids, catechin, taxifolin and procyanidins, has shown improvement of ADHD in case reports and in an open study. Aim of the present study was to evaluate the effect of Pycnogenol on ADHD symptoms. Sixty-one children were supplemented with 1 mg/kg/day Pycnogenol or placebo over a period of 4 weeks in a randomised, placebo-controlled, doubleblind study. Patients were examined at start of trial, 1 month after treatment and 1 month after end of treatment period by standard questionnaires: CAP (Child Attention Problems) teacher rating scale, Conner's Teacher Rating Scale (CTRS), the Conner's Parent Rating Scale (CPRS) and a modified Wechsler Intelligence Scale for children. Results show that 1-month Pycnogenol administration caused a significant reduction of hyperactivity, improves attention and visual-motoric coordination and concentration of children with ADHD. In the placebo group no positive effects were found. One month after termination of Pycnogenol administration a relapse of symptoms was noted. Our results point to an option to use Pycnogenol as a natural supplement to relieve ADHD symptoms of children.

Biphasic response to nitric oxide of spinal trigeminal neurons with meningeal input in rat--possible implications for the pathophysiology of headaches

Nitric oxide (NO) is suggested to play a causative role in the pathogenesis of primary headaches. Infusion of NO donors can trigger headache attacks, and products of NO metabolism are found to be increased in the cranial circulation in patients suffering from such headaches. To examine if NO is involved in mediating and maintaining spinal trigeminal neuronal activity, an animal model of meningeal nociception was used. In barbiturate-anesthetized rats, a cranial window was made to expose the parietal dura mater. An access to the medullary brain stem allowed extracellular action potentials to be recorded from neurons in the spinal trigeminal nucleus that received afferent input from the exposed dura. Slow intravenous infusion of the NO donor, sodium nitroprusside (SNP, 50 microg/kg), transiently increased spontaneous activity in a subset of neurons and, with a latency of 50 min, caused a progressive increase in impulse activity across the entire sample of neurons. A similar pattern of delayed activation was seen after topical application of the same dose of SNP onto the exposed medulla. Slow injection of the nonspecific inhibitor of NO synthase, N(omega)-nitro-l-arginine methyl ester (20 mg/kg), reduced the spontaneous activity in all neurons within 15 min. The results suggest that NO can induce delayed, slowly developing activation of central trigeminal neurons and that endogenous release of NO may contribute to the ongoing activity of these neurons. The delayed changes in neuronal activity may include gene expression of pro-nociceptive mediators. These mechanisms may be relevant for the pathogenesis of chronic headaches.