Involvement of noradrenaline transporters in S-nitrosocysteine-stimulated noradrenaline release from rat brain slices: existence of functional Na(+)-independent transporter activity

Pathologic role of nitrergic neurotransmission in mood disorders

Mood disorders are chronic, recurrent mental diseases that affect millions of individuals worldwide. Although over the past 40 years the biogenic amine models have provided meaningful links with the clinical phenomena of, and the pharmacological treatments currently employed in, mood disorders, there is still a need to examine the contribution of other systems to the neurobiology and treatment of mood disorders. This article reviews the current literature describing the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby the treatment of mood disorders. The hypothesis has arisen from several observations including (i) altered NO levels in patients with mood disorders; (ii) antidepressant effects of NO signaling blockers in both clinical and pre-clinical studies; (iii) interaction between conventional antidepressants/mood stabilizers and NO signaling modulators in several biochemical and behavioral studies; (iv) biochemical and physiological evidence of interaction between monoaminergic (serotonin, noradrenaline, and dopamine) system and NO signaling; (v) interaction between neurotrophic factors and NO signaling in mood regulation and neuroprotection; and finally (vi) a crucial role for NO signaling in the inflammatory processes involved in pathophysiology of mood disorders. These accumulating lines of evidence have provided a new insight into novel approaches for the treatment of mood disorders.

Effects of ketamine on exocytotic and non-exocytotic noradrenaline release

To characterise ketamine-induced sympathomimetic action, we examined the effects of ketamine on in vivo cardiac sympathetic nerve endings function. Using adult cats given anaesthesia with pentobarbital, dialysis probes were implanted in the left ventricular myocardium and dialysate noradrenaline (NA) concentrations were measured as an indicator of NA output at the cardiac sympathetic nerve endings. Ketamine was locally administered through the dialysis probe, and dialysate NA responses were obtained in the following conditions. (1) In the resting state, ketamine (10 mM) increased dialysate NA concentration. This increase in dialysate NA was not altered by addition of omega-conotoxin GVIA (N-type Ca(2+) channel blocker) or desipramine (membrane NA uptake blocker). (2) Sympathetic activation by electrical stimulation of the stellate ganglia (ES-SG; exocytotic NA release): ES-SG caused an increase in dialysate NA, which was further augmented by addition of desipramine. During co-administration of desipramine and ketamine, dialysate NA response to ES-SG was smaller than with desipramine alone. Further, there was no significant difference in the dialysate NA response to ES-SG between ketamine and ketamine + desipramine. These data suggested that both exocytosis and NA uptake function were impaired by ketamine. (3) Non-exocytotic NA release by ouabain: ouabain caused increases in dialysate NA. These increases in dialysate NA were suppressed by ketamine, which impaired the membrane outward NA transport evoked by ouabain. We conclude that ketamine impaired exocytotic and non-exocytotic NA release. However, ketamine spontaneously evoked NA efflux that was independent of exocytosis and insensitive to NA transporter.

Involvement of the system L amino acid transporter on uptake of S-nitroso-L-cysteine, an endogenous S-nitrosothiol, in PC12 cells

Previously, we proposed that S-nitroso-L-cysteine, an endogenous S-nitrosothiol, was incorporated via the system L-like amino acid transporter(s) in rat brain slices. In this study, we investigated the effect of S-nitroso-L-cysteine on L-[3H]leucine uptake in PC12 cells (a neuronal cell line). L-[3H]Leucine uptake in PC12 cells was Na(+) independent and significantly inhibited by an inhibitor of system L and by L-phenylalanine, L-cysteine, L-methionine and L-leucine at 1 mM. The effects of L-alanine, L-serine and L-threonine were limited. S-Nitroso-L-cysteine, but not other nitric oxide compounds, inhibited L-[3H]leucine uptake, and this inhibitory effect was eliminated by washing with buffer. System L is composed of the 4F2 light chains (LAT1 or LAT2) and the heavy chain, and the transcripts of these components were detected in RNA from PC12 cells. These findings suggest that S-nitroso-L-cysteine is incorporated via the system L amino acid transporter and thus regulates cell responses in PC12 cells.

Nonsynaptic noradrenaline release in neuro-immune responses

Evidence has recently been obtained that the branches of the autonomic nervous system, mainly, the sympathetic [25], regulate cytokine production. Not only the primary (thymus, bone marrow) and secondary (spleen, tonsils, and lymph nodes) lymphoid organs, but also many other tissues are involved in immune responses and are heavily influenced by noradrenaline (NA) derived from varicose axon terminals of the sympathetic nervous system [25, 100]. Besides NA released from nonsynaptic varicosities of noradrenergic terminals [92], circulating catecholamines (adrenaline, dopamine, NA) are also able to influence immune responses, the production of pro- and anti-inflammatory cytokines by different immune cells. The sympathetic nervous system (catecholamines) and the hypothalamic-pituitary-adrenal (HPA) axis (cortisol) are the major integrative and regulatory components of different immune responses. In our laboratory convincing evidence has been obtained that NA released non-synaptically [90, 92] from sympathetic axon terminals and enhanced in concentration in the close proximity of immune cells is able to inhibit production of proinflammatory (TNF-alpha, IFN-gamma, IL-12, IL-1) and increase antiinflammatory cytokines (IL-10) in response to LPS [25, 91], indicating a fine-tuning control of the production of TNF-alpha and other cytokines by sympathetic innervation under stressful conditions. This effects are mediated via beta2-adrenoceptors expressed on immune cells and coupled to cAMP levels.