Maximizing Electrochemical Information: A Perspective on Background-Inclusive Fast Voltammetry.

This perspective encompasses a focused review of the literature leading to a tipping point in electroanalytical chemistry. We tie together the threads of a "revolution" quietly in the making for years through the work of many authors. Long-held misconceptions about the use of background subtraction in fast voltammetry are addressed. We lay out future advantages that accompany background-inclusive voltammetry, particularly when paired with modern machine-learning algorithms for data analysis.

Serotonin uptake is largely mediated by platelets versus lymphocytes in peripheral blood cells.

The serotonin transporter (SERT), a primary target for many antidepressants, is expressed in the brain and also in peripheral blood cells. Although platelet SERT function is well accepted, lymphocyte SERT function has not been definitively characterized. Due to their small size, platelets often are found in peripheral blood mononuclear cell preparations aimed at isolating lymphocytes, monocytes, and macrophages. The presence of different cells makes it difficult to assign SERT expression and function to specific cell types. Here, we use flow cytometry and IDT307, a monoamine transporter substrate that fluoresces after uptake into cells, to investigate SERT function in lymphocyte and platelet populations independently, as well as simultaneously without prior isolation. We find that murine lymphocytes exhibit temperature-dependent IDT307 transport but uptake is independent of SERT. Lack of measurable SERT function in lymphocytes was corroborated by chronoamperometry using serotonin as a substrate. When we examined rhesus and human mixed blood cell populations, we found that platelets, and not lymphocytes, were primary contributors to SERT function. Overall, these findings indicate that lymphocyte SERT function is minimal. Moreover, flow cytometry, in conjunction with the fluorescent transporter substrate IDT307, can be widely applied to investigate SERT in platelets from populations of clinical significance.

gamma-Aminobutyric acid-type A receptor deficits cause hypothalamic-pituitary-adrenal axis hyperactivity and antidepressant drug sensitivity reminiscent of melancholic forms of depression.

BACKGROUND: The gamma-aminobutyric acid (GABA) Type A receptor deficits that are induced by global or forebrain-specific heterozygous inactivation of the gamma2 subunit gene in mouse embryos result in behavior indicative of trait anxiety and depressive states. By contrast, a comparable deficit that is delayed to adolescence is without these behavioral consequences. Here we characterized gamma2-deficient mice with respect to hypothalamic-pituitary-adrenal (HPA) axis abnormalities and antidepressant drug responses. METHODS: We analyzed the behavioral responses of gamma2(+/-) mice to desipramine and fluoxetine in novelty suppressed feeding, forced swim, tail suspension, and sucrose consumption tests as well as GABA(A) receptor deficit- and antidepressant drug treatment-induced alterations in serum corticosterone. RESULTS: Baseline corticosterone concentrations in adult gamma2-deficient mice were elevated independent of whether the genetic lesion was induced during embryogenesis or delayed to adolescence. However, the manifestation of anxious-depressive behavior in different gamma2-deficient mouse lines was correlated with early onset HPA axis hyperactivity during postnatal development. Chronic but not subchronic treatment of gamma2(+/-) mice with fluoxetine or desipramine normalized anxiety-like behavior in the novelty suppressed feeding test. Moreover, desipramine had antidepressant-like effects in that it normalized HPA axis function and depression-related behavior of gamma2(+/-) mice in the forced swim, tail suspension, and sucrose consumption tests. By contrast, fluoxetine was ineffective as an antidepressant and failed to normalize HPA axis function. CONCLUSIONS: Developmental deficits in GABAergic inhibition in the forebrain cause behavioral and endocrine abnormalities and selective antidepressant drug responsiveness indicative of anxious-depressive disorders such as melancholic depression, which are frequently characterized by HPA axis hyperactivity and greater efficacy of desipramine versus fluoxetine.

A physical model of axonal damage due to oxidative stress.

Oxidative damage is implicated in the pathogenesis of neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases, and in normal aging. Here, we model oxidative stress in neurons using photogenerated radicals in a simplified membrane-encapsulated microtubule system. Using fluorescence and differential interference contrast microscopies, we monitor photochemically induced microtubule breakdown on the supported region of membrane in encapsulating synthetic liposomes as a function of lipid composition and environment. Degradation of vesicle-encapsulated microtubules is caused by attack from free radicals formed upon UV excitation of the lipid-soluble fluorescent probe, 6-(9-anthroyloxy)stearic acid. Probe concentration was typically limited to a regime in which microtubule degradation was slow, and microtubule degradation was monitored by changes in the observed protrusion of the membrane surface. The kinetics of microtubule degradation are influenced by lipid saturation level, fluorescent probe concentration, and the presence of free-radical scavengers. This system is sufficient to reproduce some degenerative morphologies found in vivo.

Neuronal and astroglial responses to the serotonin and norepinephrine neurotoxin: 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine.

1-Methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP) causes long-term loss of forebrain serotonin (5-HT) and norepinephrine (NE) and consequently, is unlike 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its other 2'-analogs that primarily deplete striatal dopamine (DA). In the present investigation into the acute effects of 2'-NH2-MPTP in mice, profound decreases in cortical and hippocampal 5-HT and NE to 10 to 40% of control were observed as early as 30 min post-treatment and lasted throughout the ensuing 21 days. Striatal DA was decreased to 60 to 80% of control during the first 48 h but returned to normal by 72 h. Reactive gliosis, which occurs in response to neurodegeneration was not evident by immunocytochemistry but was detected by enzyme-linked immunosorbent assay, where glial fibrillary acidic protein (GFAP) was increased to 130% of control in cortex, hippocampus, and brain stem 48 to 72 h post-treatment. To explore the possibility that 5-HT modulates the astrocytic response to injury, 2'-NH2-MPTP was used to damage 5-HT axons 2 weeks before administration of the potent DA neurotoxin 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'-CH3-MPTP). Despite a 90% decrement in striatal DA in 2'-NH2-MPTP/2'-CH3-MPTP-treated mice, increases in GFAP were attenuated compared to mice treated with 2'-CH3-MPTP alone. Thus, 2'-NH2-MPTP causes severe and immediate decrements in 5-HT and NE in frontal cortex and hippocampus, yet induces a modest GFAP response compared with other MPTP analogs that have their primary effect on DA. These results demonstrate the importance of obtaining quantitative assessments of GFAP to detect astroglial responses associated with selective damage to neurotransmitter systems with low-density innervation and suggest that serotonin may facilitate the astrocytic response to striatal injury.