An inflammatory episode during brain development is discussed as first hit which could trigger a higher susceptibility for epilepsy or development of mental disorders. We addressed the early developmental actions of an IL-6 type pro-inflammatory cytokine, leukemia inhibitory factor (LIF) on cortical maturation both in vivo and in slice cultures. A rather modest enhancement of LIF signaling was used as a proxy for an early postnatal inflammation. It resulted in a dramatic interneuron synaptopathy. Our results indicate that LIF impairs development of cortical interneuron subsets and causes a lasting imbalance of excitation and inhibition. In particular, LIF not only downregulates the expression of the TrkB receptor ligand NT4, but concurrently prevents the neurotrophins from activating the MAP kinase pathway. As a consequence, strictly TrkB-dependent cortical inhibitory GABA-ergic interneurons, in particular fast-spiking basket (B) and chandelier (C) neurons are severely affected. They display an underdevelopment of the somatodendritic domain, less and smaller presynaptic boutons, a reduced expression of the calcium buffer parvalbumin, the voltage-gated potassium channel Kv3.2, the ultrafast vesicular calcium sensor synaptotagmin-2, and glutamate decarboxylase isoform GAD-65 which synthesized GABA for phasic inhibition. These presynaptic proteins are essential for the fast-spiking properties and a highly synchronous GABA release, both being critical determinants for neuronal oscillations in the cognitive gamma frequency band. Also pyramidal cells are altered: dendritic spines are lower in density and less mature, GABAARα1 at basket cell terminals and α2 at chandelier cell terminals are reduced in expression, the axon initial segment is shorter and its core scaffolding protein ßIV-spectrin is reduced. The presynaptic deficits (outlined in the graphical abstract with left: healthy; right: LIF / inflammation) suggest a serious impairment of inhibition, and calcium imaging indeed reveals a hyperexcitable network. A set of recovery experiments reveals a surprisingly slow recovery of the affected proteins, and intriguingly, synaptotagmin-2 entirely fails to recover. In summary, our study suggests LIF as a negative upstream modulator of TrkB signaling. The impaired trophic support results in a maldevelopment in particular of fast-spiking interneurons, a deficit of inhibition and cortical hyperexcitability.

The determination of ion concentrations in cells - in particular in neurons - is very important for understanding cell function and life. Calcium is an ubiquitous messenger in almost all cell types. Fluorescence lifetime imaging (FLIM) can be of advantage over intensity based fluorescence microscopy, when comparisons between micro-domains of one cell or between different cells of one cell type are performed. Several organic chromophores have been tested in cuvette experiments as well as in living cells and cell tissue with respect to their applicability in FLIM studies. The calcium concentration changes in several cell types were investigated by FLIM with two-photon excitation.

The transcellular signaling of neurotrophins is postulated, but evidence is scarce. We now show that a small number of NT4- and BDNF-overexpressing neurons in the cortical explant of thalamocortical cocultures rapidly evoked a Trk receptor-dependent upregulation of neuropeptide Y (NPY) mRNA in interneurons. In contrast to BDNF, the action of NT4 was independent of calcium influx through NMDA receptors and L-type calcium channels. NPY neurons vastly outnumbered the neurotrophin-overexpressing neurons (mostly pyramidal cells), arguing for a spread of the neurotrophin signal via axonally connected neuronal populations. Furthermore, NT4 transfection of one explant of axonally connected corticocortical cocultures evoked significantly larger numbers of NPY neurons in both explants. Delivery of the signal was not by diffusion of neurotrophins via the medium. Moreover, cortical NPY neuron numbers increased after NT4 and BDNF transfection of a cocultured tectal explant innervated selectively by cortical layer V pyramidal neurons. The transcellular induction of NPY suggests a source-to-sink model for axonal transport and a local cortical redistribution of TrkB ligands to interneurons competent for NPY expression.

The differentiation of cortical interneurons is controlled by environmental factors. Here, we describe the role of activity and neurotrophins in regulating parvalbumin (PARV) expression using organotypic cultures (OTC) of rat visual cortex as model system. In OTC, PARV expression was dramatically delayed. The organotypic proportion of approximately 6% PARV neurons was not established before 50-70 DIV, whereas in vivo all neurons are present until P20. Thalamic afferents increased cortical PARV mRNA in OTC, but not to the age-matched in vivo level. During the first 10 DIV, BDNF and NT-4 accelerated PARV mRNA expression in a Trk receptor and MEK2 dependent manner. The BDNF action required PI3 kinase signalling. PARV expression required activity. The proportion of neurons which managed to up-regulate PARV was inversely related to the duration of early transient periods of activity deprivation. Long-term activity-deprived OTC completely failed to up-regulate PARV mRNA. Both TrkB ligands failed to promote PARV expression in activity-deprived OTC. However, a few basket and chandelier neurons were observed, suggesting that the development of class-specific morphological features is activity-independent. Once established, PARV expression became resistant to late-onset activity deprivation. In conclusion, PARV expression depended on activity and TrkB ligands which appear to prime the PARV expression already before its developmental onset.

Neurotrophins are candidate molecules for regulating dendritogenesis. We report here on dendritic growth of rat visual cortex pyramidal and interneurons overexpressing `brain-derived neurotrophic factor' BDNF and `neurotrophin 4/5' NT4/5. Neurons in organotypic cultures were transfected with plasmids encoding either `enhanced green fluorescent protein' EGFP, BDNF/EGFP or NT4/5/EGFP either at the day of birth with analysis at 5 days in vitro, or at 5 days in vitro with analysis at 10 days in vitro. In pyramidal neurons, both TrkB ligands increased dendritic length and number of segments without affecting maximum branch order and number of primary dendrites. In the early time window, only infragranular neurons were responsive. Neurons in layers II/III became responsive to NT4/5, but not BDNF, during the later time window. BDNF and NT4/5 transfectants at 10 days in vitro had still significantly shorter dendrites than adult pyramidal neurons, suggesting a massive growth spurt after 10 days in vitro. However, segment numbers were already in the range of adult neurons. Although this suggested a role for BDNF, long-term activity-deprived, and thus BDNF-deprived, pyramidal cells developed a dendritic complexity not different from neurons in active cultures except for higher spine densities on neurons of layers II/III and VI. Neutralization of endogenous NT4/5 causes shorter and less branched dendrites at 10 days in vitro suggesting an essential role for NT4/5. Neutralization of BDNF had no effect. Transfected multipolar interneurons became identifiable during the second time window. Both TrkB ligands significantly increased number of segments and branch order towards the adult state with little effects on dendritic length. The results suggested that early in development BDNF and NT4/5 probably accelerate dendritogenesis in an autocrine fashion. In particular, branch formation was advanced towards the adult pattern in pyramidal cells and interneurons.

Environmental factors are known to regulate the molecular differentiation of neocortical interneurons. Their class-defining transmitter synthetic enzymes are the glutamic acid decarboxylases (GAD); yet, fairly little is known about the developmental regulation of transcription and translation of the GAD-65/67 isoforms. We have characterized the role of neuronal activity, neurotrophins and afferent systems for GAD-65/67 expression in visual cortex in organotypic cultures (OTC) compared with in vivo in order to identify cortex-intrinsic regulatory mechanisms. Spontaneously active OTC prepared at postnatal day 0 displayed from 10 days in vitro (DIV) onwards 12-14% GAD-65/GAD-67 neurons similar to in vivo . However, GAD-65 mRNA was higher, whereas GAD-67 protein was lower, than in vivo . During the first week neurotrophins increased whereas the Trk receptor inhibitor K252a and MEK inhibitors decreased both GAD mRNAs and proteins. After 10 DIV GAD expression no longer depended on neurotrophin signalling. Activity-deprived OTC revealed only 6% GAD-67 neurons and mRNA and protein were reduced by 50%. GAD-65 mRNA was less reduced, but protein was reduced by half, suggesting translational regulation. Upon recovery of activity GAD mRNAs, cell numbers, and both proteins quickly returned to normal and these 'adult' levels were resistant to late-onset deprivation. In 20 DIV activity-deprived OTC, only neurotrophin 4 increased GAD-65/67 mRNAs, rescued the percentage of GAD-67 neurons and increased both proteins in a TrkB-dependent manner. Activity deprivation had thus shifted the period of neurotrophin sensitivity to older ages. The results suggested neuronal activity as a major regulator differentially affecting transcription and translation of the GAD isoforms. The early presence of neuronal activity promoted the GAD expression in OTC to a neurotrophin-independent state suggesting that neurotrophins play a context-dependent role.

Building the complex mammalian neocortex requires appropriate numbers of neurochemically specified neurons. It is not clear how the highly diverse cortical interneurons acquire their distinctive phenotypes. The lack of genetic determination implicates environmental factors in this selection and specification process. We analysed, in organotypic visual cortex cultures, the specification of neurons expressing neuropeptide Y (NPY), a potent anticonvulsant. Endogenous brain-derived neurotrophic factor and neurotrophin 4/5 play no role in early NPY phenotype specification. Rather, the decision to express NPY is made during a period of molecular plasticity during which differentiating neurons with the potential to express NPY compete for the cytokine leukemia inhibitory factor which is produced in the cortex, but is negatively regulated by thalamic afferences. The neurons that fail in this competition are parvalbuminergic basket and chandelier neurons, which express NPY transiently, but will not acquire a permanent NPY expression. They switch into a facultative NPY expression mode, and remain responsive to the neurotrophins which modulate NPY expression later in development.

Epigenetic factors are known to influence the differentiation of neocortical neurons. The present study analyses the role of spontaneous bioelectrical activity (SBA) and neurotrophic factors on the expression of neuropeptide Y (NPY) in rat visual cortical neurons using organotypic monocultures prepared from newborn animals and in situ hybridization to detect the NPY messenger ribonucleic acid (mRNA).Spontaneously active cortex cultures display NPY mRNA expression in about 7% of all cortical neurons from 10 days in vitro (DIV) on. Blocking the SBA by chronic application of 10 mM Mg2+ for 3-30 DIV reduces the percentage of NPY neurons to about 2%. Allowing an initial phase of SBA (1-20 DIV) followed by an SBA blockade (for 21-50 DIV) results in 2% labelled neurons, indicating a dramatic reduction of NPY mRNA expression in the absence of SBA. Surprisingly, the reverse experiment (a period of SBA blockade for 1-20 DIV followed by a period of SBA recovery for 21-40 DIV) does not cause an upregulation of NPY mRNA expression. However, allowing cultures to differentiate as spontaneously active cultures, then applying a transient period of SBA blockade which is followed by a second period of SBA, does rescue the NPY mRNA expression in 7% of the cortical neurons, We conclude that SBA is a main trigger for NPY mRNA expression and it is particularly important during an early postnatal period of differentiation.We then analysed whether neurotrophic factors known to modulate cortical neuropeptide expression are able to do so in the absence of SBA. Supplementing chronically blocked cultures with the neurotrophins, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5) and the cytokine, leukaemia inhibitory factor (LIF), reveals that BDNF and NT-3 are unable to increase the percentage of NPY neurons, In contrast, LIF and NT-4/5 increase the percentage of NPY neurons to 4 and 6-7%, respectively. Moreover, neurons treated with NT-4/15 display a very high level of NPY mRNA expression in somata and in the dendritic trees. The data suggest a complex interplay and a hierarchy of epigenetic factors in regulating the neurochemical architecture of the developing neocortex.

A macroscopically oriented layer of sodium dodecyl sulfate (SDS) at the interface of water and n-hexadecane was investigated using acridine orange as a fluorescent probe. The range of angles through which the hindered out-of-plane reorientation occurs for the probe was found to correspond closely to the surface roughness predicted by the capillary wave model through the interfacial tension. The in-plane reorientation of the probe was found to be significantly slower than that in the absence of SDS, with little dependence on the SDS concentration. The in-plane and out-of-plane rotations of acridine orange appear to correspond to the two decay components measured for acridine orange in micellar solution, indicating that these macroscopically oriented surfactant monolayers can provide detailed insight into solute-micelle interactions. For SDS micelles, the behavior of the oriented interface suggests that the surfactants are aggregated with the probe in the micelle and that the SDS micellar surface is very rough.

The rotational diffusion behavior of tetracene in sodium dodecyl sulfate micelles is studied as a function of the n-propanol content of the micellar solution. Fluorescence anisotropy measurements using frequency-domain spectroscopy show that tetracene reorients faster with increasing concentration of n-propanol. This result is consistent with micellar liquid chromatographic studies and lends insight into the role of n-propanol as a mobile-phase modifier. The components of the rotational diffusion tensor are determined from the double-exponential anisotropy decay. These confirm the validity of the Debye-Stokes-Einstein model and allow calculation of the viscosity of the micelle interior. The viscosity decreases from 8 to 4 cP as the concentration of n-propanol increases from 0 to 10% (v/v). The components of the rotational diffusion tensor indicate that the solvation environment of tetracene in the micelle is structurally disordered.

The fluorescence anisotropy decays of tetracene in 1-butanol, 1-octanol, and 1-dodecanol were measured at several temperatures by using frequency domain spectroscopy. Subslip rotational diffusion is observed. The double-exponential anisotropy decays were analyzed to determine the components, D(x), D(y), and D(z), of the rotational diffusion tensor. The relative values of these components vary with temperature, indicating nonhydrodynamic rotational diffusion. Subslip behavior is found to be associated with a value of D(y)/D that is significantly larger than that predicted from hydrodynamics. The subslip phenomenon is interpreted as being a consequence of solvent structure.

ADVERTISEMENT RETURN TO ISSUEPREVArticleRelation of measurements to the shape-selective contribution to chemical separationM. J. WirthCite this: J. Phys. Chem. 1987, 91, 14, 3926–3928Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://doi.org/10.1021/j100298a040RIGHTS & PERMISSIONSArticle Views18Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (415 KB) Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTShape-selective contribution to chemical separation: experimentM. J. Wirth and D. A. HahnCite this: J. Phys. Chem. 1987, 91, 11, 3099–3102Publication Date (Print):May 1, 1987Publication History Published online1 May 2002Published inissue 1 May 1987https://pubs.acs.org/doi/10.1021/j100295a090https://doi.org/10.1021/j100295a090research-articleACS PublicationsRequest reuse permissionsArticle Views33Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

The temperature dependence of the dynamical behavior of cresyl violet in 1-dodecanol was studied by both microscopic and bulk physical techniques. Picosecond rotational diffusion measurements indicate that the solute experiences a very sharp temperature-dependent change in its environment. Steady-state absorption spectroscopy reveals that this effect is due to a change in the solvent-solute interaction of cresyl violet. /sup 13/C NMR measurement of the temperature dependence of the solvent spin-lattice relaxation time (T/sub 1/) shows that the change in solvation is due to a previously unreported change in the state of the bulk solvent.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMeasurement of small absorbances by picosecond pump-probe spectrometryG. J. Blanchard and M. J. WirthCite this: Anal. Chem. 1986, 58, 3, 532–535Publication Date (Print):March 1, 1986Publication History Published online1 May 2002Published inissue 1 March 1986https://pubs.acs.org/doi/10.1021/ac00294a007https://doi.org/10.1021/ac00294a007research-articleACS PublicationsRequest reuse permissionsArticle Views231Altmetric-Citations41LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Picosecond techniques were used to study the rotational diffusion of the ground and first excited electronic states of cresyl violet in methanol. The anisotropy decay was studied at five different wavelengths, three in the ground state and two in the excited state. It is known that the decay of the anisotropy is dependent on both the transition polarization and rotational diffusion constants. Experimentally, a different decay of the anisotropy is observed at each wavelength. The data are consistent with changes in the transition polarization but with the same diffusion constant in all cases. It is concluded that cresyl violet in methanol reorients identically in its ground and excited electronic states.

We report for the first time transform limited behavior from the picosecond synchronously pumped cw dye laser. This is accomplished by the use of an inexpensive, low-loss intra-cavity etalon. The Fourier relationship between pulse frequency width and time duration is shown to be obeyed quantitatively at three different wavelengths. The pulse profile changes as a function of wavelength and does not follow an analytical functionality at any wavelength studied. For each wavelength, the optical cavity length producing transform limited pulses is shown to be the same.

In the first decade in the development of lasers, output was achieved from a variety of gain media, but only at discrete wavelengths. Many interesting new experiments became possible; however, applications of lasers to chemical studies were limited to cases in which there was a coincidence between the absorption spectra and laser output. The availability of continuously tunable lasers has had an immediate impact on chemical applications because it has become possible both to select a laser that operates in a desired spectral region and to scan the spectrum. Presently, tunable lasers that are commercially available include dye lasers, which cover the entire visible region, and diode lasers and F-center lasers, which together cover most of the infrared region.