Lactiplantibacillus plantarum PS128 Alleviates Exaggerated Cortical Beta Oscillations and Motor Deficits in the 6-Hydroxydopamine Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by midbrain dopaminergic neuronal loss and subsequent physical impairments. Levodopa manages symptoms best, while deep brain stimulation (DBS) is effective for advanced PD patients; however, side effects occur with the diminishing therapeutic window. Recently, Lactiplantibacillus plantarum PS128 (PS128) was found to elevate dopamine levels in rodent brains, suggesting its potential to prevent PD. Here, the therapeutic efficacy of PS128 was examined in the 6-hydroxydopamine rat PD model. Suppression of the power spectral density of beta oscillations (beta PSD) in the primary motor cortex (M1) was recorded as the indicator of disease progression. We found that 6 weeks of daily PS128 supplementation suppressed M1 beta PSD as well as did levodopa and DBS. Long-term normalization of M1 beta PSD was found in PS128-fed rats, whereas levodopa and DBS showed only temporal effects. PS128 + levodopa and PS128 + DBS exhibited better therapeutic effects than did levodopa + DBS or either alone. Significantly improved motor functions in PS128-fed rats were correlated with normalization of M1 beta PSD. Brain tissue analyses further demonstrated the role of PS128 in dopaminergic neuroprotection and the enhanced availability of neurotransmitters. These findings suggest that psychobiotic PS128 might be used alongside conventional therapies to treat PD patients.

A Battery-Less, Implantable Neuro-Electronic Interface for Studying the Mechanisms of Deep Brain Stimulation in Rat Models

Although deep brain stimulation (DBS) has been a promising alternative for treating several neural disorders, the mechanisms underlying the DBS remain not fully understood. As rat models provide the advantage of recording and stimulating different disease-related regions simultaneously, this paper proposes a battery-less, implantable neuro-electronic interface suitable for studying DBS mechanisms with a freely-moving rat. The neuro-electronic interface mainly consists of a microsystem able to interact with eight different brain regions bi-directionally and simultaneously. To minimize the size of the implant, the microsystem receives power and transmits data through a single coil. In addition, particular attention is paid to the capability of recording neural activities right after each stimulation, so as to acquire information on how stimulations modulate neural activities. The microsystem has been fabricated with the standard 0.18 μm CMOS technology. The chip area is 7.74 mm (2) , and the microsystem is able to operate with a single supply voltage of 1 V. The wireless interface allows a maximum power of 10 mW to be transmitted together with either uplink or downlink data at a rate of 2 Mbps or 100 kbps, respectively. The input referred noise of recording amplifiers is 1.16 μVrms, and the stimulation voltage is tunable from 1.5 V to 4.5 V with 5-bit resolution. After the electrical functionality of the microsystem is tested, the capability of the microsystem to interface with rat brain is further examined and compared with conventional instruments. All experimental results are presented and discussed in this paper.

Direct-growth carbon nanotubes on 3D structural microelectrodes for electrophysiological recording

Direct growth of CNTs on 3D microelectrodes could detect distinguished zebrafish ECG resulting from the interfacial improvement analyzed by EIS.

Integration of silicon-via electrodes with different recording characteristics on a glass microprobe using a glass reflowing process

Electrodes on planar type microelectromechanical system (MEMS) microprobes mainly record neurons on the top-side of probe shaft (called a top-side electrode). However, it is often necessary to record neurons other than those on the top-side of the probe shaft. This study uses the glass reflowing technique to embed silicon-vias in a glass probe to implement a microprobe capable of recording neurons around the shaft. The proposed technology makes it possible to fabricate, distribute, and integrate four types of electrodes on the shaft: top-side, back-side, double-side, and sidewall electrodes. These electrodes have different recording characteristics. The in vitro and in vivo (using crayfish and rat brain) experiments in this study shows that the top-side and back-side electrodes are respectively more sensitive to neurons on the top-side and back-side of the probe shaft. In contrast, signals recorded by double-side electrode and sidewall electrode are equally sensitive to neurons around the probe shaft. This study enables the implementation and integration of these four types of electrodes, meeting the requirements of various neural applications.

A three-dimensional flexible microprobe array for neural recording assembled through electrostatic actuation

We designed, fabricated and tested a novel three-dimensional flexible microprobe to record neural signals of a lateral giant nerve fiber of the escape circuit of an American crayfish. An electrostatic actuation folded planar probes into three-dimensional neural probes with arbitrary orientations for neuroscientific applications. A batch assembly based on electrostatic forces simplified the fabrication and was non-toxic. A novel fabrication for these three-dimensional flexible probes used SU-8 and Parylene technology. The mechanical strength of the neural probe was great enough to penetrate into a bio-gel. A flexible probe both decreased the micromotion and alleviated tissue encapsulation of the implant caused by chronic inflammation of tissue when an animal breathes or moves. The cortex consisted of six horizontal layers, and the neurons of the cortex were arranged in vertical structures; the three-dimensional microelectrode arrays were suitable to investigate the cooperative activity for neurons in horizontal separate layers and in vertical cortical columns. With this flexible probe we recorded neural signals of a lateral giant cell from an American crayfish. The response amplitude of action potentials was about 343 µV during 1 ms period; the average recorded data had a ratio of signal to noise as great as 30.22 ± 3.58 dB. The improved performance of this electrode made feasible the separation of neural signals according to their distinct shapes. The cytotoxicity indicated a satisfactory biocompatibility and non-toxicity of the flexible device fabricated in this work.

An active, flexible carbon nanotube microelectrode array for recording electrocorticograms

A variety of microelectrode arrays (MEAs) has been developed for monitoring intra-cortical neural activity at a high spatio-temporal resolution, opening a promising future for brain research and neural prostheses. However, most MEAs are based on metal electrodes on rigid substrates, and the intra-cortical implantation normally causes neural damage and immune responses that impede long-term recordings. This communication presents a flexible, carbon-nanotube MEA (CMEA) with integrated circuitry. The flexibility allows the electrodes to fit on the irregular surface of the brain to record electrocorticograms in a less invasive way. Carbon nanotubes (CNTs) further improve both the electrode impedance and the charge-transfer capacity by more than six times. Moreover, the CNTs are grown on the polyimide substrate directly to improve the adhesion to the substrate. With the integrated recording circuitry, the flexible CMEA is proved capable of recording the neural activity of crayfish in vitro, as well as the electrocorticogram of a rat cortex in vivo, with an improved signal-to-noise ratio. Therefore, the proposed CMEA can be employed as a less-invasive, biocompatible and reliable neuro-electronic interface for long-term usage.

Hydrophilic modification of neural microelectrode arrays based on multi-walled carbon nanotubes

To decrease the impedance of microelectrode arrays, for neuroscience applications we have fabricated and tested MEA based on multi-walled carbon nanotubes. With decreasing physical size of a microelectrode, its impedance increases and charge-transfer capability decreases. To decrease the impedance, the effective surface area of the electrode must generally be increased. We explored the effect of plasma treatment on the surface wettability of MWCNT. With a steam-plasma treatment the surface of MWCNT becomes converted from superhydrophobic to superhydrophilic; this hydrophilic property is attributed to -OH bonding on the surface of MWCNT. We reported the synthesis at 400 °C of MWCNT on nickel-titanium multilayered metal catalysts by thermal chemical vapor deposition. Applying plasma with a power less than 25 W for 10 s improved the electrochemical and biological properties, and circumvented the limitation of the surface reverting to a hydrophobic condition; a hydrophilic state is maintained for at least one month. The MEA was used to record neural signals of a lateral giant cell from an American crayfish. The response amplitude of the action potential was about 275 µV with 1 ms period; the recorded data had a ratio of signal to noise up to 40.12 dB. The improved performance of the electrode makes feasible the separation of neural signals and the recognition of their distinct shapes. With further development the rapid treatment will be useful for long-term recording applications.

A cone-shaped 3D carbon nanotube probe for neural recording

A novel cone-shaped 3D carbon nanotube (CNT) probe is proposed as an electrode for applications in neural recording. The electrode consists of CNTs synthesized on the cone-shaped Si (cs-Si) tip by catalytic thermal chemical vapor deposition (CVD). This probe exhibits a larger CNT surface area with the same footprint area and higher spatial resolution of neural recording compared to planar-type CNT electrodes. An approach to improve CNT characteristics by O(2) plasma treatment to modify the CNT surface will be also presented. Electrochemical characterization of O(2) plasma-treated 3D CNT (OT-CNT) probes revealed low impedance per unit area (∼64.5 Ω mm(-2)) at 1 kHz and high specific capacitance per unit area (∼2.5 mF cm(-2)). Furthermore, the OT-CNT probes were employed to record the neural signals of a crayfish nerve cord. Our findings suggest that OT-CNT probes have potential advantages as high spatial resolution and superb electrochemical properties which are suitable for neural recording applications.

Abi plays an opposing role to Abl in Drosophila axonogenesis and synaptogenesis

Abl tyrosine kinase (Abl) regulates axon guidance by modulating actin dynamics. Abelson interacting protein (Abi), originally identified as a kinase substrate of Abl, also plays a key role in actin dynamics, yet its role with respect to Abl in the developing nervous system remains unclear. Here we show that mutations in abi disrupt axonal patterning in the developing Drosophila central nervous system (CNS). However, reducing abi gene dosage by half substantially rescues Abl mutant phenotypes in pupal lethality, axonal guidance defects and locomotion deficits. Moreover, we show that mutations in Abl increase synaptic growth and spontaneous synaptic transmission frequency at the neuromuscular junction. Double heterozygosity for abi and enabled (ena) also suppresses the synaptic overgrowth phenotypes of Abl mutants, suggesting that Abi acts cooperatively with Ena to antagonize Abl function in synaptogenesis. Intriguingly, overexpressing Abi or Ena alone in cultured cells dramatically redistributed peripheral F-actin to the cytoplasm, with aggregates colocalizing with Abi and/or Ena, and resulted in a reduction in neurite extension. However, co-expressing Abl with Abi or Ena redistributed cytoplasmic F-actin back to the cell periphery and restored bipolar cell morphology. These data suggest that abi and Abl have an antagonistic interaction in Drosophila axonogenesis and synaptogenesis, which possibly occurs through the modulation of F-actin reorganization.

Interfacing neurons both extracellularly and intracellularly using carbon-nanotube probes with long-term endurance

This study demonstrates that carbon nanotubes (CNTs) can be fabricated into probes directly, with which neural activity can be monitored and elicited not only extracellularly but also intracellularly. Two types of CNT probes have been made and examined with the escape neural circuit of crayfish, Procambarus clarkia. The CNT probes are demonstrated to have comparable performance to conventional Ag/AgCl (silver/silver cloride) electrodes. Impedance measurement and cyclic voltammetry further indicate that the CNT probes transmit electrical signals through not only capacitive coupling but also resistive conduction. The resistive conduction facilitates the recording of postsynaptic potentials and equilibrium membrane potentials intracellularly as well as the delivery of direct-current stimulation. Furthermore, delivering current stimuli for a long term is found to enhance rather than to degrade the recording capability of the CNT probes. The mechanism of this fruitful result is carefully investigated and discussed. Therefore, our findings here support the suggestion that CNTs are suitable for making biocompatible, durable neural probes of various configurations for diverse applications.

Flexible carbon nanotubes electrode for neural recording

This paper demonstrates a novel flexible carbon nanotubes (CNTs) electrode array for neural recording. In this device, the CNTs electrode arrays are partially embedded into the flexible Parylene-C film using a batch microfabrication process. Through this fabrication process, the CNTs can be exposed to increase the total sensing area of an electrode. Thus, the flexible CNTs electrode of low impedance is realized. In application, the flexible CNTs electrode has been employed to record the neural signal of a crayfish nerve cord for in vitro recording. The measurements demonstrate the superior performance of the presented flexible CNTs electrode with low impedance (11.07 kohms at 1 kHz) and high peak-to-peak amplitude action potential (about 410 microV). In addition, the signal-to-noise ratio (SNR) of the presented flexible CNTs electrode is about 257, whereas the SNR of the reference (a pair of Teflon-coated silver wires) is only 79. The simultaneous recording of the flexible CNTs electrode array is also demonstrated. Moreover, the flexible CNTs electrode has been employed to successfully record the spontaneous spikes from the crayfish nerve cord. The amplitude of the spontaneous peak-to-peak response is about 25 microV.

A CMOS neuroelectronic interface based on two-dimensional transistor arrays with monolithically-integrated circuitry

The ability to monitor and to elicit neural activity with a high spatiotemporal resolution has grown essential for studying the functionality of neuronal networks. Although a variety of microelectrode arrays (MEAs) has been proposed, very few MEAs are integrated with signal-processing circuitry. As a result, the maximum number of electrodes is limited by routing complexity, and the signal-to-noise ratio is degraded by parasitics and noise interference. This paper presents a single-chip neuroelectronic interface integrating oxide-semiconductor field-effect transistors (OSFETs) with signal-processing circuitry. After the chip was fabricated with the standard complementary-metal-oxide-semiconductor (CMOS) process, polygates of specific transistors were etched at die-level to form OSFETs, while metal layers were retained to connect the OSFETs into two-dimensional arrays. The complete removal of polygates was confirmed by high-resolution image scanners, and the reliability of OSFETs was examined by measuring their electrical characteristics. Through a gate oxide of only 7nm thick, each OSFET can record and stimulate neural activity extracellularly by capacitive coupling. The capability of the full chip in neural recording and stimulation was further experimented using the well-characterised escape circuit of the crayfish. Experimental results indicate that the OSFET-based neuroelectronic interface can be used to study neuronal networks as faithfully as conventional electrophysiological tools. Moreover, the proposed simple, die-level fabrication process of the OSFETs underpins the development of various field-effect biosensors on a large scale with on-chip circuitry.

Fak56 functions downstream of integrin alphaPS3betanu and suppresses MAPK activation in neuromuscular junction growth

Background

Focal adhesion kinase (FAK) functions in cell migration and signaling through activation of the mitogen-activated protein kinase (MAPK) signaling cascade. Neuronal function of FAK has been suggested to control axonal branching; however, the underlying mechanism in this process is not clear.

Results

We have generated mutants for the Drosophila FAK gene, Fak56. Null Fak56 mutants display overgrowth of larval neuromuscular junctions (NMJs). Localization of phospho-FAK and rescue experiments suggest that Fak56 is required in presynapses to restrict NMJ growth. Genetic analyses imply that FAK mediates the signaling pathway of the integrin αPS3βν heterodimer and functions redundantly with Src. At NMJs, Fak56 downregulates ERK activity, as shown by diphospho-ERK accumulation in Fak56 mutants, and suppression of Fak56 mutant NMJ phenotypes by reducing ERK activity.

Conclusion

We conclude that Fak56 is required to restrict NMJ growth during NMJ development. Fak56 mediates an extracellular signal through the integrin receptor. Unlike its conventional role in activating MAPK/ERK, Fak56 suppresses ERK activation in this process. These results suggest that Fak56 mediates a specific neuronal signaling pathway distinct from that in other cellular processes.

Micro-multi-probe electrode array to measure neural signals

A multi-electrode array (MEA) with 16 channels was designed to record simultaneously the velocity of conduction of neurons in a measurement system for bio-medical applications. MEA were fabricated with MEMS technology on a silicon-on-insulator (SOI) wafer, which controls the thickness of the probe effectively. All used probes have length 3mm and width 100mum. The thickness of the probe, 25mum, was defined by the thickness of the device layer on the SOI wafer. The multiple probes with a 16-site recording electrode array have been manufactured; their strength was tested with a force gauge and their electrical performance was tested with an impedance measurement system. The readout circuitry comprises an array of 16-site preamplifiers fully integrated on a chip that is capable of signal processing to improve the signal-noise-ratio (SNR). To demonstrate the capability, multiple neural signals were recorded simultaneously with all electrodes from each separate probe. To verify its capability of measuring neural signals, the MEA was used to measure these signals from the electrophysiology system of crayfish. The velocity of neural conduction recorded with a fabricated MEA is shown, and is comparable with a measurement with a traditional glass pipette. The MEA for recording neural signals would be improved in further development.

Glutamate-gated chloride channels inhibit juvenile hormone biosynthesis in the cockroach, Diploptera punctata

Juvenile hormone (JH) synthesized and released from endocrine gland corpus allatum (CA) plays an important role in insect metamorphosis, vitellogenesis and reproduction. Glutamate is a major neurotransmitter in the nervous system and its activated receptors possess excitatory and inhibitory forms in muscle fibers of invertebrates. Previously, we have shown that the rise of intracellular calcium through excitatory glutamate receptors, N-methyl-d-aspartate (NMDA) and non-NMDA-type channels stimulates JH synthesis in the cockroach, Diploptera punctata. Here, we demonstrate the occurrence of inhibitory chloride permeable glutamate (GluCl) receptors on CA cell membranes. Application of the GluCl channel activators, ibotenic acid (Ibo) and ivermectin, but not gamma-aminobutyric acid caused a decline in JH synthesis in glands of either high or low activity during the gonadotrophic cycle. Also, while recording the membrane potential of the isolated whole CA glands intracellularly, Ibo induced a hyperpolarizated response. Both changes in the membrane potential and inhibition of JH synthesis could be abolished by the application of the chloride channel blocker picrotoxin. Finally, we found both excitatory and inhibitory glutamate receptors cause antagonistic effects on rates of JH synthesis. These results indicate a novel function of GluCl channels in the inhibition of JH synthesis that could be a potential pathway for developing a new generation of insecticides.

Metamodulation of the crayfish escape circuit

Neuromodulation provides a means of changing the excitability of neurons or the effect of synapses, and so extends the performance range of neural circuits. Metamodulation occurs when the neuromodulatory effect is itself modulated, often in response to a change in the behavioral state of the animal. The well-studied neural circuit that mediates escape in the crayfish is modulated by serotonin, and this modulation is subject to two forms of metamodulation. First, the serotonergic modulation of the Lateral Giant (LG) command neuron for escape depends on the pattern of exposure of the cell to serotonin. High and low concentrations, and rapid and slow exposures each produce opposite modulatory effects on sensory-evoked EPSPs in LG. In addition, brief exposures produce transient modulatory effects, whereas longer exposures produce long-term facilitation. These different patterns of exposure may result from serotonin neurotransmission, paracrine transmission, and hormonal release, all of which occur in the vicinity of LG. The second form of metamodulation enables serotonergic modulation to track slow changes in the social status of the crayfish. Slowly applied serotonin facilitates LG's response in socially isolated crayfish and in new dominant and subordinate animals. Facilitation is retained in the dominant animal during two weeks of continuous pairing of the animals, but facilitation gradually changes to inhibition in the subordinate crayfish. These and related changes in serotonin modulation appear to result from changes in the population of serotonin receptors that mediate the modulatory effects in LG. Whereas the exposure-dependent metamodulation enables rapid changes in serotonergic modulation of LG to occur, the status-dependent metamodulation enables serotonergic modulation of LG to track the slow maturation of social relationships.

Dual and opposing modulatory effects of serotonin on crayfish lateral giant escape command neurons

Serotonin modulates afferent synaptic transmission to the lateral giant neurons of crayfish, which are command neurons for escape behavior. Low concentrations, or high concentrations reached gradually, are facilitatory, whereas high concentrations reached rapidly are inhibitory. The modulatory effects rapidly reverse after brief periods of application, whereas longer periods of application are followed by facilitation that persists for hours. These effects of serotonin can be reproduced by models that involve multiple interacting intracellular signaling systems that are each stimulated by serotonin. The dependence of the neuromodulatory effect on dose, rate, and duration of modulator application may be relevant to understanding the effects of natural neuromodulation on behavior and cognition and to the design of drug therapies.

Hierarchical folding of intestinal fatty acid binding protein

Intestinal fatty acid binding protein (IFABP) is a member of the lipid binding protein family, members of which have a clam shell type of motif formed by two five-stranded beta-sheets. Understanding the folding mechanism of these proteins has been hindered by the presence of an unresolved burst phase. By initiating the reaction with a sub-millisecond mixer and following its progression by Trp fluorescence, we discovered three distinct phases in the folding reaction of the W6Y mutant of IFABP from which we postulate the following sequence of events. The first phase (k(1) > 10 000 s(-1)) involves collapse of the polypeptide chain around a hydrophobic core. During the second phase (k(2) approximately 1500 s(-1)), beta-strands B-G, mostly located on the top half of the clam shell structure, propagate from this hydrophobic core. It is followed by the final phase (k(3) approximately 5 s(-1)) involving the formation of the last three beta-strands on the bottom half of the clam shell and the establishment of the native hydrogen bonding network throughout the protein molecule.

Flavohemoglobin, a globin with a peroxidase-like catalytic site

Biochemical studies of flavohemoglobin (Hmp) from Escherichia coli suggest that instead of aerobic oxygen delivery, a dioxygenase converts NO to NO3(-) and anaerobically, an NO reductase converts NO to N(2)O. To investigate the structural features underlying the chemical reactivity of Hmp, we have measured the resonance Raman spectra of the ligand-free ferric and ferrous protein and the CO derivatives of the ferrous protein. At neutral pH, the ferric protein has a five-coordinate high-spin heme, similar to peroxidases. In the ferrous protein, a strong iron-histidine stretching mode is present at 244 cm(-1). This frequency is much higher than that of any other globin discovered to date, although it is comparable to those of peroxidases, suggesting that the proximal histidine has imidazolate character. In the CO derivative, an open and a closed conformation were detected. The distal environment of the closed conformation is very polar, where the heme-bound CO strongly interacts with the B10 Tyr and/or the E7 Gln. These data demonstrate that the active site structure of Hmp is very similar to that of peroxidases and is tailored to perform oxygen chemistry.

A cooperative oxygen binding hemoglobin from Mycobacterium tuberculosis. Stabilization of heme ligands by a distal tyrosine residue

The homodimeric hemoglobin (HbN) from Mycobacterium tuberculosis displays an extremely high oxygen binding affinity and cooperativity. Sequence alignment with other hemoglobins suggests that the proximal F8 ligand is histidine, the distal E7 residue is leucine, and the B10 position is occupied by tyrosine. To determine how these heme pocket residues regulate the ligand binding affinities and physiological functions of HbN, we have measured the resonance Raman spectra of the O(2), CO, and OH(-) derivatives of the wild type protein and the B10 Tyr --> Leu and Phe mutants. Taken together these data demonstrate a unique distal environment in which the heme bound ligands strongly interact with the B10 tyrosine residue. The implications of these data on the physiological functions of HbN and another heme-containing protein, cytochrome c oxidase, are considered.

A cooperative oxygen-binding hemoglobin from Mycobacterium tuberculosis

Two putative hemoglobin genes, glbN and glbO, were recently discovered in the complete genome sequence of Mycobacterium tuberculosis H37Rv. Here, we show that the glbN gene encodes a dimeric hemoglobin (HbN) that binds oxygen cooperatively with very high affinity (P(50) = 0.013 mmHg at 20 degrees C) because of a fast combination (25 microM(-1).s(-1)) and a slow dissociation (0.2 s(-1)) rate. Resonance Raman spectroscopy and ligand association/dissociation kinetic measurements, along with mutagenesis studies, reveal that the stabilization of the bound oxygen is achieved through a tyrosine at the B10 position in the distal pocket of the heme with a conformation that is unique among the globins. Physiological studies performed with Mycobacterium bovis bacillus Calmette-Guérin demonstrate that the expression of HbN is greatly enhanced during the stationary phase in aerobic cultures but not under conditions of limited oxygen availability. The results suggest that, physiologically, the primary role of HbN may be to protect the bacilli against reactive nitrogen species produced by the host macrophage.

Submillisecond unfolding kinetics of apomyoglobin and its pH 4 intermediate

Submillisecond mixing experiments and tryptophan fluorescence spectroscopy are used to address two questions raised in earlier stopped-flow studies of the folding and unfolding kinetics of sperm whale apomyoglobin. A study of the pH 4 folding intermediate (I) revealed, surprisingly, that its folding and unfolding kinetics are measurable and fit the two-state model except for a possible burst phase in unfolding. Submillisecond mixing experiments confirm the unfolding burst phase and show that its properties are consistent with the recently discovered interconversion between two forms of I, Ia equilibrium Ib. In urea-induced unfolding, Ib is converted to Ia before Ia unfolds, and the unfolding kinetics of Ia fit the two-state model when the burst phase is assigned to Ib-->Ia. The second question is whether the Ia, Ib intermediates accumulate transiently when the native protein (N) unfolds to the acid unfolded form (U). Earlier work showed that Ia and Ib accumulate when U refolds to N at pH 6.0 and the results fit the linear folding pathway U equilibrium Ia equilibrium Ib equilibrium N. We report here that either or both Ia and Ib accumulate transiently when N unfolds to U at pH 2.7 and that the position of the rate-limiting step in the pathway changes between unfolding at pH 2. 7 and refolding at pH 6.0. In unfolding as in refolding, we do not detect a fast track that bypasses the Ia, Ib intermediates.

Ligand exchange during unfolding of cytochrome c

The productive folding pathway of cytochrome c passes through an obligatory HW intermediate in which the heme is coordinated by a solvent water molecule and a native ligand, His-18, prior to the formation of the folded HM state with both the native His-18 and Met-80 heme coordination. Two off pathway intermediates, a five-coordinated state (5C) and a bis-histidine state (HH), were also identified during the folding reaction. In the present work, the thermodynamics and the kinetics of the unfolding reaction of cytochrome c were investigated with resonance Raman scattering, tryptophan fluorescence spectroscopy, and circular dichroism. The objective of these experiments was to determine if the protein opens up and diverges into the differing heme ligation states through a many pathway mechanism or if it passes through intermediate states analogous to those observed during the folding reaction. Equilibrium unfolding results indicate that, in contrast to 5C, the stability of HH with respect to HW decreases as the concentration of GdnHCl increases. The difference in their response to the denaturant indicates that the polypeptide structure of 5C is relatively loose as compared with HH in which the polypeptide is misfolded. Time-resolved resonance Raman measurements show that strikingly similar ligand exchange reactions occur during unfolding as were observed during folding. Combined with fluorescence data, a kinetic model is proposed in which local structural rearrangements controlled by heme ligand exchange reactions appear prior to the global relaxation of the polypeptide chain.

Neuronal coincidence detection by voltage-sensitive electrical synapses

Coincidence detection is important for functions as diverse as Hebbian learning, binaural localization, and visual attention. We show here that extremely precise coincidence detection is a natural consequence of the normal function of rectifying electrical synapses. Such synapses open to bidirectional current flow when presynaptic cells depolarize relative to their postsynaptic targets and remain open until well after completion of presynaptic spikes. When multiple input neurons fire simultaneously, the synaptic currents sum effectively and produce a large excitatory postsynaptic potential. However, when some inputs are delayed relative to the rest, their contributions are reduced because the early excitatory postsynaptic potential retards the opening of additional voltage-sensitive synapses, and the late synaptic currents are shunted by already opened junctions. These mechanisms account for the ability of the lateral giant neurons of crayfish to sum synchronous inputs, but not inputs separated by only 100 microsec. This coincidence detection enables crayfish to produce reflex escape responses only to very abrupt mechanical stimuli. In light of recent evidence that electrical synapses are common in the mammalian central nervous system, the mechanisms of coincidence detection described here may be widely used in many systems.

Folding intermediates in cytochrome c

Folding of cytochrome c from its low pH guanidine hydrochloride (Gdn-HCl) denatured state revealed a new intermediate, a five-coordinate high spin species with a water molecule coordinated to the heme. Incorporation of this five-coordinated intermediate into the previously reported ligand exchange model can quantitatively account for the observed folding kinetics. In this new model, unfolded cytochrome c is converted to its native structure through an obligatory folding intermediate, the histidine-water coordination state, whereas the five-coordinate state and a bis-histidine state are off-pathway intermediates. When the concentration of Gdn-HCl in the refolding solution was increased, an acceleration of the conversion from the bis-histidine coordinated state to the histidine-water coordinated state was observed, demonstrating that the reaction requires unfolding of the mis-organized polypeptide structure associated with the bis-histidine state.

Neuronal adaptations to changes in the social dominance status of crayfish

The effect of superfused serotonin (5-HT; 50 microns) on the synaptic responses of the lateral giant (LG) interneuron in crayfish was found to depend on the social status of the animal. In socially isolated animals. 5-HT persistently increased the response of LG to sensory nerve shock. After social isolates were paired in a small cage, they fought and determined their dominant and subordinate status. After 12 d of pairing, 5-HT reversibly inhibited the response of LG in the social subordinate and reversibly increased the response of LG in the social dominant crayfish. The effect of 5-HT changed approximately linearly from response enhancement to inhibition in the new subordinate over the 12 d of pairing. If, after 12 d pairing, the subordinate was reisolated for 8 d, the response enhancement was restored. If the subordinate, instead, was paired with another subordinate and became dominant in this new pair, the inhibitory effect of 5-HT changed to an enhancing effect over the next 12 d of pairing. If, however, two dominant crayfish were paired and one became subordinate, the enhancing effect of 5-HT persisted in the new subordinate even after 38 d pairing. These different effects of serotonin result from the action of two or more molecular receptors for serotonin. A vertebrate 5-HT, agonist had no effect on social isolates but reversibly inhibited the response of LG in both dominant and subordinate crayfish. The inhibitory effects of the agonist developed approximately linearly over the first 12 d of pairing. A vertebrate 5-HT2 agonist persistently increased the response of LG in isolate crayfish and reversibly increased the response of the cell in dominant and subordinate crayfish. Finally, although neurons that might mediate these effects of superfused 5-HT are unknown, one pair of 5-HT-immunoreactive neurons appears to contact the LG axon and initial axon segment in each abdominal ganglion in its projection caudally from the thorax.

Folding of cytochrome c initiated by submillisecond mixing

Cytochrome c folding was initiated using a new solution mixer that provides a time window which covers over 90% of the burst phase unresolved by conventional stop-flow measurements. Folding was followed by resonance Raman scattering. Kinetic analysis of the high frequency Raman data indicates that a nascent phase occurs within the mixing dead time of 100 microseconds. A significant fraction of the protein was found to be trapped in a misfolded bis-histidine form during the nascent phase at pH 4.5, thereby preventing the protein from folding rapidly and homogeneously. The nascent phase was followed by a haem-ligand exchange phase that populates the native histidine-methionine coordinated form through a thermodynamically controlled equilibrium.

Ligand exchange during cytochrome c folding

Submillisecond folding of cytochrome c reveals that a nascent phase appears within the mixing dead time of 100 microseconds, followed by a ligand exchange reaction during which His 26/33, water and Met 80 are inter-exchanged as haem ligands through a thermodynamically controlled equilibrium. In the ligand exchange phase, the rate of formation of a misfolded histidine-histidine coordinated state (HH) decreases by two orders of magnitude as the pH is reduced from 5.9 to 4.5 due to the protonation of the misligated His 26/33. The activation energy barriers for the transitions from the histidine-water coordinated form (HW) to the histidine-methionine coordinated form and the HH form are 18 and 4 kcal mol-1 respectively, at pH 4.8. The activation energy barrier for protein to escape from the misligated HH to the HW form was measured to be 12 kcal mol-1, demonstrating the kinetic trapping effect of the misligated bis-histidine form. The development of the polypeptide tertiary structure near the haem is concomitant with the coordination of the native haem axial ligand.

Model studies of DNA photorepair: enthalpy of cleavage of a pyrimidine dimer measured by photothermal beam deflection calorimetry

The enzyme DNA photolyase mediates the repair of pyrimidine dimers. This repair step, a net retro [2 + 2] reaction, proceeds through either the cation or anion radical of the pyrimidine dimer. In order to understand how electron transfer makes the repair process possible, its energetics have been examined by photothermal beam deflection calorimetry, fluorescence quenching and quantum yield studies. The enthalpy for the cleavage reaction of cis-syn 1,3-dimethylthymine dimer itself was found to be -19 kcal/mol. In addition, from the redox potentials, the enthalpies for the cleavage reactions of the dimer cation radical and the anion radical were determined to be -19 kcal/mol and -28 kcal/mol, respectively.

The effect of social experience on serotonergic modulation of the escape circuit of crayfish

The neuromodulator serotonin has widespread effects in the nervous systems of many animals, often influencing aggression and dominance status. In crayfish, the effect of serotonin on the neural circuit for tailflip escape behavior was found to depend on the animal's social experience. Serotonin reversibly enhanced the response to sensory stimuli of the lateral giant (LG) tailflip command neuron in socially dominant crayfish, reversibly inhibited it in subordinate animals, and persistently enhanced it in socially isolated crayfish. Serotonin receptor agonists had opposing effects: A vertebrate serotonin type 1 receptor agonist inhibited the LG neurons in dominant and subordinate crayfish and had no effect in isolates, whereas a vertebrate serotonin type 2 receptor agonist enhanced the LG neurons' responses in all three types of crayfish. The LG neurons appear to have at least two populations of serotonin receptors that differ in efficacy in dominant, subordinate, and socially isolate crayfish.

Changes in synaptic integration during the growth of the lateral giant neuron of crayfish

1. The effect of growth on the electrotonic structure and synaptic integrative properties of the lateral giant (LG) interneuron was assessed from anatomic and electrophysiological measurements of LGs in small (1-2.4 cm) and large (9-11.2 cm) crayfish and from calculated responses of mathematical models of these neurons. Postsynaptic responses of small and large LGs were compared with model responses to determine whether the differences in the neurons' responses result from growth-related changes in their physical characteristics. 2. LG neurons in the terminal abdominal ganglia of small and large crayfish are similar in shape but differ in size according to an approximately isometric pattern of growth. The soma diameter of the large LG is 2.2 times larger than the small LG, the major ipsilateral dendrite is 2.8 times longer and 3.6 times greater in diameter, and the axon is 7.6 times longer and 4.5 times greater in diameter. The projected area of the major ipsilateral dendrite of LG in the horizontal plane of the terminal abdominal ganglion is 27 times larger in the large than in the small crayfish. 3. LG's input resistance was nearly 80% smaller in the large (167 K omega) than in the small (742 K omega) crayfish when measured at or near the initial axon segment. The cell's membrane time constant displayed an opposite relationship, with the value in the large crayfish (20.9 ms) nearly two-and-a-half times larger than the value in the small crayfish (8.6 ms). 4. Simultaneous recordings were made from the distal portion of the ipsilateral dendrite and the initial axon segment of small and large LGs to determine how excitatory postsynaptic potentials (EPSPs) are attenuated or filtered by the electrotonic properties of the different sized cells. In the small LG, the fast alpha and the slower beta components of compound EPSPs evoked by sensory nerve stimulation were similarly attenuated. In the large LG, the alpha component of the compound EPSP was much more attenuated and smoothed than the slower beta component. 5. Multicompartment models of small and large LGs were constructed and used to test whether differences in the two neurons' physical properties could account for the differences in their passive response properties.(ABSTRACT TRUNCATED AT 250 WORDS)

The onset of response habituation during the growth of the lateral giant neuron of crayfish

1. The postembryonic development of the crayfish LG tailflip command neuron's response to mechanosensory input was studied with standard electrophysiological techniques in animals between 1 and 12 cm long. 2. LG neurons are present in each abdominal hemisegment where they receive direct and indirect excitatory input from mechanosensory afferents. In both small and large crayfish, electrical stimulation of an abdominal ganglionic nerve containing those afferents evoked a compound excitatory postsynaptic potential (EPSP) with an early, reliable alpha component and a later, depression-prone beta wave. It is known that the alpha and beta components are produced by inputs from primary mechanosensory afferents and interneurons, respectively. 3. In crayfish < 2 cm long, LG was excited by the alpha component. When superthreshold, the alpha component triggered a single spike; additional excitation provided by the later beta wave presumably was preempted by refractoriness following the alpha spike and by recurrent inhibition of LG excited by the spike. LG was excited reliably by the alpha component in response to repeated superthreshold stimulation. 4. In crayfish between 2 and 3 cm, LG was excited more readily by the beta wave than by the alpha component. LG's beta spike response habituated to repeated stimulation at 1 Hz, and the beta EPSP depressed whereas the alpha component was largely unchanged. The appearance of the cellular substrates of habituation correlates with the reported onset of behavioral habituation of the tailflip response. Higher stimulus levels brought the alpha EPSP to threshold. Repetitive stimulation at these levels reliably evoked LG spikes from the alpha EPSP.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of insulin on glucose uptake in cultured cells from the central nervous system of rodent

1. Incubation of C6 glioma cultures with insulin resulted in a time and dose-dependent stimulation of 2-deoxy-D-glucose uptake. The maximal stimulation (160% of the control) was observed with 1 nM insulin and 0.05 nM caused half-maximum effect. 2. Incubation of NG 108-15 (neuroblastoma x glioma hybrid) and N2 neuroblastoma cells with 160 nM insulin did not result in a significant stimulation of this glucose uptake. 3. The basal level and stimulatory effect by insulin on this glucose uptake observed in C6 glioma cells were dependent on the presence of calcium in the medium. 4. Such an increase in glucose uptake in C6 glioma cells was also observed in the presence of diacylglycerol (DG) generating agents, such as carbachol (1 mM) and phospholipase C (0.05 unit/ml) or of DG analogs, such as sn-1,2-dioctanoyl glycerol (250 microM) and phorbol myristate acetate (1 microM). 5. Our results indicated that both calcium ion and DG levels play important roles in the regulation of glucose uptake in the glial cells, but not in neuronal cells from the brain.