Circuit analysis of experience-dependent plasticity in the developing rat barrel cortex

Sensory deprivation during a critical period reduces spine motility and disrupts receptive field structure of layer 2/3 neurons in rat barrel cortex. To determine the locus of plasticity, we used laser scanning photostimulation, allowing us to rapidly map intracortical synaptic connectivity in brain slices. Layer 2/3 neurons differed in their spatial distributions of presynaptic partners: neurons directly above barrels received, on average, significantly more layer 4 input than those above the septa separating barrels. Complementary connectivity was found in deprived cortex: neurons above septa were now strongly coupled to septal regions, while connectivity between barrel regions and layer 2/3 was reduced. These results reveal competitive interactions between barrel and septal circuits in the establishment of precise intracortical circuits.

Focal photolysis of caged glutamate produces long-term depression of hippocampal glutamate receptors

Separating contributions of pre- and postsynaptic factors to the maintenance of long-term potentiation (LTP) and long-term depression (LTD) has been confounded by their experimental interdependence. To isolate the postsynaptic contribution, glutamate-receptor-mediated currents were elicited by localized photolysis of caged glutamate in small spots along the dendrites of CA1 hippocampal pyramidal cells. With synaptic transmission blocked, pairing depolarization of pyramidal cells with repeated photolysis of caged glutamate at one site markedly and persistently depressed subsequent responses to glutamate; responses at a second, unpaired site were unchanged. Like synaptically induced LTD at the CA3-CA1 synapse, this depression was site specific, NMDA-receptor dependent and blocked by protein-phosphatase inhibitors. Thus, robust, persistent alterations of postsynaptic glutamate receptor efficacy can occur without presynaptic neurotransmitter release.

Temporal integration can readily switch between sublinear and supralinear summation

Temporal summation at dendrites of cultured rat hippocampal neurons was examined as a function of the interval separating two dendritic inputs. A novel method that relies on single-mode optical fibers to achieve rapid photorelease of glutamate was developed. Dendritic excitation achieved with this approach resembles that associated with miniature excitatory postsynaptic currents (mEPSCs), but the strengths, sites, and timing of the inputs can be precisely controlled. Dendritic summation deviated markedly from behavior predicted by passive cable theory. Subthreshold temporal summation varied as a triphasic function of the interpulse interval. As the interpulse interval decreased, local dendritic Na+ conductances were recruited to generate a marked transition from sublinear to supralinear summation. These results suggest that active dendritic conductances acting in concert with passive cable properties may serve to boost coincident synaptic inputs and attenuate noncoincident inputs.

Physical and Chemical Stability of Pemetrexed in Infusion Solutions

Background:

Pemetrexed is a multitargeted, antifolate, antineoplastic agent that is indicated for single-agent use in locally advanced or metastatic non-small-cell lung cancer after prior chemotherapy and in combination with cisplatin for the treatment of malignant pleural mesothelioma not treatable by surgery. Currently, there is no information on the long-term stability of pemetrexed beyond 24 hours.

Objective:

To evaluate the longer-term physical and chemical stability of pemetrexed 2, 10, and 20 mg/mL in polyvinyl chloride (PVC) bags of dextrose 5% injection and NaCI 0.9% injection.

Methods:

Triplicate samples of pemetrexed were prepared in the concentrations and infusion solutions required. Evaluations for physical and chemical stability were performed initially and over 2 days at 23 °C protected from light and exposed to fluorescent light, and over 31 days of storage at 4 °C protected from light. Physical stability was assessed using turbidimetric and particulate measurement as well as visual observation. Chemical stability was evaluated by HPLC.

Results:

All pemetrexed solutions remained chemically stable, with little or no loss of pemetrexed over 2 days at 23 °C, protected from light and exposed to fluorescent light, and over 31 days of storage at 4°C, protected from light. The room temperature samples were physically stable throughout the 48 hour test period. However, pemetrexed admixtures developed large numbers of microparticulates during refrigerated storage exceeding 24 hours.

Conclusions:

Pemetrexed is chemically stable for 2 days at room temperature and 31 days refrigerated in dextrose 5% injection and NaCI 0.9% injection. However, substantial numbers of microparticulates may form in pemetrexed diluted in the infusion solutions in PVC bags, especially during longer periods of refrigerated storage. Limiting the refrigerated storage period to the manufacturer-recommended 24 hours will limit particulate formation.

Rapid Ultrastructural Changes in the PSD and Surrounding Membrane after Induction of Structural LTP in Single Dendritic Spines

The structural plasticity of dendritic spines is considered to be an important basis of synaptic plasticity, learning, and memory. Here, we induced input-specific structural LTP (sLTP) in single dendritic spines in organotypic hippocampal slices from mice of either sex and performed ultrastructural analyses of the spines using efficient correlative light and electron microscopy. We observed reorganization of the PSD nanostructure, such as perforation and segmentation, at 2-3, 20, and 120 min after sLTP induction. In addition, PSD and nonsynaptic axon-spine interface (nsASI) membrane expanded unevenly during sLTP. Specifically, the PSD area showed a transient increase at 2-3 min after sLTP induction. The PSD growth was to a degree less than spine volume growth at 2-3 min and 20 min after sLTP induction but became similar at 120 min. On the other hand, the nsASI area showed a profound and lasting expansion, to a degree similar to spine volume growth throughout the process. These rapid ultrastructural changes in PSD and surrounding membrane may contribute to rapid electrophysiological plasticity during sLTP.SIGNIFICANCE STATEMENT To understand the ultrastructural changes during synaptic plasticity, it is desired to efficiently image single dendritic spines that underwent structural plasticity in electron microscopy. We induced structural long-term potentiation (sLTP) in single dendritic spines by two-photon glutamate uncaging. We then identified the same spines at different phases of sLTP and performed ultrastructural analysis by using an efficient correlative light and electron microscopy method. We found that postsynaptic density undergoes dramatic modification in its structural complexity immediately after sLTP induction. Meanwhile, the nonsynaptic axon-spine interface area shows a rapid and sustained increase throughout sLTP. Our results indicate that the uneven modification of synaptic and nonsynaptic postsynaptic membrane might contribute to rapid electrophysiological plasticity during sLTP.

Chemical evolution of the citric acid cycle: sunlight photolysis of the amino acids glutamate and aspartate

Sunlight photolysis of the amino acids glutamate and aspartate were carried out on 0.1 M aqueous solutions at pH = 7.0. The non-volatile products were identified by GC-MS analysis of derived methyl esters. The major product from glutamic acid was succinic acid, and, analogously, aspartic acid photolyzed to malonic acid. The photochemical oxidative decarboxylation of glutamate parallels its metabolism in modern cells and may provide an evolutionary link between simple amino acids and reactions of the citric acid cycle.

Photolysis accompanying peptide absorption in proteins. Electrophoresis and optical rotary dispersion studies

Exposure of proteins and polypeptides to ultraviolet radiation below 240 nm produces peptide cleavage which may or may not be accompanied by observable changes in conformation and optical rotary dispersion (ORD) properties, depending on the stability of the secondary and tertiary structure of the macromolecule under the experimental conditions. Helical and coiled forms of poly-L-glutamic acid undergo degradation at similar rates but only the helical form shows a significant change in rotatory properties. The helical form of poly-L-lysine, but neither the coiled nor beta forms, shows a change in [alpha](233) on irradiation at 233 nm. beta-Lactoglobulin shows essentially no change in [alpha](233) on irradiation in either dilute salt solution or 4 M urea at room temperature; however, in 4 M urea at 56 degrees C a large change occurs. A model is developed which shows that studies of the effect of radiation on ORD properties may be useful in providing information on possible intermediate steps in protein denaturation. The method is illustrated with results on bovine plasma albumin. A quantum yield, 4.3 x 10(-3) moles/einstein, was obtained for peptide cleavage in this protein at 225 nm. These studies, based on gel electrophoresis, also showed that the fragments produced are essentially random, suggesting that transfer of energy from aromatic residues is not an important contributor to the peptide photolysis. Possible errors which could arise in ORD and other studies involving intense ultraviolet radiation are considered.

Zur Frage der Aminosäureisomerisierung im Mikrowellenfeld Ergebnisse eines Modellversuches mit Standardlösungen

Aqueous standard-solutions of L-alanine, L-glutamic acid, and L-proline do not reveal any increase of D-enantiomers after 30 min heating--neither by the conventional method on a hotplate, nor in a standard microwave oven. A specific "microwave effect" and, hence, a special consumer risk is, in contrast to recent assumptions, not detectable. Effects on the amino acids which were observed in conventionally heated samples are explained by higher heat-exposure during the treatment of these samples.

Epidermal N-acetylation of p-aminobenzoyl glutamic acid: difference in response to ultraviolet B irradiation

Arylamine N-acetyltransferases (EC 2.3.1.5) are conjugating drug-metabolizing enzymes and consist of two major isozymes, NAT1 and NAT2. As they have different substrate specificity and expression of polymorphism, distribution of the isozymes may be detected by investigating acetylation. p-Aminobenzoyl glutamic acid (pABG), one of the specific substrates for NAT1 in human pro-monocytic cell-line, was metabolized through acetylation by 9000 x g supernatant fraction from human epidermal keratinocytes and the effect of ultraviolet B (UVB) irradiation on the acetylation was also studied. Forty-eight hours after irradiation of UVB (200 J/m2), the activity was not increased (114 +/- 8.3%, n = 3), while increase in N-acetylating capacity for 2-aminofluorene (substrate for NAT1 and NAT2) amounted to 201 +/- 16% (n = 3). These results suggest that there are at least two isozymes for N-acetylation in the human epidermic and NAT2 may be affected by UVB irradiation.

Neocortical long-term potentiation and long-term depression: site of expression investigated by infrared-guided laser stimulation

The synaptic site of expression of long-term potentiation (LTP) and long-term depression (LTD) is still a matter of debate. To address the question of presynaptic versus postsynaptic expression of neocortical LTP and LTD in a direct approach, we measured the glutamate sensitivity of apical dendrites of layer 5 pyramidal neurons during LTP and LTD. We used infrared-guided laser stimulation to release glutamate from its "caged" form with high spatial and temporal resolution. Responses to photolytically released glutamate and synaptically evoked EPSPs were recorded with patch-clamp pipettes from the neuronal somata. LTP and LTD could be induced by electrical stimulation at the same synapses in succession. The NMDA receptor-dependent LTD was accompanied by a decrease in the dendritic glutamate sensitivity, suggesting a postsynaptic expression of neocortical LTD. In contrast, LTP was never accompanied by a change in the dendritic glutamate sensitivity. A possible explanation for this finding is a presynaptic expression of neocortical LTP. Another set of experiments corroborated these results: Photolytic application of glutamate with a frequency of 5 Hz caused a long-lasting Ca2+ and NMDA receptor-dependent decrease in the dendritic glutamate sensitivity. In contrast, LTP of dendritic glutamate sensitivity was never induced by photostimulation, despite several experimental modifications to prevent washout of the induction mechanism and to induce a stronger postsynaptic Ca2+ influx. In conclusion, our findings provide strong evidence for a postsynaptic expression of neocortical LTD and favor a primarily presynaptic locus of neocortical LTP.

[Enzyme activity of glutamic acid metabolism and the Krebs cycle in the brain of rats laser-irradiated against a background of altered adrenoreceptor function]

In the in vivo experiments it was demonstrated that the effect of a helium-neon laser (lambda = 632.8 nm), at the background of altered functional status of adrenoreceptors, changes the activity of some enzymes of the glutamic acid metabolism and the Krebs cycle. This may be attributed to both the direct effect of laser radiation and the indirect effect via the adrenergic system.

Distribution and properties of functional postsynaptic kainate receptors on neocortical layer V pyramidal neurons

The distribution of glutamate receptor subtypes on the surface of neurons is highly relevant for synaptic transmission and signal processing. In the present study we investigated the location and properties of functional kainate receptors (KARs) on the somatodendritic membrane of rat neocortical layer V pyramidal neurons. Infrared-guided laser stimulation was used to apply glutamate photolytically to the soma and various sites along the apical dendrite. Electrical currents, resulting from the activation of pharmacologically isolated KARs, were measured by whole-cell patch-clamp recording. In addition, KARs on somatic and dendritic outside-out patches were activated while still within the brain tissue. We found that functional KARs are located on the entire somatodendritic membrane that was examined. Fast kinetics, a linear I-V relationship, and a relatively high single-channel conductance are characteristic features of these receptors. We provide evidence that the unitary properties of somatic and dendritic KARs are identical. Regarding the subcellular distribution of KARs, our results indicate that the density of these receptors increases toward the distal dendrite. They are located mainly at extrasynaptic sites but also mediate fast synaptic signaling triggered by afferent stimulation. The differential distribution speaks in favor of a selective targeting of KARs on central neurons and may reflect a mechanism for a location-dependent regulation of synaptic efficacy. Furthermore, it is feasible to assume that extrasynaptic KARs could be activated by a "spillover" of synaptically released glutamate, ambient glutamate in the CSF, or glutamate released from adjacent astrocytes.

[Early changes in GABA and glutamate levels and aminotransferase activity in parts of the rat brain following whole-body gamma irradiation at an absolutely lethal dose]

The contents of gamma-aminobutyric acid (GABA) and glutamate (GL) as well as GABA-aspartate- and alanine aminotransferase activities were measured in rat cerebellum, cerebral cortex and truncus cerebri 1, 3, 6, 24 and 48 hr following total-body gamma-irradiation (60Co) with a dose of 30 Gy. All the indices under study changed in a similar way in the cortex and truncus cerebri while in the cerebellum, GABA level increased and GABA-alpha-ketoglutarate aminotransfearse activity decreased 60 min after irradiation. The levels of GABA and GL in the cortex and truncus cerebri decreased immediately and increased 24 hr after irradiation. Activity of aminotransferases changed in a phase manner: changes in aspartate- and alanine aminotransferase activity were more pronounced than those of GABA-alpha-ketoglutarate aminotransferase activity and correlated with the glutamate level changes.

[Effect of pyridoxal phosphate on gamma-aminobutyric acid metabolism in different sections of the brain in irradiated animals]

A study was made of the effect of X-rays (4,5 Gy) and pyridoxal phosphate (3 mg/kg, v/v) on the activity of pyridoxal enzymes of GABA metabolism (e.g. glutamate decarboxylase, E.C. 4.1.1.15) and aminobutyrate aminotransferase (GABA-T, E.C. 2.6.1.19), as well as on GABA and glutamate content of the hemisphere cortex, brain stem and cerebellum of rabbits 6 and 10 days following irradiation and injection of a coenzyme. The height of the radiation sickness in rabbits was characterized by the manifest changes in glutamate decarboxylase and GABA-T activity, as well as in GABA and glutamate content of various brain parts differing in the structural and functional functions. The administration of pyridoxal phosphate produced pronounced activation of glutamate decarboxylase, particularly 6 days after irradiation and administration of the co-enzyme, and, to a lesser extent, influenced GABA-T function. Pyridoxal phosphate favored maintaining the GABA level above the control level in the hemisphere cortex and brain stem 6 and 10 days after exposure. The injection of pyridoxal phosphate did not normalize the glutamate content of the brain parts 6 days after exposure, but favored the normalization of GABA-T activity on day 10.