Off-Line, Multi-Detector Intensity Interferometers II: Implications and Applications

Intensity interferometry removes the stringent requirements on mechanical precision and atmospheric corrections that plague all amplitude interferometry techniques at the cost of severely limited sensitivity. A new idea we recently introduced, very high redundancy, alleviates this problem. It enables the relatively simple construction (~1cm mechanical precision) of a ground-based astronomical facility able to transform a two-dimensional field of point-like sources to a three-dimensional distribution of micro-arcsec resolved systems, each imaged in several optical bands. Each system will also have its high resolution residual timing, high quality (inside each band) spectra and light curve, emergent flux, effective temperature, polarization effects and perhaps some thermodynamic properties, all directly measured. All the above attributes can be measured in a single observation run of such a dedicated facility. We conclude that after three decades of abandonment optical intensity interferometry deserves another review, also as a ground-based alternative to the science goals of space interferometers.Comment: The article has been accepted for publication in MNRA

Coherent Emission from Magnetars

It is proposed that magnetospheric currents above the surfaces of magnetars radiate coherent emission in analogy to pulsars. Scaling the magnetospheric parameters suggests that the coherent emission from magnetars would emerge in the infra-red or optical

GABAergic nerve terminals decrease in the substantia nigra following hemitransections of the striatonigral and pallidonigral pathways.

Glutamic acid decarboxylase (GAD), the enzyme that synthesizes the neurotransmitter, GABA, was immunocytochemically localized in axon terminals as well as in small and medium-sized neurons of the rat substantia nigra. The pattern formed by GAD-containing axon terminals with the dendrites and somata of neurons in the substantia nigra was altered following ipsilateral hemitransections of the striatonigral and pallidonigral pathways. A marked reduction of GAD-positive terminals occurred throughout this brain region, but the ventral fifth of the pars reticulata showed a nearly normal pattern of GAD-positive axon terminals. The results of this investigation are consistent with results from biochemical studies which have indicated that the striatonigral and/or pallidonigral pathways are GABAergic. In addition, these results suggest that the residual GABAergic terminals remaining after hemitransection are derived from intrinsic neurons of the substantia nigra

Suppression of cathepsins B and L causes a proliferation of lysosomes and the formation of meganeurites in hippocampus.

Cultured hippocampal slices exhibited prominent ultrastructural features of brain aging after exposure to an inhibitor of cathepsins B and L. Six days of treatment with N-CBZ-L-phenylalanyl-L-alanine-diazomethylketone (ZPAD) resulted in a dramatic increase in the number of lysosomes in the perikarya of neurons and glial cells throughout the slices. Furthermore, lysosomes in CA1 and CA3 pyramidal cells were not restricted to the soma but instead were located throughout dendritic processes. Clusters of lysosomes were commonly found within bulging segments of proximal dendrites that were notable for an absence of microtubules and neurofilaments. Although pyknotic nuclei were sometimes encountered, most of the cells in slices exposed to ZPAD for 6 d appeared relatively normal. Slices given 7 d of recovery contained several unique features, compared with those processed immediately after incubation with the inhibitor. Cell bodies of CA1 neurons were largely cleared of the excess lysosomes but had gained fusiform, somatic extensions that were filled with fused lysosomes and related complex, dense bodies. These appendages, similar in form and content to structures previously referred to as "meganeurites," were not observed in CA3 neurons or granule cells. Because meganeurites were often interposed between cell body and axon, they have the potential to interfere with processes requiring axonal transport. It is suggested that inactivation of cathepsins B and L results in a proliferation of lysosomes and that meganeurite generation provides a means of storing residual catabolic organelles. The accumulated material could be eliminated by pinching off the meganeurite but, at least in some cases, this action would result in axotomy. Reduced cathepsin L activity, increased numbers of lysosomes, and the formation of meganeurites are all reported to occur during brain aging; thus, it is possible that the infusion of ZPAD into cultured slices sets in motion a greatly accelerated gerontological sequence

Newly born dentate granule neurons after pilocarpine-induced epilepsy have hilar basal dendrites with immature synapses.

Neurogenesis in the subgranular zone of the dentate gyrus persists throughout the lifespan of mammals, and the resulting newly born neurons are incorporated into existing hippocampal circuitry. Seizures increase the rate of neurogenesis in the adult rodent brain and result in granule cells in the dentate gyrus with basal dendrites. Using doublecortin (DCX) immunocytochemistry to label newly generated neurons the current study focuses on the electron microscopic features of DCX-labeled cell bodies and dendritic processes in the dentate gyrus of rats with pilocarpine-induced epilepsy. At the base of the granule cell layer clusters of cells that include up to six DCX-labeled cell bodies were observed. The cell bodies in these clusters lacked a one-to-one association with an astrocyte cell body and its processes, a relationship that is typical for newly born granule cells in control rats. Also, DCX-labeled basal dendrites in the hilus had immature synapses while those in control rats lacked synapses. These results indicate that increased neurogenesis after seizures alters the one-to-one relationship between astrocytes and DCX-labeled newly generated neurons at the base of the granule cell layer. The data also suggest that the synapses on DCX-labeled hilar basal dendrites contribute to the persistence of hilar basal dendrites on neurons born after pilocarpine-induced seizures

Spatiotemporal profile of dendritic outgrowth from newly born granule cells in the adult rat dentate gyrus.

Neurogenesis in the adult dentate gyrus occurs in the subgranular zone where newborn neurons (NNs) migrate a short distance into the granule cell layer and extend their rudimentary apical dendritic processes upon a radial glial scaffold. Using doublecortin (DCX) immunocytochemistry, these growing dendrites can be visualized because dendritic growth cones, including filipodia and lamellipodia, are labeled in both light and electron microscopic preparations. To study the rate of dendritic outgrowth of newborn dentate granule cells, single injections of 5-bromo-2-deoxyuridine (BrdU) with different survival times were combined with double immunolabeling for BrdU and DCX. At the earliest time points (4 and 12 h after BrdU injections), a rudimentary process can be observed to emanate from BrdU/DCX double-labeled cells. By 48 h the dendrites first appeared in the molecular layer. By 96 h after BrdU injection, these apical dendrites extended into the middle of the molecular layer where they ramified. The calculated rate of dendritic growth for NNs was about 15 microm per day for the first 3 days, and then a doubling in length occurred at 4 and 5 days that coincided with a retraction of the basal dendrite. In addition, electron microscopy of DCX-labeled apical dendrites showed that they were much thinner (1/4 to 1/3 the size) in diameter than unlabeled, mature apical dendrites and that they had developing synapses on them in the molecular layer

Electrophysiologic characterization of morphologically identified neurons in the cerebellar cortex of awake cats.

Intracellular recordings were obtained from 161 neurons of the cerebellar cortex of 20 awake cats. Seventeen neurons marked by intracellular pressure injection of horseradish peroxidase were morphologically identified as Purkinje cells. Seven other neurons were recovered with a morphology characteristic of Golgi II cells. In addition to intrinsic action potentials typical of cerebellar and other mammalian cortical recordings, both types of cells revealed a fast spike-like component that was relatively insensitive to injected current and could not be attributed to regenerative Na+ or Ca2+ conductances intrinsic to the penetrated neuron. In Purkinje cells, the fast spike often appeared at the initial portion of the potential configuration normally called the climbing fiber response. In the other class of cells, the fast, current-insensitive spike followed the intrinsic cell discharge. The results demonstrate distinctive patterns of electrical activity in two different types of morphologically identified cerebellar neurons. The fast spikes could reflect electrical coupling between the two types of cells. © 1980

Inhibitory, GABAergic nerve terminals decrease at sites of focal epilepsy.

Using an immunocytochemical method for the localization of the gamma-aminobutyric acid (GABA) synthesizing enzyme, glutamic acid decarboxylase (GAD), we have observed GABAergic nerve terminals distributed throughout all layers of normal monkey sensorimotor cortex. These terminals displayed ultrastructural characteristics that suggested that they arose from aspinous and sparsely spinous stellate neurons. In monkeys (Macaca mulatta and M. fascicularis) made epileptic by cortical application of alumina gel, a highly significant numerical decrease of GAD-positive nerve terminals occurred at sites of seizure foci indicating a functional loss of GABAergic inhibitory synapses. A loss of such inhibition at seizure foci could lead to epileptic activity of cortical pyramidal neurons