No abstract

The use of human brain tissue obtained at autopsy for neurochemical, pharmacological and physiological analyses is reviewed. RNA and protein samples have been found suitable for expression profiling by techniques that include RT-PCR, cDNA microarrays, western blotting, immunohistochemistry and proteomics. The rapid development of molecular biological techniques has increased the impetus for this work to be applied to studies of brain disease. It has been shown that most nucleic acids and proteins are reasonably stable postmortem. However, their abundance and integrity can exhibit marked intra-and intercase variability, making comparisons between case-groups difficult. Variability can reveal important functional and biochemical information. The correct interpretation of neurochemical data must take into account such factors as age, gender, ethnicity, medicative history, immediate ante-mortem status, agonal state and post-mortem and post-autopsy intervals. Here we consider issues associated with the sampling of DNA, RNA and proteins using human autopsy brain tissue in relation to various ante-and postmortem factors. We conclude that valid and practical measures of a variety of parameters may be made in human brain tissue, provided that specific factors are controlled.

Two-dimensional (2D) culture systems provide useful information about many biological processes. However, some applications including tissue engineering, drug transport studies, and analysis of cell growth and dynamics are better studied using three-dimensional (3D) culture systems. 3D culture systems can potentially offer higher degrees of organization and control of cell growth environments, more physiologically relevant diffusion characteristics, and permit the formation of more extensive 3D networks of cell-cell interactions. A 3D culture system has been developed using alginate as a cell scaffold, capable of maintaining the viability and function of a variety of neural cell types. Alginate was functionalized by the covalent attachment of a variety of whole proteins and peptide epitopes selected to provide sites for cell attachment. Alginate constructs were used to entrap a variety of neural cell types including astroglioma cells, astrocytes, microglia and neurons. Neural cells displayed process outgrowth over time in culture. Cell-seeded scaffolds were characterized in terms of their biochemical and biomechanical properties, effects on seeded neural cells, and suitability for use as 3D neural cell culture models.

Synaptic activity recorded from low-density networks of cultured rat hippocampal neurons was monitored using microelectrode arrays (MEAs). Neuronal networks were patterned with poly-Llysine (PLL) using microcontact printing (µCP). Polydimethysiloxane (PDMS) stamps were fabricated with relief structures resulting in patterns of 2 µm-wide lines for directing process growth and 20 µm-diameter circles for cell soma attachment. These circles were aligned to electrode sites. Different densities of neurons were plated in order to assess the minimal neuron density required for development of an active network. Spontaneous activity was observed at 10-14 days in networks using neuron densities as low as 200 cells/mm 2 . Immunocytochemistry demonstrated the distribution of dendrites along the lines and the location of foci of the presynaptic protein, synaptophysin, on neuron somas and dendrites. Scanning electron microscopy demonstrated that single fluorescent tracks contained multiple processes. Evoked responses of selected portions of the networks were produced by stimulation of specific electrode sites. In addition, the neuronal excitability of the network was increased by the bath application of high K + (10-12 mM). Application of DNQX, an AMPA antagonist, blocked all spontaneous activity, suggesting that the activity is excitatory and mediated through glutamate receptors.

Local pharmacological intervention may be needed to ensure the long-term performance of neural prosthetic devices because of insertion-related neuron loss and reactive cell responses that form compact sheaths, leading to decreased device performance. We propose that local delivery of neurotrophins would enhance neuron survival and promote neuron sprouting toward device electrodes, thus providing improved electrode-neuron communication and device performance for recording and stimulating CNS activity. In this study, three different types of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels were developed and assessed for storage capacity and release rates of the neurotrophin, nerve growth factor (NGF). Additionally, a method was developed for routine coating of microfabricated neuroprosthetic devices with the different pHEMA hydrogels. Biological responses to hydrogel-delivered NGF from the devices were measured using primary cell cultures of dorsal root ganglion (DRG) neurons. Neuron process growth was used to assess biological responses to released NGF. When targeted media concentrations were the same, responses to bath-applied NGF and NGF released from pHEMA hydrogels were not significantly different. When NGF was released from lysine-conjugated pHEMA hydrogels, a significant increase in process growth was observed. Our studies demonstrate that pHEMA coatings can be used on neural devices consistent with the needs for local neurotrophin delivery in the brain.

Biochemical surface modification has been used to direct cell attachment and growth on a biocompatible gel surface. Acrylamide-based hydrogels were photo-polymerized in the presence of an acroyl-streptavidin monomer to create planar, functionalized surfaces capable of binding biotin-labelled proteins. Soft protein lithography (microcontact printing) of proteins was used to transfer the biotinylated extracellular matrix proteins, fibronectin and laminin, and the laminin peptide biotin-IKVAV, onto modified surfaces. As a biological assay, we plated LRM55 astroglioma and primary rat hippocampal neurons on patterned hydrogels. We found both cell types to selectively adhere to areas patterned with biotin-conjugated proteins. Fluorescence and bright-field modes of microscopy were used to assess cell attachment and cell morphology on modified surfaces. LRM55 cells were found to attach to protein-stamped regions of the hydrogel only. Neurons exhibited significant neurite extension after 72h in vitro, and remained viable on protein-stamped areas for more than 4 weeks. Patterned neurons developed functionally active synapses, as measured by uptake of the dye FM1-43FX. Results from this study suggest that hydrogel surfaces can be patterned with multiple proteins to direct cell growth and attachment.

We have previously shown that the expression of NMDA receptor NR1 subunit mRNA splice variants in Alzheimer's disease (AD) brain varies according to regional susceptibility to pathological damage. Here we investigated the expression of the modulatory NR2 subunits of the NMDA receptor using quantitative RT-PCR to assay all NR2 isoforms. Significantly lower expression of NR2A and NR2B transcripts was found in susceptible regions of AD brain, whereas expression of NR2C and NR2D transcripts did not differ from that in controls.Western blot analysis confirmed a lower expression of the NR2A and NR2B isoforms at the protein level. The results suggest that NR2 subunit composition may modulate NMDA receptor-mediated excitotoxicity. NMDA receptor dysfunction might give rise to the regionally selective pattern of neuronal loss that is characteristic of AD.

Previous work had shown that the ratio of NMDA receptor NR1 subunit mRNA transcripts containing an N-terminal splice cassette to those that do not is markedly lower in regions of the Alzheimer's disease (AD) brain that are susceptible to pathological damage, compared with spared regions in the same cases or homotropic regions in controls. To elucidate the origins of this difference in proportionate expression, we measured the absolute levels of each of the eight NR1 transcripts by quantitative internally standardized RT-PCR assay. Expression of transcripts with the cassette was strongly attenuated in susceptible regions of Alzheimer's brain, whereas expression of non-cassette transcripts differed little from that in controls. The expression of other NR1 splice variants was not associated with pathology relevant to disease status, although some combinations of splice cassettes were well maintained in AD cases. The population profile of NR1 transcripts in occipital cortex differed from the profiles in other brain regions studied. Western analysis confirmed that the expression of protein isoforms containing the N-terminal peptide was very low in susceptible areas of the Alzheimer's brain. Cells that express NR1 subunits with the N-terminal cassette may be selectively vulnerable to toxicity in AD. Keywords: Alzheimer's disease, excitotoxicity, glutamate, N-methyl-D-aspartate, polyamine. NMDA receptors (NMDARs) are present on most CNS neurones (Petralia et al. 1994) and mediate Ca 2+ influx in response to glutamate (Constantine-Paton 1990;Bliss and Collingridge 1993;Seeburg 1993;Hollmann and Heinemann 1994;Constantine-Paton and Cline 1998). Their excessive activation has been implicated in hypoxia-ischemia, epilepsy, and chronic neurodegenerative disorders such as Huntington's and Alzheimer's diseases (Choi 1988;Young 1993;Olney 1994;Chen et al. 1999). The impairments in memory and cognition in Alzheimer's disease (AD) can be correlated to the neuropathological features of the disease, including neuronal loss and plaque and tangle formation in the cortex and hippocampus (Hyman et al. 1986; Albin and Greenamyre 1992; Bobinski et al. 1998). Neuronal loss is generally restricted to the pyramidal cells in layers III and IV. Damage to glutamate-innervated neurones is also observed (Albin and Greenamyre 1992). Axons, terminal boutons, glia, and endothelial and ependymal cells are relatively spared (Choi 1992).NMDARs are heteromeric assemblies comprising a ubiquitous NR1 subunit and two or more NR2 subunits (NR2 A-D) (Monyer et al. 1992;Ishii et al. 1993;Dingledine et al. 1999). An NR3 subunit has also been cloned (Sucher et al. 1995;Das et al. 1998). The function and modulation of NMDAR channels is spatially and temporally regulated (Bockers et al. 1994;Rigby et al. 1996). While the NR1 subunit is expressed ubiquitously, NR2 subunits show regional and developmental variations (Watanabe et al. 1992(Watanabe et al. , 1993Akazawa et al. 1994;Monyer et al. 1994). The NR1 subunit undergoes alternate splicing of three ex...