Biomedical subjects

Rifat J Hussain

Publications and source records attributed to Rifat J Hussain.

7 recordsLinked to original sources

PubMed2006

Myristoylated alanine rich C kinase substrate (MARCKS) heterozygous mutant mice exhibit deficits in hippocampal mossy fiber-CA3 long-term potentiation.

The myristoylated alanine-rich C kinase substrate (MARCKS) is a primary protein kinase C (PKC) substrate in brain thought to transduce PKC signaling into alterations in the filamentous (F) actin cytoskeleton. Within the adult hippocampus, MARCKS is highly expressed in the dentate gyrus (DG)-CA3 mossy fiber pathway, but is expressed at low levels in the CA3-CA1 Schaffer collateral-CA1 pathway. We have previously demonstrated that 50% reductions in MARCKS expression in heterozygous Marcks mutant mice produce robust deficits in spatial reversal learning, but not contextual fear conditioning, suggesting that only specific aspects of hippocampal function are impaired by reduction in MARCKS expression. To further elucidate the role of MARCKS in hippocampal synaptic plasticity, in the present study we examined basal synaptic transmission, paired-pulse facilitation, post-tetanic potentiation, and long-term potentiation (LTP) in the hippocampal mossy fiber-CA3 and Schaffer collateral-CA1 pathways of heterozygous Marcks mutant and wild-type mice. We found that LTP is significantly impaired in the mossy fiber-CA3 pathway, but not in the Schaffer collateral-CA1 pathway, in heterozygous Marcks mutant mice, whereas basal synaptic transmission, paired-pulse facilitation, and post-tetanic potentiation are unaffected in both pathways. These findings indicate that a 50% reduction in MARCKS expression impairs processes required for long-term, but not short-term, synaptic plasticity in the mossy fiber-CA3 pathway. The implications of these findings for the role of the mossy fiber-CA3 pathway in hippocampus-dependent learning processes are discussed.

Animals↗

PubMed2005

Effect of myristoylated alanine-rich C kinase substrate (MARCKS) overexpression on hippocampus-dependent learning and hippocampal synaptic plasticity in MARCKS transgenic mice.

The myristoylated alanine-rich C kinase substrate (MARCKS) is a primary substrate of protein kinase C (PKC) thought to regulate membrane-filamentous actin cytoskeletal plasticity in response to PKC activity in the regulation of synaptic efficacy. We have recently reported that MARCKS expression is significantly elevated (45%) in the hippocampus of DBA/2J mice, which exhibit impaired hippocampus-dependent learning and hippocampal long-term potentiation (LTP), compared with C57BL/6J mice. The latter finding led us to hypothesize that elevations in MARCKS expression are detrimental to hippocampal plasticity and function. To assess this more directly, we examined hippocampal (CA1) paired-pulse facilitation and LTP, and hippocampus-dependent learning in mice overexpressing MARCKS through the expression of a human MARCKS transgene (Tg+). The human MARCKS protein was confirmed to be expressed in the hippocampus of Tg+ mice but not in Tg- mice. Schaffer collateral paired-pulse facilitation, input-output responses, and LTP did not differ between Tg+ and Tg- mice, indicating that neurotransmitter release, short-term, and long-term synaptic plasticity are not impaired by MARCKS overexpression. In the Morris water maze, Tg+ mice exhibited a mild but significant spatial learning impairment during initial acquisition, and a more severe impairment during reversal training. Tg+ did not exhibit impaired swim speed or visible platform performance relative to Tg- mice, indicating the absence of gross sensorimotor deficits. Fear conditioning to either context or cue was not impaired in Tg+ mice. Behavioral deficits could not be attributed to differences in hippocampal PKC isozyme (alpha beta(II), gamma, epsilon, zeta) or calmodulin expression, or alterations in hippocampal cytoarchitecture or infrapyramidal mossy fiber limb length. Collectively, these results indicate that elevations in MARCKS expression are detrimental to specific aspects of hippocampal function.

Animals↗

PubMed2005

A comparison of the roles of protein kinase C in long-term potentiation in rat hippocampal areas CA1 and CA3.

1. Using agonists and antagonists with specificity toward various isozymes, we have examined the role of protein kinase C (PKC) in long-term potentiation (LTP) in rat hippocampal areas CA1 and CA3. 2. Agonists (indolactum V but not phorbol ester) and antagonists (sphingosine, staurosporine, chelerytherene) acting at all PKC isozymes reduce or block LTP induction at both sites. 3. However ingenol, a relatively specific agonist at the delta and epsilon isozymes, blocks LTP in the MF-CA3 pathway, but not in the SC-CA1 pathway. 4. Go6976, a relatively specific antagonist of the alpha and beta isozymes, blocks LTP in the SC-CA1 pathway at both ages tested (30- and 60-day-old animals), but blocks LTP in the MF-CA3 in 60 but not 30-day-old animals. 5. Our studies indicate that different PKC isozymes are crucial to LTP induction in these two areas of hippocampus, and that there are development changes in the profile of isozymes.

Animals↗

PubMed2004

An endothelial and astrocyte co-culture model of the blood-brain barrier utilizing an ultra-thin, nanofabricated silicon nitride membrane.

The endothelial cells comprising brain capillaries have extremely tight intercellular junctions which form an essentially impermeable barrier to passive transport of water soluble molecules between the blood and brain. Several in vitro models of the blood-brain barrier (BBB) have been studied, most utilizing commercially available polymer membranes affixed to plastic inserts. There is mounting evidence that direct contact between endothelial cells and astrocytes, another cell type found to have intimate interaction with the brain side of BBB capillaries, is at least partially responsible for the development of the tight intercellular junctions between BBB endothelial cells. However, the membranes commonly used for BBB in vitro models are lacking certain attributes that would permit a high degree of direct contact between astrocytes and endothelial cells cultured on opposing sides. This work is based on the hypothesis that co-culturing endothelial and astrocyte cells on opposite sides of an ultra-thin, highly porous membrane will allow for increased direct interaction between the two cell types and therefore result in a better model of the BBB. We used standard nanofabrication techniques to make membranes from low-stress silicon nitride that are at least an order of magnitude thinner and at least two times more porous than commercial membrane inserts. An experimental survey of pore sizes for the silicon nitride membranes suggested pores approximately 400 nm in diameter are adequate for restricting astrocyte cell bodies to the seeded side while allowing astrocyte processes to pass through the pores and interact with endothelial cells on the opposite side. The inclusion of a spun-on, cross-linked collagen membrane allowed for astrocyte attachment and culture on the membranes for over two weeks. Astrocytes and endothelial cells displayed markers specific to their cell types when grown on the silicon nitride membranes. The transendothelial electrical resistances, a measure of barrier tightness, of endothelial and astrocyte co-cultures on the silicon nitride membranes were comparable to the commercial membranes, but neither system showed synergy between the two cell types in forming a tighter barrier. This lack of synergy may have been due to the loss of ability of commercially available primary bovine brain microvascular endothelial cells to respond to astrocyte differentiating signals.

Animals↗

PubMed2004

Extracellular recordings from patterned neuronal networks using planar microelectrode arrays.

Neuronal cell networks have been reconstructed on planar microelectrode arrays (MEAs) from dissociated hippocampal pyramidal neurons. Microcontact printing (microCP) and a photoresist-liftoff method were used to selectively localize poly-L-lysine (PLL) on the surface of MEAs. Haptotaxis led to the organization of the neurons into networks localized adjacent to microelectrodes. Various grids of PLL with 2-25-microm-wide lines spaced by 50-200 microm with 15-25-microm nodes at intersection points were used to guide cell body attachment and neurite outgrowth. Bursting activity with spike amplitude attenuation was observed, and multichannel recordings detected instances of coincident firing activity. Finally, we present here an extracellular recording from a approximately 2 microm bundle of guided neurites.

Action Potentials↗

PubMed2003

The effects of protein kinase C activity on synaptic transmission in two areas of rat hippocampus.

The effects of three protein kinase C (PKC) agonists (phorbol ester, ingenol and indolactam-V) and two PKC antagonists (D-erythro-sphingosine and chelerythrine) on input-output (I-O) relations in the Schaffer collateral pathway to CA1 (SC-CA1) and mossy fiber pathway to CA3 (MF-CA3) were determined in rat hippocampus brain slices. In the SC-CA1 pathway, phorbol esters and indolactam-V had only small effects on field excitatory post-synaptic potentials (fEPSP) in slices from 60-day animals, although ingenol, an activator of novel PKC isozymes, caused a significant decrease of the field excitatory post-synaptic potentials amplitude in 60-day animals, but not in 30-day animals. In contrast, in the MF-CA3 pathway, PKC agonists induced a significant increase in the field excitatory post-synaptic potentials. PKC antagonists depressed the field excitatory post-synaptic potentials in the SC-CA1 pathway, but had no significant effect in the MF-CA3 pathway. In the MF-CA3 pathway, paired-pulse facilitation was abolished by PKC agonists and unaffected by antagonists. In SC-CA1, it was depressed by agonists to levels below control, whereas it was significantly increased by chelerythine. We conclude that PKC plays important but different roles in both regions. In the SC-CA1 pathway, PKC is almost maximally active under control circumstances, and PKC antagonists significantly reduce synaptic responses. In contrast, in the MF-CA3 pathway, there is no apparent activation under resting circumstances, but significant potentiation of synaptic transmission is induced when PKC is activated. There are developmental changes in the pattern of PKC isozymes, and both pre- and post-synaptic actions are important.

Alkaloids↗

PubMed2002

Electrophysiologic and behavioral effects of perinatal and acute exposure of rats to lead and polychlorinated biphenyls.

Lead and polychlorinated biphenyls (PCBs) both cause a reduction of intelligence quotient and behavioral abnormalities in exposed children that have features in common with attention deficit hyperactivity disorder. We have used rats as a model to study the effects of both perinatal and acute exposure to lead or PCBs in an effort to compare and understand the mechanisms of these nervous system decrements. Long-term potentiation (LTP) is an electrophysiologic measurement that correlates well with cognitive ability. We have determined the effects of chronic perinatal exposure to lead or PCB 153 as well as acute application of these substances to isolated brain slices, with recordings in two areas of the hippocampus, CA1 and CA3. Both substances, whether chronically or acutely applied, significantly reduced LTP in CA1 in animals at age 30 and 60 days. In CA3, they reduced LTP in 30-day animals but potentiated it in 60-day animals. Although neither lead nor PCB 153 alters baseline synaptic transmission at low stimulus strengths, at higher levels they induce changes in the same direction as those of LTP. These results show surprisingly similar actions of these quite different chemicals, and the similarity of effects on chronic and acute application indicates that effects are both pharmacologic and developmental. Behavioral studies of rats exposed to PCBs from contaminated fish show hyperactivity, impulsiveness, and increased frustration relative to unexposed controls. These results demonstrate that lead and PCBs have similar effects on synaptic plasticity and behavior and suggest that the compounds may act through a common mechanism.

Adult↗