Lentiviral Expression of Rabies Virus Glycoprotein in the Rat Hippocampus Strengthens Synaptic Plasticity.

Rabies virus (RABV) is a neurotropic virus exclusively infecting neurons in the central nervous system. RABV encodes five proteins. Among them, the viral glycoprotein (RVG) plays a key role in viral entry into neurons and rabies pathogenesis. It was shown that the nature of the C-terminus of the RABV G protein, which possesses a PDZ-binding motif (PBM), modulates the virulence of the RABV strain. The neuronal protein partners recruited by this PBM may alter host cell function. This study was conducted to investigate the effect of RVG on synaptic function in the hippocampal dentate gyrus (DG) of rat. Two µl (108 T.U./ml) of the lentiviral vector containing RVG gene was injected into the DG of rat hippocampus. After 2 weeks, the rat's brain was cross-sectioned and RVG-expressing cells were detected by fluorescent microscopy. Hippocampal synaptic activity of the infected rats was then examined by recording the local field potentials from DG after stimulation of the perforant pathway. Short-term synaptic plasticity was also assessed by double pulse stimulation. Expression of RVG in DG increased long-term potentiation population spikes (LTP-PS), whereas no facilitation of LTP-PS was found in neurons expressing δRVG (deleted PBM). Furthermore, RVG and δRVG strengthened paired-pulse facilitation. Heterosynaptic long-term depression (LTD) in the DG was significantly blocked in RVG-expressing group compared to the control group. This blockade was dependent to PBM motif as rats expressing δRVG in the DG-expressed LTD comparable to the RVG group. Our data demonstrate that RVG expression facilitates both short- and long-term synaptic plasticity in the DG indicating that it may involve both pre- and postsynaptic mechanisms to alter synaptic function. Further studies are needed to elucidate the underlying mechanisms.

Overexpression of protein kinase Mζ in the hippocampus mitigates Alzheimer's disease-related cognitive deficit in rats.

Accumulation of amyloid beta (Aß) soluble forms in the cerebral parenchyma is the mainstream concept underlying memory deficit in the early phase of Alzheimer's disease (AD). PKMζ plays a critical role in the maintenance of long-term memory. Yet, the role of this brain-specific enzyme has not been addressed in AD. We examined the impact of hippocampal PKMζ overexpression on AD-related memory impairment in rats. Oligomeric form of Aß (oAß) or vehicle was bilaterally microinjected into the dorsal hippocampus of male Wistar rats under stereotaxic surgery. One week later, 2 µl of lentiviral vector (108 T.U. / ml.) encoding PKMζ genome was microinjected into the dorsal hippocampus. Seven days later, behavioral performance was assessed using shuttle box and Morris water maze. The expression levels of GluA1, GluA2 and KCC2 were determined in the hippocampus using western blot technique. Our data showed that oAß impairs both passive avoidance and spatial learning and memory. However, overexpression of PKMζ in the dorsal hippocampus restored the behavioral performance. This improving effect was blocked by microinjection of ZIP, a PKMζ inhibitor, into the hippocampus. oAß or PKMζ did not significantly change GluA1 level in the hippocampus. Furthermore, PKMζ failed to restore elevated KCC2 level induced by oAß. However, oAß decreased GluA2 level, and overexpression of PKMζ restored its expression toward the control level. In conclusion, hippocampal overexpression of PKMζ restored memory dysfunction induced by amyloidopathy in part, through preserving hippocampal GluA2 containing AMPA receptors. PKMζ's signaling pathway could be considered as a therapeutic target to battle memory deficits in the early phase of AD.

Shining Light on the Sprout of Life: Optogenetics Applications in Stem Cell Research and Therapy.

Optogenetics is the integration of genetics and optics to achieve gain or loss of function of well-defined events in specific cells of living tissue. As a versatile tool, upon light illumination, it allows fast control of precisely defined events in biological systems from single cell to different parts of whole tissue in freely moving animals. Taking advantage of this method, a multitude of studies have been published to understand brain functions and dysfunctions. Although from the beginning, it has been used to target neurons within the neural networks and to understand how specific neurons contribute to brain function, it gradually has been extended to other fields of biology such as stem cell research and therapy. With a combination of optogenetics and stem cells, new opportunities were opened up in stem cell biology and also its integration in new circuit as a cell-based treatment strategy for more common disorders like neurodegenerative and cardiovascular one. Recently, some studies showed that engineered stem cells expressing exogenous light-activated opsins can be used in stem cell biology including tracking the differentiation of stem cells, functional analysis of embryonic stem cell-derived graft, and testing the functional integration of induced pluripotent stem cell-derived neurons. With the advent of non-invasive approach, such as transcranial excitation or inhibition, optogenetics also holds promise for non-invasive control of engineered stem cell.