Astroglial nuclear factor-kappaB regulates learning and memory and synaptic plasticity in female mice.

Astrocytes play a pivotal role in regulating synaptic plasticity and synapse formation. The nuclear factor-kappa B (NF-kappaB) family of transcription factors has recently been demonstrated to be an important modulator of synaptic plasticity and learning/memory. In this study, we investigated the role of astroglial NF-kappaB in synaptic plasticity and learning/memory using transgenic mice over-expressing an N-terminal truncated form of inhibitor of NF-kappaB alpha (IkappaBalpha) in astrocytes (GFAP-IkappaBetaalpha-dn). We demonstrated that female transgenic mice, but not males, have robust deficits in hippocampal and extra-hippocampal-dependent learning and memory. We also determined that there are significant deficits in LTP and expression of metabotropic glutamate receptor 5 and post-synaptic density protein 95 (PSD95) in female transgenic mice. These findings indicate that astroglial NF-kappaB is an important regulator of learning/memory and synaptic plasticity.

Distinct roles for ephrinB3 in the formation and function of hippocampal synapses.

The transmembrane ephrinB ligands and their Eph receptor tyrosine kinases are known to regulate excitatory synaptic functions in the hippocampus. In the CA3-CA1 synapse, ephrinB ligands are localized to the post-synaptic membrane, while their cognate Eph receptors are presumed to be pre-synaptic. Interaction of ephrinB molecules with Eph receptors leads to changes in long-term potentiation (LTP), which has been reported to be mediated by reverse signaling into the post-synaptic membrane. Here, we demonstrate that the cytoplasmic domain of ephrinB3 and hence reverse signaling is not required for ephrinB dependent learning and memory tasks or for LTP of these synapses. Consistent with previous reports, we find that ephrinB3(KO) null mutant mice exhibit a striking reduction in CA3-CA1 LTP that is associated with defective learning and memory tasks. We find the null mutants also show changes in both pre- and post-synaptic proteins including increased levels of synapsin and synaptobrevin and reduced levels of NMDA receptor subunits. These abnormalities are not observed in ephrinB3(lacZ) reverse signaling mutants that specifically delete the ephrinB3 intracellular region, supporting a cytoplasmic domain-independent forward signaling role for ephrinB3 in these processes. We also find that both ephrinB3(KO) and ephrinB3(lacZ) mice show an increased number of excitatory synapses, demonstrating a cytoplasmic-dependent reverse signaling role of ephrinB3 in regulating synapse number. Together, these data suggest that ephrinB3 may act like a receptor to transduce reverse signals to regulate the number of synapses formed in the hippocampus, and that it likely acts to stimulate forward signaling to modulate a number of other proteins involved in synaptic activity and learning/memory.

Inhibition of astroglial nuclear factor kappaB reduces inflammation and improves functional recovery after spinal cord injury.

In the central nervous system (CNS), the transcription factor nuclear factor (NF)-kappaB is a key regulator of inflammation and secondary injury processes. After trauma or disease, the expression of NF-kappaB-dependent genes is highly activated, leading to both protective and detrimental effects on CNS recovery. We demonstrate that selective inactivation of astroglial NF-kappaB in transgenic mice expressing a dominant negative (dn) form of the inhibitor of kappaB alpha under the control of an astrocyte-specific promoter (glial fibrillary acidic protein [GFAP]-dn mice) leads to a dramatic improvement in functional recovery 8 wk after contusive spinal cord injury (SCI). Histologically, GFAP mice exhibit reduced lesion volume and substantially increased white matter preservation. In parallel, they show reduced expression of proinflammatory chemokines and cytokines, such as CXCL10, CCL2, and transforming growth factor-beta2, and of chondroitin sulfate proteoglycans participating in the formation of the glial scar. We conclude that selective inhibition of NF-kappaB signaling in astrocytes results in protective effects after SCI and propose the NF-kappaB pathway as a possible new target for the development of therapeutic strategies for the treatment of SCI.

Two effective behavioral tasks for evaluating sensorimotor dysfunction following traumatic brain injury in mice.

Variants of two sensorimotor tasks, the gridwalk and spontaneous forelimb use (SFL) tasks, were assessed for their ability to reveal behavioral dysfunction following traumatic brain injury (TBI) in mice. These tests have previously been used almost exclusively in evaluating models of spinal injury, ischemia and other forebrain lesions in rats. Male C57BL/6 mice were anesthetized and given unilateral parasagittal controlled cortical impact injury or sham (n = 9) procedures, targeting right anterior (n = 9), middle (n = 9), or posterior (n = 10) locations relative to bregma. Significant forelimb and hindlimb deficits contralateral to the injured hemisphere were observed for at least 1 month and 3 weeks, respectively, on the gridwalk task depending upon insult location. The SFL task revealed a significant asymmetry in forelimb use for at least 5 months following injury. These results demonstrate the effectiveness of the SFL and gridwalk tests in evaluating sensorimotor deficits in mouse injury models involving unilateral forebrain damage.