Investigations on alterations of hippocampal circuit function following mild traumatic brain injury.

Traumatic Brain Injury (TBI) afflicts more than 1.7 million people in the United States each year and even mild TBI can lead to persistent neurological impairments. Two pervasive and disabling symptoms experienced by TBI survivors, memory deficits and a reduction in seizure threshold, are thought to be mediated by TBI-induced hippocampal dysfunction. In order to demonstrate how altered hippocampal circuit function adversely affects behavior after TBI in mice, we employ lateral fluid percussion injury, a commonly used animal model of TBI that recreates many features of human TBI including neuronal cell loss, gliosis, and ionic perturbation. Here we demonstrate a combinatorial method for investigating TBI-induced hippocampal dysfunction. Our approach incorporates multiple ex vivo physiological techniques together with animal behavior and biochemical analysis, in order to analyze post-TBI changes in the hippocampus. We begin with the experimental injury paradigm along with behavioral analysis to assess cognitive disability following TBI. Next, we feature three distinct ex vivo recording techniques: extracellular field potential recording, visualized whole-cell patch-clamping, and voltage sensitive dye recording. Finally, we demonstrate a method for regionally dissecting subregions of the hippocampus that can be useful for detailed analysis of neurochemical and metabolic alterations post-TBI. These methods have been used to examine the alterations in hippocampal circuitry following TBI and to probe the opposing changes in network circuit function that occur in the dentate gyrus and CA1 subregions of the hippocampus (see Figure 1). The ability to analyze the post-TBI changes in each subregion is essential to understanding the underlying mechanisms contributing to TBI-induced behavioral and cognitive deficits. The multi-faceted system outlined here allows investigators to push past characterization of phenomenology induced by a disease state (in this case TBI) and determine the mechanisms responsible for the observed pathology associated with TBI.

Sending mixed signals: bone morphogenetic protein in myelination and demyelination.

Developing oligodendrocytes undergo a well-characterized maturation process that is controlled by extrinsic factors that promote specification, proliferation, and differentiation. Inhibitory factors also influence oligodendrocyte development and may regulate the location and number of oligodendrocytes available for myelination. These factors may also repress regeneration and remyelination after injury. Bone morphogenetic proteins (BMPs) comprise a family of factors that inhibit oligodendrocyte development in vitro and when they are overexpressed in vivo. These effects seem to be mediated by the actions of inhibitors of DNA-binding protein on transcription factors that promote myelination. Bone morphogenetic protein signaling deletion studies have generated a complex picture in which the main effect of BMPs is on oligodendrocyte differentiation and depends on the level of signaling. Bone morphogenetic proteins are significantly upregulated in demyelinated areas in models of myelin injury and disease, and blocking of BMP signaling aids recovery. It is not yet known, however, whether this occurs by promoting differentiation of oligodendrocyte precursors or by inhibiting astrogliosis because BMPs also promote astrogliogenesis. Understanding the actions of BMPs will be important for promoting recovery in patients with demyelinating diseases and other types of CNS injury.