Raimondo D'Ambrosio - US grants

The overall goal of this proposal is to assess the impact of post-traumatic glia on hippocampal physiology. Traumatic brain injury (TBI) is associated with a wide variety of neurological deficits, including memory impairment, cognitive dysfunction and epilepsy. The pathophysiological bases of such abnormalities still remain largely unknown. However, altered hippocampal excitability appears to play an important role. While the majority of research effort focuses on neuronal and synaptic changes, normal neuronal function also depends on an accurate regulation of the extracellular ionic concentrations and cellular and extracellular volume. Glial cells have been shown to play a crucial role in the homeostasis of extracellular volume and ionic composition, in the regulation of brain tissue water content, and in determining neuronal excitability and function. In spite of such a paramount role of glia, little is known about the functional status of glial cells acutely and chronically following TBI. We propose to define the acute and chronic effects of TBI on hippocampal glial function with particular emphasis on: 1) temporal pattern of glial reactivity and their electrophysiological changes, 2) temporal pattern of neuronal and filial extracellular K+-homeostasis, 3) pathophysiological consequences on ion and water homeostasis, and 4) neuronal and glial cell volume regulation. Investigations on these post-traumatic changes will allow a more rational treatment to TBI.

DESCRIPTION (provided by applicant): Many anti-epileptic drugs (AEDs) have been introduced over the last 30 years, but the proportion of patients with inadequate control of seizures has remained unchanged at ~30%. This has led to doubts about the acute seizure models employed in preclinical AED screening because they may not capture the mechanisms most important for precipitation and control of pharmacoresistant chronic spontaneous recurrent seizures (CSRSs) in humans. Thus, there is an urgent need to develop preclinical models of pharmacoresistant epilepsy. In addition, no agent has been identified that prevents epilepsy in patients at risk, and models of epileptogenesis are also needed. Thus, substantial recent efforts have focused on the development of acquired CSRS models that closely reproduce brain insults known to be epileptogenic in humans and are, thus, likely to recruit mechanisms of ictogenesis and epileptogenesis that are relevant to the corresponding human syndrome: stroke, head injury, early-life febrile seizures, and hypoxia-ischemia. We have developed one of these etiologically realistic acquired CSRS-models in the rat, the fluid percussion injury (FPI) model of posttraumatic epilepsy (PTE), and have recently adapted it to the identification of antiepileptic (AE) and antiepileptogenic (AEG) activity. FPI is mechanically identical to human contusive closed head injury, and reproduces many of its pathophysiological sequelae. It displays focal spontaneous seizures of neocortical and limbic origin, pathology as in human PTE, and a latent period between the initiating injury and the onset of PTE. The rat frontal neocortex is more sensitive to FPI than other brain areas, resulting in faster epileptogenesis than parietal/occipita cortices and limbic structures, and generates CRSSs that are fully blocked by halothane, partially blocked by valproate, and very resistant to carbamazepine and carisbamate. Thus, FPI-induced frontal lobe PTE is a promising model of pharmacoresistant epilepsy for drug screening. However, there are substantial costs involved in all ECoG-based drug screening in chronic epilepsy models, including FPI. Further optimization of the model is needed to make FPI cost-effective for systematic preclinical drug studies. To this end we will conduct a comprehensive optimization of several parameters of FPI and ensuing injury. We will determine whether 1) controlling acute posttraumatic apnea/hypoxia allows higher incidence of PTE and more uniform seizure frequency, 2) variations in location and severity of injury better recruit frontal lobe epileptogenesis, and 3) the severity of subdural hemorrhage predicts which animals will not become epileptic. These data will be used to decrease inter- subject variability, and increase speed of epileptogenesis and incidence of PTE, which will permit cost- effective use of the FPI model in the identification of novel antiepileptic and antiepileptogenic treatments. PUBLIC HEALTH RELEVANCE: Many anti-epileptic drugs have been introduced over the last 30 years, but the proportion of patients with inadequate control of seizures has remained unchanged at ~30%, and no cure for epilepsy has been found. Better models of epilepsy are urgently needed to screen for novel antiepileptic and antiepileptogenic treatments. Our proposed studies will optimize a promising new model of posttraumatic epilepsy that is resistant to classic and new antiepileptic drugs, and adapt it for efficient routine drug screening.