Abstracts

Rationale: Neuronal hyperactivation caused by uncontrolled glutamate release from injured neurons after traumatic injury (TBI) contributes to continuing excitotoxic damage and often leads to post-traumatic epilepsy (PTE). The major mechanism for clearance of extracellular glutamate is its removal via the mainly astrocytic membrane glutamate transporter 1 (GLT1) which is depressed after brain injury and upregulated by beta lactam antibiotics. In lateral fluid percussion injury (LFPI), a common rat PTE model, reduced cortical GLT1 protein level is accompanied by progressive loss of cortical parvalbumin (PV) positive inhibitory interneurons as well as intracortical inhibition as measured by paired pulse transcranial magnetic stimulation (ppTMS) (Lee et al SFN 2013). Ceftriaxone (Cef) treatment after LFPI restores GLT1 protein levels while decreasing perilesional gliosis and suppressing posttraumatic seizures (Goodrich et al 2013). Post-TBI Cef treatment also protects against the progressive loss of GABAergic intracortical inhibition and improves PV gene expression. We now investigate whether Cef-mediated GLT1 protein increase is at least partially due to upregulated GLT1 gene expression, whether it persists after cessation of drug treatment, and whether mitigated perilesional parvalbumin-positive cell loss persists late in the epileptogenic period after LFPIMethods: Adult male rats received moderate LFPI (2.3±0.1 atm) via a craniotomy over the motor cortex, and received either Cef (200mg/kg/day) or saline, IP daily, for one week post-TBI. A sham group (n=5) received all surgical procedures except LFPI, and did not receive IP injections. Brain tissue was harvested one, two, four, and six weeks after injury for RNA extraction, and GLT1 and PV gene expression in perilesional tissue was measured by real time polymerase chain reaction (RT-PCR) (n=5/group/timepoint)Results: GLT1 gene expression is significantly decreased in saline treated post-LFPI animals compared to sham one week after surgery (p < 0.05), and is significantly higher in Cef treated animals compared to saline at the same timepoint (p < 0.05). After cessation of Cef therapy seven days after LFPI, there is no significant difference in GLT1 expression between Cef and saline groups 2 weeks post-injury, and expression is significantly decreased in both groups as compared to sham (p < 0.05). GLT1 expression in both experimental groups progressively improves toward sham levels by 6 weeks after LFPI. PV gene expression is significantly lower in saline treated animals compared to Cef treated animals 4 and 6 weeks after LFPI (p<0.05), but not at 1 and 2 weeks post-LFPI.Conclusions: Cef administration after LFPI upregulates GLT1 gene expression only during the period of treatment, with GLT1 gene expression returning to untreated levels after cessation of treatment. This transient upregulation of GLT1 is associated with a lasting decrease in the loss of PV gene expression up to 6 weeks after LFPI - the time-point at which post-traumatic seizures typically start in this model.