Altered seizure susceptibility and vesicular glutamate transporter subtype 1 immunoreactivity in a rat model of hypoxic brain injury

BACKGROUND：To the best of our knowledge, few studies have analyzed the effects of hypoxic brain injury on seizure susceptibility and pathophysiological mechanisms underlying seizure susceptibility following hypoxic brain injury. OBJECTIVE： To investigate changes in seizure susceptibility and neuronal loss, as well as expression of vesicular glutamate transporter subtype 1（VGluT1）, following hypoxic cerebral insult. DESIGN, TIME AND SETTING： A randomized controlled animal experiment was performed in the Department of Neurology, The Second Affiliated Hospital, Chongqing Medical University, between May 2006 and September 2007. MATERIALS： Seventy, male, Sprague Dawley rats, weighing 230–270 g, were used in the present study. Pentylenetetrazol （PTZ） was purchased from Sigma. Mouse NeuN monoclonal antibody and rabbit VGluT-1 polyclonal antibody were purchased from Chemicon and Gene Tex, respectively. METHODS： Rats were randomly assigned to control and hypoxia groups （n = 35 for each group）. Hypoxia was induced in rats using 8% oxygen-nitrogen gas mixture. Control rats were subjected to the same procedures, but with exposure to room air. MAIN OUTCOME MEASURES： Rats （n = 15 for each group） received intraperitoneal injections of PTZ, a sub-convulsive dose of 35 mg/kg/2 d for 20 days. The success of model establishment, as well as seizure scales, was measured. Rats from both groups, which were successfully kindled with PTZ, were divided into simple kindling and post-hypoxic kindling, respectively. A separate group, including rats from simple kindling and post-hypoxic kindling, was studied for neuronal loss and VGluT1 expression in the temporal cortex, midbrain, and hippocampal CA1 subfield using immunohistochemistry and western blot techniques, respectively. RESULTS： Seventy rats were included in the final analysis. （1）Compared with control animals （n = 7）, seizure scales were greater in hypoxic rats （n = 11）, which indicates that post-hypoxic rats reacted more sensitive to kindling. （2）The average number of neurons within the temporal cortex, midbrain, and hippocampal CA1 subfield was less in hypoxic rats than in control rats. After comparing post-hypoxia kindling with simple kindling, both the temporal cortex and hippocampal CA1 subfield exhibited obvious neuronal loss in the post-hypoxic kindling group （P 〈 0.05）. （3）Compared with hypoxia and simple kindling, the number of VGluT1 immunopositive cells was greater in the post-hypoxic kindling group （P 〈 0.05）. CONCLUSION： Hypoxic brain injury leads to increased seizure susceptibility, neuronal loss, and enhanced of VGluT1 expression.

Gender difference in acquired seizure susceptibility in adult rats after early complex febrile seizures

Gender differences are involved in many neurological disorders including epilepsy. However, little is known about the effect of gender difference on the risk of epilepsy in adults with a specific early pathological state such as complex febrile seizures（FSs） in infancy. Here we used a well-established complex FS model in rats and showed that：（1） the susceptibility to seizures induced by hyperthermia, pentylenetetrazol（PTZ）, and maximal electroshock（MES） was similar in male and female rat pups, while males were more susceptible to PTZ- and MES-induced seizures than age-matched females in normal adult rats;（2） adult rats with complex FSs in infancy acquired higher seizure susceptibility than normal rats; importantly, female FS rats were more susceptible to PTZ and MES than male FS rats; and（3） the protein expression of interleukin-1β, an infl ammatory factor associated with seizure susceptibility, was higher in adult FS females than in males, which may reflect a gender-difference phenomenon of seizure susceptibility. Our results provide direct evidence that the acquired seizure susceptibility after complex FSs is gender-dependent.