Role of nitric oxide in pentylenetetrazol-induced seizures: age-dependent effects in the immature rat.

PURPOSE: Seizure susceptibility and consequences are highly age dependent. To understand the pathophysiologic mechanisms involved in seizures and their consequences during development, we investigated the role of nitric oxide (NO) in severe pentylenetetrazol (PTZ)-induced seizures in immature rats. METHODS: Four cortical electrodes were implanted in 10-day-old (P10) and 21-day-old (P21) rats, and seizures were induced on the following day by repetitive injections of subconvulsive doses of PTZ. The effects of NG-nitro-l-arginine methyl ester (l-NAME; 10 mg/kg) and 7-nitroindazole (7NI; 40 mg/kg), two NO synthase (NOS) inhibitors, and l-arginine (l-arg; 300 mg/kg), the NOS substrate, were evaluated regarding the mean PTZ dose, seizure type and duration, and mortality rate. RESULTS: At P10, the postseizure mortality rate increased from 18-29% for the rats receiving PTZ only to 100% and 89% for the rats receiving l-NAME and 7NI, respectively; whereas l-arg had no effect. Conversely, at P21, NOS inhibitors did not affect the 82-89% mortality rate induced by PTZ alone, whereas l-arg decreased the mortality rate to 29%. In addition, all NO-related drugs increased the duration of ictal activity at P10, whereas at P21, l-arg and l-NAME affected the first seizure type, producing clonic seizures with l-arg and tonic seizures with l-NAME. CONCLUSIONS: The relative natural protection of very immature rats (P10) against PTZ-induced deaths could be linked to a high availability of l-arg and, hence, endogenous NO. At P21, the modulation of seizure type by NO-related compounds may be related to the maturation of the brain circuitry, in particular the forebrain, which is involved in the expression of clonic seizures.

An experimental model of generalized seizures for the measurement of local cerebral glucose utilization in the immature rat. I. Behavioral characterization and determination of lumped constant.

An experimental model of status epilepticus has been developed in the immature rat by administration of pentylenetetrazol (PTZ) using repetitive, timed intraperitoneal injections of subconvulsive doses. The pattern of behavioral signs has been well characterized in each age group, i.e. 10 (P10), 14 (P14), 17 (P17) and 21 postnatal days (P21). In this model, the dose of convulsant could be adjusted as a function of interindividual sensitivity and status epilepticus lated for quite a long duration to allow the measurement of local cerebral metabolic rates for glucose (LCMRglc) by means of the [14C]2-deoxyglucose method [J. Neurochem., 28 (1977) 897-916]. To estimate LCMRglc during status epilepticus, the lumped constant (LC) was re-calculated in controls and PTZ-treated rats. The control LC was 0.54 at P10 and 0.50-0.51 at the three older ages studied (P14, P17 and P21). During status epilepticus, it increased to 0.64 in P10 rats and decreased to 0.42 and 0.40, respectively, in P17 and P21 animals. At P14, LC was not affected by seizures. The measurements of brain lactate levels showed a large 4.5-10-fold increase in PTZ-treated rats as compared to controls at all ages. The results of the present study show that the immature brain responds to sustained seizure activity in a specific way according to its postnatal age. Moreover, our results underscore the necessity of re-calculation of LC to the quantification of LCMRglc in such pathological states, particularly in immature animals.

Quantitative autoradiographic measurement of local cerebral glucose utilization in freely moving rats during postnatal development.

The quantitative 2-14C-deoxyglucose autoradiographic method of Sokoloff et al. (1977) was used to measure local cerebral glucose utilization in freely moving developing rats. The animals were studied at 10, 14, 17, 21, and 35 d and at the adult stage. Glucose utilization was very low and quite uniform in 10- and 14-d-old rats, ranging from 20 to 30 mumol/100 gm/min, except in a few posterior areas. Between these 2 stages, rates of glucose utilization significantly increased in 6 areas, among which 4 were belonging to the auditory system. Between 14 and 17 d, glucose utilization significantly changed in 9 structures out of the 68 studied, mainly auditory, visual, parietal, and thalamic areas. Between the stages of 17 and 21 d, glucose utilization was increased by 50 or 100% in all brain structures studied, except in the medial habenula and white matter areas. After weaning time, rates of glucose utilization still significantly changed in 50 areas, widely distributed through all studied systems. Between 35 d and the adult stage, the average rate of glucose utilization did not change and rates of energy metabolism significantly increased in 13 brain areas. In one structure, the medial habenula, glucose utilization was already high 10 d after birth and did not change over the whole studied period. These increases in the rates of glucose utilization are consistent with the behavioral, anatomical, and functional changes known to occur during this period of development in the rat.

Morphological and neurochemical effects of diazepam and phenobarbital on selective culture of neurons from fetal rat brain.

The responses to diazepam (DZ) and phenobarbital (PhB) were studied in enriched neuronal primary cultures from rat embryo hemispheres. Cells were grown in chemically defined medium and the drugs were added for 3 days to cultures, at pharmacologically active concentrations. Following exposure to DZ or to PhB, morphological changes, such as less prominent neuronal processes, were observed in neurons. It was also shown that each drug reduced the specific uptake of 2-deoxy-D-glucose by the cells and interfered with protein and RNA metabolism. It was concluded that both DZ and PhB might affect, at least transiently, the normal growth of neurons in culture.