Michael Höller

An improved method for perfusion of the isolated brain of the rat-influence of perfusion conditions and application of analeptic and anticonvulsant drugs

A method for the perfusion of the isolated brain of the rat with synthetic fluorocarbon emulsion is described. The functional states of the brains were investigated using biochemical, biophysical, and histological methods. After 4.5 h of perfusion, all brains were in excellent condition and comparable to the in vivo state. The influence of perfusion conditions on the viability of the brains was studied. Deep hypothermia was well tolerated; at 13 degrees the EEG exhibited a mean frequency of about 8 Hz, while the mean amplitude was about 40% lower than at 28 degrees or 36 degrees. Constant-pressure perfusion did not affect brain function, provided that the pressure amplitude was very slowly decreased. During application of pentylenetetrazole (PTZ) it was found that the threshold concentration of PTZ in the perfusion medium to induce epileptic seizure discharges was 0.13 mg/ml. However, after repeated application of PTZ, the threshold concentration decreased exponentially, indicating a kindling phenomenon. It could be shown that not PTZ as such, but the spike potentials provoked by PTZ, induced the kindling effect. This was inhibited by application of primidone or phenobarbital.

Disposition of [4-14C]oestradiol-l7β in the isolated perfused brain of the rat

Abstract [4- 14 C] Oestradiol-17β was perfused through isolated brains of male and ovariectomized female rats. Two different perfusion media were used. The uptake of oestradiol-17β was higher in female brains, the highest concentrations being found in the hypophysis and hypothalamus. Oestradiol-17β was metabolized to a greater extent by female brains, the most important metabolite being oestrone. Additionally, 2-hydroxyoestradiol-17β, 6ζ-hydroxyoestradiol-17β, and 7α-hydroxyoestradiol-17β were found; 7α-hydroxyoestrone and another polar metabolite could not be definitely identified. Quantitatively, 2-hydroxylation was no more important than hydroxylation at C atom 6 or 7.

Studies on the intracerebral metabolism of anticonvulsant drugs—I. Perfusion of primidone through the isolated brain of the rat

Primidone and phenobarbital (each 85 nmoles/ml were separately perfused through the isolated brain of the rat. After 5 min of perfusion similar amounts of primidone and phenobarbital were taken up into the brain; for both drugs the concentration ratio between brain and perfusion medium was about 0.2. However, after 2 hr of perfusion the mean concentration ratio for primidone was about 0.55; for phenobarbital it was about 0.9 thus indicating a better uptake of phenobarbital. In two regions (hypophysis, mesencephalon) the concentration of phenobarbital was significantly higher than in perfusion medium. During 2 hr of perfusion of primidone, substantial quantities of phenobarbital and PEMA were formed amounting to 1400 pmoles for each metabolite. The highest concentration of the metabolites was found in septum, hypothalamus, hypophysis and mesencephalon. The in situ metabolism of primidone in the intact brain was demonstrated for the first time.

Studies on the intracerebral metabolism of anticonvulsant drugs. II: Disposition of carbamazepine in the isolated perfused rat brain

Carbamazepine (CBZ) was perfused (85 nmoles/ml) through the isolated brains of rats. After 2 hr the mean regional concentrations of the drug were between 170 and 234 nmoles/g wet weight. The total brain content of CBZ was 390 nmoles. During perfusion 82 nmoles epoxycarbamazepine (E-CBZ) were formed, most of which were found in perfusion medium. Tissue levels of E-CBZ were between 0.3 and 2.8 nmoles/g wet weight. No dihydroxycarbamazepine (DH-CBZ) could be found. Pretreatment of the rats with phenobarbital neither influenced the uptake of CBZ into the brains nor increased the formation of E-CBZ significantly.