Methylxanthine-evoked perturbation of spontaneous and evoked activities in isolated newborn rat hippocampal networks

- Early network oscillations (ENOs) are pivotal for maturation of neural networks.
- ENOs can be studied in hippocampal brain slices from newborn rats.
- <1 mM caffeine or theophylline modestly stimulates ENOs and evoked field potentials.
- >1 mM of these methylxanthines perturbs ENOs via occurrence of pronounced seizures.
- Such seizures might, partly, involve blockade of GABA-A receptors by methylxanthines.

Treatment of apnea of prematurity with methylxanthines like caffeine, aminophylline or theophylline can evoke hippocampal seizures. However, it is unknown at which interstitial brain concentrations methylxanthines promote such neonatal seizures or interfere with physiological 'early network oscillations' (ENOs) that are considered as pivotal for maturation of hippocampal neural networks. We studied theophylline and caffeine effects on ENOs in CA3 neurons (CA3-ENOs) and CA3 electrical stimulation-evoked monosynaptic CA1 field potentials (CA1-FPs) in sliced and intact hippocampi, respectively, from 8 to 10-days-old rats. Submillimolar doses of theophylline and caffeine, blocking adenosine receptors and phosphodiesterase-4 (PDE4), did not affect CA3-ENOs, ENO-associated cytosolic Ca2+ transients or CA1-FPs nor did they provoke seizure-like discharges. Low millimolar doses of theophylline (⩾1 mM) or caffeine (⩾5 mM), blocking GABAA and glycine receptors plus sarcoplasmic-endoplasmic reticulum Ca2+ ATPase (SERCA)-type Ca2+ ATPases, evoked seizure-like discharges with no indication of cytosolic Ca2+ dysregulation. Inhibiting PDE4 with rolipram or glycine receptors with strychnine had no effect on CA3-ENOs and did not occlude seizure-like events as tested with theophylline. GABAA receptor blockade induced seizure-like discharges and occluded theophylline-evoked seizure-like discharges in the slices, but not in the intact hippocampi. In summary, submillimolar methylxanthine concentrations do not acutely affect spontaneous CA3-ENOs or electrically evoked synaptic activities and low millimolar doses are needed to evoke seizure-like discharges in isolated developing hippocampal neural networks. We conclude that mechanisms of methylxanthine-related seizure-like discharges do not involve SERCA inhibition-related neuronal Ca2+ dysregulation, PDE4 blockade or adenosine and glycine receptor inhibition, whereas GABAA receptor blockade may contribute partially.