Epileptogenic action of caffeine during anoxia in the neonatal rat hippocampus

Abstract

Excessive maternal caffeine consumption can lead to fetal and neonatal pathology, but the underlying mechanisms have not been determined. Here, we report that low doses of caffeine generate seizures when applied in conjunction with brief anoxic episodes in the hippocampus of neonatal rats in vitro. In control conditions, brief (4-6 minutes) anoxic episodes reversibly depressed evoked synaptic responses and blocked the physiological pattern of network activity. In the presence of caffeine (50 microM), similar anoxic episodes generated ictal (29%) or interictal (33%) epileptiform activities often followed during reoxygenation by recurrent spontaneous seizure activity that persisted for several hours. These effects are likely mediated by a blockade of adenosine receptors by caffeine because (1) in control conditions, caffeine antagonized the inhibitory effect of selective A1 receptor agonist N6-cyclopentyladenosine on excitatory synaptic responses, and (2) epileptogenic effects of caffeine were reproduced by selective A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine and theophylline. Our findings suggest that endogenous adenosine released during anoxia acting via A1 receptors prevents seizures in the neonatal hippocampus and that the antagonism of these receptors by caffeine leads to epileptogenesis. This study suggests concerns about the safety of caffeine in the fetus and newborn.

Seizures accelerate anoxia‐induced neuronal death in the neonatal rat hippocampus

“…The first "adaptation" phase was characterized by moderate changes in the membrane potential and depression of synaptic activity. Within 3 to 5 minutese ‫گ‬amino‫گ‬utes after onset of anoxia, the evoked excitatory postsynaptic responses were strongly depressed in keeping with previous observation 16 (see Fig 1A and C). Pyramidal neurons were first slightly hyperpolarized from the resting membrane potential of Ϫ57.3 Ϯ 1.4 to Ϫ59.9 Ϯ 1.5 mV (n ϭ 16).…”

“…ADENOSINE A 1 RECEPTOR ANTAGONISTS Blockade of adenosine A 1 receptors significantly increases the incidence of seizures during anoxic episodes in the neona-tal rat hippocampus. 16 In keeping with this earlier observation, perfusion with an anoxic solution in the presence of the antagonist of the A 1 adenosine receptor DPCPX (200 nM) induced epileptiform activity of ictal tonic-clonic (n ϭ 7 of 16) or ictal clonic (n ϭ 9 of 16) type, reminiscent of the electrographic epileptiform activities recorded in vivo (Fig 3). 31 Development of AD was substantially accelerated from 17.5 Ϯ 0.2 minutes (n ϭ 23) in controls to 10.9 Ϯ 0.4 minutes (n ϭ 16) in the presence of DPCPX.…”

“…Although brief anoxic episodes induced only transient changes in hippocampal function, 16 prolongation of the anoxic episodes to reach AD invariably led to irreversible impairment of hippocampal neurons. Thus, at 0.5 to 3 hours of reoxygenation after AD, (1) depolarization of the hippocampal neurons to Ϫ7 Ϯ 2 mV, reduction of input resistance from 478 Ϯ 55 to 104 Ϯ 24 M⍀, and loss of synaptic currents were observed in whole-cell patch-clamp recordings (n ϭ 14); (2) evoked postsynaptic responses, presynaptic action potentials (af-ferent volley), and single-unit activity were lost in extracellular field recordings (Fig 2A and B; n ϭ 14); and (3) ischemic cell death was conspicuous in histological stains, including a darkening and shrinkage of the nucleus and cytoplasm and irregularity of the plasma and nuclear membranes, with pyramidal cells assuming a triangular shape (see Fig 2C).…”

“…ence of 50 M of caffeine, another less selective adenosine A 1 receptor antagonist that produces partial blockade of presynaptic A 1 receptors, 16 anoxic episodes were also associated with prominent epileptiform activity and acceleration of AD to 14.6 Ϯ 0.5 minutes (n ϭ 7).…”

“…Thus, during the first "adaptation" phase, anoxia induces reversible depression of the synaptic responses and neurons maintain the membrane potential near the control values in keeping with the results of previous studies in neonatal rat hippocampal slices 17,18 and the intact hippocampus in vitro. 16 Transition to the second "decompensation" phase was characterized by avalanche-like inward currents in the hippocampal neurons of 711 Ϯ 137 pA (n ϭ 10) and their rapid depolarization to near 0 mV (Ϫ3 Ϯ 1 mV, n ϭ 10; all neurons were lost during or after the anoxic depolarization (AD) probably because of the cellular swelling. 3 This rapid AD developed in 17.5 Ϯ 0.2 minutes (n ϭ 23) after perfusion with anoxic solution and was associated with a remarkable negative shift in field recordings of 3.2 Ϯ 0.4 mV and 43 Ϯ 8 seconds half-duration (n ϭ 23), similar to what has been observed in cerebral cortex in vivo 19 -22 as well as in adult [23][24][25][26] and neonatal 27 cortical slices.…”