Abstracts

Rationale: Pharmacological blockade of early GABA depolarization with bumetanide as well as augmentation of GABA inhibition with benzodiazepines during early postnatal development results in temporal or permanent changes of various behavioral parameters (Wang and Kriegstein, Cerebral Cortex, 2011; Mikulecka et al, Frontiers Behav Neurosci, 2014a,b). Long term effects of these manipulations on hippocampal excitability were however not yet studied. Methods: Two ways of early pharmacological manipulation of GABAergic system were used. Rat pups were repeatedly injected either with bumetanide (BUM; P3-P7; 0.3mg/kg i.p. twice a day) or clonazepam (CZP; 1mg/kg i.p.) both suspended in saline with Tween 80. Controls received saline instead. Each group consisted of 10 male Wistar rats. Body weight and health status were checked daily during period of administration. Effects of treatment on hippocampal excitability were assessed in five-month-old rats using electrically induced single pulse evoked potentials with increased stimulation intensity (0.1 – 6mA) and epileptic afterdischarges (ADs) induced with suprathreshold intensity of stimulation. Animals were stimulated six times with 20 min interval between stimulations. The amplitude of evoked potentials was measured between peaks of N1 (first negative) and P2 (second positive) waves. Threshold intensity, duration of afterdischarges and incidence of recurrent ADS were evaluated. Results: Early exposure to both tested drugs resulted in persisting increase of hippocampal excitability. Threshold intensity for ADs induction was lower by 39% in BUM and by 20% in CZP exposed animals. In average, duration of afterdischarges was 25-30% longer in both exposed groups compared to controls. Both BUM and CZP animals exhibited an increase in N1-P2 amplitude with increasing stimulation intensity in comparison to the control group. Differences were significant and more expressed in CZP group. The similar effect on N1-P2 latency was observed. Early exposure to either CZP or BUM had only minuscule effect on development. CZP animals gained less weight during drug administration, no differences were observed between controls and BUM group. Conclusions: Our data demonstrate that pharmacological modulation of both GABA mediated inhibition and excitation results in increase of hippocampal excitability in adulthood. Funding: This study was supported by grants LH 15025 of the Ministry of Education and P304/12/G069 of the Czech Science Foundation