Long-term potentiation (LTP) in the CA1 region of the hippocampus is widely believed to occur through In spite of the attention excitatory transmission processes have received in connection with LTP, potentiation of excitatory responses after tetanization could theoretically occur through impairment of synaptic inhibition. Type A y-aminobutyric acid (GABAA) receptor-mediated synaptic inhibition plays a critical role in the control of excitation in the mammalian central nervous system (6). Several studies have reported short-term changes of synaptic inhibition in connection with high-frequency stimulation (7-9). During the maintenance phase of LTP, however, orthodromically evoked early inhibitory postsynaptic potentials (IPSPs) are generally not reduced (10-12). Furthermore, postsynaptic GABA sensitivity was found to be unchanged during LTP in an extracellular study (13), and in several studies the excitability of GABAergic interneurons was found to be unchanged or even increased during LTP (14)(15)(16) Fig. 2).Stimulation. Evoked responses were elicited by stimulation of stratum radiatum Schaffer collateral/commissural fibers through a pair of insulated tungsten bipolar electrodes (stimulation range, 15-400 1uA). Tetanic stimulation (50 or 100 Hz; 1 s; single-pulse duration, 80 As) was applied via the same stimulation electrode.Drugs. Bicuculline, picrotoxin (PTX), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), 2-amino-5-phosphonopentanoic acid (AP5), and saclofen were applied by bath perfusion. CNQX, D-AP5, and saclofen were purchased from Tocris Neuramin (Bristol, U.K.); all other drugs were from Sigma. Iontophoresis. lontophoretic GABAA responses were elicited by application of GABAA-receptor agonists muscimol (50 mM, pH 3.5, in extracellular solution) or GABA (1 M, pH 3.5, in the presence of bath-applied GABAB-receptor antagonist saclofen, 100 pM) in CA1 pyramidal cells through a double-or triple-barreled extracellular iontophoretic electrode with one channel containing extracellular solution for current balancing (ejecting currents, +5 to +140 nA; retaining currents, -3 to -20 nA). The iontophoretic electrode was positioned by an independent micromanipulator as close as possible to the respective recording site.Data Acquisition. Data (voltage responses from the recording electrode) were digitized and stored on disk (Nicolet 410 oscilloscope) for subsequent off-line analysis.LY Staining and Histology. LY staining (26-28) was performed in 17 (of 57) apical dendritic recordings (29,30) and 26 (of 55) interneuron recordings (31) for morphological confirmation of cell type. The tip of the electrode was back-filled with LY (1.5% in 1 M Li2SO4 or LiCl) whereas the shaft was filled with 1 M Li2SO4 or LiCl alone. Dye injection was implemented by repetitive 400-ms hyperpolarizing current pulses (between -0.5 and -1 nA DC; 5-10 min; 0.5 Hz)

This study investigates the dynamics of an acoustically driven air bubble in water. Depending on the values of external parameters, the radial oscillations of the bubble can be either stable or chaotic. The necessary condition of chaotic behaviour is identified to be the non-zero amplitude of the bubble's afterbounces at the beginning of the next acoustic cycle, which brings memory into the system. We show that for some parameter values in the chaotic regime the dynamics can be reduced to a unimodal map. At these parameter values the periodic orbit theory is successfully applied to calculate averages of relevant physical quantities, such as the air concentration at which the bubble is in diffusive equilibrium with the surrounding liquid. Finally we investigate the convergence of the calculated quantities.

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We studied experimentally the dependence of light emission and phase space boundaries of air bubbles in water on the level of degassing down to low partial pressures of 15 mmHg. We found that the maximum obtainable light intensity increased monotonically by lowering the concentration of dissolved air in water. We also present a new technique to obtain the acoustic pressure (P(a)) and ambient radius (R0) parameters, based on the information provided by the timing of the flashes in the acoustic cycle. Using this technique we give phase diagrams of the bubble in the (R0,P(a)) and (P(a), gas concentration) space, and discuss the parametric dependence of the light intensity. The resulting power-law dependence of the relative intensity normalized by the ambient volume of the bubble on the expansion ratio indicates that more extreme conditions are attainable inside a bubble at dissolved air concentration of 15 mmHg than at 150 mmHg.

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