Search

1. Neocortical brain slices were prepared from animals 8-15 days of age and maintained in vitro. Intracellular recordings were obtained from neurons in cortical layers 2-3. The role of synaptic activity and excitatory amino acid receptors in generation of picrotoxin-induced ictal-like epileptiform activity in the immature neocortex was investigated. D-2-amino-5-phosphonovaleric acid (D-APV) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were used as selective antagonists of N-methyl-D-aspartate (NMDA) and non-NMDA receptors, respectively. 2. Ictal-like epileptiform discharges were induced by bath application of the GABAA-receptor antagonist picrotoxin. Paroxysmal discharges, 7-25 s in duration, occurred spontaneously or could be evoked by electrical stimulation. These events consisted of an initial paroxysmal depolarizing shift (PDS) followed by a long-duration depolarization (LLD) with superimposed late PDSs. 3. The amplitudes of the initial PDS, LLD, and late PDSs were linearly dependent on membrane potential, increasing with hyperpolarization and diminishing on depolarization. All responses reversed polarity near 0 mV. Under voltage-clamp conditions, both transient and sustained currents were observed, coincident with PDSs and the LLD, respectively. The duration of the ictal-like events was similar under current- and voltage-clamp conditions, suggesting activation of intrinsic membrane currents did not significantly prolong epileptiform discharges. 4. Bath application of D-APV (20 microM) decreased the amplitude and duration of both the initial PDS and LLD without affecting the time-to-onset of epileptiform activity.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of caffeine were investigated on the extracellular excitatory postsynaptic potentials (EPSPs) recorded in the stratum radiatum of CA1 of the rat hippocampal slice in response to stimulation of the Schaffer collaterals. Caffeine in concentrations from 500 microM to 10 mM caused an increase in the amplitude of the EPSP, which reached a peak after 5-10 min perfusion. This increase was antagonized by pretreatment with 20 microM trifluoperazine. Paired-pulse facilitation, augmentation and potentiation were strongly inhibited by caffeine. Augmentation was most sensitive to caffeine, being abolished by 500 microM caffeine. Long-term potentiation (LTP) induced by high-frequency stimulation was not significantly inhibited by caffeine either by 5-10 min or by 60 min perfusion with 10 mM caffeine. Moreover, the caffeine-induced increase in the low-frequency EPSP could be reversed by 30 min washout, demonstrating that it was not an LTP type increase.

Short-term potentiation of extracellular field excitatory postsynaptic potentials (EPSP's) was investigated in the stratum radiatum of CA1 of the rat hippocampal slice in vitro. A presynaptic tetanus consisting of a single train of stimuli of 250 H evoked short-term potentiation (STP), but not long-term potentiation (LTP) of small amplitude, just suprathreshold, EPSP's in a medium containing 2 mM Ca and 2 mM Mg. Increasing the number of stimuli in the tetanus enhanced the initial amplitude of the STP to a maximum of 40–70% with 30–40 stimuli, and enhanced the decay time constant of STP to a maximum of 60–80s. Increasing the Ca influx by raising external Ca, lowering Mg or adding the agent 4-aminopyridine caused a large increase in the initial amplitude of STP but only a very slight increase in the decay time of STP. LTP was frequently evoked in high Ca/Mg ratios of 2.0 or 4.0, but not in 1.0 or 0.5.

The ability of the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to suppress picrotoxin-induced epileptiform burst activity was examined. Intracellular recordings were obtained from hippocampal CA1 and CA3 pyramidal neurons maintained in vitro. Bath application of CNQX (5 microM) significantly reduced or abolished evoked paroxysmal depolarizing shifts (PDSs) in all CA1 and CA3 neurons tested. In cells where a CNQX-insensitive component in the PDS was manifest, this remaining activity was abolished by the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovaleric acid (20 microM), suggesting the existence of a NMDA-mediated synaptic potential. Our results indicate that non-NMDA receptor antagonists are capable of markedly reducing picrotoxin-induced epileptiform activity and that these receptors play an important role in generation of PDSs.

The effect of 4-aminopyridine (4-AP) on long-term potentiation (LTP) was studied in the hippocampal slice preparation of the rat. Field excitatory postsynaptic potentials (EPSPs) were recorded and evoked in the stratum radiatum of the CA1. Both the low frequency EPSP and LTP of the EPSP were significantly increased by treatment with 4-AP. These effects were inhibited by increasing the magnesium concentration from 1 to 4 mM. Pretreatment with 20 microM DL-2-amino-5-phosphonovalerate antagonized only the increase in LTP produced by 4-AP. It is suggested that 4-AP enhances Ca influx either pre- or postsynaptically and thereby increases LTP.

Unlike cold climate regions, where natural ventilation is not preferred during winter, natural ventilation is always preferred in Hong Kong for cooling because of the subtropical climate. It also provides better indoor environment quality and energy conservation. Natural ventilation performance of a residential unit is affected by internal as well as external factors. External factors are often subject to constraints beyond the control of site planners and architects. Internal factors include opening configurations and window types, which site planners and architects are free to design the way they deem proper. However, little information is available about their precise impact. An earlier study by the authors on opening configurations identified the best and the worst out of twelve configurations. The best was with cross ventilation and the worst was with single-sided ventilation. In this study, the focus is on the influence of window types. CFD simulations were performed based on the best and w...

The Hong Kong Building Environmental Assessment Method (HK-BEAM), an environmental assessment method for air-conditioned office buildings, has been developed by the Real Estate Developers Association (REDA) for use in Hong Kong. Two versions of the scheme have been developed; one for new office premises and the other for existing office premises. HK-BEAM embraces a variety of issues related to the global, local and indoor environments. The efficient use of electricity forms a major part of the assessment. The basis for the energy performance assessment method, and the criteria for obtaining the relevant credits are described and discussed.