Analysis of the excitatory and inhibitory components of postsynaptic currents recorded in pyramidal neurons and interneurons in the rat hippocampus

Histaminergic H1 and H2 Receptors Mediate the Effects of Propofol on the Noradrenalin-Inhibited Neurons in Rat Ventrolateral Preoptic Nucleus

The ventrolateral preoptic nucleus is a sleep-promoting nucleus located in the basal forebrain. A commonly used intravenous anesthetic, propofol, had been reported to induce sleep spindles and augment the firing rate of neurons in ventrolateral preoptic nucleus, but the underlining mechanism is yet to be known. By using patch clamp recording on neuron in acute brain slice, present study tested if histaminergic H1 and H2 receptors play a role in the effect of propofol on the noradrenalin-inhibited neurons in ventrolateral preoptic nucleus. We found that the firing rate of noradrenalin-inhibited neurons were significantly augmented by propofol; the frequency of inhibitory postsynaptic currents of noradrenalin-inhibited neuron were evidently attenuated by propofol; such inhibition effect was suppressed by histamine; and both triprolidine (antagonist for H1 histamine receptor) and ranitidine (antagonist for H2 histamine receptor) were able to increase the inhibition rate of propofol in presence of histamine. Present study demonstrated that propofol-induced inhibition of inhibitory postsynaptic currents on noradrenalin-inhibited neurons were mediated by histaminergic H1 and H2 receptors.

Bilirubin enhances neuronal excitability by increasing glutamatergic transmission in the rat lateral superior olive

Hyperbilirubinemia is one of the most common clinical phenomena observed in human newborns. To achieve effective therapeutic treatment, numerous studies have been done to determine the molecular mechanisms of bilirubin-induced neuronal excitotoxicity. However, there is no conclusive evidence for the involvement of glutamatergic synaptic transmission in bilirubin-induced neuronal hyperexcitation and excitotoxicity. In the present study, using gramicidin-perforated patch-clamp techniques, spontaneous excitatory postsynaptic currents (sEPSCs) were recorded from lateral superior olive (LSO) neurons isolated from postnatal 11-14-day-old (P11-14) rats. The application of 3 μM bilirubin increased the frequency, but not the amplitude, of sEPSCs. The action of bilirubin was tetrodotoxin (TTX)-insensitive, as bilirubin also increased the frequency, but not the amplitude, of mEPSCs. The amplitudes of GABA-activated (I(GABA)) and glutamate-activated (I(glu)) currents were not affected by bilirubin. Under current-clamp conditions, no spontaneous action potentials were observed in control solution. However, the application of 3 μM bilirubin for 4-6 min evoked a considerable rate of action-potential firing. The evoked firing was partially occluded by D,L-2-amino-5-phosphonovaleric acid (APV), an NMDA receptor antagonist, but completely inhibited by a combination of APV and 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX), an AMPA receptor antagonist. These results indicate that bilirubin facilitates presynaptic glutamate release, enhances glutamatergic synaptic transmission by activating postsynaptic AMPA and NMDA receptors, and leads to neuronal hyperexcitation. This study provides a better understanding of the mechanism of bilirubin-induced excitotoxicity and determines for the first time that both AMPA and NMDA receptors are likely involved in the excitotoxicity produced by bilirubin.

Modulation of synaptic transmission and analysis of neuroprotective effects of valproic Acid and derivates in rat embryonic motoneurons

Amyotrophic lateral sclerosis is a devastating motoneuron disorder for which no effective treatment exists. There is some evidence for neuroprotective effects of valproic acid (VPA). The beneficial effects, however, are limited due to the adverse effects of VPA. To overcome this problem, a number of VPA derivates with fewer side effects have been synthesized. In the present study, we investigated the viability of highly purified embryonic motoneurons cultured on glial feeder layers, composed of either astrocytes or Schwann cells, or in monoculture, in presence of VPA and its three derivates 3-propyl-heptanoic acid (3-PHA), PE-4-yn enantiomers (R- and S-PE-4-yn). An excitotoxic stimulus, kainate (KA), was added at day in vitro 9 (DIV9) and the neuroprotective effect of either simultaneous incubation (DIV9) or pre-incubation (DIV1) of VPA and its derivates was tested. The survival of motoneurons under simultaneous application of KA and VPA derivates was not remarkably increased. Pre-incubation with VPA and even more with the derivates before the addition of KA, however, significantly reduced their vulnerability against the KA-induced neurotoxic effect. Our data suggest that the neuroprotective capacities of VPA and its three derivates tested here drastically increase when they are added several days before KA. Most prominent neuroprotective effects were seen for the PE-4-yn enantiomers. Patch-clamp experiments revealed an antiexcitotoxic effect of the S-PE-4-yn enantiomer that reduces the frequency of postsynaptic currents and enhances the inhibitory postsynaptic transmission dependent on the co-culture condition.