Development of calcium action potentials in mouse hippocampal cell cultures

The Chinese herbal medicine Chai-Hu-Long-Ku-Mu-Li-Tan (TW-001) exerts anticonvulsant effects against different experimental models of seizure in rats

We evaluated the anticonvulsant effect of Chai-Hu-Long-Ku-Mu-Li-Tan (TW-001), a Chinese herbal medicine, and its mechanisms in several standard rodent models of generalized seizure. TW-001 (4 g/kg, p.o.) significantly increased the threshold for tonic electroconvulsions and the threshold for tonic seizures in response to i.v. infusion of pentylenetetrazole (PTZ). In the s.c. PTZ seizure test, both the incidence and severity of seizures were decreased by TW-001. TW-001 (1-10 mg/ml) did not alter resting membrane potential or input resistance of the hippocampal CA1 neurons, but elicited a reversible suppression of stimulus-triggered epileptiform activity in area CA1 and spontaneously occuring epileptiform burst discharges in area CA3 elicited by picrotoxin. Both field excitatory postsynaptic potentials and population spikes were reversibly depressed by TW-001 (0.5-15 mg/ml) in a concentration-dependent manner. The sensitivity of postsynaptic neurons to a glutamate-receptor agonist, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid or N-methyl-D-aspartate, was not altered by TW-001 (10 mg/ml). However, TW-001 (5 mg/ml) clearly increased the magnitude of paired-pulse facilitation. TW-001 (5-10 mg/ml) reversibly limited the repetitive firing and reduced the maximal rate of rise of action potentials elicited by injection of depolarizing current pulses (0.4 nA, 200 ms) into the pyramidal cells. TW-001 (1-10 mg/ml) exerted a concentration-dependent reduction of the tetrodotoxin-sensitive sodium currents and high voltage-activated calcium currents. These results suggest that TW-001 is an interesting new anticonvulsant agent that exerts its anticonvulsant activity through inhibition of sodium and calcium channels, stabilizing neuronal membrane excitability and inhibiting glutamate release.

L-deprenyl (selegiline) limits the repetitive firing of action potentials in rat hippocampal CA1 neurons via a dopaminergic mechanism

The effects of L-deprenyl (selegiline), a highly selective monoamine oxidase type B (MAO-B) inhibitor, on cell excitability of rat hippocampal CA1 neurons were examined in slice preparations using intracellular recording techniques. Superfusion of L-deprenyl (10 and 20 microM) reversibly limited the repetitive firing (RF) of action potentials elicited by injection of depolarizing current pulses (100 ms) into the pyramidal cells. At a concentration of 1-50 microM, L-deprenyl did not alter resting membrane potential or input resistance of the hippocampal CA1 neurons. The limitation of RF by L-deprenyl (20 microM) was accompanied by the reduction of the maximal rate of rise (Vmax) of the action potentials in a non-voltage-dependent manner. In 80% of recorded cells, application of L-deprenyl (20 microM) produced an increase in the amplitude and duration of afterhyperpolarization (AHP). The limitation of L-deprenyl on RF was mimicked by other MAO-B inhibitors, pargyline and 4-phenylpyridine. In addition, the ability of L-deprenyl to limit RF was not observed in the hippocampal CA1 neurons taken from dopamine (DA)-depleted rats. Moreover, we also observed that the L-deprenyl-induced limitation of RF was specifically antagonized by (+/-)-7-bromo-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzaz epine (SKF-83566, 5 microM), a selective D1 dopaminergic receptor antagonist. However, the D2 dopaminergic receptor antagonist, sulpiride (5 microM), had no effect on L-deprenyl's action. These results indicate that the MAO-B inhibitory ability leading to an increase of the dopaminergic tone in the hippocampus is involved, at least in part, in the L-deprenyl-induced reduction of neuronal excitability in the CA1 region of rat hippocampus and that the D1 dopaminergic receptor is involved in L-deprenyl's action.

Properties of the fast sodium channels in pyramidal neurones isolated from the CA1 and CA3 areas of the hippocampus of postnatal rats

The fast sodium (Na)current of hippocampal neurones was recorded using the intracellular perfusion method. Neurones were isolated from the CA1 and CA3 hippocampal subregions separately, after treatment of the tissue with trypsin. There were no differences between the current-voltage (I-V) characteristics of CA1 and CA3 neurones. In contrast to this, the steady-state inactivation (h infinity) of both types of neurones was significantly different. Additionally, there were two subpopulations of CA1 neurones, which showed different courses of h infinity. Compared with CA1 neurones, the steady-state activation and inactivation curves of CA3 neurones overlapped much more in the potential range -80 mV to -50 mV. These results are consistent with the well-known fact that CA3 neurones show spontaneous burst activity, while CA1 cells do not. The time constant of activation (tau m) depended upon the membrane potential in the same way for all CA3 neurones investigated. However, there were two different subpopulations of CA3 cells, showing different voltage dependence of the time constant of inactivation. We conclude that these differences reflect two types of pyramidal cells within the same subregion.

Membrane currents in hippocampal neurons

This chapter reviews properties and functions of endogenous ionic currents in hippocampal neurones. Currents considered are: Na currents INa(fast) and INa(slow); Ca currents; K currents--delayed rectifier IK(DR), transient IK(A), 'delay' current IK(D) and M current IK(M); inward rectifiers IQ, IK(IR) and ICl(V); Ca-activated currents IK(Ca) (IC and IAHP), ICl(Ca) and Ication(Ca); Na-activated currents; and anoxia-induced currents.

Determination of the birth date and proliferative state of dissociated cells from fetal rat brain

The proliferative status and time of origin of dissociated cells from cerebral cortex, basal ganglia, diencephalon, mesencephalon and rhombencephalon of the fetal rat brain have been analyzed. The distributions of cells in different phases of the cell cycle after dissociation and after 7 days in culture have been determined with flow cytofluorometry. Two separate DNA indicators, propidium iodide and Hoechst 33258, have been used. Almost all of the dissociated cells recovered from the 5 brain regions, between embryonic days 15 and 20, are in G1, or growth arrest phase of the cell cycle. In contrast, only about 55% of the liver cells (same fetal age) are in G1, or growth arrest phase. The times of the last in vivo mitoses of the dissociated cells have been determined by maternal injection of [3H]thymidine and autoradiography of cultures. The majority of the cells recovered on embryonic days 16 and 17 from the 5 brain regions appeared to have undergone DNA synthesis within a period of 24 h prior to dissociation. When the fetuses were sacrificed 96 h after the injection, less than 20% of the cells were labelled, and grain density was drastically reduced. Most labelled cells survive in the serum-free culture medium for more than 7 days. Dissociated cultures of synchronized and birth-dated cells from different brain regions of fetal rat should prove particularly useful for the study of cellular development and function.

Delayed neurotoxicity of excitatory amino acids in vitro

The acute neurotoxicity produced by glutamate and related excitatory amino acids is probably caused by depolarization leading to excessive anionic and cationic fluxes and osmotic lysis. Recently, a more delayed form of glutamate neurotoxicity, which is critically dependent upon calcium influx, has been described in cultured neocortex. We investigated this phenomenon in cultures of dispersed rat hippocampal neurons. When these cultures were briefly incubated with various excitatory amino acids in low extracellular chloride, there was no acute toxicity, but a gradual drop-out of neurons occurred over the next day. When calcium was removed from the extracellular medium during amino acid incubation, this late neuronal loss was not seen. Interestingly, blocking excitatory amino acid receptors in cultures after the amino acid exposure also prevented this delayed neuronal death. In addition, these treated cultures contained neurons with normal physiological properties, and had concentrations of adenosine triphosphate that were close to control values. The findings suggest an amino acid-induced calcium influx may elevate the release of endogenous excitatory transmitter, likely glutamate, and/or increase the sensitivity of these neurons to glutamate. These in vitro observations may partially explain the delayed neuronal loss seen in some pathological conditions affecting man.

Expression of membrane currents in rat diencephalic neurons in serum-free culture

The whole-cell gigaseal voltage clamp technique has been used to investigate the timing of expression and type of voltage-dependent ionic currents in dissociated primary cultures of fetal rat (E17) diencephalic neurons grown in a serum-free defined medium. The expression of membrane currents varied among cells at any particular time in culture. Despite this variability, certain characteristics of the appearance of ionic currents emerge from this study. These are: (i) the earliest appearing membrane current is a voltage-dependent outward current carried by K+. In some cells, it is the classical delayed rectifier current, whereas in others it is the transient outward current (IA). (ii) The earliest appearing inward current is carried by Na+. In some cells the channels are first expressed in the neurites and then in or near the cell body. The early neuritic Na+ channels are blocked by cobalt or cadmium as well as by tetrodotoxin (TTX). In others, the early Na+ channels appear in or near the cell body and are only blocked by TTX. (iii) With additional time in culture, a majority of cells exhibit a Ca2+ current at the time of Na+ channel appearance in or near the cell body as well as a transient Ca2+-dependent outward current. The Ca2+ current is only a small fraction of the total inward current. These inward currents show the classical pharmacologic profile. The complex pattern of expression of ionic current may reflect multiple populations of neurons with different developmental sequences resulting from differences in cell age and lineage.

Ultrastructural localization of the calcium-binding protein parvalbumin in neurons of the song system of the zebra finch, Poephila guttata

The distribution of parvalbumin (PV) within neurons of the vocal motor nucleus hyperstriatum ventralepars caudalis (HVc) was investigated in the forebrain of adult male zebra finches by means of light and electron microscopy using the indirect immunoperoxidase technique. Parvalbumin-reaction product was located in the amorphous material of perikarya, dendrites and nuclei, and associated to microtubuli, postsynaptic densities and intracellular membranes; it was found in some axons and Gray type-2 boutons, but rarely in type-1 boutons and never in the Golgi apparatus. These observations suggest that parvalbumin may regulate calcium-dependent processes at the postsynaptic membrane and in the cytosol. Furthermore, the partial association of parvalbumin to microtubuli points to an involvement in calcium-dependent tubular functions. Calcium currents and microtubular assembly or transport may be relevant for the known functions of HVc in song learning.

Electrophysiological studies on the postnatal development of intracerebellar nuclei neurons in rat cerebellar slices maintained in vitro. II. Membrane conductances

The development of membrane conductances of intracerebellar nuclei neurons was studied in the rat since birth up to the weaning period by the use of thick sagittal cerebellar slices maintained in vitro. Mature nuclear neurons express fast sodium and slowly inactivating sodium conductances, as well as calcium conductances. As early as birth, fast sodium and calcium conductances appear well developed whereas slowly inactivating sodium conductances mature within the first postnatal week.