Biomedical subjects

A E Schaffner

Publications and source records attributed to A E Schaffner.

At least 19 recordsLinked to original sources

PubMed1998

Kainate induces an intracellular Na+-activated current in cultured embryonic rat hippocampal neurones.

1. In embryonic rat hippocampal neurones cultured for < 3 days, kainate induced an inward current at negative potentials that recovered to baseline levels immediately upon termination of agonist application. However, in neurones cultured for longer, the kainate-induced current was often followed by a long-lasting inward current that slowly recovered to baseline levels. The amplitude of the delayed current (Idelay) triggered by kainate was positively related both to the duration of application at constant agonist concentration and to concentration at constant application duration. 2. Idelay could last for several minutes and was accompanied by a conductance increase, which closely paralleled current amplitude. Depression of the kainate-induced current response at receptor level with CNQX or at ionic level with Na+-free solution eliminated Idelay. However, when applied during Idelay neither CNQX nor Na+-free solution had any effect on Idelay. Li+ effected the same response as Na+ in mediating kainate-induced Idelay. 3. GABA-activated Cl- current, which was associated with the same amount of inwardly directed charge flow at the same potential as that induced by kainate, did not trigger a long-lasting delayed current. 4. Idelay depended on the existence of extracellular K+ and its amplitude increased with the increase in K+ concentration. Neither applying Cl-- or Ca2+-free solutions nor increasing intracellular Ca2+ buffering speed and capacity altered Idelay. Exposure to the specific KCa channel blockers apamin and charybdotoxin also failed to alter Idelay. However, Idelay could be blocked by Cs+, Ba2+ and high concentrations of 4-aminopyridine (4-AP) and TEA. 5. Inside-out excised patch-clamp recordings revealed that low density or highly clustered Na+-activated K+ channels were expressed in the cell bodies of cultured embryonic rat hippocampal neurones. These could be the elementary channels underlying Idelay.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1998

Astrocytes regulate developmental changes in the chloride ion gradient of embryonic rat ventral spinal cord neurons in culture.

1. Embryonic rat ventral spinal cord neurons were dissociated at day 15 and grown on: (i) poly-D-lysine (PDL); (ii) a confluent monolayer of type I astrocytes; or (iii) PDL in astrocyte-conditioned medium (ACM) to examine the influence of astroglia on the regulation of GABAA receptor/Cl- channel properties. 2. Potentiometric oxonol dye recordings of intact cells indicated that embryonic neurons were uniformly depolarized by muscimol. The depolarizing effects disappeared in cells dissociated during the early postnatal period and recovered in culture for 24 h. Similar recordings using the calcium-imaging dye fura-2 AM revealed that GABA or muscimol triggered a sustained rise in cytosolic Ca2+ (Ca2+c ) in embryonic neurons that was dependent on extracellular Ca2+, blocked by bicuculline and nifedipine and sensitive to changes in extracellular chloride. The incidence and amplitude of the Ca2+ response decreased with time in vitro and was accelerated in neurons cultured on astrocytes compared with those on PDL. 3. Perforated patch-clamp recordings revealed that GABA depolarized neurons in a Cl--dependent and bicuculline-sensitive manner. Both the resting membrane potential and the GABA equilibrium potential became more hyperpolarized with time in vitro. 4. Astrocytes and ACM accelerated the transformation of GABAergic potential responses from depolarizing to hyperpolarizing. The change occurred over the first 4 days in co-culture or in ACM but took more than 2 weeks in neurons cultured on PDL alone. 5. The intrinsic, elementary properties of GABAA receptor/Cl- channels including open time and unitary conductance changed independently of the presence of astrocytes or ACM. Mean open time of the dominant kinetic component decreased and conductance increased with time in vitro. 6. In sum, astrocytes accelerate the developmental change in the Cl- ion gradient extrinsic to GABAA receptor/Cl- channels, which is critical for triggering Ca2+ entry, without influencing parallel changes in the intrinsic properties of the channels.

Animals↗

PubMed1997

Astrocytes regulate amino acid receptor current densities in embryonic rat hippocampal neurons.

Embryonic rat hippocampal neurons were cultured in a serum-free defined medium (MEM/N3) either directly on poly-D-lysine (PDL) or on a confluent monolayer of postnatal cortical astrocytes, C6 glioma cells, or Rat2 fibroblasts. Neurons on PDL were grown in MEM/N3 or in MEM/N3 conditioned for 24 h by astrocytes or C6 cells. Membrane capacitance (Cm) and gamma-aminobutyric acid (GABA)-, glycine-, kainate-, and N-methyl-D-aspartate (NMDA)-induced currents were quantified using whole-cell patch-clamp recordings. Cm as well as the amplitude and the density of these currents in neurons cultured on astrocytes were significantly greater than those in neurons grown on PDL after 24 and 48 h. C6 cells mimicked astrocytes in promoting Cm and GABA-, glycine-, and NMDA-evoked, but not kainate-evoked, currents. Cm and currents in neurons grown on Rat2 cells were comparable to those in neurons on PDL. Astrocytes maintained in culture for 3 months were noticeably less effective than freshly prepared ones just grown to confluence. Suppression of spontaneous cytoplasmic Ca2+ (Ca[c]2+) elevations in astrocytes by 1,2-bis(2-aminophenoxy) ehane-N, N, N, N-tetraacetic acid acetoxymethyl ester (BAPTA-AM) loaded intracellularly blocked the observed modulatory effects. Medium conditioned by either astrocytes or C6 cells mimicked the effects of direct coculture of neurons on these cells in promoting Cm and amino acid-evoked currents. Inclusion of antagonists at GABA and glutamate receptors in coculture experiments blocked the observed effects. Thus, diffusible substances synthesized and/ or secreted by astrocytes in a Ca(c)2+-dependent manner can regulate neuronal growth and aminoacid receptor function, and these effects may involve neuronal GABA and glutamate receptors.

Animals↗

PubMed1997

Proton-induced cation current in embryonic rat spinal cord neurons changes ion dependency over time in vitro.

A rapid increase in proton concentration [H+]0 induces Na+ conductance in a variety of cell types. Here we report that H+ trigger a cation-selective channel whose ion dependency changes over time in culture. Whole-cell recordings of ventral spinal cord neurons dissociated at E15 and cultured for up to 14 days revealed that more than 80% had H(+)-induced inward current responses exhibiting a rapid decay phase. The current response was activated beginning about pH 6.8. Following decay, several minutes were required for complete recovery. More modest decreases in pH, which by themselves failed to activate this current, depressed those triggered by effective changes in pH. The currents recorded from cells in culture for less than 7 days could be abolished completely in the absence of Ca2+ and persisted in Na(+)-free and Ba(2+)-containing solutions. Ensemble analysis of current fluctuations recorded at the peak of the current allowed us to estimate a unitary channel conductance of 7.0 pS and a mean open time of 4.1 ms. In neurons cultured 2 weeks or more, protons induced an inward current response with similar kinetic properties, but with [Na+]0 dependency. Thus, proton-activated cation conductance in embryonic rat spinal cord neurons is self-limiting and involves brief openings of cation-selective channels whose ion dependency changes over time in culture.

Animals↗

PubMed1997

GABA induces GABAergic MSCs in cultured embryonic rat thalamic neurons.

Application of 0.1-10 microM GABA in the vicinity of cultured embryonic rat thalamic neurons recorded with patch pipettes in the presence of 2 microM TTX induced or increased the frequency of miniature synaptic currents (MSCs) that reversed polarity at the Cl- equilibrium potential. These MSCs were blocked by the GABAA receptor antagonist bicuculline and exhibited exponential decay kinetics that closely paralleled those estimated from fluctuation analysis of Cl- channels activated pharmacologically by applying 1-10 microM GABA to the same cells. We conclude that the MSCs are mediated by GABA. Application of the GABAA receptor agonist muscimol activated Cl- current but failed to induce GABAergic MSCs while submicromolar concentrations of GABA evoked GABAergic MSCs but did not activate Cl- channels. The GABAB receptor agonist (-)baclofen did not mimic GABA in inducing MSCs. Induction of GABAergic MSCs by GABA required extracellular Ca2+. Verapamil and Co2+, which block voltage-dependent calcium channels, completely blocked GABA-induced MSCs independent of their effects on the direct activation of a Cl- current response. The results indicate that GABA can trigger GABAergic Cl(-)-dependent MSCs in a Cao(2+)-dependent manner. The mechanism may involve a novel receptor and/or signal transduction pathway.

Animals↗

PubMed1996

Upregulation of GABAA current by astrocytes in cultured embryonic rat hippocampal neurons.

Embryonic rat hippocampal neurons were cultured on poly-D-lysine (PDL) or a monolayer of postnatal cortical astrocytes to reveal putative changes in neuronal physiology that involve astrocyte-derived signals during the first 4 d of culture, GABA-induced Cl- current (IGABA) was quantified using outside-out and whole-cell patch-clamp recordings beginning at 30 min, when cells had become adherent. The amplitude and density (current normalized to membrane capacitance) of IGABA in neurons grown on astrocytes became statistically greater than that recorded in neurons grown on PDL after 2 hr in culture (HIC). Although the current density remained unchanged in neurons on astrocytes, that in neurons on PDL decreased and became statistically lower beginning after 2 HIC. The differences in amplitude and density of IGABA in the two groups of neurons were maintained during the 4 d experiment. The upregulation effect of astrocytes on neuronal IGABA required intimate contact between the neuronal cell body and underlying astrocytes. Suppression of spontaneous Cac2+ elevations in astrocytes by bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid that was loaded intracellularly decreased their modulatory effects on IGABA. IGABA in all cells was blocked completely by bicuculline and exhibited virtually identical affinity constants, Hill coefficients, and potentiation by diazepam in the two groups. Outside-out patch recordings revealed identical unitary properties of IGABA in the two groups. More channels per unit of membrane area could explain the astrocyte enhancement of IGABA. The results reveal that cortical astrocytes potentiate IGABA in hippocampal neurons in a contact-dependent manner via a mechanism involving astrocyte Cac2+ elevation.

Animals↗

PubMed1996

Early upregulation of medium neurofilament gene expression in developing spinal cord of the wobbler mouse mutant.

Homozygous wobbler mouse mutants develop a progressive paralysis due to spinal motoneuron degeneration. To understand the molecular aspect underlying the genetic defect we have studied the embryonic (from E13) and postnatal expression of the three neurofilament and choline acetyltransferase genes in each member from several wild-type (wt) and wobbler (wr) progenies. There are no variations among wt littermates at all ages studied. In contrast, analyses of neurofilament mRNA reveals a 3-4-fold increase of medium neurofilament (NFM) mRNA in wobbler mice (wr/wr). The pattern of increased NFM mRNA during development, prior to the appearance of the wobbler phenotype, among littermates (from heterozygous carriers) conforms to a mendelian inheritance of a single gene defect 1:2:1 (wr/wr:wr/+:+/+). Light and heavy neurofilament mRNA levels are also increased later in development exclusively in those individuals with high NFM mRNA values indicating that increase of the latter is associated with increase of the light and heavy subunit expression. Also NF proteins are increased. Expression of choline acetyltransferase gene is instead always comparable to normal control. Our study provides novel insights into the nature of the wobbler defect, strengthening the hypothesis that neurofilament accumulation plays a pivotal role in the etiopathogenesis of motoneuron degeneration.

Animals↗

PubMed1995

GABA-induced motility of spinal neuroblasts develops along a ventrodorsal gradient and can be mimicked by agonists of GABAA and GABAB receptors.

During embryogenesis, neuroblasts proliferate within germinal zones, then migrate to their final positions. Although many neurons migrate along radial glial fibers, evidence suggests that environmental factors, as yet unidentified, also influence neuroblast movement. In vivo, nerve growth factor (NGF) and gamma-aminobutyric acid (GABA) colocalize near target destinations of migratory neuroblasts. In vitro, embryonic spinal neurons migrate towards NGF and GABA (Behar et al.: J Neurosci 14:29-38, 1994), implying that the molecules may act as chemoattractants in vivo. Here, we have used an in vitro assay of migration to show that migratory responses to these attractants develop along a ventrodorsal gradient that parallels terminal mitosis during cord development, and that GABA stimulates chemokinesis (motility without a gradient) via heterogeneous receptors involving separate signalling pathways. Both GABAA (muscimol) and GABAB (baclofen) agonists mimicked the effects of GABA in stimulating chemokinesis. Muscimol-induced motility was only blocked by GABAA antagonists (bicuculline or picrotoxin), whereas migration to baclofen was blocked by antagonists of both GABAA and GABAB (2-hydroxysaclofen) receptors. Migration to baclofen, but not muscimol, was abolished in the presence of 8-bromo cAMP or pertussis toxin, indicating that the former, but not the latter, attractant may stimulate motility via Gi/Go GTP binding proteins, and that PKA may modulate migratory responses to baclofen. Migration to GABA was partially attenuated by each of the GABA receptor antagonists. These results lead us to conclude that the natural ligand stimulates neuroblast motility via heterogeneous receptors coupled to different signalling mechanisms.

Age Factors↗

PubMed1995

Acetylcholine esterase and peripherin mRNA level decrease in wobbler mouse.

Homozygote wobbler mice develop motoneurone degeneration. Throughout development the expression of choline acetyltransferase, of trkC receptor and F3 adhesion molecule genes is similar in wobbler and wild-type spinal cord. Acetylcholinesterase mRNA level instead is decreased to about 50% with respect to wild-type values in one forth of P5 and P10 wobbler progeny, putative wr/wr individuals; at P21 its expression is equally highly reduced in known homozygotes and it is reduced to 35% of normal values in about one half of the progeny, putative heterozygotes. Thus, similarly to medium neurofilament gene over-expression, reduced acetylcholinesterase gene expression is an early molecular marker for the wobbler mutation before onset of the illness.

Acetylcholinesterase↗

PubMed1995

Investigation of the factors necessary for growth of hippocampal neurons in a defined system.

We have developed an in vitro system that combines the use of a defined medium with a chemically defined surface for the differentiation of embryonic rat hippocampal neurons. Cells were grown on silica substrates modified with two chemically distinct molecules: poly-D-lysine and an amine-containing organosilane. Cells were dissociated by mechanical or enzymatic methods and grown in serum-containing versus serum-free medium on these surfaces. Our results demonstrate that optimal survival and growth in serum-free medium occurs on the artificial surfaces. X-ray photoelectron spectroscopy (XPS) was used to analyze the surfaces both before and after cell cultures. In addition, surface properties such as elemental composition, the initial thickness of the substrate material, and the thickness of material deposited during the course of cell culture were quantified after cell removal. Taken together, the results from the cell culture and surface analysis demonstrate that the media, proteins deposited from the media onto the surface, surface composition, and properties intrinsic to neuronal membranes all interact in a complex fashion to determine whether or not the cells will adhere and survive in culture. In particular, the role of material deposited from the medium onto the culture substratum may be more important than have been previously appreciated. This system allow for the study of neuronal differentiation in a well-defined environment.

Animals↗

PubMed1995

Acetylcholine receptor aggregation at nerve-muscle contacts in mammalian cultures: induction by ventral spinal cord neurons is specific to axons.

We used a novel mammalian coculture system to study ACh receptor (AChR) redistribution and synaptic structure at nerve-muscle contacts. Ventral spinal cord (VSC) neurons were plated on cultures containing extensive myotubes but few fibroblasts. Neurite-induced redistribution of AChRs occurred within 6 hr after plating neurons and was maximal between 36-48 hr. This AChR redistribution appeared in two patterns: (1) AChR density at sites directly apposed to the neurite where neurites crossed preexisting AChR patches was sharply reduced, (2) Newly aggregated AChRs formed swaths lateral to the neurite path. VSC neurons induced more AChR aggregation than hippocampal, superior cervical ganglion and dorsal root ganglion neurons. The 43 and 58 kDa postsynaptic proteins were colocalized with AChR-enriched domains in all VSC neurite-induced aggregates whereas the colocalization of laminin was variable. Electron microscopy of regions with neurite-induced AChR aggregation showed postsynaptic membrane specializations characteristic of developing synapses and, in older cultures, features of more mature synaptic structure. Thus, the coculture system is useful for studying early stages of neuromuscular junction (NMJ) formation. Neurites in these cocultures were identified as axons or dendrites by morphological criteria and by their immunoreactivity for synaptophysin and phosphorylated heavy neurofilament subunits or for microtubule associated protein 2 (MAP2), respectively. Axons showed a 10-fold higher induction of AChR aggregation than did dendrites. Thus, at least one essential signaling molecule necessary for the induction of AChR aggregation at sites of interaction with muscle appears to be expressed in a polarized fashion in developing VSC neurons.

Animals↗

PubMed1994

Correlation of gp140trk expression and NGF-induced neuroblast chemotaxis in the embryonic rat spinal cord.

During rat embryogenesis, fibers containing nerve growth factor (NGF) are present near the target destinations of migratory spinal neuroblasts, suggesting that diffusible gradients of NGF provide signals to newly generated neurons in the developing cord. In vitro, pM concentrations of NGF induce neuroblast chemotaxis (directed migration along a chemical gradient), indicating evoked motility is mediated by high-affinity receptors. Binding of 125I-labelled NGF to fetal cord cells provides additional evidence that rat spinal neuroblasts express the high-affinity receptors; however, their presence has not been directly demonstrated. In the present study, we used immunocytochemistry to show that the high-affinity NGF receptor protein, gp140trk (trk) is detectable in embryonic spinal tissue sections and in cord dissociates. Correlation of trk expression with NGF-induced chemotaxis revealed that both the receptor protein expression and functional responses to NGF develop along a ventro-dorsal gradient that parallels the in vivo pattern of neurogenesis and migration. Analysis of the temporal changes in trk immunoreactivity demonstrated that expression of gp140trk is bimodal, possibly reflecting multiple effects of NGF during development. Chemotaxis to NGF was blocked by nM concentrations of the kinase inhibitor, K252a, suggesting that NGF stimulates motility via high-affinity receptors coupled to kinase activity. Elevated 3',5'-cyclic adenosine monophosphate (cAMP) also attenuated NGF-induced chemotaxis, presenting preliminary evidence that protein kinase A (PKA) may regulate motility responses to NGF.

Animals↗

PubMed1994

Fast presynaptic GABAA receptor-mediated Cl- conductance in cultured rat hippocampal neurones.

1. Hippocampal neurones cultured from the 18-day-old embryonic rat for 3 days to 3 weeks were recorded with Cl(-)-filled patch pipettes. Spontaneous synaptic currents, which reversed at the equilibrium potential for Cl- ions (ECl) and were blocked by the GABAA (gamma-aminobutyric acid) receptor antagonists bicuculline or picrotoxin, were recorded in every culture. At 25 degrees C and -80 mV they decayed with a time constant > or = 20 ms that invariably increased at positive potentials. After 2 weeks, 50-75% of all neurones were GABA immunoreactive. 2. In pairs-recordings, coincident synaptic currents in both cells were either spontaneous or evoked by stimulation of one cell. In the presence of tetrodotoxin and using pipettes containing lidocaine (lignocaine) N-ethyl bromide, coincident spontaneous Cl- transients still occurred in both neurones far more frequently than expected by chance. 3. Holding the potential of one neurone at a positive value reversed the synaptic transients in that cell and, in half of the cells, increased the frequency of coincident events in both cells. 4. In neurones where depolarization increased the frequency of coinciding events and all regenerative current apparent at the soma was abolished, short depolarizing pulses occasionally evoked all-or-none, pre- and postsynaptic currents with matching transmission failures and identical delays in transmission. 5. The results suggest that the same pulse of GABA simultaneously activates GABAA receptor-coupled Cl- channels on both sides of the same synaptic cleft, producing immediate auto-transmission in the absence of collaterals or interneurones.

Animals↗

PubMed1994

GABA-induced chemokinesis and NGF-induced chemotaxis of embryonic spinal cord neurons.

During CNS development, neuroblasts proliferate within germinal zones of the neuroepithelium, and then migrate to their final positions. Although many neurons are thought to migrate along processes of radial glial fibers, increasing evidence suggests environmental factors also influence nerve cell movement. Extracellular matrix molecules are thought to be involved in guiding neuronal migration, and molecules such as NGF and GABA exert trophic effects on immature neurons. The nature of the signals that initiate and direct neuroblast migration, however, is unknown. In vitro, NGF and GABA promote neurite outgrowth from cultured cells, and NGF induces axonal chemotaxis (directed migration along a chemical gradient). At earlier developmental stages, these molecules could influence neuroblast movement. Therefore, we investigated whether these molecules induce embryonic neuronal migration. Using an in vitro microchemotaxis assay, we show that rat embryonic spinal cord neurons migrate toward picomolar NGF and femtomolar GABA beginning at embryonic day 13 (E13). Cells exhibit chemotactic responses to NGF while GABA stimulates chemokinesis (increased random movement). GABA effects are mimicked by muscimol and inhibited by bicuculline and picrotoxin, suggesting GABA motility signals are mediated by GABA receptor proteins. Expression of GABA receptors by embryonic cord cells has been previously reported (Mandler et al., 1990; Walton et al., 1993). We used polymerase chain reaction analysis to demonstrate the presence of NGF and trk mRNA in E13 and E14 cord cells, indicating the cells express message for both NGF and high-affinity NGF receptors. Immunohistochemistry of E13 spinal cord sections indicates that NGF and GABA colocalize in fibers close to the target destinations of migrating neurons, suggesting diffusible gradients of these molecules provide chemoattractant signals to migratory cells. Thus, in vitro, neuroblast migration is induced by specific signaling molecules that are present in the developing spinal cord, and may stimulate migration of embryonic neurons prior to synaptogenesis.

Animals↗

PubMed1993

Tonic GABA secretion of cultured rat hippocampal neurons rapidly transformed by Zn2+ into quantal release.

Different mechanisms of neurotransmitter secretion at synapses have been ascribed to quantal, transient signals [4-9] and to continuous, tonic activity [11, 21, 25]. Quantal transmission is imputed to be the release of transmitter packets, or quanta [6], assembled and stored in vesicles present in presynaptic terminals [2,8]. We report that 300 microM Zn2+ rapidly transformed tonic Cl- conductance mediated by the transmitter gamma-aminobutyric acid (GABA) into transient synaptic-like signals. After addition of Zn2+, the size of the elementary fluctuations in the Cl- current progressively increased while randomly activated Cl- channel kinetics remained unchanged and accounted for the bi-exponential time course of average transient decay. The results suggest that Zn2+ rapidly transforms tonic GABA secretion into quantal-like transient release.

Animals↗

PubMed1993

Single-cell [Ca2+]i analysis and biochemical characterization of pinealocytes immobilized with novel attachment peptide preparation.

Single-cell image analysis of rat pinealocytes has been difficult because they do not attach readily to coated or uncoated surfaces and typically adhere in clusters to fibroblast-like cells. In the present report, a new method for the rapid attachment of rat pinealocytes is described. Cells were prepared using papain digestion and density centrifugation and then were placed on coverslips or slides coated with PepTite-2000, a preparation containing the attachment peptide sequence Arg-Gly-Asp. Cells immobilized with this preparation responded to norepinephrine treatment with an increase in cyclic AMP and melatonin production. Single-cell analysis of Fura-2-loaded cells revealed that norepinephrine increased [Ca2+]i. This development makes it possible to conduct routine single-cell image analysis and other studies of freshly isolated rat pinealocytes.

Amino Acid Sequence↗

PubMed1993

Quantitative analysis of transient GABA expression in embryonic and early postnatal rat spinal cord neurons.

GABA expression was investigated using biochemical analysis of spinal cord homogenates and immunocytochemical analysis of cells acutely dissociated from the embryonic and postnatal rat spinal cord. gamma-Aminobutyric acid (GABA) was detected by both methods as early as embryonic day 13 (E13). At E13, the percentage of neurons that were GABA+ was 0.5%. This value increased during embryogenesis, peaked during the first two postnatal weeks to just over 50%, and declined to approximately 20% by the third postnatal week emphasizing the transient nature of GABA expression. At E17 there was a pronounced, positive ventro-dorsal and rostro-caudal gradient of GABA+ cells that persisted until just before birth. At this time the gradients reversed in cervical and lumbosacral regions indicating that GABA immunoreactivity in discrete anatomical regions is also a transient phenomenon. During the embryonic period GABA immunoreactivity was diffusely distributed throughout cell bodies and proximal processes. At E21, both GABA and synaptophysin were present in the same cells. However the two antigens did not co-localize point for point. By postnatal day 21 GABA immunoreactivity appeared in puncta that co-localized entirely with puncta of synaptophysin immunoreactivity. The sizable percentage of neurons that transiently express GABA during development, and the fact that it can be detected prior to the synaptic form of glutamic acid decarboxylase (GAD65), suggest that the amino acid may play a significant role during differentiation before it functions as an inhibitory neurotransmitter.

Animals↗

PubMed1993

Quantal and subquantal GABAergic transmissions in cultured rat hippocampal neurons.

At the neuromuscular junction, spontaneous miniature excitatory synaptic currents mediated by acetylcholine are considered elementary, "quantal" transmissions. These miniature conductances can be quantitatively dichotomized into a large-mode class whose mode is the mean of a normal, bell-shaped distribution and a small-mode class whose distribution is skewed to lower values with its mode being a fraction of the large-mode class. The large-mode class constitutes the population of synaptic signals originally utilized to formulate tenets of "quantal" transmission, which have been tacitly adopted in more recent studies of fast transmission at central synapses. Large- and small-mode conductance classes of inhibitory synaptic elementary conductances mediated by GABA have now been recorded in cultured hippocampal neurons (Vautrin J, Schaffner AE, Barker JL, 1991, Neurosci Lett 138:67). Pairs of hippocampal neurons were patch-recorded at optimal signal-to-noise and, using time course analysis, two elementary fluctuations (0.1-0.3 nS and 1-2 nS) were found within synaptic conductances evoked either by presynaptic action potentials or by presynaptic terminal stimulation. These results were interpreted with a simple model that shows how different frequencies of unitary GABA release can generate either small-mode, skew-distributed conductance (0.5-3 kHz) or large-mode, normally-distributed conductances (> or = 10 kHz). Only the latter satisfies the original tenets of the classic quantal theory.

Action Potentials↗