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PubMed1984

Electrophysiological properties of in vitro hippocampal pyramidal cells from normal and staggerer mutant mice.

Electrophysiological properties of intracellularly recorded CA1 pyramidal cells from normal and staggerer mice were compared by using hippocampal slices maintained in vitro. In staggerer mice, the passive membrane properties of these neurons as well as their synaptic potentials elicited by stratum radiatum stimulation were very similar to those observed in normal mice. In control and mutant mice and in standard Krebs solution, CA1 pyramidal cells mainly fired tetrodoxin (TTX)-sensitive fast spikes but could also generate slow spikes. In both groups, replacement of calcium (Ca) by barium (Ba) or introduction of TEA in the bathing medium prolonged the repolarization of the fast spikes and suppressed the brief spike afterhyperpolarization which normally followed them, thus suggesting that both events involve fast potassium conductances. Furthermore, in both groups of animals, TEA and Ba enhanced the slow spikes and induced the appearance of prolonged depolarizations. These slow events were TTX-resistant and were abolished by the Ca channel blockers cadmium or cobalt, thus suggesting that they are Ca-dependent. On the whole, the present results indicate that the staggerer mutation which yields marked abnormalities in the bioelectrical properties of cerebellar Purkinje cells has no such effect on CA1 pyramidal cells.

Animals↗

PubMed1989

Classical conditioning reduces amplitude and duration of calcium-dependent afterhyperpolarization in rabbit hippocampal pyramidal cells.

1. The afterhyperpolarization (AHP) that follows action potentials was studied in CA1 hippocampal pyramidal cells from classically conditioned and control rabbits. Measurements of the AHP were obtained with intracellular recordings from CA1 cells within hippocampal slices. 2. The AHP of rabbit CA1 pyramidal cells was found to be accompanied by a conductance increase. The AHP was reduced by bath applications of the calcium channel blockers, cadmium and cobalt, by bath application of the cholinergic agonist, carbamylcholine chloride, and intracellular injection of the calcium chelator, ethylene glycol-bis(B-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). 3. The AHP was markedly reduced in cells from rabbits that were well-trained with the nictitating membrane conditioning procedure, as compared with cells from pseudoconditioned or naive control animals. The difference in AHP amplitudes between conditioned and control groups increased as the number of spikes elicited by the stimulation pulse increased from one to four. Both the duration (measured as the time constant of AHP decay) and amplitude of the AHP were reduced in cells from conditioned animals. 4. The reduced AHP in cells from conditioned animals remained reduced in a medium that contained 0.5 microM tetrodotoxin (TTX) and 5.0 mM tetraethylammonium chloride (TEA); the AHP following calcium spikes was measured under these conditions. Since this medium eliminated synaptic transmission elicited by Schaeffer collateral stimulation, the AHP reduction in pyramidal cells from conditioned animals was not due to a modification in synaptic properties. There were no significant differences in the mean voltage thresholds, amplitudes, or durations of calcium spikes between cells from animals in the three groups. Thus the AHP reduction appears to be due to a modification of a Ca2+ -dependent K+ conductance and was not due to a secondary effect of reductions in calcium conductances underlying the spike. 5. In medium containing TTX and TEA, the amount of injected current required to elicit a calcium spike (current threshold) was significantly greater in cells from conditioned animals than in cells from control animals. This increase in current threshold persisted in 4-aminopyridine (4-AP)-containing medium and so cannot be attributed entirely to conditioning-specific increases in the A-current. 6. The conditioning-specific AHP reduction resulted in increased excitability in cells from conditioned animals versus pseudoconditioned control animals. Cells from conditioned animals fired more spikes to trains of 100-ms depolarizing current pulses than did cells from controls.

4-Aminopyridine↗

PubMed1985

Age-related changes of pyramidal cell basal dendrites in layers III and V of human motor cortex: a quantitative Golgi study.

Age-related changes of pyramidal cell basal dendrites in layers III and V of human motor cortex (area 4) were analyzed quantitatively in Golgi-impregnated sections by Sholl's method of concentric circles (Sholl 1953). The present data suggested that basal dendrites of the pyramidal cells were decreased in number with advancing age, and that the decrease was more prominent in basal dendrites of layer V pyramidal cells than in those of layer III pyramidal cells.

Adolescent↗

PubMed1991

5-Hydroxytryptamine hyperpolarizes CA3 hippocampal pyramidal cells through an increase in potassium conductance.

The firing rate of hippocampal pyramidal cells recorded from the CA3 subfield is inhibited by 5-hydroxytryptamine (5-HT, serotonin) or by electrical stimulation of the ascending serotonergic fibers from the raphe. The mechanism of action of this inhibitory effect produced by 5-HT has not been determined. Intracellular recording techniques in the hippocampal slice preparation were used to measure the effect of 5-HT perfusion on membrane properties of CA3 pyramidal cells. In 15 out of 16 cells tested, 5-HT elicited a pronounced hyperpolarization concomitant with a decrease in membrane resistance. The hyperpolarization was not altered with either potassium chloride or potassium methylsulphate electrodes; the hyperpolarization by 5-HT was not present when electrodes were filled with cesium chloride. The reversal potential of the 5-HT mediated response was determined to be-105.5 mV in 3 mM KCl buffer using single electrode voltage clamp techniques. Based on these results we conclude that the mechanism of action of the 5-HT inhibition of CA3 hippocampal pyramidal cell excitability is due to an increase in potassium conductance.

Animals↗

PubMed1991

Effects of cholinergic agonists on two non-pyramidal cell types in rat hippocampal slices.

In the hippocampus, pyramidal cells (PCs) are not the only cell type sensitive to cholinergic stimulation. Two non-pyramidal cell types from animals as young as 8 days demonstrated clear, direct responses to application of cholinergic agonists. These cholinergic actions are excitatory, mostly blocked by muscarinic antagonists, and persist under conditions which block synaptic transmission (TTX, low Ca2+/high Mg2+). Cholinergic agonists may affect different conductances in interneurons than in PCs, sometimes resulting in rapid depolarization. Demonstration of direct excitatory cholinergic effects on inhibitory interneurons supports the view that cholinergically-evoked hyperpolarizations in PCs are due to local circuit interactions.

Acetylcholine↗

PubMed1987

Cholinomimetics induce theta rhythm and reduce hippocampal pyramidal cell excitability.

The actions of cholinomimetics and of physostigmine were tested on two parameters reflecting hippocampal activity, namely theta activity and pyramidal cell excitability. In rats pretreated with methylscopolamine and anaesthetized with urethane i.v. administration of the cholinomimetics oxotremorine and arecoline and the cholinesterase blocker physostigmine evoked theta wave activity in the hippocampus, which was blocked by scopolamine. Spectral analysis demonstrated that the frequency of the theta waves induced was dose-related, ranging from about 3 Hz to between 5 and 6 Hz. theta Activity could not be induced by arecoline in animals with large septal lesions. Pyramidal cell excitability is known to be increased by endogenous acetylcholine released from cholinergic fibres. In the present study, however, i.v. injections of oxotremorine, arecoline and physostigmine in doses that induce theta activity diminished the excitability of CA1 pyramidal cells in a dose-dependent manner, as judged by the reduction in the amplitude of the population spike and the dendritic epsp. These depressant effects were attenuated by scopolamine but not by methylscopolamine. The depressant effect of arecoline was attenuated in rats with extensive lesions in the medial septal area. The present findings demonstrate that exogenously administered cholinomimetics only partly mimic the action of endogenous acetylcholine in the hippocampus. The central sites of action of exogenously administered cholinomimetics for mediation of theta activity and alteration of pyramidal cell excitability remain to be elucidated.

Acetylcholinesterase↗

PubMed1991

Depression of purine induced inhibition during NMDA receptor mediated activation of hippocampal pyramidal cells--an iontophoretic study.

Single pyramidal cells in the rat hippocampal slice preparation were stimulated by iontophoretic application of excitatory amino acids and acetylcholine. The purine adenosine 5'-monophosphate (AMP), applied iontophoretically, readily depressed acetylcholine stimulated cell firing, was less effective on quisqualic acid stimulated cells and virtually ineffective during stimulation by N-methyl-D,L-aspartate (NMA). Inhibition could be restored if the AMP ejection current was increased 3-fold. In contrast, the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) exerted a comparable level of inhibition under all 3 neuroexcitants. These data support previously published results which suggest that purine mediated inhibition may be reduced during NMDA receptor channel activation. This may have important implications for the action of adenosine during seizures and ischaemic events as well as neuronal phenomena such as long term potentiation.

Acetylcholine↗

PubMed1976

[Dendroarchitectonic study of the pyramidal cells of the medial frontal cortex of the macaca].

A comparative study of "normal" and "improperly oriented" pyramidal cells has been performed in the medial frontal lobe cortex of the monkey (Macacus Irus). The comparison of the observed number of topological types for each group of dendrites shows that the apical dendrites of each type of cells have a different growth. The apical dendrites of the normal pyramidal cells grow by monochotomous branching on random segments and have much more spines on the first order segments, the apical dendrites of the improperly oriented pyramidal cells grow by branching on pendant arcs (terminal growth model), and have fewer spines. The functional signification of these differences remains actually obscure.

Animals↗

PubMed1981

Mechanisms of norepinephrine actions on hippocampal pyramidal cells in vitro.

Responses of pyramidal cells to topical application of norepinephrine (NE) were studied by intracellular recording in hippocampal slices in vitro. Norepinephrine hyperpolarized CA1 cells. Simultaneously, there was a decreased response to constant hyperpolarizing and depolarizing current pulses. The number of spikes evoked by constant depolarizing pulses was reduced. Spontaneous activity, when present, was reduced or abolished. The response to depolarizing current pulses was reduced more than the response to hyperpolarizing current pulses. The reduction of the depolarizing response was minimal for the first 6-8 msec of the pulse, whereafter it increased. The effects persisted after blocking synaptic transmission with low calcium-high magnesium concentrations in the incubation fluid. We conclude that the hyperpolarization is most likely due to a conductance increase. The mechanism behind the reduced response to depolarizing current pulses is discussed.

Animals↗

PubMedDate not supplied

Hippocampal pyramidal cell loss in human status epilepticus.

A pilot case-control quantitative study of the hippocampus in patients with severe status epilepticus was performed to identify specific patterns of pyramidal cell loss. Pyramidal cell densities from five patients who died following status epilepticus were compared with five normal controls and five controls matched for age, hypoxia/ischemia, previous epilepsy, and alcohol abuse. Neuronal densities were greatest in the normal control group and least in patients with status epilepticus. Significant reductions were identified in Sommer's sector (prosubiculum and CA1) as well as in CA3 when compared to normal controls.

Age Factors↗

PubMed1989

Localization of tetrodotoxin-sensitive field potentials of CA1 pyramidal cells in the rat hippocampus.

1. The role of tetrodotoxin (TTX)-sensitive (Na+) channels in the generation of antidromic and orthodromic field potentials of the CA1 pyramidal cell population was examined by local application of TTX in the in vitro rat hippocampal slice preparation. 2. The sensitivity of alvear (antidromic) and stratum oriens (SO)-evoked potentials to TTX application (10-100 microM) was tested in stratum pyramidale and over the entire extent of pyramidal cell apical dendrites in stratum radiatum. Stratum radiatum (SR)-evoked potentials were examined at the level of pyramidal cell bodies and over the proximal 200 microns of the apical dendritic region. 3. Pressure application of TTX confined to stratum pyramidale or regions of stratum radiatum selectively blocked the negative component of antidromic and SO-evoked population discharge in the cell body layer and over the initial 200 microns of stratum radiatum. 4. SR stimulation evoked a complex field potential in the proximal stratum radiatum (less than 150 microns) composed of at least three components: 1) A short-duration (approximately 3 ms) negativity of shorter peak latency than the population spike recorded simultaneously in stratum pyramidale. This potential was highly sensitive to TTX and appeared to be instrumental in the generation of the cell body population response. 2) A long-duration negativity (approximately 20 ms) evoked at stimulation strengths that were subthreshold for both the short-duration negativity in proximal stratum radiatum and the cell body population spike. Although apparently less sensitive to TTX, this potential was reduced in amplitude with repeated TTX application; and 3) a slow (approximately 12 ms) positive-going potential that was only observed after eliminating all TTX-sensitive conductance mechanisms in the proximal stratum radiatum. 5. The latency difference between the SR-evoked short-duration negativity of proximal stratum radiatum and the population spike in stratum pyramidale decreased or reversed during the course of multiple discharge induced by the addition of bicuculline or picrotoxin (5-10 microM) to the perfusate. 6. These data indicate the presence of TTX-sensitive presumed Na+ channels over the initial 200 microns of pyramidal cell apical dendrites capable of supporting active conduction of population discharge evoked by antidromic or SO stimulation. The sensitivity of SR-evoked potentials to TTX suggests that a synaptic potential generated in the distal apical dendrites is capable of triggering both a slow active depolarization and a fast spike-like discharge in the proximal apical dendritic region.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1988

Buspirone attenuates synaptic activation of hippocampal pyramidal cells.

The actions of 5-hydroxytryptamine (5-HT) and buspirone, an anxiolytic agent that displays high and selective affinity for 5-HT1A receptor sites, on synaptic activation of hippocampal CA1 pyramidal cells were studied in vitro. Whereas 5-HT application leads to a rapid hyperpolarization and decreased input resistance in pyramidal cells, buspirone has no measurable effects on membrane potential and input resistance. However, unlike 5-HT, buspirone application leads to a gradual and reversible reduction in excitatory postsynaptic potentials (EPSPs) elicited by stimulation of afferents in the stratum radiatum. Concurrent with this attenuation of the EPSP, buspirone decreases the excitability of afferent fibers in the stratum radiatum as evidenced by conduction slowing, increased refractory period, and decreased ability to generate repetitive impulses. 5-HT has no measurable effect on the afferent fibers. The attenuation of the EPSPs and the decrease in afferent fiber excitability appear to be independent of 5-HT receptors as 5-HT neither shares nor antagonizes the effects of buspirone. Thus, both 5-HT and buspirone can contribute to reduced spike activity in pyramidal cells, but they do so via different mechanisms: 5-HT hyperpolarizes pyramidal cells whereas buspirone attenuates their synaptic activation, possibly via action on the presynaptic fibers in the stratum radiatum.

Afferent Pathways↗

PubMed1976

[Quantitative studies on the dendritic spine distribution on the lamina-5 pyramidal cells in the anterior gyrus cinguli of the rat].

At three months old male rats the spine-distribution of the main dendrite and of the apical and basal dendrites of 36 lamina V-pyramidal cells of the regio cingularis (anterior cingulate cortex) was analyzed (from every subregion -- neocortex, mesoneocortex, mesoarchicortex -- 12 neurons). 1. The limbic pyramidal neurons show the same spine-distribution at their main dendrite as neocortical neurons of other brain regions and other mammal-species do: after an initial segment with poor spines only there follows an rapid increase of the spine-values with an amount at a range of 150 mum from the perikaryon, thereafter spine-values decrease continuously and slowly up the branching into the terminal bundle. 2. Basal and apical lateral dendrites however show another spine-distribution: basally there is an increase of the spine-values from the 1st up to the 3rd order, followed by a decrease at subsequent orders. Apically spine-density decreases from the 1st up to the 4th order. 3. The spine-distribution at the parts of the dendritic tree is discussed as a general biological sign of pyramidal cells. 4. The total number of spines of lamina V-pyramidal cells in the regio cingularis (anterior cingulate cortex) is less than those in the sensomotoric cortex and in the hippocampus, which corresponds with the lower differentiation of the limbic cortex. 5. By means of a variance-analysis the pyramidal spine-values of the three subregions were compared: concerning the total number of spines of a pyramidal neuron there are significant differences between the three subregions; the values are in the ratio of 3 to 2 to 1 (Regio praecentralis agranularis, 2461; mesoneocortex, 1664; mesoarchicortex, 800). The significantly least spine-density of all parts of the dendritic tree you can find in lamina V-pyramidal cells of the mesoarchicortex. 6. The equality of the basal and apical spine-values in the mesoneocortex is due to less specialization of these neurons. 7. The spine-values for a single dendritic field (EDF) show the differences between the limbic subregions clearly: there are significant differences between the three subregions concerning not only the number of spines but also the spine-densities apically and basally.

Animals↗

PubMed1975

Network analysis of dendritic fields of pyramidal cells in neocortex and Purkinje cells in the cerebellum of the rat.

The connectivity within the dendritic array of Purkinje cells in the cerebellum and pyramidal cells of the neocortex of the rat, stained by the Golgi-Cox method, has been quantified by the method of network analysis. Connectivity was characterized either by applying the system of Strahler ordering, which assigns a relative order of magnitude to each branch of the arborescence or by the identification of unique topological branching patterns within the tree. The former method has been used to define the entire dendritic array of the Purkinje cell and the apical system of neocortical pyramids. It has been shown that the relation between the numbers of branches of successive Strahler order in Purkinje cells form an inverse geometric series in which the highest order is unity and the ratio between successive orders approximates to 3. On the other hand, the apical dendrites of neocortical pyramids exhibit two bifurcation ratios, i.e. a ratio of 3 between low orders and a ratio of 4 between higher orders. A computer simulation technique was used to generate networks of a size comparable with the Purkinje cell networks and grown according to two hypotheses namely, a 'terminal growth model' in which additional segments were added randomly to the terminal branches only and a 'segmental growth model' in which additional segments were added randomly to any branch within the array including terminal branches. Subsequent ordering of the simulated trees revealed that the relation between the numbers of successive orders for networks generated according to the 'segmental model' tended towards an inverse geometric series with a ratio of 4 and that generated according to the 'terminal model' tended towards a ratio of 3. This result showed that the dendritic tree of Purkinje cells grow in a manner indistinguishable from a system adding branches to random terminal segments and that neocortical apical dendrites add their collateral branches to random segments of the apical shaft but that the collateral branches themselves grow by random terminal branching. The possibility that such conclusions may be influenced by loss of branches incurred by either a failure of impregnation, by sectioning, or by environmental influences was investigated by means of a computer technique...

Animals↗

PubMed1976

[Studies on the spine density in lamina V pyramidal cells of the visual cortex in young and subadult rats after dark-rearing and destruction of the dorsal nucleus in the lateral geniculate body].

1. Dark reared 50 days old rats have a significantly diminuished number of spines at the apical dendrite of the lamina-V-pyramidal cells in the visual cortex. 2. Likewise we could ascertain a significant diminution of spines after destroying the upsilateral Cgld. The topistical distribution of spine density differs in both investigated series. 3. The spine diminution at the apical dendrites of lamina-V-pyramidal cells differs in this way: pyramidal cells with thick apical dendrites show a weaker spine diminution than the pyramidal cells with thin apical dendrites. 4. Some topistical problems concerning specific afferents in the visual cortex are discussed.

Age Factors↗

PubMed1990

Temporal profile of interneuron and pyramidal cell protein synthesis in rat hippocampus following cerebral ischemia.

Cellular protein synthesis was investigated in the rat hippocampus 2-100 h following 20 min of cerebral ischemia induced by four-vessel occlusion. [3H]-Phenylalanine was retrogradely infused through the external carotid artery for 30 min. This method limited the distribution of the tracer to one hemisphere and required 1/50th of the tracer amount used for intravenous tracer infusion. Cellular [3H]phenylalanine incorporation was examined in hematoxyline and eosin-stained sections coated with nuclear emulsion. A score for relative protein synthesis was estimated from counts of silver grains across neuron somata with undamaged morphology. Shortly after ischemia a generalized complete arrest of protein synthesis was observed. In CA1 pyramidal cells, this was followed by a transient incomplete regeneration (9-20 h) and later (46-100 h) persistent cessation of protein synthesis. By contrast protein synthesis in interneurons, CA3c pyramidal cells and granule cells recovered to preischemic levels 9-100 h after ischemia, as did the CA3ab pyramidal cells 46-100 h postischemia. Moreover, eosinophilic cell changes were seen in hilar and CA3c neurons at all postischemic stages and in CA1 pyramidal cells 46-72 h after ischemia. [3H]Phenylalanine incorporation was absent in neurons demonstrating eosinophilic cell changes. From the rapid recovery of protein synthesis in hippocampal interneurons, we conclude that changes in interneuronal protein synthesis per se are not involved in the pathophysiology of the delayed ischemic CA1 pyramidal cell death.

Animals↗

PubMed1990

Dendritic action potentials activated by NMDA receptor-mediated EPSPs in CA1 hippocampal pyramidal cells.

Intradendritic recordings were obtained in rat CA1 hippocampal pyramidal cells. Repetitive stimulation produced substantial short-term potentiation of the dendritic excitatory postsynaptic potential (EPSP) which was partly attributable to activation of n-methyl-D-aspartate receptors. Accompanying the potentiated synaptic response were Na(+)-mediated spikes which appeared to originate at multiple sites in the dendritic arbor. These discrete dendritic action potentials are rarely distinguishable in somatic recordings, but may contribute to the subthreshold response at the pyramidal cell body. In addition, dendritic spikes may interact with other voltage-dependent dendritic conductances.

2-Amino-5-phosphonovalerate↗

PubMed1988

Glutamate decarboxylase-immunoreactive neurons in the aging rat hippocampus are more resistant to ischemia than CA1 pyramidal cells.

Glutamate decarboxylase (GAD)-immunoreactive, supposedly GABAergic inhibitory, neurons in various fields of the rat hippocampus and pyramidal cells in area CA1 were quantified 1 week after transient cerebral ischemia by 4-vessel occlusion. Whereas the number of CA1 pyramidal cells in Toluidine blue-stained semithin sections were found reduced by 50% when compared with controls there was no loss of GAD-immunoreactive cells in vibratome sections of hippocampus proper and fascia dentata. These data suggest that GABAergic hippocampal neurons are more resistant to ischemia than CA1 pyramidal cells.

Aging↗