Biomedical subjects

A R Kriegstein

Publications and source records attributed to A R Kriegstein.

51 records · Page 3Linked to original sources

PubMed1987

Evidence for the inhibitory neurotransmitter gamma-aminobutyric acid in aspiny and sparsely spiny nonpyramidal neurons of the turtle dorsal cortex.

In order to learn more about the anatomical substrate for gamma-aminobutyric acid (GABA)-mediated inhibition in cortical structures, the intrinsic neuronal organization of turtle dorsal cortex was studied by using Golgi impregnation, immunohistochemical localization of GABA and its synthetic enzyme glutamic acid decarboxylase (GAD), and histochemical localization of the presynaptic GABA-degrading enzyme GABA-transaminase (GABA-T). GABAergic markers are found in neurons identical in morphology and distribution to Golgi-impregnated aspiny and sparsely spiny nonpyramidal neurons with locally arborizing axons and appear to label most if not all of the nonpyramidal neurons. In addition, the GABAergic markers are found in punctate structures in a distribution characteristic of presumed inhibitory terminals. The spine-laden pyramidal neurons, the principal projecting cell type in the dorsal cortex, are devoid of labelling for GABAergic markers but are surrounded by presumed GABAergic terminals. The data complement previous physiological and ultrastructural studies that implicate aspiny and sparsely spiny nonpyramidal neurons as mediators of intrinsic inhibition of pyramidal neurons in turtle cortex. The results also suggest similarities in the functional organization of intrinsic inhibitory elements in turtle and mammalian cortex.

4-Aminobutyrate Transaminase↗

PubMed1987

Cellular and synaptic physiology and epileptogenesis of developing rat neocortical neurons in vitro.

The cellular and synaptic physiology of developing rat neocortical neurons was studied using the in vitro slice method. Rats aged 1-28 days were used for analysis. During the first two postnatal weeks several sequential changes occur in membrane properties and evoked synaptic potentials. Immature neurons had higher input resistances, more linear I-V characteristics, longer membrane time constants, and slower rising and falling phases of action potentials. The developmental increase in rate of rise of the action potential suggests an increasing density of voltage-dependent Na+-channels are inserted in neuronal membranes during postnatal development. The higher input resistance of young cells might be due to their small size and differences in membrane properties. The long time constant indicates a higher specific membrane resistivity of immature neurons. Postsynaptic potentials (PSPs) recorded in young neurons were longer in latency, longer in duration, and more fragile during repetitive activation than their mature counterparts. In addition, PSPs evoked in neurons of animals less than 1 week old did not contain inhibitory postsynaptic components. These physiological features of immature neocortical neurons help explain the pattern of epileptogenesis in young animals. When neonatal cortical slices were exposed to the gamma-aminobutyric acid (GABA) antagonists penicillin or bicuculline, the frequency of occurrence of discharges resembling epileptiform depolarization shifts approached that found in mature slices only during the second postnatal week. Depolarization shifts at younger ages were less stereotyped and more sensitive to stimulus parameters than those in mature neurons.

Animals↗

PubMed1987

Glutamate neurotoxicity in cortical cell culture.

The central neurotoxicity of the excitatory amino acid neurotransmitter glutamate has been postulated to participate in the pathogenesis of the neuronal cell loss associated with several neurological disease states, but the complexity of the intact nervous system has impeded detailed analysis of the phenomenon. In the present study, glutamate neurotoxicity was studied with novel precision in dissociated cell cultures prepared from the fetal mouse neocortex. Brief exposure to glutamate was found to produce morphological changes in mature cortical neurons beginning as quickly as 90 sec after exposure, followed by widespread neuronal degeneration over the next hours. Quantitative dose-toxicity study suggested an ED50 of 50-100 microM for a 5 min exposure to glutamate. Immature cortical neurons and glia were not injured by such exposures to glutamate. Uptake processes probably do not limit GNT in culture, as the uptake inhibitor dihydrokainate did not potentiate GNT. Possibly reflecting the lack of uptake limitation, glutamate was found to be actually more potent than kainate as a neurotoxin in these cultures, a dramatic reversal of the in vivo potency rank order. Some neurons regularly survived brief glutamate exposure; these possibly glutamate-resistant neurons had electrophysiologic properties, including chemosensitivity to glutamate, that were grossly similar to those of the original population.

Animals↗

PubMed1987

Synaptic responses of cortical pyramidal neurons to light stimulation in the isolated turtle visual system.

The resistance of the turtle brain to hypoxic injury permits a unique in vitro preparation in which the organization and function of visual cortex can be explored. Intracellular recordings from cortical pyramidal neurons revealed biphasic responses to flashes of light, consisting of an early phase (50-100 msec) of concurrent inhibitory and excitatory activation, followed by a longer, inhibitory phase (250-600 msec) composed of summated Cl- -dependent postsynaptic potentials mediated by GABA. This response sequence results from the coactivation of pyramidal and GABAergic non-pyramidal cells, followed by feed-forward and possibly feed-back pyramidal cell inhibition, and is partly dependent on differences in the membrane properties of pyramidal and non-pyramidal neurons.

Action Potentials↗

PubMed1986

Monoclonal antibodies to the turtle cortex reveal neuronal subsets, antigenic cross-reactivity with the mammalian neocortex, and forebrain structures sharing a pallial derivation.

The dorsal cortex of the pond turtle (Pseudemys scripta) is a relatively simple structure consisting of two principal classes of neurons that occupy three distinct layers. Morphological, pharmacological, and physiological data suggest many similarities to the mammalian neocortex, rendering it an interesting preparation for comparative studies. We prepared monoclonal antibodies to the turtle dorsal cortex by immunizing mice with cortical tissue from adult turtles. Twelve antibodies were generated that recognize specific components of the turtle cortex. Among these, eight antibodies label only neurons and four label only ependymal glial cells. Differences in tissue staining pattern and immunoglobulin class suggest a heterogeneity of antigenic specificity among the antibodies. The staining patterns of three of our antibodies are described. TC3, like all other neuron-marking antibodies generated, labels a subset of both pyramidal and stellate cell types. It also cross-reacts with a subset of mammalian cortical neurons and labels them with a pattern similar to that observed in the turtle cortex. TC5 stains ependymal cells and their glial processes in the turtle cortex, and cross-reacts with fibrous astrocytelike processes in mammalian neocortical white matter. TC9 appears to recognize antigens of neurons sharing a pallial derivation in turtle.

Animals↗

PubMed1986

Turtle hippocampal cortex contains distinct cell types, burst-firing neurons, and an epileptogenic subfield.

The dorsal and medial telencephalon of reptiles consists of a simple trilaminar cortex. The turtle dorsal cortex has been identified as a favorable physiological preparation that may bear a phylogenetic relationship to mammalian neocortex. While anatomical studies have likened the reptilian medial cortical region to mammalian hippocampus, its physiological properties have not been explored. We therefore used intracellular and extracellular recording techniques to examine the cellular and synaptic physiology of turtle "hippocampal" or medial cortex. Turtle medial cortex contains two principal classes of neurons, pyramidal cells and stellate neurons. Recordings with Lucifer yellow CH (LY)-filled microelectrodes allowed us to correlate the physiological properties of medial cortical neurons with their cellular morphology. Pyramidal neurons were situated in a single cellular layer and had spiny apical dendrites extending into the molecular layer. These cells fired relatively long-duration action potentials (APs) and showed frequency adaptation to suprathreshold current pulse injections. Stellate cells were usually found in the subcellular and molecular layers and had aspiny dendrites. In contrast to pyramidal cells, they fired brief APs and displayed no frequency adaptation. A discrete population of cells in the dorsal portion of medial cortex (DMC) was capable of bursting endogenously or in response to synaptic activation. Bursts usually contained an underlying slow depolarization and often occurred at regular intervals. Intracellular LY injections confirmed that these cells were pyramidal in morphology. Electrical stimulation of afferent fibers revealed that pyramidal cells and stellate neurons differed in their synaptic responses. In ventral medial cortex (VMC), afferent stimulation evoked a multiphasic response in most pyramidal cells, whereas stellate cells were synaptically excited. Orthodromic activation of DMC bursting cells resulted in a powerful excitation--often a short burst--and subsequent inhibition. Stellate neurons in DMC also had a biphasic synaptic response consisting of both an early excitation and a late inhibition. Experiments using intracellular chloride (Cl-) injection or focal bicuculline application suggested that part of the inhibitory component of the pyramidal cell synaptic response was dependent on a gamma-aminobutyric acid (GABA)-mediated increase in Cl- conductance. These results correlated with our immunohistochemical studies that revealed the presence of GABAergic neurons in medial cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

Cellular physiology of the turtle visual cortex: synaptic properties and intrinsic circuitry.

We have examined the synaptic physiology of the isolated dorsal cortex of the turtle, Pseudemys scripta elegans. Electrical stimulation of afferent pathways elicited distinct, stereotyped responses in pyramidal and stellate neurons. Single shocks evoked a long-lasting barrage of excitatory postsynaptic potentials (EPSPs) in stellate cells, and led to a burst of several action potentials. Under the same circumstances, pyramidal cells displayed a small amount of short-latency excitation, but this was accompanied by a profound and prolonged set of inhibitory post-synaptic potentials (IPSPs). Synaptic excitation of the distal dendrites of pyramidal cells could evoke dendritic action potentials that were visible at the soma as small all-or-none spikes rising from the hyperpolarized level of the IPSP. There appeared to be two mechanistically different types of IPSPs in pyramidal cells. The first occurred at short latency, could produce a very large conductance increase, reversed polarity at -71 mV, and was chloride-dependent. The second was generally smaller and more protracted, had a relatively negative reversal potential of -85 to -95 mV, and was insensitive to chloride injection. Focal application of small doses of the putative inhibitory neurotransmitter gamma-aminobutyric acid (GABA) onto the somata of pyramidal cells caused a conductance increase and hyperpolarization. This response had features in common with the short-latency IPSP, including an identical reversal potential. Application of large doses of GABA to the somata of pyramidal cells or smaller doses to their dendrites elicited multiphasic or purely depolarizing responses that were at least partly due to time- or space-dependent shifts of the equilibrium potential of the response. Bicuculline methiodide, a potent GABA antagonist, depressed both the responses to GABA and the short-latency IPSP, but not the long-latency IPSP; synchronized epileptiform burst discharges also resulted. These findings, together with responses to locally applied electric shocks and the excitatory amino acid glutamate, suggested that inhibition of pyramidal cells was generated intrinsically by stellate cells, and that the cortical circuit provides pathways for both feedforward and feedback GABAergic inhibition. The data also suggest that pyramidal cells are mutually excitatory. These features are similar to the basic intrinsic circuitry in the telencephalic cortices of mammals.

Animals↗

PubMed1986

Cellular physiology of the turtle visual cortex: distinctive properties of pyramidal and stellate neurons.

The electrophysiological properties of neurons in the three-layered dorsal cortex of the turtle, Pseudemys scripta elegans, have been studied in vitro. Intracellular recordings suggested two distinct classes of neuronal behavior. Cell labeling with either Lucifer Yellow or horseradish peroxidase revealed that these behaviors correlated with the two morphological classes of cortical neurons: pyramidal cells and stellate cells. Examination of Golgi-stained neurons of dorsal cortex did not uncover any other obvious classes. Pyramidal cells had their somata in the cell layer, and extended several densely spined apical dendrites through the molecular layer to the pia. They also had spiny basilar dendrites directed through the subcellular layer toward the ependymal border. Physiologically, pyramidal cells had relatively prolonged action potentials that showed marked frequency adaptation during a sustained suprathreshold current pulse. Their most striking characteristic was a tendency to fire two discrete sizes of action potential, one small (mean = 34 mV) and of relatively low threshold, the other large (mean = 76 mV) and of higher threshold. We hypothesize that at least some small spikes arise from distal dendritic sites, whereas large spikes are somatically generated. Both spikes were tetrodotoxin-sensitive, although calcium-dependent electrogenesis occurred when potassium channels were blocked. In contrast to pyramidal cells, the somata of stellate cells were found in the molecular and subcellular zones. Their dendrites tended to be horizontally oriented and spine-free. Stellate cells had relatively brief action potentials, each of which was followed by a large but short-lasting undershoot of membrane potential. Stellate cells showed little or no spike frequency adaptation. Spike amplitudes were always relatively uniform and large (mean = 73 mV). Thus, in the dorsal cortex of turtles, the pyramidal cells, which are projection neurons, and stellate cells, which are local GABAergic inhibitory neurons, have distinctly different membrane characteristics. The physiological properties of the two types of turtle cortical neurons are very similar to their counterparts in cortical structures of the mammalian telencephalon.

Action Potentials↗

PubMed1985

The influence of dopamine on epileptiform burst activity in hippocampal pyramidal neurons.

Dopamine (DA) application to guinea pig hippocampal CA1 neurons in vitro causes hyperpolarization of the resting potential, increase in conductance, and increase in amplitude and duration of the afterhyperpolarization (AHP). Since these changes could influence repetitive firing, we performed experiments to determine whether DA-induced effects would suppress epileptogenesis in the hippocampus. Epileptiform bursts were induced by adding penicillin (3.4 mM) to the perfusion medium. Focal application of DA (40-160 microns) onto CA1 cells (n = 15) produced a hyperpolarization averaging 4.5 mV beginning in 5-20 s and lasting up to 3 min. DA also caused an increase in the amplitude and duration of slow AHPs. The frequency of spontaneous epileptiform events however was not affected. CA3 neurons (n = 6) responded to DA application with an initial 1-3 mV depolarization beginning within 5-30 s and lasting 1-2 min. In 3 cases a small hyperpolarization lasting several minutes subsequently developed. AHP duration increased 70% and amplitude increased 35% (n = 4). Along with these membrane changes the frequency of epileptiform bursting in CA3 cells slowed for 1-3 min. We added DA (10-80 microM) to the perfusion medium to see whether a significant decrease in epileptiform burst frequency might occur in the follower CA1 region if greater numbers of pacemaker CA2 and CA3 cells were exposed to DA. Spontaneous CA1 bursting was reversibly slowed, the interburst interval became variable and increased from a mean of 4 to a mean of 5-7 s (n = 6). These results suggest that DA may play a role in decreasing the incidence or frequency of epileptogenic discharges in vivo.

Animals↗

PubMed1983

Cholinergic enhancement of penicillin-induced epileptiform discharges in pyramidal neurons of the guinea pig hippocampus.

Acetylcholine (1-20 mM) was applied to guinea pig hippocampal slices bathed in normal and penicillin-containing media. Recordings in the CA 1 pyramidal cell layer in the presence of penicillin showed that acetylcholine caused a prolonged enhancement of the extracellular field potential. Intracellular recordings documented an increase in duration of cell bursting, a decrease in burst afterhyperpolarization, and a membrane depolarization lasting 1-5 min. These results suggest that the actions of acetylcholine to increase membrane excitability interact with penicillin-induced disinhibition to enhance hippocampal epileptogenesis.

Acetylcholine↗

PubMed1983

Morphological classification of rat cortical neurons in cell culture.

Neurons in "mature" (4- to 6-week-old) dissociated cell cultures of 15-day gestational age rat fetal cortex were injected with Lucifer Yellow in order to compare their detailed morphological features with those of cortical neurons in situ, and in order to determine which features of cellular morphology were dependent on local environmental conditions. Neurons were characterized by their cell form (pyramidal, multipolar, fusiform, etc.), dendritic branching pattern, spine density, and axonal projections. The neurons in culture appeared to display all the morphological features seen in cortical neurons in situ. These characteristics appeared to be independent of whether an individual neuron grew in a dense or sparse region of the culture. In addition, examination of neurons during early differentiation indicated that many of their morphological features developed as soon as the neurons could be recognized and before extensive synapse formation occurred.

Animals↗

PubMed1977

Stages in the post-hatching development of Aplysia californica.

In order to study the development of the nervous system of the marine mollusc, Aplysia californica, it is necessary objectively to assess the maturity of individual specimens. This can be done by defining stages in the life cycle. The post-hatching development can be divided into four phases: planktonic, metamorphic, juvenile, and adult. These phases can be further subdivided into 13 stages on the basis of behavioral and morphological characteristics visible in living specimens: Stage 1, newly hatched; Stage 2, eyes develop; Stage 3, the larval heart beats; Stage 4, maximum shell size is reached; Stage 5, the propodium develops; Stage 6, red spots appear; Stage 7, the velum is shed; Stage 8, eyebrows appear; Stage 9, pink color develops; Stage 10, white spots appear; Stage 11, rhinophores grow; Stage 12, the genital groove forms; Stage 13, egg laying begins. Reconstructions from serial sections taken from specimens fixed at each of these stages reveal the sequence of formation of the major organ systems. The nervous system develops gradually. The cerebral and pedal ganglia are present at Stage 1, the optic ganglia develop at Stage 2, the abdominal, pleural, and osphradial ganglia at Stage 3, the buccal ganglia at Stage 5, and the genital ganglion at Stage 13. Because Aplysia develops gradually, it is possible to analyze the contribution which gastropod torsion makes to the different phases of the life cycle. The Aplysia embryo undergoes 120 degrees torsion prior to Stage 1. The major visceral organs, the digestive system, heart, gill, and visceral nervous system, develop sybsequently in their post-torsional positions. After metamorphosis, there is a partial de-torsion which involves only the digestive system. Torsion of the digestive system may therefore be beneficial only to the pre-metamorphic larva, and not to the postmetamorphic juvenile.

Animals↗

PubMed1977

Development of the nervous system of Aplysia californica.

The ability to grow the marine molluse Aplysia under laboratory conditions allows a detailed study of the formation of the nervous system and of the development of specific identified cells. I have found that the ganglia develop in a specific temporal order. Cerebral and pedal ganglia develop at hatching, the abdominal, pleural, and osphradial ganglia 3 weeks after hatching, and the buccal ganglia at 4 weeks. The origin of the abdominal ganglion is complex; its anlage forms at 3 weeks from three larval ganglia that fuse to form the abdominal ganglion. Individual cells cannot be distinguished from one another by their location within the ganglion or by their appearance alone until metamorphosis at 5 weeks. After metamorphosis, the identified neuron, R2, suddenly becomes recognizable because of a significant increase in its size.

Abdomen↗

PubMed1974

Metamorphosis of Aplysia californica in laboratory culture.

To utilize the advantages offered by the large identified nerve cells of the marine mollusc Aplysia californica for cellular biological studies of development, we have devised simple techniques for growing this species in the laboratory in large number with a generation time as short as nineteen weeks. We have used the cultured animals to study the life cycle from fertilized egg to reproductive adult. The major developmental and behavioral changes occur at metamorphosis, when the larvae settle on the seaweed Laurencia pacifica and the locomotor and feeding behaviors are transformed into their adult forms. We have examined the timetable for the abandonment of larval behaviors and the emergence of adult ones and found that the transition from swimming to crawling occurs first and marks the onset of metamorphosis. The change from ciliary feeding to radular feeding occurs later and signals the end of metamorphosis. Other adult behaviors, such as the reflex responses and fixed-action patterns of the mantle organs, appear after metamorphosis.

Animals↗

PubMedDate not supplied

Abnormal action-potential bursts and synchronized, GABA-mediated inhibitory potentials in an in vitro model of focal epilepsy.

Focal, freeze-induced lesions were made in isolated hemispheres of turtle cerebral cortex in vitro, permitting the investigation of epileptiform discharges in a preparation with preserved intracortical circuitry. Freeze lesions resulted in interictal discharges and occasional ictal-like events. The interictal discharges were dependent upon activation of non-NMDA excitatory amino acid receptors and were affected by but did not require NMDA receptor activation. Voltage clamp and current clamp recordings revealed abnormal bursts of low-amplitude action potentials in 36% of recorded neurons, while large, repetitive inhibitory potentials, mediated by GABAA receptors, were recorded in 90% of the neurons. Thus, prominent findings in this model include abnormalities of both excitatory and inhibitory activity. Since these changes in neuronal excitability resulted from a localized physical injury, they may resemble the changes that occur in acute posttraumatic epilepsy.

Action Potentials↗