PubMed Health⌕ Search

Biomedical subjects

S T Kitai

Publications and source records attributed to S T Kitai.

At least 91 records · Page 5Linked to original sources
PubMed1986

Electrophysiology of rat thalamo-cortical relay neurons: an in vivo intracellular recording and labeling study.

Membrane properties and responses to frontal cortical stimulation were studied on electrophysiologically and morphologically identified thalamo-cortical neurons in anesthetized rats. Those neurons generated membrane responses resembling the low-threshold Ca-spike, gK(Ca) and IA that have been previously demonstrated in in vitro studies of thalamic neurons. Stimulation of the frontal cortex evoked a sequence of responses; antidromic spike, initial depolarization, long duration hyperpolarization and a short period of depolarization. The initial depolarization was considered to be a monosynaptic excitatory postsynaptic potential (EPSP) which overlapped with an inhibitory postsynaptic potential (IPSP). Major constituents of the long duration hyperpolarization were considered to be short duration IPSPs and long duration disfacilitations of cortical inputs.

Animals↗
PubMed1986

Intracellular recordings from rat nucleus accumbens neurons in vitro.

Intracellular recordings were obtained from rat nucleus accumbens (NAC) neurons in brain slice preparations. Local stimulations evoked depolarizing postsynaptic potential (DPSP). Injections of low intensity depolarizing currents decreased the amplitude of the DPSP and reversed a later portion of the DPSP into a hyperpolarizing potential. Superfusion of pentobarbital facilitated the reversal of this later portion of DPSP and bicuculline abolished this polarity reversal. These data suggested that the DPSP evoked by local stimulation consisted of a combination of an excitatory and an inhibitory postsynaptic potential, and that the latter was probably mediated by gamma-aminobutyric acid.

Animals↗
PubMed1986

The organization of divergent axonal projections from the midbrain raphe nuclei in the rat.

The intranuclear organization of divergently projecting neurons of the midbrain raphe in the rat was studied by using double retrograde axonal tracing. Paired injections of the tracers N-[acetyl-3H] WGA and horseradish peroxidase were made within known projection targets of the midbrain raphe (caudate-putamen, amygdala, hippocampus, substantia nigra, and locus coeruleus). After injections of either tracer in the aforementioned targets, retrograde labeled neurons were found mainly ipsilaterally and within midline portions of the dorsal raphe nucleus, its caudal B6 portion, and within the linear and superior central nuclei of the median raphe complex. There are discrete intranuclear distributions of raphe neurons that project to these forebrain and brainstem sites, and there is an overall rostrocaudal topographic order within the raphe with neurons projecting to the neostriatum, amygdala, and substantia nigra residing most rostrally and neurons projecting to the hippocampus and/or locus coeruleus occupying caudal portions of the B6 and superior central nuclei. Such distributions of projection neurons suggest the existence of an "encephalotopic" intranuclear organization within the raphe; that is, each central nervous system structure that receives midbrain raphe projections has its own unique representation within a topographically distinct portion of one or more of the raphe subgroups. These findings suggest an overall functional organization within the midbrain raphe nuclear complex whereby rostral portions are associated with the basal ganglia and related nuclei, and caudal portions relate to the limbic system. An intermediate representation of amygdala-projecting raphe neurons functionally conjoins the two. Collateralized neurons are found within complex zones of overlap in the topographically organized distributions of raphe neurons projecting to functionally related structures.

Amygdala↗
PubMed1986

The glutamate decarboxylase-, leucine enkephalin-, methionine enkephalin- and substance P-immunoreactive neurons in the neostriatum of the rat and cat: evidence for partial population overlap.

We have examined the populations of neurons in the neostriatum of both rat and cat that are immunoreactive for glutamate decarboxylase, [Leu]enkephalin, [Met]enkephalin and substance P. Neurons that were immunoreactive for glutamate decarboxylase made up 47% of the neurons in our samples from the rat and ranged from 39 to 49% of the neurons in the cat. Those immunoreactive for [Leu]enkephalin made up 44-49% of the neurons in rat neostriatum, and 38-47% in the cat, and those immunoreactive for [Met]enkephalin made up 36-41% of the neurons in rat and 43-49% of the neurons in the cat. Substance P-immunoreactive neurons made up 30-38% of neurons in rat and 32-39% in cat. Most substance P neurons (particularly the most darkly staining ones) were, however, clustered such that they were most numerous in the patch compartment of neostriatum; within the patches the substance P neurons comprised 59% of neurons in the rat and 55% in cat, but in the matrix substance P neurons comprised only 32% of neurons in the rat and 25% in the cat. Samples taken from sections processed for two-color double labeling immunocytochemistry revealed that 12% of neurons label for both glutamate decarboxylase and [Leu]enkephalin, 12% for both glutamate decarboxylase and [Met]enkephalin, 11-12% for both glutamate decarboxylase and substance P, and 17% for both [Met]enkephalin and substance P. These results provide evidence for chemical heterogeneity within the medium-sized neostriatal neurons, and provide the first evidence for coexistence of glutamate decarboxylase and substance P within a single neuron, and the first evidence for the coexistence for substance P and [Met]enkephalin within single neurons of the central nervous system.

Animals↗
PubMed1986

The morphology and divergent axonal organization of midbrain raphe projection neurons in the rat.

The morphology of dorsal raphe neurons was examined using intracellular injections of horseradish peroxidase (HRP) and the Golgi technique. Light microscopic examination of HRP-labeled projection neurons revealed a neuron type with radiating, poorly branched and sparsely spined dendrites and terminal dendritic thickets. The stem axon of these neurons left the nucleus ventrally but gave off a beaded collateral while still within the parent cell's dendritic domain. Somatodendritic morphology from Golgi-Kopsch stained material coincided with intracellular HRP findings and the dorsal raphe may consist of varieties of one basic morphological type of neuron. Intracellular recordings made during the HRP injection experiments confirmed that stimulation of the ventral medial tegmentum elicited an antidromic action potential and an inhibitory postsynaptic potential in dorsal raphe projection neurons. The order of axonal projections arising from the midbrain raphe nuclei was examined using a double retrograde axonal tracing technique. After paired HRP and [3H] wheat germ agglutinin injections within certain projection targets of the dorsal and median raphe neurons (caudate-putamen, amygdala, hippocampus, substantia nigra and locus coeruleus), each target structure was found to have its own unique representation within a topographically distinct portion of one or more of the raphe subgroups. Neurons projecting to the caudate-putamen and substantia nigra occupied rather rostral portions. Neurons projecting to the hippocampus and locus coeruleus resided more caudally. Neurons projecting to the amygdala were situated intermediately. Overall, rostrocaudal topography in the intranuclear distributions of raphe projection neurons resulted in the formation of complex overlap zones where collateralized neurons always resided.

Action Potentials↗
PubMed1985

Effects of 4-aminopyridine (4-AP) on rat neostriatal neurons in an in vitro slice preparation.

Effects of 4-aminopyridine (4-AP) on the rat neostriatal neuron were studied using the in vitro slice preparation. The intracellularly recorded neurons had resting membrane potentials of more than 50 mV and were capable of generating action potentials with the amplitude greater than 60 mV. Application of 4-AP in the superfusing media depolarizes the cell membrane and increases its input resistance. Local electrical stimulation induces excitatory postsynaptic potentials (EPSPs) overlapping with inhibitory postsynaptic potentials (IPSPs) in these neurons. 4-AP application enhances the amplitude and duration of the postsynaptic potentials. With application of higher concentration of 4-AP, local stimulation induces a second EPSP and a bicuculline sensitive long duration depolarization. These results indicate that 4-AP clearly has effects on local stimulation-induced postsynaptic responses of neostriatal neurons. Possible mechanisms underlying the 4-AP actions on neurotransmission in the neostriatal slice are discussed.

4-Aminopyridine↗
PubMed1985

Local stimulation induced GABAergic response in rat striatal slice preparations: intracellular recordings on QX-314 injected neurons.

Gamma-aminobutyric acid (GABA)ergic responses evoked by electrical stimulation in the neostriatal slice preparation were studied in neurons injected intracellularly with Na-conductance blocker QX-314. Local stimulation elicited depolarizing postsynaptic potentials (DPSPs) in the QX-314-injected neurons when the membrane potential was more negative than -60 mV. When DPSPs were minimized by depolarizing current injection in the QX-314-injected neuron, hyperpolarization was clearly observed following local stimulation. The maximum duration of the hyperpolarizing response to strong local stimulation was about 130 ms. The hyperpolarizing response was blocked by the addition of bicuculline or picrotoxin to the Ringer solution. Intracellular Cl- injections produced changes in the pattern of the local stimulation-induced responses; the initial depolarizing response was followed by a relatively large amplitude long duration depolarization. The polarity of the long duration depolarizing response could not be reversed by depolarizing currents which were normally sufficient to reverse the polarity of DPSPs in the neurons without Cl- injection. The application of pentobarbital enhanced the amplitude and the duration of the hyperpolarizing responses. The reversal potential of the pentobarbital-enhanced response was estimated to be -60 mV. On the basis of their reversal potential, sensitivity to injected Cl-, sensitivity to GABA blockers picrotoxin and bicuculline, and the effect of pentobarbital, these hyperpolarizing responses are shown to be GABAergic Cl-mediated inhibitory postsynaptic potentials (IPSPs).

Animals↗
PubMed1985

Projection neurons of the nucleus accumbens: an intracellular labeling study.

Projection neurons of nucleus accumbens (NAC) of the rat were identified by either antidromic activation from stimulation of midbrain ventral tegmental area-substantia nigra (VTA-SN) regions, or by tracing axons of intracellularly labeled NAC neurons into the ventral pallidum. The morphology of these NAC projection neurons were determined to be medium spiny neurons similar to those identified in the caudate-putamen.

Animals↗
PubMed1985

Active membrane properties of rat neostriatal neurons in an in vitro slice preparation.

The active membrane properties of rat neostriatal neurons have been studied in an in vitro slice preparation. All the neurons examined had resting membrane potentials of more than 50 mV and generated action potentials with amplitudes exceeding 70 mV. The morphological characteristics of the neurons identified by intracellular labeling with HRP indicated that they were medium spiny neurons. Depolarizing current injection through the recording microelectrode generated slow depolarizing potentials and repetitive action potentials with frequencies ranging from less than 10 Hz to over 300 Hz. Adaptation of action potentials was observed when long duration depolarizing current was injected. Depolarizing current injections revealed that the membrane of the striatal neuron had an anomalous rectification when the membrane potential was depolarized to the resting potential. A possible bases for the anomalous rectification might involve inactivation of K-conductance and slow inward Ca- and/or Na-currents. Local electrical stimulation evoked depolarizing postsynaptic potentials (DPSPs) followed by long-lasting small depolarizations. In a double stimulation test, a potentiation of the test DPSP was observed at interstimulus time interval of up to 80 ms. Post-tetanic potentiation of DPSPs was also seen in these neurons. Tests utilizing depolarizing current injection, intracellular Cl- injection, and Cl-conductance blocking drugs indicated that the DPSPs were composed of EPSPs and overlapping IPSPs. The nature of the long-lasting small depolarization succeeding the DPSPs could not be conclusively determined. However, available data suggest that the slow inward Ca-current may be responsible for this response.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Regenerative potentials in rat neostriatal neurons in an in vitro slice preparation.

Regenerative potentials in rat neostriatal neurons were studied using the in vitro slice preparation. Some of the recorded neurons were intracellularly labeled with HRP. All had the morphological characteristics of the medium spiny neuron. Application of TTX (10(-5) g/ml) to the superfusing medium abolished fast action potentials generated by intracellularly injected depolarizing current. Application of TEA prolonged the spike duration by decreasing its repolarizing rate without affecting rising phase. After suppression of K-conductance by TEA, depolarizing current elicited both fast and slow all or none action potentials. Combined treatment with TTX and TEA revealed two types of depolarizing potentials, a slowly rising graded depolarizing potential and slow action potential. Substitution of Ca++ with Mg++ in the medium diminished the amplitude of these potentials. They were also blocked by application of Co++ into the superfusion medium. The duration of slow action potentials were increased with increase in the intensity of current pulse, with decrease in the resting membrane potential, and with increase in the concentration of TEA in the bathing medium. In the normal Ringer solution, local stimulation elicited depolarizing postsynaptic responses (DPSPs). Large DPSPs evoked by strong local stimulation triggered one or two fast action potentials. In some neurons, large DPSPs could trigger both fast and slow action potentials. They were consistently triggered after application of TEA (1 mM) to the medium. When a relatively high concentration of TEA (4 mM) was applied to the Ringer solution, locally evoked DPSPs could trigger only slow action potentials. In double stimulation experiments, a large reduction in the amplitude and the duration of test DPSPs was observed up to about 150 ms interstimulus interval.

Animals↗
PubMed1984

Passive electrical membrane properties of rat neostriatal neurons in an in vitro slice preparation.

The passive electrical membrane properties of rat neostriatal neurons were studied in in vitro slice preparations. The data are only from neurons having stable resting membrane potentials of more than 50 mV and able to generate action potentials of amplitudes greater than 70 mV evoked by local or intracellular stimulation. All neurons measured for current-voltage relationship (n = 52) showed non-linearity of the input resistance in the hyperpolarizing direction. The mean input resistance at the resting membrane potential was 16.6 M omega. Depolarizing postsynaptic potentials evoked by local stimulation were decreased both in their amplitude and half-decay time by inward current injections exceeding more than 1 nA due to the strong membrane rectification at these levels of hyperpolarization. The mean membrane time constant (tau 0) was 5.3 ms, as measured from the semilogarithmic plots of transmembrane potential shift produced by small hyperpolarizing current pulses. In some neurons, the equalizing term (tau 1) could be determined as well and had a mean value of 1.0 ms. Measurement of (tau 0) using the strength-latency relation showed a similar value (5.0 ms) to that measured from the voltage transients. Intracellular labeling of the recorded neurons with horseradish peroxidase suggested that the recordings were obtained from medium spiny neurons.

Animals↗
PubMed1984

The ultrastructural morphology of the subthalamic-nigral axon terminals intracellularly labeled with horseradish peroxidase.

The labeled axons of neurons intracellularly injected with horseradish peroxidase (HRP) in the rat subthalamic nucleus (STH) were studied with electron microscopy. The main axons and the efferent daughter branches were all myelinated. The morphology of the intrinsic axon terminals within STH was obscured by the dark HRP reaction products, but the labeled efferent STH terminals in the substantia nigra (SN) were revealed to contain small oval vesicles and formed asymmetrical synapses with dendrites of SN neurons.

Animals↗
PubMed1984

Morphological and electrophysiological characteristics of pyramidal tract neurons in the rat.

Responses evoked in neurons of rat sensorimotor cortex upon stimulation of the pyramidal tract and ipsilateral cerebral peduncle were analysed using intracellular recording. Neurons responding antidromically to pyramidal tract stimulation (PT cells) and neurons failing to respond antidromically but exhibiting orthodromic responses were both stained by intracellular injection of horseradish peroxidase (HRP). Layer V pyramidal neurons, including those responding antidromically, exhibited prominent long lasting membrane hyperpolarizations and inhibitions of action potentials following pyramidal tract or cerebral peduncle stimulation. Upon passage of polarizing intracellular current two components were identified within the hyperpolarizing potential. A short duration initial component readily reversed with hyperpolarizing current. Frequently this earlier component overlapped a period of early excitation consisting of action potentials arising from recurrent EPSPs or large slow depolarizing potentials (SDPs). The second, much longer duration hyperpolarizing component did not reverse with passage of hyperpolarizing current and was often followed by a rebound period of depolarization and action potential generation. Both the excitatory and the inhibitory portions of these responses could be demonstrated in animals with acute thalamic transections severing the ascending lemniscal pathway to cortex. Following intracellular staining with HRP, two types of PT cells were identified by their different intracortical axonal arborizations. Most of the injected neurons had local axonal fields extending widely in layers V and VI, but with few or no collaterals extending radially toward the more superficial layers. A second type of PT cell had axon collaterals limited to a narrow zone around the dendritic field but extending radially as far as layer I. Cells of both types were observed to send axon collaterals into neostriatum. Both types of neurons exhibited morphological and physiological characteristics of slow PT cells, and we could find no cells comparable to the fast conducting PT cells observed in other species.

Animals↗
PubMed1983

An intracellular HRP study of the rat globus pallidus. II. Fine structural characteristics and synaptic connections of medially located large GP neurons.

In order to classify the presynaptic elements contacting the principle class of globus pallidus neurons, electron microscopic examination of serial sections made from a medially located large globus pallidus neuron, labeled with intracellular horseradish peroxidase, was undertaken. In addition, the use of labeled and light microscopically reconstructed material allowed us to quantitatively determine the distribution of each bouton type along the soma and dendrites. Six types of presynaptic terminals contacting the labeled cell have been recognized. Type 1 endings, the most numerous (84%), make symmetrical contacts on all portions of the cell, except spines, contain large pleomorphic, and a few large dense-core vesicles. Type 2 endings are filled with small spherical-to-ellipsoidal synaptic vesicles. They make asymmetrical contacts only with higher-order dendrites and account for 12% of synaptic contacts onto the labeled neuron. Type 3 endings are large, contain sparsely distributed large pleomorphic vesicles, and make two symmetrical synapses per bouton, one onto a spine head and the other onto the underlying dendritic shaft. They are infrequent (0.2%), being found only in association with dendritic spines. Type 4 endings contain large pleomorphic synaptic vesicles and no dense-core vesicles. They make symmetrical contacts with the short primary dendrites. Type 5 endings contain a mixture of small clear pleomorphic vesicles and numerous large dense-core vesicles. They contact only the cell body and the short primary dendrites, making up 20% of somatic synaptic contacts but less than 1% of contacts onto dendrites. Type 6 boutons contain oval and flattened synaptic vesicles and establish symmetrical contacts with higher-order dendritic branches and the cell body.

Animals↗
PubMed1983

The fine structure of the rat subthalamic nucleus: an electron microscopic study.

The normal ultrastructure of the rat subthalamic nucleus (STH) was studied. The STH consisted of tightly packed neurons distributed within a neuropil filled with large numbers of blood vessels and thinly myelinated fibers. The somata of STH neurons (diameters, D, between 10 and 25 micron) contained abundant organelles but had only a small amount of both smooth and rough endoplasmic reticulum. The nuclei had deeply invaginated nuclear envelopes and pale nucleoplasm with little heterochromatin. STH neurons often were tightly apposed without any intervening glial membranes. Similar appositions were also found between somata and dendrites, dendrites and dendrites, and dendrites and initial axon segments. Although puncta adhaerentia were often observed, no gap junctions were found on any of these membrane appositions. In the neuropil, the dendrites were mostly smooth and thin (D between 0.5 and 1 micron) with an occasional stubby spine or thin dendritic appendage. At least two types of axon terminals were identified. Type 1 terminals (D up to 1 micron) contained medium-sized round vesicles (D about 45 nm) and formed asymmetrical synapses. Type 2 terminals were often large (D up to 5 micron) and contained both round and slightly flattened vesicles (D up to 50 nm). The type 2 terminals frequently formed adherens junctions with their postsynaptic targets in addition to forming relatively symmetrical synaptic junctions. The remaining axon terminals included a small number of terminals with various morphological characteristics and possibly some tangentially sectioned type 1 and type 2 terminals. Therefore they have not been classified as individual types in this study. A quantitative analysis indicated that the type 1 terminals formed synapses mainly with thin dendrites whereas the type 2 terminals formed synapses mainly with somata and larger dendrites.

Animals↗