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S T Kitai

Publications and source records attributed to S T Kitai.

At least 109 records · Page 6Linked to original sources
PubMed1983

The morphology of intracellularly labeled rat subthalamic neurons: a light microscopic analysis.

Light microscopic analysis of rat subthalamic (STH) neurons which were intracellularly labeled with horseradish peroxidase, following the acquisition of electrophysiological data, revealed the following: (1) The somata of STH neurons were polygonal or oval with occasionally a few somatic spines. Usually three or four primary dendrites arose from the soma. Dendritic trunks tapered slightly and divided into long, thin, sparsely spined branches. Dendrites of some STH neurons extended into the cerebral peduncle. (2) Reconstruction of the dendritic field was made in three different planes. In either sagittal or frontal planes, the dendritic field was usually oval and the long axis was parallel to the main axis of STH. In the horizontal plane, the dendritic field of all neurons was polygonal. (3) The axons of all the neurons analyzed originated from the soma and were traced beyond the borders of STH, thus indicating that they were projection neurons. All the parent axons bifurcated at least once. After bifurcation, one axon branch coursed dorsolaterally within the cerebral peduncle and terminated in the globus pallidus. The other branch coursed caudally or mediocaudally and arborized in the substantia nigra. Frequently, the axon branches projecting toward the globus pallidus emitted fine axon collaterals within the entopeduncular nucleus. (4) About one-half of the analyzed STH neurons had intranuclear axon collaterals. The neurons with intranuclear collaterals had a higher dendritic tips/stems ratio than neurons without intranuclear collaterals. This observation indicated that STH neurons could be divided into two groups according to their axonal morphology. (5) The axonal terminal arborization observed in all the target sites (i.e., globus pallidus, entopeduncular nucleus, STH, and substantia nigra) were formed with varicose collateral branches which also gave rise to short filaments with beaded endings. Some of these projection neurons could therefore communicate with the target neurons in the globus pallidus, substantia nigra, entopeduncular nucleus, as well as STH through their collateral system.

Animals↗
PubMed1983

Pallidal inputs to subthalamus: intracellular analysis.

Neuronal responses of the subthalamic nucleus (STH) to stimulation of the globus pallidus (GP) and the substantia nigra (SN) were studied by intracellular recording in the decorticated rat. (1) GP and SN stimulation evoked antidromic spikes in STH neurons with a mean latency of 1.2 ms and 1.1 ms, respectively. Based on the above latencies, the mean conduction velocity of the STH neurons projecting toward GP was estimated to be 2.5 m/s, and that toward SN was 1.4 m/s. Many STH neurons could be activated following stimulation of both GP and SN, indicating that single STH neurons project to two diversely distant areas. In spite of differences in conduction distance of GP and SN from STH, differences in the conduction velocities of bifurcating axons make it possible for a simultaneous arrival of impulses in the target areas to which these STH neurons project. (2) GP stimulation evoked short duration (5-24 ms) hyperpolarizing potentials which were usually followed by depolarizing potentials with durations of 10-20 ms. These potentials were tested by intracellular current applications and intracellular injections of chloride ions. The results indicated that the hyper- and depolarizing potentials were IPSPs and EPSPs respectively. These IPSPs were considered to be monosynaptic in nature since changes in the stimulus intensities of GP did not alter the latency of IPSPs. The mean latency of the IPSPs was 1.3 ms. Based on the above mean latency the mean conduction velocity of GP axons projecting to STH was estimated to be 3.8 m/s. (3) Analysis of electrical properties of STH neurons indicated that: (i) input resistance estimated by a current-voltage relationship ranged from 9 to 28 M omega; (ii) the membrane showed rectification in the hyperpolarizing direction; (iii) direct stimulation of neurons by depolarizing current pulses produced repetitive firings with frequencies up to 500 Hz. (4) Morphology of the recorded STH neurons was identified by intracellular labeling of neurons with horseradish peroxidase. Light microscopic analysis indicated that the recorded neurons were Golgi type I neurons with bifurcating axons projecting toward GP and SN.

Animals↗
PubMed1983

Origins of post synaptic potentials evoked in spiny neostriatal projection neurons by thalamic stimulation in the rat.

Stimulation of thalamic intralaminar nuclei or structures along the intrathalamic trajectory of thalamostriatal axons evoked complex EPSPs and subsequent hyperpolarizations in rat neostriatal spiny neurons identified by intracellular injection of horseradish peroxidase and/or antidromic activation from substantia nigra. In intact urethane-anesthetized rats, the initial EPSP portion of the response consisted of several components and lasted up to 75 ms. Short (1-10 ms) latency components exhibiting latency variations suggestive of a polysynaptic origin were often observed, and sometimes were the earliest components of the response. However, individual components of the excitatory response could not be clearly distinguished in most neurons and the earliest excitatory component usually appeared to be monosynaptic. After large acute aspiration lesions of ipsilateral cerebral cortex, the early polysynaptic EPSP components of thalamic-evoked EPSPs were absent or greatly attenuated. This suggested that most or all of the short latency polysynaptic EPSP components arose via a thalamo-cortico-striatal route. A short latency (1.6-4.0 ms) monosynaptic EPSP and a second excitatory component with a longer and more variable latency (8-28 ms) remained intact after acute decortication. These were not dependent upon intact corticothalamic or corticostriatal axons, since they were both still present in experiments performed as long as 4 days following ipsilateral hemidecortication. The longer latency excitatory response was shown to be polysynaptic by its latency variation with changes in stimulus intensity and frequency. This component of the response was abolished after acute thalamic hemitransections separating thalamostriatal neurons from their axons. In these experiments, stimulation of thalamostriatal axons rostral to the transection continued to evoke monosynaptic EPSPs in neostriatal spiny neurons. These EPSPs ranged from 1.8 to 3.0 ms in latency, had peak amplitudes up to 11 mV and were 20-37 ms in duration.

Animals↗
PubMed1983

Disfacilitation and long-lasting inhibition of neostriatal neurons in the rat.

Excitatory postsynaptic potentials evoked in rat neostriatal spiny projections neurons were followed by a long (100-300 ms) period of membrane hyperpolarization, followed in turn by a late depolarization. Concomitant with these changes in membrane potential were inhibition and subsequent excitation of spontaneous firing and excitatory activity evoked from substantia nigra and cerebral peduncle, but not from cortical stimulating sites. Thalamic-evoked excitatory activity was sometimes sensitive and sometimes insensitive to this inhibition, which has previously been believed to result from intrinsic inhibitory synaptic activity among neostriatal neurons. In intracellular recordings from neostriatal neurons in urethane anesthetized rats this long-lasting inhibitory response (1) exhibited alterations with intracellularly applied steady currents comparable to those of the EPSP, (2) failed to respond to intracellular injection of chloride ions, (3) was associated with either a decrease or no detectable change in the input conductance of the neurons, and (4) was abolished after lesions that interrupted polysynaptic pathways to neostriatum through intracortical and intrathalamic synaptic circuits. These findings indicate that the long lasting inhibitory portion of the responses of neostriatal neurons arises from a phasic inhibition of tonically active corticostriatal and thalamostriatal neurons and a concurrent decrease in the excitability of polysynaptic pathways converging on neostriatal neurons.

Afferent Pathways↗
PubMed1983

Rapid and simple determination of delivery after iontophoretic and pressure injections of radiolabeled tracer substances.

A fluorographic method is described using X-ray film analysis for the determination of delivery of radiolabeled tracer substances both in Agar plates and in tissue sections. This method is most useful in neuroanatomical autoradiographic studies for providing rapid identification of delivery, placement, and extent of an injection site after iontophoresis or pressure injections of radiolabeled axonal tracer substances.

Animals↗
PubMed1983

A short duration GABAergic inhibition in identified neostriatal medium spiny neurons: in vitro slice study.

Inhibition in the neostriatum was investigated in rat in vitro slice preparation using intracellular recording and labeling technique. The initial response recorded following local stimulation is a monosynaptically activated EPSP. In 17% of the neurons tested, IPSPs were observed following EPSPs evoked by local stimulation. In paired shock experiments reduction of test EPSP amplitude or action potentials occurred over interstimulus intervals (ISIs) of 3-38 msec. In some neurons, a pulse injection of depolarizing current was used to trigger an action potential which was in a paired shock, used to condition a test monosynaptically induced EPSP. Test EPSPs were shunted over ISIs less than 45 msec. Paired shock performed on the slices perfused with the medium containing GABA antagonists (e.g., bicuculline methiodide, picrotoxin, or penicillin-G) resulted invariably in potentiation of test EPSPs. Inhibition in the neostriatum in vitro is demonstrated as reduction in test amplitude in paired shock tests, by the presence of IPSPs and by the shunting of EPSPs conditioned by an action potential triggered by direct depolarization. Neurons exhibiting these forms of inhibition were intracellularly labelled with HRP and identified as medium spiny neurons. These results indicate that striatal GABAergic medium spiny neurons which are known to have an extensive axon collateral plexus play in a role in a short lasting inhibition observed in the striatum.

Animals↗
PubMed1983

Three-dimensional structure of dendritic spines in the rat neostriatum.

Dendritic spines of rat neostriatal neurons were examined by light microscopy and high voltage stereo electron microscopy (HVEM) following selective staining by intracellular microinjection of horseradish peroxidase. Conventionally prepared material also was used for quantitative analysis of dendritic spines from serial thin sections of neostriatum. Stereo electron microscopy of semithin sections from rat neostriatum fixed using a protocol designed to preserve cytoskeletal integrity was employed to examine the organization of the dendritic spine cytoplasm. Light microscopic and HVEM examination of spiny dendrites and quantitative analysis of serial thin sections from normal material revealed no distinct spine types but rather continuous and independent variation of spine head diameter, stalk diameter, and stalk length. Likewise, there was no systematic relationship between any of these spine dimensions and dendritic diameter. Spine head membrane surface area was directly related to the area of the synaptic junctional membrane of the spine head. In semithin sections, the cytoplasm of the spine contained membranous saccules of spine apparatus and a delicate cytoskeletal network composed of microfilaments and a set of finer and more variable cytoskeletal filaments. It is proposed that this cytoskeletal network together with the spine apparatus is responsible for the maintenance and alteration of spine shape and in this way controls the effectiveness of axospinous synapses.

Animals↗
PubMed1982

An intracellular HRP study of the rat globus pallidus. I. Responses and light microscopic analysis.

A study of the intracellularly recorded responses of rat globus pallidus neurons to activation of striopallidal fibers was combined with light microscopic examination of the morphology of these same neurons using intracellular horseradish peroxidase. The response to stimulation of caudate-putamen is an inhibitory postsynaptic potential with observed latencies ranging from 5.1 to 9.8 msec. These values correspond to conduction velocities of 0.4 to 0.8 m/second for striopallidal fibers. Comparison with extracellular controls shows no excitatory component to the response. All recovered and analyzed neurons (n = 11) were of the large type of pallidal neuron known from Golgi studies but the addition that two subtypes could be recognized. Large neurons located medially in the nucleus had dendritic fields with large dorsoventral extent (ca. 1 mm) when compared to their mediolateral and rostrocaudal dimensions (ca. 0.4 mm) and these neurons emitted no axon collaterals. Large neurons located laterally in the nucleus had disklike dendritic fields with both dorsoventral and rostrocaudal dimensions being on the order of 1 mm but with a minor axis of approximately 100 micrometers. The axons of these neurons possessed collaterals. As a consequence of their disk-shaped dendritic field, neurons belonging to the laterally placed subgroup and occupying the narrow (ca. 100 micrometers thick) striopallidal border zone known to receive a distinct input from neostriatum have dendrites restricted to that zone.

Afferent Pathways↗
PubMed1982

Morphology of the substantia nigra pars reticulata projection neurons intracellularly labeled with HRP.

The technique of intracellular recording and staining of the same neuron with horseradish peroxidase (HRP) was used to study the soma-dendritic and axonal morphology of nigrothalamic and nigrotectal cells in the rats. The nigrothalamic and nigrotectal cells were spread throughout the dorsoventral extent of the pars reticulata (SNR) and exhibited the same soma-dendritic and axonal features. Both populations consisted of medium-sized and large cells with extensive dendritic fields overlapping in all three directions. Their axons collateralized within the substantia nigra (SN) and in the mesencephalic tegmentum. The intrinsic collaterals were thin and branched partly within the dendritic field of a parent cell partly in remote regions of the SNR, and even in the pars compacta (SNC). The extrinsic branches involved thin arborizations in the rostroventral mesencephalic reticular substance and thicker descending and ascending collaterals. This material was supplemented by physiologically nonidentified HRP stained medium-sized and large neurons located in the SNR. The two kinds displayed the same extent and orientation of their dendrites but the branching patterns differed slightly. Proximal dendrites of all cells were coarse and smooth; thinner distal dendrites had varicosities and spinelike appendages. Some dendrites, specially those near the crus cerebri, terminated in dendritic thickets bearing many pleomorphic appendages. The orientation of dendritic fields varied with dorsoventral position of cells within the SNR. The most ventral region of the SNR contained neurons with dendrites oriented parallel to the crus cerebri and thus remained confined to the deepest stratum. The dendrites of cells in the central region of SNR were oriented mainly anteroposteriorly and ventrally, the ventral dendrites terminating in the ventralmost layer. Cells in the dorsolateral part of the SNR were characterized by the large dorsoventral extent of their dendrites which penetrated the entire thickness of SN. This variation in the arrangement of dendritic fields indicates that the SN is organized in three dorsoventral layers.

Animals↗
PubMed1982

Serotonergic excitation from dorsal raphe stimulation recorded intracellularly from rat caudate-putamen.

Similar to other afferents to rat caudate-putamen, stimulation of the dorsal raphe nucleus evokes a series of 3 responses which can be recorded intracellularly. An initial depolarization is followed by a long-lasting inhibition which is, in turn, terminated by another period of depolarization. Pharmacological manipulations demonstrate that the initial depolarizing potential is serotonergic. Depletion of serotonin by means of prior treatment with para-chlorophenylalanine leads to a reduction in the amplitude of the depolarization which can be evoked by maximal stimulation of dorsal raphe. Neither the long-lasting hyperpolarization nor the late excitation which follow the initial depolarization is affected. Replacement of serotonin in levels by injection of 5-hydroxytryptophan results in a restoration of the amplitude of the depolarizing response. The latency of the initial depolarization is, however, unchanged in serotonin-depleted animals. This together with the observation in some cells of a component of the initial depolarization resistant to para-chlorophenylalanine treatment, suggests that there is a non-serotonergic excitation which precedes that mediated by serotonin.

5-Hydroxytryptophan↗
PubMed1982

A Golgi study of rat neostriatal neurons: light microscopic analysis.

At least two types of large neurons (somatic cross-sectional areas, SA greater than 300 microns2) and five-types of medium neurons (SA between 100 and 300 microns2) were distinguished in Golgi preparations of the adult rat neostriatum. Type I large cells had aspinous somata with long, radiating, sparsely spined dendrites which were sometimes varicose distally, whereas type II large cells had spines on both somatic and dendritic surfaces. Type I medium cells had aspinous somata and proximal dendrites, but their distal dendrites were densely covered with spines. Type II medium cells had somatic spines, and their radiating dendrites were sparsely spined. Other medium cells had no somatic spines: Type III cells had poorly branched and sparsely spined dendrites. Type IV cells had profusely branched, sparsely spined dendrites. Type V cells had radiating and varicose dendrites which could also be sparsely spined. Several small neurons (SA mostly less than 100 microns2) were also found in the rat neostriatum: Some had aspinous soma with sparsely spined dendrites; others had somatic spines. Except for the type II large cells, intrinsic axon collaterals were observed for every type of neuron, indicating that they all had local integrating functions.

Animals↗
PubMed1982

Morphology and intracellular responses of an identified dorsal raphe projection neuron.

Stimulation of ventral medial tegmentum elicits an antidromic action potential and an inhibitory postsynaptic potential in dorsal raphe projection neurons. The inhibitory postsynaptic potential is not wholly due to activation of recurrent inhibitory circuits as it is not monosynaptic and its onset precedes the antidromic action potential. Light microscopic examination of horseradish peroxidase-filled projection neurons reveals a neuron type with radiating, poorly branched dendrites and terminal dendritic thickets. The axon of the exemplary neuron presented is seen to leave the nucleus but gives off a single collateral while still within the parent cell's dendritic domain.

Action Potentials↗
PubMed1982

Origins of postsynaptic potentials evoked in identified rat neostriatal neurons by stimulation in substantia nigra.

Responses of striatal neurons to stimulation in substantia nigra were recorded intracellularly in intact rats and after acute or chronic unilateral lesions of cerebral cortex or after combined cortical lesions and unilateral thalamic transections. Spiny striatal efferent neurons were identified by intracellular injection of horseradish peroxidase. In intact animals substantia nigra stimulation evoked a complex response with both excitatory and inhibitory phases. Acute unilateral decortication abolished the inhibitory phase of the response and reduced the amplitude of the initial EPSP. Thus, part of the excitatory phase and most or all of the inhibitory phase of the response result from polysynaptic routes to striatum involving cerebral cortex. The remaining EPSP observed in acute decorticate animals exhibited two components distinguished on the basis of their time courses. The latter of these was abolished by thalamic transections. The earlier component was shown to be a monosynaptic EPSP evoked by axon collaterals of cortical efferent neurons projecting to brainstem and was not observed in animals subjected to chronic decortication. After removal of all of these non-nigral response components a small long latency EPSP could be evoked by nigral stimulation. The EPSP is probably due to activation of dopaminergic nigro-striatal axons.

Animals↗
PubMed1982

Neuronal interactions in the substantia nigra pars reticulata through axon collaterals of the projection neurons. An electrophysiological and morphological study.

Substantia nigra pars reticulata (SNr) neurons, antidromically activated following stimulation of the dorsal thalamus and/or superior colliculus were intracellularly stained with HRP. Light microscopic analysis revealed that the labeled SNr neurons have axon collaterals arborizing within SNr. Axon collaterals of SNr neurons partially overlapped with the dendritic fields of their parent cells and also extended beyond the parent dendritic fields. The labeled axon terminals did not closely appose the parent cell processes, suggesting that the collaterals most likely terminate on neurons other than the parent cell. Electrical stimulation of either the thalamus or the superior colliculus induced monosynaptic and polysynaptic IPSPs in SNr cells. The polysynaptic IPSPs evoked from thalamic stimulation disappeared following hemitransection of the brain just rostral to the thalamus while the monosynaptic IPSPs remained the same. Since there are no known afferents from either thalamus or superior colliculus to SNr, we consider that these monosynaptic IPSPs are due to activation of the recurrent collaterals of SNr projection cells. The results of this study indicate that projection neurons of SNr also have an inhibitory role within the SNr.

Animals↗
PubMed1982

Morphological and physiological properties of neostriatal neurons: an intracellular horseradish peroxidase study in the rat.

The physiological and morphological (light and electron microscopic) properties of four categories of neostriatal neurons (two types of medium spiny cells and two types of aspiny cells) were analyzed using the technique of intracellular recording and intracellular labeling with horseradish peroxidase. All of the neurons in this study had excitatory responses following stimulation of the cortex and substantia nigra except for the large aspiny neuron for which only substantia nigra inputs were tested. Morphologically, these neurons differed with respect to the size and shape of their somata, density and distribution of dendritic spines and distribution of their axons and axon collaterals. Ultrastructurally, observed somatic differences included the quantity and distribution of organelles and conformation of the nuclear envelope. The axons of one type of medium spiny neuron and the large aspiny neuron were myelinated. Unmyelinated axon collaterals arose from the axons of both types of medium spiny neurons and formed synapses on the dendritic shafts and possibly with the necks of spines of other neostriatal neurons. The parent axons of the most common type of medium spiny neurons were followed to the globus pallidus and, in some cases, to the internal capsule.

Animals↗
PubMed1982

Large neostriatal neurons in the rat: an electron microscopic study of gold-toned Golgi-stained cells.

The large neurons in the rat neostriatum consist of at least two morphologically distinct types in Golgi preparations: Type I large cells had smooth somata whereas type II large cells had somatic spines. In the present study, the ultrastructural morphology of the Golgi-stained large neostriatal neurons in the rat was analyzed by the gold-toning technique. In addition, the ultrastructural morphology of type I medium (spiny) neurons was also studied for comparison. The results revealed that the type I medium neurons had unindented nucleus with small amount of organelles whereas both types of large neostriatal neurons had deeply indented nucleus and large amount of cytoplasmic organelles. The type I large neurons had much fewer synaptic contacts on the somata than the type II large neurons, the latter also had synapses on their somatic spines. Our data also support the possibility that some large neostriatal neurons may have long axons by the fact that some of these cells had myelinated axons. Our result should be very useful in interpreting morphological data obtained with techniques such as immunocytochemistry or retrograde labeling which enables only partial labeling of somata and dendrites.

Animals↗
PubMed1981

A collateral pathway to the neostriatum from corticofugal neurons of the rat sensory-motor cortex: an intracellular HRP study.

A projection from large pyramidal cells in layer V of the rat somatic sensory-motor (SSM) cortex both to the neostriatum and the brainstem was demonstrated by intracellular recording and injection of horseradish peroxidase (HRP). Layer V neurons that project to the brainstem were identified either by antidromic activation from the cerebral peduncle or by tracing the HRP-labeled axon into the internal capsule in histochemically processed sections. Intracellular responses to stimulation of the hindlimb, forelimb or mystacial pad were also examined. Five of 20 HRP-injected neurons that project to the brainstem had a fine collateral branch within the striatum. These branched corticostriatal cells respond at short latency (7--12 msec) to somatic sensory stimulation. All of the injected corticofugal neurons that had a striatal collateral were large pyramidal neurons located in layer Vb of the forelimb and head areas of SSM cortex. Branched corticofugal neurons have a rich basal dendritic field and a prominent apical dendrite that arborizes in the superficial cortical layers. Intracortical axon collaterals from the branched cells ramify in layers V and VI, and also project to the upper layers of cortex near the apical dentrite. Beyond the cortex, the main axon has no collateral branches, except for a single laterally directed branch in the neostriatum. The diameter of the striatal collateral is small (about 0.5 micrometer) compared to that of the main axon (2.0--2.5 micrometers). It is concluded that these branched cells provided a parallel input to the neostriatum and to brainstem or spinal motor centers.

Animals↗