Stellate Cells In Layer Research Articles

Development of full-length Trk B-immunoreactive structures in the hippocampal formation of the macaque monkey.

Distribution and morphological changes of cells containing the signal transducing neurotrophin receptor, full-length Trk B (fl-Trk B), were investigated in the hippocampal formation of the macaque monkey between embryonic day 140 and the adult stage. Western blot analysis showed that one main protein band, which migrated at 141 kDa, was detected in both the embryonic and adult hippocampal formation. In the pyramidal cells in CA1 and CA3 subfields, the subiculum, and the entorhinal cortex, fl-Trk B-immunoreactive dendrites were observable in the embryonic stage. In contrast, in the granule cells of the dentate gyrus, few dendrites were immunoreactive during embryonic and early developmental stages. This difference may be due to the later growth of the granule cells of the dentate gyrus. The existence of fl-Trk B immunoreactivity in the cell body and dendrites in the embryonic hippocampal neurons, suggests that BDNF and/or NT4/5 act on the hippocampal cells by autocrine/paracrine mechanisms. In the entorhinal cortex, fl-Trk B immunoreactivity became localized in the stellate cells in layer II and the pyramidal cells in layers III, V and VI in adulthood. This indicates that BDNF and/or NT4/5 are important for the maintenance of the projection neurons in the entorhinal cortex at the adult stage. The strongest fl-Trk B immunoreactivity in the hippocampal neurons occurred at postnatal month 4, corresponding to the period of greatest synapse production in the monkey hippocampus, suggesting that BDNF and/or NT4/5 with fl-Trk B may play a role in synapse formation in the monkey hippocampus.

Electroresponsiveness of medial entorhinal cortex layer III neurons in vitro

The entorhinal cortex funnels sensory information from the entire cortical mantle into the hippocampal formation via the perforant path. A major component of this pathway originates from the stellate cells in layer II and terminates on the dentate granule cells to activate the hippocampal trisynaptic circuit. In addition, there is also a significant, albeit less characterized, component of the perforant path that originates in entorhinal layer III pyramidal cells and terminates directly in area CA1. As a step in understanding the functional role of this monosynaptic component of the perforant path, we undertook the electrophysiological characterization of entorhinal layer III neurons in an in vitro rat brain slice preparation using intracellular recording techniques with sharp micropipettes and under current-clamp conditions. Cells were also intracellularly injected with biocytin to assess their pyramidal cell morphology. Layer III pyramidal cells did not display either the rhythmic subthreshold membrane potential oscillations nor spike-cluster discharge that characterizes the spiny stellate cells from layer II. In contrast, layer III pyramidal cells displayed a robust tendency towards spontaneous activity in the form of regular tonic discharge. Analysis of the voltage–current relations also demonstrated, in these neurons, a rather linear membrane voltage behaviour in the subthreshold range with the exception of pronounced inward rectification in the depolarizing direction. Depolarizing inward rectification was unaffected by Ca 2+-conductance block but was abolished by voltage-gated Na +-conductance block with tetrodotoxin, suggesting that a persistent Na +-conductance provides much of the inward current sustaining tonic discharge. In addition, in the presence of tetrodotoxin, an intermediate threshold (∼−50 mV) Ca 2+-dependent rebound potential was also observed which could constitute another pacemaker mechanism. A high-threshold Ca 2+-conductance was also found to contribute to the action potential as judged by the decrease in spike duration towards the peak observed during Ca 2+-conductance block. On the other hand, Ca 2+-conductance block increased spike duration at the base and abolished the monophasic spike afterhyperpolarization. Analysis of the input–output relations revealed firing properties similar to those of regularly spiking neocortical cells. Current–pulse driven spike trains displayed moderate adaptation and were followed by a Ca 2+-dependent slow afterhyperpolarization. In summary, the intrinsic electroresponsiveness of entorhinal layer III pyramidal cells suggest that these neurons may perform a rather high-fidelity transfer function of incoming neocortical sensory information directly to the CA1 hippocampal subfield. The pronounced excitability of layer III cells, due to both Na + and Ca 2+ conductances, may also be related to their tendency towards degeneration in epilepsy.

Distribution and synaptic localization of immunocytochemically identified NMDA receptor subunit proteins in sensory-motor and visual cortices of monkey and human

NMDA receptors are composed of multiple receptor subunit proteins, of which NMDAR1 appears to be a critical component for normal receptor function (Nakanishi, 1992). In this study, quantitative immunocytochemical methods were used at the light and electron microscopic levels to localize NMDAR1 subunits in the primary motor (M1) and somatic sensory (S1) cortex of monkeys, and in the primary visual cortices (V1) of monkey and human. Three principal features of NMDAR1 subunit organization were examined in detail in the monkey cortex: (1) the laminar and cellular distribution patterns, relying in part on double-labeling paradigms with the calcium-binding proteins parvalbumin (PV) and calretinin (CR) as markers for discrete subpopulations of GABAergic interneurons; (2) the codistribution of NMDAR1 subunits with non-NMDA ionotropic receptor subunits; (3) a quantitative assessment of the percentages of asymmetrical synapses in layers II/III, IV, and V/VI that were NMDAR1 immunoreactive. In monkey M1, S1, and V1, NMDAR 1 immunoreactivity was present in all layers, localized primarily to large numbers of pyramidal cell somata and proximal apical dendrites, to presumptive spiny stellate cells in layer IV of V1, and to the vast majority (approximately 80-90%) of PV-immunoreactive cells. By contrast, NMDAR1 immunoreactivity was present in only a very small percentage of the CR-immunoreactive cells (approximately 6-9%). Colocalization with non-NMDA receptor subunits showed that all cells (100%) that contained GluR2/3 subunits were also NMDAR1 immunoreactive. In addition, the complete codistribution of GluR5/6/7 subunits with GluR2/3 subunits suggests, indirectly, that all GluR5/6/7-immunoreactive cells are also NMDAR1 immunoreactive. The laminar and cellular distribution patterns of immunostaining in human V1 were very similar to those in monkey V1. Electron microscopy of monkey sections confirmed an extensive dendritic and synaptic localization of NMDAR1 subunits. Labeling of synapses was present on asymmetrical postsynaptic densities associated with both dendritic shafts and spines. In supragranular layers of V1, a greater percentage of asymmetrical synapses were NMDAR1 immunopositive (44%) in comparison to layer IVC beta (34%) or deep layers (19%). In contrast, in area 3b of S1, the percentage of labeled synapses was greatest in layer IV (45%) in comparison to superficial (26%) and deep (37%) layers, while in M1, the percentages of labeled synapses were similar between superficial (46%) and deep (40%) layers. Taken together, these data indicate that NMDAR1-immunoreactive cells in neocortex represent a morphologically, functionally, and neurochemically heterogeneous population.(ABSTRACT TRUNCATED AT 400 WORDS)

Innervation of cat visual areas 17 and 18 by physiologically identified X‐ and Y‐ type thalamic afferents. II. Identification of postsynaptic targets by GABA immunocytochemistry and Golgi impregnation

The precise location of physiologically identified specific afferent input on the different types of cell in the visual cortex and the identification of the neurotransmitters of these cells are essential to a better understanding of the first stage of cortical processing. A combination of anatomical, neurochemical, and physiological methods was used to identify the cortical neurones that receive synaptic input from X- and Y-type afferents, which are thought to originate from cells of the lateral geniculate nucleus. One method relied on chance contacts made between single physiologically characterised axons, which had been injected with horseradish peroxidase (HRP), and the processes of cells impregnated by the Golgi method. These experiments revealed that both X and Y axons formed synapses on the dendrites of spiny stellate cells in layer 4. Y axons in both areas 17 and 18 established multiple synaptic contacts on basal dendrites of layer 3 pyramidal cells. One X axon contacted the apical dendrite of a layer 5 pyramidal cell and one Y axon contacted the dendrite of a large cell with smooth dendrites in layer 3. The maximum number of synapses made between one axon and a single postsynaptic cell was eight, although in most cases it was only one. It was concluded that one axon only provides a small fraction of the geniculate afferent input to an individual cell. A second method revealed that the somata in layer 4 in synaptic contact with the HRP-filled axon terminals were GABA-immunoreactive, and therefore might be involved in inhibitory processes. From light microscopic data it was found that somata receiving contacts from X axons in area 17 were significantly smaller (average diameter 15 microns) than those contacted by the Y axons in areas 17 and 18 (average diameter 24 microns). Somatic contacts were extremely rare in layer 6. These data show that the X and Y afferents may activate separate subsets of inhibitory neurones.

Stellate cells differentiate successively in the cat sensorimotor cortex during early postnatal ontogeny

Golgi and Golgi-Kopsch techniques were used to investigate maturation of stellate and pyramidal cells and development of stellate-pyramidal connections in kittens of the following ages: 2, 7, 14, 21, 28 and 34 days. By two weeks, stellate cells in layer V have become mature. Layer III stellate cells with vertical axon ramifications are differentiated by 2–3 weeks of life and in 3-week-olds the horizontal spread of axon collaterals amounts to 1300 μm. Layer II stellate cells which are poorly developed in newborns acquire the greatest number of collaterals and a complex axon branching pattern by 4 weeks of age.

Retrograde transport of gamma-amino[3H]butyric acid reveals specific interlaminar connections in the striate cortex of monkey.

Several lines of evidence suggest that gamma-aminobutyric acid is an inhibitory neurotransmitter in the cerebral cortex. To study the intracortical projection of neurons that selectively accumulate this amino acid, we injected radioactive gamma-aminobutyric acid into the upper layers of the striate cortex of monkeys along tracks at an oblique angle to the pia. Sections from the injected area were then processed by a combination of autoradiography and Golgi impregnation to reveal the distribution of labeled neurons and their morphological characteristics. Labeled neurons always occurred around the injection site in each layer. In addition, a consistent radial pattern of perikaryal labeling was observed in layers IVc-VI below the injection track in layers I-IVa. The closer the injection track was to the pia the deeper the peak density of labeled cells appeared. After injection in layers IVa and the lower part of III, the highest number of labeled neurons was in layer IVc; after injection in the upper part of layer III, most labeled neurons were in layer V; and, after injection in layers I and II, the proportion of labeled neurons increased in the lower part of layer V and in layer VI. All these neurons in the infragranular layers are presumably labeled by retrograde axonal transport via the labeled fiber bundles that extended from upper to lower layers. Thirty-four Golgi-stained neurons of various types were also examined for retrograde labeling. Two were labeled, and both were aspiny stellate cells in layer V. The arrangement of these putative GABAergic neurones, with axons that ascend from lower to upper layers in a regular pattern and arborize locally, would enable them to mediate inhibition within cortical columns and between neighboring columns.

Cytoplasmic inclusions of neurons in the monkey visual cortex (area 19)

Several unusual neuronal inclusions were found in certain cells of the rhesus monkey visual cortex (Area 19): 1. Filamentous bodies, present in the small stellate cells of layer IV, globoid, 0.3-0.6 mum in diameter, consisting of fine 50 A filaments in a hexagonal meshwork. These are often associated with the labyrinthine bodies. 2. Labyrinthine bodies found exclusively in the small stellate cells of layer IV, including certain neurons with dispersed ribosomes. These are 0.4-0.7 mum in diameter and consist of 900 A wide tubes which interconnect with one another. The walls of these tubes are continuous and made up of a sheet or honeycomb lacework of small hexagonal 150 A subunits. 3. This inclusion, an aggregate 0.3-0.7 mum in size, consists of small membrane-bounded vesicles with a single dense granule associated with other non-membrane bound small dense droplets. The inclusions are always associated with the maturing face of the Golgi complex of certain layer IV pyramidal cells; as such, they may be an unusual product of the Golgi apparatus. These observations were confirmed by examination of stereo pairs of electron micrographs. Speculations are made with regard to possible functions for these inclusions.

Synaptic termination of afferents from the ventrolateral nucleus of the thalamus in the cat motor cortex. A light and electron microscopy study.

AbstractThe synaptic termination in the cat motor cortex of afferents from the ventrolateral nucleus of the thalamus (VL) has been studied with experimental light and electron microscopic methods. The distribution of normal synapses on motor cortex pyramidal, stellate, and Betz cells was also examined.Synapses in the motor cortex can be classified into two general types. The first and most prominent type contains flat vesicles, lacks a compact postsynaptic density, and corresponds to Colonnier's ('68) symmetrical synapse.Stellate neurons receive synapses of both types on their cell bodies and proximal dendritic shafts, while pyramidal cells have only symmetrical synapses at these sites. The dendritic spines of both stellate and pyramidal cells are contacted by predominantly asymmetrical synapses. Betz cells, like smaller pyramidal neurons, receive only symmetrical synapses on their cell bodies. The proximal portions of the Betz cells apical dendrites, however, receive both asymmetrical and symmetrical synapses.Following VL lesions, degenerating synapses were mainly found in three cortical layers: the upper third of layer I (18%), layer III (66%), and layer VI (13%). Degenerating synapses were not seen in the lower two‐thirds of layer I or in layer II, and were only rarely seen in layer V (3%).Ninety‐one percent of the VL synapses were found on spines and 8% on stellate‐type dendritic shafts. Stellate cell bodies rarely received VL synapses (1%) and none occurred on pyramidal or Betz cell bodies and their proximal dendrites. A VL synapse within layer III was found on two dendritic spines of a Betz cell apical dendrite. Thus, part of the VL input to layer III synapses on the processes of both motor cortex output neurons (Betz cells in layer V) and cortical interneurons (stellate cells in layer III).