Large Pyramidal Neurons Of Layer Research Articles

Long-Term Consequences of Perinatal Hypoxia and Their Possible Pharmacological Correction: Responses of Neocortical Nerve Cells and Synapses

The morphological characteristics of neurons and synaptic contacts in the neocortex following acute perinatal hypoxia and subsequent use of Saliphene were studied in later ontogeny (days 80–90) in 28 Wistar rats. Controls consisted of intact animals of the same age. Light and electron microscopy studies were performed, along with immunocytochemical detection of synaptophysin and morphometric studies. These investigations showed that hypoxia in the perinatal period leads to structural rearrangements in neocortical neurons in adult animals. Degeneration of some large pyramidal neurons in layer V was seen, with decreases in the density of synaptic contacts (almost twofold) in the deep layers of the neocortex. These impairments were probably due to modifications to the developmental program for structures and interneuronal contacts. The data obtained here provide evidence that the Russian formulation “Saliphene” has protective actions on neurons and their differentiation and synaptogenesis after hypoxia. This suggests that this formulation is clinically effective and provides grounds for continuing studies in this direction.

I-wave origin and modulation

The human motor cortex can be activated by transcranial magnetic stimulation (TMS) evoking a high-frequency repetitive discharge of corticospinal neurones. The exact physiologic mechanisms producing the corticospinal activity still remain unclear because of the complexity of the interactions between the currents induced in the brain and the circuits of cerebral cortex, composed of multiple excitatory and inhibitory neurons and axons of different size, location, orientation and function. The aim of current paper is to evaluate whether the main characteristics of the activity evoked by single- and paired-pulse and repetitive TMS, can be accounted by the interaction of the induced currents in the brain with the key anatomic features of a simple cortical circuit composed of the superficial population of excitatory pyramidal neurons of layers II and III, the large pyramidal neurons in layer V, and the inhibitory GABA cells. This circuit represents the minimum architecture necessary for capturing the most essential cortical input-output operations of neocortex. The interaction between the induced currents in the brain and this simple model of cortical circuitry might explain the characteristics and nature of the repetitive discharge evoked by TMS, including its regular and rhythmic nature and its dose-dependency and pharmacologic modulation. The integrative properties of the circuit also provide a good framework for the interpretation of the changes in the cortical output produced by paired and repetitive TMS.

Distribution of neurofilament proteins in the lateral geniculate nucleus, primary visual cortex, and area MT of adult Cebus monkeys

We investigated the distribution pattern of SMI-32-immunopositive cells in the lateral geniculate nucleus (LGN) and in the primary (V1) and middle temporal (MT) cortical visual areas of the adult New World monkey Cebus apella. In the LGN, the reaction for SMI-32 labeled cells in both the magnocellular (M) and parvocellular (P) layers. However, the cellular label was heavier in M layers, which also showed a more intense labeling in the neuropil. In V1, the reaction showed a lamination pattern, with the heaviest labeling occurring in layer 4B and upper layer 6 (layers that project to area MT). Area MT shows a dense band of labeled neuropil and large pyramidal neurons in layer 3, large darkly labeled but less densely packed neurons in layer 5, and a population of small, lightly labeled cells in layer 6. These results resemble those found in other New and Old World monkeys, which suggest that the preferential labeling of projection neurons associated with fast-conducting pathways to the extrastriate dorsal stream is a common characteristic of simian primates. In the superficial layers of V1 in Cebus monkeys, however, SMI-32-labeled neurons are found in both cytochrome oxidase blobs and interblob regions. In this aspect, our results in Cebus are similar to those found in the Old World monkey Macaca and different from those described for squirrel monkey, a smaller New World Monkey. In Cebus, as well as in Macaca, there is no correlation between SMI-32 distribution and the blob pattern.

A voltage-gated potassium channel, Kv3.1b, is expressed by a subpopulation of large pyramidal neurons in layer 5 of the macaque monkey cortex

In the cerebral cortex, the voltage-gated potassium channel, Kv3.1b, a splicing variant of Kv3.1, has been associated with fast-firing interneurons. Here, we report strong expression of Kv3.1b-protein and mRNA in both Betz and Meynert pyramidal cells of the monkey, as shown by immunohistochemistry and in situ hybridization. Strong expression also occurs in large pyramidal neurons in layer 5 of several cortical areas. In addition, most of these Betz and layer 5 pyramids, and about 10% of the labeled Meynert cells weakly co-expressed the calcium binding protein parvalbumin. Electron microscopy shows that the expression of Kv3.1b is localized to the somal and proximal dendritic cytoplasmic membrane, as expected for a channel protein. These results suggest that some large pyramidal neurons may constitute a functional subpopulation, with a distinctive distribution of voltage-gated potassium channels capable of influencing their repetitive firing properties.

Modulation of Excitability by α-Dendrotoxin-Sensitive Potassium Channels in Neocortical Pyramidal Neurons

Many neurons transduce synaptic inputs into action potentials (APs) according to rules that reflect their intrinsic membrane properties. Voltage-gated potassium channels, being numerous and diverse constituents of neuronal membrane, are important participants in neuronal excitability and thus in synaptic integration. Here we address the role of dendrotoxin-sensitive "D-type" potassium channels in the excitability of large pyramidal neurons in layer 5 of the rat neocortex. Low concentrations of 4-aminopyridine or alpha-dendrotoxin (alpha-DTX) dramatically increased excitability: the firing threshold for action potentials was hyperpolarized by 4-8 mV, and the firing frequency during a 1-sec-long 500 pA somatic current step was doubled. In nucleated outside-out patches pulled from the soma, alpha-DTX reversibly blocked a slowly inactivating potassium current that comprised approximately 6% of the total. This current first turned on at voltages just hyperpolarized to the threshold for spiking and activated steeply with depolarization. By assaying alpha-DTX-sensitive current in outside-out patches pulled from the axon and primary apical dendrite, it was found that this current was concentrated near the soma. We conclude that alpha-DTX-sensitive channels are present on large layer 5 pyramidal neurons at relatively low density, but their strategic location close to the site of action potential initiation in the axon may ensure that they have a disproportionate effect on neuronal excitability. Modulation of this class of channel would generate a powerful upregulation or downregulation of neuronal output after the integration of synaptic inputs.

Localization of α1B-adrenergic receptor in female rat brain regions involved in stress and neuroendocrine function

Activation of α 1-adrenergic receptors has been linked to the control of blood pressure, neuroendocrine secretion, reproductive behavior and mood. The present study describes the distribution of α 1B-adrenergic receptor immunoreactivity in female rat brain regions involved in stress and neuroendocrine function. The pattern of immunolabeling seen resembles that obtained in previous in situ hybridization studies. Several hypothalamic areas that control pituitary function showed intense fiber and/or cell immunolabeling, including the paraventricular nucleus of the hypothalamus, the supraoptic nucleus, and the median eminence. Some regions such as the arcuate nucleus, the median eminence, and dorsal hypothalamus exhibit intense labeling of axonal varicosities, while other regions exhibit only perikarya immunolabeling. α 1B-adrenergic receptor immunoreactivity was also observed in large pyramidal neurons of layer V of the cerebral cortex, the frontal cortex showing a particularly strong immunoreactivity. Virtually all thalamic regions were labeled, especially the lateral and ventral areas. In addition, labeled cells were present in hippocampus, the medial septum, the horizontal and vertical limbs of the diagonal band of Broca, and the caudate putamen. Finally, some midbrain and hindbrain regions important for motor function were immunoreactive. Because ligands specific for α 1-adrenergic receptor subtypes are not available, the present immunocytochemical study not only addresses the subcellular and regional distribution of α 1B-adrenergic receptors but may also provide clues about receptor subtype-specific function.

Cellular localization of adenosine A1 receptors in rat forebrain: Immunohistochemical analysis using adenosine A1 receptor-specific monoclonal antibody

Monoclonal antibodies were generated against the adenosine A1 receptor (A1R) purified from rat brain. In immunoblot analyses of purified or partially purified A1R preparations from rat brain, these antibodies recognized a solitary band, the size of which corresponded to that expected for A1R. These antibodies recognized not only the native form of A1R but also the deglycosylated form of A1R. Immunocytochemical analysis of Chinese hamster ovarian cells that were transfected stably with rat A1R cDNA showed that their cell bodies were stained intensely by these antibodies, whereas nontransfected Chinese hamster ovarian cells were not. These antibodies detected the A1R naturally present in the DDT(1)( )MF-2 smooth muscle cells. One of these antibodies (the 511CA antibody) was then used to examine the immunohistochemical distribution of A1Rs in rat forebrain. On light microscopy, A1R immunoreactivity was observed in the cerebral cortex, septum, basal ganglia, hippocampal formation, and thalamus. However, in some regions of the forebrain, regional differences in staining intensity were found as follows: In the cerebral cortex, the strongest immunoreactivity was found in the large pyramidal neurons of layer V. This immunoreactivity was detected in the pyramidal cell bodies, dendrites, and axon initial segments. In the hippocampus, A1R immunoreactivity was detected mainly in the stratum pyramidale. The pyramidal cells in fields CA2-CA3 of the hippocampus were stained more intensely or more clearly than those in field CA1 or the dentate gyrus. More intense A1R immunoreactivity of the apical dendrites was detected in field CA2 compared with other hippocampal fields and the dentate gyrus. Many interneurons of the hippocampus were stained by the 511CA antibody. The subcellular distribution of A1Rs in the forebrain was examined by using a digital deconvolution system and electron microscopy. In the cerebral cortex, the view obtained by removing the background haze by deconvolution revealed that the immunofluoresence-labeled A1Rs were distributed on the surfaces of the cell bodies and dendrites and in the cytoplasm of layer V neurons as small spots. In field CA1, immunoreactivity was detected in the areas surrounding pyramidal cells. Electron microscopy revealed the presence of A1R-immunoreactive products in both the presynaptic terminals and the postsynaptic structures. The specific cellular distribution of A1Rs is consistent with the physiological premise that endogeneously released adenosine exerts control over the excitability of forebrain neurons at both presynaptic and postsynaptic sites through A1Rs.

Pyramidal cells in primary auditory cortex project to cochlear nucleus in rat

Recent work has demonstrated that the auditory cortex in rat sends direct projections to the auditory nuclei of the brainstem, including the cochlear nucleus and superior olive. To determine the cortical origin of the projections to cochlear nucleus, Fast Blue, a retrograde fluorescent tracer, was injected into the cochlear nucleus. Labeled cells in the forebrain were then studied with light microscopy and mapped. The projection was found to originate from large pyramidal neurons in layer V of primary auditory cortex. The projection was predominantly ipsilateral, and no labeled neurons were found in other cortical areas. These data imply that primary auditory cortex exerts influence over ascending auditory information at the earliest stages of the central auditory system.

Effects of prenatal nicotine exposure on the morphogenesis of somatosensory cortex

Human reports as well as animal studies have recorded accelerated motor activity, learning, and memory deficits in offsprings of mothers exposed to nicotine during pregnancy. Morphological correlation of these neurobehavioural defects has not been done to date. Here, the cerebral cortex has been evaluated after prenatal nicotine exposure. Groups of pregnant rats were injected IP with nicotine at 2.5 mg/kg/day dosage from gestational day (GD) 6 to term. Morphology of the somatosensory cortex was analysed and compared with that of the control group up to postnatal day (PND) 40. A significant reduction in body weight and brain weight on PND 10 and 20, respectively was observed in nicotine exposed group as compared to age matched controls. Morphometric analysis of the somatosensory cortex showed a reduction in cortical thickness up to PND 20 and decreased cell size at PND 10, 20, and 40 in nicotine-exposed brains. Neuronal density of Layer 5 of somatosensory cortex was greater at PND 20 and 40 in the experimental group. Golgi staining of large pyramidal neurons of Layer 5 showed significantly decreased dendritic branching and increased dendritic spine density in the experimental group at all ages studied. Irregular arrangement of cisternae of rough endoplasmic reticulum, paucity of free ribosomes, and frequent cytoplasmic vacuoles were noted by electron microscopy in many neurons up to PND 40. A large number of electron dense cells were observed in nicotine exposed brains at all the time intervals studied. The morphological features of somatosensory cortex observed after prenatal nicotine administration suggest that the drug delays neuronal maturation and affects intracytoplasmic membrane systems.

Distribution of neurons expressing substance P receptor messenger RNA in immature and adult cat visual cortex

We have investigated the expression of messenger RNA (mRNA) encoding substance P receptor (SPR) in the visual cortex of adult cats and 17-day-old kittens, using in situ hybridization histochemistry with two digoxigenin-labeled oligodeoxynucleotides complementary to the SPR mRNA. In the adult cortex, a subset of large pyramidal neurons of layer V and layer III is heavily labeled. Other, mainly pyramidal neurons in layers II, III and V are less intensely labeled, but most neurons in these layers appear unlabeled. Neurons in layer IV and VI, and in the white matter do not show hybridization signals above background levels. In the 17-day-old kitten, SPR mRNA-expressing cells are confined to layer V and to the upper white matter (subplate zone), whereas supragranular neurons do not yet contain SPR mRNA. A few neurons in layer VI display moderate labeling. Astrocytes, identified with anti-glial fibrillary acid protein antibodies, did not express detectable levels of SPR mRNA in both adult and kitten visual cortex. These results indicate that SPR mRNA expression is transient in neurons of the white matter, and is developmentally regulated in supragranular layers. In addition, the localization of SPR mRNA in a subset of pyramidal cells suggests that substance P modulates the excitability of certain projection neurons which are the origin of extrinsic connections.

Delayed changes of chromogranin A immunoreactivity (CgA ir) in human striate cortex during postnatal development

The changes in chromogranin A expression in the human striate cortex from birth till 67 years were studied by immunohistochemical method in 18 autopsied patients. The first chromogranin A immunoreactivity (CgA ir) was identified at birth in layer IV (especially IVc) mainly as fine nerve terminals. By 6 months, the first perikaryal reactivity was noted in the large pyramidal neurons of layer V. The smaller neurons in layers IV, V and VI showed a progressive increase in CgA ir from 15 months to about 17 years. At approximately 9 years, immunoreactivity began to be noted in supragranular neurons in layers II and III. The final laminar distribution of CgA ir seemed to be attained at about 25 years with relatively little change thereafter. The CgA ir in the striate cortex demonstrates a prolonged period of developmental changes, lasting from birth to about 25 years.

Connections between pyramidal neurons in layer 5 of cat visual cortex (area 17).

The structural features of two physiologically-characterised pyramidal neurons (PC1 and PC2) closely situated in layer 5b in the visual cortex (area 17) of a single cat were studied using a combination of electrophysiological and anatomical techniques. Both PC1 and PC2 had exceptionally large somata (30-40 microns in diameter). On the basis of this and other morphological features cell PC1 was classified as a Meynert cell. PC1 possessed a very large (2.75 degrees X 4.50 degrees) binocularly driven standard complex receptive field. PC2 was also binocularly driven with a small, B-type receptive field. Both cells had the same preference for the direction and orientation of visual stimuli. PC1 and PC2 could be antidromically activated from stimulating electrodes positioned above the dorsal lateral geniculate nucleus with a response latency indicating that these cells probably innervated the visual tectum or pretectum. In addition to corticoefferent axons, the two neurons possessed extensive intracortical axon arbors that ramified extensively in layers 5 and 6 of the medial and lateral banks of the lateral gyrus in area 17. Axon collaterals from both PC1 and PC2 also innervated a small common target region in area 18. A total of 313 boutons from the axonal arbors of PC1 and PC2 were examined in the electron microscope. All of the identified synaptic junctions were found to establish Gray type 1 asymmetrical contacts. The combined ultrastructural data for both neurons indicated that 80% of boutons were onto dendritic spine heads, with 14%, 6%, and 1% onto small-, medium-, and large-calibre dendritic shafts, respectively. The spectrum of postsynaptic targets showed little variation with respect to lamina, distance from somata, or cortical area. Other large pyramidal neurons in layer 5 and spiny neurons in layer 6 were identified as receiving synaptic input from either PC1 or PC2. Using a computer graphics system, rotations of the bouton distributions revealed the existence of a clustered innervation of layers 5 and 6 in areas 17 and 18 derived from the two identified neurons. The bouton distributions strongly resembled the tangential pattern described previously for the functional slab-like organisation of the cortex. The results provide a morphological basis for the clustered intrinsic connectivity of pyramidal cells in layers 5 and 6 of the cat visual cortex. Furthermore, the results indicate the widespread excitatory influence of large pyramidal neurons on other cells projecting subcortically to sites dealing with visually guided behavior.

Structural and functional changes in neurons and glia in the sensomotor cortex in experimental neurosis.

1. In rabbits with experimental neurosis metabolic disturbances are found in the sensomotor cortex, and are reflected in a 26% increase in size of the nuclei of the large pyramidal neurons in layer V, and the appearance of pale and dark cells with stained basophilic substance, and acidophilic cells characteristic of a state of hypoxia. 2. The number of neurons with two, three, and four perineuronal satellites is increased; the number of neurons without satellites or with only one satellite is reduced. The reaction of the perineuronal glia is productive in character: The mean number of perineuronal satellites is increased by 26%; a considerable number of branched oligodendrogliocytes appeared. As a result of hypoxia the amount of total glia is reduced. 3. The development of extensive connections of all types of glia with neurons and blood vessels indicates active involvement of the glial cells in the process of compensation and repair. The distinctive features of response of the perineuronal, free glia, and the microglia confirm the view that the degree of participation of these cells in neuronal metabolism differs. 4. Histological and hypoxic changes found in neurons and neuroglia are evidence of the complex structural and metabolic changes taking place in vascular, neuronal, and neuroglial cells of the sensomotor cortex in this form of experimental pathology. The results can be used to further the study of mechanisms of compensation of disturbances of higher nervous activity and of pathogenetically based treatment.

RELATION OF DISCHARGE FREQUENCY TO CONDUCTION VELOCITY IN PYRAMIDAL TRACT NEURONS.

RELATION OF DISCHARGE FREQUENCY TO CONDUCTION VELOCITY IN PYRAMIDAL TRACT NEURONS.