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PubMed1978

Properties of the pyramidal tract neuron system within the precentral wrist and hand area of primate motor cortex.

1. To obtain basic anatomical data that will be useful in interpreting the results of studies of primate pyramidal tract neurons (PTNs), extracellular, single-unit recording techniques were used to determine a number of the properties of the PTN population within the electrically defined, precentral wrist zone of the monkey's motor cortex. 2. Recordings were obtained from a total of 1,375 antidromically identified PT and corticospinal tract (CST) cells. A mathematical model was then used to correct the statistics of the sample for variations in the probability of unit detection, which arise from variations in neuronal size and extracellular field dimensions. 3. Both the experimentally observed and theoretically corrected results suggest that the PT projection from this cortical zone is derived principally from slowly conducting, and presumably small to medium-sized cells (an estimated 85% of the resident PTN population). 4. Both the fast and slow cell subpopulations were found to be concentrated within cortical layer V, where they tend to congregate in small, mixed clusters of 2 to 5 neurons. Estimates of the total packing density of PTNs within layer V of this cortical zone suggest that they account for only 10-20% of the neurons within this major efferent layer. 5. 70% of the slow and 82% of the fast PT neurons within this cortical area were found to send their axons into the contralateral, lateral corticospinal tract. Thus, in futur functional studies of PTNs in this cortical area, it can be assumed that three of every four neurons will in fact influence segmental cells of one category or another directly. 6. Extensive data are also presented on the incidence of axon collateral branching from PT and CST cells to the red nucleus, the medial medullary reticular formation and the cuneate nucleus. 7. Some general implications of these findings for the design of future functional studies of anatomically identified motor cortex cell systems are then discussed.

Action Potentials↗
PubMed1978

Functional characteristics of unmyelinated fibres in the hippocampal cortex.

(1) In transverse hippocampal slices (350 micrometer thick), taken from guinea pigs initially anaesthetized with ether, intracortical afferent fibres were activated by small current pulses delivered through tungsten microelectrodes. Extracellular potentials were recorded from the zone of activated fibres in dendritic layers while intracellular recordings were made from the soma of CA1 pyramidal cells. (2) When recording was made from the same level as the stimulating cathode, the extracellular potential consisted of a diphasic deflection followed by a larger negative wave with a superimposed population spike. The negative wave corresponded to an intracellularly recorded EPSP, and is called an extracellular EPSP, whereas the initial diphasic deflection had no intracellular counterpart. (3) The initial diphasic deflection was linearly related to the size of both the intracellular and extracellular EPSP. It was not changed by removal of calcium ions from the bathing fluid, whereas all postsynaptic activity disappeared. The diphasic deflection was propagated along fibres lying parallel to the pyramidal layer with a velocity of 0.3 m/sec. It could follow short bursts of stimulation at 300 Hz. The absolute refractory period was 2.0 msec. (4) The initial diphasic deflection is interpreted as the compound action potential of the largely unmyelinated afferent fibres to the CA1 neurones.

Afferent Pathways↗
PubMed1977

The involvement of the noradrenergic system arising from the locus coeruleus in the postnatal development of the cortex in rat brain.

The effect on the developing cerebral cortex and hippocampus of removing the noradrenergic input was investigated in 3-month-old rats following unilateral electrolytic lesions performed semistereotaxically at 15 h postnatal. In 5 animals there was a significant reduction (mean = 74%) in noradrenaline in the cortex ipsilateral to the lesion, and the neuronal morphology on the two sides was studied with the Golgi technique. There was no apparent difference in the morphology of pyramidal cells in parietal cortex with respect to soma depth, apical dendritic length, number of basal dendrites or number of spines on selected dendritic regions. There was a small but significant increase in the number of dendritic branches of pyramidal cells in layers II and IV on the side ipsilateral to the lesion. No layer VI cells were identified which had retained their contact with layer I. An examination of the cell morphology of CA1 pyramidal and dentate granule cells in the hippocampus revealed no obvious differences between the two sides. These results suggest that the trophic influence of the noradrenergic innervation on the postnatal development of cells in the cerebral cortex and hippocampus, if it exists at all, is relatively minor.

Animals↗
PubMed1979

Cortical neurons projecting to the pontine nuclei in the cat. An experimental study with the horseradish peroxidase technique.

Horseradish peroxidase (HRP) injections in various portions of the cat pontine nuclei resulted in retrograde labeling of neurons in layer V of the ipsilateral cerebral cortex. Corticopontine neurons, pyramidal in type, have been found to be labeled in the entire cortex, confirming the previous findings of anterograde degeneration studies. Most (91%) of the labeled cells were 14--26 micrometer in diameter (mean 19.4 +/- 4.5 micrometer SD). Small (10--20 micrometer) and medium (20--40 micrometer) cells represent 51.5% and 47.7%, respectively, of the total number of the labeled neurons. The populations of the neurons of various sizes were almost identical in different cortical areas, and were different from the populations of corticoreticular and corticospinal cells. Corticopontine cells were well labeled in experimental cases of 3-days' survival time, confirming the topographical organization established previously by degeneration studies for this projection system. However, in cases of shorter survival time (20--27 h), the number of labeled neurons was very small. The relative paucity of labeled corticopontine neurons in the sigmoid and lateral gyri is discussed with reference to other cortical descending neurons (e.g., the corticotectal, corticoreticular and corticospinal) which have hitherto been identified morphologically as well as physiologically.

Animals↗
PubMed1979

The projection of the visual cortex on the Clare-Bishop area in the cat. A degeneration study with the electron microscope.

Following large lesions of the cat visual cortex, the distribution of degenerating terminal boutons in the Clare-Bishop area was studied electron microscopically. Degenerating boutons were found throughout the cortical layers but mostly in layer III (51% of the total number of degenerating boutons) and layer V (24%). A smaller number of boutons were found in layers II (12%) and IV (9%), and very few in layers VI (3%) and I (1%). No degenerating terminals were observed in the upper two-thirds of layer I. Seventy-six per cent of the total degenerating boutons terminated on dendritic spines, 22% on dendritic shafts, and 2% on somata. Some degenerating boutons made synaptic contacts with somata and dendrites of nonpyramidal neurons. For example, one degenerating bouton was observed in contact with an apical dendrite of a fusiform cell. Three examples of dendritic spines, with which degenerating boutons made synaptic contracts, were found to belong to spinous stallate cells. No degenerating boutons were observed making synaptic contacts with profiles that could conclusively be traced to pyramidal cell somata.

Animals↗
PubMed1978

[Quantitative examinations of stellate cells in the region of the cingulate gyrus in the rat].

Brains of three months old male rats were handled by a modified Golgi-Kopsch method. Stellate cells of the gyrus cinguli were drawn, classified into four types and analyzed quantitatively. The values of the four types were compared by means of a varianz analysis. The four types are: isodendritic stellate cells without spines (I/OS), isodendritic stellate cells with spines (AI/OS), anisodendritic stellate cells without spines (AI/OS), anisodendritic stellate cells with spines (AI/MS). Type I/OS and type AI/MS are the most contrary one. Main results are: 1. The lengths of the dendritic branches show maximum values in the 3rd order. The dendritic lengths exhibit great deviations in all the four types. The alteration of the lengths values from one to the next order is similar the basal dendritic tree of primitive pyramidal neurons. The same analogy you can find for the dendritic numbers of corresponding orders: highest numbers are in the 2nd order, in the following orders the numbers decrease permanently. Isodendritic stellate cells without spines have significantly more dendrites of the 1st order compared with the other three types. 2. The branching pattern --- revealed in the number of free dendritic endings --- shows differences between isodendritic stellate cells without spines and anisodendritic stellate cells with spines. 3. The total lengths of the dendritic branches and the lengthes of the single dendritic fields are similar in significant differences: least lengths there are in anisodendritic stellate cells with spines, they are significantly different from isodendritic stellate cells with and without spines. 4. There are differences in the values of spines and varicosities between all types which causes the possibility of classifying stellate cells according to this parameter. This is valid for spines values of the orders, spines values of single dendritic fields and for the total number of spines for one neuron. 5. Localization and extending in the layers: most stellate cells extend through several layers. The isodendritic type is preferentially localizes in layer III, the anisodendritic one in layer V.

Animals↗
PubMed1978

Intracellular recordings from the motor cortex during EEG arousal in unanaesthetized brain preparations of the cat.

1. Intracellular recordings were made from 92 neurones in the precruciate cortex of encéphale isolé and midpontine pretrigeminal preparations of the cat. 2. All but only one of these cells showed appreciable changes in the membrane potential during the transition from the cortical slow wave phase to the EEG arousal occurring spontaneously or induced by stimulating the midbrain reticular formation. Thus, 38 cells were depolarized (D-type cells), 48 cells hyperpolarized (H-type cells) and 5 cells showed an early hyperpolarization and a later depolarization (mixed type). 3. The latency of intracellular responses to reticular stimulation was shorter in the D-type cells than the H-type or mixed-type cells, and shorter for each of the D- and H-types in the cells of the superficial layers than those of the deep layers. 4. The D-type cells were distributed widely through laminae I to V, but the majority was sampled in lamina II. The H-type cells were located in laminae III-VI with the mode at the upper half of lamina III. The mixed-type cells were mostly located in laminge V and VI. 5. Antidromically identified slow pyramidal tract (PT) cells n=9) all belonged to the D-type, and fast PT cells either to the H- (n=11) or the mixed type (n=4). 6. These results suggest that the EEG arousal is a state composed of both excitatory and inhibitory responses of cortical cells which are processed from the superficial to the deep layers.

Animals↗
PubMed1975

A golgi study of the optic tectum of the tegu lizard, Tupinambis nigropunctatus.

The dendritic patterns of cells in the optic tectum of the tegu lizard, Tupinambis nigropunctatus, were analyzed with the Ramon-Moliner modification of the Golgi-Cox technique. Cell types were compared with those described by other authors in the tectum of other reptiles; particular comparisons of our results were made with the description of cell types in the chameleon (Ramń, 1896), as the latter is the most complete analysis in the literature. The periventricular gray layers 3 and 5 consist primarily of two cell types--piriform or pyramidal shaped cells and horizontal cells. Cells in the medial portion of the tectum, in an area coextensive with the bilateral spinal projection zone, possess dendrites that extend across the midline. The latter cells have either fusiform or pyramidal shaped somas. The central white zone, layer 6, contains fibers, large fusiform or pyramidal shaped cells, fusiform cells, and small horizontal cells. The central gray zone, layer 7, is composed predominately of fusiform cells which have dendrites extending to the superficial optic layers, large polygonal cells, and horizontal cells. The superficial gray and white layers, layers 8-13, contain polygonal, fusiform, stellate, and horizontal elements. Layer 14 is composed solely of afferent optic tract fibers. Several differences in the occurrence and distribution of cell types between the tegu and the other reptiles studied are noted. Additionally, the laminar distribution of retinal, tectotectal, telencephalic, and spinal projections in the tegutectum can be related to the distribution of cell types, and those cells which may be postsynaptic to specific inputs can be identified. The highly differentiated laminar structure of the reptilian optic tectum, both in regard to cell type and to afferent and efferent connections, may serve as a model for studying some functional properties of lamination common to cortical structures.

Animals↗
PubMed1979

Rehabilitation following early malnutrition in the rat: body weight, brain size, and cerebral cortex development.

Sprague-Dawley rats were malnourished by giving their mothers an 8% casein diet starting at day 10 of gestation, while controls were fed a 24% casein diet. Starting at postnatal day 20 (P20), rehabilitation of the malnourished animals was attempted by: (1) feeding both mother and young a 24% casein diet, (2) leaving the pups with their mothers until they were 40 days old, and (3) reducing the litter size from 8 to 4 pups. Observations were made on aldehyde-perfused tissue from animals 20, 40 and 70 days old. The somatosensory cortex from one hemisphere was embedded in Araldite, and that from the other side was processed fro Golgi staining. At 20 days of age the body weight of the malnourished animals was 21% that of the controls, but at 70 days it was no longer different. The anterior-posterior length, the width, and the height of the cerebral hemispheres were also significantly reduced at P20, but the differences had disappeared by P70. The thickness of area 3 of the cerebral cortex was measured in 1 micron sections. It was significantly reduced in the malnourished animals at P20, but at P40, following rehabilitation, the difference was no longer statistically significant. In tangential 1 micron sections the fraction of the volume of tissue occupied by neuropil was measured in layers II through IV. At P20 it was significantly reduced only in the upper half of layers II/III of the malnourished animals; at P40 this difference was no longer present. The mean volume of upper layer II/III cell bodies was estimated and found to be significantly reduced in the experimental animals at P20 but not at P40. In the Golgi preparations, pyramidal cells in upper layer II/III were studied. Their estimated volume, as well as the thickness of their basal dendrites, was significantly reduced in the 20 day malnourished animals, but not in the rehabilitated animals. These results show that animals severely malnourished until 20 days of age can reach normal body weight and attain cerebral hemispheres of normal size when proper nutrition is provided. The effects of malnutrition on the cerebral cortex of these animals are most apparent in upper layer II/III which, during the time of nutritional restriction, is the least developed of the cortical layers. However, when proper nutrition is provided, the cerebral cortex may attain normal morphology.

Animals↗
PubMed1975

Varieties and distribution of non-pyramidal cells in the somatic sensory cortex of the squirrel monkey.

The morphology and distribution of cells which do not conform to the conventional pyramidal pattern have been investigated in rapid Golgi, Golgi-Kopsch and Golgi-Cox preparations from cortical areas 3, 1 and 2 of juvenile and mature squirrel monkeys. The material has been analyzed qualitatively and quantitatively by means of a computer program which permits cells to be rotated so as to display their three-dimensional architecture. Nine non-pyramidal types are identified of which one is a rare giant cell and another, forming a major proportion of the cells in layer VI, is considered to be a modified form of pyramidal cell. Of the other seven types, two have horizontally distributed axons, one essentially confined to layer II, the other sending long (up to 1 mm) branches anter-posteriorly through all layers. Two types have vertical axons. One, corresponding to the "double bouquet dendritique" cell of Cajal, is mainly situated in layer II or the upper part of layer III and has a cluster of large axon branches which descend to layers IV and V and which enclose and terminate on the apical dendrites of pyramidal cells. The other type is the only non-pyramidal cell which has a relatively high concentration of dendritic spines in the adult animal. Its soma lies in layer IV and it has several strongly recurrent, thick axonal branches ascending to layer II, also enclosing the apical dendrites of pyramidal cells. The dendritic field is not truly stellate but is drawn out into a pronounced ascending tuft which ascends into layer IIIb. The cell thus resembles a "star-pyramid" of Lorente de Nó. Nevertheless such cells have many features, notably the distribution of their axons and the distribution of dendritic spines which are identical to those of the well-known "spiny stellate" cell of the visual cortex. Conversely the same features both in these cells and in the spiny stellate cells of the visual cortex (which were also eamined) differ markedly from those of small pyramidal cells with somata of similar dimensions. The three remaining non-pyramida cell types have locally ramifying axons which appear to terminate predominantly on pyramidal cells. In one, the axon forms smoothly curving arcades in layer III, in another it is intensely tangled in layer IV and in the third it is bush-like in layers II-IV. continued.

Age Factors↗