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P Landry

Publications and source records attributed to P Landry.

At least 37 records · Page 2Linked to original sources
PubMed1988

Somatosensory cortical neurons with an identifiable electrophysiological signature.

In both cats and rats, neurons with a distinctively narrow action potential were recognized as a small subset of all neurons isolated in the somatosensory cortex. These cells were characterized by generally having a spontaneous activity, some evidence of an afferent input, a sensitivity to glutamate but a relative resistance to depolarization block induced by glutamate and a marked insensitivity to acetylcholine. Two were filled with horseradish peroxidase (HRP) and recovered. Although others have suggested that such neurons are interneurons, following reconstruction it was apparent that the two cells filled with HRP were pyramidal cells. These observations suggest that there may be more than one class of cortical neurons with thin spikes.

Action Potentials↗
PubMed1987

Morphological and electrophysiological characteristics of somatosensory thalamocortical axons studied with intra-axonal staining and recording in the cat.

The intracortical arborizations of thalamocortical fibers arising from the ventroposterolateral (VPL) nucleus in the cat were studied following intra-axonal injections of horseradish peroxidase (HRP). The axons were impaled 1.5 to 3 mm below the surface of the cortex, identified electrophysiologically by stimulating the VPL nucleus and functionally by stimulating the somatic receptive field with natural stimuli. Many of the results obtained in a previous study using similar techniques (Landry and Deschênes 1981) were confirmed by the present experiments. Fibers activated by cutaneous stimulation arborized either in area 3b or 1 but some did send branches to both areas. Also, the intracortical arborization of a rapidly adapting cutaneous afferent fiber in area 2 is described. The size and tangential extent of the fiber in area 2 are similar to those arborizing in other areas of the primary somatosensory cortex and consist of multiple patches separated by uninvaded gaps. One fiber activated by stimulation of deep tissue receptors gave rise to two bushes that arborized along a rostrocaudal axis exclusively in area 3b. Terminal boutons and varicosities were found mostly in layers VI, IV, the bottom third of III and the upper portion of V, but some fibers did send a few collateral branches to layer II and the bottom part of layer I. The results suggest that in the forebrain representation, the same modality and submodality can be recorded in more that one cytoarchitectonic area but that areas 3b, 1 and 2 should not be considered as a single functionally homogeneous area. Counts of terminals suggest that a single fiber arborizing in area 1 makes as many as 3 times the number of synapses made in area 2 or 3b. Since fibers appear to be modality and submodality specific, if convergence of modality, submodality and/or body areas occur in the cortex, then this must be preferentially, but not exclusively, done by thalamic fibers of different functions which arborize in the same cytoarchitectonic area and synapse upon a shared postsynaptic target. In the same experiments intra-axonal recordings revealed the presence of two hyperpolarizing after potentials elicited by a preceding action potential. The first after potential was associated with a decrease in excitability of the fiber and an increase in membrane resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

Bicuculline-induced alterations of response properties in functionally identified ventroposterior thalamic neurones.

Extracellular recordings of 105 neurones in the cat's somatosensory thalamus were obtained with carbon fibre-containing multibarrel micropipettes. The responses of cells to natural stimulation of cutaneous or deep structures were characterized and the responses to electrical stimulation of primary somatosensory cortex were determined. Receptive fields were mapped and the functional properties were examined before and during the microiontophoretic administration of glutamate, gamma-aminobutyric acid (GABA) and bicuculline methiodide (BMI). Modality and submodality properties of all cells tested apparently remained unchanged qualitatively, despite all pharmacological interventions. BMI lowered the response threshold of a majority of the 48 cells tested for this variable, although almost 25% responded with elevated thresholds. BMI changed the temporal properties of the responses of both thalamocortical relay neurones and of presumed interneurones. Discharges evoked by natural stimuli and by electrical stimulation of the cortex were prolonged and their pattern was altered. Decreases in the frequency of bursts of discharges were often observed with BMI, and these bursts were invariably prolonged and the interspike interval profiles were altered. Receptive field size changes were observed only in 8 of 48 neurones. For two of these, the field size decreased, while for the others there were small increases.

Action Potentials↗
PubMed1985

Identification of two populations of corticothalamic neurons in cat primary somatosensory cortex.

Extracellular and intracellular recordings of corticothalamic (CT) cells were performed in the primary somatosensory cortex of the cat. CT neurons were antidromically activated by electrically stimulating the ventroposterior lateral (VPL) nucleus of the thalamus and were classified into two types according to their physiological properties. Type 1 had no spontaneous activity and no identifiable somatic receptive field. Type 2 fired action potentials spontaneously and responded to mechanical stimulation of the skin or underlying tissues. Axonal conduction velocities were slower for type 1 cells and their cell bodies were located slightly deeper in the cortex than those of type 2 cells. Both types of CT neurons exhibited inhibitory postsynaptic potentials in response to VPL stimulation but an early synaptic excitation and rebound discharge was observed almost exclusively in type 2 cells. These results suggest that only type 2 CT cells can modify the activity of thalamic neurons through a corticothalamic feedback loop.

Action Potentials↗
PubMed1984

Interhemispheric reciprocal interaction between ventroposterolateral thalamic nuclei involving cortical relay neurons.

Extracellular and intracellular recordings were performed in the somatosensory cortex of cats anesthetized with sodium pentobarbital. Commissural neurons identified antidromically from the corpus callosum (CC) were activated synaptically at latencies compatible with a monosynaptic delay following stimulation of the thalamic ventroposterolateral (VPL) nucleus. Corticothalamic cells identified antidromically from the VPL nucleus were synaptically driven at latencies compatible with either a mono- or disynaptic delay following CC stimulation. We propose that an interhemispheric reciprocal interaction exists between VPL nuclei via cortical relay cells involving commissural and corticothalamic 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↗
PubMed1984

Functional role of GABA in cat primary somatosensory cortex: shaping receptive fields of cortical neurons.

Extracellular recordings of 209 neurons were obtained with carbon fiber-containing multibarrel micropipettes. The cells were isolated in the primary somatosensory cortex of cats anesthetized with barbiturate and classified according to the nature of their response to natural stimuli, the nature of the surrounding multiunit responses to the same stimuli, the response to thalamic stimulation, and their depth in the cortex. To study factors controlling the excitability of somatosensory neurons, their receptive fields were examined in the presence of iontophoretically administered gamma-aminobutyric acid (GABA), glutamate, and bicuculline methiodide (BMI). Even when the neurons were depolarized to perithreshold levels with glutamate, or when local inhibitory influences mediated by GABA were antagonized by BMI, the apparent specificity for one class of afferent input was maintained. Neurons responding to stimulation of either cutaneous or deep receptors maintained their modality specificity, and neurons in cutaneous rapidly adapting regions never took on slowly adapting properties. When ejected at currents that did not elicit action potentials, glutamate lowered the threshold for activation by cutaneous stimuli but did not enlarge the receptive field. With larger ejecting currents, the neurons developed an on-going discharge, but even at these higher doses, glutamate did not produce an increase in the receptive-field size. Some neurons in regions of cortex exhibiting slowly adapting multiunit responses were relatively insensitive to glutamate. These cells required four to five times more glutamate to evoke discharges than did most neurons. Other cells, previously unresponsive to somatic stimuli, could be shown to possess distinct cutaneous receptive fields when either glutamate or BMI was ejected in their vicinity. Iontophoretically administered BMI altered the firing pattern of somatosensory neurons, causing them to discharge in bursts of 3-15 impulses. BMI enlarged the receptive-field size of neurons in regions displaying rapidly adapting multiunit background discharges but not in those regions with slowly adapting multiunit discharges. This differential effect of BMI, suggesting that GABA controls receptive-field size in rapidly adapting regions, also indicates that neurons in rapidly adapting regions differ pharmacologically from those in other submodality regions. In all cortical regions, BMI blocked the poststimulus inhibitory period that normally followed thalamic stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1984

[Adenomatoid odontogenic tumor].

A case of odontogenic adenomatoid tumor is presented in which it is stressed that conservative surgical enucleation of the lesion is the treatment of choice. The clinical, radiographic and histopathologic features of this tumor are discussed. Close attention and supervision of the developing dentition allows early diagnosis and treatment thus avoiding the needless sacrifice of adjacent teeth and bone.

Adolescent↗
PubMed1982

Geometry and orientation of thalamocortical arborizations in the cat somatosensory cortex as revealed by computer reconstruction.

The geometry of the intracortical arborization of single neurons from the ventroposterolateral thalamic nucleus in cat was studied with computer reconstruction after intraaxonal injections of horseradish peroxidase in fibers whose receptive field had been identified. The terminal arbors of slowly (SA) and rapidly (RA) adapting thalamocortical neurons were often (60%) composed of two separated bushes of 300-600 microns in diameter separated by a region of about the same size containing much less terminal ramifications. The bushes were aligned mainly along the mediolateral axis of the brain. It is proposed that this structural feature underlies the RA-SA banding already described in the somatosensory areas by physiological experiments.

Afferent Pathways↗
PubMed1982

A reanalysis of the ventrolateral input in slow and fast pyramidal tract neurons of the cat motor cortex.

In deeply anesthetized cats the temporal characteristics of ventro-lateral (thalamic) excitatory postsynaptic potentials (EPSPs) induced in pyramidal tract cells were studied with an averaging technique. Stimulation of the ventrolateral thalamus induced EPSPs in all pyramidal tract neurons at latencies of 1-5 ms. It was found that there was a positive relationship between the latency and rise time of stimulation-induced EPSPs and the latency of antidromic invasions of pyramidal tract neurons. In response to two closely spaced shocks the second EPSP had the same latency and amplitude as the first one in both slow and fast pyramidal tract neurons. Moreover, the span of antidromic latencies of ventrolateral thalamic relay cells to motor cortex stimulation showed that these thalamic neurons had the necessary conduction velocities to account for the distribution EPSP latencies recorded in pyramidal tract neurons. From these electrophysiological results, it has been concluded that slow and fast pyramidal tract morphological evidence, obtained at the electron-microscopic level, supporting this conclusion. Terminal degeneration induced by a lesion in the ventrolateral thalamus was found on the apical dendrite of a slow pyramidal tract neurons that had been injected with horseradish peroxidase. It is proposed that the matching between the latencies of EPSPs evoked from the ventrolateral thalamus and the latencies of antidromic invasions of pyramidal tract neurons may reflect a matching between the conduction velocity of thalamocortical and cortico-spinal neurons and/or it may be due to the electrotonic properties of the apical dendrites.

Animals↗
PubMed1981

Intracortical arborizations and receptive fields of identified ventrobasal thalamocortical afferents to the primary somatic sensory cortex in the cat.

The intracortical arborizations of neurons from the ventroposterolateral thalamic nucleus (VPL) in the cat were studied by intraaxonal injections of horseradish peroxidase (HRP) following identification of their receptive fields. In the primary somatic sensory cortex (SI) VPL cells terminated in different cytoarchitectonic areas according to their receptive field modality. Fibers excited by deep tissue or joint rotation arborized preferentially in area 3a. Those responding tonically to cutaneous stimuli were located in the anterior part of area 3b; hairdriven cells terminated in area 3b and in the rostral pole of area 1. All fibers had a similar laminar distribution within SI. Axons terminated mostly in layers VI, iV, and the lower part of layer III. None terminated in layers I and II. Most terminal arbors were oriented along the mediolateral axis of the brain. The main arborization of a single VPL cell formed a bush of about 500 micrometers in diameter. some fibers generated two such bushes with an uninvaded region of about 300 micrometer between them. It is proposed that this patchy organization underlies in part the columnar organization of areas SI. Many VPL cells had secondary projection sites in SI. These were issued from smaller-sized collaterals and were located in a different cytoarchitectonic area than that of the main terminal plexuses. A significant number of these collaterals projected to area 4, Insufficient filling of the collaterals by HRP prevented a more complete characterization of the secondary arbors.

Afferent Pathways↗
PubMed1980

Intracortical distribution of axonal collaterals of pyramidal tract cells in the cat motor cortex.

Slow and fast pyramidal tract cells (Pt cells) from the cat motor cortex were identified antidromically and injected with horseradish peroxidase (HRP). The axonal collaterals of these cells were mapped following HRP histochemistry with benzidine di-hydrochloride. All cells, slow or fast, show a similar arrangement of their collaterals. A proximal axonal network of 0.5-0.8 mm in diameter delimits a local field of action for collaterals in layers V and VI. The tangential expansion of this local field corresponds to that of the basal dendritic domain of Pt neurons. Much longer collaterals running for millimeters in the lower gray or white matter were observed in all cells. They form at a cortical level a distal field of action for Pt neurons. Many of these long branches were traced to other regions of area 4 or toward other cytoarchitectonic areas. In one case a collateral was seen entering and dividing in area 3a. Due to limitations of the HRP technique most of these long branches could not be followed to their terminals. On the basis of the laminar distribution of Pt cell collaterals (mostly in layers V and VI) synaptic sites where recurrent excitation and inhibition are produced on Pt neurons are discussed.

Animals↗