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M Deschênes

Publications and source records attributed to M Deschênes.

At least 37 records · Page 2Linked to original sources
PubMed1999

Predictors of clinical response to transjugular intrahepatic portosystemic shunt (TIPS) in cirrhotic patients with refractory ascites.

OBJECTIVE: Transjugular intrahepatic portosystemic shunt (TIPS) is used increasingly as a treatment for refractory ascites. The aim of the present study was to determine the prognostic value of different parameters in predicting a favorable evolution following TIPS in a cohort of 53 cirrhotic patients without organic renal disease and with refractory ascites. METHODS: Patients were classified as good responders if they survived more than 6 months, without severe chronic hepatic encephalopathy and with good control of ascites. The prognostic value for a good outcome was evaluated using age, creatinine clearance, plasma renin activity, plasma aldosterone, and Pugh score. RESULTS: Good control of ascites was obtained in 90%. The cumulative survival rate was 54% at 6 months, 48% at 1 yr, and 39% at 2 yr. The vast majority of patients died of complications of hepatic insufficiency. Severe chronic hepatic encephalopathy developed in 26%. Overall, a good clinical response was observed in 47%. Creatinine clearance was identified as the only pre-TIPS factor to be significantly and independently associated with a good clinical response to TIPS for refractory ascites. A good clinical response was observed in 57% of patients with a creatinine clearance >36 ml/min compared to 9% of those with a clearance <36 ml/min (p < 0.01). This cutoff point in creatinine clearance had a sensitivity of 96% and a specificity of 36%; positive predictive and negative predictive values were 57% and 90%, respectively. CONCLUSIONS: TIPS might be useful for the treatment of refractory ascites in cirrhotic patients without severe renal function impairment. However, the TIPS usefulness still has to be demonstrated compared to large volume paracentesis or Leveen shunt. In patients with poor renal function or with liver failure after TIPS, liver transplantation should be considered.

Adult↗
PubMed1999

Risk factors for the development of bacterial infections in hospitalized patients with cirrhosis.

OBJECTIVE: Bacterial infection is a frequent and severe complication of cirrhosis. Cirrhotic patients admitted for gastrointestinal bleeding are at high risk of such a complication and have been targeted in trials of antibiotic prophylaxis. However, it has not been shown that these patients are at a higher risk than cirrhotic patients hospitalized for other reasons. This prospective study was performed to assess the risk of bacterial infection in unselected hospitalized cirrhotic patients and to evaluate possible risk factors for this complication. METHODS: One hundred-forty hospitalized cirrhotic patients without clinical evidence of infection at the time of initial presentation were followed-up prospectively for manifestations of infection. RESULTS: Twenty-eight (20%) patients developed an infection during their hospitalization. Infections without a specific site (39%) and spontaneous bacterial peritonitis (32%) were the most common diagnoses. Univariate analysis showed that patients who developed an infection were more likely to have a low serum albumin level, to be admitted for gastrointestinal bleeding, to stay in the intensive care unit, and to undergo therapeutic endoscopy. Logistic regression identified admission for gastrointestinal bleeding (odds ratio (OR) = 4.3, 95% confidence interval (CI) = 1.7-10.9) and a low serum albumin (OR = 1.3, 95% CI = 1.03-1.22) as the only two variables independently associated with the development of an infection. CONCLUSION: The present study indicates that patients with severe cirrhosis who are admitted for gastrointestinal bleeding have a higher risk of developing a bacterial infection during their hospitalization than other cirrhotic patients.

Adult↗
PubMed1998

Early allograft dysfunction after liver transplantation: a definition and predictors of outcome. National Institute of Diabetes and Digestive and Kidney Diseases Liver Transplantation Database.

BACKGROUND: Poor graft function early after liver transplantation is an important cause of morbidity and mortality. We defined early allograft dysfunction (EAD) using readily available indices of function and identified donor, graft, and pretransplant recipient factors associated with this outcome. METHODS: This study examined 710 adult recipients of a first, single-organ liver transplantation for non-fulminant liver disease at three United States centers. EAD was defined by the presence of at least one of the following between 2 and 7 days after liver transplantation: serum bilirubin >10 mg/dl, prothrombin time (PT) > or =17 sec, and hepatic encephalopathy. RESULTS: EAD incidence was 23%. Median intensive care unit (ICU) and hospital stays were longer for recipients with EAD than those without (4 days vs. 3 days, P = 0.0001; 24 vs. 15 days, P = 0.0001, respectively). Three-year recipient and graft survival were worse in those with EAD than in those without (68% vs. 83%, P = .0001; 61% vs. 79%, P = 0.0001). A logistic regression model combining donor, graft, and recipient factors predicted EAD better than models examining these factors in isolation. Pretransplant recipient elevations in PT and bilirubin, awaiting a graft in hospital or ICU, donor age > or =50 years, donor hospital stay >3 days, preprocurement acidosis, and cold ischemia time > or =15 hr were independently associated with EAD. CONCLUSION: Recipients who develop EAD have longer ICU and hospital stays and greater mortality than those without. Donor, graft, and recipient risk factors all contribute to the development of EAD. Results of these analyses identify factors that, if modified, may alter the risk of EAD.

Adolescent↗
PubMed1998

Projection and innervation patterns of individual thalamic reticular axons in the thalamus of the adult rat: a three-dimensional, graphic, and morphometric analysis.

The gamma-aminobutyric acid-ergic thalamic reticular nucleus (Rt), which carries matching topographical maps of both the thalamus and cortex and in which constituent cells can synaptically communicate between each other, is the major extrinsic source of thalamic inhibitions and disinhibitions. Whether all the Rt axonal projections into the thalamus are similarly organized and have common projection and innervation patterns are questions of great interest to further our knowledge of the functioning of the Rt. The present study provides architectural and morphometric data of individual, anterogradely labeled axonal arbors that arose from distinct parts of the Rt. One hundred twenty-seven Rt neurons from all regions of Rt were marked juxtacellularly with biocytin or Neurobiotin in urethane-anesthetized adult rats. Eighteen two-dimensional and 14 three-dimensional reconstructions of single tracer-filled Rt neurons were made from serial, frontal, horizontal, or sagittal sections. Both the somatodendritic and axonal fields of tracer-filled Rt cells were mapped in three dimensions and illustrated to provide a complementary stereotaxic reference for future studies. Most marked units projected to a single nucleus of the anterior, dorsal, intralaminar, posterior, or ventral thalamus. Axons emerging from cells in distinct sectors of the Rt projected to distinct nuclei. Within a sector, neurons with separate dendritic fields innervated separate regions either in a single nucleus or into different but functionally related thalamic nuclei. Neurons with an overlap of their dendritic fields gave rise either to overlapping axonal arborizations or, more rarely, to distinct axonal arbors within two different thalamic nuclei implicated in the same function. In rare instances, an Rt axon could project within these two nuclei. Thalamic reticular axons commonly displayed a single well-circumscribed arbor containing a total of about 4,000 +/- 1,000 boutons. Every arbor was composed of a dense central core, which encompassed a thalamic volume of 5-63 x 10(6) microm3 and was made up of patches of maximal innervation density (10 +/- 4 boutons/tissue cube of 25 microm each side), surrounded by a sparse component. The metric relationships between the Rt axonal arbors and the dendrites of their target thalamocortical neurons were determined. Both the size and maximal innervation density of the axonal patches were found to fit in with the somatodendritic architecture of the target cells. The Rt axonal projections of adult rats are thus characterized by their (1) well-focused terminal field with a patchy distribution of boutons and (2) parallel organization with a certain degree of divergence. The role of the Rt-mediated thalamic inhibition and disinhibition may be to contrast significant with nonrelevant ongoing thalamocortical information.

Animals↗
PubMed1998

The organization of corticothalamic projections: reciprocity versus parity.

All neocortical areas receive inputs from and project back to the thalamus. It is often said that the corticothalamic projections are organized in a way that reciprocates the spatial distribution of thalamocortical pathways. The present review examines to what extent this rule of reciprocity is actually supported by the most recent neuroanatomical data, particularly those relating to the central organization of the vibrissal sensory system in the rat. A critical survey of previous studies is made and new results are presented concerning the fine-grained organization of corticothalamic projections in this sensory system. Together, prior results and the present set of new data confirm the existence of both, reciprocal and nonreciprocal patterns of corticothalamic connectivity. This conclusion leads us to propose that the spatial organization of corticothalamic connections complies with a more fundamental rule, the rule of parity, from which reciprocity follows as a general, but not obligatory consequence. The rule of parity states that the distribution of corticothalamic projections across and within the thalamic nuclei is determined by the branching patterns of the different classes of prethalamic afferents. The anatomical, developmental and physiological consequences of this rule are discussed. The rule of parity suggests that, according to the behavioral context, both prethalamic and corticothalamic pathways may function in a feedback mode.

Animals↗
PubMed1998

Anatomical evidence for a mechanism of lateral inhibition in the rat thalamus.

The aim of this study was to determine whether or not thalamic reticular nucleus (Rt) neurons form synaptic connections with the thalamocortical (TC) neurons from which they receive synaptic contacts. Therefore, we examined, in adult rats, the relationships between single TC and Rt neurons, which had been marked simultaneously with an anterograde/retrograde tracer (biocytin or Neurobiotin), using the extracellular or juxtacellular technique. (i) From 30 successful extracellular microapplications of marker into the Rt, 22 gave retrogradely marked TC somatodendritic arbors at the fringe of or clear outside the anterogradely darkly stained Rt axon terminal fields. Following biocytin application into the thalamus, few cells were retrogradely stained in the Rt at the periphery of the anterogradely labelled axon terminal field. (ii) The juxtacellular filling of a single Rt cell was accompanied by the back-filling of a single TC neuron (n = 4 pairs), which presumably formed synaptic contacts with the former cell. The somatodendritic complex of the back-filled TC neuron was located outside the Rt cell's axonal arbor. These anatomical data provide clear evidence that Rt and thalamic neurons predominantly form between themselves open rather than closed loop connections. Because TC neurons make glutamatergic synapses onto Rt cells, which are GABAergic, and are the first elements synaptically activated by prethalamic afferents into the TC-Rt network, the present results strongly support the hypothesis that Rt neurons principally generate a mechanism of lateral inhibition in the thalamus.

Animals↗
PubMed1997

Intracortical axonal projections of lamina VI cells of the primary somatosensory cortex in the rat: a single-cell labeling study.

A sample of 84 neurons in lamina VIa of rat somatosensory cortex (S1) was juxtacellularly labeled with biocytin, and the axons of the neurons were traced. Three classes of cells were identified as corticothalamic, corticocortical, and local circuit neurons. Corticothalamic cells (46%) are small, short pyramids projecting either to the ventral posteromedial nucleus alone or to the posterior group as well. The former are in upper lamina VI, have apical dendrites terminating in layer IV, and have intracortical collaterals ascending to layer IV as a narrow column about the size of a barrel. The latter are in the lower half of lamina VI, have apical dendrites terminating in layer V, and have a more extensive network of collaterals terminating in the upper part of lamina V. Corticothalamic cells do not project to distant cortical targets through branching axons. Corticocortical cells (44%) are small, short pyramids, inverted or modified pyramids, or bipolar spiny neurons. They send collaterals principally to infragranular layers of S1 and branches to the second somatosensory cortex, the motor cortex, or the corpus callosum. Local circuit neurons (10%) are basket cells, concentrated in upper lamina VI, having smooth, beaded dendrites and a rich collateral network densely covered with varicosities in layers V and VI. We conclude that (1) dendritic morphology and axonal arborizations of corticothalamic cells relate to the projection target; (2) many apparently diverse layer VI cells project to other cortical fields; and (3) lamina VI is a network for corticothalamic and corticocortical communication.

Animals↗
PubMed1997

Dendrodendritic and axoaxonic synapses in the thalamic reticular nucleus of the adult rat.

Currently, it is believed that cell-cell communications occur in the thalamic reticular nucleus (RT) during thalamocortical operations, but the anatomical substrate underlying these intrinsic interactions has not been characterized fully in the rat yet. To further our knowledge on this issue, we stained juxtacellularly rat RT neurons with biocytin or Neurobiotin and examined their intrinsic axon collaterals and "axon-like processes" at both light and electron microscopic levels. Of 111 tracer-filled RT cells for which the axon could be followed from its origin up to the thalamus, 12 displayed short-range, poorly ramifying varicose local axon collaterals, which remained undistinguishable from parent distal dendrites, raising the question as to whether their varicosities were presynaptic terminals. Correlated light and electron microscopic observations of the proximal part of these intrinsic varicose axonal segments revealed that their varicosities and intervaricose segments were, in fact, postsynaptic structures contacted by a large number of boutons that, for the most, formed asymmetric synapses and were nonimmunoreactive for GABA. Similarly, the so-called "axon-like processes" stemming from the soma or dendrites also were identified as postsynaptic structures. Two unexpected observations were made in the course of this analysis. First, the hillock and initial segment of some RT axons were found to receive asymmetric synaptic inputs from GABA-negative terminals. Second, examination of serial ultrathin sections of dendritic bundles cut in their longitudinal plane revealed the existence of several short symmetric dendrodendritic synapses and numerous puncta adhaerentia between component dendrites. In conclusion, dendrodendritic junctions might be a prominent anatomical substrate underlying interneuronal communications in the RT of the adult rat. Furthermore, excitatory axoaxonic synapses on the axon hillock, initial segment, and local axon collaterals might represent a powerful synaptic drive for synchronizing the firing of RT neurons. Future studies are essential to verify whether excitatory axoaxonic synapses with the axon hillock are a general feature in the RT.

Animals↗
PubMed1997

Lack of relationship between preoperative measures of the severity of cirrhosis and short-term survival after liver transplantation.

The purpose of this study was to evaluate the prognostic value of clinical measures of the severity of disease in cirrhotic patients who were candidates for liver transplantation at our institution. The records of the 132 cirrhotic patients who were candidates for a first transplantation between January 1, 1987, and December 31, 1994, were reviewed. One hundred nine patients (82.6%) received grafts, and 23 (17.4%) died while on the waiting list. The variables examined included level of medical urgency at the time of enlistment, date of transplantation, serum creatinine level, variables that constitute the Child-Pugh score and Shaw's risk score (serum bilirubin and albumin, prothrombin time, ascites, encephalopathy, nutritional status, age, and operative blood loss), and 6-month survival status after transplantation. The proportion of patients who died awaiting a graft increased as a function of the Child-Pugh score at enlistment (score 5-6, 0%, n = 6; score 7-9, 7%, n = 54; score 10-11, 18%, n = 33; score 12-15, 33%, n = 39; P = .01). Six-month survival rates after transplantation were similar irrespective of the Child-Pugh score or Shaw's risk score. Stepwise multiple logistic regression models identified the degree of ascites, serum bilirubin, and operative blood loss as significant variables for the prediction of overall mortality 6 months posttransplantation (model chi 2 = 12.8; P = .025; r = 0.32), but the model explained only 10% of the outcomes observed. We concluded that the Child-Pugh score is a valid prognostic index for survival up to the time of transplantation for cirrhotic patients on the waiting list; however, clinical measures of the severity of cirrhosis are poor predictors of 6-month survival after transplantation.

Adolescent↗
PubMed1996

A single-cell study of the axonal projections arising from the posterior intralaminar thalamic nuclei in the rat.

Thalamostriatal projections arising from the posterior intralaminar nuclei (P1; the parafascicular nucleus and the adjacent caudalmost part of the posterior thalamic group) were studied in rats by tracing the axons of small pools of neurons labelled anterogradely with biocytin. Thirteen P1 cells were also stained by juxta cellular application of the tracer. Relay cells of P1 nuclei have a morphology that differs radically from the classical descriptions of the bushy cells which represent the main neuronal type of the sensory thalamic relay nuclei. P1 cells have ovoid or polygonal somata of approximately 20-25 microm, from which emerge four or five thick, long and poorly branched dendrites bearing spines and filamentous appendages; their dendritic domains extend for up to 1.5 mm. Before leaving the nucleus 20% of axons give off collaterals that ramify locally. All axons course through the thalamic reticular nucleus, where they also distribute collaterals, and arborize massively in the striatum and sparsely in the cerebral cortex. At the striatal level four or five collaterals leave the main axon and terminate in patches scattered dorsoventrally within a rostrocaudally oriented slab. As revealed by calbindin D-28k immunohistochemistry, only the matrix compartment receives terminations from P1 axons. The cortical branch form small terminal puffs centred upon layer VI of the motor cortex. Before entering the striatum some axons of the parafascicular nucleus give rise to descending collaterals that arborize in the entopeduncular nucleus, in the subthalamic nucleus and in the vicinity of the red nucleus. Other axons arising from the caudal part of the posterior group send descending branches only to the entopeduncular nucleus. These findings show that P1 cells belong to a distinct category of thalamic relay neurons which, beside their massive projection to the striatum, also distribute collaterals to other components of the basal ganglia. Moreover, these results provide the first direct evidence that virtually all P1 cells project to both striatum and cerebral cortex. Finally, it is proposed on the basis of morphological, histochemical and hodological criteria that the caudal part of the posterior thalamic group in the rat is homologous to the suprageniculate-limitans nuclei of cats and primates.

Afferent Pathways↗
PubMed1995

Two different types of thalamic fibers innervate the rat striatum.

Thalamostriatal projections were studied in rats by tracing the axons of small pools of thalamic neurons labeled anterogradely with biocytin. Single-cell mapping of these projections revealed two types of thalamostriatal fibers. The first type arises from the bushy relay cells of the central lateral and associative thalamic nuclei which arborize sparsely in the striatum by means of long varicose axon collaterals. The second type of fiber arises from large, reticular-like, relay cells located in the parafascicular and ethmoid nuclei. These latter fibers form dense clusters of terminations within the striatum and they also send branches to other components of the basal ganglia. These different morphological features suggest that the two types of fibers subserve different functions.

Animals↗
PubMed1995

Thalamic reticular input to the rat visual thalamus: a single fiber study using biocytin as an anterograde tracer.

This study describes the axonal projections of single thalamic reticular (TR) neurons within the visual thalamus in rats. Experiments were performed under urethane anesthesia and reticular cells were labeled by extracellular or juxtacellular microiontophoretic applications of biocytin. The axonal arborizations of 19 TR cells projecting to the dorsal lateral geniculate nucleus (DLG) or to the lateral dorsal/lateral posterior complex (LD/LP) were reconstructed from serial horizontal sections. It was found that single TR cells projected within the limits of a single thalamic nucleus, either the DLG or the LD/LP complex, where their terminal fields formed rostrocaudally oriented rods (length: approximately 800 microns; diameter: approximately 100 microns) densely packed with grape-like boutons and varicosities. In addition, none of the labeled TR cells possessed recurrent axonal collaterals that ramified within the reticular complex itself. The functional implications of these morphological data for the synchronization of thalamic oscillations are discussed.

Animals↗
PubMed1995

Corticothalamic projections from the cortical barrel field to the somatosensory thalamus in rats: a single-fibre study using biocytin as an anterograde tracer.

This study investigated the pattern of axonal projections of single corticothalamic neurons from the cortical barrel field representing the vibrissae in the rat. Microiontophoretic injections of biocytin were performed in cortical layers V and VI to label small pools of corticothalamic cells and their intrathalamic axonal projections. After a survival period of 48 h, the animals were perfused and the tissue was processed for biocytin histochemistry. On the basis of the intrathalamic distribution of axonal fields and of the types of terminations found in the thalamus, four types of corticothalamic projections were identified. (i) Cells of the upper part of layer VI projected exclusively to the ventral posteromedial (VPm) nucleus, where they arborized in long rostrocaudally oriented bands or 'rods'. (ii) All cells of the lower part of layer VI projected to the medial part of the thalamic posterior group (Pom) but the vast majority of them also collateralized in VPm where they participated in the formation of rods. (iii) A minority of corticothalamic cells in the lower portion of layer VI, possibly located under the interbarrel spaces (septae), arborized exclusively in Pom. (iv) The corticothalamic projection of layer V cells originated from collaterals of corticofugal cells whose main axons ran caudally towards the brainstem. These collaterals arborized exclusively in Pom or in the central lateral nucleus. All corticothalamic cells from layer VI displayed the same type of axonal network, made of long branches decorated by terminal buttons emitted en passant at the tip of fine stalks. Corticothalamic fibres arising from layer V pyramids, however, remained smooth as they ran across the lateral thalamus and they generated in Pom one or two clusters of large boutons. All corticothalamic axons derived from layer VI cells, but not those derived from layer V cells, gave off collaterals as they traversed the thalamic reticular complex. These observations are discussed in the light of previous studies bearing on the topological organization and function of corticothalamic projections to VPm and Pom in rats. The possibility that a similar cellular specificity and a similar organizational plan may characterize corticothalamic relationships in other sensory systems is also considered.

Animals↗
PubMed1995

The axonal arborization of single thalamic reticular neurons in the somatosensory thalamus of the rat.

This study describes the axonal projections of single neurons of the thalamic reticular complex within the somatosensory thalamic nuclei in rats. Experiments were performed under urethane anaesthesia and reticular cells were labelled by extracellular microiontophoretic applications of biocytin. The axonal arborization of 25 thalamic reticular cells projecting to the ventrobasal (VB) nucleus and/or to the posterior thalamic (Po) complex were reconstructed from serial horizontal sections. Reticular cells labelled with biocytin display somatodendritic features similar to those reported previously. Their cell body is fusiform and their dendrites bear few spines and show a high degree of streaming along the horizontal curved axis of the nucleus. In most cells, axon-like beaded processes stem out from dendrites but, contrary to previous descriptions, no intrareticular axonal collateral was observed. The axonal arborization of most thalamic reticular cells is confined within the limits of a single thalamic nucleus; only two neurons were seen projecting to both the VB and the Po nuclei. In VB, termination fields form short rods (diameter approximately 150 microns, length approximately 200-300 microns) densely packed with grape-like boutons and varicosities; termination fields in Pro are larger, much less dense, and they are contained within a horizontal slab of tissue (thickness approximately 200 microns, mediolateral width approximately 400 microns, rostrocaudal length approximately 1 mm. By charting the position of all labelled cells within the thickness of the thalamic reticular complex, a strip-like arrangement was revealed. Cells projecting to Po occupy the innermost portion of the nucleus whereas those projecting to the ventral-posteromedial and ventral-posterolateral nuclei are located respectively in the middle and in the outer tiers of the nucleus. This strip-like reciprocity was confirmed by separate biocytin injections performed in VB and in Po. These results show that inhibition of reticular origin is distributed within the rat dorsal thalamus in a highly specific manner, most likely according to a principle of reciprocity within the somatotopic representation of the body.

Animals↗
PubMed1995

Toxic megacolon complicating pseudomembranous enterocolitis.

PURPOSE: Toxic megacolon is a rare complication of pseudomembranous enterocolitis. We reviewed our recent experience with this complication. METHODS: The first five patients of the series were studied retrospectively, and six others were followed prospectively. RESULTS: Between June 1992 and May 1994, 11 patients (8 male, 3 female) developed toxic megacolon secondary to pseudomembranous enterocolitis. Mean age was 60.7 +/- 11.8 (range, 40-79) years. Presenting symptoms and signs included diarrhea, 100 percent; malaise, 91 percent; abdominal pain, 82 percent; abdominal distention, 82 percent; abdominal tenderness, 72 percent; anemia less than 12 gm, 72 percent; albumin less than 3 gm, 64 percent; tachycardia greater than 100, 55 percent; fever greater than 38.5 degrees celsius, 45 percent; shock or hypotension, 45 percent. Predisposing factors included antibiotics, 64 percent; immunosuppressants or chemotherapy, 36 percent; antidiarrheals, 27 percent; and barium enema in one patient. Five patients (45 percent) had more than one predisposing factor. X-rays showed transverse colon dilation and loss of haustrations in eight patients (72 percent), with a mean diameter of 9.9 +/- 3.4 cm. Flexible proctosigmoidoscopy showed pseudomembranes in all scoped patients, and toxin assay for Clostridium difficile was positive in all patients. One patient had emergency surgery. Ten patients were initially treated medically with nasogastric suction and intravenous resuscitation (90 percent) and antibiotics (100 percent), usually in the intensive care unit (80 percent). Four patients did not respond and underwent surgery; two others improved, then deteriorated, and also underwent surgery. Altogether, 7 of 11 patients (64 percent) underwent surgery. Three patients (27 percent) responded well to medical treatment. One patient was deemed too ill to undergo surgery and died. Mean delay to surgery was 3.0 +/- 1.3 days. No sealed or overt perforation was found at laparotomy. All patients who underwent surgery had a subtotal colectomy, with either a Hartmann's stump (71 percent) or a mucous fistula (29 percent). Eventually, five of seven patients who were operated on and two of four medically treated patients died (overall mortality, 64 percent). Only one patient underwent closure of ileostomy and anastomosis. CONCLUSION: Toxic megacolon complicating pseudomembranous enterocolitis is a serious problem that carries a high morbidity and mortality rate, regardless of treatment.

Adult↗
PubMed1995

Corticothalamic projections from the primary visual cortex in rats: a single fiber study using biocytin as an anterograde tracer.

This study investigates the pattern of axonal projections of single corticothalamic neurons from the rat primary visual cortex. Microiontophoretic injections of biocytin were made in cortical laminae V and VI to label small pools of corticothalamic cells and their intrathalamic axonal projections. After a survival period of 48 h, the animals were perfused and the tissue was processed for biocytin histochemistry. On the basis of the intrathalamic distribution of axonal fields and the types of terminations found in the thalamus, three types of corticothalamic projections were identified. (1) Cells of the upper part of lamina VI projected to the dorsal lateral geniculate nucleus where they arborized in rostrocaudally oriented bands or "rods" parallel to the lines of projection of retinal afferents. (2) Cells of the lower part of lamina VI projected to the lateral part of the lateral posterior nucleus and they also sent collaterals to the dorsal lateral geniculate nucleus where they participated in the formation of rods. (3) The corticothalamic projection of lamina V cells originated from collaterals of corticofugal cells whose main axons reached the tectum and/or the pontine nuclei. These collaterals never terminated within the dorsal lateral geniculate nucleus; they arborized in the lateral posterior, lateral dorsal and ventral lateral geniculate nuclei. All corticothalamic cells from lamina VI displayed the same type of axonal network made of long branches decorated by terminal boutons emitted "en passant" at the tip of fine stalks. Corticothalamic fibers arising from lamina V, however, generated varicose endings in restricted regions of their target nuclei. All corticothalamic axons derived from lamina VI cells, but not those derived from lamina V cells, gave off collaterals as they traversed the thalamic reticular complex. These results demonstrate that corticothalamic fibers arising from the rat primary visual cortex display a lamina-dependent projection pattern. In the light of previous studies on the topographical organization of corticothalamic projections, it is proposed that a similar organizational plan characterizes corticothalamic relationships in other sensory systems in the rat and in other species.

Animals↗