Regional study of spinal alpha 2-adrenoceptor densities after intraspinal noradrenergic-rich implants on adult rats bearing complete spinal cord transection or selective chemical noradrenergic denervation.

One of the challenges of restorative neuronal transplantation in the CNS of mammals is the appropriate integration of grafted cells in the host circuitry. One key parameter is the specific influence of grafted cells upon corresponding receptors. In order to test this issue on the lesioned spinal cord of adult rats, two models of spinal cord denervation were used: the first one consisted of a complete transection 1 week prior to an intraspinal transplantation of embryonic locus coeruleus (LC) primordia cell suspension; the second one was a chemical destruction of the spinal noradrenergic (NA) system 1 month prior to a similar transplantation. Five weeks after transplantation, spinal sections were processed for autoradiographic quantification of alpha 2-adrenoceptor binding sites densities. In most regions, alpha 2-adrenoceptor densities remained comparable or higher than before graft; interestingly, in lumbar dorsal horn, lumbar intermediate zone and sacral distal dorsal horn of transected-grafted rats, they returned to control level. Results are discussed in relation to the parallel study performed concerning alpha 1-adrenoceptors.

[Experimental medullary lesions: prevention of the extension of secondary lesions and formation of glial scarring]. / Lésions médullaires expérimentales: prévention de l'extension des lésions secondaires et de la formation des cicatrices gliales.

Early treatment of spinal cord lesions is undertaken following two lines of research carried in adult rats: First, the reduction of secondary lesions, immediately after the trauma, second, the prevention of glial scar formation in the following days. In the first case, after a photochemical focal lesion at thoracic level (T8), a specific, non competitive antagonist of NMDA, TCP, is injected systemically. The result is the reduction of the extent of the lesion, as measured in serial coronal sections, the improvement of the performance in two functional tests of hindlimb function, and the improvement of somatosensory evoked potentials. In the second case, the spinal cord of rats were hemisected at thoracic level (T8-T9), and a suspension of liposomes containing a cholesterol derivative (7 beta-OH cholesteryl-oleate) was administered through a sub dural catheter, 2 days after the section. Histological investigations evidenced a reduction of astrocyte hyperplasia and hypertrophy, together with the blocking of the expression of a cell adhesion molecule, the so-called polysialic N-CAM. This resulted, within 5 weeks after the lesion, in the growth of axons in the denervated dorsal horn, below hemisection originating from the contralateral side. In conclusion, these two experimental studies constitute the basis for a coherent strategy of treatment in spinal cord traumatic lesions. Their sequential application could even improve the functional outcome of spinal cord lesions. However, these two research lines do not exclude other associated treatments such as the local applications of growth factors, which can potentiate both neuron survival and axonal sprouting.

[Spinal cord injuries: comments on preventive and curative strategy]. / Lésions médullaires traumatiques: réflexions sur une stratégie préventive et curative.

Research for the cure for paralysis caused by spinal cord injury has followed three complementary lines: Limitation of secondary lesions; the use of antagonists of excitatory amino acids has proven affective in reducing the extent of the lesions. Control of the glial scar; an oxygenated derivative of cholesterol can reduce the proliferation of reactive astrocytes and their hypertrophy, and permit the regrowth of axons in a denervated territory. Transplantation of embryonic neurons below the lesion allows to reinnervate denervated sites and reestablish reflex functions.

Growth of the perichondrium and the chondroepiphysis: experimental approach in the rat proximal tibial epiphysis.

In the present paper we study the participation of the perichondrium in chondroepiphysis development analyzing its in vitro growth pattern without the perichondrium. We also advance the descriptive morphological results. We have observed that the chondroepiphysis without perichondrium grew with an almost normal pattern. Most of the cells that participated in chondroepiphysis growth came from the lateral region of the growth plate.

Morphogenesis of cartilage canals: experimental approach in the rat tibia.

This paper studies the participation of vessels in the canal morphogenesis. The proximal chondroepiphysis of the left tibia of 44 five-day-old rats was exposed and the vessels of the intercondylar fossae, near the attachment of cruciate ligaments, were cauterized. In addition to the vascular lesion this assay induced a perichondral lesion. However, the canal appeared and joined to the secondary ossification center. 36 tibiae of 4-day-old rats were removed under sterile conditions and cultured in a serum-free chemically defined medium. The cultures were carried out for as long as 15 days. A canal lumen structure was found on the first days of culture, and grew in depth to the central region of the chondroepiphysis during the culture. The secondary ossification center was not found. The vessels and mesenchymal cells observed in the control canal were not found in the culture. We suggest that the presence of vessels, perivascular cells or perichondrium does not appear to be necessary in canal morphogenesis.

Relationship between the cartilage canal and the perichondrium in the rat proximal tibial epiphysis.

One of the most widespread hypotheses for chondral canal morphogenesis suggests that the canal is an extension of the perichondrium. To study the possible relation between perichondrium and chondral canal morphology, the proximal epiphyses in the tibias of 42 rats were studied from birth to their 29th day. The study was divided into three periods: from birth to the 4th day before canal appearance; from the 5th day, the moment of canal appearance, until the appearance of the secondary ossification center of the epiphysis on the 9th day; the 3rd ran from this point on the 10th day until its full development. We have also divided the canal into three regions: entrance, neck and bottom. The central portion (lumen) and canal wall were analyzed in each region. Our results show the perichondrium to be a complex structure, composed of a series of cellular layers in a biphasic extracellular matrix (eosinophil and basophil). The canal walls are lined by a layer of elongated cells. In the lumen there are many different cell types: fibroblasts, histiocytes, multinuclear giant cells and multivacuolated cells. Our study of the canal, its walls and lumen show no morphological structure that is reminiscent of the perichondrium. These results suggest that the canal is not itself a continuation of the perichondrium.

The contribution of the inferior endocardial cushion of the atrioventricular canal to cardiac septation and to the development of the atrioventricular valves: study in the chick embryo.

The contribution of the inferior endocardial cushion of the atrioventricular canal to cardiac septation and to the development of the atrioventricular valves was studied in the chick embryo by in vivo labelling techniques. The study was performed in White Leghorn chick embryos in which the dorsal cushion was labelled at stage 20-21 (Hamburger and Hamilton, 1951), when the endocardial cushions were not yet fused. The embryos were sacrificed at stage 35 (mature heart). These experiments allow us to conclude that the inferior atrioventricular cushion gives origin to: a) that part of the cardiac septum between the septal insertion of the antero-septal leaflet of the mitral valve and the fibrous ridge which is the equivalent to the human septal leaflet of the tricuspid valve (atrioventricular septum); b) the region of the interatrial and the interventricular septa adjacent to the atrioventricular septum; c) the portion of the antero-septal leaflet of the mitral valve which inserts into the septum; d) the fibrous ridge corresponding to the septal leaflet of the tricuspid valve. Microdissection shows that, when they appear at stage 18, the superior and inferior endocardial cushions of the atrioventricular canal are in continuity, without boundaries, with both the interatrial and interventricular septa. Therefore, each atrioventricular orifice opens into its corresponding ventricle, there being no stage in the development of the chick embryo heart in which the atrioventricular orifices are connected to the left ventricle at the same time. The development of the atrioventricular canal is similar in the chick and human.