Biomedical subjects

J M Krum

Publications and source records attributed to J M Krum.

22 records · Page 2Linked to original sources

PubMed1988

Patterns of angiogenesis in neural transplant models: II. Fetal neocortical transplants.

Vascular integration between transplanted fetal CNS tissues and host brain is essential for long-term transplant survival. This study compares the time course and mechanism of vascularization in allografts of fetal cerebral cortex inserted either into the fourth ventricle or directly into the parietal cortex or hippocampus of perinatal rats. Recipient animals were administered 3H-thymidine after various postoperative time periods. The tissues were processed for light microscopic autoradiography to determine the temporal pattern of endothelial proliferation at the graft sites. Correlative electron microscopy depicted the morphological changes in transplant vasculature. Some recipients were prelabelled with 3H-thymidine prior to transplantation to determine if host vessels invaded the grafts; conversely, some donor tissues were prelabelled in utero to ascertain if the intrinsic vascular anlagen survived. Intraventricular transplants contained patent vessels, probably originating from the host pia mater, as early as 24 hours postoperative. Intraparenchymal transplants had patent vessels by 72 hours and a more complete network by 5 days. Prelabelling experiments and ultrastructural observations demonstrated that adjacent host pial vessels became incorporated into the perimeter of the intraventricular transplants and later grew centrally into the grafts. Intraparenchymal transplants also contained host vessels that exhibited a similar growth pattern. Intrinsic graft vessels remained viable and continued their development, and presumably anastomosed with the ingrowing host vasculature. Temporal labelling studies revealed that both vessel populations attained their highest proliferative rates within 72 hours after transplantation. This study demonstrates that the vasculature which develops within both intraventricular and intraparenchymal fetal CNS transplants is chimeric, consisting of intrinsic fetal vasculature and proliferating host vessels. The mechanism of transplant vascularization may be significant with regard to astrocytic, immunological, or blood-brain-barrier characteristics at these transplantation sites.

Animals↗

PubMed1987

Patterns of angiogenesis in neural transplant models: I. Autonomic tissue transplants.

Functional vascular connections must form rapidly to prevent ischemic damage to grafted neural tissues. The temporal sequence by which transplant circulation is re-established provides information about the angiogenic capacity of either intact or damaged CNS blood vessels. This study compares the time course and mechanism of vascular reperfusion in allografts of superior cervical ganglia or adrenal medulla inserted either into the fourth ventricle or directly into the parietal cortex of perinatal rats. Tritiated thymidine was administered to recipients to determine angiogenic patterns at various postoperative time periods. After processing for light microscopic autoradiography, host and graft endothelial labelling indices were determined in order to establish the temporal sequence and location of vascular proliferation. Correlative electron microscopy depicted the morphological changes in transplant vasculature. Some recipients were prelabelled with 3H thymidine prior to transplantation to determine if host vessels invaded the grafts. Intraventricular graft vessels initially collapsed but sustained minimal ischemic damage and were completely reperfused by 24 hours postoperative. Adjacent intact host vessels attained peak 3H thymidine incorporation at 20 hours. Intrinsic graft vessels were radioactively labelled only after 48 hours. Intraparenchymal transplants surrounded by minimal trauma exhibited a similar temporal sequence of reperfusion and host endothelial proliferation. Intrinsic graft vessels in intraparenchymal grafts sustained more severe damage. With increased trauma, a concomitant delay in graft reperfusion time was observed. Grafts within prelabelled hosts rarely contained any labelled endothelium, indicating that anastomotic connections were made between original, intrinsic graft vessels and nearby host vascular sprouts. This study demonstrates that mature autonomic tissue stimulates the growth of adjacent host vessels when transplanted to undamaged brain surfaces. The anastomosis of nascent host vessels with pre-existing graft vessels is responsible for the rapid re-establishment of circulation within the transplants. A similar mechanism occurs within intraparenchymal grafts, although the rapidity of reperfusion appears to be predicated on the amount of trauma present at the graft site.

Adrenal Medulla↗

PubMedDate not supplied

Cytoskeletal protein immunoexpression in fetal neural grafts: distribution of phosphorylated and nonphosphorylated neurofilament protein and microtubule-associated protein 2 (MAP-2).

The present study examined the immunocytochemical expression of important cytoskeletal proteins within the neurons of an extended series of neocortical grafts and smaller group of ventral mesencephalic (nigral) grafts. Using antibodies that were directed at all three neurofilament (NF) epitopes, NF-L, NF-M, and NF-H, we attempted to determine whether these neurons would have an altered cytoskeletal profile following the stress of transplantation, because previous studies have shown such changes following ischemia or direct brain injury. We studied phosphorylated NF protein, which is found predominantly in axons, nonphosphorylated NF protein, which is found predominantly in the somata-dendritic compartment, and MAP-2, a specific microtubule marker that is localized exclusively in the somato-dendritic compartment. The results show that in all neocortical grafts examined, both phosphorylated and nonphosphorylated NF immunoexpression was significantly downregulated and appeared only in relatively few axons and somatic profiles, respectively, even though there were numerous Nissl-stained neuronal profiles in the grafts. There was no particular pattern to the immunopositive profiles. At later times occasional neuronal profiles were positive for phosphorylated NF protein, suggesting a reaction to cellular injury. In contrast to neocortical grafts, the cytoskeletal profiles of MAP-2 and phosphorylated NF protein in nigral grafts appeared very similar to age-matched control although the nonphosphorylated NF protein expression did appear somewhat lessened at 1-2 mo postoperative. Because cytoskeletal proteins play important roles in neuronal size, shape, and structural stability, they may subserve key cellular issues in neural grafting. These results show a significant loss of cytoskeletal protein expression in neocortical grafts that does not occur in nigral grafts. These results suggest that fetal neurons from different brain regions (i.e., graft source) may respond differently to the grafting procedure insofar as their cytoskeletal makeup is concerned. In addition, a potential lack of appropriate growth substrates or synaptic contacts may also produce cytoskeletal alterations. As such, the cytoskeletal protein profiles in central nervous system (CNS) grafts may be useful markers for functional performance, perhaps reflecting a degree of cellular injury.

Animals↗

PubMedDate not supplied

Developmental expression of calcium-binding protein-containing neurons in neocortical transplants.

The present study examined the development of calcium binding protein-containing neurons in a timed series of fetal neocortical transplants. The immunoexpression of parvalbumin and calbindin, which are subpopulations of GABAergic neurons, have been widely studied in normal development and in disease and injury states. Because of their purported resistance to oxidative injury by their ability to buffer Ca++ influx, these neurons have been particularly studied following ischemia. Because it is likely that oxidative stress is associated with the grafting procedure, we sought to determine if these neurons displayed enhanced survival characteristics. Normally, parvalbumin and calbindin represent about 5-10% of cortical neurons. Within 2-4 wk after grafting the expression of both proteins increased markedly in that a relatively larger number of neurons (27% for parvalbumin) were immunopositive. This increase was transitory, however, and by 4 mo and beyond, confocal microscopic data showed a reduction of over 50% of parvalbumin (+) neurons and processes. Calbindin (+) processes showed a qualitative change in that they were smaller with less terminal branching. Electron microscopy confirmed a substantial reduction in parvalbumin synaptic contacts. Interestingly, in older grafts, remaining parvalbumin neurons were those that were strongly NSE (+) suggesting a link between normal metabolism and Ca++ buffering in grafted neurons. It is possible that in early grafts certain neuronal populations transiently upregulated calcium binding proteins as a defensive mechanism against Ca++ influx associated with oxidative stress. Over time, however, following physiological normalization within grafts, the calcium binding protein (+) neurons are diminished, possibly due to lack of appropriate afferent input to the interneuronal pool.

Animals↗