PubMed Health⌕ Search

Biomedical subjects

K Novak

Publications and source records attributed to K Novak.

70 records · Page 4Linked to original sources
PubMed1995

Age and dose-related effects of hippocampal ibotenic acid on lesion size, mortality, and nonspatial working memory in infant rats.

Three experiments are presented in which the neural and behavioral consequences of multiple ibotenic acid (IBO) injections into the hippocampus were examined in Sprague-Dawley rat pups. Rat pups were 11 or 15 days of age at the time of surgery (SURG11, SURG15), the dose of IBO was either 1 microgram in 1 microliter, 2.5 micrograms in 0.5 microliters, or 5 micrograms in 1 microliter for each of four injections, and pups were allowed to survive for 3 or 7 days after the lesion was made. The Fink-Heimer silver stain was used in Experiment 1 to examine the extent of neural damage following unilateral lesions and showed that the degeneration was primarily located in the hippocampus. The magnitude of the damage was greatest in younger pups and in those which received the higher of the two concentrations (injection volume was not a factor). Degenerating fibers were seen in the columns of the fornix as well as precommissural fornix fibers, but only in SURG15 animals when damage extended into the dorsal subiculum. Mortality rates following multiple IBO injections were very high in infant rats, in some cases as high as 60%. Experiments 2 and 3 examined the effects of bilateral lesions on neuroanatomy and behavior. Bilateral lesions were somewhat smaller than unilateral lesions, and as for unilateral lesions, degeneration in pre- and postcommissural fornix was seen only in SURG15 animals. The behavioral task used in Experiments 2 and 3 was patterned single alteration, a memory-based appetitive learning discrimination. Earlier work has shown that damage to the infant hippocampus results in moderate deficits in this task at 30-s intervals and more substantial deficits at 60-s intertrial intervals. This was not the case in the present studies: regardless of age at surgery or time postlesion, all infant rats tested learned this discrimination at the two intertrial intervals. As has been recently reported for adult rats, excitotoxic lesions of the hippocampus in infant rats do not produce the same patterns of behavioral deficits as electrolytic lesions.

Age Factors↗
PubMed1994

Localization of freezing injury in articular cartilage.

In order to improve techniques for cryopreservation of articular cartilage, a study has been carried out to assess localization of cryoinjury in intact articular cartilage. Osteochondral dowels taken from the femoral condyles of sheep were subjected to graded freezing in the presence and absence of a cryoprotectant (10% DMSO). The graded freezing technique involves slow cooling (1 degree C/min) to various subzero temperatures before either rapid warming or rapid cooling by plunging in liquid nitrogen. This protocol allows assessment of the separate effects of rapid and slow freezing which damage cells in different ways, and the effects of cryoprotectants on the different types of damage. To assay damage, thin slices of cartilage were cut with a vibratome, which allows viable cells within the matrix to be observed microscopically. Injury was assessed by staining with fluorescent dyes to indicate damage to the plasma membrane. In general, tissue response was similar to that of cell suspensions, showing at least two mechanisms of injury acting on the cells: one at slow cooling rates and another at rapid cooling rates. The primary effect of DMSO was to reduce injury due to slow cooling. When the location of injury within the tissue was examined, it was found that chondrocytes of the intermediate layer were injured more extensively than those of either the deep or superficial layers.

Animals↗
PubMed1993

Comparison of nine methods of indicating the direction to objects: data from blind adults.

Nine methods of indicating the direction to object locations were tested on twenty blind adult subjects. The task was to indicate the location of active auditory targets distributed in a semicircle with a 1.7 m radius around the subject. Target location, practice, and feedback were systematically varied for each method. The greatest accuracy and lowest variability were found for pointing methods that used body parts (directing the nose at the target, facing it with the chest, and pointing with the index finger) and extensions of body parts (pointing with a hand-held cane or with a short stick). Two less accurate methods involved rotating a dial. The least accurate methods involved drawing and a verbal description in terms of clockface labels. Method interacted significantly with target location, and with individual differences. In general, the body-part and extension method were affected less than other methods by target location and individual differences. The findings suggest that a pointing response that uses body part or an extension of a body part is the best choice for experimental or diagnostic measurement of object location by blind subjects. Differences between the results of this study of blind subjects and auditory localization accuracy in sighted subjects are discussed, and the implications for spatial processing in the blind are considered.

Adult↗
PubMed1993

Risk factors for postimplantation pancreatitis and pancreatic thrombosis in pancreas transplant recipients.

Reperfusion pancreatitis and pancreatic thrombosis are 2 complications of pancreatic transplantation that are associated with both an increased patient morbidity and a decrease in pancreas graft survival rates. These complications are thought to be related to donor factors, procurement and preservation variables, and postimplantation recipient management. We reviewed our experience with 41 consecutive pancreas transplant patients (18 females, 23 males) performed in association with kidney transplants (n = 34), whole (n = 5) and segmental (n = 2). The average cold ischemia time (CIT) was 11.5 hr. Donor and recipient variables were related to two outcomes: (1) postoperative pancreatitis (n = 9) and (2) postoperative pancreatic thrombosis (n = 6). Steroid administration to the donor resulted in significant reduction of postimplantation pancreatitis (P < 0.001). Also, postoperative pancreatitis was significantly less common (P < 0.02) in recipients given calcium channel blockers in the early postoperative period. Pancreatic thrombosis was significantly more common in male recipients (P < 0.04) and was also significantly related to CIT (P < 0.05). These data indicate that proper donor management and pretreatment with high-dose steroids, together with shortening of CIT and postoperative administration of calcium channel blockers, are protective against pancreatic thrombosis and pancreatitis.

Female↗
PubMed1992

Metabolic and biochemical status of articular cartilage following cryopreservation and transplantation: a rabbit model.

To determine the fate of transplanted cryopreserved articular cartilage, an animal model employing the proximal humerus in the rabbit has been developed. Previous studies have been hindered by problems of postoperative joint instability, secondary injury due to immobilization, and paucity of cartilage for analysis. This experiment demonstrates the survival and function of transplanted cartilage by quantitative assessment of metabolic and biochemical parameters. Forty-five New Zealand white rabbits underwent transplantation of the right proximal humerus. In 29 animals, the proximal half of the humerus was resected and replaced by a cryopreserved osteoarticular allograft. Autograft procedures were carried out in the remaining animals. Following sacrifice at 3, 6, 9, and 12 months postoperatively, articular cartilage was analyzed for gross appearance, collagen synthesis, proteoglycan synthesis, and water, hydroxyproline, hexosamine, and hexuronic acid contents. The results indicate that the cryopreserved osteoarticular allografts retained their metabolic and biochemical integrity and behaved as viable and biologically functional units 1 year postoperatively.

Animals↗
PubMed1991

Effects of pregnancy, estradiol, and progesterone on pressor responsiveness to angiotensin II.

The pressor and heart rate responses to infused angiotensin (ANG) II were measured in conscious pregnant Long-Evans rats. Responses were recorded 7 days after chronic indwelling venous and arterial cannulas were implanted (virgin rats) and again at days 7, 14, and 21 of pregnancy. A significant reduction in the pressor response was noted as early as day 7 of pregnancy; this is comparable to the human condition. It was also noted that the reflex bradycardia associated with the pressor response was entirely absent at 21 days. To determine a possible cause of these pregnancy-induced changes, ovariectomized rats were injected subcutaneously for 10 days with estradiol, progesterone, or a combination of both. They were then tested for pressor responses to ANG II. None of the hormone-injected groups showed any significant deviation in their pressor response compared with saline-injected controls. Similar results were obtained in acutely prepared rats under chloroform anesthesia. However, the magnitude of the pressor response in the chloroformed animals was significantly reduced compared with the conscious unrestrained animals. It is concluded that 1) the rat is an appropriate model of human pregnancy in which to study changes in ANG responsiveness in pregnancy and 2) neither estradiol nor progesterone is responsible for the reduced pressor response.

Angiotensin II↗
PubMed1991

[Primary liver carcinoma in the Subotica City Hospital 1962-1990].

The authors have presented their observations in 108 pathologically processed cases of primary hepatic carcinoma (PHC). The material includes the period from 1962 to 1990. The most frequent form of PHC was hepatocellular (67.5%), the cholangiocellular (29.5%) and rarest, the mixed hepato-cholangiocellular form (2.9%). X-ray diagnostics were applied (celiacography, arteriography), laparoscopy, ultrasonography, aimed and blind aspirational biopsy, and laboratory examinations (alkaline phosphatase, transaminases, bilirubin, gamma-CT and so on). Somewhat more attention is given to the problem of HBV infection as the cause of primary hepatic carcinoma development. Pre-existing liver tissue diseases are also pleaded for (chronic aggressive hepatitis, hepatic cirrhosis, ect.). Beside the many diagnostic procedures, the diagnosis of primary hepatic carcinoma is usually established too late, and the therapy still remains unsatisfactory.

Adult↗
PubMedDate not supplied

Osteochondral dowel transplantation for repair of focal defects in the knee: an outcome study using an ovine model.

OBJECTIVE: A model system was developed to objectively assess the quality of articular cartilage after surgical reconstruction of focal defects in the median femoral condyle using osteochondral dowel grafts. STUDY DESIGN: The surgical technique was developed and customized to reproducibly minimize surgical trauma and graft instability in order to improve the survival of the transplanted cartilage and the long-term integrity of the joint surfaces. ANIMALS OR SAMPLE POPULATION: 24 adult female Suffolk-Romanoff crossbred sheep. METHODS: Biomechanical creep testing, paravital staining for chondrocyte viability, histological analysis, and gross morphological analysis were performed at 3, 6, and 12 months postoperatively to compare fresh autografted osteochondral dowels with allografts that had been subject to a freezing protocol known to kill chondrocytes. The latter was used to investigate the time course of cartilage degeneration after injury. These two groups were also compared with normal unoperated control tissue. RESULTS: Biomechanical behavior, chondrocyte survival, and cartilage histology differed significantly between fresh grafts and those that had been frozen. CONCLUSIONS: Indentation testing and paravital staining were able to identify degenerative changes earlier than other methods of assessment. The technique developed here reproducibly and reliably transplanted osteochondral dowel grafts while minimizing the confounding effects of surgical trauma and graft instability. CLINICAL RELEVANCE: The technique provides both a promising surgical technique for the repair of focal defects of the medial femoral condyle and a sensitive model for the future study of cryopreservation strategies for articular cartilage.

Animals↗