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Biomedical subjects

J Fung

Publications and source records attributed to J Fung.

At least 73 records · Page 4Linked to original sources
PubMed2000

Logistics and technique for procurement of intestinal, pancreatic, and hepatic grafts from the same donor.

OBJECTIVE: To assess a technique for simultaneous recovery of the intestine, pancreas, and liver from the same donor. SUMMARY BACKGROUND DATA: With the more frequent use of pancreatic and intestinal transplantation, a procurement procedure is needed that permits retrieval of both organs as well as the liver from the same cadaveric donor for transplantation to different recipients. It is believed by many procurement officers and surgeons, however, that this objective is not technically feasible. METHODS: A technique for simultaneous recovery of the intestine, pancreas, and liver was used in 13 multiorgan cadaver donors during a 26-month period, with transplantation of the organs to 33 recipients. The intestine was removed from 11 donors separately and in continuity with the pancreas in the other 2. Six additional pancreases were excised and transplanted separately. Thirteen livers were retrieved, one of which was discarded because of steatorrhea. Ten of the remaining 12 livers were transplanted intact; the other 2 were split in situ and used as reduced-size hepatic allografts in four recipients. RESULTS: None of the 11 intestinal, 6 pancreatic, 2 intestinal-pancreatic, or 14 whole or partial liver allografts sustained serious ischemic injury or were lost as a result of technical complications. One liver recipient died 25 months after surgery of recurrent C virus hepatitis. The other 32 recipients had adequate allograft function with a mean follow-up of 8 months. CONCLUSION: It was possible using the described technique to retrieve intestine, pancreas, and liver allografts safely from the same donor and to transplant these organs to different recipients.

Adolescent↗
PubMed1999

Induction of pulmonary cytochrome P4501A1: interactive effects of nicotine and mecamylamine.

The effect of the nicotinic receptor antagonist mecamylamine on nicotine-mediated convulsions and induction of pulmonary cytochrome P4501A1 (CYP1A1) was examined in the rat. Mecamylamine blocked the convulsions and inhibited CYP1A1 induction by nicotine at the level of CYP1A1 activity (93%) and protein (97%), but independently induced the enzyme also at the level of activity and protein. The results show that mecamylamine antagonizes both the CYP1A1 induction and convulsions by nicotine but, independently, is an inducer of the enzyme. The results indicate that CYP1A1 induction is not a consequence of the convulsant effects of nicotine.

Animals↗
PubMed1999

Cytomegalovirus PP65 antigenemia monitoring as a guide for preemptive therapy: a cost effective strategy for prevention of cytomegalovirus disease in adult liver transplant recipients.

BACKGROUND: The aim of the study was to assess the incidence of cytomegalovirus (CMV) infection and disease in adult liver transplant recipients, using routine preemptive therapy guided by the pp65 antigenemia test. METHODS: Antigenemia was monitored weekly after liver transplantation (OLTX) for the first 3 months, and once a month for another 3 months. CMV seronegative recipients were treated preemptively for the first positive antigenemia. Seropositive recipients were treated only when their antigenemia count reached a threshold of > or =100 positive cells per 200,000 leukocytes. RESULTS: A total of 144 patients were included between June 1994 and April 1995, of which 137 (95%) were primary OLTX. The percentage of positive antigenemia and CMV disease was 55 and 8%, respectively. Seventy-eight (54%) patients were protocol-monitored for the entire follow-up (group 1) and received appropriate preemptive therapy, although 66 (46%) patients had protocol violation by having missed blood samples or blood drawn at unscheduled times (group 2). Using Cox's proportional hazards model, patients with a first antigenemia count of >11 leukocytes had a significantly higher rate of CMV disease compared to patients with an antigenemia count < or =11 leukocytes (RR = 7.3, 95% confidence interval = 2.2 to 24.5). In a multivariate Cox regression analysis, adjustments were made to control for: group 1 versus group 2, use of OKT3, and serology risk categories. This analysis showed that the relative rate of CMV disease was still significantly higher among patients with antigenemia count >11 leukocytes (adjusted RR = 4.9, 95% confidence interval = 1.3 to 18.1). The estimated cost of preemptive therapy was less than that of prophylaxis with i.v. (14-day course) or oral (90-day course) ganciclovir. CONCLUSIONS: Preemptive therapy guided by pp65 antigenemia is a useful and cost effective strategy for prevention of CMV disease.

Adult↗
PubMed1999

Coordinate up-regulation of CYP1A1 and heme oxygenase-1 (HO-1) expression and modulation of delta-aminolevulinic acid synthase and tryptophan pyrrolase activities in pyridine-treated rats.

To determine the changes in heme metabolism associated with induction of cytochrome P450 expression by pyridine, we compared the time course of CYP1A expression with the time course of (i) expression of heme oxygenase-1 (HO-1) (EC 1.14.99.3), (ii) activity of delta-aminolevulinic acid synthetase (ALAS) (EC 2.3.1.37), and (iii) heme saturation of tryptophan pyrrolase (TPO) (EC 1.13.11.11) in tissues of rats administered a single 100 or 150 mg/kg i.p. dose of pyridine. Both mRNA and protein of HO-1 and CYP1A1 were induced in the liver, kidney, and lung, with the induction of HO-1 mRNA preceding and paralleling that of CYP1A1 mRNA in the liver and lung but not kidney. Induction of CYP1A1 mRNA expression peaked within 9-12 hr and returned to control levels by 24 hr in all tissues examined, whereas induction of HO-1 mRNA expression was sustained for 48 hr in the lung and liver. In contrast to the transient up-regulation of CYP1A1 mRNA, increased microsomal CYP1A1 protein was sustained in all three tissues. Similar to the induction of HO-1 expression, lipid peroxidation was stimulated by pyridine treatment in the kidney, lung, and liver, but with the stimulation being more persistent in the liver and lung than in the kidney. Increased hepatic CYP1A1 or CYP1A2 activity was preceded by increased activities of HO-1 and ALAS. Pyridine treatment negatively modulated heme saturation of hepatic TPO. The findings indicate that pyridine stimulates the synthesis, utilization, and degradation of heme in a coordinate manner, and suggest that these alterations in heme metabolism may contribute to CYP1A1 induction by pyridine.

5-Aminolevulinate Synthetase↗
PubMed1999

Health care concerns and guidelines for adults with Down syndrome.

Down syndrome (DS) is the most common cause of mental retardation in North America, yet little information is available on the natural history of DS in adults. We report on significant medical problems of adults with DS (DS adults) residing in a British Columbia provincial residential center, Woodlands, over the 12-year period from 1981 through 1992. Prospective, yearly health care reviews on 38 DS adults are summarized according to age. Group 1 consists of 18 middle-aged DS adults less than 50 years old, and group 2 comprises 20 elderly DS adults 50 years and older. Significant health problems in all DS adults include untreated congenital heart anomalies (15. 8%), acquired cardiac disease (15.8%), pulmonary hypertension (7.8%), recurrent respiratory infections/aspiration leading to chronic pulmonary interstitial changes (30%), complications from presenile dementia/Alzheimer-type disease (42%), adult-onset epilepsy (36.8%), osteoarthritic degeneration of the spine (31.6%), osteoporosis with resultant fractures of the long bones (55%) or vertebral bodies (30%), and untreated atlantooccipital instability (7.9%). Acquired sensory deficits are significant problems including loss of vision due to early onset of adult cataracts (50%), recurrent keratitis (21%) or keratoconus (15.8%), and significant hearing loss (25%). Behavioral problems (50%), loss of cognitive abilities, and onset of symptoms of Alzheimer disease (group 1: 5.5%; group 2: 75%) pose ongoing challenges for care. In conclusion, the quality of life for adults with DS can be improved by routine, systematic health care screening to identify treatable diseases that may be missed because of poor communication or confusion due to Alzheimer disease.

Adult↗
PubMed1999

Cytochrome P450 1A1 in rat peripheral blood lymphocytes: inducibility in vivo and bioactivation of benzo[a]pyrene in the Salmonella typhimurium mutagenicity assay in vitro.

The presence and inducibility of CYP1A1 in freshly isolated peripheral blood lymphocytes was examined in untreated rats and in rats pretreated with agents known to induce the enzyme in other tissues, as well as dexamethasone [CAS #50-02-2], which is not commonly associated with CYP1A1 induction. CYP1A1 but not CYP1A2 was detected by Western blot analysis of lymphocytes from untreated rats and was induced in lymphocytes from rats treated with the known CYP1A inducers beta-naphthoflavone [CAS #6051-87-2] or 3-methylcholanthrene [CAS #56-49-5] (7.3-fold), cigarette smoke (2. 8-fold), and pyridine [CAS #108-86-1] (2.6-fold). CYP1A1 was also induced in lymphocytes from rats treated with the nonprototypic inducer dexamethasone (17.7-fold) or bromobenzene [CAS #108-86-1] (3. 9-fold). Lymphocyte homogenate from rats treated with the inducers also catalyzed NADPH-dependent bioactivation of benzo[a]pyrene [CAS #50-32-8] to mutagens. The benzo(a)pyrene mutagenicity was detected using Salmonella typhimurium TA100 in the Ames test, and correlated positively with lymphocyte CYP1A1 content. The data show that CYP1A1 is present in rat peripheral blood lymphocytes in vivo, and is inducible by prototypic, as well as nonprototypic, inducers of the enzyme.

Animals↗
PubMed1999

Cytogenetic changes in radiation-induced tumors of the thyroid.

Thyroid carcinoma incidence is increased significantly after ionizing irradiation; however, the possible mechanisms have not yet been identified. To provide clues for an understanding of the radiation-induced transformation of thyroid epithelium, we analyzed the karyotypes of 56 childhood thyroid tumors that appeared in Belarus after the Chernobyl nuclear accident in 1986. We also studied eight secondary thyroid tumors that developed after radiotherapy. Metaphase preparations obtained from primary cultures were analyzed by G-banding. Clonal structural aberrations were found in 13 of 56 Belarussian cases and in 6 of 8 secondary tumors that developed after radiotherapy. Furthermore, we detected multiple chromosomal aberrations as well as complex rearrangements in some of these tumors and performed a detailed analysis of marker chromosomes from a single case using spectral karyotyping and comparative genomic hybridization in a childhood tumor from Belarus with a near-triploid karyotype. Both comparative genomic hybridization and spectral karyotyping analysis revealed structural alterations affecting identical chromosomes 1, 2, 9, and 13, among others. In addition to the known hot spots of alterations in papillary thyroid carcinomas on chromosomes 1q and 10q, a comprehensive breakpoint analysis in the pooled data set revealed novel breakpoints on chromosomes 4q, 5q, 6p, 12q, 13q, and 14q. The chromosomal aberrations in these tumors may provide suitable starting points for the positional cloning of genes involved in radiation-induced tumorigenesis.

Adolescent↗
PubMed1999

Adaptation of the walking pattern to uphill walking in normal and spinal-cord injured subjects.

Lower-limb movements and muscle-activity patterns were assessed from seven normal and seven ambulatory subjects with incomplete spinal-cord injury (SCI) during level and uphill treadmill walking (5, 10 and 15 degrees). Increasing the treadmill grade from 0 degrees to 15 degrees induced an increasingly flexed posture of the hip, knee and ankle during initial contact in all normal subjects, resulting in a larger excursion throughout stance. This adaptation process actually began in mid-swing with a graded increase in hip flexion and ankle dorsiflexion as well as a gradual decrease in knee extension. In SCI subjects, a similar trend was found at the hip joint for both swing and stance phases, whereas the knee angle showed very limited changes and the ankle angle showed large variations with grade throughout the walking cycle. A distinct coordination pattern between the hip and knee was observed in normal subjects, but not in SCI subjects during level walking. The same coordination pattern was preserved in all normal subjects and in five of seven SCI subjects during uphill walking. The duration of electromyographic (EMG) activity of thigh muscles was progressively increased during uphill walking, whereas no significant changes occurred in leg muscles. In SCI subjects, EMG durations of both thigh and leg muscles, which were already active throughout stance during level walking, were not significantly affected by uphill walking. The peak amplitude of EMG activity of the vastus lateralis, medial hamstrings, soleus, medial gastrocnemius and tibialis anterior was progressively increased during uphill walking in normal subjects. In SCI subjects, the peak amplitude of EMG activity of the medial hamstrings was adapted in a similar fashion, whereas the vastus lateralis, soleus and medial gastrocnemius showed very limited adaptation during uphill walking. We conclude that SCI subjects can adapt to uphill treadmill walking within certain limits, but they use different strategies to adapt to the changing locomotor demands.

Adaptation, Physiological↗
PubMed1999

Prognosis, treatment, and recurrence of breast cancer for women attending or not attending the Screening Mammography Program of British Columbia.

Breast cancer screening programs have been initiated in many countries in the past decade. To determine the impact of the Screening Mammography Program of British Columbia (SMPBC), disease and treatment outcomes for women with breast cancer diagnosed in BC between 1989 and 1996 were compared on the basis of attendance at the SMPBC. An SMPBC attender was a women diagnosed with breast cancer within three years of an SMPBC screen, regardless whether the cancer was detected as a result of that screen. Of the 13,636 women aged 40-89 years diagnosed with breast cancer in BC during the study period, 2,647 (19.4%) were SMPBC attenders. 73.5% of SMPBC attenders (N = 1,946) and 74.2% of non-attenders (N = 8,149) were referred to the BC Cancer Agency and had pathology, staging, treatment, and outcome information available. SMPBC attenders compared with non-attenders were more likely to have in situ disease alone, and those with invasive cancers had smaller tumors which were less likely to have grade III histology and less likely to have spread to axillary lymph nodes (all P < 0.001). SMPBC attenders were more likely to be treated with breast conservation and less likely to receive adjuvant chemotherapy or tamoxifen (P < 0.001). Log-rank tests showed local (P = 0.017), distant (P < 0.001), and overall (P < 0.001) disease-free survival were better for SMPBC attenders. These favorable surrogate endpoints suggest that the benefits of breast screening as demonstrated by randomized trials can be translated into community practice by an organized breast screening program.

Adult↗
PubMed1999

Patient-specific probes for preimplantation genetic diagnosis of structural and numerical aberrations in interphase cells.

PURPOSE: Our purpose was to evaluate the utility of translocation breakpoint-spanning DNA probes for prenatal genetic diagnosis of structural and numerical chromosome aberrations in interphase cells. METHODS: Breakpoint-spanning translocation probes were isolated from large insert DNA libraries and labeled so that the breakpoint regions were stained in different colors. Hybridization conditions were optimized using blastomeres biopsied from donated embryos. Probes were then applied to analyze patient blastomeres. RESULTS: We prepared translocation breakpoint-specific probes for 18 in vitro fertilization patients. Here, we describe the preparation of probes for two patients carrying balanced translocations involving chromosome 11 [t(11;22)(q23;q11), t(6;11)(p22.1;p15.3)]. The breakpoint cloning procedure could be accomplished in about 3-5 weeks. Additional time was needed to optimize probes. Application of probes demonstrated numerical as well as structural abnormalities. CONCLUSIONS: Breakpoint-spanning probes allow chromosome analysis in interphase cells as required for preimplantation genetic diagnosis screening of blastomeres.

Chromosomes, Human, Pair 11↗
PubMed1999

A prospective study on conversion from sandimmune to neoral in stable adult liver transplant recipients.

Neoral is a microemulsion formulation of cyclosporin (CyA), which has more consistent and better pharmacokinetics parameters with improved bioavailability compared to conversional formulation of Sandimmune. Sixty-four stable adults (age >18 years), who had received liver transplants (LTx) and were on Sandimmune-based immunosuppression, were converted to Neoral on milligram for milligram basis. Mean age was 52.5 +/- 13.5 years and male/female distribution was 22/42. Mean interval from LTx to conversion was 109.2 +/- 136 months. In 13 patients (20%) the dose of Neoral was reduced because of an increase in serum creatinine (N = 9), hyperkalemia (N = 1), headache (N = 1), peripheral parasthesia (N = 1), and a general sense of discomfort (N = 1). Interestingly, in two patients a decrease in the trough concentration was observed with the increase in liver enzymes. Both patients responded to an increase in Neoral dose. The present study suggests while the majority of the stable liver transplant patients (77%) can be safely converted to Neoral from Sandimmune on a milligram to milligram basis, they need to be carefully monitored for renal function, liver function, and trough concentration of CyA.

Adult↗
PubMed1999

Prevention and treatment of cytomegalovirus infection in organ transplant recipients.

Cytomegalovirus (CMV) is the most common viral pathogen in organ transplant recipients. The patients at highest risk of developing CMV disease are seronegative recipients of seropositive donors, and seropositive recipients who receive antilymphocyte agents such as OKT3 and antithymocyte globulin (ATG) for induction or for rejection. There have been many trials of CMV prevention, but they are difficult to compare with one another because of variability in definitions and end points. Two modalities that have been used to prevent CMV disease are prophylaxis and preemptive therapy. In prophylaxis all patients are given an antiviral agent in order to prevent CMV disease, while in preemptive therapy (also called targeted prophylaxis) only patients who are identified as 'high risk' are selected for treatment. Selected trials of prophylaxis and preemptive therapy in solid-organ recipients are reviewed. The factors to be considered in using one modality or the other are side effects from antivirals, cost of monitoring and antivirals, efficacy of the two modalities, and potential emergence of drug resistance. Sensitive tests that have been used for early diagnosis and monitoring of CMV are antigenemia and the polymerase chain reaction (PCR). Antigen pp65 is a lower matrix protein and can be detected in peripheral blood leukocytes. The sensitivity and specificity are high and vary from 89% to 100% and 92% to 96%, respectively. Currently, many authors believe that the antigenemia test is more useful than the PCR test. The antigenemia test is useful for viral monitoring as a guide for preemptive therapy after organ transplantation. Persistence of high counts of antigenemia may indicate inadequate antiviral therapy or emergence of resistance. Recurrence of positive antigenemia after treatment of CMV disease can be a sign of relapse. Transplant patients who develop resistance to antiviral drugs are usually seronegative recipients who receive an organ from a seropositive donor and have several courses of antivirals for CMV disease. Ganciclovir is the most frequent antiviral agent used in transplant recipients and is usually well tolerated. Resistance to ganciclovir may occur and is usually secondary to virus mutation in the UL97 gene. The availability of sensitive diagnostic tests such as pp65 antigenemia has made the early diagnosis of CMV possible in organ transplant recipients. CMV is being treated much earlier now, and progression to disseminated disease is uncommon. Prudent use of antiviral drugs will hopefully limit the problem of drug resistance.

Antiviral Agents↗
PubMed1999

Molecular cloning of translocation breakpoints in a case of constitutional translocation t(11;22)(q23;q11) and preparation of probes for preimplantation genetic diagnosis.

In vitro fertilization (IVF) centres with preimplantation genetic diagnosis (PGD) programmes are often confronted with the problem of identifying chromosomal abnormalities in interphase cells biopsied from preimplantation embryos of carriers of a reciprocal translocation. The present authors have developed a DNA testing based approach to analyse embryos from translocation carriers, and this report describes breakpoint-spanning probes to detect abnormalities in cases of the most common human translocation (i.e. the t(11;22)(q23;q11)). Screening a yeast artificial chromosome (YAC) library for probes covering the respective breakpoint regions in the patient lead to probes for the breakpoint on chromosome 11q23. The physically mapped YAC and bacterial artificial chromosome (BAC) clones from chromosome 22 were then integrated with the cytogenetic map, which allowed localization of the breakpoint on chromosome 22q11 to an interval of less than 84 kb between markers D22S184 and KI457 and to prepare probes suitable for interphase cell analysis. In summary, breakpoint localization could be accomplished in about 4 weeks with additional time needed to optimize probes for use in PGD.

Abortion, Spontaneous↗
PubMed1999

What have we learned about primary liver transplantation under tacrolimus immunosuppression? Long-term follow-up of the first 1000 patients.

OBJECTIVE: To summarize the long-term efficacy and safety of tacrolimus in orthotopic liver transplant (OLT) recipients, as well as to examine the factors that influence long-term morbidity and mortality rates. BACKGROUND: Tacrolimus (FK506, Prograf) was introduced as primary immunosuppression for primary liver transplantation in 1989; many subsequent trials have verified the association of tacrolimus with decreased rates of acute rejection and steroid-resistant rejection after OLT. Cumulative experience with tacrolimus has also defined its short- and intermediate-term toxicity. METHODS: One thousand consecutive patients undergoing primary OLT at a single center from August 1989 to December 1992, under tacrolimus immunosuppression, were followed until January 1999. Patients were categorized by age. Mean follow-up was 93.4+/-11 months after OLT. Patient survival, graft survival (with corresponding causes of death and retransplantation), and rejection rates (and corresponding doses of immunosuppression) were examined as efficacy parameters. Hypertension, renal function, incidence of malignancies, incidence of diabetes, and other toxicities were examined as safety parameters. RESULTS: Actual 6-year overall patient survival rate was 68.1% and graft survival rate was 62.5%, with significant differences in the patterns of survival among the different age groups. After the first post-OLT year, infection, recurrence of disease, de novo malignancies, and cardiovascular events were the main causes of graft loss and death during the long-term follow-up. Graft loss related to either acute or chronic rejection was rare. The rate of acute rejection beyond 2 years was approximately 3% per year, and most were steroid-responsive. Approximately 70% of the patients were receiving tacrolimus monotherapy beyond year 1; at the latest follow-up, 74.2% were maintained on tacrolimus alone. In 6.1% of the survivors, end-stage renal disease developed during the follow-up period, requiring either dialysis or kidney transplantation. Hyperkalemia and hypertension was observed in approximately one third of the patients. Insulin-dependent diabetes mellitus (including patients who had diabetes before the transplant) was observed in 14% in year 1, dropping to 11% in year 7. In 82 patients, de novo malignancies developed; in 41 patients, lymphoproliferative disorders developed during the entire follow-up period. CONCLUSIONS: Long-term patient and graft survival rates are excellent under tacrolimus immunosuppression. Pediatric patients have a better long-term outcome than adults, in part because of the limited recurrence of the original disease, which was the most common cause of late graft loss (other than patient death, most commonly the result of late de novo malignancies and cardiovascular events). Graft loss from late rejection was rare.

Adolescent↗
PubMed1999

Attributes of quiet stance in the chronic spinal cat.

Standing is a dynamic task that requires antigravity support of the body mass and active regulation of the position of the body center of mass. This study examined the extent to which the chronic spinal cat can maintain postural orientation during stance and adapt to changes in stance distance (fore-hindpaw separation). Intact cats adapt to changes in stance distance by maintaining a constant horizontal orientation of the trunk and changing orientation of the limbs, while keeping intralimb geometry constant and aligning the ground reaction forces closely with the limb axes. Postural adaptation was compared in four cats before and after spinalization at the T(6) level, in terms of the forces exerted by each paw against the support, body geometry (kinematics) and electromyographic (EMG) activity recorded from chronic, indwelling electrodes, as well as the computed net torques in the fore and hindlimbs. Five fore-hindpaw distances spanning the preferred distance were tested before spinalization, with a total range of 20 cm from the shortest to the longest stance. After spinalization, the cats were trained on a daily basis to stand on the force platform, and all four cats were able to support their full body weight. Three of the four cats could adapt to changes in stance distance, but the range was smaller and biased toward the shorter distances. The fourth cat could stand only at one stance distance, which was 8 cm shorter than the preferred distance before spinalization. All cats shifted their center of pressure closer to the forelimbs after spinalization, but the amount of shift could largely be accounted for by the weight loss in the hindquarters. The three cats that could adapt to changes in stance distance used a similar strategy as the intact cat by constraining the trunk and changing orientation of the limb axes in close relation with the forces exerted by each limb. However, different postures in the fore- and hindlimbs were adopted, particularly at the scapula (more extended) and pelvis (tipped more anteriorly). Other changes from control included a redistribution of net extensor torque across the joints of the forelimb and of the hindlimb. We concluded that the general form of body axis orientation is relatively conserved in the spinal cat, suggesting that the lumbosacral spinal circuitry includes rudimentary set points for hindlimb geometry. Both mechanical and neural elements can contribute toward maintaining body geometry through stiffness regulation and spinal reflexes.

Adaptation, Physiological↗
PubMed1999

Weight support and balance during perturbed stance in the chronic spinal cat.

The intact cat maintains balance during unexpected disturbances of stance through automatic postural responses that are stereotyped and rapid. The extent to which the chronic spinal cat can maintain balance during stance is unclear, and there have been no quantitative studies that examined this question directly. This study examined whether the isolated lumbosacral cord of the chronic spinal cat can generate automatic postural responses in the hindlimbs during translation of the support surface. Responses to 16 directions of linear translation in the horizontal plane were quantified before and after spinalization at the T(6) level in terms of forces exerted by each paw against the support, motion of the body segments (kinematics), and electromyographic (EMG) activity. After spinalization, the cats were trained on a daily basis to stand on the force platform, and all four cats were able to support their full body weight. The cats usually required assistance for balance or stability in the horizontal plane, which was provided by an experimenter exerting gentle lateral force at the level of the hips. Three of the four animals could maintain independent stance for a brief period (10 s) after the experimenter stabilized them. The fourth cat maintained weight support but always required assistance with balance. Perturbations were delivered during the periods of independent stance in three cats and during assisted stance in the fourth. A response to translation in the spinal cats was observed only in those muscles that were tonically active to maintain stance and never in the flexors. Moreover, latencies were increased and amplitudes of activation were diminished compared with control. Nevertheless, flexors and extensors were recruited easily during behaviors such as paw shake and stepping. It is concluded that centers above the lumbosacral cord are required for the full elaboration of automatic postural responses. Although the spinal cat can achieve good weight support, it cannot maintain balance during stance except for brief periods and within narrow limits. This limited stability is probably achieved through spinal reflex mechanisms and the stiffness characteristics of the tonically active extensors.

Adaptation, Physiological↗