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Biomedical subjects

C A Cohen

Publications and source records attributed to C A Cohen.

At least 37 records · Page 2Linked to original sources
PubMed1988

Reversal of a trimethyltin-induced learning deficit by desglycinamide-8-arginine vasopressin.

Trimethyltin (TMT) is an organometal neurotoxin which produces lesions primarily in the limbic system. Selectivity seems to depend upon the dose, but the hippocampus and related entorhinal cortical structures, of importance for learning and memory, are most often described as target sites. We have previously demonstrated that subjects treated with a moderate dose of TMT prior to acquisition sessions, are unable to learn a forward autoshaping task with a 6 sec delay of reinforcement, but are capable of acquiring the same task when no delay of reinforcement is used. These data suggested that the performance deficit is one of learning (i.e. consolidation) rather than of memory (i.e. storage), retrieval, or sensorimotor impairment. To more rigorously test this hypothesis, we determined if performance of a task already learned would be impaired by the neurotoxin. Adult male Long Evans rats were given 10 acquisition sessions of 24 trials, following which TMT (6.0 mg/kg, p.o.) was administered. One month later, these rats performed the lever-touching behavior as well as controls, despite the fact that the same dose of TMT interfered with learning if given one month prior to acquisition sessions, thus confirming our hypothesis. In a second experiment we determined if the peptide analog of vasopressin, desglycinamide-8-arginine vasopressin (DGAVP), could reverse a learning deficit in a population of non-learners. Rats were treated with TMT or water vehicle one month prior to autoshaping. TMT significantly retarded acquisition. After 10 sessions of 12 trials each, non-learners (i.e. rats treated with TMT that failed to associate the lever with delivery of a reinforcer) were administered saline or DGAVP (7.5 micrograms/kg, s.c.) 1 hr before sessions 11-13; treatment was discontinued prior to sessions 14 and 15. Peptide treated subjects showed evidence of acquisition and exhibited higher levels of lever-directed behavior than saline treated nonlearners. Performance was maintained after DGAVP treatment was discontinued, indicating that the learning-enhancing action of DGAVP was not transient or state-dependent.

Animals↗
PubMed1988

Different methods for producing neonatal undernutrition in rats cause different brain changes in the face of equivalent somatic growth parameters.

Similar degrees of undernutrition were induced in neonatal rat pups using a modified Slob technique and a large-litter manipulation. From birth, large litters and Slob litters were comprised of 20 and 10 pups, respectively. On days 2, 4 and 6, half of the pups in the Slob group were cross-fostered to nonlactating foster aunts, while the remaining half of each litter (controls), as well as the large-litter rats were cross-fostered to a lactating dam. On day 10, undernourished Slob and large-litter pups showed similar body weight and body length deficits compared with controls, but differences between the two undernourished groups emerged when regional brain weight and nucleic acids and proteins were examined. The acute intermittent undernutrition of the modified Slob technique had more severe consequences than the large-litter manipulation for brain growth and development. Therefore, two methods of inducing early postnatal undernutrition may yield equivalent somatic effects, but very different brain growth parameters.

Animals↗
PubMed1988

Maturational influences on perseveration of avoidance and reversal learning after selected brain damage in rats.

In Experiment I, 18 weanling and 18 adult male rats received bilateral electrolytic lesions of the dorsomedial or ventrolateral prefrontal cortex, or the hippocampus, while 12 additional pups and adults served as nonoperated controls (n = 6/group). Subjects were observed for perseverative responding in acquisition of a stepup avoidance task, followed by reversal training and extinction. Thirty days later, subjects were retrained and tested in the same manner. During initial training, the numbers of trials to criteria, errors, and latencies on the last 5 trials all indicated significant effects from age, primarily, and surgery, secondarily. After 30 days, surgical effects assumed a more dominant role, with hippocampal and ventrolateral damage producing the greatest extent of response perseveration. Experiment II replicated the essential procedural sequence as Experiment I, but included damage from combined lesions. 24 weanlings and 24 adults received bilateral lesions to the dorsomedial prefrontal cortex, the dorsomedial prefrontal cortex plus caudate nucleus, or sham lesions. Subjects from this experiment were trained after 7 days or 60 days recovery (n = 6/group). The acquisition results indicated that all independent variables were significant, but only the age effect attained significance in the extinction data. Both experiments point to the profound influence of age at the time of damage in accounting for recovery of avoidance behavior.

Aging↗
PubMed1987

Selective learning impairment of delayed reinforcement autoshaped behavior caused by low doses of trimethyltin.

The organometal neurotoxin trimethyltin (TMT), induces impaired learning and memory for various tasks. However, administration is also associated with other "non-specific" behavioral changes which may be responsible for effects on conditioned behaviors. To determine if TMT treatment causes a specific learning impairment, three experiments were done using variations of a delay of reinforcement autoshaping task in which rats learn to associate the presentation and retraction of a lever with the delivery of a food pellet reinforcer. No significant effects of TMT treatment were found with a short (4 s) delay of reinforcement, indicating that rats were motivated and had the sensorimotor capacity for learning. When the delay was increased to 6 s, 3.0 or 6.0 mg TMT/kg produced dose-related reductions in behaviors directed towards the lever. Performance of a group given 7.5 mg TMT/kg, while still impaired relative to controls, appeared to be better than the performance of groups given lower doses. This paradoxical effect was investigated with a latent inhibition paradigm, in which rats were pre-exposed to the Skinner boxes for several sessions without delivery of food reinforcement. Control rats showed retardation of autoshaping when food reinforcement was subsequently introduced. Rats given 7.5 mg TMT/kg exhibited elevated levels of lever responding during pre-exposure and autoshaping sessions. The results indicate that 7.5 mg TMT/kg produces learning impairments which are confounded by hyperreactivity to the environment and an inability to suppress behavior toward irrelevant stimuli. In contrast, low doses of TMT cause learning impairments which are not confounded by hyperreactivity, and may prove to be useful models for studying specific associational dysfunctions.

Animals↗
PubMed1984

Hydrogen peroxide contrast echocardiography: quantification in vivo of myocardial risk area during coronary occlusion and of the necrotic area remaining after myocardial reperfusion.

During sustained coronary occlusion in canine preparations, the extent of regions that fail to show contrast enhancement when imaged by supra-aortic hydrogen peroxide contrast echocardiography (SHPCE) has been shown to correlate well for single cross sections with the extent of malperfused myocardium "at risk" of infarction. In the present study, SHPCE was investigated as a means of determining the fraction of total left ventricular mass at risk during occlusion. Since necrotic tissue has low blood flow even when reperfused, we also investigated the potential of quantitating the extent of infarcted myocardium by measuring the extent of contrast defects seen with SHPCE performed during reperfusion. In 20 dogs the fraction of the left ventricle showing a contrast defect during coronary occlusion correlated well with the fraction of the left ventricular mass "at risk" by an autoradiographic technique (autoradiography = 0.83 echocardiography + 8.6%; r = .89, SEE = 4.5%). SHPCE was also performed after 3 hr of reperfusion following occlusions varying in duration from 60 to 150 min. The fraction of the ventricle showing a contrast defect during reperfusion predicted the infarcted portion of the left ventricle as shown by triphenyl tetrazolium chloride staining (% left ventricle infarcted = 0.81 echocardiography + 3.3%; r = .84, SEE = 5.3%). Observer variability for the fraction of the ventricle showing a contrast defect was excellent during both occlusion and reperfusion. The ratio of the left ventricular extent of contrast-negative regions during reperfusion and occlusion was used to calculate a necrosis-to-risk index in vivo that correlated relatively well with the myocardial necrosis-to-risk ratio determined morphologically (r = .77, SEE = 16%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Clinical manifestations of inspiratory muscle fatigue.

Twelve patients exhibiting difficulties during discontinuation of artificial ventilation permitted us to investigate physical examination techniques used in diagnosing inspiratory muscle fatigue. Diaphragmatic and intercostal electromyographic tracings, arterial blood gases, rate and depth of ventilation, and thoracoabdominal motion were monitored during spontaneous breathing. Six patients showed electromyographic evidence of inspiratory muscle fatigue. A sequence of events leading to respiratory acidemia emerged--namely electromyographic evidence of fatigue, accompanied or followed by an increased respiratory rate, in turn followed by alternation between abdominal and rib cage breathing (respiratory alternans), paradoxical inward abdominal motion during inspiration (abdominal paradox), and finally an increase in PaCO2 associated with a fall in minute ventilation and respiratory rate, and worsening of respiratory acidemia. The abnormalities of respiratory movements may be reliable clinical signs of inspiratory muscle fatigue, particularly when accompanied by tachypnea and hypercapnia.

Adult↗
PubMed1981

HLA and alopecia areata in Jerusalem.

A study of 46 patients with Alopecia areata in Jerusalem showed a significant increase in the frequency of HLA-B18 (23.9%) as compared to the control population (7.4%) with a relative risk of 3.9%. This association of HLA-B18 with AA was independent of the origin of patients, sex, age of onset and type of alopecia areata.

Alopecia Areata↗
PubMed1980

Chronic neck and back pain: a reassessment of usual surgical treatment.

One hundred seventeen patients with chronic (noncancerous) back or neck pain had multidisciplinary evaluation in the Medical College of Virginia Pain Center and were followed up for one year. They ranged in age from 26 to 57 years. The 57 patients who had surgery had an average of 2.5 procedures (either laminectomies or back fusion) and only five of them returned to work. By contrast, 16 of 60 patients who had not had operation were able to secure employment after evaluation and treatment in the Pain Center.

Back Pain↗
PubMed1980

Scapulocostal syndrome: diagnosis and treatment.

The scapulocostal syndrome is an often encountered yet infrequently diagnosed cause of back and/or shoulder pain. Results of examination and treatment in the three cases described point out the necessary differential diagnosis to effectively screen these groups of patients from among those with more complex diseases.

Adult↗