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Biomedical subjects

S Carlson

Publications and source records attributed to S Carlson.

At least 19 recordsLinked to original sources
PubMed1992

Functional properties of dorsolateral prefrontal cortical neurons in awake monkey.

Electrophysiological single-cell responses were studied in 134 neurons in Walker's areas 46 and 9 of the prefrontal cortex of two stumptail macaques. The neurons were systematically tested for various visual, auditory and somatosensory stimuli. In addition, the rate of neuronal discharges were observed in relation to provoked or spontaneous eye or limb movements. More than half (52.2%) of the neurons responded to stimulation, and the majority of them gave visual responses. Eighty percent of the visual neurons responded to the presentation of various objects, the remaining being selective for meaningful objects or the appearance and movements of the experimenter. Auditory, somatosensory, somatomotor and oculomotor responses were also encountered; 9.0% of the recorded neurons were multimodal. Despite the large stimulus repertoire 47.8% of the neurons were found to be only spontaneously active.

Animals↗
PubMed1992

Collagens facilitate epithelial migration in restitution of native guinea pig intestinal epithelium.

An in vitro intestinal epithelial wound/repair model in which epithelium is stripped from villus tips and the wound is resealed during the following 60 minutes has previously been described. The process, termed epithelial restitution, results in part from the rapid migration of epithelial cells shouldering the wound over the denuded basement membrane. The present report examines the requirements for epithelial cell-basement membrane interactions during restitution in this model. Addition of heparin, soluble matrix components, or a variety of antibodies to matrix components (laminin; fibronectin; collagen I, III, IV) does not impair restitution. Although inhibition of protein synthesis alone also does not retard restitution, in the simultaneous presence of antibody to type III and IV collagen restitution is impeded as judged functionally and structurally. Preincubation of tissues with 20 mmol/L cis-OH-proline (a condition known to inhibit cellular secretion of newly synthesized collagen) similarly inhibited structurally and functionally defined restitution only if antibodies to type III and IV collagen were simultaneously present. These results suggest that collagen-epithelial cell interactions are important in restitution after injury, and if necessary, collagen can be produced locally and rapidly at the site of injury to allow restitution to normally proceed.

Animals↗
PubMed1992

Increased sexual behavior in male Macaca arctoides monkeys produced by atipamezole, a selective alpha 2-adrenoceptor antagonist.

The effect of a highly selective and potent alpha 2-adrenoceptor antagonist, atipamezole, on sexual behavior was studied in three stumptail macaques (Macaca arctoides). Following IM administration of atipamezole or saline control, the behavior of the male monkey with a female monkey was observed for 30 min. Atipamezole dose dependently (0.01-0.15 or 0.30 mg/kg) produced a significant increase in the number of ejaculations in all three monkeys, including an old one with decreased sexual activity in control conditions. Both ejaculations obtained by copulation and masturbation were increased. It is concluded that atipamezole is effective in increasing sexual behavior in male stumptail monkeys.

Adrenergic alpha-Antagonists↗
PubMed1992

Effects of medetomidine, an alpha-2 adrenoceptor agonist, and atipamezole, an alpha-2 antagonist, on spatial memory performance in adult and aged rats.

The effects of a novel, highly selective alpha-2 agonist, medetomidine, and its antagonist, atipamezole, were studied on the working memory of rats performing a spatial delayed alternation task. Testing was performed in two stages, at the age of 8.3 months (mean) and again when the rats were 17.6 months (mean). A low dose (3 micrograms/kg) and a high dose (30 micrograms/kg) of medetomidine improved the performance of the old rats in the memory task but had no effect on the young rats. The dose-response curve of medetomidine resembles that of guanfacine, another alpha-2 agonist. At the low dose of medetomidine (3 micrograms/kg) the animals showed no signs of sedation. Since medetomidine even at a low dose has a beneficial effect on the memory performance of old rats, it could be a good candidate for the treatment of age-associated memory dysfunction.

Adrenergic alpha-Agonists↗
PubMed1992

Amino acids and serotonin in Limax maximum after a tryptophan devoid diet.

1. Animals avoid diets lacking an essential amino acid, such as tryptophan (TRP), the precursor for serotonin (5-HT). 5-HT is important in the control of feeding. 2. To study the effects of TRP deprivation, slugs were fed TRP-devoid (DEV) or control (COR) diets. 3. Food intake was depressed in DEV, as expected, but after 2 weeks, the serontonergic metacerebral giant cell in DEV was still functional. 4. Neither brain 5-HT nor plasma TRP concentration was affected. 5. Compared with food-restricted animals that had reductions in most amino acids, the DEV group sustained a marked plasma amino acid imbalance.

Amino Acids↗
PubMed1992

Prevention of hyperbaric-associated middle ear barotrauma.

STUDY OBJECTIVE: To determine the efficacy of topical nasal decongestant in the prevention of middle ear barotrauma in patients undergoing hyperbaric oxygen therapy. DESIGN: Prospective, parallel, double-blind, randomized trial. SETTING: University-affiliated community hospital emergency department with hyperbaric oxygen facilities. PARTICIPANTS: Sixty patients undergoing hyperbaric oxygen therapy; 30 subjects in each treatment arm. INTERVENTIONS: After randomization, consenting patients were given two sprays of oxymetazoline hydrochloride or sterile water, 15 minutes before hyperbaric oxygen therapy. Collected data included patient demographics, ear examinations before and after hyperbaric oxygen treatment, and subjective ear complaints. The otoscopic appearance of the tympanic membrane was graded according to the amount of hemorrhage in the eardrum, with Teed scores ranging from 0 (symptoms only) to 5 (gross hemorrhage and rupture). RESULTS: The treatment groups were similar with regard to age, sex, and medical history. Ear discomfort during hyperbaric oxygen therapy was present in 63% (19 of 30) of those receiving oxymetazoline versus 67% (20 of 30) of the control group (P = .99). Likewise, both groups had similar Teed scores after hyperbaric oxygen therapy (P = .88). No adverse effects were noted. CONCLUSION: The results of this pilot study suggest that topical decongestants may not be effective in preventing middle ear barotrauma during hyperbaric oxygen therapy.

Administration, Topical↗
PubMed1992

Response characteristics of tooth pulp-driven postsynaptic neurons in the spinal trigeminal subnucleus oralis of the cat.

Neuronal activity in the spinal trigeminal subnucleus oralis in response to electrical tooth stimulation was recorded in the anaesthetized cat in order to compare the electrophysiological characteristics of the oralis neurons with those of subnucleus caudalis and interpolaris neurons recorded in previous studies. The most sensitive oralis neurons had lower thresholds and shorter latencies than the most sensitive caudalis and interpolaris neurons. The thresholds of the oralis neurons were lower and their strength-duration curves flatter than those depicting liminal dental pain in man but similar to those depicting liminal jaw reflexes in the cat. Noxious conditioning stimulus elevated the threshold of only 1 of 10 neurons tested. The converging input from the skin and oral mucosa was from low-threshold mechanoreceptors. The results indicate that the response properties of the subnucleus oralis neurons differ significantly from those of other spinal subnuclei. Human pain thresholds cannot be explained by the liminal response properties of oralis neurons. These neurons might be important in the mediation of liminal reflex events evoked by dental stimuli.

Animals↗
PubMed1991

Effects of atipamezole, a novel alpha 2-adrenoceptor antagonist, in open-field, plus-maze, two compartment exploratory, and forced swimming tests in the rat.

The behavioral effects of atipamezole (0.5-4.5 mg/kg), a new and highly selective alpha 2-adrenoceptor antagonist, were studied in four behavioral models: open-field, elevated plus-maze, two compartment exploratory test and forced swimming test. Atipamezole (1.5 and 4.5 mg/kg) produced a dose-dependent suppression of locomotor activity in the open field test. In the two compartment exploratory test, the same doses of atipamezole decreased locomotor activity in a 5 min test but not in a 10 min test. The numbers of transitions between the compartments were not significantly affected by atipamezole. Doses of 0.5-4.5 mg/kg did not significantly change the time spent in the open arms or the total number of arm entries in the plus-maze, and doses of 1.5 and 4.5 mg/kg decreased defecation marginally. Vocalization during the forced swimming test was increased by atipamezole (1.5 mg/kg) but the duration of immobility was not increased over the dose range (0.5-1.5 mg/kg) of atipamezole used. Our results suggest that, in the rat, atipamezole decreases motor activity in the early phase of the exploration of new surroundings. In the doses used, atipamezole may suppress defecation and increase vocalization in rats.

Adrenergic alpha-Antagonists↗
PubMed1991

Attempted reversal of cocaine-induced antinociceptive effects with naloxone, an opioid antagonist.

We attempted to reverse the behavioral and neuronal antinociceptive effects of cocaine with naloxone, an opioid antagonist. Cocaine (20 mg/kg i.p.) produced a strong analgesic effect in the formalin test and in the tail pinch test. These cocaine-induced analgesic effects could be reversed by naloxone at a very high dose (10 mg/kg) but not at a dose (1 mg/kg) which was sufficient to attenuate morphine (10 mg/kg)-induced analgesia. Naloxone alone at a dose of 10 mg/kg did not produce significant effects. In general, nociceptively evoked responses in medial thalamic neurons were suppressed by cocaine (20 mg/kg), and this suppression was attenuated by naloxone (10 mg/kg). The results suggest that opioid receptors which are not involved in mediating morphine-induced analgesia and which have a low sensitivity to naloxone are involved in cocaine-induced central analgesia.

Analgesics↗
PubMed1991

Hypothalamic dopaminergic neurons in transgenic dwarf mice: histofluorescence, immunocytochemical, and in situ hybridization studies.

Spontaneous dwarf mice, in which both growth hormone (GH) and prolactin (PRL) are undetectable, are severely deficient in the PRL-inhibiting catecholamine dopamine (DA), as well as its synthetic enzyme, tyrosine hydroxylase (TH), in the basal hypothalamus (Phelps et al., Cell Tissue Res., 240:19-25, 1985; Phelps, Brain Res., 416:354-358, 1987). In contrast, transgenically constructed dwarf mice (Behringer et al., Genes Dev., 2:453-461, 1988) show complete ablation of pituitary GH cells, but PRL cells are retained at a level of approximately 10% of normal. In order to determine the feedback effect of this reduced, rather than absent, PRL on hypothalamic DA neurons, brains of transgenic dwarf mice were examined for catecholamine transmitters by histofluorescence, for the synthetic enzyme TH by immunocytochemistry, and for TH mRNA expression by in situ hybridization. DA histofluorescence in transgenic dwarfs was comparable to that of normal littermate mice in nonpituitary regulating areas (perikarya of zona incerta [A13] of hypothalamus and in midbrain substantia nigra area [A9]). Arcuate nucleus (A12) DA neurons that inhibit PRL secretion, however, showed dim to absent fluorescence in perikarya and in external median eminence terminals in dwarfs. There were reduced (P less than 0.05) numbers of A12 TH-immunoreactive neurons in transgenic dwarfs, to approximately 60% of those in normal mice. In contrast, TH-positive neurons in other hypothalamic areas (A13, A14) had average populations equivalent to those in normal mice. Quantification of TH mRNA abundance by in situ hybridization using both image analysis of hybridization over the arcuate nucleus, and grain counts per individual A12 cell in this nucleus, indicated that relative mRNA levels were the same in normal and transgenic dwarfs. The observations indicate that reduction in pituitary PRL is accompanied by defective expression in hypothalamic tuberoinfundibular neurons, which is severe at the DA neurotransmitter level, significant regarding observable TH immunoreactivity, and undetectable with regard to TH mRNA expression. Collectively, the findings suggest that posttranscriptional processes are involved with the mediation of PRL feedback upon hypothalamic neurons. Technically and quantitatively, the report presents the feasibility of simultaneous evaluation of transmitter histofluorescence, synthetic enzyme immunocytochemistry, and mRNA expression in individual animals.

Animals↗
PubMed1991

Effect of perivascular sympathectomy on distal adrenergic innervation in the hands of monkeys.

Perivascular sympathectomy has been thought to cause distal adrenergic denervation. We performed perivascular sympathectomy for a distance of 1 cm. on two common digital arteries in the right hands of two anaesthetised Macaca arctoides monkeys. Four days later, samples were taken for glyoxylic acid-induced fluorescence examination of the operated and opposite control hand. The distal adrenergic nerves were morphologically normal in appearance after the perivascular sympathectomy. The operation should perhaps be called adventitectomy rather than perivascular sympathectomy and its positive effects may be due to the loss of adventitial support for the vasospastic arteries rather than adrenergic denervation.

Adrenergic Fibers↗
PubMed1991

Clinical and electroretinographic comparison between Aland Island eye disease and a newly found related disease with X-chromosomal inheritance.

Two subjects representing AIED (Aland Island Eye Disease) and a family with 5 males affected with an AIED related X-linked hereditary eye disease were studied clinically and electrophysiologically. The clinical picture of AIED includes myopia and astigmatism, reduced visual acuity, nystagmus, ocular albinism, hemeralopia and dyschromatopsia (No. 300600, McKusick 1990). The subjects with the related disease showed astigmatism with or without myopia, reduced visual acuity, slight hemeralopia, normal color vision in 3/5 subjects, no ocular albinism and nystagmus only in one case. In both diseases the ERG was abnormal showing defective a- and b-waves, but there were also differences. The most notable was the greater reduction of the b-wave amplitude in the mixed (rod and cone) responses for the white stimulus in the ERG of the AIED related disease. With regard to the pathogenesis we propose that in both diseases rod and cone functions are defective but in an AIED related disease a defective cone function inhibits the transmission of the rod signals to the rod bipolars, causing greatly reduced mixed responses. The clinical and ERG findings of this study suggest that the 5 subjects of our family do not represent AIED but another X-linked hereditary eye disease. The investigation to find out the gene locus of this disease is going on.

Adolescent↗
PubMed1991

Supraphysiologic L-tryptophan elicits cytoskeletal and macromolecular permeability alterations in hamster small intestinal epithelium in vitro.

We have previously shown that Na(+)-coupled transport of glucose and amino acids across the apical membrane of intestinal absorptive cells is accompanied by alterations in cytoskeletal structure and altered sieving of small hydrophilic solutes by tight junctions. Here we report that in response to the essential amino acid L-tryptophan at lumenal concentrations likely to be supraphysiological (1 mM or greater), these responses are so exaggerated as to induce disruption of tight junctions and transepithelial macromolecular leaks. Since these effects of L-tryptophan are energy and Na+ dependent and occur with mucosal but not serosal exposure to L-tryptophan, it appears they are triggered by activation of a Na(+)-nutrient cotransporter in the apical membrane of absorptive cells rather than by the presence of an unidentified trace contaminant. Our findings suggest the possibility that dietary supplementation by L-tryptophan may result in loss of the intestinal epithelial barrier to dietary antigens. We speculate that such a response to supraphysiologic tryptophan may contribute, in part, to the recently recognized curious tryptophan-induced eosinophilia myalgia syndrome.

Animals↗
PubMed1990

Effects of phlorizin and sodium on glucose-elicited alterations of cell junctions in intestinal epithelia.

Glucose alters absorptive cell tight junction structure and, as deduced from an impedance analysis model, diminishes tight junction resistance in the small intestine (J.R. Pappenheimer, J. Membr. Biol. 100: 137-148, 1987; and J.L. Madara and J.R. Pappenheimer, J. Membr. Biol. 100: 149-164, 1987). Here we provide further evidence in support of this hypothesis using the conventional approach of analysis of mucosal sheets mounted in Ussing chambers. This approach offers advantages for investigating underlying mechanisms, including the effects of ions and inhibitors on the regulation of intercellular junctions by glucose. We show that phlorizin blocks a resistance decrease elicited by glucose and demonstrate that substitution of choline for sodium also prevents the response. The dilatations in absorptive cell tight junctions that accompany this glucose-elicited response are similarly prevented by phlorizin exposure or sodium substitution. The effects of phlorizin on junctional permeability can also be demonstrated in vivo. Phlorizin reduces the transjunctional flux of creatinine in glucose-perfused intestines of anesthetized animals, even when account is taken of the reduction of fluid absorption caused by phlorizin. Last, in vivo perfusion studies suggest that although, at 25 mM luminal glucose, virtually all glucose absorption is transcellular, at a luminal glucose concentration of 125 mM approximately 30% of glucose absorption occurs paracellularly because of solvent drag across tight junctions of altered permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1990

C. difficile toxin A increases intestinal permeability and induces Cl- secretion.

Mucosal sheets of guinea pig ileum mounted in Ussing chambers were used to determine effects of highly purified Clostridium difficile toxin A on intestinal structure and barrier function in the absence of recruited neutrophils and blood flow. With the use of standard electrophysiological and morphological techniques, our results indicate that 5 micrograms/ml mucosal toxin A induces substantial alteration in epithelial permeability and in structure of absorptive cells. Transepithelial fluxes of mannitol (3.6 A) and inulin (11.5 A) increased 20-80 min after toxin A exposure (63 +/- 13 vs. 149 +/- 14 and 2.33 +/- 0.43 vs. 7.03 +/- 1.0 nmol.cm-2.h-1 for mannitol and inulin; controls vs. toxin exposed, respectively, both P less than 0.01). Toxin A exposure diminished short-circuit current (153 +/- 8 vs. 77 +/- 6 microA/cm2 for control and toxin exposed, respectively, P less than 0.001), decreased transepithelial electrical resistance (61.6 +/- 3 vs. 50.1 +/- 3.9 omega.cm2 for control and toxin exposed, respectively, P less than 0.05), increased passive permeation of Na+ (19.1 +/- 0.9 vs. 27.4 +/- 0.9 mumol.cm-2.h-1 for control and toxin exposed, respectively), and induced a Cl- secretory response (net flux 3.65 +/- 3.0 vs. -4.62 +/- 2.6 mumol.cm-2.h-1, for control and toxin exposed, respectively, P less than 0.05) over the 2-h experimental time course. Toxin A-induced structural alterations of villus tip absorptive cells were strikingly similar to those induced by the actin-binding agent cytochalasin D. Specifically, cells displayed constricted subjunctional zones, flared microvillus brush borders, condensation of microfilaments in the zone of the perijunctional actomyosin ring, and breakdown of intercellular tight junctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

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Humans↗