Browsing by Author "FADIC, R"

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    ASSEMBLY AND DISASSEMBLY OF AXONAL MICROTUBULES OF THE TOAD XENOPUS-LAEVIS UNDER THE EFFECT OF TEMPERATURE
    (1992) ALVAREZ, J; FADIC, R
    In toads Xenopus laevis living at 11-degrees (winter), the microtubular density of 4-mum myelinated axons of lumbosacral nerves was assessed with the electron microscope. In controls, the density was 11.2 microtubules/mum2. In nerves incubated at 0-degrees, microtubules decreased following a simple exponential curve with a half time of 4.7 min (k = 0.149 min-1); residual microtubules were 4.5%. After rewarming, the full complement of microtubules reappeared within 60 min. In steady state, the microtubular density exhibited a linear relationship with temperature (range: 0-22-degrees; slope 0.94 microtubules/mum2 per degree; r, 0.96). After heating the nerve by 11-degrees above the physiological temperature, microtubules increased by 83%, whereby the pool of unpolymerized tubulin was at least 2.7 mg/ml of axoplasm. A seasonal variation of the microtubular density was observed which accorded with the environmental temperature. The macroscopic kinetics of microtubule disassembly in the axoplasm is similar to that reported for purified tubulin but that of assembly is slower. Microtubules of peripheral axons of Xenopus are cold-labile and vary during the annual cycle.
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    CHANGES IN CONTRALATERAL SYNAPTIC ACETYLCHOLINESTERASE FOLLOWING MOTOR-NERVE SECTION IN RATS
    (1988) FADIC, R; SOZA, MA; INESTROSA, NC
    We report here that denervation of rat extensor digitorum longus, soleus and diaphragm muscle results in an increase of a subset of asymmetric acetylcholinesterase (class II A-forms) in the contralateral muscle, within a few days. This observation is interesting because it suggests a specific regulation of one asymmetric enzyme fraction, which is solubilized only in the presence of chelating agents and is thought to reside in the basal lamina.
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    EFFECTS OF BODY-TEMPERATURE ON CHEMOSENSORY ACTIVITY OF THE CAT CAROTID-BODY INSITU
    (1991) LOYOLA, H; FADIC, R; CARDENAS, H; LARRAIN, C; ZAPATA, P
    The effects of changes in body core temperature (T(B)) upon the frequency of chemosensory discharges (f(x)) from one carotid nerve were studied in pentobarbitone anesthetized cats. Raising T(B) from 35 to 40-degrees-C increased f(x) in some cats, an effect more commonly seen after contralateral carotid neurotomy. In other animals, the simultaneously increased alveolar ventilation counteracted the above effect. A multiple correlation analysis of global data showed predicted increases in f(x) in response to raising T(B) at different CO2 levels.
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    MOTOR-NERVE REGULATES MUSCLE EXTRACELLULAR-MATRIX PROTEOGLYCAN EXPRESSION
    (1990) FADIC, R; BRANDAN, E; INESTROSA, NC
    Denervation of rat leg muscles caused a 2-3 fold increase in 35S-sulfate and 3H-glucosamine incorporation into proteoglycans of the muscle extracellular matrix. The size of the proteoglycans and the glycosaminoglycan chain length and degree of sulfation were unchanged. Because the rate of degradation of proteolyglycans was also unchanged by denervation, we infer that denervation increases proteoglycan synthesis. Muscle reinnervation restored the original rate of synthesis of proteoglycans. Paralysis of innervated muscle caused increased incorporation of sulfate comparable to that seen in denervation. Thus motor nerve activity appears to regulate the level of proteoglycans in the muscle extracellular matrix.
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    NERVE REGULATION OF CLASS-I AND CLASS-II-ASYMMETRIC FORMS OF ACETYLCHOLINESTERASE IN RAT SKELETAL-MUSCLES
    (1989) FADIC, R; INESTROSA, NC
    Two classes of collagen-tailed, asymmetric forms (A-forms) of acetylcholinesterase (AChE) have been described in skeletal muscles of vertebrates. They are distinguished by their different solubilization requirements: class I A-forms are solubilized in the presence of high salt, whereas class II A-forms require in addition a chelating agent for solubilization. We report here that class II A-forms are less sensitive to nerve section than are class I A-forms. The latter form decreases faster and to a lower level of activity after denervation. The decay of both AChE classes is more rapidly in short-stump nerves than in long ones. The effect of nerve section on class II A-forms appears to be dependent on the particular muscle group being studied. Both classes of A-forms reappear after muscle reinervation, but the class I A-forms recovered earlier. More interestingly, both classes of A-forms increase in normally innervated skeletal muscles after contralateral nerve injury. In this case, however, the class II A-forms change first. Muscular disuse induced by contralateral tenotomy is also followed by a rise in class II A-forms. Our results, showing differences in response and flexibility in the changes of the two classes of A-forms in several experimental conditions, represent a relevant contribution to the understanding of the regulation and functional role of the asymmetric forms of AChE in vertebrate skeletal muscles.
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    THERMAL EFFECTS ON VENTILATION IN CATS - PARTICIPATION OF CAROTID-BODY CHEMORECEPTORS
    (1991) FADIC, R; LARRAIN, C; ZAPATA, P
    In pentobarbitone anesthetized cats, raising body temperature from 37 to 40-degrees-C by external heat increased respiratory frequency, tidal volume, frequency of spontaneous gasps and mean inspiratory flow. It reduced end-tidal CO2 pressure, together with inspiratory and expiratory durations. After bilateral section of the carotid nerves, raising body temperature still induced hyperventilation, but the increase in gasp frequency was less pronounced and no significant change in tidal volume was observed. In comparison to steady ventilatory values in the intact condition, significant reductions in tidal volume at 38-degrees-C and in gasp frequency at 37, 39 and 40-degrees-C were observed after bilateral carotid neurotomy. Brief hyperoxic tests induced transient decreases in tidal volume and increases in end-tidal CO2 pressure which were significantly larger at 40-degrees-C than at 37-degrees-C. These changes disappeared after bilateral carotid neurotomy. Anesthetic block of both carotid nerves produced transient reductions in tidal volume at any given temperature. We conclude that carotid body afferents contribute to the hyperventilation evoked by hyperthermia. After their interruption, such contribution is replaceable from other thermal afferents.