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Biomedical subjects

E T Segura

Publications and source records attributed to E T Segura.

At least 19 recordsLinked to original sources
PubMed1991

Beta-adrenergic control of the water permeability of the skin during rehydration in the toad Bufo arenarum.

1. Toads dehydrated to 80% of their standard weight (% SW) were rehydrated during 3 hr in distilled water. 2. Water permeability of the skin was positively correlated with the degree of dehydration in the range 80-100% SW. 3. Systemic administration of the beta-adrenergic agonist isoproterenol (5 mg/kg) 90 min after rehydration started (animals fully hydrated) increased skin permeability to the values observed in 80% SW dehydrated animals. 4. The administration of the beta-adrenergic blocker propranolol (5 mg/kg) 15 min before rehydration started produced a long-lasting decrease in water permeability during the 3 hr of rehydration. 5. The results are consistent with the hypothesis of a beta-adrenergic control of the water permeability of the skin during rehydration.

Animals↗
PubMed1990

Footshock affects heart and brain MAO and MAO inhibitory activity and open field behavior in rats.

This study examined the effects, after 1 min or 2 hr, of one footshock session on the activity of MAO in rat heart and brain, the MAO inhibitory activity of these tissues, and the animal's behavior in an open field. Internal ambulation was reduced at both times; the lowest score was registered at 1 min. The number of boluses emitted during the test was higher in the group tested at 2 hr than in the other groups. One min after shocks MAO activity in heart and brain was decreased. In the heart MAO was still decreased 2 hr later, then reaching the lowest levels, while at that time, brain MAO was not different from controls. When assayed separately (MAO A and B), only the A form was found to change. MAO inhibitory activity in heart was increased at both times, the highest activity observed 2 hr after footshock. Brain MAO inhibitory activity was increased only in the 1-min group. Ex vivo competition experiments with clorgyline suggested presence in vivo of a reversible MAO inhibitor. The time-dependent response to stress of both MAO activity and MAO inhibitory activity in the tissues correlates with the responses observed in the open field test. These findings suggest that the observed biochemical changes might be related to increased autonomic activity and to the state of fear and anxiety evoked by the stressful procedure.

Animals↗
PubMed1989

Antidiuretic responses to osmotic cutaneous stimulation in the toad, Bufo arenarum. A possible adaptive control mechanism for urine production.

Osmotic stimulation of the skin of the toad Bufo arenarum with isotonic (115 mM) or hypertonic (400 mM) NaCl solutions produced a marked and reversible antidiuresis within 5 min. No changes in plasma osmolarity were detected in the course of this response. Hypophysectomized animals exhibited a lower and delayed antidiuresis when exposed to a hypertonic environment (400 mM NaCl). This antidiuretic response was drastically reduced in normal toads after ten consecutive days of administration of the sympatoplexic guanethidine. The existence of a feed-forward control of urine production initiated by cutaneous osmotic sensors and involving an adrenergic component is proposed.

Animals↗
PubMed1989

Repeated (isolation) stress increases tribulin-like activity in the rat.

1. The effect of repeated isolation stress on MAO inhibitory activity (tribulin) in rat tissues as well as on plasma catecholamine levels was investigated. 2. Animals were subjected to a daily period of isolation (9 min) and sacrificed on days 1, 2, 4, and 5. 3. In brain and cerebellum the levels of both inhibitory activities were found to be significantly higher in animals sacrificed on days 1-2 than in either controls or animals sacrificed on days 4-5. 4. In heart and kidney the highest levels of both activities were found in animals sacrificed on days 4-5. 5. Plasma levels of dopamine on day 4 were significantly higher than those in controls or in any of the experimental groups. Plasma levels of epinephrine showed step-by-step increments from day 1 up to day 5, reaching statistical significance only on day 5. Plasma levels of norepinephrine were significantly increased on days 2, 4, and 5. 6. Under the experimental conditions of this study, we have shown a rapid and short-lasting increment of tribulin in the central nervous system. Its disappearance on days 4-5 could be related to adaptation to the novel situation. Changes in the peripheral tissues appeared later, and a similar adaptation was absent during the period of observation. 7. Tribulin would be related to the stressful situation not only as an anxiety-promoting agent but also in contributing to the maintenance of high levels of circulating catecholamines.

Animals↗
PubMed1987

Short-term changes in natripheric and hydrosmotic water fluxes across the skin and in urine production due to increases in the osmolarity of the external environment in the toad.

1. Sudden decreases in the osmotic gradient across the skin due to the replacement of water of the bath by 115 mM NaCl had no effect on water uptake of intact or hypophysectomized toads. 2. A concomitant decrease in the urine production was observed in intact but not in hypophysectomized animals. 3. Addition of amiloride chlorydrate (0.25 mM) to the 115 mM NaCl bath induced a significant decrease in water uptake both in intact and in hypophysectomized toads. 4. The osmotic permeability coefficient (LPD) increased significantly during the osmotic gradient reduction with 115 mM NaCl plus 0.25 mM amiloride or 230 mM sucrose in both groups. 5. No changes in the plasmatic osmolarity were detected during the development of these responses to the osmotic gradient reduction. 6. These results are consistent with the hypothesis of short-term changes in the natripheric and hydrosmotic fluxes of water across the skin and in urine production triggered by the osmotic gradient reduction. The possible participation of arginine vasotocin in these responses is discussed.

Acclimatization↗
PubMed1987

Antidiuretic responses to osmotic, ionic or volume stimulation of the brain in the unanesthetized toad, Bufo arenarum Hensel.

Single injections of 15 microliter of 1 M NaCl or 2M sucrose into the carotid system of normal unanesthetized toads induced a rapid and significant decrease of urine production. This appears to be the first report on the existence of a Verney-like phenomena in a non-mammalian vertebrate. This antidiuresis was blocked out in the hypophysectomized diencephalic lesioned animal. Concurrently, small volumes (4 microliters) of 1 M NaCl but not 2 M sucrose also induced antidiuresis when injected into the midbrain tegmentum of normal but not of hypophysectomized diencephalic lesioned toads. Larger volumes (6 microliters) of 2 M sucrose were needed to induce a similar antidiuresis in normals. Furthermore, even larger volumes (more than 8 microliters) of any of both solutions were able to induce oliguria in normal as well as in hypophysectomized toads. On the basis of these results, the following conclusion would be drawn: the brain of the toad is able to detect ionic and osmotic stimuli, these stimuli apparently affect different receptors in the brain, the antidiuresis initiated by these mechanisms is dependent on diencephalic integrity.

Animals↗
PubMed1987

Effects of temperature and general anesthesia on the water gain and the inulin space of the brain of the toad, Bufo arenarum Hensel.

1. The water gain in vitro and the inulin space of the brain of the toad were measured under different experimental conditions. 2. There exists a highly positive correlation between water uptake by the brain and the acclimation-incubation temperature, 7 degrees-37 degrees C. 3. Regional differences in the water gain and inulin space were also demonstrated when measured at 20 degrees C. Higher gains were observed in hemispheres, mesodiencephalon and rhombencephalon. 4. The water gain was higher for whole brains obtained under deep anesthesia with ether or urethane but not under nembutal. The inulin space was also higher under ether but lower under urethane. Nembutal had no effect in this case either. 5. A hypothesis about the possible role of water and electrolyte movements in the mechanism of action of some general anesthetics is advanced.

Anesthesia, General↗
PubMed1985

Prolactin binding sites in the brain and kidneys of the toad, Bufo arenarum Hensel.

(125I)-ovine prolactin (oPRL) binding was found in several brain areas of the toad, Bufo arenarum Hensel. The olfactory bulb, cerebral hemispheres, and both dorsal and ventral mesencephalic regions showed saturable, high affinity, (125I)-oPRL binding, ranging between 5.6 to 29.9 fmol/mg protein, while the association constant (Ka) by Scatchard analysis was between 4.0 to 8.7 x 10(9) M-1. This binding was compared with the Scatchard plot of the kidney, which has been already described by other groups, and gave 41.7 fmol/mg protein and Ka 2.5 x 10(9) M-1. Liver showed no binding and in the cerebral hemispheres (125I)-oPRL was not displaced by non-lactogenic hormones, indicating that binding was hormone and tissue specific.

Animals↗
PubMed1984

Electrolyte sensitivity of the skin in the toad, Bufo arenarum Hensel.

Experiments on the responsiveness of the skin to solutions of different electrolytes and sucrose have been done in the toad in vivo and in vitro. Brain pithed animals showed a strong flexor "on" response of the hindlimb when the foot was plunged into a saline solution. The delay of this response was strictly proportional to the concentration of the bath from 0.5 to 1 M. The flexor response was invariably elicited by solutions of different salts: NaCl, KCl, Na2SO4, CaCl, MgSO4 and choline chloride, but not by a solution of sucrose with the same osmolarity. On the other hand, a contrast "off" response with strong flexion was also systematically observed when a limb adapted to electrolyte solution was displaced to distilled water. Patches of skin were also exposed to increasing concentrations of NaCl in vitro and the discharges of its afferent nerve were recorded. A clear cut correlation between the osmolarity of the bath and the rate of discharges was observed. The contrast "off" response to distilled water after exposure to NaCl was also observed in the patches of skin, as an increase in nervous discharges. The spontaneous basal firing observed in water, as well as the induced responses by electrolytes, were reversibly blocked by decreasing the temperature of the bath to 0 C. These results indicate that detectors of salinity are present in the skin of the toad. These detectors appear to be sensitive to the ionization but not to the osmolarity of the bath.

Animals↗
PubMed1981

[Theories and models of the function of the hippocampus].

Different and frequently opposed theories and models of the hippocampal function have been developed. A first type of theories proposed that when some expectatives are not accomplished the hippocampus would inhibit: a) attention, b) activation or c) non-reward responses. A second type of theories supported that the hippocampal function would be the selection of the information to be stored: a) into the trace, b) into the long-term memory. A third type of theories proposed that in the hippocampus it would be stored: a) contextual maps, b) spatial maps, c) temporal maps, d) attentional-associative networks, e) contingencies detectors, f) semantics systems, g) recognition memory, h) work memory. The common element among all theories would be the detection of the differences between a neural model and a new input, as Sokolov proposed in 1960.

Animals↗
PubMed1980

Behavioral changes along escape learning in toads.

Current learning theories consider escape learning as a variation in response dominance into a "habit family". These responses would integrate a repertory of "species-specific reactions" which is displayed when an aggressive or sudden stimulus is presented. We have found that toads (Bufo arenarum Hensel) show a clear correlation between escape learning performance and different rates of responses. Burrowing responses diminished, and orientation responses towards the door increased along trials, concomitantly with correct responses acquisition.

Animals↗
PubMed1979

Pressure and heart rate responses to raised carotid pressure in the toad.

Neither transient nor steady occlusion of the bilateral carotid arterial trunks had noticeable effects on blood pressure or heart rate of the toad Bufo arenarum Hensel. Distension of isolated carotid labyrinths had no circulatory effects, whereas distension of unisolated carotid trunks by fluid infusion caused an increase in blood pressure proportional to the applied pressure. A simultaneous tachycardia was recorded. These circulatory effects seem to depend on the venous return to the heart because carotid distension was followed by a proportional rise in right atrial pressure. Consequently infusion of small volumes of saline into the right atrium also promoted tachycardia and hypertension. These responses seem not to depend on central nervous mechanisms because they persisted after complete deafferentation or removal of the bulbomesencephalic centers.

Animals↗
PubMed1977

Effect of exogenous corticotropin and climatic conditions on bovine adrenal cortical function.

Interactions between three climatic conditions and exogenous adrenocorticotropin (200 IU) or saline on glucocorticoids of plasma were tested in six pregnant Holstein heifers. Animals were under cold (5 C, 30% relative humidity), thermoneutral (18 C, 50% relative humidity), and hot (35 C, and 80% relative humidity) conditions. Effects of treatment, interactions of environment with treatment, and environment with treatment with interval on glucocorticoids of plasma were measured through timed intervals of blood collection at pre- and postintravenous injection of a treatment solution. Adrenocorticotropin elevated corticoid concentrations in plasma, but interactions of environment with treatment and environment by treatment by sampling interval were nil for responses of corticoids in plasma.

Acclimatization↗
PubMed1975

Effects of sodium pentobarbital upon cardiovascular responses to mesencephalic reticular stimulation in rats.

In nineteen rats the cardiovascular responses to the electrical stimulation of the lateral mesencephalic reticular formation (MRF) were recorded before, during and after different doses of sodium pentobarbital injected intravenously. Before pentobarbital, stimulation of the MRF induced cardiovascular changes in 100% of cases. The following four patterns were observed: a) hypertension plus bradycardia (N = 11; 57.9%); b) hypertension without chronotropic effects (N = 4; 21%); c) hypertension plus tachycardia (N = 3; 15.8%), and d) hypotension without chronotropic effects (N = 1;5.3%). Administration of small doses of sodium pentobarbital induced drastic variations in the incidence of the aforementioned patterns of response as follows: a) N = 3; 15.8%; b) N = 2; 10.4%; c) N = 11; 58%; d) N = 0. Other two complementary patterns appeared: e) no changes in blood pressure plus bradycardia N = 1; 5.2%, and f) lack of response: N = 2; 10.4%. When the cumulative doses were over than 19 mg/kg no systematization was possible due to the extreme variability of the responses. This change in the characteristics of the cardiovascular effects of the stimulation of the MRF is supposed to be due to a demasking effect of barbiturates which depressing reticular neurons allows a cardioacceleratory component of the response to become apparent.

Animals↗