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E T Segura

Publications and source records attributed to E T Segura.

At least 19 recordsLinked to original sources
PubMed1999

Influence of age on stress responses to metabolic cage housing in rats.

1. We studied the effect of isolation stress in 3- and 12-month-old rats individually housed in metabolic cages for 7 days. Urine (24 hr) was collected daily from one group of animals of each age. The other group was tested in an open field and on a hot plate on days 1 and 7. 2. Total deambulation in the open-field test was lower in young than in older rats both on day 1 (54.7 +/- 9.9 vs 80 +/- 8.9 crossings/session; P < 0.04) and on day 7 (21 +/- 9 vs 48 +/- 7 crossings per session; P < 0.04) and decreased significantly in the two groups when tested on day 7 (P < 0.03). Latency to paw-licking in the hot-plate test was longer in young than in older animals on day 1 (14 +/- 2 vs 8 +/- 4 sec; P < 0.05) but was similar in the two groups on day 7. 3. Urinary excretions of norepinephrine (NE) and epinephrine (E) were determined by HPLC with electrochemical detection. Urinary NE in day 1 was similar in young and older animals (2627 +/- 828 vs 3069 +/- 598 ng/24 hr). In young animals NE excretion decreased along the study and was significantly (P < 0.02) lower than on day 1 during the last 3 days of the study. Conversely, in older animals urinary excretion of NE remained similar throughout the study. On day 7 urinary excretion of NE in older animals was about two fold that in young rats. Urinary E was similar in young and older rats (341 +/- 127 vs 532 +/- 256 ng/24 hr) on day 1 and showed a tendency to increase throughout the study. 4. Urinary monoamine oxidase inhibitory (IMAO) activity was determined by testing the ability of urine extracts to inhibit rat liver MAO activity in vitro and was higher in young than in older animals throughout the study (day 1, 54.8 +/- 4.2 vs 25.1 +/- 5.1%; P < 0.02). In young rats excretion of IMAO was significantly higher during the last 3 days of the study than on day 1 (P < 0.05). In older animals urinary IMAO showed a tendency to increase at the end of the study. 5. Isolation stress caused by housing rats in metabolic cages results in different behavioral and metabolic responses in young and older animals. Young animals exhibit a lower locomotor and analgesic response and excrete lower amounts of NE and higher IMAO activity in the urine than older rats. The metabolic and behavioral responses to isolation stress are highly dependent on the age of the animals tested. These results should be taken into consideration when designing experiments requiring the use of metabolic cages.

Age Factors↗
PubMed1996

Prazosin and stress effect on tumoral growth of 7,12-dimethylbenz[A]anthracene-induced rat mammary tumors.

Repeated isolation stress and prazosin effect were evaluated in 7,12-dimetylbenz[A]anthracene (DMBA) mammary tumors. Tumor volume was significantly lower in stressed than in control animals from 10 to 52 days considering day 1 the moment when tumors became palpable and treatment began. Control Prazosin (0.5 mg/kg) rats showed diminished tumor volume after 40 days. Stress Prazosin curve was similar to stress alone. The proportion of progressing tumors in control was significantly higher than in stressed groups, regardless of Prazosin administration. Body weight gain was similar in every group throughout the experiment. Behavioral studies were performed when stress effect was no longer evident. Grooming and the number of fecal boli were similar in all groups, as well as prolactin serum levels, suggesting that habituation took place. No significant differences were observed between groups for estrogen receptors. However, a greater concentration of progesterone receptors was found in Stressed rats, compared to all other groups. We conclude that the decrease of tumor volume provoked by stress could not be reversed by the alpha 1-adrenergic antagonist prazosin. Then, it appears that the main effect of stress is not mediated by the alpha 1-adrenergic receptors. Higher progesterone receptors in stressed rats could explain the differences observed.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1995

Instrumental learning in toads (Bufo arenarum): reinforcer magnitude and the medial pallium.

Two experiments studied the effects of shifts in the amount of water reinforcement on the instrumental performance of toads (Bufo arenarum) using one trial per day. In the first experiment, a shift from a large to a small reward magnitude led to a gradual change in performance without evidence of negative contrast. A shift from large or small reward magnitude to extinction led to similar extinction rates and provided no indication of the magnitude of reinforcement extinction effect. In the second experiment, the gradual change in performance (with no contrast) after a shift from a large to a small reward magnitude was completely eliminated by ablation of the medial pallium. These results provide support for the hypothesis that the medial pallium in amphibians is homologous to the hippocampal formation in mammals and also indicate that species differences in these learning phenomena may be related to the differential development and differentiation of the hippocampal formation.

Animals↗
PubMed1994

Stressor predictability influences open field behavior, pain sensitivity and brain MAO inhibitory activity (tribulin) in the rat.

The effects of predictable or unpredictable shocks on ambulation, pain sensitivity, plasma catecholamines and heart and brain monoamine oxidase (MAO) inhibitory activity were investigated in rats. Animals showed plasma catecholamines and heart MAO inhibitory activity sensitization irrespective of type of treatment, while differences between groups were observed when open field and hot plate tests and brain MAO inhibitory activity were considered. These effects parallel those observed using the classic triadic design leading to the helpless state. Our results suggest that predictability per se is able to generate this phenomenon.

Animals↗
PubMed1994

Learning under partial reinforcement in the toad (Bufo arenarum): effects of lesions in the medial pallium.

Two experiments studied the adjustment of toads (Bufo arenarum) to partial reinforcement in a runway. In Experiment 1, two groups received 24 daily trials of either continuous reinforcement (CR) or 50% partial reinforcement (PR). Training parameters that facilitate the PR extinction effect (greater resistance to extinction after PR than CR training) in rats were selected. PR impaired performance during acquisition but had no effect on performance during extinction relative to CR. In Experiment 2, four groups were trained in a factorial design involving CR and PR, and a lesion of the medial pallium and a sham operation. Performance during acquisition was again impaired by PR, but the medial pallium lesions had no effect. The lesion, however, increased resistance to extinction after both CR and PR training. The results are discussed in relation to comparative research on learning and to the hypothesized homology of the amphibian medial pallium and the mammalian hippocampal formation.

Animals↗
PubMed1993

The stress-induced reduction in monoamine oxidase (MAO) A activity is reversed by benzodiazepines: role of peripheral benzodiazepine receptors.

1. The effect of benzodiazepine pretreatment on the stress-induced decrease in MAO activity in rat tissues using footshock as stress model was investigated. 2. Animals were injected with vehicle, Lorazepam (1.25 mg/kg), or Clonazepam (0.5 mg/kg) 2 hr before or with PK 11195 (0.45 mg/kg) 2.5 hr before being subjected to one session of 10 inescapable footshocks or to a sham session. At the end of the session animals were sacrificed and MAO A and B activities in hearts and brains were determined. 3. Pretreatment of the animals with both Lorazepam and Clonazepam abolished the decrease induced by footshock in MAO A activity in brain. Pretreatment with Lorazepam but not with Clonazepam abolished the stress-induced decrease in MAO A in the heart. Pretreatment with PK 11195 before Lorazepam reversed its effects in the heart but not in the brain. Neither footshock nor any of the drugs used had any effect on heart and brain MAO B. 4. Our results suggest that in the heart but not in the brain, peripheral benzodiazepine receptors play a role in the regulation of MAO A activity under stress conditions.

Analysis of Variance↗
PubMed1993

Effects of lesions in the medial pallium on instrumental learning in the toad (Bufo arenarum).

Lesions of the medial pallium in toads significantly retarded extinction of a water-reinforced instrumental response in a runway training situation, relative to sham-operated and intact controls. The lesion had no effect on acquisition or in the amount of water uptake during acquisition. The results suggest that the medial pallium of toads plays a role in response inhibition. This possibility is discussed in relation to the results of analogous experiments with hippocampectomized rats.

Animals↗
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↗