Browsing by Author "Belmar, J"

Now showing 1 - 8 of 8
  • No Thumbnail Available
    Item
    Allopregnanolone-induced modification of presynaptic basal and K+-induced [3H]-norepinephrine efflux from rat cortical slices during the estrous cycle
    (1998) Belmar, J; Cuellar, C; Llona, I; Arancibia, S; Kusch, C; Tapia-Arancibia, L; Pinter, A; Perez, H
    Superfused frontal slices of cerebral cortex were preloaded with [H-3]-norepinephrine ([H-3]NE). Basal [H-3]NE efflux and Kf-induced [H-3]NE release were studied during the estrous cycle and in the presence of neurosteroids. Basal [H-3]NE efflux showed estrous cycle-related variations, with lowest values found during estrus and diestrus II. Allopregnanolone (10(-9) M) potentiated basal [H-3]NE efflux from the Ist minute of its application; the effect of the steroid was still present after 20 min. This effect was also dependent upon the estrous cycle, since basal [H-3]NE efflux was mainly increased during estrus diestrus I, and to a lesser degree only during proestrus. During diestrus II and after ovariectomy, basal [H-3]NE efflux was no longer affected by the neurosteroid. In the presence of yohimbine (10(-6) M), the effect of allopregnanolone on basal efflux was potentiated only during the first 3 min but vanished thereafter. Allopregnanolone (10(-9) M) potentiated the K+-induced [H-3]NE release during estrus, but pregnenolone (10(-9) M) was ineffective, suggesting specificity of the neurosteroid. Yohimbine (10(-6) M) also potentiated K+-induced [H-3]NE release. When applied simultaneously with allopregnanolone (10(-9) M), a potentiating effect on [H-3]NE release was observed. The present results suggest that allopregnanolone is a neurosteroid able to modulate norepinephrine release in the cerebral cortex in an estrous cycle-dependent manner, and that the effect could involve noradrenergic alpha-2 receptors.
  • No Thumbnail Available
    Item
    Effects of mild protein prenatal malnutrition and subsequent postnatal nutritional rehabilitation on noradrenaline release and neuronal density in the rat occipital cortex
    (1999) Soto-Moyano, R; Fernandez, V; Sanhueza, M; Belmar, J; Kusch, C; Perez, H; Ruiz, S; Hernandez, A
    There is evidence that severe malnutrition started during gestation and continued through lactation affects adversely the morphologic development of the neocortex leading to increased neuronal cell packing density and decreased dendritic branching. Nevertheless, the effect of purely mild protein prenatal malnutrition on neocortical development remains rather unexplored. This study evaluates the effects of mild protein prenatal malnutrition (8% casein diet, calorically compensated by carbohydrates) and subsequent postnatal nutritional rehabilitation (25% casein diet) on: (i) the potassium-induced release of [H-3]-noradrenaline (NA) in occipital cortex slices obtained from 1- and 22-day-old pups; and (ii) the packing density of neurons in lateral, dorso-lateral and dorsal regions of the occipital cortex of 22-day-old pups by using the optical dissector method. The experiments were performed in rats normally fed during gestation and lactation (G(+)L(+)), malnourished during gestation but rehabilitated during lactation (G(-)L(+)) and malnourished during gestation and lactation (G(-)L(-)). At day 1 of age, no significant differences in body and brain weights were observed between prenatally well-nourished and malnourished pups. Nevertheless, at this early age, pups born from mothers submitted to the 8% casein diet had significantly higher cortical net percent NA release than pups born from mothers receiving the 25% casein diet. At weaning (22 days of age) G(-)L(+) rats had, compared to the G(+)L(+) group, similar body weight, brain weight and [H-3]-NA release values, but significantly higher neuron density scores in the lateral region of the occipital cortex. In contrast, at 22 days of age, G(-)L(-) rats exhibited, compared to G(+)L(+) animals, significant deficits in body and brain weights as well as significant increases in cortical net percent NA release together with enhanced packing density of neurons in the lateral, dorso-lateral and dorsal regions of the occipital cortex. Moreover, in G(-)L(-) animals was not found the laterodorsal histogenetic gradient of neuronal cell packing density observed in G(+)L(+) rats. Results suggest that mild prenatal malnutrition per se is able to induce deleterious effects on cortical neuronal density, in spite of nutritional rehabilitation during lactation, through a mechanism involving central NA hyperactivity during gestation. Prosecution of malnutrition after birth magnifies both neurochemical and morphometric disorders. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Malnutrition early in life impairs alpha-2 adrenoreceptor regulation of noradrenaline release in the rat cerebral cortex
    (1996) Belmar, J; Carreno, P; Hernandez, A; SotoMoyano, R
    Experimental studies have shown that malnutrition early in life results in enhanced release of noradrenaline (NA) in the brain. The disturbed mechanism underlying this neurochemical disorder is pearly understood. To test the possibility that early malnutrition could disrupt the feedback mechanism regulating the release of NA at central axon terminals, the ability of the adrenoreceptor agonist clonidine to depress NA overflow was studied in rat cortex slices arising from malnourished rats. Protein-energy malnutrition was induced by increasing litter size from 8 to 18 pups per nurse. Results show that clonidine (5 x 10(-6) M) induced a significant decrease of the spontaneous release of NA in occipital cortex slices obtained from 23-24 day-old normal rats and of the potassium-evoked release of NA in slices arised from normal animals of 45-50 days of age. On the contrary, clonidine induced a significant increase of both the spontaneous and evoked outflow of the neurotransmitter in slices arised from malnourished rats of the two ages. Results indicate that protein-energy malnutrition impairs the alpha-2 receptor mechanisms regulating central NA overflow, probably by altering during development the quantity and/or quality of the adrenoreceptor population.
  • No Thumbnail Available
    Item
    Prenatal malnutrition-induced functional alterations in callosal connections and in interhemispheric asymmetry in rats are prevented by reduction of noradrenaline synthesis during gestation
    (1998) Soto-Moyano, R; Alarcon, S; Hernández, A; Pérez, H; Ruiz, S; Carreño, P; Kusch, C; Belmar, J
    Prenatal malnutrition results in increased concentration and release of central noradrenaline, a neurotransmitter that is an important regulator of normal regressive events such as axonal pruning and synaptic elimination. This suggests that some of the functional disturbances in brain induced by prenatal malnutrition could be due at least in part to increased noradrenaline activity that may enhance regressive events during early stages of development. To test this hypothesis we studied whether chronic administration of alpha-methyl-p-tyrosine, an inhibitor of tyrosine hydroxylase, to rats during gestation might prevent long-term deleterious effects of prenatal malnutrition on functional properties of interhemispheric connections of the visual cortex, and on asymmetry of visual evoked responses. The experiments were conducted on normal and malnourished rats 45-50 d of age. Prenatal malnutrition was induced by restricting the food consumption of pregnant rats to 40%, from d 8 postconception to parturition. At birth, prenatally malnourished rats had significantly greater whole-brain noradrenaline concentration as well as significantly enhanced noradrenaline release in the visual cortex. At 45-50 d of age, the malnourished group had a significantly smaller cortical area, exhibiting transcallosal evoked responses; in addition, the amplitude of these responses was significantly smaller. Malnourished rats showed a significant reduction of the normal interhemispheric asymmetry of visual evoked responses. The addition of 0.3% alpha-methyl-p-tyrosine to the diet of malnourished pregnant rats during the last 2 wk of gestation prevented functional disorders induced in the offspring by prenatal malnutrition on interhemispheric connectivity of visual areas and on interhemispheric bioelectrical asymmetry, probably by reducing the elevated brain noradrenaline activity and thereby restoring the normal trophic role of this neurotransmitter.
  • No Thumbnail Available
    Item
    Prenatal protein restriction alters synaptic mechanisms of callosal connections in the rat visual cortex
    (1998) Soto-Moyano, R; Alarcón, S; Belmar, J; Kusch, C; Pérez, H; Ruiz, S; Hernández, A
    Mild prenatal protein malnutrition, induced by reduction of the casein content of the maternal diet from 25 to 8%, calorically compensated by the addition of excess carbohydrates, leads to so-called "hidden" malnutrition in the rat. This form of malnutrition results in normal body and brain weights of pups at birth, but in significant alterations of their central nervous system neurochemical profiles. Since severe forms of prenatal malnutrition induce morpho-functional deficits on callosal interhemispheric communication together with brain neurochemical disturbances, we evaluated, in rats born from mothers submitted to an 8% casein diet, the potassium-induced release of [H-3]-noradrenaline in visual cortex slices, as well as functional properties of callosal-cortical synapses by determining cerebral cortical excitability to callosal inputs and fatigability and temporal summation of transcallosal evoked responses. Rats born from mothers submitted to a 25% casein diet served as controls. At birth prenatally malnourished pups had significantly higher cortical percent net noradrenaline release (14.79+/-1.11) than controls (9.14+/-1.26). At 45-50 days of age, rehabilitated previously malnourished rats showed, when compared to controls: (i) significantly reduced percent net noradrenaline release in the visual cortex (4.50+/-0.52 vs 11.31+/-1.14); (ii) decreased cortical excitability to callosal inputs as revealed by significantly increased chronaxie (607.2+/-82.8 mu s vs 351.3+/-47.7 mu s); (iii) enhanced fatigability of transcallosal evoked responses as revealed by significantly decreased stimulus frequency required to fatigate the responses (4.9+/-0.8 Hz vs 9.2+/-1.3 Hz); and (iv) decreased ability of callosal-cortical synapses to perform temporal summation, as revealed by significantly reduced percent response increment to double-shock (54.2+/-6.2 vs 83.0 +/- 11.0, for a 3.2-ms interstimulus time interval). These changes, resulting from mild prenatal protein restriction, are discussed in relationship to developmental processes leading to the formation of synaptic contacts between callosal axons and their appropriate cortical target during perinatal age. (C) 1998 ISDN. Published by Elsevier Science Ltd.
  • No Thumbnail Available
    Item
    Rapid and opposite effects of dexamethasone on in vivo and in vitro hypothalamic somatostatin release
    (1997) Estupina, C; Belmar, J; TapiaArancibia, L; Astier, H; Arancibia, S
    We have previously reported the rapid response of hypothalamic somatostatin (SS) neurons to acute stress. Since it is well known that glucocorticoids (GC) are involved in neuroendocrinal stress regulation, we investigate in this study the effects of acute administration of dexamethasone (Dex) on both in vivo and in vitro SS release. Freely moving animals received stereotaxic implant of a push-pull cannula into the median eminence for 10 days, and then they were perfused with artificial cerebrospinal fluid for 120-150 min. An i.p. injection of Dex (200 or 300 mu g/100 g) induced, 15-30 min later, a mean increase in SS hypothalamic output of 62.6+/-6.2% of basal secretion. By contrast, after 15 min incubation of hypothalamic fragments with either 10(-7) or 10(-6) M Dex, SS release decreased abruptly to 57.3+/-3.3% (n=16; P<0.001 compared with basal re lease) and 78.0+/-9.5% (n=13; P<0.05 compared with basal release) of basal release, respectively. Other Dex concentrations induced no variations, giving the dose-effect curve an abrupt ''on-off'' effect. The inhibitory effect was blocked by picrotoxin (10(-4) M) and was immediately reversed when Dex was removed from the medium. Specificity was tested by using another steroid, estradiol, and another tissue, cortex. The rapid action of GC whatever the model used and in particular the blocking in vitro effect of picrotoxin could suggest that GCs act at the level of the membrane and could operate physiologically in response to stress. In addition, the opposite in vivo and in vitro effects on SS release would indicate that GCs exert two different controls on SS neurons.
  • No Thumbnail Available
    Item
    Responsiveness to depolarization of hypothalamic neurons secreting somatostatin under stress and estrous cycle conditions: Involvement of GABAergic and steroidal interactions
    (1997) Arancibia, S; Estupina, C; Pesco, J; Belmar, J; TapiaArancibia, L
    We studied the sensitivity to a depolarizing stimulus of hypothalamic fragments dissected from cycling female donor rats exposed or not to 30-min stress at 4 degrees C. The neuronal response was estimated in terms of the ability of tissue to release somatostatin when stimulated with 40 mM K+. The data showed no differences in response to K+, regardless of the ovarian cycle of the female donors, whereas tissues dissected from ovariectomized or pregnant rats responded significantly to K+. However, when donors underwent previous cold stress, significant differences were noted at all stages of the cycle, except diestrus-1, compared with control rats, We tested whether GABA and/or neuroactive steroids could be involved in this phenomenon and observed no GABA inhibition of somatostatin release in vitro, but inhibition occurred in the presence of a neuroactive steroid, THDOC, The effect of GABA in vivo on somatostatin release was estrogen dependent because bicuculline modified the total amount of somatostatin secreted in estrus but not in diestrus II, Finally, in hypothalamic primary cultures, GABA inhibition of somatostatin release was only detected when steroids were present in the media throughout culture.
  • No Thumbnail Available
    Item
    Variations in hypothalamic somatostatin release and content during the estrous cycle in the rat - Effects of ovariectomy and estrogen supplementation
    (1996) Estupina, C; Pinter, A; Belmar, J; Astier, H; Arancibia, S
    To investigate the secretory pattern of somatostatin (SS) from the median eminence (ME) in the female rat, as well as estrogenic influence on this secretion, we measured both SS release and hypothalamic content in cycling, 10-day ovariectomized, and ovariectomized rats treated with estradiol for 3 days before. Animals were stereotaxically implanted with a push-pull cannula into the ME, and 10 days later the hypothalamic structure was perfused with artificial cerebrospinal fluid for 120-150 min at a regular flow rate of 17 mu l/min. Secretion peaks were observed in the pattern of SS release, whatever the stage of the estrous cycle. The mean amplitude of SS peaks was similar throughout the cycle: 11.7 +/- 4.0, 8.6 +/- 1.5 and 10.5 +/- 1.3 pg at proestrus, estrus and diestrus, respectively, and it was affected neither by ovariectomy (7.4 +/- 1.3 pg) nor by estrogen replacement (5.5 +/- 1.0 pg). By contrast, mean SS release levels in the proestrus phase were significantly higher than those measured in the other phases: 21.6 +/- 2.1 vs. 17.7 +/- 1.2 pg/15 min in diestrus (p < 0.05) and vs. 12.0 +/- 0.7 pg/15 min in estrus (p < 0.001). Hypothalamic SS content showed variations quite similar to those observed during its release, i.e. with the highest values corresponding to the proestrus phase (1,170.5 +/- 224.9 pg/mg of tissue) and to the diestrus (1,156.5 +/- 332.1 pg/mg of tissue) and the lowest values in the estrus (511.5 +/- 52.9 pg/mg of tissue; p < 0.05 vs. proestrus and diestrus). In addition, the lowest SS content and secretion values were found in ovariectomized animals: 95.5 +/- 5.1 pg/mg of tissue (p < 0.001 compared to the values obtained for each stage of the estrous cycle) and 10.0 +/- 0.9 pg/15 min (p < 0.001 vs. proestrus and diestrus), respectively. Patterns of SS release and SS hypothalamic content were not modified by estradiol treatment in ovariectomized animals. Our results suggest that (1) whatever the stage of the estrous cycle, SS release from the ME is not uniform and exhibits irregular peaks; (2) mean SS release levels were subjected to gonadal influence; (3) the occurrence of SS peaks seems to be estrogen-independent, and (4) variations in hypothalamic SS content were generally in good agreement with those of neurohormone release.