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Biomedical subjects

L M Romero

Publications and source records attributed to L M Romero.

At least 19 recordsLinked to original sources
PubMed2000

Effects of weather on corticosterone responses in wild free-living passerine birds.

Harsh weather can have devastating effects on both the survival and the breeding success of wild animals. Corticosterone, released in response to the stress caused by harsh conditions, may trigger physiological and behavioral changes that help ameliorate these effects. We examined three species of Arctic-breeding passerine birds for correlations between circulating plasma corticosterone levels and weather conditions at the time of capture. Furthermore, because persistently poor weather conditions may be required to initiate a stress response, we also looked for a relationship between corticosterone levels and weather conditions over the 24 and 72 h preceding capture. None of the three species showed substantial effects of weather on unstressed corticosterone levels during the breeding season, although one species showed a significant relationship with stress-induced corticosterone levels. In two species, however, variations in weather during molt (an energetically costly period when birds replace their feathers) explained from 35 to 88% of the individual variation in corticosterone levels. In a third molting species, weather conditions in the preceding 24 and 72 h explained between 20 and 30% of the individual variation in corticosterone levels. It thus appears that adverse weather may be a potent stimulator of corticosterone release during molt, but not during the breeding season. Although extreme weather conditions (those experienced once every few years) can disrupt breeding, since none of the birds abandoned breeding we might conclude that the storms in this study were well within the ability of the birds to cope physiologically.

Animals↗
PubMed2000

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions.

The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stress-response or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole.

Animals↗
PubMed1999

Diel rhythms of basal and stress-induced corticosterone in a wild, seasonal vertebrate, Gambel's white-crowned sparrow.

Glucocorticoids have a wide array of actions in vertebrates. Daily fluctuations in basal levels of glucocorticoids are thought to regulate homeostatic mechanisms. In contrast, elevated levels secreted in response to stress stimulate changes in physiology and behavior. These changes are thought to aid an animal in avoiding chronic stress or death. Twenty-four-hour rhythms in basal and stress-induced glucocorticoids have been detected in laboratory mammals, but studies in wild, seasonal vertebrates are rare. Identification of plasticity in hormone secretion in wild vertebrates is critical to understanding the effects of hormones on physiology and behavior, and therefore the success of an animal in its natural environment. In the present study, we characterized diel patterns of basal and stress-induced corticosterone (the avian glucocorticoid) under two photoperiods in Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii). In contrast to previous findings in the white-crowned sparrow, we demonstrated a robust rhythm in basal corticosterone secretion, in which corticosterone reaches peak levels at the end of the inactive period, and has returned to trough levels just after the active period has begun. We also demonstrated a diel rhythm in secretion of corticosterone in response to a stressor, showing the greatest response at the beginning of the active period. Patterns of CORT secretion were similar under both photoperiods. These patterns show interesting similarities and differences to classical mammalian rhythms.

Animals↗
PubMed1999

Alterations in hypothalamic-pituitary-adrenal function associated with captivity in Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii).

Gambel's white-crowned sparrows were captured and brought into captivity in order to study seasonal changes in the function of the hypothalamic-pituitary-adrenal (HPA) axis in captive birds. 30 min of restraint elicited a rise in corticosterone titers that varied depending upon the season and physiological state of the birds. Restraint elevated corticosterone titers significantly more during the fall (within 2 weeks of capture from the wild) than during either the winter or during a prealternate or prebasic molt. We also examined what changes in the HPA axis could account for altered corticosterone levels. Exogenous ACTH significantly elevated corticosterone levels beyond the response to restraint during the fall, indicating a dramatic enhancement of the adrenal's ability to secrete corticosterone. Exogenous ACTH was ineffective at other times, suggesting that the adrenal's ability to release corticosterone often limits circulating levels. We further inferred the pituitary's ACTH secretory ability by injecting exogenous corticotrophin-releasing factor, arginine vasotocin, and mesotocin and measuring corticosterone release. Pituitaries failed to respond to any exogenous releasing factor during the fall, suggesting that the pituitary may be the site in the HPA axis regulating corticosterone release at this time. When compared to wild-caught birds, these results suggest that captivity alters both adrenal and pituitary function during restraint in white-crowned sparrows, and that this change depends upon the season and/or physiological state of the animal. Captivity thus appears to have a profound affect on the function of the HPA axis, and these results reiterate the caution that must be used to extrapolate laboratory data to field conditions.

Adrenocorticotropic Hormone↗
PubMed1998

The hypothalamus and adrenal regulate modulation of corticosterone release in redpolls (Carduelis flammea--an arctic-breeding song bird).

Free-living redpolls (Carduelis flammea-a species that breeds in the Alaskan Arctic), modulate corticosterone release in response to capture and restraint depending upon the breeding site. We extended these findings to adults undergoing a prebasic molt (the energetically costly replacement of feathers) and to juveniles. Results indicate not only that the stress response is dramatically reduced at one breeding site, but that the stress response during molt and in juveniles is lower still. In fact, juveniles failed to secrete any corticosterone in response to capture and handling, suggesting a stress hyporesponsive period. We also examined possible mechanisms underlying stress modulation. Corticosterone binding protein capacity does not change, and the stress response is only correlated with the overall condition of the bird (assessed by fat storage) at one site, suggesting that neither can explain the different corticosterone responses. Adrenal insensitivity also does not appear to fully explain reduced maximal output since exogenous ACTH enhanced corticosterone release. Exogenous ACTH, however, cannot stimulate corticosterone to stress-induced levels at the high-response site, implying reduced adrenal capacity. Redpoll pituitaries responded to exogenous corticotrophin-releasing factor and arginine vasotocin, suggesting a mechanism upstream from the pituitary blunts corticosterone release. Taken together, these results indicate that corticosterone release in this species is modulated depending upon the ecological and physiological state of the animal, and that the maximal corticosterone response is controlled at multiple sites in the hypothalamic-pituitary-adrenal axis.

Adrenal Glands↗
PubMed1998

Hormones and territorial behavior during breeding in snow buntings (Plectrophenax nivalis): an Arctic-breeding songbird.

We examined hormonal profiles and behavior associated with maintaining a single-purpose territory in an Arctic-breeding songbird-the snow bunting (Plectrophenax nivalis). Snow buntings differ from many other Arctic-breeding passerines by using nest cavities, an uncommon and defended resource, but not relying upon the surrounding territory for forage. Circulating levels of testosterone in males were high when territories were established and then decreased over the breeding season. LH secretion was enhanced in females while laying eggs, followed by detectable levels of estradiol during incubation. Both sexes showed equivalent corticosterone responses to the stress of being captured and held. Male snow buntings vigorously defended territories in response to a simulated territorial intrusion both when initiating breeding and when feeding young. Exogenous testosterone implants surprisingly inhibited physical aggression but enhanced singing when birds were feeding young, thus suggesting that song and physical aggression are mediated by different hormonal mechanisms at this time of year. Together, these results contrast with hormonal profiles and behavior in other Arctic-breeding passerines.

Animals↗
PubMed1998

Neurally active stress peptide inhibits territorial defense in wild birds.

It is unclear whether the behavioral effects of peptides in laboratory studies always reflect natural conditions. Here we test whether we can detect measurable behavioral changes after rapidly injecting peptides into the brains of wild birds. We used a modified stereotaxic-like technique to inject corticotrophin-releasing factor (CRF) and arginine vasotocin (AVT, the nonmammalian form of arginine vasopressin), two hormones important in the stress response, into the brains of wild, freely behaving, male white-crowned sparrows (Zonotrichia leucophrys). We then monitored subsequent territorial behavior to determine whether CRF or AVT altered this behavior. Surprisingly, the potent stressors of capture and surgery did not eliminate territorial behavior, with many birds resuming territorial defense within 60-90 min after surgery. Centrally acting CRF, however, significantly reduced territorial defense whereas centrally acting AVT had no effect. These results indicate that the behavioral affects of peptides can be studied under natural conditions.

Animals↗
PubMed1998

Changes in pituitary and adrenal sensitivities allow the snow bunting (Plectrophenax nivalis), an Arctic-breeding song bird, to modulate corticosterone release seasonally.

Several free-living avian species have recently been shown to seasonally modulate corticosterone release in response to capture and restraint. We examined possible mechanisms underlying seasonal adrenocortical modulation in snow buntings (Plectrophenax nivalis), a species that breeds and molts (the energetically costly replacement of feathers) in the Alaskan Arctic Snow buntings dramatically reduced baseline and maximal corticosterone titers during molt compared to the breeding season. This effect is not explained by changes in either corticosterone binding protein capacity or the overall condition of the bird (assessed by weight and fat storage). Although the adrenal's capacity to secrete corticosterone is reduced during molt, adrenal insensitivity does not fully explain reduced maximal output since exogenous adrenocorticotropic-hormone enhanced corticosterone release during both seasons. In contrast, no exogenous adrenocorticotropic hormone releasing factor (corticotrophin-releasing factor, arginine vasotocin or mesotocin) enhanced corticosterone secretion during molt. This suggests that the pituitary's endogenous adrenocorticotropic secretion was maximal in response to capture and handling, making the pituitary an important site regulating corticosterone levels. Taken together, these results indicate that seasonal modulation of corticosterone release in this species is controlled at both the adrenal and pituitary glands.

Adrenal Glands↗
PubMed1998

Seasonal changes in adrenal sensitivity alter corticosterone levels in Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii).

Recent work indicates that Gambel's white-crowned sparrows modulate corticosterone release seasonally in response to capture and restraint. Free-living white-crowned sparrows dramatically elevate both baseline and stress-induced corticosterone levels during the breeding season compared with either wintering or migrating birds. Although corticosteroid binding globulin capacity also rises during breeding, it does not fully compensate for elevated glucocorticoid levels. Consequently, we examined what hypothalamic-pituitary-adrenal axis changes could account for seasonal changes in glucocorticoid levels. During winter and fall migration, exogenous ACTH failed to elevate corticosterone levels beyond the response to capture and handling, suggesting that the adrenal's ability to release corticosterone limits circulating levels during these seasons. In contrast, not only were corticosterone levels higher during breeding, but adrenals further responded to an exogenous ACTH signal, indicating a dramatic enhancement of the adrenal's ability to secrete corticosterone. Furthermore, we inferred the pituitary's ACTH secretory ability by injecting exogenous corticotrophin-releasing factor (CRF), arginine vasotocin (AVT) and mesotocin and measured corticosterone release. Pituitaries in breeding birds appear to respond to exogenous CRF and AVT, suggesting hypothalamic control of corticosterone release during this season. Taken together, these results suggest that seasonal modulation of corticosterone release in this species is controlled primarily at the adrenal.

Adrenal Glands↗
PubMed1998

Hypothalamic-pituitary-adrenal axis changes allow seasonal modulation of corticosterone in a bird.

We examined possible mechanisms underlying seasonal stress modulation in Lapland longspurs (Calcarius lapponicus), a species that breeds and molts (the energetically costly replacement of feathers) in the Alaskan Arctic. Free-living Lapland longspurs show dramatically reduced maximal corticosterone release during molt compared with the breeding season, an effect lost in captive birds. Neither changes in corticosterone binding proteins nor the overall condition of the bird (assessed by weight and fat storage) can explain different seasonal corticosterone responses. Adrenal insensitivity also does not fully explain reduced maximal output because exogenous ACTH enhanced corticosterone release during molt. Exogenous ACTH in molting birds, however, cannot stimulate corticosterone to stress-induced levels during breeding, implying reduced adrenal capacity. Lapland longspur pituitaries appeared to respond to exogenous corticotropin-releasing factor, arginine vasotocin, and mesotocin (the avian equivalents of arginine vasopressin and oxytocin) during molt, suggesting that a mechanism upstream of the pituitary blunts corticosterone release. Taken together, these results indicate that seasonal modulation of corticosterone release in this species is controlled at multiple sites in the hypothalamic-pituitary-adrenal axis.

Animals↗
PubMed1997

A novel stereotaxic-like method for injecting into the lateral ventricles of small passerine birds.

Recently, there has been an increase in the interest in various aspects of the biology of small passerine birds. In order to apply many modern neurobiological techniques, it would be useful to be able to surgically inject hormones and drugs directly into passerine brains. We describe a novel and cost-effective stereotaxic-like technique for injecting substances into the lateral ventricles of small passerine birds. The technique is rapid, reducing the period of anesthesia, and reliable. In addition, using this technique, we injected [3H]cysteine (to label newly synthesized proteins) with small doses of colchicine. Colchicine decreased the content of newly synthesized protein in the median eminence, thus suggesting that colchicine inhibited protein transport. The technique should prove useful in a number of neurobiologial applications.

Animals↗
PubMed1997

Season and migration alters the corticosterone response to capture and handling in an Arctic migrant, the white-crowned sparrow (Zonotrichia leucophrys gambelii).

The Gambel's race of white-crowned sparrow (Zonotrichia leucophrys gambelii) migrates each year from their wintering grounds in the Southwestern United States to the Arctic to breed. Associated with this migration is a change in both the nonstressed and the stress-induced levels of circulating plasma corticosterone. Birds were captured at two sites on their wintering grounds (New Mexico and Arizona). Although stress-induced corticosterone levels were elevated at each site compared to nonstressed levels, there were no differences between wintering sites. These were also similar to levels in birds caught in Washington state during fall migration. In contrast, nonstressed corticosterone values were greatly elevated in birds on their breeding grounds in Alaska and similar to stress-induced levels in wintering birds. Corticosterone levels rose even further in response to the stress of capture and handling in breeding birds. These augmented corticosterone levels during breeding were not associated with weather. Both nonstressed and stress-induced corticosterone levels were similar in birds caught on their breeding grounds on two different years, one with temperatures during mid-May of approximately 0 degree C during a snow storm and the other with temperatures in the mid-20s. These results suggest that seasonal physiological changes, and not local conditions, underlie seasonal changes in corticosterone levels. Furthermore, birds caught in Washington state during spring migration had intermediate levels of both nonstressed and stress-induced corticosterone. Corticosterone release may function differently during spring and fall migrations.

Adipose Tissue↗
PubMed1995

Adrenocorticotropin secretagog release: stimulation by frustration and paradoxically by reward presentation.

Colchicine blockade of axonal transport from the paraventricular nucleus to the median eminence was used to indirectly infer adrenocorticotropin (ACTH) secretagog release in response to a reward presentation and the psychological stressor of frustration. After training rats to drink at the same time of day for 30 min for 2-3 weeks, basal arginine vasopressin (AVP), but not corticotropin-releasing factor (CRF) or oxytocin (OT), concentrations were elevated. The frustration of presenting empty water bottles resulted in increased corticosterone concentrations. Concordantly, CRF, AVP, and OT contents in the median eminence decreased compared to controls. All three secretagogs are thus apparently involved in the corticosterone response to frustration. As expected, water presentation decreased both ACTH and corticosterone. Paradoxically, however, CRF, AVP, and OT contents also decreased compared to controls. The discrepancy of ACTH and corticosterone concentrations declining despite release of secretagogs cannot be explained by decreased adrenal or pituitary sensitivities since both exogenous ACTH and CRF elevated corticosterone and ACTH, respectively, in rewarded rats. Secretagog release, therefore, may not always be associated with stimulation of ACTH release.

Adrenocorticotropic Hormone↗
PubMed1995

Patterns of adrenocorticotropin secretagog release in response to social interactions and various degrees of novelty.

Colchicine blockade of axonal transport from the paraventricular nucleus to the median eminence was used to indirectly infer ACTH secretagog release in response to the psychological stressors of social interactions and various degrees of novelty. Placing a rat in a new cage with either the smell or presence of a novel conspecific decreased arginine vasopressin and oxytocin (OT) contents, but not corticotropin-releasing factor content. Secretagog contents were unchanged in rats in their home cages faced with a novel conspecific. Secretagog release during social stress is thus primarily a function of being in a novel setting. For different degrees of novelty, rats were placed in either a novel cage, a novel bucket, or a novel bucket smelling of another rat. Whereas secretagog contents were unchanged with a novel cage, OT content alone decreased in response to both the bucket and the unclean bucket. Despite a graded corticosterone response, there was no distinction in the OT response, suggesting that the colchicine technique cannot accurately reflect gradations of stressors.

Adaptation, Psychological↗
PubMed1993

Patterns of adrenocorticotropin secretagog release with hypoglycemia, novelty, and restraint after colchicine blockade of axonal transport.

Colchicine blockade of axonal transport from the paraventricular nucleus to the median eminence was used to indirectly infer hypothalamic ACTH secretagog release in awake rats. Median eminence contents of CRF, arginine vasopressin (AVP) and oxytocin (OT) were determined by RIA after insulin-induced hypoglycemia, restraint, and novelty. Insulin decreased circulating glucose concentrations and increased ACTH and corticosterone values. Median eminence CRF and AVP content declined but OT content did not. Both novelty and restraint stressors increased circulating ACTH and corticosterone concentrations. Secretagog measurements indicated decreases in OT content without concomitant decreases in either CRF or AVP with both stressors. These results indicate that: 1) colchicine blockade of axonal transport is useful in studying patterns of secretagog release in animals undergoing psychological stressors; 2) in contrast to physical stressors, OT appears to be a major component of the hypothalamic-pituitary-adrenal response to psychological stress; 3) the patterns of secretagog release differ with regards to physical and psychological stressors.

Adrenocorticotropic Hormone↗
PubMed1992

Possible mechanism by which stress accelerates growth of virally derived tumors.

Stress accelerates the growth of certain types of tumors. Here we report a possible metabolic mechanism underlying this phenomenon. Some early features of transformation include increased number of glucose transporters and greatly enhanced rates of glucose uptake; this adaptation accommodates the vast energy demands needed for neoplastic growth. In contrast, glucocorticoids, a class of steroid hormones secreted during stress, inhibit glucose transport in various tissues; this is one route by which circulating glucose concentrations are raised during stress. We reasoned that should transformed cells become resistant to this inhibitory action of glucocorticoids, such cells would gain preferential access to these elevated concentrations of glucose. In agreement with this, we observed that Fujinami sarcoma virus-transformed fibroblasts became resistant to this glucocorticoid action both in vitro and in the rat. As a result, under conditions where glucocorticoids exerted catabolic effects upon nontransformed fibroblasts (inhibition of metabolism and ATP concentrations), the opposite occurred in the virally transformed cells. We observe that this glucocorticoid resistance upon transformation cannot be explained by depletion of glucocorticoid receptors; previous studies have suggested that transformation causes an alteration in trafficking of such receptors. Because of this resistance of transformed fibroblasts to the inhibitory effects of glucocorticoids upon glucose transport, glucose stores throughout the body are, in effect, preferentially shunted to such tumors during stress.

Adenosine Triphosphate↗
PubMed1988

Intrinsic and extrinsic innervation of the amphibians esophagic myenteric plexuses.

The innervation of Rana ridibunda esophagus myenteric plexuses has been studied by the following methods: demonstration of cholinesterase activity; FIF method for catecholamines; immunohistochemistry for VIP, SP and SOM, and conventional electron microscopy. The cholinergic innervation is important in the esophagus wall where, in addition to the well known extrinsic component, there is a rich intrinsic plexus with cells and fibres widely distributed. The esophagus, together with the intestine, are the Rana gut portions where the adrenergic component is more broadly expressed. The adrenergic innervation seems to be almost entirely of extrinsic origin. We have shown that, for the tested peptides, there is an intrinsic innervation represented by VIP, SP and SOM like plexuses. We do not discard nonetheless an extrinsic component. The ultrastructure reveals the morphological characteristics of the enteric neurons as well as the fine inter-relationships between the nervous elements and the functional components of the esophagic wall.

Animals↗