Biochemistry and physiology of monoamine oxidase (MAO) activity in the ring dove (Streptopelia risoria). I. Characteristics of MAO activity in vitro

Monoamine oxidase (MAO) activity was measured in ring dove (Streptopelia risoria) tissues using a fluorometric assay with kynuramine as substrate. Harmaline inhibited MAO activity in a time-dependent manner, and preincubation of enzyme with the drug did not affect its activity. Pargyline produced a slow-onsetting inhibition of activity which was enhanced by preincubation of enzyme and inhibitor. Harmaline displayed reversible non-competitive inhibition of MAO activity. Oxygen is also a substrate for dove MAO, and the reaction apparently involves "ping-pong", double-displacement kinetics. Dove MAO activity is temperature-dependent, with an activation energy of 13.1 kcal/mole.     

Melatonin and the phagocytic process of heterophils from the ring dove (Streptopelia risoria)

A functional connection between the pineal gland and the immune system in mammals and birds has been established. This study investigates the effect of melatonin upon the non-specific immunity of heterophils isolated from the ring dove. The different stages of the phagocytic process: adherence to nylon fiber, spontaneous and induced mobility, ingestion of latex beads and digestion were evaluated for heterophils incubated in the presence of 5, 25, 50, 75, or 100 \sgmaelig;M of melatonin. In addition, the chemoattractant power of the hormone for heterophils was studied. The 100 \sgmaelig;M melatonin dose possessed a significant chemoattractant ability for heterophils whilst ingestion of latex particles was enhanced at all doses studied. The superoxide anion level, as measured by the free radicals produced during the metabolic burst, is decreased after incubation with 100 \sgmaelig;M of melatonin.     

External factors affecting the duration of broody behavior in the ring dove (Streptopelia risoria)

The object of this study was to investigate factors which determine the duration of sitting in ring doves. This normally lasts ca. 19 days from laying, with very small variation. The period is made up of 15 days incubating eggs and 4-5 days brooding squabs. The duration of sitting is unaffected by substituting fresh or sterile eggs, and can only be slightly influenced by substituting foster squabs or new eggs just before or after hatching. The sitting period appears to be predetermined to run for 19 days following laying. The maintenance of sitting, however, requires the presence of the nest and eggs, and can be drastically varied by keeping subjects in continuous daylight or on a day of 6 hr light:6 hr dark (6 L:6 D). Birds kept on ahemeral cycles (11 L: 10 D; 13 L:14 D) displayed significantly different periods of incubation on infertile eggs and recycling, indicative of an endogenous circadian basis to the timing mechanism.     

Haemolytic and bactericidal activity of serum from the ring dove (Streptopelia risoria) after treatment with exogenous prolactin

The purpose of this study was to elucidate the effect of exogenous prolactin on the haemolytic and bactericidal capacity of serum obtained from ring doves (Streptopelia risoria) previously injected with either bovine serum albumin or saline solution. Haemolytic activity was measured in CH-50 units (which represents the capacity of serum complement to lyse 50% of sheep red blood cells in the presence of specific antibody) and the bactericidal activity was estimated from the number of colony-forming units ofStaphylococcus aureus which survived after 24 h of incubation in the presence of serum. The results indicated that: (1) bovine serum albumin stimulated both haemolytic and bactericidal activity, the highest values occurring 24 h and 4 days after administration, respectively. (2) Prolactin induced an increase in the haemolytic activity of complement. (3) The administration of bovine serum albumin to animals previously treated with prolactin produced a greater stimulation than either bovine serum albumin or prolactin alone.Abbreviations BSA bovine serum albumin - CFT complement fixation test - CFU colony-forming units - CH-50 units, the reciprocal of the complement dilution with 50% lysis of the hemolysin-treated erythrocytes - IU international units - PBS phosphate-buffered saline solution - SS saline solution     

Melatonin, lipid peroxidation, and age in heterophils from the ring dove (Streptopelia risoria)

Numerous recent studies have shown the ability of physiological as well as all pharmacological concentrations of melatonin to prevent oxidative stress. We have found that incubating avian heterophils from young birds with a pharmacological concentration of 100 μM (23 × 10⁶ pg/ml) melatonin reduced superoxide anion levels by modulating the activity of superoxide dismutase while also enhancing phagocytosis. There was also a decline in lipid peroxidation levels with both physiological and pharmacological concentrations of this indolamine.

In the present work, we evaluated malonaldehyde (MDA) levels as an indicator of lipid peroxidation (both basal and antigen-induced) in young and old animals (ring doves) at different times of day (16:00 and 00:00) and with two incubation times (15 and 60 min). The lipid peroxidation was also measured in heterophils from old animals, incubated with the physiological concentrations of melatonin measured in young animals (50 and 300 pg/ml, diurnal and nocturnal, respectively). The results, expressed as nmol MDA/mg protein, show that MDA levels were higher in heterophils of old animals than in the young birds in all the experimental groups studied at both 16:00 and 00:00 (00:00 is the time at which the lowest peroxidation levels were obtained). Incubation with melatonin was found to reduce MDA levels, with the maximum reduction being after the 60 min incubation time and the nocturnal melatonin concentration. At both concentrations (diurnal and nocturnal), melatonin also counteracted the enhancement of MDA levels caused by latex beads, with the effect being greater at the longer incubation time. In conclusion, the results are further evidence of the antioxidant effect of melatonin even at physiological concentrations, and suggest its utility as a therapeutic agent in some pathological processes associated with age.     

Effect of stress and dexamethasone treatment on circadian rhythms of melatonin and corticosterone in ring dove (Streptopelia risoria)

The possible relationship between the circadian rhythm of blood levels of melatonin and corticosterone in ring dove (Streptopelia risoria) subjected to both immobilization stress and immobilization stress plus dexamethasone treatment were studied. The results show changes in the circadian rhythm of melatonin, with increased day-time levels in situations of stress accompanied by increased corticosterone levels. The highest blood melatonin levels over the 24 h of the study were obtained when the animals were treated with dexamethasone and then subjected to stress. Given the antioxidant role of melatonin, our results support the idea of melatonin-corticosterone coupling with the possibility that melatonin released in situations of stress counteracts the adverse effects of glucocorticoids on the organism.     

Glucocorticoids and parental hyperphagia in ring doves (Streptopelia risoria)

These studies explored the possibility that glucocorticoids promote parental care in ring doves by mediating, at least in part, the pronounced increase in food consumption that parent doves exhibit while provisioning their young. Plasma concentrations of the endogenous glucocorticoid corticosterone were found to be significantly higher in breeding females during the posthatching phase than during the incubation period. These differences were not observed in male breeding partners, but sex differences in daily activity rhythms are well documented in breeding doves, and blood sampling at different times of day would be required to adequately characterize the pattern of corticosterone in males during these breeding stages. In studies on nonbreeding doves, twice-daily intracerebroventricular (icv) injections of the synthetic glucocorticoid dexamethasone (DEX) increased food intake by 25-50% in both sexes, and further studies in males revealed that the increase was directly related to the dose of DEX administered. The highest dose of DEX given icv (1.0 microg/day) was not effective in stimulating feeding when given systemically, thereby suggesting that the hyperphagic action of DEX is exerted directly on the central nervous system. The icv infusion of the selective glucocorticoid receptor antagonist RU38486 blocked the hyperphagic effects of twice-daily icv injections of DEX in both sexes. Collectively, these data support the hypothesis that corticosterone contributes to the parental hyperphagia exhibited by breeding doves during the posthatching period. They also suggest that these orexigenic effects are mediated in part by CNS binding sites that resemble mammalian glucocorticoid receptors.     

Changes in emotionality following section of the tractus occipito-mesencephalicus in the barbary dove (Streptopelia risoria)

Section of the efferent pathways from the archistriatum in the Barbary Dove, leads to an immediate and persisting change in emotionality. The birds no longer react fearfully to the presence of a model predator, whereas control groups in which either the tractus occipito-mesencephalicus remains intact, or when the midline connections of the anterior commissure only are sectioned, continue to behave normally. This lack of responsiveness remains even under conditions of changing endogenous levels of hormone in the course of a normal breeding cycle.     

The characteristics and distribution of monoamine oxidase (MAO) activity in different tissues of the rainbow trout, Salmo gairdneri

Monoamine oxidase (MAO) activity was determined fluorometrically in brain, intestine, kidney and liver tissues of the rainbow trout, Salmo gairdneri. MAO activity was inhibited by various drugs in a concentration-related manner, with single sigmoid inhibition curves, the inhibitors of type A MAO, harmaline and clorgyline being more effective than deprenyl, an inhibitor of type B MAO. Intestine exhibited greatest MAO activity followed by liver and brain with kidney showing least activity. The Michaelis constants (Km) also showed variability between tissues. Inhibition of MAO by harmaline was non-competitive and dependent on the concentration of substrate present.     

Oviposition of fertile eggs and postponement of subsequent egg laying in ring doves (Streptopelia risoria).

Within the 45 days after an oviposition, fewer female doves which had laid fertile eggs laid a subsequent clutch than did females which had laid infertile eggs. During incubation the fertile eggs were replaced by infertile ones; therefore, this difference was not a result of raising squabs.     

Aromatase inhibition abolishes courtship behaviours in the ring dove (Streptopelia risoria) and reduces androgen and progesterone receptors in the hypothalamus and anterior pituitary gland

The aim of this study was to determine in the ring dove, the effects of aromatase inhibition on the expression of aggressive courtship and nest-soliciting behaviours in relation to the distribution of cells containing immunoreactive androgen (AR) and progesterone (PR) receptor in the hypothalamus and pituitary gland. Isolated sexually experienced ring doves were transferred in opposite sex pairs to individual breeding cages, and then injected with the aromatase inhibitor, fadrozole (four males and four females), or saline vehicle (four males and four females) for 3 days at 12 hourly intervals. Saline-injected control males displayed aggressive courtship behaviours (bow-cooing and hop-charging) and nest-soliciting throughout the study, and control females displayed nest-soliciting. By day 3, fadrozole treatment resulted in the disappearance of all these behaviours and in a decrease or disappearance of AR and PR in the anterior pituitary gland, and in the nucleus preopticus paraventricularis magnocellularis (PPM), nucleus preopticus medialis (POM), nucleus hypothalami lateralis posterioris (PLH), and ventral, lateral and dorsal nucleus tuberalis in the hypothalamus (VTu, LTu, DTu). In the nucleus preopticus anterior (POA), fadrozole treatment decreased AR in both sexes and decreased PR in females but not in males. Cells containing co-localized nuclear AR and PR were found in all hypothalamic areas examined, and in the anterior pituitary gland. Fadrozole is suggested to reduce the local availability of estrogen required indirectly for the induction of AR, and except in cells containing PR in the male POA, for the direct induction of PR. It is suggested that aggressive courtship behaviour is terminated by “cross talk” between aromatase-independent PR and aromatase-dependent AR co-localized in neurons in the POA. Aromatase-independent PR may increase in the male POA in response to visual cues provided by a partner. Aromatase-dependent PR in the POM, and basal hypothalamus may play a role in the facilitatory effect of progesterone on estrogen-induced nest-orientated behaviours. (Mol Cell Biochem 276: 193–204, 2005)     

Distribution of gastrin-releasing peptide immunoreactivity in the brain of the collared dove (Streptopelia decaocto)

The distribution of immunoreactivity after applying an antibody against gastrin-releasing peptide (GRP) was studied in the brain of the collared dove (Streptopelia decaocto). In the forebrain GRP-immunoreactive (GRP-ir) cells were found in the hyperstriatum accessorium, medial and lateral parts of the neostriatum, corticoidea dorsolateralis and temporoparieto-occipitalis areas, hippocampus, pre- and parahippocampal areas and prepiriform cortex. In the brainstem, GRP-ir cells were restricted mainly to the substantia nigra and ventral tegmental nucleus. Areas with densely packed GRP-ir clusters of varicosities were the medial intermediate hyperstriatum ventrale and lateral septal nucleus; dense GRP-ir neuropil was found in the parolfactory lobe, and in the dorsal half of the intermediate and caudal archistriatum. The ventral lamina medullaris contained many GRP-ir fibers. Forebrain areas devoid of immunoreactivity were the basal nucleus, ectostriatum, rostral archistriatum, most of the paleostriatum augmentatum and the lateral bed nucleus of the stria terminalis. Moderate densities of GRP-ir elements were found in the other telencephalic areas and further in, among others, the preoptic and hypothalamic region, ventral area of Tsai, cerulean nuclei, parabrachial complex, dorsal glossopharyngeal and vagus motor nuclei and medial nuclei of the solitary complex. The observations are compared with data from the literature and the implications for the definition of specific centers within the avian brain are discussed, with emphasis on systems with a role in visceral and motivational functions and in learning.     

Distribution of monoamine oxidase activity in tissues of the urodeles Ambystoma tigrinum (tiger salamander) and Necturus maculosus (mudpuppy)

1. Monoamine oxidase (MAO) activity was determined fluorometrically in tissues of adult mudpuppies, and pre- (young) and post- (adult) metamorphic tiger salamanders. 2. From responses to specific inhibitors it was determined that 95% activity was MAO type A in all tissues. 3. In young salamanders MAO activity was greater in brain and intestine of males than of females, and was considerably higher in kidney of both sexes and in intestine of males compared to adults. 4. MAO activity was distributed differently in the mudpuppy compared to the salamander. Intestine and liver contained high activity and brain had relatively little MAO activity compared to salamander. 5. The apparent Michaelis constant of MAO activity in the different groups and tissues was generally similar, suggesting a similarity of the MAO molecule.     

On the method of Glenner for the histochemical demonstration of the monoamine oxidase (MAO).

The method of Glenner et al. for the histochemical demonstration of MAO activity was studied by means of scanning microdensitometry and discrete measurement of optical density (lambda=590 nm) of the liver and brain tissues sections. The experiments indicated that: (1) The optimal time of incubation (the thickness of sections is 15 mum) is 60-90 min. (2) The histochemical reaction proceeds with the following substrates: dopamine, noradrenalin, serotonin, and tryptamine. (3) Iproniazid is the best inhibitor for preincubation whereas for simultaneous inhibition the substrate semicarbazide is better. (4) The incubation under the anaerobic conditions caused a considerable decrease of the stain intensity of the sections. We consider these data to indicate that both the aldehydes and acids formed under oxidation may take part in direct reduction of NBT to diformazan. (5) The histochemical reaction for MAO without substrates testifies to the presence of endogenous amines or other redox reactions leading to the reduction of NBT.     

Concentrations of plasma prolactin and luteinizing hormone following nest deprivation and renesting in ring doves (Streptopelia risoria)

Ring doves with increased plasma prolactin and low plasma LH (Group A) or with low plasma prolactin and low plasma LH (Group B) which had been incubating sterile eggs for 12 or 18 days, respectively, had their nests and eggs removed for 3 days. Upon nest return, observations were made on the birds' readiness to renest and on changes in plasma prolactin and LH. Birds from Group A demonstrated a far greater tendency to resume incubation than birds from Group B. Nest deprivation resulted in a sharp fall in the concentration of plasma prolactin in birds which were deprived of their nests after 12 days of incubation (Group A). Following resumption of incubation no subsequent increase in the prolactin levels was observed in Group A or B. The concentration of plasma LH rose sharply after nest deprivation in both sexes of both groups and declined after return of the nests. Birds in Groups A and B which returned to their nests laid a new clutch of eggs while continuing to incubate. The total length of uninterrupted sitting following nest return was 20.9 +/- 0.48 days (n = 8). These results suggest that (1) once the mechanism responsible for the increase in plasma prolactin during incubation is disrupted, it cannot be reactivated unless the whole reproductive cycle is repeated. (2) The inhibition of LH secretion during incubation involves neural mechanisms which do not necessarily involve the anti-gonadotrophic action of prolactin.