The development of the hypothalamus-pituitary-adrenal axis during infancy may be affected by antenatal glucocorticoid therapy

BACKGROUND

Developmental changes in the hypothalamus-pituitary-adrenal (HPA) axis during infancy have been reported in term infants, but those in preterm infants have yet to be elucidated. If developmental changes in the HPA axis of preterm infants are modulated by any factors, it may affect their future health. Few studies have examined the lasting consequences of antenatal glucocorticoids on the development of the HPA axis.

METHODS

We measured pre- and post-palivizumab vaccination salivary cortisol values in two conforming periods of three-months intervals during infancy, and compared cortisol values and the response of cortisol secretion between groups with and without antenatal glucocorticoid (AG) therapy.

RESULTS

Although the strength of the response of cortisol secretion to palivizumab fell age-dependently (until late infancy) in the Non-AG group, the opposite pattern was exhibited in the AG group. The changes of the delta cortisol values between the 2 groups were significant.

CONCLUSIONS

This study suggests that the HPA axis of preterm infants whose mothers receive AG therapy may be upregulated during infancy, possibly leading to long lasting health problems.

Differential allocation in relation to mate song quality in the Bengalese finch

Postmating sexual selection plays an important part in the evolution of secondary sexual characters. Based on differential allocation theory that predicts biased reproductive investment of females depending on the attractiveness of mates, a number of previous studies have shown that egg production is related in various ways to ornamental sexual traits of males, but evidence for behavioural sexual traits is less abundant. In this study we examine such maternal effects in relation to birdsong. Because the Bengalese finch is a monomorphic songbird, courtship song serves a key role in mate choice. To take into account individual female differences in egg production performance, we sequentially paired naïve, captive, female Bengalese finches to two different males, and investigated if their reproductive investment (clutch size, egg mass and hatchling sex ratio) was related to the song traits of their mates. We found that clutch size and egg mass were highly repeatable within individual females while sex ratio was not. Despite the inflexibility of egg mass within each female, egg mass increased when females were mated to males with longer songs. In addition, we found a non-significant weak tendency toward male-biased sex ratio in relation to longer song duration of mates. Our findings suggest that females mated to better mates adjusted their reproductive investment by producing heavier eggs and possibly offspring of the more costly sex.

Identification, localisation and functional implication of 26RFa orthologue peptide in the brain of zebra finch (Taeniopygia guttata)

Several neuropeptides with the C-terminal Arg-Phe-NH(2) (RFa) sequence have been identified in the hypothalamus of a variety of vertebrates. The present study was conducted to isolate novel RFa peptides from the zebra finch brain. Peptides were isolated by immunoaffinity purification using an antibody that recognises avian RFa peptides. The isolated peptide consisted of 25 amino acids with RFa at its C-terminus. The sequence was SGTLGNLAEEINGYNRRKGGFTFRFa. Alignment of the peptide with vertebrate 26RFa has revealed that the identified peptide is the zebra finch 26RFa. We also cloned the precursor cDNA encoding this peptide. Synteny analysis of the gene showed a high conservation of this gene among vertebrates. In addition, we cloned the cDNA encoding a putative 26RFa receptor, G protein-coupled receptor 103 (GPR103) in the zebra finch brain. GPR103 cDNA encoded a 432 amino acid protein that has seven transmembrane domains. In situ hybridisation analysis in the brain showed that the expression of 26RFa mRNA is confined to the anterior-medial hypothalamic area, ventromedial nucleus of the hypothalamus and the lateral hypothalamic area, the brain regions that are involved in the regulation of feeding behaviour, whereas GPR103 mRNA is distributed throughout the brain in addition to the hypothalamic nuclei. When administered centrally in free-feeding male zebra finches, 26RFa increased food intake 24 h after injection without body mass change. Diencephalic GPR103 mRNA expression was up-regulated by fasting for 10 h. Our data suggest that the hypothalamic 26RFa-its receptor system plays an important role in the central control of food intake and energy homeostasis in the zebra finch.

A multiplex PCR assay for molecular sexing of the naked mole-rat (Heterocephalus glaber)

For molecular sexing of the naked mole-rat (Heterocephalus glaber), we designed a PCR primer set to amplify part of the Y-linked DBY gene. When this primer set was applied to the samples of known sex with the 16S rRNA gene (16S rDNA) primers as control, PCR products were successfully obtained as two DNA bands in males, a male-specific 163 bp DBY band and a 446 bp band of 16S rDNA shared with females, whereas females showed only the common band. This result shows that this multiplex PCR assay is useful for sex identification of H. glaber.

Partial lesions in the anterior forebrain pathway affect song production in adult Bengalese finches

The avian song system consists of two main parts: the descending motor pathway and the anterior forebrain (AF) pathway. The former directly controls the motor act of singing, but the role of the AF pathway in real-time song production is not understood; lesioning a nucleus in the AF pathway in adult zebra finches did not cause any notable effects. Here we show that in a related species of songbirds, the Bengalese finch, a partial lesion located in Area X, a nucleus of the avian basal ganglia that is part of the AF pathway, causes a transient but substantial song motor deficit. This is the first demonstration that the AF pathway is involved in real-time song production in adulthood.

Limited auditory memory for conspecific songs in a non-territorial songbird

Males of territorial songbird species have to remember a large number of conspecific songs to defend their territories, while non-territorial songbirds do not need to. A study of a territorial species suggested seemingly unlimited auditory memory size. We measured auditory memory in Bengalese finches, a non-territorial songbird species, to examine whether the auditory memory size for conspecific songs depends on the ecological requirements for song use. Five birds were trained by operant techniques to classify song stimuli into two arbitrary categories. The learning curve reached an asymptote within approximately 100 sessions in all five birds and only eight songs were concurrently remembered on average. Results suggest that ecological requirements for song use are correlated with the auditory song memory capacity.

Perception of temporal properties in self-generated songs by Bengalese finches (Lonchura striata var. domestica)

In the songbird forebrain, neuronal selectivity for temporal properties of each bird's self-generated song has been well described, but the behavioral and perceptual correlates of this selectivity are not known. By operant procedures, the authors trained Bengalese finches (Lonchura striata var. domestica) to discriminate between songs that were played normally and in reverse. Male Bengalese finches learned the discrimination quicker when their self-generated song was used as a stimulus than when a song of another conspecific bird was used. When the global note order was retained but each note was locally reversed, the song was more likely to be regarded as a forward song by the singer himself, but not by other birds. These results provide psychophysical evidence that the special processing of the self-generated song observed at the neural level might reflect an individual's perception of his self-produced song.

Lesion of a higher-order song nucleus disrupts phrase level complexity in Bengalese finches

Studies in zebra finches failed to demonstrate the involvement of the NIf, a higher-order song nucleus afferent to the HVc, in the production of learned song. The song of the Bengalese finch, a related species, has a higher level of temporal organization; multiple song phrases are organized into a song. We hypothesized that the NIf might control this complexity. To test this, we bilaterally lesioned the NIf in adult male Bengalese finches. The songs of birds with multi-phrase organization changed into simpler, mono-phrase songs. This is the first demonstration of the NIfs involvement in the production of birdsong. Zebra finch songs are syntactically simple and deterministic, and this might have caused the difficulty in demonstrating the function of the NIf in zebra finches.

Effect of testosterone on the distribution of vasotocin immunoreactivity in the brain of the zebra finch, Taeniopygia guttata castanotis

The distribution of vasopressin or vasotocin immunoreactive cells and fibers in the lateral septum and the bed nucleus of the stria terminalis are sexually dimorphic in many vertebrates including several species of birds examined to date. We examined the vasotocin-like immunoreactivity in the zebra finch brain. Male birds had a higher level of immunoreactive staining in some telencephalic and diencephalic regions. The density of immunostaining increased in the testosterone-treated females to levels typically seen in males. The sexual dimorphism and testosterone dependence of the vasotocin-like immunoreactivity are similar to that found in the canary. Thus this pattern of vasotocin localization and testosterone dependence may be a general feature in brains of passerine songbirds.

Adult Bengalese finches (Lonchura striata var. domestica) require real-time auditory feedback to produce normal song syntax

Songbirds develop their songs by imitating songs of adults. For song learning to proceed normally, the bird's hearing must remain intact throughout the song development process. In many species, song learning takes place during one period early in life, and no more new song elements are learned thereafter. In these so-called close-ended learners, it has long been assumed that once song development is complete, audition is no longer necessary to maintain the motor patterns of full song. However, many of these close-ended learners maintain plasticity in overall song organization; the number and the sequence of song elements included in a song of an individual vary from one utterance to another, although no new song elements are added or lost in adulthood. It is conceivable that these species rely on continued auditory feedback to produce normal song syntax. The Bengalese finch is a close-ended learner that produces considerably variable songs as an adult. In the present study, we found that Bengalese finches require real-time auditory feedback for motor control even after song learning is complete; deafening adult finches resulted in development of abnormal song syntax in as little as 5 days. We also found that there was considerable individual variation in the degree of song deterioration after deafening. The neural mechanisms underlying adult song production in different species of songbirds may be more diverse than has been traditionally considered.

Auditory perception of conspecific and heterospecific vocalizations in birds: evidence for special processes

Budgerigars (Melopsittacus undulatus), canaries (Serinus canaria), and zebra finches (Poephila guttata castanotis) were tested for their ability to discriminate among distance calls of each species. For comparison, starlings (Sturnus vulgaris) were tested on the same sounds. Response latencies to detect a change in a repeating background of sound were taken as a measure of the perceptual similarity among calls. All 4 species showed clear evidence of 3 perceptual categories corresponding to the calls of the 3 species. Also, budgerigars, canaries, and zebra finches showed an enhanced ability to discriminate among calls of their own species over the calls of the others. Starlings discriminated more efficiently among canary calls than among budgerigar or zebra finch calls. The results show species differences in discrimination of species-specific acoustic communication signals and provide insight into the nature of specialized perceptual processes.

Oxytocin inhibits male sexual behavior in prairie voles

Intracerebroventricular (ICV) injection of oxytocin (300 ng) produced an immediate cessation in sexual behavior in sexually active male prairie voles (Microtus ochrogaster). Other social behaviors including social contact, aggression, and autogrooming were not significantly affected by oxytocin, but males that received oxytocin ICV, versus injections that missed the ventricles, showed more sleep postures. Sexual behavior remained inhibited for at least 24 hours and was not activated in tests with a novel receptive female. Sexual and social behavior were not significantly altered in animals in which the oxytocin injection missed the ventricles or in saline-treated males. These findings are consistent with the hypothesis that oxytocin plays a role in sexual satiety.

Temporal modulation transfer functions in the European starling (Sturnus vulgaris): I. Psychophysical modulation detection thresholds

Temporal modulation transfer functions (TMTF) were obtained from four European starlings (Sturnus vulgaris) using a psychophysical Go/NoGo procedure combined with the method of constant stimuli. The TMTF for a continuous, broad-band noise of 55 dB SPL had a low-pass characteristic with a cut-off frequency of 123 Hz. For an 800 ms gated stimulus of the same sound-pressure level, the TMTF had the shape of a band-pass filter with the most sensitive modulation frequency at around 20 Hz. At 75 dB the band-pass shape of the TMTF was preserved, whereas at 35 dB SPL the TMTF had a low-pass characteristic. The cut-off frequency of the TMTF for continuous noise depends on which part of the spectrum carries the information on the envelope fluctuations. If only sound energy below 1 or 1.5 kHz is modulated, then the cut-off frequencies are 40 and 38 Hz, respectively. If only sound above 3 kHz carries the information on the modulation, then the cut-off frequency is 125 Hz and the shape of the TMTF is similar to that found for broadband noise. The results are discussed with respect to the coding of sinusoidal amplitude modulations by the auditory system and to different measures of time, frequency and intensity resolution in the starling.

Perception of distance calls by budgerigars (Melopsittacus undulatus) and zebra finches (Poephila guttata): assessing species-specific advantages

Budgerigars (Melopsittacus undulatus) and zebra finches (Poephila guttata) share a common functional class of vocalizations called distance calls. The perception of species-specific distance calls by both species was measured with a habituation-dishabituation operant paradigm. Changes in discrimination performance were noted as listening conditions were modified or stimulus properties were altered. Both species showed better performance for calls of their own species. For zebra finches this tendency increased slightly when a background noise was added to the testing environment. Shifting the frequency region of the calls affected the discrimination performance of male budgerigars but not females or zebra finches. Reversing the temporal order of the calls affected the perceptual advantage for conspecific vocalizations in zebra finches but not in budgerigars. These results highlight species differences in perceiving acoustic communication signals.

Detection of gaps in noise by budgerigars (Melopsittacus undulatus) and zebra finches (Poephila guttata)

Temporal gap detection thresholds were obtained for two species of birds, budgerigars and zebra finches, which are known to have different auditory filter bandwidths. Both species showed gap detection thresholds of about 2.5 msec for broadband noise stimuli. Comparing octave bands of noise centered at 1, 3, and 5 kHz, zebra finches showed the smallest gap thresholds for the noise band centered at 5 kHz whereas budgerigars showed the smallest gap detection thresholds for the noise band centered at 3 kHz. The results from zebra finches are generally consistent with filter theories of auditory spectro-temporal perception whereas the result from budgerigars are not. In aggregate, these comparative data suggest the relation between spectral and temporal resolving power in these two species may involve different mechanisms.

Detection of auditory sinusoids of fixed and uncertain frequency by budgerigars (Melopsittacus undulatus) and zebra finches (Poephila guttata)

Three budgerigars and three zebra finches were tested for their ability to detect sinusoidal stimuli in the presence of broadband noise. Masked thresholds for 1, 2, and 4 KHz pure tones were measured with a fixed frequency condition, in which only one test frequency was presented in a session, and with an uncertain frequency condition, in which three signal frequencies were presented in random order in one session. The critical signal/noise ratios obtained in the fixed frequency condition were similar to those reported in a previous study (Okanoya and Dooling, 1987) for both species. When tested in the uncertain frequency condition, critical ratios for zebra finches increased for 1.5 dB at 1 KHz signal but remained unchanged 2 and 4 kHz. The critical ratios for budgerigars showed no difference at any frequency in the uncertain frequency condition. These results suggest that (1) budgerigars and zebra finches are similar in the degree to which attention factors are involved in the detection of signals in noise, and (2) the unusual shape of the budgerigar critical ratio function is not the result of central attentional processes.

Hearing and vocalizations in hybrid Waterslager-Roller canaries (Serinus canarius)

A male canary from the Belgian Waterslager strain, which is known for its elevated high-frequency thresholds and a female of German Roller canary with normal high-frequency thresholds were bred. Operant techniques and a psychophysical tracking procedure were used to measure auditory sensitivity of six F1 hybrid canaries from this cross. Three patterns of auditory sensitivity were observed in the six hybrid birds. Four birds showed elevated high-frequency hearing characteristic of the Belgian Waterslager strain; one bird showed normal hearing, and one bird showed an intermediate pattern of auditory sensitivity. A spectral analysis of contact calls recorded from these F1 hybrid canaries showed a spectral distribution of energy which was intermediate between that of Belgian Waterslager strain and the German Roller strain. These results suggest there may be a relation between hearing sensitivity and the spectral distribution of energy in the calls of domestic canaries. Such hybrids may prove useful for examining the genetic basis of more complex behaviors such as vocal learning.

Speech perception by budgerigars (Melopsittacus undulatus): the voiced-voiceless distinction

Discrimination of synthetic speech sounds from the bilabial, alveolar, and velar voice onset time (VOT) series was studied in 5 budgerigars. The birds were trained, using operant conditioning procedures, to detect changes in a repeating background of sound consisting of a synthetic speech token. Response latencies for detection were measured and were used to construct similarity matrices. Multidimensional scaling procedures were then used to produce spatial maps of these speech sounds, in which perceptual similarity was represented by spatial proximity. The results of these experiments suggest that budgerigars discriminate among synthetic speech sounds from these three VOT continua, especially between those from the bilabial and alveolar series, in a categorical fashion.

Strain differences in auditory thresholds in the canary (Serinus canarius)

Canaries (Serinus canarius) of the Belgian waterslager strain from two different colonies were trained with operant techniques for audiometric testing. For both young and old birds, absolute thresholds in the middle- to high-frequency region of the audiogram were between 30 and 40 dB (SPL) higher than those of other song birds, including canaries of other strains. Thus the Belgian waterslager canary, selectively bred for loud, low-pitched song, has also developed poor high-frequency hearing.

Hearing in passerine and psittacine birds: a comparative study of absolute and masked auditory thresholds

Operant conditioning and a psychophysical tracking procedure were used to measure auditory thresholds for pure tones in quiet and in noise for seven species of small birds--the budgerigar, canary, cockatiel, European starling, song sparrow, swamp sparrow, and the zebra finch. Audibility curves are roughly similar among the seven birds, with the maximum sensitivity between 2 and 5 kHz and poorer sensitivity outside this narrow region. Critical ratios (signal-to-noise ratio at masked threshold) were calculated from pure-tone thresholds in noise. Except for the budgerigar, the critical ratio functions of all birds increase at the rate of 3 dB/octave. This pattern is typical of that observed in most vertebrates. Critical ratios in the budgerigar, on the other hand, decrease gradually from 0.5 kHz to 2.8 kHz and increase dramatically above 2.8 kHz. The present research demonstrates that the critical ratio function for the budgerigar is not only different from other vertebrates but also different from other birds.