Characterization of baroreflex gain in the domestic pigeon (Columba livia)

Birds have a remarkable capacity to regulate circulation yet little is known about the avian baroreflex. Although both linear regression and curve-fitting techniques are frequently used to assess baroreflex function in mammals, only the former technique has been used in birds. We characterized baroreflex gain in domestic pigeons (Columba livia) and compared gain values derived from applying linear regression to ramp changes in mean arterial pressure (MAP) to values derived from fitting a four-parameter sigmoidal function to steady-state alterations in MAP. We found that, unlike mammals, pigeons do not display circadian patterns in MAP, HR or gain derived from bolus injections of vasoactive drugs. The pressor, but not depressor response, was attenuated by administration of the NMDA-antagonist ketamine, suggesting that central processing of the baroreflex may be similar in birds and mammals despite anatomical differences in arterial baroreceptive zones. Because graded infusions of vasoactive drugs could not consistently produce a plateau in the HR response, fitting data to a sigmoidal curve was difficult. Thus, we propose that variations of the Oxford method and linear regression analysis are superior method to assess baroreflex gain in pigeons than curve fitting.     

The directionality of the ear of the pigeon (Columba livia)

Summary The directionality of cochlear microphonic potentials in the azimuthal plane was investigated in the pigeon (Columba livia), using acoustic free-field stimulation (pure tones of 0.25–6 kHz).At high frequencies in the pigeon's hearing range (4–6 kHz), changing azimuth resulted in a maximum change of the cochlear microphonic amplitude by about 20 dB (SPL). The directionality decreased clearly with decreasing frequency.Acoustic blocking of the contralateral ear canal could reduce the directional sensitivity of the ipsilateral ear by maximally 8 dB. This indicates a significant sound transmission through the bird's interaural pathways. However, the magnitude of these effects compared to those obtained by sound diffraction (maximum > 15 dB) suggests that pressure gradients at the tympanic membrane are only of subordinate importance for the generation of directional cues.The comparison of interaural intensity differences with previous behavioral results confirms the hypothesis that interaural intensity difference is the primary directional cue of azimuthal sound localization in the high-frequency range (2–6 kHz).Abbreviations CM cochlear microphonic potential - IID interaural intensity difference - IID-MRA minimum resolvable angle calculated from interaural intensity difference - MRA minimum resolvable angle - OTD interaural ongoing time difference - RMS root mean square - SPL sound pressure level     

Genetic analyses of visual pigments of the pigeon (Columba livia)

We isolated five classes of retinal opsin genes rh1(Cl), rh2(Cl), sws1(Cl), sws2(Cl), and lws(Cl) from the pigeon; these encode RH1(Cl), RH2(Cl), SWS1(Cl), SWS2(Cl), and LWS(Cl) opsins, respectively. Upon binding to 11-cis-retinal, these opsins regenerate the corresponding photosensitive molecules, visual pigments. The absorbance spectra of visual pigments have a broad bell shape with the peak, being called lambdamax. Previously, the SWS1(Cl) opsin cDNA was isolated from the pigeon retinal RNA, expressed in cultured COS1 cells, reconstituted with 11-cis-retinal, and the lambdamax of the resulting SWS1(Cl) pigment was shown to be 393 nm. In this article, using the same methods, the lambdamax values of RH1(Cl), RH2(Cl), SWS2(Cl), and LWS(Cl) pigments were determined to be 502, 503, 448, and 559 nm, respectively. The pigeon is also known for its UV vision, detecting light at 320-380 nm. Being the only pigments that absorb light below 400 nm, the SWS1(Cl) pigments must mediate its UV vision. We also determined that a nonretinal P(Cl) pigment in the pineal gland of the pigeon has a lambdamax value at 481 nm.     

Accumulation of calcium and phosphorus in pigeon (Columba livia) embryos

Summary Calcium and phosphorus were measured in the yolk and albumen of fertile pigeon (Columba livia) eggs incubated for 0–17 days, and in embryos and hatchlings. Shell provided most of the calcium for skeletal mineralization of the embryos, whereas phosphorus was derived from the yolk and albumen. Mobilization of calcium from the shell to the embryo commenced at approximately day 11 of incubation, accumulating both in the embryo and the yolk sac. There was 1.4 times more calcium in squab yolk sacs than that contained in newly laid egg yolks. The results suggest that whereas general patterns of calcium and phosphorus accumulation during embryogenesis in altricial birds closely resemble those of precocial birds, calcium mobilization from the shell begins later, proceeds at a slower rate and results in a less mineralized hatchling.CIDA/NSERC Visiting Research Associate Permanent address: Department of Animal Science, University of Peradeniya, Peradeniya, Sri Lanka     

Morphologic study of the efferent ductules of the pigeon (Columba livia)

The efferent ductules of the pigeon are localized in the epididymal region and are topographically divided into proximal and distal, both portions being lined with stereociliated pseudostratified epithelium. Transmission electron microscopy shows five distinct cell types: light, dark, and angular non-ciliated cells with possible apocrine secretory role cells and halo cells, possibly intraepithelial leucocytes. The proximal efferent ductules have the widest diameter among all ductules in the epididymal region.     

A behavioral study of vibrational sensitivity in the pigeon (Columba livia)

Summary The pigeon (Columba livia) has a well-developed ability to detect weak vibrations. Using the method of heart-rate conditioning the vibrational sensitivity was determined for four pigeons at an error probability of P<0.025. The threshold-frequency relationships indicate that the greatest sensitivity to vibrational stimuli is found in the frequency range from 300 to 1,000 Hz with thresholds of about 0.1 m; lowest threshold is 0.04 m at 500 Hz (Fig. 4). Pigeons can respond not only to the frequency of a stimulus, but also to its intensity. The interval decrement (in %) of ECG is a positive correlative function of the stimulus intensity, the calculated values being approximately 4–5% per order of magnitude of the stimulus amplitude (in m) at best frequencies (Fig. 5). The value of vibration detection for birds is discussed.Abbreviation ECG electrocardiogram     

Drinking behavior and jaw muscle (EMG) activity in the pigeon (Columba livia)

The relation between jaw movements and jaw muscle activity was examined during two different types of drinking in pigeons: tip and rictus drinking. The amplitude and duration of jaw opening is greater for rictus than for tip drinking, but both types involve individual cycles of jaw-opening and closing movements, organized into bouts. Cycle duration increases gradually over the initial portion of the bout and is relatively constant thereafter.Each drinking cycle is composed of an initial rapid jaw-opening component, a sustained opening phase of variable duration and a closing movement. The initial and final phases are related, respectively, to activity in the upper beak levator (protractor) and the jaw closer (adductor, pterygoid) muscles. The amplitude and duration of the sustained phase are correlated with the magnitude and duration of activity in the lower jaw opener (depressor). The kinematic and electromyographic organization of jaw movements during drinking is discussed in relation to the morphology of the jaw apparatus and the functional requirements of the behavior.Abbreviations AMEM adductor mandibulae externus muscle - DM depressor mandibulae muscle - EMG electromyographic - PQP protractor quadrati et pterygoidei muscle - PTP pseudotemporalis profundus muscle - PVL/PVM pterygoideus ventralis muscle, pars lateralis and medialis     

An attempt to confirm magnetic sensitivity in the pigeon,Columba livia

Summary An attempt was made to test the sensitivity of homing pigeons to weak magnetic variations of the order of the ones naturally occuring on earth. Pigeons were first subjected to a cardiac orienting reflex test to 50 magnetic stimuli and to 50 control stimuli presented alone and randomly interdigitated. They were then subjected to a differential nociceptive conditioning procedure using the same magnetic and control stimuli for 100 trials under each stimulus condition. Cardiac activity was used as an index of reactivity throughout the study. The tests were performed in uniform magnetic fields using 1 m diameter Helmholtz coils. Results indicate that the magnetic stimuli presentations did not evoke a cardiac orienting reflex when compared to the cardiac orienting response of control pigeons to a neutral luminous stimulus. Moreover, results from the conditioning tests indicate that the magnetic stimuli were not used by the pigeons as a cue presaging the forthcoming shock. It is concluded that, in the present experimental situation, homing pigeons did not respond to small changes in the ambiant magnetic field with changes in autonomic functioning. Results are discussed in the context of the inappropriateness of the stimuli and tests used to show magnetic sensitivity in birds.This research was carried out as part of a doctoral dissertation in the Département de Psychologie at the Université de Louvain (Belgique). The author is indebted to Professor G. Thinès, Director of the Centre de Psychologie Expérimentale et Comparée of the Université de Louvain for his guidance and encouragement as dissertation adviser. We would also like to express our appreciation to Dr. A. Vandenplass, director of the Institut Royal Metéorologique de Belgique and the Fédération Royale Colombophile de Belgique and to Professor J.L. Koenigsfeld from the University of Liège for their interest and cooperation in this research. Dr. Marco Citta and Louis Laurencelle gave computer assistance and Francois Labelle made the technical drawings. This research was supported by the Centre de Psychologie Expérimentale et Comparée and the Fédération Royale Colombophile de Belgique and made possible by a special leave of absence granted to the author by the Université du Québec à Montréal.     

Vascular reactivity of the brain in the pigeon Columba livia

In experiments on awake relatively unrestrained pigeons, studies have been made on the reactions of the cerebrovascular bed to fixed functional loads of physical (orthostasis) and chemical (inhalation of hypoxic and hypercapnic gas mixtures) nature. Using hydrogen clearance method, the increase in the intensity of local cerebral blood flow in different structures of the telencephalon during inhalation of the mentioned gas mixtures was demonstrated. Bilateral vagotomy resulted in inversed reactions. Influence of functional loads was accompanied by changes in rheoencephalographic parameters. The data obtained suggest the existence of an evident reactivity of cerebral vessels in birds which is controlled by neurogenic mechanism of regulation of vascular tone.     

Day/night differences in pineal indoles in the adult pigeon (Columba livia)

Day/night differences in concentrations of 5-hydroxy and 5-methoxy indole metabolites in the pineal gland of the pigeon are described. A simultaneous determination of 5-hydroxytryptamine (serotonin), 5-hydroxyindoleacetic acid, 5-hydroxytryptophol, N-acetyl-5-hydroxytryptamine (N-acetyl serotonin), 5-methoxyindoleacetic acid, 5-methoxytryptophol, tryptophan, indoleacetic acid and melatonin was accomplished using a recently developed procedure employing high-performance liquid chromatography with electrochemical detection. As in mammalian species, an inverse relationship was observed between N-acetylated indoles and serotonin and its acid metabolites. Melatonin and N-acetyl serotonin were increased approximately three-fold at night to concentrations of 0.730 and 1.79 ng/pineal respectively. Daytime serotonin values were 44.9 +/- 13.0 ng/pineal and decreased to 12.3 +/- 6.5 ng/pineal during the dark phase.