Biomedical subjects

M Nichelmann

Publications and source records attributed to M Nichelmann.

At least 19 recordsLinked to original sources

PubMed2001

Ontogeny of heart rate responses to exogenous melatonin in Muscovy duck and chicken embryos.

One of the major physiological effects of melatonin is coupling the internal clock with different organ functions. Despite the long list of functional responses to melatonin discovered in the past, it has been unclear when responsiveness to melatonin develops during ontogeny. The aim of the present study was therefore to investigate in Muscovy duck and chicken embryos, when they start to exhibit heart rate (HR) changes to exogenous melatonin. HR was recorded continuously in Muscovy duck embryos from day 24 of incubation (D24) and in chicken embryos from D17 until hatching. Every day four doses of 10 microg melatonin were injected into each egg at 30 min intervals. In Muscovy duck embryos HR responses to melatonin were first observed on D25; from D27 all embryos responded. In all cases HR decreased immediately after the injection. HR deviation from baseline values and duration of decreased HR period increased during the experimental period. Chicken embryos showed similar responses as Muscovy ducks from D17 onwards; from D18 the response rate was 100%. On D19 dose-response data revealed a partial responsiveness to exogenous melatonin at doses of 0.1 to 1 ng and full responsiveness from 10 ng to 10 microg. The time of the first occurrence of HR responses to melatonin coincides with published results on the start of periodic pineal melatonin secretion. These data suggest that the output signal of the avian internal clock, periodic plasma melatonin fluctuations, could result in periodic cardiac function already prenatally in these two avian species.

Animals↗

PubMed1999

Biological rhythms in birds--development, insights and perspectives.

The aim of this review is to show that probably the internal clock of precocial birds is imprinted in the prenatal period by exogenous factors (zeitgeber). The activity of organ functions occurs early during embryonic development, before this function is ultimately necessary to ensure the survival of the embryo. Prenatal activation of some functional systems may have a training effect on the postnatal efficiency. The development of physiological control systems is influenced by endogenous and exogenous factors during the late prenatal and early postnatal period: epigenetic adaptation processes play an important role in the development of animals; they have acquired characteristics which are innated but not genetically fixed. As a rule, the actual value during the determination period has a very strong influence on the set-point of the system. This will be explained using the example of thermoregulation. It is shown in detail that it seems to be possible to imprint the prenatal development of circadian rhythms by periodic changes of the light-dark cycle but not by rhythmic influence of acoustic signals. Altogether, there are more questions open than solved concerning the perinatal genesis of circadian rhythms in birds. Topics are given for the future research.

Animals↗

PubMed1999

Development of heart rate rhythmicity in Muscovy duck embryos.

The heart rate (HR) of Muscovy duck embryos (Cairina moschata f. domestica) was continuously recorded from as early as the 21st day of incubation (D21) until hatching (D34/35). The aim of the study was to investigate the influence of phonoperiods consisting of different acoustic stimuli on the course of HR and the development of HR periodicities during this period. Incubation was carried out at a constant temperature and in constant darkness. Until D25 HR was dominated by decelerative fluctuations only, indicating a main input from the parasympathetic system on the heart. Later sympathetic influences increased progressively. HR periodicity was investigated by means of chi 2-periodogram and fast Fourier transformation. Between D26 and D30 statistically significant and stable HR periodicities developed gradually. They had periods in the range from 5 to 38 h. Ultra-, circa- and infradian rhythms (< 20, 24 +/- 4 and > 28 h, respectively) occurred in parallel in some cases in the same embryo. The for the HR course important periods were dissimilar between individual embryos and had different intensities. There was no indication that acoustic stimulation (phonoperiods) had any effect on the development of HR periodicities.

Acoustic Stimulation↗

PubMed1998

Development of heart rate irregularities in chick embryos.

Heart rate (HR) irregularities in chick embryos were defined as large fluctuations (>10 beats/min) comprising irregular, brief deceleration and/or acceleration of instantaneous HR (IHR). IHR was determined directly from the arterial blood pressure while adequate gas exchange was maintained through an eggshell and chorioallantoic membrane. Five embryos were examined on each day from day 11 to day 19 of incubation. Baseline HR was stable until day 12-13, and on around day 13-14 transient, rapid deceleration of HR (termed V pattern) began to appear, with a subsequent increase in its frequency and magnitude. The acceleration patterns (lambda, avian omega, and periodic patterns) appeared later, and the IHR became increasingly irregular, with additional, spontaneous deceleration and acceleration patterns toward hatching. Additional experiments with intravenous administration of autonomic drugs clearly showed that rapid deceleration of HR was mediated by parasympathetic nervous function but did not always show clear relations of sympathomimetic and sympathetic blocking agents to the acceleration patterns.

Allantois↗

PubMed1997

Temperature guardian neurons in the preoptic area of the hypothalamus.

Applying the slice method extracellular recordings of 218 hypothalamic neurons in Muscovy ducks during sinusoidal temperature changes were investigated. Seven neurons reacted in a hitherto unknown manner to temperatures very near the physiological limits. Four were exclusively sensitive to temperatures around 36.1 degrees C and three to temperatures around 42.3 degrees C. We recommend to call this kind of neurons temperature guardian neurons. The presented results suggest that the current neuronal model of temperature regulation of vertebrates should be extended by aspects of the two-tier theory of Bligh [J. Bligh, The thermosensitivity of the hypothalamus and thermoregulation in mammals, Biol. Rev. 41 (1966) 317-367].

Animals↗

PubMed1997

Ontogeny of thermoregulation during the prenatal period in birds.

In contrast to the well-known thermoregulatory processes in the postnatal period the ontogeny of the thermoregulatory effector system as well as the central nervous control elements in the prenatal period is underinvestigated. Because of this, the aim of this paper is to characterize the development of thermoregulatory mechanisms in the embryonic period of one avian species, the Muscovy duck, Cairina moschata. The experiments were carried out in three series. In the first the influence of low ambient temperatures on call producing activity was investigated, in the second the oxygen consumption of single or pooled embryos was measured in the temperature range between 34.0 and 40.5 degrees C and in the last oxygen consumption, colonic temperature and preferred temperature were examined in birds incubated in reduced temperatures (34.5 degrees C) during the last 7 days before hatching. The results of experiments led to the conclusion, that (1) some days before hatching temperature perception is very well developed, (2) endothermic reactions occur in the last quarter of embryonic development, (3) the thermoregulatory setpoint is adjustable during the perinatal period. Altogether, embryos of the Muscovy duck show in the last days of incubation typical endothermic reactions. They activate the heat production as well as the heat loss mechanisms to control the body temperature. Besides this, when vocalization is used, behavioral thermoregulatory mechanisms support the autonomic reactions.

Age Factors↗

PubMed1997

Influence of prenatal and postnatal acclimation on nervous and peripheral thermoregulation.

The aim of the present study was to investigate whether prenatal and postnatal adaptation to different ambient temperatures affects the autonomic (heat production, heat loss, rectal or colonic temperature), behavioral (preferred ambient temperature) and nervous mechanisms (neuronal thermosensitivity of the preoptical area of the anterior hypothalamus) of thermoregulation. The experiments were carried out in postnatal, differently acclimated adult rabbits (60 days at 6-7, 20 and 30 degrees C) and adult rats (3 to 6 weeks at 5 and 21 degrees C) and in differently incubated 1- to 10-day-old Muscovy ducklings and turkeys (last week of incubation at 34.5, 37.5 and 38.5 degrees C). The results of the experiments are summarized as follows: (1) Postnatal acclimation changes the threshold ambient temperature of heat loss and heat production. For example, cold-acclimated rabbits have a lower threshold temperature for evaporative heat loss and thermoregulatory heat production than heat-acclimated ones. (2) Prenatal acclimation changes postnatal thermoregulatory behavior as well as autonomic thermoregulatory mechanisms. Birds incubated at higher (38.5 degrees C) or lower (34.5 degrees C) temperatures than the usual 37.5 degrees C for the last week of embryonic development have higher or lower preferred ambient temperatures during the first 10 days post hatching. Besides this, cold-incubated birds have a higher heat/ production and clonic temperature in the first days post hatching than normally/ incubated or heat-incubated ones. (3) Extracellular recordings from hypothalamic neurons in brain slices from differently acclimated rats have shown that adaptation to different ambient temperatures changes firstly the temperature sensitivity of the hypothalamic neurons and secondly the modulatory action of the neuropeptides bombesin and thyrotropin releasing hormone.

Adaptation, Biological↗

PubMed1996

Effects of ambient temperature, age and wind speed on the thermal balance of layer-strain fowls.

1. In White Leghorn laying hybrids aged 14 to 399 d the effects were measured of ambient temperature (Ta) and wind speed (WS) on heat production (HP), evaporative heat loss (EHL), nonevaporative heat loss with or without considering heat storage (NEHL1 or NEHL2), conductance (c), total insulation (I) and colonic temperature (Tc) as well as on biological optimum temperature (BOT), thermoneutral temperature (TNT) and threshold temperature for evaporative heat loss (Te). 2. All thermal balance variables were affected by age, Ta and WS. 3. The relationships between Ta and HP or NEHL2 were best expressed in terms of a polynomial function at low WS, and in terms of a linear function at medium and high WS; the relationship between Ta and NEHL1 at all WS studied was best described in terms of linear functions, the slope of which increased with decreasing Ta and rising WS; those between Ta, EHL and c were best described in terms of exponential functions and between Ta and I in terms of quadratic functions, the rate of increase of which was higher at low Ta and medium and high WS. 4. The description of relationships between the age of birds and their HP, EHL, NEHL1 and NEHL2 was performed after logarithmic transformation and yielded a linearly decreasing function with advancing age. 5. Threshold temperatures increased as WS increased from 0.2 to 1.2 m/s; for EHL (Te) by up to 7.5 K, for Tc (BOT) and for HP (TNT) by 10 K. 6. The effects of age, Ta and WS on HP and both forms of NEHL were summarised by multiple regression equations.

Aging↗

PubMed1995

A method for noninvasive, long-term recording of the avian embryo heart rate.

A technique for obtaining a noninvasive electrocardiogram (ECG) from avian embryos is described. Accounts of electronic signal processing and computer-aided long-term recording are included. Furthermore, an algorithm is demonstrated for extracting the relevant information on heart rate from noisy data samples. The method provides the basis for monitoring the heart rate of the avian embryo on different time scales and under different influences.

Animals↗

PubMed1993

[Sexual behavior of muscovy ducks under conditions of intensive husbandry of adult animals: dependence on the time of day, husbandry conditions, body mass and health status].

Sexual behaviour of muscovy ducks kept under intensive husbandry conditions is described comprehensively. To characterize the sexual activity qualitatively four different categories were used. It could be demonstrated a typical diurnal rhythm of mating activity with a maximum in the afternoon. The mating activity was diminished also at the end of the laying period. Body mass as well as state of health have an influence on quality and quantity of mating activity. Body weight, mating activity and size of foot pads are correlated with each other; the higher the body weight the higher the size of foot pads and the lower the mating activity. Besides of this, the mating activity is influenced by keeping conditions and genetic factors.

Animal Husbandry↗

PubMed1986