[Changes in vegetative parameters during and after normobaric hypoxic hypoxia in newborn rabbits]. / Veränderungen vegetativer Parameter während und nach normobarer hypoxischer Hypoxie bei neugeborenen Kaninchen.

68 awake spontaneously breathing newborn rabbits were investigated in five series; 43 animals were exposed to a hypoxic atmosphere (FiO2 = 0.05) for 3 h during the 1st day of life. Heart rate, rectal temperature and intracranial pressure were recorded. Arterial blood samples were analyzed for pO2, ASTRUP-values, glucose and lactate content; O2-saturation was calculated. The vegetative situation at the end of the hypoxic period was characterized by low heart rate, low body temperatures (less than or equal to 25 degrees C), reduced glucose concentration and a lactate acidosis, compensated by low pCO2 (less than 2 kPa). At the 2nd posthypoxic day all parameters were normalized. If CO2-gas (FiCO2 = 0.05) is added to the hypoxic atmosphere (normocarbic pCO2-values in the arterial blood), the glucose and lactate content remained on the normal level; the diminution of heart rate and rectal temperature was smaller. Under the conditions of severe hypoxia in contrast to the adult rabbits the newborns are able to maintain their life processes for a longer time, but this fact need not be identical with the prevention of posthypoxic brain damage. In the cases of normocarbic pCO2-values, the hypoxic tolerance was elevated in the way of improved O2-delivery to the tissues.

The effect of O2-lack on the cerebrum in neonatal rabbits: first results of an in vivo NMR 31P-spectroscopic study.

Two- and 10-day-old urethan anesthetized rabbits were investigated. The ATP content as well as the intracellular pH-value were analysed during hypoxia and following reoxygenation. In contrast to the 2-day-old animals, we found delayed decreasing ATP content in 10-day-old rabbits as well as a delayed increase during the reoxygenation. The return to normal pH-values during the reoxygenation takes more time in older animals.

[The postnatal development of EMG reactions of limb muscles to free fall stimulation. II. Studies of early postnatal hypoxic-burdoned rabbits]. / Die postnatale Entwicklung von EMG-Reaktionen der Extremitätenmuskulatur bei Fallreizungen. II. Untersuchungen am frühpostnatal hypoxisch belasteten Kaninchen.

12 rabbits ("Deutscher Riese") were exposed to a hypoxic atmosphere (FiO2 = 0.05) for 3 h at their 1st day of life. At the 7th or 13th day of life, steel wire electrodes were chronically implanted into 3 leg muscles in order to record the electromyograms (EMG). The myographic activity was derived during free fall (height of drop = 0.5 m) until the age of 20 days. The quantitatively analysed EMG data were compared with corresponding data of undisturbed growing control animals. Using various EMG parameters, a quantitative separation of hypoxic animals from the controls was successfully done by a discriminant analysis, the animals being 8 and 20 days of age, respectively. It can be concluded that 1. already a single perinatal hypoxic load influences the supraspinal motor system permanently at least up to the age of 20 days, and that 2. this supraspinal influence on the investigated vestibulospinal reaction changes with increasing age of the rabbits.

[Morphometric studies of the postnatal development of the articular system of the bulbus oculi in rabbits]. / Morphometrische Untersuchungen zur postnatalen Entwicklung des Gelenksystems des Bulbus oculi beim Kaninchen.

The postnatal development of oculo-motor reactions is probably caused partly by changes of the passive mechanical properties of the bulb joint system. The YOUNG's elasticity modulus seems to be a suitable parameter to describe these changes. For its calculation, the length and the cross section area of the extraocular muscles as well as the dimensions of the ocular bulb are necessary. Moreover, the bulb mass is needed to analyse the inertia of the bulb during each movement. The postnatal growth of these parameters was investigated and, by means of the linear regression analysis, we looked for the best fitted mathematical expression. By this, there is the possibility to estimate the morphological data for detailed longitudinal analysis of changes of the oculo-motor function if the age and the body mass, are known.

[Morphological studies of postnatal changes of the sound transport apparatus in the middle ear of humans and rabbits]. / Morphologische Untersuchungen über postnatale Veränderungen des Schallantransportapparates im Mittelohr bei Mensch und Kaninchen.

The dimensions of the tympanic membrane and middle ear ossicles, respectively, were measured, in order to investigate the postnatal development of sound transport function. In human we observed only a small increase of the tympanic membrane area between the 7th postconceptional month and the 32nd year of life. This growth has no functional effect on the sound transport. In contrast, in rabbits all measured parameters with the exception of the stapes plate area show an increase until the 12th day of life. Thus, the amplification factor doubles in this species during the first 2 weeks of life. The temporal parallelism of the middle ear development with the ontogenesis of the acoustic function seems to exist in humans, but does not in rabbits.

A follow-up study of perinatally hypoxic rabbits.

Rabbits, surviving a severe 3-hours-lasting hypoxia (FiO2 = 0.05) during the 1st day of life, grew up together with their littermates. In animals aged 10 and 20 days, respectively, the vestibular induced tonic eye deviations were investigated during tilting around the three orthogonal body axes. The spontaneous head-body-motor coordination was analysed by means of a search coil technique in 14 days old rabbits. Perinatally hypoxic rabbits exhibit a compensation of initially reduced torsional tonic eye deviation and an overcompensation of the vertical ones at the 20th postnatal day in comparison to controls. Moreover, we found reduced amplitudes and velocities of spontaneous head saccades in perinatally hypoxic animals 14 days old. We assume a retarded development of the neuronal nets of the brain stem reticular formation in the hypoxic rabbits accompanied by an insufficient visuo-vestibular interaction.

[Saccadic eye movements during sinusoidal rotational stimulation in rabbits in the postnatal period]. / Saccadische Augenbewegungen während sinusförmiger Drehreizung bei Kaninchen in der Postnatalperiode.

Electro-oculograms were recorded from rabbits of the 5th, 11th, 18th and 25th day of life as well as from adult animals by means of chronically implanted silver wire electrodes. The sinusoidal rotation of the fixed alert animals in the horizontal plane were carried out by frequencies of 0.05, 0.2, 0.5 and 1.0 Hz using amplitudes of 15 degrees, 22.5 degrees and 45 degrees (peak to peak: 30 degrees, 45 degrees and 90 degrees). The saccade-(Sc)-threshold as well as the Sc-frequency were determined and the phase angle between stimulus and eye movement was measured. The Sc-threshold depends on the stimulation amplitude and shows a longer postnatal development in small 15 degrees-amplitude stimulations than in more intensive ones. The Sc-frequency appears to be an age-, amplitude- and frequency-dependent parameter. It rises with advancing age and increasing stimulation amplitude, respectively. The number of Sc increases also with growing rotational frequency up to a maximum and decreases when using further rising frequencies. In contrast to eye movements without Sc, the phase angle is diminished in movements interrupted by Sc-reactions. This phenomenon as well as the decreasing phase angle with increasing rotational frequency occur in all age groups. Thus, the Sc cause a better temporal precision of vestibular-guided stabilization of the retinal image during the postnatal ontogenesis from the first time of their appearance onward.

[Postnatal development of the sound-transporting apparatus in the middle ear of rabbits]. / Die postnatale Entwicklung des Schallantransportapparates im Mittelohr des Kaninchens.

The middle ear apparatus realized a multiplicatory function during the transfer of the vibrational energy, depending on the area ratio of pars tensa of tympanic membrane and of stapes footplate as well as the lever ratio of long arms of manubrium and of incus. These structures exhibit a size increase during the postnatal development, but the sequel on the multiplicatory function in rabbits is unknown. The middle ear structures of 46 rabbits, 1 to 30 d old, were prepared and measured. The area of pars tensa and the levers of malleus and incus increase with age. After the 10th d of life, no statistical significant growth were measurable. But the calculated multiplicatory factor of single animals indicate the end of the development at the 15th postnatal d. In contrast, the cochlear function attains the adult values not till the 26th d of life. It is 10 d longer than the middle ear growth.

The development of air-righting reflex in postnatal growing rabbits.

The investigations were carried out in 6 growing rabbits from the 5th day of life up to the 17th day in intervals of 3 days, as well as in 6 adult animals. The movements of the animals were filmed during free fall by means of a high speed camera (1000 pictures/s) in the frontal or the lateral view. The age-dependent development of head and shoulder rotation is described; the latency of this sensorimotor reaction decreases, and the head rotation velocity increases. The air-righting reflex is interpreted as a programmed command act. The postnatal changes in the timing of this reflex allow conclusions regarding the functional development of the spinal cord along the craniocaudal axis.

[Passive mechanical characteristics of the eyeball joint system during rabbit ontogenesis]. / Die passiv mechanischen Eigenschaften des Gelenksystems des Bulbus oculi während der Ontogenese des Kaninchens.

The postnatal development of vestibulo-ocular reactions is among other factor probably caused by changes of the passivee mechanical properties of the bulb joint system. Therefore, curarized rabbits from the newborn up to the adult age were studied in respect of the passiv deviation of the ocular bulb. The required force of stepwise traction (5 degrees each) of the bulb between the primary position and a 20 degrees deviation was measured. A linear enhancement of the force with increasing deviation angles was found in all age groups. Force relief resulted in a hysteresis in each case, the bulb did not reach the primary position. There were no differences of the force between newborns and adult animals, but 16 to 20 d old rabbits exhibited a statistical significant decrease of the required force in all deviation steps, except in 5 degrees.

[Conduction time in the oculomotor nerve during postnatal development of the rabbit]. / Die Leitungszeit im N. oculomotorius während der postnatalen Entwicklung des Kaninchens.

Investigations of eye movements after electrical ampullar nerve stimulation in postnatal growing rabbits have shown a shortening of the latency. To analyse the time portions, necessary for the passage of an excitation through the different structures of the vestibulo-ocular reflex are, the knowledge of the conduction time of the oculomotor nerve is also essential. Therefore, the length of the nerve and the mean diameter of the nerve fibres were measured, the corresponding nerve conduction velocity was taken from the literature as well as the conduction time was calculated. The conduction time decreases only from the birth to the 18th postnatal d and reaches the half value of the newborns. It portion of the latency is 5% in all age groups.

[Ontogenesis of the corneo-retinal potential in rabbits]. / Zur Ontogenese des korneo-retinalen Potentials beim Kaninchen.

The postnatal ontogenesis of the corneo-retinal potential in rabbits are unknown up to date. Therefore, in 32 young animals between the 1st and the 40th day of life and 6 adult rabbits this potential was measured during 10 degrees bulb deviation. The potential increases with age from 35 micro V in adults. The potential's development shows temporal conformity to postnatal ontogenesis of retina and ERG.

[Electromyographic studies of the musculus rectus nasalis in postnatal growing rabbits while turning the animal on the horizontal level]. / Elektromyographische Untersuchungen des Musculus rectus nasalis beim postnatal wachsenden Kaninchen während der Drehung des Tieres in der Horizontalebene

In rabbits aged 1-15 days and in a comparative group of adult animals, the EMG of the musculus rectus nasalis was recorded during a turn after speed jumps from 0 degrees/sec to 30 degrees/sec, 60 degrees/sec and 144 degrees/sec, respectively, through a path of 360 degrees. From the first day of life, an electrical activity consistent with the rapid and slow phase of the nystagmus was found. The EMG potentials, the so-called bursts, underwent qualitative changes with age that can be taken to reflect increasing maturation both of centralnervous mechanisms of inhibition and a functional transformation of the eye-muscles. The number of bursts increased with age during the turn; the latency period from the onset of turning to the appearance of the bursts was reduced. The differences observed at the three turning speeds are discussed with regard to the age of the animals.