The development of connections in the tecto-thalamo-telencephalic visual system of the brain in 13-day-old chick embryos

Light and electron microscopic studies have been made on degenerative changes in the nervous tissue induced by experimental destruction of the median brain bulb at the 5th day of incubation, in parts of the tecto-thalamo-telencephalic visual system in 13-day chick embryos (in the visual tectum, round nucleus of the thalamus and ectostriatum of the telencephalon). It was shown that to this period tecto-thalamic connections are already formed in the visual system, whereas thalamo-telencephalic connections are, presumably, indirect ones.     

Estradiol secretion by the ovary of 19-day-old hypophysectomized and sham-operated chick embryos

The amounts of estradiol released into culture media by ovaries from 19-day-old hypophysectomized (decapitated) and sham-operated chick embryos were determined by RIA. Per single ovary, ovaries from decapitated embryos secreted slightly less estradiol than ovaries from sham-operated ones during a 4-h culture period (837 +/- 413 vs 935 +/- 378 pg), but this difference was not significant. On an ovarian weight basis, ovaries from decapitated embryos secreted slightly more estradiol than ovaries from sham-operated ones (1.15 vs 0.91 ng), but this difference was not significant either. It is concluded from these results that the hypophysis does not control estradiol secretion by the ovary in the 19-day-old chick embryo.     

Biochemical characteristics of adhesion factors isolated from the retina of 8-day-old chick embryos

While isoelectrofocusing the extracts obtained after dissociation of the retina of eight day old chick embryos, two active protein fractions were found: AF I with pI 3 and AF II with pI below 3. The content of these fractions in the extracts depended on the method of dissociation: treatment with EDTA increased the content of AF II, whereas trypsin treatment increased the yield of AF I. After electrophoresis in the denaturating conditions both fractions were divided in two components. The effect of AF I on aggregation of retinal cells, unlike that of AF II, does not depend on the presence of bivalent cations in the medium and is realized within 1 h of interaction with the cells at 4 degrees. It is suggested that the retinal extracts of eight day old chick embryos contain substances providing two types of adhesiveness: Ca2+-independent (AF I) and Ca2+-dependent (AF II).     

Chronotropism and blood flow patterns following teratogenic doses of catecholamines in 5-day-old chick embryos.

In vivo heart rates of 5-day-old chick embryos were recorded from electrodes placed in close proximity to the heart. L-epinephrine (4X10(-10) mole), 1-norepinephrine (1X10(-9)mole) and 1-isoproterenol (1.6X10(-10)mole) in 5 microliter of isotonic saline transiently accerlerated the mean heart rate by almost 9 percent. L-phenylephrine (2X10(-9)mole/5microliter) and the experimental procedure produced no appreciable effect. The positive chronotropic effect of the catecholamines was found to be highly significant (P less than 0.0005) as computed by Student's t test. However, no direct relationship could be established between the chronotropic response and the aortic arch anomalies produced. A prolonged reduction of blood flow in the primitive heart tube and the sixth aortic arch after administration of epinephrine and isoproterenol is apparently related to the induction of hypoplastic right pulmonary artery with absent or hypoplastic right ductus arteriosus.     

Transepithelial potential in mesonephric nephrons of 7-day-old chick embryos in relation to the histochemically detected sodium pump

In order to obtain basic information on the transport properties of differentiating embryonic nephrons, we examined the 7-day-old chick mesonephros by measuring the transtubular epithelial potential difference (TPD) and by histochemical detection of Na,K-ATPase activity. TPD as an indicator of the electrogenic transport was measured in individual segments of superficial nephrons in vivo. Their electric polarity was always lumen-negative. TPD was reduced by addition of 10 mM KCN applied to the mesonephric nephrons from the outside. In the proximal tubules, TPD was significantly lower (mean+/-SD: -1.0+/-0.5 mV) than in the distal and collecting tubules (-2.2+/-1.0 mV, p< or =0.05). Activity of the sodium pump was evaluated histochemically by detection of ouabain-sensitive potassium-dependent p-nitrophenyl phosphatase in cryostat sections of the mesonephros. The enzyme activity was demonstrated only in distal tubules and in the collecting ducts, but not in the proximal tubules. These findings have revealed significant differences between embryonic nephron segments: the distal tubule, in contrast to the proximal one, is supplied by the sodium pump and is able to generate higher TPD. Therefore, we consider that it is only the distal nephron, which possesses the ability of active transport.     

Comparative study of the structural organization of the 2 divisions of the hindbrain of 10-day-old chick embryos

Light and electron microscopic investigation has been made of the main structural components of the nervous tissue in two divisions of the telencephalon (the dorsal ventricular ridge and striatum) in 10-day chick embryos. Special attention was paid to the degree of maturation of cellular elements of the nervous tissue, the development of neuropil and the level of synaptogenesis. The data obtained suggest heterochronous maturation of the divisions investigated. Striatum, being phylogenetically more ancient structure, is formed prior to the dorsal ventricular ridge.     

Effects of corticosterone on brain cholinergic enzymes in chick embryos

The effects of corticosterone on the cholinergic enzymes, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were studied in the chick embryonic brain. Chick embryos received either 0.25, 0.5, or 1.0 g of corticosterone via the air sac daily for three days during either embryonic days 6 through 8 (E6-E8), of cerebral neurogenesis, or days 10 through 12 (E10-E12), a period of cerebellar neurogenesis. Enzyme activities were determined in cerebral hemispheres, optic lobes, cerebellum and remaining brain at 10, 15, and 20 days of incubation. In embryos treated from E6 to E8, ChAT activity was generally higher at day 10 in cerebral hemispheres and optic lobes (cerebellum was not determined) while AChE activity was not affected. At day 20 ChAT activity of treated chick embryos was lower in the cerebral hemispheres and optic lobes, but not in the cerebellum; AChE activity was higher in the cerebral hemispheres, lower in the optic lobes, and not changed in the cerebellum as compared to controls. However, in embryos treated from E10 to E12 both cerebellar ChAT and AChE activities were higher at day 15 in comparison to controls. These data show that the hormonal effects were most prominent only in the brain areas undergoing neurogenesis during the period of hormonal treatment. Since AChE activity is also present in nonneuronal cells, the observed alterations caused by corticosterone may reflect glial cell responses to the hormone. Whether the hormone affects the final number and/or maturation of cholinergic neurons and/or glial cells remain to be investigated.     

Acoustic and somatosensory evoked responses in the brain hemispheres of chick embryos.

The author explored the auditory projection in the brain hemispheres of 16- to 21-day-old chick embryos, using biaural stimulation, and the somatosensory projection, using electrical stimulation of the contralateral sciatic nerve. The first auditory evoked responses appeared on the surface of the hemisphere at the beginning of the 18th day of incubation and were localized in its mediolateral part. Up to hatching, the latent period of the surface response shortened from 76.3 msec to 28.9 msec and its amplitude augmented from 10.6 muV to 36.2 muV. If the electrode was plunged into the tissue, the evoked responses with the optimum latent period and amplitude parameters were recorded at a depth of 2-2.5 mm (latent period 20.2 msec, amplitude 40-45 muV). The maximum surface somatosensory responses were found in the medial occipital quadrant of the contralateral hemisphere. They developed from the second half of the 17th day of incubation. Up to the end of incubation the mean latent period shortened from 58.3 msec to 21.6 msec and the mean amplitude increased from 11.8 muV to 28.7 muV. What was at first a simple negative wave developed into a positive-negative complex by the end of incubation. Evoked responses at a depth of about 3.5 mm from the surface of the hemisphere had the optimum parameters (latent period 18.4 msec, amplitude 30.2 muV).     

Effects of dopamine on spontaneous activity generated by isolated spinal cord in 16- to 20-day-old chick embryos

The effects were investigated of applying L-DOPA, dopamine (DA), and noradrenaline (NA) on spontaneous activity (cyclic fluctuations in electrotonic dorsal and ventral root (DR and VR) potentials generated by a section of spinal cord isolated from 16 to 20-day-old chick embryos. A low concentration of L-DOPA (30–150 µm) intensified operation of the spinal generator, giving rise to above-threshold rhythm (i.e., spike activity in the DR and the VR). At a high concentration, L-DOPA produced inhibition of generator operation, although spontaneous activity did intensify during subsequent washout of the substance, with the onset of above-threshold rhythm. Both DA and NA failed to affect spontaneous activity in the VR and the DR at a concentration to 50 µM but a concentration of 100 µM produced inhibition. Application of 20 µM 2-amino-5-phosphonovaleric acid blocked the reinforced spontaneous activity produced by low L-DOPA concentrations. Activity generated by the neuronal network of the isolated dorsal horn rose under the effects of low L-DOPA concentrations; rhythmic activity was observed neither before nor after applying this substance in isolated ventral horn. Findings obtained would point to the occurrence of a direct (i.e., non-catecholamine dependent) excitatory influence of L-DOPA on the neuronal network of the chick embryo dorsal horn.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 338–343, May–June, 1991.     

The development of superficial infraslow potential oscillations of the brain in chick embryos.

The development of superficial infraslow potential oscillations (ISPO) of brain hemispheres, cerebellum and optic lobes was studied in chick embryos between day 9 and 21 of incubation. The ISPO were firstly registered in brain hemispheres at day 10 of incubation, i.e. 5 days before the onset of spontaneous EEG activity. The ISPO in 10-day-old embryos had an average frequency of 9.9 c/min and an amplitude of 0.14 mV. During further development till hatching the frequency decreased to 7.5 c/min and the amplitude increased to 1.39 mV. Similar ISPO with the same developmental trend were also registered from the surface of the cerebellum and optic lobes. Superficial ISPO were not synchronized either between both hemispheres or between different fields of the same hemisphere.     

Ratio of concentration of ions of uni- and bivalent metals in the tissues of developing chick embryos and 1-day-old chickens]

The ratio of concentrations Na+/K+ decreases in the brain and liver and increases in the cardiac muscle during the chick embryogenesis. The maximum concentration of Ca2+ was noted in the tissues under study on 14th day of chick embryonic development and its content decreased reliably at the subsequent stages. The concentration of Mg2+ in the tissues under study decreased during the embryogenesis as well.     

Lipid composition of brain myelin from normal and hyperphenylalaninemic chick embryos

The influence of hyperphenylalaninemia on the lipid composition of brain myelin has been investigated in 19-day-old chick embryos. CNP-ase activity was used as myelin marker enzyme for myelin isolation. CNP-ase activity was significantly lower in hyperphenylalaninemic myelin when compared with control. No significant differences were observed after experimental treatment in the total lipid content of myelin as well as in the proportion of cholesterol:phospholipid:galactolipid. Nevertheless, a clear increase in the percentage of esterified cholesterol was found. No appreciable alterations were observed in the phospholipid composition of brain myelin from both control and hyperphenylalaninemic chick embryos. However, the ratio of unsaturated to saturated fatty acids in serine plasmalogen and sphingomyelin was considerably increased by this treatment. This ratio in choline and ethanolamine phosphatides from treated embryos did not differ from that of controls.     

Cholinesterase in the amnion of chick embryos

Cholinesterase (ChE) activity in amnion was studied in developing chick embryos and the enzyme's substrate-inhibitory characteristics were established. The enzyme activity increased until the 8th day of incubation and then gradually decreased; on day 12-15 the activity is 40% only of the maximal one. On the basis of substrate-inhibitory analysis the enzyme was referred to propionyl-cholinesterases. Relations between age changes in ChE activity and morphological structure of smooth-muscle amnion tissue, its differentiation during development and functional activity of amnion are discussed.