Adrenal steroids as modulators of nerve cell function

Adrenal steroids modulate the function of nerve cells. Some, but not all actions of these steroids take place after binding to intracellular receptor systems and translocation of the steroid-receptor complex into the cell nucleus. Studies on the rat brain revealed heterogeneity of receptors. One population of receptor sites is present in abundance in extrahypothalamic limbic brain regions, e.g. neurons of the hippocampus, septum and amygdala. This neuronal receptor system displays a stringent binding specificity towards corticosterone, which is the naturally occurring glucocorticoid of the rat. Focussing the studies on the corticosterone receptor system in hippocampal neurons has provided further insight in the understanding of some of the actions of the steroid. Certain hippocampus-associated behaviors and indices of neurotransmission (serotonin) were disturbed after removal of the adrenals, but selectively restored after replacement with a low dose of corticosterone. The specificity, localization and dose-dependency of the corticosterone action on behavior and neurotransmission corresponds to the properties of its receptor system. The responsiveness to corticosterone is altered after changes in number of receptor sites. Chronic stress or high doses of exogenous corticosterone cause a long-term reduction. Other factors involved in regulation of receptor number are the neurotransmitter serotonin and neuropeptides related to ACTH and vasopressin. These substances restore changes in number of hippocampal corticosterone receptor sites due to aging, endocrine or neural deficiencies. Our results show that the number of corticosterone receptors is a sensitive index for brain functioning. Thus, the receptor system mediates some of the modulatory actions of corticosterone on nerve cell function and it may adjust its capacity under the influence of neural and endocrine factors.     

Interaction of lead toxicity and riboflavin status in chicks (Gallus domesticus)

Chicks (Gallus domesticus) were fed diets containing 0 or 2000 ppm lead (Pb) and adequate, marginal or deficient levels of riboflavin. In comparison to adequate, marginal riboflavin depressed growth at 2000 ppm Pb but not at 0 ppm Pb. Deficient riboflavin depressed growth at both Pb levels, and Pb depressed growth at all riboflavin levels. Hepatic glutathione reductase activity was reduced by riboflavin deficiency, but Pb was without effect. Hepatic non-protein sulfhydryl concentrations were increased by Pb, and the increases were greater at the lower riboflavin levels. Dietary Pb appears to increase the level of riboflavin required in chick diets.     

Implication of iron in seizure syndrome of mutant chicks (Gallus domesticus)

1. An investigation was made of systemic iron in paroxysmal (px) chicks. 2. Serum transferrin levels in px chicks are greatly increased (P less than 0.05) over control levels, but iron-binding capacity is decreased (P less than 0.05). 3. The delayed (by 10 days) increase in px hemoglobin (P less than 0.01) may be due to the general debilitation seen in px syndrome. 4. An attempt to determine brain iron showed no deposits comparable to mammalian brain iron distribution, but this was consistent with inability of others to locate iron in adult chicken brain tissue.     

Responses of domestic chicks (Gallus gallus domesticus) to multimodal aposematic signals

Many aposematic prey combine their visual warning signals withadditional signals. Together, these signals constitute a multimodalor multicomponent warning display. The additional signals arethought to increase the effects of the visual signals on predators.Olfactory signals are much emphasized, but later studies haveshown that also auditory signals like the buzzing of certaininsects might have multimodal effects. The wasp displays typicalvisual aposematic signals, black and yellow stripes, but doesalso emit a characteristic buzzing. We wanted to test if, andin what way, the visual and acoustic display of the wasp hasan aversive function on the predators. We therefore conducteda 12-trial discrimination-learning task on inexperienced chicksto study whether there are innate biases toward these signalsand how they affect the speed of avoidance learning. We alsoperformed three extinction-learning trials to study how memorablethe signals were to the chicks. We show that the visual signalsin the display of the wasp contribute to the protection frompredators but in different ways; the yellow color had an aversiveeffect on inexperienced predators, while the striped patternimproved the aversion learning. The sound did not enhance theinnate aversions but increased the aversion learning of stripesin green prey.     

Enhanced release of cholecystokinin by dietary amino acids in chicks (Gallus domesticus)

1. The effect of dietary amino acids and protein on cholecystokinin (CCK) release into plasma was investigated in chicks by feeding a meal through a stomach tube, followed by the CCK determination with specific CCK-8 antibody. 2. The results showed that both isolated soya protein and an amino acid mixture simulating the amino acid composition of the soya protein increased the release of CCK, though to a lesser extent with a delayed response in the former, when added to a protein-free diet. 3. Among amino acids added singly to the protein-free diet, phenylalanine was more efficient than arginine and valine, exerting a response almost identical to the complete amino acid mixture.     

Ultradian activity rhythms in large groups of newly hatched chicks (Gallus gallus domesticus)

A clutch of young chicks housed with a mother hen exhibit ultradian (within day) rhythms of activity corresponding to the brooding cycle of the hen. In the present study clear evidence was found of ultradian activity rhythms in newly hatched domestic chicks housed in groups larger than natural clutch size without a mother hen or any other obvious external time-keeper. No consistent synchrony was found between groups housed in different pens within the same room. The ultradian rhythms disappeared with time and little evidence of group rhythmicity remained by the third night. This disappearance over time suggests that the presence of a mother hen may be pivotal for the long-term maintenance of these rhythms. The ultradian rhythm of the chicks may also play an important role in the initiation of brooding cycles during the behavioural transition of the mother hen from incubation to brooding. Computer simulations of individual activity rhythms were found to reproduce the observations made on a group basis. This was achievable even when individual chick rhythms were modelled as independent of each other, thus no assumptions of social facilitation are necessary to obtain ultradian activity rhythms on a group level.     

Plasma lipoprotein profiles in broiler chicks (Gallus domesticus): effects of early overfeeding

1. Twenty-eight day old broiler chicks gavage fed for 22 days consumed 40% more feed and gained 100-110 g more than control birds. 2. Normal feeding resumed on day 41, by day 63 feed intakes and body weights of overfed and control birds were equal. 3. Moderate differences in lipid compositions of LDL and VLDL were observed at 41 and 50 but not at 63 days. 4. In contrast to mammals where early over feeding predisposes to adult obesity, lipoprotein profiles and ad lib feeding patterns of chicks are not readily altered by dietary measures.     

Tissue glycogen and lactate levels in starved and in protein-fed domestic fowl chicks (Gallus domesticus)

The levels of glycogen, protein and lactate in the tissues of 3- and 5-day-old domestic fowl chicks either starved or fed a protein diet (hard-boiled egg white) have been studied. The patterns of change in the parameters studied were much similar in both experimental groups compared to fed controls. Tissue and circulating levels of lactate were very low in protein-fed chicks, they are lowest in the starved ones. Plasma glucose levels were diminished in starved and protein-fed groups vs. controls, as were their tissue glycogen levels, the latter being lowest in starved chicks. The availability of dietary amino acids could not prevent the effects of the lack of dietary carbohydrate observed in starved chicks, as the weight of liver, circulating glucose and lactate levels were significantly lowered in these animals compared with controls.     

Effect of phenylalanine on pancreatic amylase secretion in chicks (Gallus domesticus).

1. Effect of phenylalanine (Phe) on pancreatic amylase secretion in growing chicks was investigated in four experiments. 2. In Experiment 1, birds were injected through a wing vein with 0.25 ml Phe at 0, 0.1, 0.5, 2.5 and 12.5 mM in physiological saline. No significant difference was observed in amylase secretion among treatments. 3. Effect of various concentrations of Phe with cholecystokinin (CCK, 0.31 Crick unit) on amylase secretion was investigated in Experiment 2. Amylase secretion increased with time, although no significant effect was detected in Phe treatment. 4. Efficacy of Phe and tyrosine (Tyr) injection with CCK on amylase secretion was compared. There was no significant difference between Phe and Tyr treatments. 5. Birds were injected intraperitoneally with dl-p-chlorophenylalanine (p-CP), which is an inhibitor of phenylalanine hydroxylase, or saline 1 day before the collection of pancreatic amylase in Experiment 4. Both chicks showed increased amylase secretion with CCK (0.31 Crick unit), whereas the response was at a drastically reduced rate in chicks with the p-CP treatment.     

Effect of Escherichia coli infection on growth and protein metabolism in broiler chicks (Gallus domesticus)

1. A controlled experimental Escherichia coli infection was developed in broiler chicks. 2. Infection with E. coli significantly reduced feed intake, altered growth of the whole body, eviscerated carcass, skeletal muscles, heart and liver. Organ weight and/or the proportions of organs within the body were affected. 3. Protein accumulation in the eviscerated carcass, extensor digitorum communis and sartorius muscles was severely inhibited by infection, and to a greater extent than body weight. 4. Failure of muscle tissue to accumulate protein was associated with a significant decline in protein synthesis, when measured in vitro (-48%; P less than 0.05) and in vivo (-42%; P less than 0.001). Protein degradation also declined (-28.7%), but to a smaller extent than protein synthesis. 5. Although the infected chicks showed no viable bacteria at day 12 after infection, chicks did not reach the same body weight as controls by day 30 after infection.     

Effect of dietary protein and fat content on tri-iodothyronine-induced thermogenesis in young chicks (Gallus domesticus)

1. The effect of dietary protein and fat content on tri-iodothyronine (T3) induced thermogenesis was studied in young chicks (Gallus domesticus). 2. Irrespective of dietary protein and fat contents employed, energy and fat retained were consistently decreased and heat production was increased, but protein retained was not affected by the T3 administration throughout the experiments. 3. Little or no effect of dietary protein and fat contents on T3-induced thermogenesis was observed. 4. Increased heat production by the T3 administration was primarily brought about by a reduction in retained fat which served as fuel to give rise to extraneous heat.     

Prenatal music stimulation facilitates the postnatal functional development of the auditory as well as visual system in chicks (Gallus domesticus)

Rhythmic sound or music is known to improve cognition in animals and humans. We wanted to evaluate the effects of prenatal repetitive music stimulation on the remodelling of the auditory cortex and visual Wulst in chicks. Fertilized eggs (0 day) of white leghorn chicken (Gallus domesticus) during incubation were exposed either to music or no sound from embryonic day 10 until hatching. Auditory and visual perceptual learning and synaptic plasticity, as evident by synaptophysin and PSD-95 expression, were done at posthatch days (PH) 1, 2 and 3. The number of responders was significantly higher in the music stimulated group as compared to controls at PH1 in both auditory and visual preference tests. The stimulated chicks took significantly lesser time to enter and spent more time in the maternal area in both preference tests. A significantly higher expression of synaptophysin and PSD-95 was observed in the stimulated group in comparison to control at PH1-3 both in the auditory cortex and visual Wulst. A significant inter-hemispheric and gender-based difference in expression was also found in all groups. These results suggest facilitation of postnatal perceptual behaviour and synaptic plasticity in both auditory and visual systems following prenatal stimulation with complex rhythmic music.     

Transport of putrescine across duodenal,jejunal and ileal brush-border membrane of chicks (Gallus domesticus)

Luminal polyamines and their absorption are essential for proliferation of the enterocytes and, therefore, nutrition, health and development of the animal. The transport systems that facilitate the uptake of putrescine were characterized in chick duodenal, jejunal and ileal brush-border membrane vesicles prepared by MgCl2 precipitation from three-week-old chicks. An inwardly-directed Na+ gradient did not stimulate putrescine uptake and, therefore, putrescine transport in chick intestine. In the duodenum, jejunum and ileum, kinetics of putrescine transport fitted a model with a single affinity component plus a non-saturable component. The affinity (Kt) for [3H]putrescine transport across the brush-border membrane increased along the length of the small intestine. A model of intermediate affinity converged to the data obtained for [3H]putrescine transport with Kt approximating 1.07 and 1.05 mM or duodenum and jejunum, respectively; and high affinity with a Kt of 0.35 mM for the ileum. The polyamines cadaverine, putrescine, spermidine and spermine strongly inhibited the uptake of [3H]putrescine into chick brush-border membrane vesicles, more so for the jejunum and ileum than the duodenum. The kinetics of cadaverine, spermidine and spermine inhibition are suggestive of competitive inhibition of putrescine transport. These uptake data indicate that a single-affinity system facilitates the intestinal transport of putrescine in the chick; and the affinity of transporter for putrescine is higher in the ileum than in the proximal sections of the small intestine. In addition, this study shows that the ileum of chicks plays an important role in regulating cellular putrescine concentration.     

Modification of lead toxicity and organ distribution by dietary sulfur amino acids in chicks (Gallus domesticus)

Chicks (Gallus domesticus) were fed a basal diet deficient in methionine and total sulfur amino acids with 0 or 1000 ppm added lead for 21 days. Methionine or methionine and cystine addition improved growth regardless of dietary lead level. Cystine addition alone improved growth only when lead was present. Relative inhibition of growth by lead was greater with diets containing no added methionine. Hepatic non-protein sulfhydryl concentration was increased by lead and all amino acid additions. Organ lead concentrations were generally lower with added amino acids. Dietary methionine appears to counteract lead toxicity more effectively than cystine.     

A simple method for measuring immunoglobulin synthesis in vivo in the spleen of chicks (Gallus domesticus)

1. Spleen immunoglobulin (IgG) synthesis was measured in vivo in chicks at 3 weeks of age by a large dose injection of labelled phenylalanine in combination with the isolation of IgG by immunological precipitation against anti-chicken IgG. 2. No appreciable amount of radioactivity was detected in serum IgG for the first 60 min of the isotope injection via the wing vein, indicating a minimum time lag necessary for the secretion of newly synthesized IgG into the circulation. 3. Synthesis rates of total spleen protein and spleen IgG were found to be 17.5 and 4.8 mg/day, respectively, suggesting that IgG synthesis would contribute to 27% of the total protein synthesis in the spleen of young chicks.     

Extra-lingual chemoreceptors in the chicken (Gallus domesticus)

The oral aversion behaviour of the chicken (head shaking, beakwiping and tongue/beak movements) was measured following oralstimulation with 0.1 M quinine hydrochloride, 40% sucrose, 3M sodium chloride, 5 M acetic acid and pure methyl anthranilate.Section of the lingual and laryngolingual nerves did not affectthe oral aversion behaviour and therefore demonstrates the presenceof functional extra-lingual chemoreceptors. The results arediscussed in relation to previous anatomical findings.     

Development of responsiveness to the individual maternal “clucking” by domestic chicks (Gallus gallus domesticus)

Sixty-nine chicks, brooded by hens, were given the choice of approaching the clucking sound of the familiar hen or another clucking source. The effects of age and prenatal experience of clucking on the responsiveness to their hen's clucking were also investigated. Eighty-three percent of all chicks tested chose the familiar hen clucking after a certain age. By 4 days of age, 29% of artificially incubated chicks approached the clucking of a familiar hen. Seventy-four percent of naturally incubated chicks and 89% of chicks artificially incubated until pipping and then naturally incubated, showed this discrimination. This corresponds well to the natural situation, in which the hen remains in the nest with the chicks for up to 3 days after hatching. The results also indicate that late prenatal experience of the maternal call is of importance for the later responsiveness to this call.     

Ontogeny of magnetoreception in chickens (Gallus gallus domesticus)

Chickens are precocial birds, capable of moving independently from within a few hours of hatching, and thus provide a useful model to investigate the development of magnetoreception in young birds. Chicks show some sharply-timed behavioural changes at around 11 days of age that may be indicative of improvements in navigation ability around this age. We trained Young (<10 days, n = 7) and Old (11 days or older, n = 6) chicks to find a hidden imprinting stimulus behind one of four screens in a square arena. Once criterion was reached, the directional choices of chicks were recorded in unrewarded tests in the geomagnetic field and in an experimental field shifted by 90° clockwise. These tests were separated with rewarded training trials to avoid extinction. In the first, and the first 3 tests, no indication was found that chicks chose the correct unimodal magnetic direction. Instead, in all tests, Old chicks preferred the screens in the same magnetic axis as the training direction in tests in the geomagnetic and shifted experimental fields significantly more than Young chicks (P < 0.05). Choices of Young chicks were no different to chance in tests, whereas choices by Old chicks were significantly different from chance (P < 0.05). Our findings support the hypothesis that magnetoreception appears in the second week of life in the chicken. It is, however, unclear when a truly directional magnetic response (i.e. an unimodal, rather than axial, response in our test) develops that could be used by the chicks for accurate navigation.